Showing 1–50 of 504 results for author: Smith, S

Gamma-Ray and AntiMatter Survey(GRAMS) experiment

Authors: J. Zeng, T. Aramaki, D. Ames, K. Aoyama, S. Arai, S. Arai, J. Asaadi, A. Bamba, N. Cannady, P. Coppi, G. De Nolfo, M. Errando, L. Fabris, T. Fujiwara, Y. Fukazawa, P. Ghosh, K. Hagino, T. Hakamata, N. Hiroshima, M. Ichihashi, Y. Ichinohe, Y. Inoue, K. Ishikawa, K. Ishiwata, T. Iwata , et al. (41 additional authors not shown)

Abstract: The Gamma-Ray and AntiMatter Survey (GRAMS) is a next-generation experiment using a Liquid Argon Time Projection Chamber (LArTPC) detector to measure MeV gamma rays and antiparticles. MeV gamma-ray observations are important for understanding multi-messenger and time-domain astronomy, enabling exploration of the universe's most potent events, such as supernovae and neutron star mergers. Despite th… ▽ More The Gamma-Ray and AntiMatter Survey (GRAMS) is a next-generation experiment using a Liquid Argon Time Projection Chamber (LArTPC) detector to measure MeV gamma rays and antiparticles. MeV gamma-ray observations are important for understanding multi-messenger and time-domain astronomy, enabling exploration of the universe's most potent events, such as supernovae and neutron star mergers. Despite the significance of MeV gamma-rays, GRAMS could also explore the so-called 'MeV gap' region to improve MeV gamma-ray measurement sensitivity that was restricted by the challenge of accurately reconstructing Compton events. Aside from gamma-ray detection, the GRAMS proposed method also serves as an antiparticle spectrometer, targeting the low-energy range of cosmic antinuclei measurements. This work will provide updates on the current status and progress towards the prototype balloon flight with a small-scale LArTPC (pGRAMS) scheduled for early 2026, as well as the recent progress on antihelium-3 sensitivity calculation. △ Less

Submitted 16 December, 2025; originally announced December 2025.

Comments: 9 pages, 4 figures, proceeding for The XIX International Conference on Topics in Astroparticle and Underground Physics (TAUP2025)

Giant Outer Transiting Exoplanet Mass (GOTEM) Survey.VII. TOI-6041: a multi-planet system including a warm Neptune exhibiting strong TTVs

Authors: N. Heidari, A. Alnajjarine, H. P. Osborn, D. Dragomir, P. Dalba, W. Benz, G. Hébrard, J. Laskar, N. Billot, M. N. Günther, T. G. Wilson, Y. Alibert, A. Bonfanti, A. Bieryla, C. Broeg, A. C. M. Correia, J. A. Egger, Z. Essack, E. Furlan, D. Gandolfi, N. Grieves, S. Howell, D. LaCourse, C. Pezzotti, T. Pritchard , et al. (79 additional authors not shown)

Abstract: We present the characterization of the TOI-6041 system, a bright ($V = 9.84 \pm 0.03$) G7-type star hosting at least two planets. The inner planet, TOI-6041b, is a warm Neptune with a radius of $4.55^{+0.18}_{-0.17}\,R_\oplus$, initially identified as a single-transit event in \textit{TESS} photometry. Subsequent observations with \textit{TESS} and \textit{CHEOPS} revealed additional transits, ena… ▽ More We present the characterization of the TOI-6041 system, a bright ($V = 9.84 \pm 0.03$) G7-type star hosting at least two planets. The inner planet, TOI-6041b, is a warm Neptune with a radius of $4.55^{+0.18}_{-0.17}\,R_\oplus$, initially identified as a single-transit event in \textit{TESS} photometry. Subsequent observations with \textit{TESS} and \textit{CHEOPS} revealed additional transits, enabling the determination of its $26.04945^{+0.00033}_{-0.00034}$~d orbital period and the detection of significant transit timing variations (TTVs), exhibiting a peak-to-peak amplitude of about 1~hour. Radial velocity (RV) measurements obtained with the APF spectrographs allow us to place a $3σ$ upper mass limit of $28.9\,M_\oplus$ on TOI-6041b. In addition, the RV data reveal a second companion, TOI-6041c, on an 88~d orbit, with a minimum mass of $0.25\,M_{\mathrm{Jup}}$. A preliminary TTV analysis suggests that the observed variations could be caused by gravitational perturbations from planet c; however, reproducing the observed amplitudes requires a relatively high eccentricity of about 0.3 for planet c. Our dynamical stability analysis indicates that such a configuration is dynamically viable and places a $1σ$ upper limit on the mass of TOI-6041c at $0.8\,M_{\mathrm{Jup}}$. An alternative is the presence of a third, low-mass planet located between planets b and c, or on an inner orbit relative to planet b -- particularly near a mean-motion resonance with planet b -- which could account for the observed variations. These findings remain tentative, and further RV and photometric observations are essential to better constrain the mass of planet b and to refine the TTV modeling, thereby improving our understanding of the system's dynamical architecture. △ Less

Submitted 1 December, 2025; originally announced December 2025.

Comments: Accepted for publication in A&A, 22 pages, 8 plots

Spectropolarimetric Evolution Reveals Dual-Axis Ejecta in the Atypical Magnetar-Powered SN 2012au

Authors: Sabrina DeSoto, JenniferL. Hoffman, G. Grant Williams, Christopher Bilinski, Douglas C. Leonard, Peter A. Milne, Christopher Pickens, Manisha Shrestha, Nathan Smith, Paul S. Smith

Abstract: We present six epochs of optical spectropolarimetric observations of the unique and slow-evolving Type Ib supernova (SN) 2012au, between 0 and 295 days post R-band maximum. The polarization levels seen throughout our observations are on average 0.87% +/- 0.05% higher than those of any Type Ib SN~yet studied, suggesting either that it is the most asymmetric of the sample, or if all SNe Ib have simi… ▽ More We present six epochs of optical spectropolarimetric observations of the unique and slow-evolving Type Ib supernova (SN) 2012au, between 0 and 295 days post R-band maximum. The polarization levels seen throughout our observations are on average 0.87% +/- 0.05% higher than those of any Type Ib SN~yet studied, suggesting either that it is the most asymmetric of the sample, or if all SNe Ib have similar asymmetry, that it is viewed at a more optimum angle. Significant continuum polarization indicates that the photosphere exhibited a global departure from spherical symmetry at the level of 10%-40% at the earliest times (days 0--40), which decreased to 0%-20% by days 57--90. During the early photospheric phase, the ejecta maintained a near-constant orientation of 12°-20° on the sky, as shown by the dominant axis in the Stokes q-u plane. Polarization signatures in the Fe II λλλ4924, 5018, 5169 lines shared this axis. Meanwhile, high levels of polarization associated with the He I lines traced distinct q-u loops with a dramatic rotation away from the dominant axis, indicating that the early-time ejecta were also characterized by hot, fast, helium-rich material concentrated near the poles. At day 295, during the transition to the nebular phase, a new, highly elongated structure became prominent in the ejecta, with an axis orthogonal to the dominant axis that defined the photospheric phase. This dual-axis geometry may link SN 2012au's high luminosity and asymmetric structure to a magnetar powering mechanism. △ Less

Submitted 12 November, 2025; originally announced November 2025.

HARPS-N, TESS, and CHEOPS discover a transiting sub-Neptune and two outer companions around the bright solar analogue HD 85426

Authors: F. Lienhard, A. Mortier, A. Collier Cameron, M. Cretignier, L. Borsato, A. Anna John, J. A. Egger, M. Stalport, T. G. Wilson, A. Deline, A. Fortier, D. W. Latham, L. Malavolta, P. F. L. Maxted, S. G. Sousa, S. L. Grimm, L. Buchhave, Y. Alibert, B. S. Lakeland, X. Dumusque, J. Cabrera, L. Naponiello, A. C. M. Correia, F. Rescigno, L. Fossati , et al. (74 additional authors not shown)

Abstract: We provide a detailed characterisation of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star ($M_{\ast}$: 0.99 $\text{M}_{\odot}$; $R_{\ast}$: 1.13 $\text{R}_{\odot}$; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 days and a blackbody equilibrium temperature of $824^{+11}_{-11}$ K. By jointly analysing HARPS-N RVs, TE… ▽ More We provide a detailed characterisation of the planetary system orbiting HD 85426 (TOI-1774). This bright G-type star ($M_{\ast}$: 0.99 $\text{M}_{\odot}$; $R_{\ast}$: 1.13 $\text{R}_{\odot}$; age: 7.4 Gyr; V mag: 8.25) hosts a transiting sub-Neptune, HD 85426 b, with an orbital period of 16.71 days and a blackbody equilibrium temperature of $824^{+11}_{-11}$ K. By jointly analysing HARPS-N RVs, TESS, and CHEOPS photometric data and using two different stellar activity mitigation techniques, we constrain planet b's mass to $6.0^{+1.5}_{-1.6}$ $\text{M}_{\oplus}$ and $8.5^{+1.3}_{-1.4} $ $\text{M}_{\oplus}$, depending on the mitigation technique. We investigate the dependence of these results on the priors, data selection, and inclusion of other Keplerians in the modelling. Using this approach, we identify the presence of two non-transiting planetary companions with minimum masses near 10 $\text{M}_{\oplus}$ and orbital periods of 35.7 and 89 days. Additionally, we reject the initial hypothesis that the 35.7-day periodic signal was due to stellar activity. We also determine HD 85426 b's radius to be $2.78^{+0.05}_{-0.04}$ $\text{R}_{\oplus}$ and compute a transmission spectroscopy metric in the range of 82 to 115, making this planet a highly valuable target for atmospheric characterisation. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 27 pages, 20 figures, accepted for publication in MNRAS

Mass determination of the three long-period Neptune- and sub-Neptune-sized planets transiting TOI-282

Authors: A. Barone, F. Rodler, D. Gandolfi, A. Bonfanti, P. Leonardi, L. Visca, M. Fridlund, M. Brogi, L. Fossati, P. E. Cubillos, W. D. Cochran, S. Csizmadia, J. Livingston, G. Nowak, E. Pallé, C. M. Persson, S. Redfield, H. Schmerling, A. M. S. Smith

Abstract: TOI-282 is a bright (V=9.38) F8 main-sequence star known to host three transiting long-period ($P_b$=22.9 d, $P_c$=56.0 d, and $P_d$=84.3 d) small ($R_p\approx$ 2-4 $R_{\oplus}$) planets. The orbital period ratio of the two outermost planets, namely TOI-282 c and d, is close to the 3:2 commensurability, suggesting that the planets might be trapped in a mean motion resonance. We combined space-born… ▽ More TOI-282 is a bright (V=9.38) F8 main-sequence star known to host three transiting long-period ($P_b$=22.9 d, $P_c$=56.0 d, and $P_d$=84.3 d) small ($R_p\approx$ 2-4 $R_{\oplus}$) planets. The orbital period ratio of the two outermost planets, namely TOI-282 c and d, is close to the 3:2 commensurability, suggesting that the planets might be trapped in a mean motion resonance. We combined space-borne photometry from the TESS telescope with high-precision HARPS and ESPRESSO Doppler measurements to refine orbital parameters, measure the planetary masses, and investigate the architecture and evolution of the system. We performed a Markov chain Monte Carlo joint analysis of the transit light curves and radial velocity time series, and carried out a dynamical analysis to model transit timing variations and Doppler measurements along with N-body integration. In agreement with previous results, we found that TOI-282 b, c, and d have radii of $R_b=2.69 \pm 0.23 \ R_{\oplus}$, $R_c=4.13^{+0.16}_{-0.14} \ R_{\oplus}$, and $R_d=3.11 \pm 0.15 \ R_{\oplus}$, respectively. We measured planetary masses of $M_b=6.2\pm1.6 \ M_{\oplus}$, $M_c=9.2\pm2.0 \ M_{\oplus}$, and $M_d=5.8^{+0.9}_{-1.1} \ M_{\oplus}$, which imply mean densities of $ρ_b=1.8^{+0.7}_{-0.6} \ \text{g cm}^{-3}$, $ρ_c=0.7 \pm 0.2 \ \text{g cm}^{-3}$, and $ρ_d=1.1^{+0.3}_{-0.2} \ \text{g cm}^{-3}$, respectively. The three planets may be water worlds, making TOI-282 an interesting system for future atmospheric follow-up observations with JWST and ELT. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: 20 pages, 13 figures

NGTS-11 c: a transiting Neptune-mass planet interior to the warm Saturn NGTS-11 b

Authors: David R. Anderson, Jose I. Vines, Katharine Hesse, Louise Dyregaard Nielsen, Rafael Brahm, Maximiliano Moyano, Peter J. Wheatley, Khalid Barkaoui, Allyson Bieryla, Matthew R. Burleigh, Ryan Cloutier, Karen A. Collins, Phil Evans, Steve B. Howell, John Kielkopf, Pablo Lewin, Richard P. Schwarz, Avi Shporer, Thiam-Guan Tan, Mathilde Timmermans, Amaury H. M. J. Triaud, Carl Ziegler, Ioannis Apergis, David J. Armstrong, Douglas R. Alves , et al. (34 additional authors not shown)

Abstract: We report the discovery of NGTS-11 c, a transiting warm Neptune ($P \approx 12.8$ d; $M_{p} = 1.2^{+0.3}_{-0.2} M_{\mathrm{Nep}}$; $R_{p} = 1.24 \pm 0.03 R_{\mathrm{Nep}}$), in an orbit interior to the previously reported transiting warm Saturn NGTS-11 b ($P \approx 35.5$ d). We also find evidence of a third outer companion orbiting the K-dwarf NGTS-11. We first detected transits of NGTS-11 c in T… ▽ More We report the discovery of NGTS-11 c, a transiting warm Neptune ($P \approx 12.8$ d; $M_{p} = 1.2^{+0.3}_{-0.2} M_{\mathrm{Nep}}$; $R_{p} = 1.24 \pm 0.03 R_{\mathrm{Nep}}$), in an orbit interior to the previously reported transiting warm Saturn NGTS-11 b ($P \approx 35.5$ d). We also find evidence of a third outer companion orbiting the K-dwarf NGTS-11. We first detected transits of NGTS-11 c in TESS light curves and confirmed them with follow-up transits from NGTS and many other ground-based facilities. Radial-velocity monitoring with the HARPS and FEROS spectrographs revealed the mass of NGTS-11 c and provides evidence for a long-period companion ($P > 2300$ d; $M_{p} \sin i > 3.6 M_{\mathrm{Jup}}$). Taking into account the two additional bodies in our expanded datasets, we find that the mass of NGTS-11 b ($M_{p} = 0.63 \pm 0.09 M_{\mathrm{Sat}}$; $R_{p} = 0.97 \pm 0.02 R_{\mathrm{Sat}}$) is lower than previously reported ($M_{p} = 1.2 \pm 0.3 M_{\mathrm{Sat}}$). Given their near-circular and compact orbits, NGTS-11 c and b are unlikely to have reached their present locations via high-eccentricity migration. Instead, they probably either formed in situ or formed farther out and then underwent disk migration. A comparison of NGTS-11 with the eight other known systems hosting multiple well-characterized warm giants shows that it is most similar to Kepler-56. Finally, we find that the commonly used 10-day boundary between hot and warm Jupiters is empirically well supported. △ Less

Submitted 15 October, 2025; originally announced October 2025.

Comments: 12 pages, 6 figures, submitted to ApJ

An Ultra-Short Period Super-Earth and Sub-Neptune Spanning the Radius Valley Orbiting the Kinematic Thick Disk Star TOI-2345

Authors: Yoshi Nike Emilia Eschen, Thomas G. Wilson, Andrea Bonfanti, Carina M. Persson, Sérgio G. Sousa, Monika Lendl, Alexis Heitzmann, Attila E. Simon, Göran Olofsson, Amadeo Castro-González, Jo Ann Egger, Luca Fossati, Alexander James Mustill, Hugh P. Osborn, Hugo G. Vivien, Yann Alibert, Roi Alonso, Tamas Bárczy, David Barrado, Susana C. C. Barros, Wolfgang Baumjohann, Willy Benz, Nicolas Billot, Luca Borsato, Alexis Brandeker , et al. (72 additional authors not shown)

Abstract: A crucial chemical link between stars and their orbiting exoplanets is thought to exist. If universal, this connection could affect the formation and evolution of all planets. Therefore, this potential vital link needs testing by characterising exoplanets around chemically-diverse stars. We present the discovery of two planets orbiting the metal-poor, kinematic thick-disk K-dwarf TOI-2345. TOI-234… ▽ More A crucial chemical link between stars and their orbiting exoplanets is thought to exist. If universal, this connection could affect the formation and evolution of all planets. Therefore, this potential vital link needs testing by characterising exoplanets around chemically-diverse stars. We present the discovery of two planets orbiting the metal-poor, kinematic thick-disk K-dwarf TOI-2345. TOI-2345 b is a super-Earth with a period of 1.05 days and TOI-2345 c is a sub-Neptune with a period of 21 days. In addition to the target being observed in 4 TESS sectors, we obtained 5 CHEOPS visits and 26 radial velocities from HARPS. By conducting a joint analysis of all the data, we find TOI-2345 b to have a radius of $1.504\substack{+0.047\\-0.044}$ R$_\oplus$ and a mass of $3.49\pm0.85$ M$_\oplus$; and TOI-2345 c to have a radius of $2.451\substack{+0.045\\-0.046}$ R$_\oplus$ and a mass of $7.27\substack{+2.27\\-2.45}$ M$_\oplus$. To explore chemical links between these planets and their host star, we model their interior structures newly accounting for devolatised stellar abundances. TOI-2345 adds to the limited sample of well characterised planetary systems around thick disk stars. This system challenges theories of formation and populations of planets around thick disk stars with its Ultra-Short Period super-Earth and the wide period distribution of these two planets spanning the radius valley. △ Less

Submitted 14 October, 2025; originally announced October 2025.

Comments: Accepted for publication in MNRAS

No Observational Evidence for Dark Matter Nor a Large Metallicity Spread in the Extreme Milky Way Satellite Ursa Major III / UNIONS 1

Authors: William Cerny, Daisy Bissonette, Alexander P. Ji, Marla Geha, Anirudh Chiti, Simon E. T. Smith, Joshua D. Simon, Andrew B. Pace, Evan N. Kirby, Kim A. Venn, Ting S. Li, Alice M. Luna

Abstract: The extremely-low-luminosity, compact Milky Way satellite Ursa Major III / UNIONS 1 (UMaIII/U1; $L_V = 11 \ L_{\odot}$; $a_{1/2} = 3$ pc) was found to have a substantial velocity dispersion at the time of its discovery ($σ_v = 3.7^{+1.4}_{-1.0} \rm \ km \ s^{-1}$), suggesting that it might be an exceptional, highly dark-matter-dominated dwarf galaxy with very few stars. However, significant questi… ▽ More The extremely-low-luminosity, compact Milky Way satellite Ursa Major III / UNIONS 1 (UMaIII/U1; $L_V = 11 \ L_{\odot}$; $a_{1/2} = 3$ pc) was found to have a substantial velocity dispersion at the time of its discovery ($σ_v = 3.7^{+1.4}_{-1.0} \rm \ km \ s^{-1}$), suggesting that it might be an exceptional, highly dark-matter-dominated dwarf galaxy with very few stars. However, significant questions remained about the system's dark matter content and nature as a dwarf galaxy due to the small member sample ($N=11$), possible spectroscopic binaries, and the lack of any metallicity information. Here, we present new spectroscopic observations covering $N=16$ members that both dynamically and chemically test UMaIII/U1's true nature. From higher-precision Keck/DEIMOS spectra, we find a 95% confidence level velocity dispersion limit of $σ_v< 2.3 \rm \ km \ s^{-1}$, with a $\sim$120:1 likelihood ratio now favoring the expected stellar-only dispersion of $σ_* \approx 0.1 \rm \ km \ s^{-1}$ over the original $3.7 \rm \ km \ s^{-1}$ dispersion. There is now no observational evidence for dark matter in the system. From Keck/LRIS spectra targeting the Calcium II K line, we also measure the first metallicities for 12 member stars, finding a mean metallicity of $\rm [Fe/H] = -2.65 \; \pm \, 0.1$ (stat.) $\pm \,0.3$ (zeropoint) with a metallicity dispersion limit of $σ_{\rm [Fe/H]} < 0.35$ dex (at the 95% credible level). Together, these properties are more consistent with UMaIII/U1 being a star cluster, though the dwarf galaxy scenario is not fully ruled out. Under this interpretation, UMaIII/U1 ranks among the faintest and most metal-poor star clusters yet discovered. △ Less

Submitted 2 December, 2025; v1 submitted 2 October, 2025; originally announced October 2025.

Comments: 11+8 pages; 6 figures. Accepted to ApJL with minor text revisions; results unchanged

The Yasone catalogue: three new Milky Way satellites and 17 further hypercompact candidates

Authors: J. Untzaga, M. Mezcua, S. Bonoli, N. Bastian, J. F. Navarro, S. E. T. Smith, F. Pérez-Toledo, D. Boyea

Abstract: We present the discovery of three new low-latitude (|b| ~ 20$^{\circ}$) Milky Way satellites: Yasone-1, Yasone-2, and Yasone-3. They were identified in our search for compact stellar overdensities in the Panoramic Survey Telescope and Rapid Response System 1, supported by follow-up deep photometric imaging from the Gran Telescopio Canarias OSIRIS instrument and Gaia astrometric data. These three n… ▽ More We present the discovery of three new low-latitude (|b| ~ 20$^{\circ}$) Milky Way satellites: Yasone-1, Yasone-2, and Yasone-3. They were identified in our search for compact stellar overdensities in the Panoramic Survey Telescope and Rapid Response System 1, supported by follow-up deep photometric imaging from the Gran Telescopio Canarias OSIRIS instrument and Gaia astrometric data. These three new Milky Way satellites are found as compact stellar overdensities that exhibit structural and photometric properties consistent with old, metal-poor populations. All three are best described by isochrone fits corresponding to an age of ~12 Gyr and subsolar metallicities: [Fe/H] ~ -1.5 for Yasone-1 and Yasone-2, and [Fe/H] ~ -2.0 for Yasone-3. Yasone-1, located at a heliocentric distance of 12 kpc, has a physical half-light radius of 1.40 pc, an absolute V-band magnitude of +2.36, and a total stellar mass of 18.2 M$_{\odot}$. Yasone-2, at a distance of 20 kpc, has a slightly larger size of 2.44 pc, a brighter V-band magnitude of +1.83, and a higher mass of 28.0 M$_{\odot}$. Yasone-3, located at 15 kpc, is the faintest and least massive of the three, with M$_{V}$ = +2.52, a stellar mass of 14.4 M$_{\odot}$, and a half-light radius of 2.09 pc. We also report a fourth (Yasone-4), lower-confidence hypercompact candidate located at Galactic latitude (b ~ 48$^{\circ}$), identified by replicating our search using the photometric catalogue of the Hyper Suprime-Cam Subaru Strategic Program Public Release. Finally, we present the discovery of sixteen (Yasone-5 to Yasone-20) new hypercompact cluster candidates in the Galactic disc. We discuss the possibility that any of the Yasone clusters may host an intermediate-mass black hole, and we advocate for follow-up spectroscopic observations to further constrain their nature. △ Less

Submitted 18 September, 2025; originally announced September 2025.

Comments: Submitted to MNRAS on September 17th with manuscript ID: MN-25-2168-MJ, 15 pages, 10 figures

Systematic Bayesian Evaluation of Resonance Parameters in 19Ne for the 15O(alpha,gamma)19Ne and 18F(p,alpha)15O Reactions

Authors: S. H. Kim, K. Y. Chae, C. H. Kim, C. D. Nesaraja, M. S. Smith

Abstract: We present a comprehensive evaluation of the nuclear structure properties of 19Ne using a novel and rigorous Bayesian statistical framework. Precise characterization of 19Ne resonance parameters is critical for accurately determining reaction rates of the astrophysically significant 15O(alpha, gamma)19Ne and 18F(p, alpha)15O reactions, which govern breakout from the hot CNO cycle in X-ray bursts a… ▽ More We present a comprehensive evaluation of the nuclear structure properties of 19Ne using a novel and rigorous Bayesian statistical framework. Precise characterization of 19Ne resonance parameters is critical for accurately determining reaction rates of the astrophysically significant 15O(alpha, gamma)19Ne and 18F(p, alpha)15O reactions, which govern breakout from the hot CNO cycle in X-ray bursts and influence gamma-ray emission in novae, respectively. By reconstructing likelihood functions from published experimental data, including asymmetric uncertainties and upper or lower limits, we derive posterior distributions for resonance energies, decay widths, and branching ratios. Our Bayesian approach systematically incorporates previously reported discrepancies among measurements, providing a statistically robust and consistent treatment of these uncertainties. The evaluated resonance parameters and associated uncertainties provide crucial input for stellar nucleosynthesis modeling, contributing to a refined understanding of explosive astrophysical phenomena. △ Less

Submitted 17 September, 2025; originally announced September 2025.

Transit Timing Variations in HIP 41378: CHEOPS and TESS confirm a non-transiting sixth planet in the system

Authors: P. Leonardi, L. Borsato, L. Pagliaro, D. Kubyshkina, J. A. Egger, T. G. Wilson, A. Heitzmann, A. Brandeker, M. N. Günther, V. Nascimbeni, A. Leleu, S. G. Sousa, A. Bonfanti, G. Mantovan, G. Piotto, L. Fossati, D. Nardiello, T. Zingales, V. Adibekyan, C. Pezzotti, B. Akinsanmi, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado , et al. (67 additional authors not shown)

Abstract: In multiple-planet systems, gravitational interactions of exoplanets could lead to transit timing variations (TTVs), whose amplitude becomes significantly enhanced when planets are in or near mean-motion resonances (MMRs). In cases where both TTVs and radial velocity (RV) measurements are available, combined analysis can break degeneracies and provide robust planetary and system characterization,… ▽ More In multiple-planet systems, gravitational interactions of exoplanets could lead to transit timing variations (TTVs), whose amplitude becomes significantly enhanced when planets are in or near mean-motion resonances (MMRs). In cases where both TTVs and radial velocity (RV) measurements are available, combined analysis can break degeneracies and provide robust planetary and system characterization, even detecting non-transiting planets. In this context, HIP 41378 hosts five confirmed transiting planets with periods ranging from 15 to over 542 days, providing a unique dynamical laboratory for investigating wide multi-planet systems analogous to the Solar System. In this study, we present an intensive space-based photometric follow-up of HIP 41378, combining 15 new CHEOPS observations with eight TESS sectors, alongside data from K2, Spitzer, HST, and HARPS. We dynamically modeled the TTVs and RV signals of the two inner sub-Neptunes via N-body integration. These planets, HIP 41378 b ($P_{b}$ = 15.57 days) and HIP 41378 c ($P_{c}$ = 31.71 days), are close to ($Δ\sim1.8$ %) a 2:1 period commensurability. We report a clear detection of TTVs with amplitudes of 20 mins for planet b and greater than 3 hrs for planet c. We dynamically confirm the planetary nature of HIP 41378 g, a non-transiting planet with a period of about 64 days and a mass of about 7 $M_{\oplus}$, close to a 2:1 commensurability with planet c, suggesting a possible MMR chain in the inner system. Our precise determination of the masses, eccentricities, and radii of HIP 41378 b and c enabled us to investigate their possible volatile-rich compositions. Finally, by leveraging on the last TESS sectors we constrained the period of HIP 41378 d to three possible aliases ($P_{d} =$ 278, 371, and 1113 days) suggesting that the system could be placed in a double quasi resonant chain, highlighting its complex dynamical architecture. △ Less

Submitted 1 November, 2025; v1 submitted 17 September, 2025; originally announced September 2025.

Comments: 22 pages, 11 figures. Accepted for publication on Astronomy & Astrophysics

Journal ref: A&A 702, A211 (2025)

A four-planet system orbiting the old thick disk star TOI-1203

Authors: D. Gandolfi, A. Alnajjarine, L. M. Serrano, J. A. Egger, K. W. F. Lam, J. Cabrera, A. P. Hatzes, M. Fridlund, M. Garbaccio Gili, T. G. Wilson, W. D. Cochran, A. Brandeker, E. Goffo, S. G. Sousa, G. Nowak, A. Heitzmann, C. Hellier, J. Venturini, J. Livingston, A. Bonfanti, O. Barragán, V. Adibekyan, E. Knudstrup, Y. Alibert, S. Grziwa , et al. (98 additional authors not shown)

Abstract: TOI-1203 is a bright (V=8.6) G3 V star known to host a transiting warm sub-Neptune on a 25.5 d orbit. Here we report on an intensive high-precision radial velocity and photometric follow-up campaign carried out with the HARPS spectrograph and the CHEOPS space telescope. We found that TOI-1203 has an enhancement of $α$ elements relative to iron of [$α$/Fe]=$0.21\pm0.04$. With an age of $\sim$12.5 G… ▽ More TOI-1203 is a bright (V=8.6) G3 V star known to host a transiting warm sub-Neptune on a 25.5 d orbit. Here we report on an intensive high-precision radial velocity and photometric follow-up campaign carried out with the HARPS spectrograph and the CHEOPS space telescope. We found that TOI-1203 has an enhancement of $α$ elements relative to iron of [$α$/Fe]=$0.21\pm0.04$. With an age of $\sim$12.5 Gyr, TOI-1203 belongs to the old, $α$-element enhanced stellar population of the galactic thick disk. We spectroscopically confirmed the planetary nature of the 25.5 d sub-Neptune TOI-1203 d, measured its mass ($M_{d}=7.39\pm0.62~M_{\oplus}$) and refined its radius ($R_{d}=2.918_{-0.045}^{+0.046}~R_{\oplus}$). We discovered the presence of an additional transiting super-Earth on a 4.2 d orbit (TOI-1203 b) with a mass of $M_{b}=3.51_{-0.32}^{+0.33}~M_{\oplus}$ and a radius of $R_{b}=1.520_{-0.046}^{+0.045}~R_{\oplus}$. We also revealed the presence of two additional low-mass planets at 13.1 d and 204.6 d (TOI-1203 c and e), with minimum masses of $5.46_{-0.50}^{+0.51}~M_{\oplus}$ and $42.10_{-1.78}^{+1.83}~M_{\oplus}$. We found that the outer planet TOI-1203 e lies on an eccentric orbit with $e_{e}=0.152\pm0.029$. We performed a stability analysis of the system confirming that there are configurations consistent with the observed parameters that are dynamically stable over billion-year timescales. While analyzing the HARPS time series, we discovered that the FWHM of the HARPS cross-correlation function shows a significant long-period signal ($\sim$615 d) that has no counterpart in the radial velocity data or in the remaining HARPS ancillary time series. We significantly detected the same signal in the FWHM of the Th-Ar calibration lines used to compute the nightly wavelength solution, and attributed this systematic effect to a long-term variation of the HARPS instrumental profile. △ Less

Submitted 12 September, 2025; originally announced September 2025.

Comments: Accepted for publication in A&A. Abstract abridged as per arXiv directive

Improved characterization of the TOI-2141 system: a dense sub-Neptune with non-transiting inner and outer companions

Authors: R. Luque, K. W. F. Lam, J. Cabrera, A. Bonfanti, Y. N. E. Eschen, G. Olofsson, W. Benz, N. Billot, A. Brandeker, A. C. M. Correia, L. Fossati, D. Gandolfi, H. P. Osborn, C. Pezzotti, S. G. Sousa, T. G. Wilson, S. Wolf, Y. Alibert, R. Alonso, J. Asquier, T. Bárczy, D. Barrado, S. C. C. Barros, W. Baumjohann, F. Biondi , et al. (65 additional authors not shown)

Abstract: We aim to refine the fundamental parameters of the TOI-2141 planetary system, which includes a transiting sub-Neptune orbiting a Sun-like star in a relatively long orbit of 18.26 days, by combining new photometric and spectroscopic observations. We analyze new space-based photometry from TESS and CHEOPS as well as 61 radial velocity measurements from HARPS-N. We perform individual and joint photom… ▽ More We aim to refine the fundamental parameters of the TOI-2141 planetary system, which includes a transiting sub-Neptune orbiting a Sun-like star in a relatively long orbit of 18.26 days, by combining new photometric and spectroscopic observations. We analyze new space-based photometry from TESS and CHEOPS as well as 61 radial velocity measurements from HARPS-N. We perform individual and joint photometric and RV analyses using several modeling tools within a Bayesian model comparison framework. We refine the radius and mass of the transiting planet TOI-2141 b to 3.15 $\pm$ 0.04 $R_\oplus$ and 20.1 $\pm$ 1.6 $M_\oplus$, respectively, five and two times more precise than the previously reported values. Our radial velocity analysis reveals two additional non-transiting companions with orbital periods of 5.46 and 60.45 days. Despite the innermost planet's high geometric transit probability, we find no evidence for transits in the photometric data. The bulk properties of TOI-2141 b suggest a significant volatile envelope atop an Earth-like core, with modeling indicating a hydrogen-rich atmosphere that may have experienced mild photoevaporation over the system's history. Planets b and c must exhibit a modest mutual inclination of at least 2.4 degrees. △ Less

Submitted 31 August, 2025; originally announced September 2025.

Comments: Accepted for publication in A&A

TOI-1438: A rare system with two short-period sub-Neptunes and a tentative long-period Jupiter-like planet orbiting a K0V star

Authors: Carina M. Persson, Emil Knudstrup, Ilaria Carleo, Lorena Acuña-Aguirre, Grzegorz Nowak, Alexandra Muresan, Dawid Jankowski, Krzysztof Gozdziewski, Rafael A. García, Savita Mathur, Dinil B. Palakkatharappil, Lina Borg, Alexander J. Mustill, Rafael Barrena, Malcolm Fridlund, Davide Gandolfi, Artie P. Hatzes, Judith Korth, Rafael Luque, Eduardo L. Martín, Thomas Masseron, Giuseppe Morello, Felipe Murgas, Jaume Orell-Miquel, Enric Palle , et al. (22 additional authors not shown)

Abstract: We present the detection and characterisation of the TOI-1438 multi-planet system discovered by TESS. We collected a series of follow-up observations including high-spectral resolution observations with HARPS-N over a period of five years. Our modelling shows that the K0V star hosts two transiting sub-Neptunes with Rb = 3.04 +/- 0.19 RE, Rc = 2.75 +/- 0.14 RE, Mb = 9.4 +/- 1.8 ME, and Mc = 10.6 +/… ▽ More We present the detection and characterisation of the TOI-1438 multi-planet system discovered by TESS. We collected a series of follow-up observations including high-spectral resolution observations with HARPS-N over a period of five years. Our modelling shows that the K0V star hosts two transiting sub-Neptunes with Rb = 3.04 +/- 0.19 RE, Rc = 2.75 +/- 0.14 RE, Mb = 9.4 +/- 1.8 ME, and Mc = 10.6 +/- 2.1 ME. The orbital periods of planets b and c are 5.1 and 9.4 days, respectively, corresponding to instellations of 145 +/- 10 and 65 +/- 4 FE. The bulk densities are 1.8 +/- 0.5 and 2.9 +/- 0.7 g cm-3, respectively, suggesting a volatile-rich interior composition. We computed a set of planet interior structure models. Planet b presents a high-metallicity envelope that can accommodate up to 2.5 % in H/He in mass, while planet c cannot have more than 0.2 % as H/He in mass. For any composition of the core considered (Fe-rock or ice-rock), both planets would require a volatile-rich envelope. In addition to the two planets, the radial velocity (RV) data clearly reveal a third signal, likely coming from a non-transiting planet, with an orbital period of 7.6 +1.6 -2.4 years and a radial velocity semi-amplitude of 35+3-5 m s-1. Our best fit model finds a minimum mass of 2.1 +/- 0.3 MJ and an eccentricity of 0.25+0.08-0.11. However, several RV activity indicators also show strong signals at similar periods, suggesting this signal might (partly) originate from stellar activity. More data over a longer period of time are needed to conclusively determine the nature of this signal. If it is confirmed as a triple-planet system, TOI-1438 would be one of the few detected systems to date characterised by an architecture with two small, short-period planets and one massive, long-period planet, where the inner and outer systems are separated by an orbital period ratio of the order of a few hundred. △ Less

Submitted 29 August, 2025; originally announced August 2025.

Comments: 31 pages, 21 figures. Accepted by Astronomy & Astrophysics (A&A) 31 July 2025

Journal ref: A&A 702, A69 (2025)

The CHEOPS view of HD 95338b: refined transit parameters, and a search for exomoons

Authors: Sz. Kálmán, A. E. Simon, A. Deline, Sz. Csizmadia, Gy. M. Szabó, D. Ehrenreich, T. G. Wilson, M. N. Günther, A. Heitzmann, S. G. Sousa, M. Farnir, A. Bonfanti, A. M. S. Smith, A. Pál, G. Scandariato, V. Adibekyan, A. Brandeker, S. Charnoz, B. Akinsanmi, S. C. C. Barros, X. Song, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues , et al. (68 additional authors not shown)

Abstract: Despite the ever-increasing number of known exoplanets, no uncontested detections have been made of their satellites, known as exomoons. The quest to find exomoons is at the forefront of exoplanetary sciences. Certain space-born instruments are thought to be suitable for this purpose. We show the progress made with the CHaracterizing ExOPlanets Satellite (CHEOPS) in this field using the HD 95338 p… ▽ More Despite the ever-increasing number of known exoplanets, no uncontested detections have been made of their satellites, known as exomoons. The quest to find exomoons is at the forefront of exoplanetary sciences. Certain space-born instruments are thought to be suitable for this purpose. We show the progress made with the CHaracterizing ExOPlanets Satellite (CHEOPS) in this field using the HD 95338 planetary system. We present a novel methodology as an important step in the quest to find exomoons. We utilize ground-based spectroscopic data in combination with Gaia observations to obtain precise stellar parameters. These are then used as input in the analysis of the planetary transits observed by CHEOPS and the Transiting Exoplanet Survey Satellite (TESS). In addition, we search for the signs of satellites primarily in the form of additional transits in the Hill sphere of the eccentric Neptune-sized planet HD 95338b in a sequential approach based on four CHEOPS visits. We also briefly explore the transit timing variations of the planet. We present refined stellar and planetary parameters, narrowing down the uncertainty on the planet-to-star radius ratio by a factor of $10$. We also pin down the ephemeris of HD 95338b. Using injection/retrieval tests, we show that a $5 σ$ detection of an exomoon would be possible at $R_{\rm Moon} = 0.8$~$R_\oplus$ with the methodology presented here. We exclude the transit of an exomoon in the system with $R_{\rm Moon} \approx 0.6$~$R_\oplus$ at the $1σ$ level. The algorithm used for finding the transit-like event can be used as a baseline for other similar targets, observed by CHEOPS or other missions. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: Accepted for publication in A&A on 15/07/2025. 22 pages, 12 figures

Journal ref: A&A 701, A240 (2025)

The KELT-7b atmospheric thermal-inversion conundrum revisited with CHEOPS, TESS, and additional data

Authors: Z. Garai, A. Krenn, P. E. Cubillos, G. Bruno, A. M. S. Smith, T. G. Wilson, A. Brandeker, M. N. Günther, A. Heitzmann, L. Carone, V. Singh, M. Lendl, O. D. S. Demangeon, Y. Alibert, R. Alonso, J. Asquier, T. Bárczy, D. Barrado, S. C. Barros, W. Baumjohann, W. Benz, N. Billot, L. Borsato, C. Broeg, A. Collier Cameron , et al. (62 additional authors not shown)

Abstract: Ultrahot Jupiters are predicted to show inverted temperature-pressure (T-P) profiles in the presence of optical absorbers such as TiO and VO. An inverted T-P profile of KELT-7b was recently detected, in line with these predictions, but such diagnoses are known to be model-dependent. We used CHEOPS, TESS, and literature data to characterize the atmosphere of KELT-7b, reassess its T-P profile, measu… ▽ More Ultrahot Jupiters are predicted to show inverted temperature-pressure (T-P) profiles in the presence of optical absorbers such as TiO and VO. An inverted T-P profile of KELT-7b was recently detected, in line with these predictions, but such diagnoses are known to be model-dependent. We used CHEOPS, TESS, and literature data to characterize the atmosphere of KELT-7b, reassess its T-P profile, measure its albedo, and search for distortions in its CHEOPS transit light curve due to stellar rotation. We jointly fitted CHEOPS and TESS data to measure the occultation depths and modeled CHEOPS transits including gravity darkening. Emission and transmission retrievals were performed, and the albedo was calculated in the CHEOPS and TESS passbands. Thermochemical-equilibrium retrievals yield a non-inverted T-P profile, while free-chemistry retrievals yield an inverted profile with likely unphysical TiO/VO abundances. A 3D GCM supports a TiO-driven inversion. We report a low geometric albedo of $A_\mathrm{g} = 0.05 \pm 0.06$, consistent with inefficient heat redistribution and supported by a GCM with magnetic drag. CHEOPS data provide no constraint on the sky-projected orbital obliquity. Retrieval results strongly depend on the chemical framework. Free-chemistry fits are better but risk unphysical solutions for ultrahot Jupiters. We applied a coherent stellar variability correction to CHEOPS and TESS data; future observations would benefit from similar treatment. △ Less

Submitted 25 June, 2025; originally announced June 2025.

Comments: Accepted for publication in A&A

Dark skies of the slightly eccentric WASP-18 b from its optical-to-infrared dayside emission

Authors: A. Deline, P. E. Cubillos, L. Carone, B. -O. Demory, M. Lendl, W. Benz, A. Brandeker, M. N. Günther, A. Heitzmann, S. C. C. Barros, L. Kreidberg, G. Bruno, D. Kitzmann, A. Bonfanti, M. Farnir, C. M. Persson, S. G. Sousa, T. G. Wilson, D. Ehrenreich, V. Singh, N. Iro, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues , et al. (64 additional authors not shown)

Abstract: We performed a joint analysis of phase-curve observations of the ultra-hot Jupiter WASP-18 b from the visible to the mid-infrared, using data from CHEOPS, TESS and Spitzer. We aim to characterise the planetary atmosphere with a consistent view over the large wavelength range covered using GCMs and retrieval analyses, and including JWST data. We obtained new ephemerides with unprecedented precision… ▽ More We performed a joint analysis of phase-curve observations of the ultra-hot Jupiter WASP-18 b from the visible to the mid-infrared, using data from CHEOPS, TESS and Spitzer. We aim to characterise the planetary atmosphere with a consistent view over the large wavelength range covered using GCMs and retrieval analyses, and including JWST data. We obtained new ephemerides with unprecedented precisions of 1 second and 1.4 millisecond on the time of inferior conjunction and orbital period, respectively. We computed a planetary radius of $R_p = 1.1926 \pm 0.0077 R_J$ with a precision of 0.65% (or 550 km). Based on a timing inconsistency with JWST, we discuss and confirm orbital eccentricity ($e = 0.00852 \pm 0.00091$). We also constrain the argument of periastron to $ω= 261.9^{+1.3}_{-1.4}$ deg. We show that the large dayside emission implies the presence of magnetic drag and super-solar metallicity. We find a steep thermally inverted gradient in the planetary atmosphere, which is common for UHJs. We detected the presence of strong CO emission lines at 4.5 $μ$m from an excess of dayside brightness in the Spitzer/IRAC/Ch2 passband. Using these models to constrain the reflected contribution in the CHEOPS passband, we derived an extremely low geometric albedo of $A_g^\text{CHEOPS} = 0.027 \pm 0.011$. △ Less

Submitted 27 May, 2025; v1 submitted 2 May, 2025; originally announced May 2025.

Comments: 31 pages, 17 figures, 13 tables (including the appendix); accepted for publication in A&A

Journal ref: A&A 699, A150 (2025)

JWST's sharper view of EX Lup: cold water from ice sublimation during accretion outbursts

Authors: Sarah A. Smith, Carlos E. Romero-Mirza, Andrea Banzatti, Christian Rab, Peter Abraham, Agnes Kospal, Rik Claes, Carlo F. Manara, Karin I. Oberg, Jeroen Bouwman, Fernando Cruz-Saenz de Miera, Joel D. Green

Abstract: The unstable accretion phases during pre-main-sequence evolution of T Tauri stars produce variable irradiation and heating of planet-forming regions. A strong accretion outburst was observed with Spitzer-IRS in 2008 in EX Lup, the prototype of EXor variables, and found to increase the mid-infrared water and OH emission and decrease organic emission, suggesting large chemical changes. We present he… ▽ More The unstable accretion phases during pre-main-sequence evolution of T Tauri stars produce variable irradiation and heating of planet-forming regions. A strong accretion outburst was observed with Spitzer-IRS in 2008 in EX Lup, the prototype of EXor variables, and found to increase the mid-infrared water and OH emission and decrease organic emission, suggesting large chemical changes. We present here two JWST-MIRI epochs of quiescent EX Lup in 2022 and 2023 obtained over a decade after the 2008 outburst and several months after a moderate burst in 2022. With JWST's sharper spectral view, we can now analyze water emission as a function of temperature in the two MIRI epochs and, approximately, also in the previous Spitzer epochs. This new analysis shows a strong cold water vapor ``burst" in low-energy lines during the 2008 outburst, which we consider clear evidence for enhanced ice sublimation due to a recession of the snowline, as found in protostellar envelopes. JWST shows that EX Lup still has an unusually strong emission from cold water in comparison to other T Tauri disks, suggesting > 10-yr-long freeze-out timescales in the inner disk surface. EX Lup demonstrates that outbursts can significantly change the observed organic-to-water ratios and increase the cold water reservoir, providing chemical signatures to study the recent accretion history of disks. This study provides an unprecedented demonstration of the chemical evolution triggered by accretion outbursts in the Class II phase and of the high potential of time-domain experiments to reveal processes that may have fundamental implications on planet-forming bodies near the snowline. △ Less

Submitted 17 April, 2025; originally announced April 2025.

Comments: Accepted for publication in ApJ Letters

UNIONS: The Ultraviolet Near-Infrared Optical Northern Survey

Authors: Stephen Gwyn, Alan W. McConnachie, Jean-Charles Cuillandre, Ken C. Chambers, Eugene A. Magnier, Michael J. Hudson, Masamune Oguri, Hisanori Furusawa, Hendrik Hildebrandt, Raymond Carlberg, Sara L. Ellison, Junko Furusawa, Raphaël Gavazzi, Rodrigo Ibata, Yannick Mellier, Ken Osato, H. Aussel, Lucie Baumont, Manuel Bayer, Olivier Boulade, Patrick Côté, David Chemaly, Cail Daley, Pierre-Alain Duc, A. Ellien , et al. (64 additional authors not shown)

Abstract: The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10σ$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are… ▽ More The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10σ$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are $[u,g,r,i,z] = [23.7, 24.5, 24.2, 23.8, 23.3]$\ in AB magnitudes. UNIONS is addressing some of the most fundamental questions in astronomy, including the properties of dark matter, the growth of structure in the Universe from the very smallest galaxies to large-scale structure, and the assembly of the Milky Way. It is set to become the major ground-based legacy survey for the northern hemisphere for the next decade and provides an essential northern complement to the static-sky science of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. UNIONS supports the core science mission of the {\it Euclid} space mission by providing the data necessary in the northern hemisphere for the calibration of the wavelength dependence of the {\it Euclid} point-spread function and derivation of photometric redshifts in the North Galactic Cap. This region contains the highest quality sky for {\it Euclid}, with low backgrounds from the zodiacal light, stellar density, extinction, and emission from Galactic cirrus. Here, we describe the UNIONS survey components, science goals, data products, and the current status of the overall program. △ Less

Submitted 17 March, 2025; originally announced March 2025.

Comments: submitted to AJ

Characterization of a TES-based Anti-Coincidence Detector for Future Large Field-of-View X-ray Calorimetry Missions

Authors: Samuel V. Hull, Joseph S. Adams, Simon R. Bandler, Matthew Cherry, James A. Chervenak, Renata Cumbee, Xavier Defay, Enectali Figueroa-Feliciano, Fred M. Finkbeiner, Joshua Fuhrman, Richard L. Kelley, Christopher Kenney, Caroline A. Kilbourne, Noah Kurinsky, Jennette Mateo, Haruka Muramatsu, Frederick S. Porter, Kazuhiro Sakai, Aviv Simchony, Stephen J. Smith, Zoe Smith, Nicholas A. Wakeham, Edward J. Wassell, Sang H. Yoon, Betty A. Young

Abstract: Microcalorimeter instruments aboard future X-ray observatories will require an anti-coincidence (anti-co) detector to veto charged particle events and reduce the non-X-ray background. We have developed a large-format, TES-based prototype anti-coincidence detector that is particularly suitable for use with spatially-extended (~ 10 cm^2}) TES microcalorimeter arrays, as would be used for a future la… ▽ More Microcalorimeter instruments aboard future X-ray observatories will require an anti-coincidence (anti-co) detector to veto charged particle events and reduce the non-X-ray background. We have developed a large-format, TES-based prototype anti-coincidence detector that is particularly suitable for use with spatially-extended (~ 10 cm^2}) TES microcalorimeter arrays, as would be used for a future large field-of-view X-ray missions. This prototype was developed in the context of the Line Emission Mapper (LEM) probe concept, which required a ~ 14 cm^2 anti-co detector with > 95% live time and a low-energy threshold below 20 keV. Our anti-co design employs parallel networks of quasiparticle-trap-assisted electrothermal feedback TESs (QETs) to detect the athermal phonon signal produced in the detector substrate by incident charged particles. We developed multiple prototype anti-co designs featuring 12 channels and up to 6300 QETs. Here we focus on a design utilizing tungsten TESs and present characterization results. Broad energy range measurements have been performed (4.1 keV -- 5.5 MeV). Based on noise and responsivity measurements, the implied low-energy threshold is < 1 keV and a live time fraction of > 96% can be achieved up to 5.5 MeV. We also find evidence of mm-scale-or-better spatial resolution and discuss the potential utility of this for future missions. Finally, we discuss the early development of a soild-state physics model of the anti-co towards understanding phonon propagation and quasiparticle production in the detector. △ Less

Submitted 19 February, 2025; originally announced February 2025.

Comments: 26 pages, 16 figures

Quantifying the Detectability of Milky Way Satellites with Image Simulations: a Case Study with KiDS

Authors: Shiyang Zhang, Hendrik Hildebrandt, Ziang Yan, Simon E. T. Smith, Massimiliano Gatto, Massimo Dall'Ora, Crescenzo Tortora, Shun-Sheng Li, Dominik Elsässer

Abstract: Ultra-faint dwarf galaxies, which can be detected as resolved satellite systems of the Milky Way, are critical to understanding galaxy formation, evolution, and the nature of dark matter, as they are the oldest, smallest, most metal-poor, and most dark matter-dominated stellar systems known. Quantifying the sensitivity of surveys is essential for understanding their capability and limitations in s… ▽ More Ultra-faint dwarf galaxies, which can be detected as resolved satellite systems of the Milky Way, are critical to understanding galaxy formation, evolution, and the nature of dark matter, as they are the oldest, smallest, most metal-poor, and most dark matter-dominated stellar systems known. Quantifying the sensitivity of surveys is essential for understanding their capability and limitations in searching for ultra-faint satellites. In this paper, we present the first study of the image-level observational selection function for Kilo-Degree Survey (KiDS) based on the Synthetic UniveRses For Surveys (surfs)-based KiDS-Legacy-Like Simulations. We generate mock satellites and simulate images that include resolved stellar populations of the mock satellites and the background galaxies, capturing realistic observational effects such as source blending, photometric uncertainties, and star-galaxy separation. The matched-filter method is applied to recover the injected satellites. We derive the observational selection function of the survey in terms of the luminosity, half-light radius, and heliocentric distance of the satellites. Compared to a catalogue-level simulation as used in previous studies, the image-level simulation provides a more realistic assessment of survey sensitivity, accounting for observational limitations that are neglected in catalogue-level simulations. The image-level simulation shows a detection loss for compact sources with a distance $d \gtrsim 100~\rm kpc$. We argue that this is because compact sources are more likely to be identified as single sources rather than being resolved during the source extraction process. △ Less

Submitted 6 May, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: 17 pages, 15 figures, 3 tables, submitted to Astronomy & Astrophysics

Journal ref: A&A 698, A108 (2025)

The X-ray Integral Field Unit at the end of the Athena reformulation phase

Authors: Philippe Peille, Didier Barret, Edoardo Cucchetti, Vincent Albouys, Luigi Piro, Aurora Simionescu, Massimo Cappi, Elise Bellouard, Céline Cénac-Morthé, Christophe Daniel, Alice Pradines, Alexis Finoguenov, Richard Kelley, J. Miguel Mas-Hesse, Stéphane Paltani, Gregor Rauw, Agata Rozanska, Jiri Svoboda, Joern Wilms, Marc Audard, Enrico Bozzo, Elisa Costantini, Mauro Dadina, Thomas Dauser, Anne Decourchelle , et al. (257 additional authors not shown)

Abstract: The Athena mission entered a redefinition phase in July 2022, driven by the imperative to reduce the mission cost at completion for the European Space Agency below an acceptable target, while maintaining the flagship nature of its science return. This notably called for a complete redesign of the X-ray Integral Field Unit (X-IFU) cryogenic architecture towards a simpler active cooling chain. Passi… ▽ More The Athena mission entered a redefinition phase in July 2022, driven by the imperative to reduce the mission cost at completion for the European Space Agency below an acceptable target, while maintaining the flagship nature of its science return. This notably called for a complete redesign of the X-ray Integral Field Unit (X-IFU) cryogenic architecture towards a simpler active cooling chain. Passive cooling via successive radiative panels at spacecraft level is now used to provide a 50 K thermal environment to an X-IFU owned cryostat. 4.5 K cooling is achieved via a single remote active cryocooler unit, while a multi-stage Adiabatic Demagnetization Refrigerator ensures heat lift down to the 50 mK required by the detectors. Amidst these changes, the core concept of the readout chain remains robust, employing Transition Edge Sensor microcalorimeters and a SQUID-based Time-Division Multiplexing scheme. Noteworthy is the introduction of a slower pixel. This enables an increase in the multiplexing factor (from 34 to 48) without compromising the instrument energy resolution, hence keeping significant system margins to the new 4 eV resolution requirement. This allows reducing the number of channels by more than a factor two, and thus the resource demands on the system, while keeping a 4' field of view (compared to 5' before). In this article, we will give an overview of this new architecture, before detailing its anticipated performances. Finally, we will present the new X-IFU schedule, with its short term focus on demonstration activities towards a mission adoption in early 2027. △ Less

Submitted 15 February, 2025; originally announced February 2025.

Comments: 44 pages, 14 figures, accepted for publication in Experimental Astronomy

Deep in the Fields of the Andromeda Halo: Discovery of the Pegasus VII dwarf galaxy in UNIONS

Authors: Simon E. T. Smith, Alan W. McConnachie, Stephen Gwyn, Christian R. Hayes, Massimiliano Gatto, Ken Chambers, Jean-Charles Cuillandre, Michael J. Hudson, Eugene Magnier, Nicolas Martin, Julio Navarro

Abstract: We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 sub-group which has been uncovered in the $ri$ photometric catalogs from the Ultraviolet Near-Infrared Optical Northern Survey and confirmed with follow-up imaging from both the Canada-France-Hawaii Telescope and the Gemini-North Telescope. This system has an absolute $V$-band magnitude of $-5.7 \pm 0.2$ mag an… ▽ More We present the newly discovered dwarf galaxy Pegasus VII (Peg VII), a member of the M31 sub-group which has been uncovered in the $ri$ photometric catalogs from the Ultraviolet Near-Infrared Optical Northern Survey and confirmed with follow-up imaging from both the Canada-France-Hawaii Telescope and the Gemini-North Telescope. This system has an absolute $V$-band magnitude of $-5.7 \pm 0.2$ mag and a physical half-light radius of $177^{+36}_{-34}$ pc, which is characteristic of dynamically-confirmed Milky Way satellite dwarf galaxies and about 5 times more extended than the most extended M31 globular clusters. Peg VII lies at a three-dimensional separation from M31 of $331^{+15}_{-4}$ kpc and a significant elongation ($ε\sim 0.5$) towards the projected direction of M31 could be indicative of a past tidal interaction, but additional investigation into the orbit, star formation history, and whether any gas remains in the galaxy is needed to better understand the evolution of Peg VII. △ Less

Submitted 13 February, 2025; originally announced February 2025.

Comments: 13 pages, 5 figures, accepted for publication in ApJ

Searching for Hot Water World Candidates with CHEOPS: Refining the radii and analysing the internal structures and atmospheric lifetimes of TOI-238 b and TOI-1685 b

Authors: J. A. Egger, D. Kubyshkina, Y. Alibert, H. P. Osborn, A. Bonfanti, T. G. Wilson, A. Brandeker, M. N. Günther, M. Lendl, D. Kitzmann, L. Fossati, C. Mordasini, S. G. Sousa, V. Adibekyan, M. Fridlund, C. Pezzotti, D. Gandolfi, S. Ulmer-Moll, R. Alonso, T. Bárczy, D. Barrado Navascues, S. C. Barros, W. Baumjohann, W. Benz, N. Billot , et al. (63 additional authors not shown)

Abstract: Studying the composition of exoplanets is one of the most promising approaches to observationally constrain planet formation and evolution processes. However, this endeavour is complicated for small exoplanets by the fact that a wide range of compositions is compatible with their bulk properties. To overcome this issue, we identify triangular regions in the mass-radius space where part of this deg… ▽ More Studying the composition of exoplanets is one of the most promising approaches to observationally constrain planet formation and evolution processes. However, this endeavour is complicated for small exoplanets by the fact that a wide range of compositions is compatible with their bulk properties. To overcome this issue, we identify triangular regions in the mass-radius space where part of this degeneracy is lifted for close-in planets, since low-mass H/He envelopes would not be stable due to high-energy stellar irradiation. Planets in these Hot Water World triangles need to contain at least some heavier volatiles and are therefore interesting targets for atmospheric follow-up observations. We perform a demographic study to show that only few well-characterised planets in these regions are currently known and introduce our CHEOPS GTO programme aimed at identifying more of these potential hot water worlds. Here, we present CHEOPS observations for the first two targets of our programme, TOI-238 b and TOI-1685 b. Combined with TESS photometry and published RVs, we use the precise radii and masses of both planets to study their location relative to the corresponding Hot Water World triangles, perform an interior structure analysis and study the lifetimes of H/He and water-dominated atmospheres under these conditions. We find that TOI-238 b lies, at the 1-sigma level, inside the corresponding triangle. While a pure H/He atmosphere would have evaporated after 0.4-1.3 Myr, it is likely that a water-dominated atmosphere would have survived until the current age of the system, which makes TOI-238 b a promising hot water world candidate. Conversely, TOI-1685 b lies below the mass-radius model for a pure silicate planet, meaning that even though a water-dominated atmosphere would be compatible both with our internal structure and evaporation analysis, we cannot rule out the planet to be a bare core. △ Less

Submitted 11 February, 2025; originally announced February 2025.

Comments: 25 pages, 16 figures, accepted for publication in A&A

Journal ref: A&A 696, A28 (2025)

Transit-timing variations in the AU Mic system observed with CHEOPS

Authors: Á. Boldog, Gy. M. Szabó, L. Kriskovics, L. Borsato, D. Gandolfi, M. Lendl, M. N. Günther, A. Heitzmann, T. G. Wilson, A. Brandeker, Z. Garai, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann, W. Benz, N. Billot, C. Broeg, A. Collier Cameron, A. C. M. Correia, Sz. Csizmadia, P. E. Cubillos, M. B. Davies , et al. (64 additional authors not shown)

Abstract: AU Mic is a very active M dwarf with an edge-on debris disk and two transiting sub-Neptunes with a possible third planetary companion. The two transiting planets exhibit significant transit-timing variations (TTVs) that are caused by the gravitational interaction between the bodies in the system. Using photometrical observations taken with the CHaracterizing ExOPlanet Satellite (CHEOPS), our goal… ▽ More AU Mic is a very active M dwarf with an edge-on debris disk and two transiting sub-Neptunes with a possible third planetary companion. The two transiting planets exhibit significant transit-timing variations (TTVs) that are caused by the gravitational interaction between the bodies in the system. Using photometrical observations taken with the CHaracterizing ExOPlanet Satellite (CHEOPS), our goal is to constrain the planetary radii, the orbital distances and periods of AU Mic b and c. We aim to determine the superperiod of the TTVs for AU Mic b and to update the transit ephemeris for both planets. Based on the observed TTVs, we study the possible presence of a third planet in the system. We conducted high precision photometric observations with CHEOPS in 2022 and 2023. We used Allesfitter to fit the planetary transits and to constrain the planetary and orbital parameters. We combined our new measurements with results from previous years to determine the periods and amplitudes of the TTVs. We applied dynamical modelling based on TTV measurements from the 2018-2023 period to reconstruct the perceived variations. The orbital distances and periods for AU Mic b and c agree with the results from previous works. However, the values for the planetary radii deviate slightly from previous values, which we attribute to the effect of stellar spots. AU Mic c showed very strong TTVs, with transits that occurred ~80 minutes later in 2023 than in 2021. Through dynamical analysis of the system, we found that the observed TTVs can be explained by a third planet with an orbital period of ~12.6 days and a mass of 0.203+0.022-0.024 M_E. We explored the orbital geometry of the system and found that AU Mic c has a misaligned retrograde orbit. Due limited number of observations the exact configuration and planetary parameters could not be determined. Further monitoring with CHEOPS may improve these results. △ Less

Submitted 23 January, 2025; originally announced January 2025.

Comments: 15 pages, 10 figures

Characterizing WASP-43b's interior structure: unveiling tidal decay and apsidal motion

Authors: Lia Marta Bernabò, Szilárd Csizmadia, Alexis M. S. Smith, Jan-Vincent Harre, Szilárd Kálmán, Juan Cabrera, Heike Rauer, Davide Gandolfi, Lorenzo Pino, David Ehrenreich, Artie Hatzes

Abstract: Context. Recent developments in exoplanetary research highlight the importance of Love numbers in understanding their internal dynamics, formation, migration history and their potential habitability. Love numbers represent crucial parameters that gauge how exoplanets respond to external forces such as tidal interactions and rotational effects. By measuring these responses, we can gain insights int… ▽ More Context. Recent developments in exoplanetary research highlight the importance of Love numbers in understanding their internal dynamics, formation, migration history and their potential habitability. Love numbers represent crucial parameters that gauge how exoplanets respond to external forces such as tidal interactions and rotational effects. By measuring these responses, we can gain insights into the internal structure, composition, and density distribution of exoplanets. The rate of apsidal precession of a planetary orbit is directly linked to the second-order fluid Love number, thus we can gain valuable insights into the mass distribution of the planet. Aims. In this context, we aim to re-determine the orbital parameters of WASP-43b-in particular, orbital period, eccentricity, and argument of the periastron-and its orbital evolution. We study the outcomes of the tidal interaction with the host star:whether tidal decay and periastron precession are occurring in the system. Method. We observed the system with HARPS, whose data we present for the first time, and we also analyse the newly acquired JWST full-phase light curve. We fit jointly archival and new radial velocity and transit and occultation mid-times, including tidal decay, periastron precession and long-term acceleration in the system. Results. We detected a tidal decay rate of \dotP_a=(-1.99pm0.50) and a periastron precession rate of \dotomega=(0.1851+0.0070-0.0077)=(0.1727+0.0083-0.0089)deg/d=(621.72+29.88-32.04)arcsec/d. This is the first time that both periastron precession and tidal decay are simultaneously detected in an exoplanetary system. The observed tidal interactions can neither be explained by the tidal contribution to apsidal motion of a non-aligned stellar or planetary rotation axis nor by assuming non-synchronous rotation for the planet, and a value for the planetary Love number cannot be derived. [...] △ Less

Submitted 7 January, 2025; originally announced January 2025.

Comments: 17 pages, 16 figures, 11 tables

Journal ref: A&A 694, A233 (2025)

CHEOPS observations confirm nodal precession in the WASP-33 system

Authors: A. M. S. Smith, Sz. Csizmadia, V. Van Grootel, M. Lendl, C. M. Persson, G. Olofsson, D. Ehrenreich, M. N. Günther, A. Heitzmann, S. C. C. Barros, A. Bonfanti, A. Brandeker, J. Cabrera, O. D. S. Demangeon, L. Fossati, J. -V. Harre, M. J. Hooton, S. Hoyer, Sz. Kalman, S. Salmon, S. G. Sousa, Gy. M. Szabó, T. G. Wilson, Y. Alibert, R. Alonso , et al. (64 additional authors not shown)

Abstract: Aims: We aim to observe the transits and occultations of WASP-33b, which orbits a rapidly-rotating $δ$ Scuti pulsator, with the goal of measuring the orbital obliquity via the gravity-darkening effect, and constraining the geometric albedo via the occultation depth. Methods: We observed four transits and four occultations with CHEOPS, and employ a variety of techniques to remove the effects of the… ▽ More Aims: We aim to observe the transits and occultations of WASP-33b, which orbits a rapidly-rotating $δ$ Scuti pulsator, with the goal of measuring the orbital obliquity via the gravity-darkening effect, and constraining the geometric albedo via the occultation depth. Methods: We observed four transits and four occultations with CHEOPS, and employ a variety of techniques to remove the effects of the stellar pulsations from the light curves, as well as the usual CHEOPS systematic effects. We also performed a comprehensive analysis of low-resolution spectral and Gaia data to re-determine the stellar properties of WASP-33. Results: We measure an orbital obliquity 111.3 +0.2 -0.7 degrees, which is consistent with previous measurements made via Doppler tomography. We also measure the planetary impact parameter, and confirm that this parameter is undergoing rapid secular evolution as a result of nodal precession of the planetary orbit. This precession allows us to determine the second-order fluid Love number of the star, which we find agrees well with the predictions of theoretical stellar models. We are unable to robustly measure a unique value of the occultation depth, and emphasise the need for long-baseline observations to better measure the pulsation periods. △ Less

Submitted 11 December, 2024; originally announced December 2024.

Comments: 18 pages, 12 figures. Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 2025 693 A128

A joint effort to discover and characterize two resonant mini Neptunes around TOI-1803 with TESS, HARPS-N and CHEOPS

Authors: T. Zingales, L. Malavolta, L. Borsato, D. Turrini, A. Bonfanti, D. Polychroni, G. Mantovan, D. Nardiello, V. Nascimbeni, A. F. Lanza, A. Bekkelien, A. Sozzetti, C. Broeg, L. Naponiello, M. Lendl, A. S. Bonomo, A. E. Simon, S. Desidera, G. Piotto, L. Mancini, M. J. Hooton, A. Bignamini, J. A. Egger, A. Maggio, Y. Alibert , et al. (108 additional authors not shown)

Abstract: We present the discovery of two mini Neptunes near a 2:1 orbital resonance configuration orbiting the K0 star TOI-1803. We describe their orbital architecture in detail and suggest some possible formation and evolution scenarios. Using CHEOPS, TESS, and HARPS-N datasets we can estimate the radius and the mass of both planets. We used a multidimensional Gaussian Process with a quasi-periodic kernel… ▽ More We present the discovery of two mini Neptunes near a 2:1 orbital resonance configuration orbiting the K0 star TOI-1803. We describe their orbital architecture in detail and suggest some possible formation and evolution scenarios. Using CHEOPS, TESS, and HARPS-N datasets we can estimate the radius and the mass of both planets. We used a multidimensional Gaussian Process with a quasi-periodic kernel to disentangle the planetary components from the stellar activity in the HARPS-N dataset. We performed dynamical modeling to explain the orbital configuration and performed planetary formation and evolution simulations. For the least dense planet, we define possible atmospheric characterization scenarios with simulated JWST observations. TOI-1803 b and TOI-1803 c have orbital periods of $\sim$6.3 and $\sim$12.9 days, respectively, residing in close proximity to a 2:1 orbital resonance. Ground-based photometric follow-up observations revealed significant transit timing variations (TTV) with an amplitude of $\sim$10 min and $\sim$40 min, respectively, for planet -b and -c. With the masses computed from the radial velocities data set, we obtained a density of (0.39$\pm$0.10) $ρ_{earth}$ and (0.076$\pm$0.038) $ρ_{earth}$ for planet -b and -c, respectively. TOI-1803 c is among the least dense mini Neptunes currently known, and due to its inflated atmosphere, it is a suitable target for transmission spectroscopy with JWST. We report the discovery of two mini Neptunes close to a 2:1 orbital resonance. The detection of significant TTVs from ground-based photometry opens scenarios for a more precise mass determination. TOI-1803 c is one of the least dense mini Neptune known so far, and it is of great interest among the scientific community since it could constrain our formation scenarios. △ Less

Submitted 6 December, 2024; originally announced December 2024.

Comments: 26 Pages, 21 Figures Accepted for Publication in Astronomy & Astrophysics

Journal ref: A&A 695, A273 (2025)

In-situ observations of resident space objects with the CHEOPS space telescope

Authors: Nicolas Billot, Stephan Hellmich, Willy Benz, Andrea Fortier, David Ehrenreich, Christopher Broeg, Alexis Heitzmann, Anja Bekkelien, Alexis Brandeker, Yann Alibert, Roi Alonso, Tamas Bárczy, David Barrado Navascues, Susana C. C. Barros, Wolfgang Baumjohann, Federico Biondi, Luca Borsato, Andrew Collier Cameron, Carlos Corral van Damme, Alexandre C. M. Correia, Szilard Csizmadia, Patricio E. Cubillos, Melvyn B. Davies, Magali Deleuil, Adrien Deline , et al. (58 additional authors not shown)

Abstract: The CHaracterising ExOPlanet Satellite (CHEOPS) is a partnership between the European Space Agency and Switzerland with important contributions by 10 additional ESA member States. It is the first S-class mission in the ESA Science Programme. CHEOPS has been flying on a Sun-synchronous low Earth orbit since December 2019, collecting millions of short-exposure images in the visible domain to study e… ▽ More The CHaracterising ExOPlanet Satellite (CHEOPS) is a partnership between the European Space Agency and Switzerland with important contributions by 10 additional ESA member States. It is the first S-class mission in the ESA Science Programme. CHEOPS has been flying on a Sun-synchronous low Earth orbit since December 2019, collecting millions of short-exposure images in the visible domain to study exoplanet properties. A small yet increasing fraction of CHEOPS images show linear trails caused by resident space objects crossing the instrument field of view. To characterize the population of satellites and orbital debris observed by CHEOPS, all and every science images acquired over the past 3 years have been scanned with a Hough transform algorithm to identify the characteristic linear features that these objects cause on the images. Thousands of trails have been detected. This statistically significant sample shows interesting trends and features such as an increased occurrence rate over the past years as well as the fingerprint of the Starlink constellation. The cross-matching of individual trails with catalogued objects is underway as we aim to measure their distance at the time of observation and deduce the apparent magnitude of the detected objects. As space agencies and private companies are developing new space-based surveillance and tracking activities to catalogue and characterize the distribution of small debris, the CHEOPS experience is timely and relevant. With the first CHEOPS mission extension currently running until the end of 2026, and a possible second extension until the end of 2029, the longer time coverage will make our dataset even more valuable to the community, especially for characterizing objects with recurrent crossings. △ Less

Submitted 27 November, 2024; originally announced November 2024.

Comments: 9 pages, 8 figures, Special Issue of the Journal of Space Safety Engineering

Journal ref: Journal of Space Safety Engineering, Volume 11, Issue 3, September 2024, Pages 498-506

A possible misaligned orbit for the young planet AU Mic c

Authors: H. Yu, Z. Garai, M. Cretignier, Gy. M. Szabó, S. Aigrain, D. Gandolfi, E. M. Bryant, A. C. M. Correia, B. Klein, A. Brandeker, J. E. Owen, M. N. Günther, J. N. Winn, A. Heitzmann, H. M. Cegla, T. G. Wilson, S. Gill, L. Kriskovics, O. Barragán, A. Boldog, L. D. Nielsen, N. Billot, M. Lafarga, A. Meech, Y. Alibert , et al. (76 additional authors not shown)

Abstract: The AU Microscopii planetary system is only 24 Myr old, and its geometry may provide clues about the early dynamical history of planetary systems. Here, we present the first measurement of the Rossiter-McLaughlin effect for the warm sub-Neptune AU Mic c, using two transits observed simultaneously with the European Southern Observatory's (ESO's) Very Large Telescope (VLT)/Echelle SPectrograph for R… ▽ More The AU Microscopii planetary system is only 24 Myr old, and its geometry may provide clues about the early dynamical history of planetary systems. Here, we present the first measurement of the Rossiter-McLaughlin effect for the warm sub-Neptune AU Mic c, using two transits observed simultaneously with the European Southern Observatory's (ESO's) Very Large Telescope (VLT)/Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), CHaracterising ExOPlanet Satellite (CHEOPS), and Next-Generation Transit Survey (NGTS). After correcting for flares and for the magnetic activity of the host star, and accounting for transit-timing variations, we find the sky-projected spin-orbit angle of planet c to be in the range $λ_c=67.8_{-49.0}^{+31.7}$\,degrees (1-$σ$). We examine the possibility that planet c is misaligned with respect to the orbit of the inner planet b ($λ_b=-2.96_{-10.30}^{+10.44}$\,degrees), and the equatorial plane of the host star, and discuss scenarios that could explain both this and the planet's high density, including secular interactions with other bodies in the system or a giant impact. We note that a significantly misaligned orbit for planet c is in some degree of tension with the dynamical stability of the system, and with the fact that we see both planets in transit, though these arguments alone do not preclude such an orbit. Further observations would be highly desirable to constrain the spin-orbit angle of planet c more precisely. △ Less

Submitted 20 December, 2024; v1 submitted 25 November, 2024; originally announced November 2024.

Comments: Accepted for publication in MNRAS

NGTS-33b: A Young Super-Jupiter Hosted by a Fast Rotating Massive Hot Star

Authors: Douglas R. Alves, James S. Jenkins, Jose I. Vines, Matthew P. Battley, Monika Lendl, François Bouchy, Louise D. Nielsen, Samuel Gill, Maximiliano Moyano, D. R. Anderson, Matthew R. Burleigh, Sarah L. Casewell, Michael R. Goad, Faith Hawthorn, Alicia Kendall, James McCormac, Ares Osborn, Alexis M. S. Smith, Stephane Udry, Peter J. Wheatley, Suman Saha, Lena Parc, Arianna Nigioni, Ioannis Apergis, Gavin Ramsay

Abstract: In the last few decades planet search surveys have been focusing on solar type stars, and only recently the high-mass regimes. This is mostly due to challenges arising from the lack of instrumental precision, and more importantly, the inherent active nature of fast rotating massive stars. Here we report NGTS-33b (TOI-6442b), a super-Jupiter planet with mass, radius and orbital period of 3.6 $\pm$… ▽ More In the last few decades planet search surveys have been focusing on solar type stars, and only recently the high-mass regimes. This is mostly due to challenges arising from the lack of instrumental precision, and more importantly, the inherent active nature of fast rotating massive stars. Here we report NGTS-33b (TOI-6442b), a super-Jupiter planet with mass, radius and orbital period of 3.6 $\pm$ 0.3 M$_{\rm jup}$, 1.64 $\pm$ 0.07 R$_{\rm jup}$ and $2.827972 \pm 0.000001$ days, respectively. The host is a fast rotating ($0.6654 \pm 0.0006$ day) and hot (T$_{\rm eff}$ = 7437 $\pm$ 72 K) A9V type star, with a mass and radius of 1.60 $\pm$ 0.11 M$_{\odot}$ and 1.47 $\pm$ 0.06 R$_{\odot}$, respectively. Planet structure and Gyrochronology models shows that NGTS-33 is also very young with age limits of 10-50 Myr. In addition, membership analysis points towards the star being part of the Vela OB2 association, which has an age of $\sim$ 20-35 Myr, thus providing further evidences about the young nature of NGTS-33. Its low bulk density of 0.19$\pm$0.03 g cm$^{-3}$ is 13$\%$ smaller than expected when compared to transiting hot Jupiters with similar masses. Such cannot be solely explained by its age, where an up to 15$\%$ inflated atmosphere is expected from planet structure models. Finally, we found that its emission spectroscopy metric is similar to JWST community targets, making the planet an interesting target for atmospheric follow-up. Therefore, NGTS-33b's discovery will not only add to the scarce population of young, massive and hot Jupiters, but will also help place further strong constraints on current formation and evolution models for such planetary systems. △ Less

Submitted 13 November, 2024; originally announced November 2024.

Comments: 19 pages, 17 figures, 7 tables, accepted for publication in MNRAS

A close outer companion to the ultra-hot Jupiter TOI-2109 b?

Authors: J. -V. Harre, A. M. S. Smith, S. C. C. Barros, V. Singh, J. Korth, A. Brandeker, A. Collier Cameron, M. Lendl, T. G. Wilson, L. Borsato, Sz. Csizmadia, J. Cabrera, H. Parviainen, A. C. M. Correia, B. Akinsanmi, N. Rosario, P. Leonardi, L. M. Serrano, Y. Alibert, R. Alonso, J. Asquier, T. Bárczy, D. Barrado Navascues, W. Baumjohann, W. Benz , et al. (64 additional authors not shown)

Abstract: Hot Jupiters with close-by planetary companions are rare, with only a handful of them having been discovered so far. This could be due to their suggested dynamical histories, leading to the possible ejection of other planets. TOI-2109 b is special in this regard because it is the hot Jupiter with the closest relative separation from its host star, being separated by less than 2.3 stellar radii. Un… ▽ More Hot Jupiters with close-by planetary companions are rare, with only a handful of them having been discovered so far. This could be due to their suggested dynamical histories, leading to the possible ejection of other planets. TOI-2109 b is special in this regard because it is the hot Jupiter with the closest relative separation from its host star, being separated by less than 2.3 stellar radii. Unexpectedly, transit timing measurements from recently obtained CHEOPS observations show low amplitude transit-timing variations (TTVs). We aim to search for signs of orbital decay and to characterise the apparent TTVs, trying to gain information about a possible companion. We fit the newly obtained CHEOPS light curves using TLCM and extract the resulting mid-transit timings. Successively, we use these measurements in combination with TESS and archival photometric data and radial velocity data to estimate the rate of tidal orbital decay of TOI-2109 b, as well as characterise the TTVs using the N-body code TRADES and the photodynamical approach of PyTTV. We find tentative evidence at $3σ$ for orbital decay in the TOI-2109 system, when we correct the mid-transit timings using the best-fitting sinusoidal model of the TTVs. We do not detect additional transits in the available photometric data, but find evidence towards the authenticity of the apparent TTVs, indicating a close-by, outer companion with $P_\mathrm{c} > 1.125\,$d. Due to the fast rotation of the star, the new planetary candidate cannot be detected in the available radial velocity (RV) measurements, and its parameters can only be loosely constrained by our joint TTV and RV modelling. TOI-2109 could join a small group of rare hot Jupiter systems that host close-by planetary companions, only one of which (WASP-47 b) has an outer companion. More high-precision photometric measurements are necessary to confirm the planetary companion. △ Less

Submitted 12 November, 2024; originally announced November 2024.

Comments: Accepted for publication in A&A. 21 pages, 21 figures

Journal ref: A&A 692, A254 (2024)

Architecture of TOI-561 planetary system

Authors: G. Piotto, T. Zingales, L. Borsato, J. A. Egger, A. C. M. Correia, A. E. Simon, H. G. Florén, S. G. Sousa, P. F. L. Maxted, D. Nardiello, L. Malavolta, T. G. Wilson, Y. Alibert, V. Adibekyan, A. Bonfanti, R. Luque, N. C. Santos, M. J. Hooton, L. Fossati, A. M. S. Smith, S. Salmon, G. Lacedelli, R. Alonso, T. Bárczy, D. Barrado Navascues , et al. (68 additional authors not shown)

Abstract: We present new observations from CHEOPS and TESS to clarify the architecture of the planetary system hosted by the old Galactic thick disk star TOI-561. Our global analysis, which also includes previously published photometric and radial velocity data, incontrovertibly proves that TOI-561 is hosting at least four transiting planets with periods of 0.44 days (TOI-561 b), 10.8 days (TOI-561 c), 25.7… ▽ More We present new observations from CHEOPS and TESS to clarify the architecture of the planetary system hosted by the old Galactic thick disk star TOI-561. Our global analysis, which also includes previously published photometric and radial velocity data, incontrovertibly proves that TOI-561 is hosting at least four transiting planets with periods of 0.44 days (TOI-561 b), 10.8 days (TOI-561 c), 25.7 days (TOI-561 d), and 77.1 days (TOI-561 e) and a fifth non-transiting candidate, TOI-561f with a period of 433 days. The precise characterisation of TOI-561's orbital architecture is interesting since old and metal-poor thick disk stars are less likely to host ultra-short period Super-Earths like TOI-561 b. The new period of planet -e is consistent with the value obtained using radial velocity alone and is now known to be $77.14399\pm0.00025$ days, thanks to the new CHEOPS and TESS transits. The new data allowed us to improve its radius ($R_p = 2.517 \pm 0.045 R_{\oplus}$ from 5$\%$ to 2$\%$ precision) and mass ($M_p = 12.4 \pm 1.4 M_{\oplus}$) estimates, implying a density of $ρ_p = 0.778 \pm 0.097 ρ_{\oplus}$. Thanks to recent TESS observations and the focused CHEOPS visit of the transit of TOI-561 e, a good candidate for exomoon searches, the planet's period is finally constrained, allowing us to predict transit times through 2030 with 20-minute accuracy. We present an updated version of the internal structure of the four transiting planets. We finally performed a detailed stability analysis, which confirmed the long-term stability of the outer planet TOI-561 f. △ Less

Submitted 31 October, 2024; v1 submitted 23 October, 2024; originally announced October 2024.

Comments: 13 pages, 10 Figures. Accepted on MNRAS. Updated the author list

Spectropolarimetry of SN 2023ixf reveals both circumstellar material and helium core to be aspherical

Authors: Manisha Shrestha, Sabrina DeSoto, David J. Sand, G. Grant Williams, Jennifer L. Hoffman, Nathan Smith, Paul S. Smith, Peter Milne, Callum McCall, Justyn R. Maund, Iain A Steele, Klaas Wiersema, Jennifer E. Andrews, Christopher Bilinski, Ramya M. Anche, K. Azalee Bostroem, Griffin Hosseinzadeh, Jeniveve Pearson, Douglas C. Leonard, Brian Hsu, Yize Dong, Emily Hoang, Daryl Janzen, Jacob E. Jencson, Saurabh W. Jha , et al. (11 additional authors not shown)

Abstract: We present multi-epoch optical spectropolarimetric and imaging polarimetric observations of the nearby Type II supernova (SN) 2023ixf discovered in M101 at a distance of 6.85 Mpc. The first imaging polarimetric observations were taken +2.33 days (60085.08 MJD) after the explosion, while the last imaging polarimetric data points (+73.19 and +76.19 days) were acquired after the fall from the light c… ▽ More We present multi-epoch optical spectropolarimetric and imaging polarimetric observations of the nearby Type II supernova (SN) 2023ixf discovered in M101 at a distance of 6.85 Mpc. The first imaging polarimetric observations were taken +2.33 days (60085.08 MJD) after the explosion, while the last imaging polarimetric data points (+73.19 and +76.19 days) were acquired after the fall from the light curve plateau. At +2.33 days there is strong evidence of circumstellar material (CSM) interaction in the spectra and the light curve. A significant level of intrinsic polarization $p_r = 1.02\pm 0.07 \% $ is seen during this phase which indicates that this CSM is aspherical. We find that the polarization evolves with time toward the interstellar polarization level during the photospheric phase, which suggests that the recombination photosphere is spherically symmetric. There is a jump in polarization ($p_r =0.45 \pm 0.08 \% $ and $p_r =0.62 \pm 0.08 \% $) at +73.19 and +76.19 days when the light curve falls from the plateau. This is a phase where polarimetric data is sensitive to non-spherical inner ejecta or a decrease in optical depth into the single scattering regime. We also present spectropolarimetric data that reveal line (de)polarization during most of the observed epochs. In addition, at +14.50 days we see an ``inverse P Cygni" profile in the H and He line polarization, which clearly indicates the presence of asymmetrically distributed material overlying the photosphere. The overall temporal evolution of polarization is typical for Type II SNe, but the high level of polarization during the rising phase has only been observed in SN 2023ixf. △ Less

Submitted 3 March, 2025; v1 submitted 10 October, 2024; originally announced October 2024.

Comments: 15 pages, 7 figures, accepted for publication in ApJL

The CHEOPS view on the climate of WASP-3 b

Authors: G. Scandariato, L. Carone, P. E. Cubillos, P. F. L. Maxted, T. Zingales, M. N. Günther, A. Heitzmann, M. Lendl, T. G. Wilson, A. Bonfanti, G. Bruno, A. Krenn, E. Meier Valdes, V. Singh, M. I. Swayne, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann, W. Benz, N. Billot, L. Borsato, A. Brandeker , et al. (61 additional authors not shown)

Abstract: Hot Jupiters are giant planets subject to intense stellar radiation. The physical and chemical properties of their atmosphere makes them the most amenable targets for the atmospheric characterization. In this paper we analyze the photometry collected during the secondary eclipses of the hot Jupiter WASP-3 b by CHEOPS, TESS and Spitzer. Our aim is to characterize the atmosphere of the planet by m… ▽ More Hot Jupiters are giant planets subject to intense stellar radiation. The physical and chemical properties of their atmosphere makes them the most amenable targets for the atmospheric characterization. In this paper we analyze the photometry collected during the secondary eclipses of the hot Jupiter WASP-3 b by CHEOPS, TESS and Spitzer. Our aim is to characterize the atmosphere of the planet by measuring the secondary eclipse depth in several passbands and constrain the planetary dayside spectrum. Our update of the stellar and planetary properties is consistent with previous works. The analysis of the occultations returns an eclipse depth of 92+-21 ppm in the CHEOPS passband, 83+-27 ppm for TESS and >2000 ppm in the IRAC 1-2-4 Spitzer passbands. Using the eclipse depths in the Spitzer bands we propose a set of likely emission spectra which constrain the emission contribution in the \cheops and TESS passbands to approximately a few dozens of parts per million. This allowed us to measure a geometric albedo of 0.21+-0.07 in the CHEOPS passband, while the TESS data lead to a 95\% upper limit of $\sim$0.2. WASP-3 b belongs to the group of ultra-hot Jupiters which are characterized by low Bond albedo (<0.3+-0.1), as predicted by different atmospheric models. On the other hand, it unexpectedly seems to efficiently recirculate the absorbed stellar energy, unlike similar highly irradiated planets. To explain this inconsistency, we propose that other energy recirculation mechanisms may be at play other than advection (for example, dissociation and recombination of H_2). Another possibility is that the observations in different bandpasses probe different atmospheric layers, making the atmospheric analysis difficult without an appropriate modeling of the thermal emission spectrum of WASP-3 b, which is not feasible with the limited spectroscopic data available to date. △ Less

Submitted 24 September, 2024; originally announced September 2024.

Journal ref: A&A 692, A129 (2024)

First operation of LArTPC in the stratosphere as an engineering GRAMS balloon flight (eGRAMS)

Authors: R. Nakajima, S. Arai, K. Aoyama, Y. Utsumi, T. Tamba, H. Odaka, M. Tanaka, K. Yorita, S. Arai, T. Aramaki, J. Asaadi, A. Bamba, N. Cannady, P. Coppi, G. De Nolfo, M. Errando, L. Fabris, T. Fujiwara, Y. Fukazawa, P. Ghosh, K. Hagino, T. Hakamata, U. Hijikata, N. Hiroshima, M. Ichihashi , et al. (39 additional authors not shown)

Abstract: GRAMS (Gamma-Ray and AntiMatter Survey) is a next-generation balloon/satellite experiment utilizing a LArTPC (Liquid Argon Time Projection Chamber), to simultaneously target astrophysical observations of cosmic MeV gamma-rays and conduct an indirect dark matter search using antimatter. While LArTPCs are widely used in particle physics experiments, they have never been operated at balloon altitudes… ▽ More GRAMS (Gamma-Ray and AntiMatter Survey) is a next-generation balloon/satellite experiment utilizing a LArTPC (Liquid Argon Time Projection Chamber), to simultaneously target astrophysical observations of cosmic MeV gamma-rays and conduct an indirect dark matter search using antimatter. While LArTPCs are widely used in particle physics experiments, they have never been operated at balloon altitudes. An engineering balloon flight with a small-scale LArTPC (eGRAMS) was conducted on July 27th, 2023, to establish a system for safely operating a LArTPC at balloon altitudes and to obtain cosmic-ray data from the LArTPC. The flight was launched from the Japan Aerospace Exploration Agency's (JAXA) Taiki Aerospace Research Field in Hokkaido, Japan. The total flight duration was 3 hours and 12 minutes, including a level flight of 44 minutes at a maximum altitude of 28.9 km. The flight system was landed on the sea and successfully recovered. The LArTPC was successfully operated throughout the flight, and about 0.5 million events of the cosmic-ray data including muons, protons, and Compton scattering gamma-ray candidates, were collected. This pioneering flight demonstrates the feasibility of operating a LArTPC in high-altitude environments, paving the way for future GRAMS missions and advancing our capabilities in MeV gamma-ray astronomy and dark matter research. △ Less

Submitted 25 November, 2024; v1 submitted 20 September, 2024; originally announced September 2024.

Journal ref: Progress of Theoretical and Experimental Physics, Volume 2024, Issue 12, December 2024, 123F01

System performance of a cryogenic test-bed for the time-division multiplexing readout for NewAthena X-IFU

Authors: Davide Vaccaro, Jan van der Kuur, Paul van der Hulst, Tobias Vos, Martin de Wit, Luciano Gottardi, Kevin Ravensberg, Emanuele Taralli, Joseph Adams, Simon Bandler, Douglas Bennet, James Chervenak, Bertrand Doriese, Malcolm Durkin, Johnathon Gard, Carl Reintsema, Kazuhiro Sakai, Steven Smith, Joel Ullom, Nicholas Wakeham, Jan-Willem den Herder, Brian jackson, Pourya Khosropanah, Jian-Rong Gao, Peter Roelfsema , et al. (1 additional authors not shown)

Abstract: The X-ray Integral Field Unit (X-IFU) is an instrument of ESA's future NewAthena space observatory, with the goal to provide high-energy resolution ($<$ 4 eV at X-ray energies up to 7 keV) and high-spatial resolution (9") spectroscopic imaging over the X-ray energy range from 200 eV to 12 keV, by means of an array of about 1500 transition-edge sensors (TES) read out via SQUID time-division multipl… ▽ More The X-ray Integral Field Unit (X-IFU) is an instrument of ESA's future NewAthena space observatory, with the goal to provide high-energy resolution ($<$ 4 eV at X-ray energies up to 7 keV) and high-spatial resolution (9") spectroscopic imaging over the X-ray energy range from 200 eV to 12 keV, by means of an array of about 1500 transition-edge sensors (TES) read out via SQUID time-division multiplexing (TDM). A TDM-based laboratory test-bed has been assembled at SRON, hosting an array of $75\times 75\ \upmu$m$^2$ TESs that are read out via 2-column $\times$ 32-row TDM. A system component that is critical to high-performance operation is the wiring harness that connects the room-temperature electronics to the cryogenic readout componentry. We report here on our characterization of such a test-bed, whose harness has a length close to what envisioned for X-IFU, which allowed to achieve a co-added energy resolution at a level of 2.7~eV FWHM at 6~keV via 32-row readout. In addition, we provide an outlook on the integration of TDM readout into the X-IFU Focal-Plane Assembly Development Model. △ Less

Submitted 5 November, 2024; v1 submitted 9 September, 2024; originally announced September 2024.

Comments: Submitted for publication to Journal of Astronomical Telescopes, Instrumentation and Systems. arXiv admin note: text overlap with arXiv:2403.02978

Journal ref: Journal of Astronomical Telescopes, Instruments, and Systems, Vol. 10, Issue 4, 046002 (December 2024)

The K2-24 planetary system revisited by CHEOPS

Authors: V. Nascimbeni, L. Borsato, P. Leonardi, S. G. Sousa, T. G. Wilson, A. Fortier, A. Heitzmann, G. Mantovan, R. Luque, T. Zingales, G. Piotto, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues, S. C. Barros, W. Baumjohann, T. Beck, W. Benz, N. Billot, F. Biondi, A. Brandeker, C. Broeg, M. -D. Busch, A. Collier Cameron , et al. (60 additional authors not shown)

Abstract: K2-24 is a planetary system composed of two transiting low-density Neptunians locked in an almost perfect 2:1 resonance and showing large TTVs, i.e., an excellent laboratory to search for signatures of planetary migration. Previous studies performed with K2, Spitzer and RV data tentatively claimed a significant non-zero eccentricity for one or both planets, possibly high enough to challenge the sc… ▽ More K2-24 is a planetary system composed of two transiting low-density Neptunians locked in an almost perfect 2:1 resonance and showing large TTVs, i.e., an excellent laboratory to search for signatures of planetary migration. Previous studies performed with K2, Spitzer and RV data tentatively claimed a significant non-zero eccentricity for one or both planets, possibly high enough to challenge the scenario of pure disk migration through resonant capture. With 13 new CHEOPS light curves (seven of planet -b, six of planet -c), we carried out a global photometric and dynamical re-analysis by including all the available literature data as well. We got the most accurate set of planetary parameters to date for the K2-24 system, including radii and masses at 1% and 5% precision (now essentially limited by the uncertainty on stellar parameters) and non-zero eccentricities $e_b=0.0498_{-0.0018}^{+0.0011}$, $e_c=0.0282_{-0.0007}^{+0.0003}$ detected at very high significance for both planets. Such relatively large values imply the need for an additional physical mechanism of eccentricity excitation during or after the migration stage. Also, while the accuracy of the previous TTV model had drifted by up to 0.5 days at the current time, we constrained the orbital solution firmly enough to predict the forthcoming transits for the next ~15 years, thus enabling an efficient follow-up with top-level facilities such as JWST or ESPRESSO. △ Less

Submitted 16 September, 2024; v1 submitted 4 September, 2024; originally announced September 2024.

Comments: 19 pages, 11 figures, 8 tables. Accepted for publication in A&A on September 4, 2024. Typos corrected

Journal ref: A&A 690, A349 (2024)

Mass determination of two Jupiter-sized planets orbiting slightly evolved stars: TOI-2420 b and TOI-2485 b

Authors: Ilaria Carleo, Oscar Barrágan, Carina M. Persson, Malcolm Fridlund, Kristine W. F. Lam, Sergio Messina, Davide Gandolfi, Alexis M. S. Smith, Marshall C. Johnson, William Cochran, Hannah L. M. Osborn, Rafael Brahm, David R. Ciardi, Karen A. Collins, Mark E. Everett, Steven Giacalone, Eike W. Guenther, Artie Hatzes, Coel Hellier, Jonathan Horner Petr Kabáth, Judith Korth, Phillip MacQueen, Thomas Masseron, Felipe Murgas, Grzegorz Nowak , et al. (45 additional authors not shown)

Abstract: Hot and warm Jupiters might have undergone the same formation and evolution path, but the two populations exhibit different distributions of orbital parameters, challenging our understanding on their actual origin. The present work, which is the results of our warm Jupiters survey carried out with the CHIRON spectrograph within the KESPRINT collaboration, aims to address this challenge by studying… ▽ More Hot and warm Jupiters might have undergone the same formation and evolution path, but the two populations exhibit different distributions of orbital parameters, challenging our understanding on their actual origin. The present work, which is the results of our warm Jupiters survey carried out with the CHIRON spectrograph within the KESPRINT collaboration, aims to address this challenge by studying two planets that could help bridge the gap between the two populations. We report the confirmation and mass determination of a hot Jupiter (orbital period shorter than 10 days), TOI-2420\,b, and a warm Jupiter, TOI-2485\,b. We performed a joint analysis using a wide variety of spectral and photometric data in order to characterize these planetary systems. We found that TOI-2420\,b has an orbital period of P$_{\rm b}$=5.8 days, a mass of M$_{\rm b}$=0.9 M$_{\rm J}$ and a radius of R$_{\rm b}$=1.3 R$_{\rm J}$, with a planetary density of 0.477 \gc; while TOI-2485\,b has an orbital period of P$_{\rm b}$=11.2 days, a mass of M$_{\rm b}$=2.4 M$_{\rm J}$ and a radius of R$_{\rm b}$=1.1 R$_{\rm J}$ with density 2.36 \gc. With current parameters, the migration history for TOI-2420\,b and TOI-2485\,b is unclear: the high-eccentricity migration scenarios cannot be ruled out, and TOI-2485\,b's characteristics may rather support this scenario. △ Less

Submitted 10 August, 2024; originally announced August 2024.

TOI-757 b: an eccentric transiting mini-Neptune on a 17.5-d orbit

Authors: A. Alqasim, N. Grieves, N. M. Rosário, D. Gandolfi, J. H. Livingston, S. Sousa, K. A. Collins, J. K. Teske, M. Fridlund, J. A. Egger, J. Cabrera, C. Hellier, A. F. Lanza, V. Van Eylen, F. Bouchy, R. J. Oelkers, G. Srdoc, S. Shectman, M. Günther, E. Goffo, T. Wilson, L. M. Serrano, A. Brandeker, S. X. Wang, A. Heitzmann , et al. (107 additional authors not shown)

Abstract: We report the spectroscopic confirmation and fundamental properties of TOI-757 b, a mini-Neptune on a 17.5-day orbit transiting a bright star ($V = 9.7$ mag) discovered by the TESS mission. We acquired high-precision radial velocity measurements with the HARPS, ESPRESSO, and PFS spectrographs to confirm the planet detection and determine its mass. We also acquired space-borne transit photometry wi… ▽ More We report the spectroscopic confirmation and fundamental properties of TOI-757 b, a mini-Neptune on a 17.5-day orbit transiting a bright star ($V = 9.7$ mag) discovered by the TESS mission. We acquired high-precision radial velocity measurements with the HARPS, ESPRESSO, and PFS spectrographs to confirm the planet detection and determine its mass. We also acquired space-borne transit photometry with the CHEOPS space telescope to place stronger constraints on the planet radius, supported with ground-based LCOGT photometry. WASP and KELT photometry were used to help constrain the stellar rotation period. We also determined the fundamental parameters of the host star. We find that TOI-757 b has a radius of $R_{\mathrm{p}} = 2.5 \pm 0.1 R_{\oplus}$ and a mass of $M_{\mathrm{p}} = 10.5^{+2.2}_{-2.1} M_{\oplus}$, implying a bulk density of $ρ_{\text{p}} = 3.6 \pm 0.8$ g cm$^{-3}$. Our internal composition modeling was unable to constrain the composition of TOI-757 b, highlighting the importance of atmospheric observations for the system. We also find the planet to be highly eccentric with $e$ = 0.39$^{+0.08}_{-0.07}$, making it one of the very few highly eccentric planets among precisely characterized mini-Neptunes. Based on comparisons to other similar eccentric systems, we find a likely scenario for TOI-757 b's formation to be high eccentricity migration due to a distant outer companion. We additionally propose the possibility of a more intrinsic explanation for the high eccentricity due to star-star interactions during the earlier epoch of the Galactic disk formation, given the low metallicity and older age of TOI-757. △ Less

Submitted 29 July, 2024; originally announced July 2024.

Comments: Accepted for publication in MNRAS; 26 pages, 14 figures, 6 tables

Characterisation of the Warm-Jupiter TOI-1130 system with CHEOPS and photo-dynamical approach

Authors: L. Borsato, D. Degen, A. Leleu, M. J. Hooton, J. A. Egger, A. Bekkelien, A. Brandeker, A. Collier Cameron, M. N. Günther, V. Nascimbeni, C. M. Persson, A. Bonfanti, T. G. Wilson, A. C. M. Correia, T. Zingales, T. Guillot, A. H. M. J. Triaud, G. Piotto, D. Gandolfi, L. Abe, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues, S. C. C. Barros , et al. (71 additional authors not shown)

Abstract: Among the thousands of exoplanets discovered to date, approximately a few hundred gas giants on short-period orbits are classified as "lonely" and only a few are in a multi-planet system with a smaller companion on a close orbit. The processes that formed multi-planet systems hosting gas giants on close orbits are poorly understood, and only a few examples of this kind of system have been observed… ▽ More Among the thousands of exoplanets discovered to date, approximately a few hundred gas giants on short-period orbits are classified as "lonely" and only a few are in a multi-planet system with a smaller companion on a close orbit. The processes that formed multi-planet systems hosting gas giants on close orbits are poorly understood, and only a few examples of this kind of system have been observed and well characterised. Within the contest of multi-planet system hosting gas-giant on short orbits, we characterise TOI-1130 system by measuring masses and orbital parameters. This is a 2-transiting planet system with a Jupiter-like planet (c) on a 8.35 days orbit and a Neptune-like planet (b) on an inner (4.07 days) orbit. Both planets show strong anti-correlated transit timing variations (TTVs). Furthermore, radial velocity (RV) analysis showed an additional linear trend, a possible hint of a non-transiting candidate planet on a far outer orbit. Since 2019, extensive transit and radial velocity observations of the TOI-1130 have been acquired using TESS and various ground-based facilities. We present a new photo-dynamical analysis of all available transit and RV data, with the addition of new CHEOPS and ASTEP+ data that achieve the best precision to date on the planetary radii and masses and on the timings of each transit. We were able to model interior structure of planet b constraining the presence of a gaseous envelope of H/He, while it was not possible to assess the possible water content. Furthermore, we analysed the resonant state of the two transiting planets, and we found that they lie just outside the resonant region. This could be the result of the tidal evolution that the system underwent. We obtained both masses of the planets with a precision less than 1.5%, and radii with a precision of about 1% and 3% for planet b and c, respectively. △ Less

Submitted 8 July, 2024; originally announced July 2024.

Comments: 22 pages, 10 figures, Accepted for publication by Astronomy and Astrophysics

Journal ref: A&A 689, A52 (2024)

Unveiling the internal structure and formation history of the three planets transiting HIP 29442 (TOI-469) with CHEOPS

Authors: J. A. Egger, H. P. Osborn, D. Kubyshkina, C. Mordasini, Y. Alibert, M. N. Günther, M. Lendl, A. Brandeker, A. Heitzmann, A. Leleu, M. Damasso, A. Bonfanti, T. G. Wilson, S. G. Sousa, J. Haldemann, L. Delrez, M. J. Hooton, T. Zingales, R. Luque, R. Alonso, J. Asquier, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann , et al. (69 additional authors not shown)

Abstract: Multiplanetary systems spanning the radius valley are ideal testing grounds for exploring the proposed explanations for the observed bimodality in the radius distribution of close-in exoplanets. One such system is HIP 29442 (TOI-469), an evolved K0V star hosting two super-Earths and a sub-Neptune. We observe HIP 29442 with CHEOPS for a total of 9.6 days, which we model jointly with 2 sectors of TE… ▽ More Multiplanetary systems spanning the radius valley are ideal testing grounds for exploring the proposed explanations for the observed bimodality in the radius distribution of close-in exoplanets. One such system is HIP 29442 (TOI-469), an evolved K0V star hosting two super-Earths and a sub-Neptune. We observe HIP 29442 with CHEOPS for a total of 9.6 days, which we model jointly with 2 sectors of TESS data to derive planetary radii of $3.410\pm0.046$, $1.551\pm0.045$ and $1.538\pm0.049$ R$_\oplus$ for planets b, c and d, which orbit HIP 29442 with periods of 13.6, 3.5 and 6.4 days. For planet d, this value deviates by more than 3 sigma from the median value reported in the discovery paper, leading us to conclude that caution is required when using TESS photometry to determine the radii of small planets with low per-transit S/N and large gaps between observations. Given the high precision of these new radii, combining them with published RVs from ESPRESSO and HIRES provides us with ideal conditions to investigate the internal structure and formation pathways of the planets in the system. We introduce the publicly available code plaNETic, a fast and robust neural network-based Bayesian internal structure modelling framework. We then apply hydrodynamic models to explore the upper atmospheric properties of these inferred structures. Finally, we identify planetary system analogues in a synthetic population generated with the Bern model for planet formation and evolution. Based on this analysis, we find that the planets likely formed on opposing sides of the water iceline from a protoplanetary disk with an intermediate solid mass. We finally report that the observed parameters of the HIP 29442 system are compatible with both a scenario where the second peak in the bimodal radius distribution corresponds to sub-Neptunes with a pure H/He envelope as well as a scenario with water-rich sub-Neptunes. △ Less

Submitted 26 June, 2024; originally announced June 2024.

Comments: 30 pages, 17 figures, accepted for publication in A&A

Journal ref: A&A 688, A223 (2024)

A gamma-ray flare from TXS 1508+572: characterizing the jet of a $z=4.31$ blazar in the early Universe

Authors: Andrea Gokus, Markus Böttcher, Manel Errando, Michael Kreter, Jonas Heßdörfer, Florian Eppel, Matthias Kadler, Paul S. Smith, Petra Benke, Leonid I. Gurvits, Alex Kraus, Mikhail Lisakov, Felicia McBride, Eduardo Ros, Florian Rösch, Jörn Wilms

Abstract: Blazars can be detected from very large distances due to their high luminosity. However, the detection of $γ$-ray emission of blazars beyond $z=3$ has only been confirmed for a small number of sources. Such observations probe the growth of supermassive black holes close to the peak of star formation in the history of galaxy evolution. As a result from a continuous monitoring of a sample of 80… ▽ More Blazars can be detected from very large distances due to their high luminosity. However, the detection of $γ$-ray emission of blazars beyond $z=3$ has only been confirmed for a small number of sources. Such observations probe the growth of supermassive black holes close to the peak of star formation in the history of galaxy evolution. As a result from a continuous monitoring of a sample of 80 $z>3$ blazars with Fermi-LAT, we present the first detection of a $γ$-ray flare from the $z=4.31$ blazar TXS 1508+572. This source showed high $γ$-ray activity from February to August 2022, reaching a peak luminosity comparable to the most luminous flares ever detected with Fermi -LAT. We conducted a multiwavelength observing campaign involving XMM-Newton, Swift, the Effelsberg 100-m radio telescope and the Very Long Baseline Array. In addition, we make use of the monitoring programs by the Zwicky Transient Facility and NEOWISE at optical and infrared wavelengths, respectively. We find that the source is particularly variable in the infrared band on daily time scales. The spectral energy distribution collected during our campaign is well described by a one-zone leptonic model, with the $γ$-ray flare originating from an increase of external Compton emission as a result of a fresh injection of accelerated electrons. △ Less

Submitted 1 August, 2024; v1 submitted 11 June, 2024; originally announced June 2024.

Comments: 19 pages, 8 figures; accepted by ApJ on July 30 - Initial version on arXiv is the submitted one

CHEOPS in-flight performance: A comprehensive look at the first 3.5 years of operations

Authors: A. Fortier, A. E. Simon, C. Broeg, G. Olofsson, A. Deline, T. G. Wilson, P. F. L. Maxted, A. Brandeker, A. Collier Cameron, M. Beck, A. Bekkelien, N. Billot, A. Bonfanti, G. Bruno, J. Cabrera, L. Delrez, B. -O. Demory, D. Futyan, H. -G. Florén, M. N. Günther, A. Heitzmann, S. Hoyer, K. G. Isaak, S. G. Sousa, M. Stalport , et al. (106 additional authors not shown)

Abstract: CHEOPS is a space telescope specifically designed to monitor transiting exoplanets orbiting bright stars. In September 2023, CHEOPS completed its nominal mission and remains in excellent operational conditions. The mission has been extended until the end of 2026. Scientific and instrumental data have been collected throughout in-orbit commissioning and nominal operations, enabling a comprehensive… ▽ More CHEOPS is a space telescope specifically designed to monitor transiting exoplanets orbiting bright stars. In September 2023, CHEOPS completed its nominal mission and remains in excellent operational conditions. The mission has been extended until the end of 2026. Scientific and instrumental data have been collected throughout in-orbit commissioning and nominal operations, enabling a comprehensive analysis of the mission's performance. In this article, we present the results of this analysis with a twofold goal. First, we aim to inform the scientific community about the present status of the mission and what can be expected as the instrument ages. Secondly, we intend for this publication to serve as a legacy document for future missions, providing insights and lessons learned from the successful operation of CHEOPS. To evaluate the instrument performance in flight, we developed a comprehensive monitoring and characterisation programme. It consists of dedicated observations that allow us to characterise the instrument's response. In addition to the standard collection of nominal science and housekeeping data, these observations provide input for detecting, modelling, and correcting instrument systematics, discovering and addressing anomalies, and comparing the instrument's actual performance with expectations. The precision of the CHEOPS measurements has enabled the mission objectives to be met and exceeded. Careful modelling of the instrumental systematics allows the data quality to be significantly improved during the light curve analysis phase, resulting in more precise scientific measurements. CHEOPS is compliant with the driving scientific requirements of the mission. Although visible, the ageing of the instrument has not affected the mission's performance. △ Less

Submitted 3 June, 2024; originally announced June 2024.

Comments: Accepted for publication in Astronomy and Astrophysics

HIP 41378 observed by CHEOPS: Where is planet d?

Authors: S. Sulis, L. Borsato, S. Grouffal, H. P. Osborn, A. Santerne, A. Brandeker, M. N. Günther, A. Heitzmann, M. Lendl, M. Fridlund, D. Gandolfi, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues, S. C. Barros, W. Baumjohann, T. Beck, W. Benz, M. Bergomi, N. Billot, A. Bonfanti, C. Broeg, A. Collier Cameron, C. Corral van Damme , et al. (62 additional authors not shown)

Abstract: HIP 41378 d is a long-period planet that has only been observed to transit twice, three years apart, with K2. According to stability considerations and a partial detection of the Rossiter-McLaughlin effect, $P_\mathrm{d} = 278.36$ d has been determined to be the most likely orbital period. We targeted HIP 41378 d with CHEOPS at the predicted transit timing based on $P_\mathrm{d}= 278.36$ d, but th… ▽ More HIP 41378 d is a long-period planet that has only been observed to transit twice, three years apart, with K2. According to stability considerations and a partial detection of the Rossiter-McLaughlin effect, $P_\mathrm{d} = 278.36$ d has been determined to be the most likely orbital period. We targeted HIP 41378 d with CHEOPS at the predicted transit timing based on $P_\mathrm{d}= 278.36$ d, but the observations show no transit. We find that large ($>22.4$ hours) transit timing variations (TTVs) could explain this non-detection during the CHEOPS observation window. We also investigated the possibility of an incorrect orbital solution, which would have major implications for our knowledge of this system. If $P_\mathrm{d} \neq 278.36$ d, the periods that minimize the eccentricity would be $101.22$ d and $371.14$ d. The shortest orbital period will be tested by TESS, which will observe HIP 41378 in Sector 88 starting in January 2025. Our study shows the importance of a mission like CHEOPS, which today is the only mission able to make long observations (i.e., from space) to track the ephemeris of long-period planets possibly affected by large TTVs. △ Less

Submitted 30 May, 2024; originally announced May 2024.

Comments: Accepted for publication in Astronomy and Astrophysics

Journal ref: A&A 686, L18 (2024)

Photo-dynamical characterisation of the TOI-178 resonant chain

Authors: A. Leleu, J. -B. Delisle, L. Delrez, E. M. Bryant, A. Brandeker, H. P. Osborn, N. Hara, T. G. Wilson, N. Billot, M. Lendl, D. Ehrenreich, H. Chakraborty, M. N. Günther, M. J. Hooton, Y. Alibert, R. Alonso, D. R. Alves, D. R. Anderson, I. Apergis, D. Armstrong, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, M. P. Battley, W. Baumjohann , et al. (82 additional authors not shown)

Abstract: The TOI-178 system consists of a nearby late K-dwarf transited by six planets in the super-Earth to mini-Neptune regime, with radii ranging from 1.2 to 2.9 earth radius and orbital periods between 1.9 and 20.7 days. All planets but the innermost one form a chain of Laplace resonances. The fine-tuning and fragility of such orbital configurations ensure that no significant scattering or collision ev… ▽ More The TOI-178 system consists of a nearby late K-dwarf transited by six planets in the super-Earth to mini-Neptune regime, with radii ranging from 1.2 to 2.9 earth radius and orbital periods between 1.9 and 20.7 days. All planets but the innermost one form a chain of Laplace resonances. The fine-tuning and fragility of such orbital configurations ensure that no significant scattering or collision event has taken place since the formation and migration of the planets in the protoplanetary disc, hence providing important anchors for planet formation models. We aim to improve the characterisation of the architecture of this key system, and in particular the masses and radii of its planets. In addition, since this system is one of the few resonant chains that can be characterised by both photometry and radial velocities, we aim to use it as a test bench for the robustness of the planetary mass determination with each technique. We perform a global analysis of all available photometry and radial velocity. We also try different sets of priors on the masses and eccentricity, as well as different stellar activity models, to study their effects on the masses estimated by each method. We show how stellar activity is preventing us from obtaining a robust mass estimation for the three outer planets using radial velocity data alone. We also show that our joint photo-dynamical and radial velocity analysis resulted in a robust mass determination for planets c to g, with precision of 12% for the mass of planet c, and better than 10% for planets d to g. The new precisions on the radii range from 2 to 3%. The understanding of this synergy between photometric and radial velocity measurements will be valuable during the PLATO mission. We also show that TOI-178 is indeed currently locked in the resonant configuration, librating around an equilibrium of the chain. △ Less

Submitted 22 May, 2024; originally announced May 2024.

Journal ref: A&A 688, A211 (2024)

Characterisation of the TOI-421 planetary system using CHEOPS, TESS, and archival radial velocity data

Authors: A. F. Krenn, D. Kubyshkina, L. Fossati, J. A. Egger, A. Bonfanti, A. Deline, D. Ehrenreich, M. Beck, W. Benz, J. Cabrera, T. G. Wilson, A. Leleu, S. G. Sousa, V. Adibekyan, A. C. M. Correira, Y. Alibert, L. Delrez, M. Lendl, J. A. Patel, J. Venturini, R. Alonso, G. Anglada, J. Asquier, T. Bárczy, D. Barrado Navascues , et al. (66 additional authors not shown)

Abstract: The TOI-421 planetary system contains two sub-Neptune-type planets and is a prime target to study the formation and evolution of planets and their atmospheres. The inner planet is especially interesting as the existence of a hydrogen-dominated atmosphere at its orbital separation cannot be explained by current formation models without previous orbital migration. We jointly analysed photometric dat… ▽ More The TOI-421 planetary system contains two sub-Neptune-type planets and is a prime target to study the formation and evolution of planets and their atmospheres. The inner planet is especially interesting as the existence of a hydrogen-dominated atmosphere at its orbital separation cannot be explained by current formation models without previous orbital migration. We jointly analysed photometric data of three TESS sectors and six CHEOPS visits as well as 156 radial velocity data points to retrieve improved planetary parameters. We also searched for TTVs and modelled the interior structure of the planets. Finally, we simulated the evolution of the primordial H-He atmospheres of the planets using two different modelling frameworks. We determine the planetary radii and masses of TOI-421 b and c to be $R_{\rm b} = 2.64 \pm 0.08 \, R_{\oplus}$, $M_{\rm b} = 6.7 \pm 0.6 \, M_{\oplus}$, $R_{\rm c} = 5.09 \pm 0.07 \, R_{\oplus}$, and $M_{\rm c} = 14.1 \pm 1.4 \, M_{\oplus}$. We do not detect any statistically significant TTV signals. Assuming the presence of a hydrogen-dominated atmosphere, the interior structure modelling results in both planets having extensive envelopes. While the modelling of the atmospheric evolution predicts for TOI-421 b to have lost any primordial atmosphere that it could have accreted at its current orbital position, TOI-421 c could have started out with an initial atmospheric mass fraction somewhere between 10 and 35%. We conclude that the low observed mean density of TOI-421 b can only be explained by either a bias in the measured planetary parameters (e.g. driven by high-altitude clouds) and/or in the context of orbital migration. We also find that the results of atmospheric evolution models are strongly dependent on the employed planetary structure model. △ Less

Submitted 17 April, 2024; originally announced April 2024.

Comments: 21 pages, 12 figures, accepted for publication in A&A

NGTS-30 b/TOI-4862 b: An 1 Gyr old 98-day transiting warm Jupiter

Authors: M. P. Battley, K. A. Collins, S. Ulmer-Moll, S. N. Quinn, M. Lendl, S. Gill, R. Brahm, M. J. Hobson, H. P. Osborn, A. Deline, J. P. Faria, A. B. Claringbold, H. Chakraborty, K. G. Stassun, C. Hellier, D. R. Alves, C. Ziegler, D. R. Anderson, I. Apergis, D. J. Armstrong, D. Bayliss, Y. Beletsky, A. Bieryla, F. Bouchy, M. R. Burleigh , et al. (41 additional authors not shown)

Abstract: Long-period transiting exoplanets bridge the gap between the bulk of transit- and Doppler-based exoplanet discoveries, providing key insights into the formation and evolution of planetary systems. The wider separation between these planets and their host stars results in the exoplanets typically experiencing less radiation from their host stars; hence, they should maintain more of their original a… ▽ More Long-period transiting exoplanets bridge the gap between the bulk of transit- and Doppler-based exoplanet discoveries, providing key insights into the formation and evolution of planetary systems. The wider separation between these planets and their host stars results in the exoplanets typically experiencing less radiation from their host stars; hence, they should maintain more of their original atmospheres, which can be probed during transit via transmission spectroscopy. Although the known population of long-period transiting exoplanets is relatively sparse, surveys performed by the Transiting Exoplanet Survey Satellite (TESS) and the Next Generation Transit Survey (NGTS) are now discovering new exoplanets to fill in this crucial region of the exoplanetary parameter space. This study presents the detection and characterisation of NGTS-30 b/TOI-4862 b, a new long-period transiting exoplanet detected by following up on a single-transit candidate found in the TESS mission. Through monitoring using a combination of photometric instruments (TESS, NGTS, and EulerCam) and spectroscopic instruments (CORALIE, FEROS, HARPS, and PFS), NGTS-30 b/TOI-4862 b was found to be a long-period (P = 98.29838 day) Jupiter-sized (0.928 RJ; 0.960 MJ) planet transiting a 1.1 Gyr old G-type star. With a moderate eccentricity of 0.294, its equilibrium temperature could be expected to vary from 274 K to 500 K over the course of its orbit. Through interior modelling, NGTS-30 b/TOI-4862 b was found to have a heavy element mass fraction of 0.23 and a heavy element enrichment (Zp/Z_star) of 20, making it metal-enriched compared to its host star. NGTS-30 b/TOI-4862 b is one of the youngest well-characterised long-period exoplanets found to date and will therefore be important in the quest to understanding the formation and evolution of exoplanets across the full range of orbital separations and ages. △ Less

Submitted 3 April, 2024; originally announced April 2024.

Comments: 18 pages, 14 figures, accepted for publication in A&A

The phase curve of the ultra-hot Jupiter WASP-167b as seen by TESS

Authors: Sz. Kálmán, A. Derekas, Sz. Csizmadia, A. Pál, R. Szabó, A. M. S. Smith, K. Nagy, V. Hegedűs, T. Mitnyan, L. Szigeti, Gy. M. Szabó

Abstract: Ultra-hot Jupiters (UHJs) orbiting pulsating A/F stars represent an important subset of the exoplanetary demographic, as they are excellent candidates for the study of exoplanetary atmospheres, as well as being astrophysical laboratories for the investigation of planet-to-star interactions. We analyse the \texttt{TESS} (Transiting Exoplanet Survey Satellite) light curve of the WASP-167 system, con… ▽ More Ultra-hot Jupiters (UHJs) orbiting pulsating A/F stars represent an important subset of the exoplanetary demographic, as they are excellent candidates for the study of exoplanetary atmospheres, as well as being astrophysical laboratories for the investigation of planet-to-star interactions. We analyse the \texttt{TESS} (Transiting Exoplanet Survey Satellite) light curve of the WASP-167 system, consisting of an F1V star and a substellar companion on a $\sim 2.02$ day orbit. We model the combination of the ellipsoidal variability and the Doppler beaming to measure the mass of WASP-167b, and the reflection effect to obtain constraints on the geometric albedo, while placing a special emphasis on noise separation. We implement a basic model to determine the dayside ($T_{\rm Day}$), nightside ($T_{\rm Night}$) and intrinsic ($T_{\rm Internal}$) temperatures of WASP-167b and put a constraint on its Bond albedo. We confirm the transit parameters of the planet seen in the literature. We find that a resonant $\sim 2P^{-1}$ stellar signal (which may originate from planet-to-star interactions) interferes with the phase curve analysis. After considerate treatment of this signal, we find $M_p = 0.34 \pm 0.22$~$M_J$. We measure a dayside temperature of $2790 \pm 100$ K, classifying WASP-167b as an UHJ. We find a $2σ$ upper limit of $0.51$ on its Bond albedo, and determine the geometric albedo at $0.34 \pm 0.11$ ($1 σ$ uncertainty). With an occultation depth of $106.8 \pm 27.3$ ppm in the \texttt{TESS} passband, the UHJ WASP-167b will be an excellent target for atmospheric studies, especially those at thermal wavelength ranges, where the stellar pulsations are expected to be be less influential. △ Less

Submitted 28 March, 2024; originally announced March 2024.

Comments: 19 pages, 15 figures, resubmitted to Astronomy and Astrophysics after minor revision

Journal ref: A&A 687, A144 (2024)

Detailed cool star flare morphology with CHEOPS and TESS

Authors: G. Bruno, I. Pagano, G. Scandariato, H. -G. Florén, A. Brandeker, G. Olofsson, P. F. L. Maxted, A. Fortier, S. G. Sousa, S. Sulis, V. Van Grootel, Z. Garai, A. Boldog, L. Kriskovics, M. Gy. Szabó, D. Gandolfi, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann, M. Beck, T. Beck, W. Benz , et al. (57 additional authors not shown)

Abstract: Context. White-light stellar flares are proxies for some of the most energetic types of flares, but their triggering mechanism is still poorly understood. As they are associated with strong X and UV emission, their study is particularly relevant to estimate the amount of high-energy irradiation onto the atmospheres of exoplanets, especially those in their stars' habitable zone. Aims. We used the h… ▽ More Context. White-light stellar flares are proxies for some of the most energetic types of flares, but their triggering mechanism is still poorly understood. As they are associated with strong X and UV emission, their study is particularly relevant to estimate the amount of high-energy irradiation onto the atmospheres of exoplanets, especially those in their stars' habitable zone. Aims. We used the high-cadence, high-photometric capabilities of the CHEOPS and TESS space telescopes to study the detailed morphology of white-light flares occurring in a sample of 130 late-K and M stars, and compared our findings with results obtained at a lower cadence. We developed dedicated software for this purpose. Results. Multi-peak flares represent a significant percentage ($\gtrsim 30$\%) of the detected outburst events. Our findings suggest that high-impulse flares are more frequent than suspected from lower-cadence data, so that the most impactful flux levels that hit close-in exoplanets might be more time-limited than expected. We found significant differences in the duration distributions of single-peak and complex flare components, but not in their peak luminosity. A statistical analysis of the flare parameter distributions provides marginal support for their description with a log-normal instead of a power-law function, leaving the door open to several flare formation scenarios. We tentatively confirmed previous results about quasi-periodic pulsations in high-cadence photometry, report the possible detection of a pre-flare dip, and did not find hints of photometric variability due to an undetected flare background. Conclusions. The high-cadence study of stellar hosts might be crucial to evaluate the impact of their flares on close-in exoplanets, as their impulsive phase emission might otherwise be incorrectly estimated. Future telescopes such as PLATO and Ariel will help in this respect. △ Less

Submitted 25 March, 2024; originally announced March 2024.

Comments: 28 pages, 25 figures, 4 tables, to be published in Astronomy & Astrophysics