Showing 1–50 of 244 results for author: Helling, C

Chemical Tracers for 3D Atmospheric Asymmetries on WASP-69 b

Authors: Nidhi Bangera, Ludmila Carone, Vikas Soni, Kenneth Goodis Gordon, Luca Fossati, Helena Lecoq-Molinos, Paul B. Rimmer, Peter Woitke, Christiane Helling

Abstract: Warm giant exoplanets exhibit strong three-dimensional temperature contrasts that can significantly alter atmospheric chemistry through quenching and photochemistry, yet transmission spectra are commonly interpreted using one-dimensional, limb-averaged models. Such simplifications may bias inferred atmospheric properties, particularly metallicity and C/O ratio. In this work we investigate the rela… ▽ More Warm giant exoplanets exhibit strong three-dimensional temperature contrasts that can significantly alter atmospheric chemistry through quenching and photochemistry, yet transmission spectra are commonly interpreted using one-dimensional, limb-averaged models. Such simplifications may bias inferred atmospheric properties, particularly metallicity and C/O ratio. In this work we investigate the relative influence of atmospheric composition and three-dimensional thermal structure on atmospheric chemistry and transmission spectra using WASP-69b as a test case. WASP-69b is a ~900K warm Saturn, residing in a thermal regime especially sensitive to disequilibrium chemistry. We use three-dimensional general circulation model derived pressure-temperature profiles as inputs for a one-dimensional photochemical-kinetics model to resolve longitudinal and latitudinal chemical asymmetries across the atmosphere. We find that CH4 exhibits strong latitudinal variations linked to deep quench temperatures, while SO2 shows longitudinal asymmetries driven by upper-atmospheric photochemistry and irradiation geometry. In contrast, CO2 remains comparatively insensitive to spatial thermal variations and emerges as a robust tracer of atmospheric metallicity. Synthethic transmission spectra reveal that three-dimensional chemical asymmetries can produce spectral variations comparable to those induced by metallicity itself, demonstrating that limb-averaged interpretations can mask substantial spatial structure in warm giant exoplanet atmospheres. △ Less

Submitted 12 August, 2026; originally announced August 2026.

Comments: 25 pages, 12 figures. Accepted for publication in ApJ

CHEOPS photometry from 2024 reveals a reversal in the transit-timing variations of AU Mic c

Authors: Z. Garai, Gy. M. Szabó, D. Gandolfi, A. Brandeker, A. Bonfanti, N. Billot, W. Benz, A. Heitzmann, G. Olofsson, L. Kriskovics, Á. Boldog, L. Borsato, A. Bekkelien, G. Bruno, H. P. Osborn, S. Ulmer-Moll, T. G. Wilson, Y. Alibert, R. Alonso, T. Bárczy, D. Barrado, S. C. C. Barros, W. Baumjohann, C. Broeg, A. Castro-González , et al. (68 additional authors not shown)

Abstract: We present new CHEOPS transit observations of AU Mic b and AU Mic c obtained between June and September 2024, extending the baseline of transit-timing measurements of this young planetary system. For AU Mic b, the timing signal is well established, with a semi-amplitude (10 $\pm$ 3 min) and a characteristic modulation timescale (1168 $\pm$ 20 d) consistent with previous determinations. By contrast… ▽ More We present new CHEOPS transit observations of AU Mic b and AU Mic c obtained between June and September 2024, extending the baseline of transit-timing measurements of this young planetary system. For AU Mic b, the timing signal is well established, with a semi-amplitude (10 $\pm$ 3 min) and a characteristic modulation timescale (1168 $\pm$ 20 d) consistent with previous determinations. By contrast, the new CHEOPS data show that the large transit-timing deviation of AU Mic c reported previously was not sustained. After the steadily increasing timing trend observed in 2022 and 2023, the 2024 timings returned closer to the zero point of the observed-minus-calculated diagram, indicating a reversal of the previously reported behavior. For AU Mic c, both the transit-timing semi-amplitude (46 $\pm$ 26 min) and the characteristic modulation timescale (2150 $\pm$ 110 d) remain tentative. These results highlight the importance of continued long-term monitoring of the AU Mic system. △ Less

Submitted 2 August, 2026; originally announced August 2026.

Comments: Accepted for publication in A&A

The Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES) Data Reduction Pipeline

Authors: Sandipan P. D. Borthakur, Tõnis Eenmäe, Nikolai Piskunov, Luca Fossati, Mihkel Kama, Thomas Marquart, Anni Kasikov, Heleri Ramler, Anna Aret, Christiane Helling, Laurits Leedjärv, Linn Boldt-Christmas

Abstract: We introduce the data reduction pipeline for the Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES). TOFES is installed in the Coudé room and will be connected to the 1.5 m Tartu Observatory AZT-12 telescope through a four-channel instrument adapter to be mounted at the Cassegrain focus of the telescope. The spectrograph has an average spectral resolution of 30,000 and covers the 390 to 900… ▽ More We introduce the data reduction pipeline for the Tartu Observatory Fiber-fed Echelle Spectrograph (TOFES). TOFES is installed in the Coudé room and will be connected to the 1.5 m Tartu Observatory AZT-12 telescope through a four-channel instrument adapter to be mounted at the Cassegrain focus of the telescope. The spectrograph has an average spectral resolution of 30,000 and covers the 390 to 900 nm wavelength band in a single exposure. The data reduction pipeline, based on the PyReduce package, was tested on spectra of the Sun. We also present the Spectroscopy-Toolbox package, which was developed to provide additional tools for diagnostics and spectral line identification for radial velocity measurements. The spectrograph will address a range of scientific questions, including the stellar characterisation of Herbig AeBe stars to measure accretion contamination from their protoplanetary disks, the stellar characterisation of exoplanet host-stars including the Ariel space mission targets, and radial velocity monitoring of large-scale atmospheric variability in massive stars. △ Less

Submitted 31 July, 2026; originally announced July 2026.

Comments: Accepted for publication in the Publication of the Astronomical Society of the Pacific (PASP) journal, 27 pages (6 pages in References and Appendices), 18 figures, 1 Table in Appendix B

Cracking under pressure --- investigating mitigation approaches for silicon fractures on ATLAS strip tracker petals at cold temperatures

Authors: S. H. Abidi, J. -H. Arling, M. J. Basso, S. Beaupre, I. Bloch, A. J. Blue, M. Caspar, J. Chen, S. Díez Cornell, U. Epstein, E. K. Filmer, A. Fournier, L. Franconi, A. Gabrielli, J. A. Hallford, S. Heim, C. M. Helling, N. P. Hessey, R. M. Jacobs, T. Kuhl, M. Licht, C. K. Mahajan, S. Manson, K. Mauer, S. Oerdek , et al. (13 additional authors not shown)

Abstract: For the High-Luminosity upgrade of the Large Hadron Collider, the ATLAS experiment will replace its current Inner Detector with an all-silicon Inner Tracker (ITk), consisting of pixel and strip detectors. The strip detector will consist of a central region or "barrel" assembled with staves and forward regions or "end-caps" assembled with petals. The ITk will nominally operate with liquid… ▽ More For the High-Luminosity upgrade of the Large Hadron Collider, the ATLAS experiment will replace its current Inner Detector with an all-silicon Inner Tracker (ITk), consisting of pixel and strip detectors. The strip detector will consist of a central region or "barrel" assembled with staves and forward regions or "end-caps" assembled with petals. The ITk will nominally operate with liquid $\textrm{CO}^2$ cooling at $-35\,^\circ\textrm{C}$; however, in the event of cooling system failures, it is possible that sensors will experience temperatures below $-35\,^\circ\textrm{C}$. At these low temperatures, it has been observed that the silicon sensors within modules --- the fundamental readout units of the detector --- can physically crack, rendering the modules inoperable. Understanding and resolving the issue of sensor cracking was one of the most important and urgent issues for the ITk project. This paper presents part of the mitigation strategies developed for petals. These mitigation strategies are based on modifications to the choice of adhesive and its deposition pattern for module assembly and petal loading. The most promising mitigation strategy presented here prevents cracking to temperatures as low as $-45\,^\circ\textrm{C}$, which can be expected in case of cooling system problems, with a small percentage of cracks observed after being cycled to $-55\,^\circ\textrm{C}$, which can be expected in case of catastrophic cooling system failures. △ Less

Submitted 27 July, 2026; originally announced July 2026.

Comments: 39 pages; published in JINST

Journal ref: JINST 21 P07026 (2026)

Phase-dependent chemistry of WASP-43 b revealed with a suite of one-, two-, and three-dimensional models

Authors: Robin Baeyens, Julianne I. Moses, Jasmina Blecic, Elspeth K. H. Lee, Lucas Teinturier, Shang-Min Tsai, Jeehyun Yang, Jingxuan Yang, Ludmila Carone, Renyu Hu, Sven Kiefer, Anjali A. A. Piette, Taylor J. Bell, Nicolas Crouzet, Ian Dobbs-Dixon, Christiane Helling, Nicolas Iro, Dominic Samra, Olivia Venot, Jean-Michel Désert

Abstract: Our goal is to investigate the chemistry of the hot Jupiter WASP-43 b in detail using theoretical models, considering the constraints of the James Webb Space Telescope MIRI phase curve. With a suite of pseudo-two-dimensional and three-dimensional photochemical models, we simulate the composition of WASP-43 b in various configurations, and compare them with atmospheric retrieval models. We confirm… ▽ More Our goal is to investigate the chemistry of the hot Jupiter WASP-43 b in detail using theoretical models, considering the constraints of the James Webb Space Telescope MIRI phase curve. With a suite of pseudo-two-dimensional and three-dimensional photochemical models, we simulate the composition of WASP-43 b in various configurations, and compare them with atmospheric retrieval models. We confirm that disequilibrium chemistry in our theoretical models reduces the methane concentration on the planet night side for wind jet speeds > 500 m/s. Varying the metallicity in the models induces large changes in the CO$_2$ and SO$_2$ concentrations, with SO$_2$ producing mid-infrared absorption features in synthetic emission spectra of the night side at atmospheric metallicities > 10x solar. Our models provide evidence for pole-to-equator circulation enhancing the CH$_4$, NH$_3$, and HCN abundances, which is nonetheless insufficient for detectable spectral features. Finally, we show that H$_2$O, CO, and CO$_2$ are robustly modeled, but species affected by photochemistry are more sensitive to model-specific assumptions and pathways. We conclude that horizontal quenching is the prime mechanism that explains the non-detection of methane in the MIRI phase-curve of WASP-43 b. This mechanism requires only moderate wind speeds and is operative at various thermal structures and atmospheric metallicities. Furthermore, coupled carbon-sulfur chemistry leads to an additional decrease in methane compared to previous models in the literature that did not contain sulfur chemistry. We do not favor a high metallicity as it would have led to observable SO$_2$ features in the MIRI spectra. Our study shows that phase-dependent photochemistry models are essential tools in the interpretation of hot-Jupiter phase curves, but benchmarking is needed to improve the accuracy of photochemical models in the future. △ Less

Submitted 9 July, 2026; originally announced July 2026.

Comments: 25 pages, 18 figures, accepted for publication in A&A

The panchromatic JWST dayside spectrum of WASP-121 b reveals a refractory-rich formation

Authors: K. Angelique Kahle, Paul Mollière, Laura Kreidberg, Bertram Bitsch, Mara Attia, Silke S. Dainese, Nicholas Storm, Daniel Valentine, Thomas M. Evans-Soma, H. J. Hoeijmakers, Stefan Pelletier, Ludmila Carone, Cyril Gapp, Yoav Rotman, Sophia R. Vaughan, D. A. Christie, Louis-Philippe Coulombe, Christiane Helling, Thomas Henning

Abstract: One path to understand how planets form is to link their present-day atmospheric composition to predictions from planet formation models. For the hottest planets, the abundances of refractory species can provide a useful formation tracer, complementing the traditionally used C/O and overall metallicity. Here we investigate the refractory abundance in the atmosphere of the ultra-hot Jupiter WASP-12… ▽ More One path to understand how planets form is to link their present-day atmospheric composition to predictions from planet formation models. For the hottest planets, the abundances of refractory species can provide a useful formation tracer, complementing the traditionally used C/O and overall metallicity. Here we investigate the refractory abundance in the atmosphere of the ultra-hot Jupiter WASP-121 b, combining new JWST MIRI/LRS observations with archival NIRSpec/G395H and NIRISS/SOSS data to obtain a panchromatic dayside emission spectrum from 0.6 to 12 $μ$m. Our retrieval analysis detects the refractory tracer SiO gas at high confidence, in addition to previously detected volatile species. The atmosphere is enriched in volatile and refractory species, with enhanced refractory-to-volatile ratios of Si/O=$3.54^{+0.86}_{-0.69}$x stellar and Si/C=$3.05^{+1.12}_{-0.80}$x stellar, relative to new stellar abundance constraints from ESPRESSO data. In addition, we confirm the depletion of TiO and the need for an additional source of reflected light opacity with a geometric albedo of $0.22\pm0.03$. The retrieved dayside temperature profile has a strong inversion layer, with a more complex structure than standard parameterizations can accommodate, and an eclipse map analysis indicates a small eastward hotspot offset of $4.8^{+2.7\circ}_{-2.8}$. Comparing our results with models of planet formation, we find that the measured enrichment pattern was shaped by accretion from multiple reservoirs, either through a mixture of solid and gas accretion interior to the water ice line or through continued solid accretion during inward migration from farther out in the disk. Finally, we model the planet's dynamical history and find that it could reach its current high-obliquity orbit as a consequence of a post-formation dynamical event, such as planet-planet scattering or von Zeipel-Lidov-Kozai cycles. △ Less

Submitted 19 June, 2026; originally announced June 2026.

Comments: Submitted to Astronomy & Astrophysics, comments welcome

Metal Oxide Clusters in Gas Giant Exoplanet Atmospheres

Authors: Deepak Bisht, Christiane Helling, David Gobrecht, Ludmila Carone, Helena Lecoq-Molinos, Peter Woitke, Markus Aichhorn, Jan Philip Sindel, Amit Reza

Abstract: This study investigates the thermal stability and absorption of metal oxide clusters in exoplanetary atmospheres. Utilizing our thermochemical data, we analyze eight distinct cluster families: magnesium oxide (MgO), silicon monoxide (SiO), titanium monoxide (TiO), vanadium monoxide (VO), titanium dioxide (TiO$_2$), vanadium dioxide (VO$_2$), aluminum oxide (Al$_2$O$_3$), and vanadium pentoxide (V… ▽ More This study investigates the thermal stability and absorption of metal oxide clusters in exoplanetary atmospheres. Utilizing our thermochemical data, we analyze eight distinct cluster families: magnesium oxide (MgO), silicon monoxide (SiO), titanium monoxide (TiO), vanadium monoxide (VO), titanium dioxide (TiO$_2$), vanadium dioxide (VO$_2$), aluminum oxide (Al$_2$O$_3$), and vanadium pentoxide (V$_2$O$_5$). Equilibrium cluster populations as a function of gas temperature and pressure reveal distinct stability regimes. Under solar elemental abundances, (TiO$_2$)$\rm\rm_N$ and (Al$_2$O$_3$)$\rm_N$ are favored at higher temperatures, while (MgO)$\rm_N$ and (SiO)$\rm_N$ dominate at lower temperatures. Computed absorption spectra exhibit strong size- and composition-dependent absorption features in the mid-infrared (8--50~$μ$m), many of which fall within the wavelength range accessible to \texttt{JWST/MIRI}. We further coupled cluster thermodynamics with 3D general circulation model (GCM) outputs to investigate the cluster stability across the ultra-hot Jupiters (UHJs) WASP-121 b and WASP-18 b, the hot Jupiter (HJ) WASP-39 b, and the warm Jupiter (WJ) WASP-69 b. In WASP-121 b and WASP-18 b, extreme dayside temperatures suppress large-cluster stability, yielding atmospheres dominated by metal ions at low pressures and neutral metals at depth, with limited cluster survival on the nightside and morning terminator. In WASP-39 b, larger clusters are not thermochemically favoured despite the enhanced metallicity; instead, equilibrium chemistry stabilises smaller species, with only TiO showing a tendency toward stable larger cluster forms, likely due to its open d-orbitals. In contrast, WASP-69 b favors the formation of larger metal oxide clusters across an extended pressure range, highlighting WJs as a favorable environment for metal oxide cluster stability. △ Less

Submitted 15 June, 2026; originally announced June 2026.

Comments: The paper has been accepted in The Astrophysical Journal(ApJ)

An Ultra-Short Period Super-Earth and a Sub-Neptune Orbiting the K dwarf TOI-4311

Authors: Yoshi Nike Emilia Eschen, Thomas G. Wilson, Andrew Collier Cameron, Alexander James Mustill, Jo Ann Egger, Solène Ulmer-Moll, Davide Gandolfi, Alexis M. S. Smith, Olivier D. S. Demangeon, Sérgio G. Sousa, Andrea Bonfanti, Alexandre C. M. Correia, Vardan Adibekyan, Gaia Lacedelli, Alexis Brandeker, Camilla Pezzotti, Babatunde Akinsanmi, Yann Alibert, Roi Alonso, Tamas Bárczy, David Barrado, Susana C. C. Barros, Wolfgang Baumjohann, Willy Benz, Nicolas Billot , et al. (73 additional authors not shown)

Abstract: We report the discovery and characterisation of the multi-planetary system around TOI-4311, a K dwarf kinematically between the Galactic thick disk and Hercules stream. TOI-4311 hosts an ultra-short-period super-Earth (P$\sim$0.99 d, $1.376\substack{+0.077\\-0.080}$ R$_\oplus$) and a longer period sub-Neptune (P$\sim$15 d, $2.47\substack{+0.12\\-0.11}$ R$_\oplus$) that was first detected in the TE… ▽ More We report the discovery and characterisation of the multi-planetary system around TOI-4311, a K dwarf kinematically between the Galactic thick disk and Hercules stream. TOI-4311 hosts an ultra-short-period super-Earth (P$\sim$0.99 d, $1.376\substack{+0.077\\-0.080}$ R$_\oplus$) and a longer period sub-Neptune (P$\sim$15 d, $2.47\substack{+0.12\\-0.11}$ R$_\oplus$) that was first detected in the TESS photometry. Using follow-up observations with CHEOPS and HARPS, we refine the planetary radius of both planets, derive the mass of planet b ($4.5\substack{+1.5\\-1.4}$ M$_\oplus$) and confirm the planetary nature of planet c. Intriguingly, a third periodic signal is clearly detected in our HARPS RVs that we cannot link to stellar activity. This signal could be attributed to a third planet (P$\sim$38 d, Msin(i)=$26.4\substack{+6.3\\-6.8}$ M$_\oplus$) in the system, however with the current photometric dataset we do not find a transit. Our dynamical analysis highlights that this potential outer planet would remain stable. Using the precise radius and mass for TOI-4311 b we model its interior structure and find that it is very dense given the host star's galactic kinematics and chemistry. Hence this system could challenge current formation theories and provide insights into planet formation across the galaxy. △ Less

Submitted 12 May, 2026; originally announced May 2026.

Comments: Accepted for publication in MNRAS

The multi-planet system TOI-5624: Four transiting sub-Neptunes with an outer companion revealed by transit-timing variations

Authors: A. Bonfanti, D. Gandolfi, P. Leonardi, H. P. Osborn, L. M. Serrano, G. Hébrard, N. Billot, A. Bekkelien, G. Olofsson, C. Broeg, D. Nardiello, S. G. Sousa, T. G. Wilson, A. C. M. Correia, C. Pezzotti, A. Brandeker, L. Fossati, M. Gillon, M. Stalport, B. Akinsanmi, Y. Alibert, R. Alonso, J. Asquier, T. Bárczy, D. Barrado , et al. (74 additional authors not shown)

Abstract: Following the 2022 alert of a TESS object of interest transiting TOI-5624 (a G7 V star $\sim$100 pc away), a CHEOPS campaign in 2023 detected four planetary signals at $P_b\approx3.4$, $P_c\approx7.9$, $P_d\approx13.7$, and $P_e\approx21.5$ days, later confirmed by additional TESS and CHEOPS photometry in 2024-2025. After analysing the TESS & CHEOPS photometric data, we extracted and modelled the… ▽ More Following the 2022 alert of a TESS object of interest transiting TOI-5624 (a G7 V star $\sim$100 pc away), a CHEOPS campaign in 2023 detected four planetary signals at $P_b\approx3.4$, $P_c\approx7.9$, $P_d\approx13.7$, and $P_e\approx21.5$ days, later confirmed by additional TESS and CHEOPS photometry in 2024-2025. After analysing the TESS & CHEOPS photometric data, we extracted and modelled the HARPS-N & SOPHIE RV time series using two independent methodologies both within an MCMC framework. We further integrated the N-body equations of motion, while simultaneously fitting the transit times and the detrended RVs, to dynamically characterise the system. We present the discovery of four transiting sub-Neptunes with radii of $R_b=2.314\pm0.035 R_{\oplus}$, $R_c=2.474\pm0.042 R_{\oplus}$, $R_d=3.584_{-0.050}^{+0.051} R_{\oplus}$, and $R_e=3.247_{-0.043}^{+0.042} R_{\oplus}$ and masses of $M_b=9.4\pm1.4 M_{\oplus}$, $M_c=4.8\pm1.9 M_{\oplus}$, $M_d=4.9\pm2.2 M_{\oplus}$, and $M_e=8.9_{-3.0}^{+2.9} M_{\oplus}$. Our photometric analysis reveals that the outermost transiting planet TOI-5624 e shows significant TTVs. We find a robust Keplerian signal in the RV time series close to the 2:1 period commensurability with TOI-5624 e, which explains the TTV pattern exhibited by TOI-5624 e according to our dynamical analysis. We label this non-transiting planet as TOI-5624 f and find its minimum mass to be $M_f\sin{i_f}=13.0\pm3.7 M_{\oplus}$. Among the known systems hosting more than four planets, the remarkable precision with which the radii have been measured (<1.7%) and the firm assessment (>3$σ$) of the mass for at least three planets has been previously reached only for TRAPPIST-1. Additional photometric observations will enable a better sample of the TTV modulation and a more robust dynamical determination of the masses. △ Less

Submitted 21 April, 2026; v1 submitted 16 April, 2026; originally announced April 2026.

Comments: Accepted for publication in A&A. 22 pages (13 in the main text), 4 figures (+9 in the Appendix), 2 tables (+7 in the Appendix). Abstract abridged to satisfy the arXiv submission requirements

Journal ref: A&A 709, A265 (2026)

Inhomogeneous magnetic coupling in exoplanets: the stop & go of WASP-18 b's atmospheric flows

Authors: Aljona Blöcker, Ludmila Carone, Christiane Helling

Abstract: Early studies of ionization in hot Jupiter atmospheres suggest that magnetic coupling can shape their dynamics. These effects may be most pronounced in ultra-hot Jupiters that sustain global magnetic fields. WASP-18 b hosts an ionized dayside atmosphere extending deep enough to be strongly influenced by magnetic forces. Phase curve observations suggest effective magnetic drag, yet its impact on th… ▽ More Early studies of ionization in hot Jupiter atmospheres suggest that magnetic coupling can shape their dynamics. These effects may be most pronounced in ultra-hot Jupiters that sustain global magnetic fields. WASP-18 b hosts an ionized dayside atmosphere extending deep enough to be strongly influenced by magnetic forces. Phase curve observations suggest effective magnetic drag, yet its impact on the atmospheric circulation remains poorly constrained. This work explores how magnetic drag in an inhomogeneously ionized atmosphere shapes local and global dynamics to provide a pathway to constrain the planet's magnetic field strength. An analytical parameterization for anisotropic magnetic drag, including both Pedersen and Hall drag components, and associated frictional heating in the globally neutral atmosphere, is implemented in the 3D General Circulation Model ExoRad to study WASP-18 b's atmosphere. Climate characteristics are compared for different drag formulations to assess whether anisotropic physics is required to capture magnetic coupling effects. Anisotropic magnetic drag and frictional heating, both set by local ionization, strongly affect wind strength and direction in the upper atmosphere, modify the day-night circulation, and produce observable temperature asymmetries. They enhance the evening-morning terminator temperature difference near 0.1 bar and generate two off-equator hotspots with reduced eastward shift. The terminator regions are particularly sensitive to how magnetic drag is modeled. Anisotropic magnetic drag damps and redirects dayside-to-nightside winds, partially decoupling the equatorial flow at the morning terminator while maintaining the nightside jet. Locally varying drag forces and frictional heating create asymmetric temperature patterns manifesting as primary and secondary hotspot regions. △ Less

Submitted 2 April, 2026; v1 submitted 20 February, 2026; originally announced February 2026.

Journal ref: A&A 708, A84 (2026)

Impact of Cold Noise on the tracking performance of ATLAS ITk short strip barrel modules using a charged particle beam

Authors: Tony Affolder, Jan-Hendrik Arling, Sten Astrand, Ilyas Benaoumeur, Jakub Bucko, Sergio Diez Cornell, Bruce Joseph Gallop, Navid Ghorbanian, Yajun He, Cole Michael Helling, Nigel Hessey, Lennart Huth, Callan Jessiman, Christoph Thomas Klein, John Stakely Keller, Jiri Kroll, Jiri Kvasnicka, Konstantin Mauer, Alexandra Murphy, Anne-Luise Poley, Dilia Maria Portillo Quintero, Peter Phillips, Radek Privara, Eduardo Torres Reoyo, Pavel Tuma , et al. (1 additional authors not shown)

Abstract: The inner tracking system of the ATLAS experiment will be upgraded to a full silicon detector in 2030 for HL-LHC. The new tracking system is called ITk, the Inner Tracker. It is required to be operable with efficiency higher than 99\% and noise hit occupancy smaller than 0.1\%. During the pre-production phase of the ITk project, many short-strip modules were observed to exhibit so-called "Cold Noi… ▽ More The inner tracking system of the ATLAS experiment will be upgraded to a full silicon detector in 2030 for HL-LHC. The new tracking system is called ITk, the Inner Tracker. It is required to be operable with efficiency higher than 99\% and noise hit occupancy smaller than 0.1\%. During the pre-production phase of the ITk project, many short-strip modules were observed to exhibit so-called "Cold Noise (CN)", wherein clusters of strips displayed very high noise when the modules were operated at temperatures below~$-35\degree$C. To investigate the CN impact and ensure the quality of module production, huge amount of effort have been put in by the collaboration. This paper focuses on the impact of CN on the tracking performance by examining two short strip modules that exhibit CN: one is non-irradiated, while the other one has been irradiated to the maximum expected end-of-lifetime fluence. For each module, the global and single strip tracking performance are evaluated. △ Less

Submitted 8 January, 2026; originally announced January 2026.

Direct imaging characterization of cool gaseous planets

Authors: Michiel Min, Jo Barstow, Laura C. Mayorga, Hannah Wakeford, Jason Wang, Renyu Hu, Beth Biller, José A. Caballero, Ludmila Carone, Sarah Casewell, Katy L. Chubb, Mario Damiano, Siddharth Gandhi, Antonio García Muñoz, Christiane Helling, Finnegan Keller, Nataliea Lowson, Evert Nasedkin, Ryan MacDonald, Jean-Baptiste Ruffio, Evgenya Shkolnik, Christopher C. Stark

Abstract: Cool gas giant exoplanets, particularly those with properties similar to those of Jupiter and Saturn, remain poorly characterized due to current observational limitations. This white paper outlines the transformative science case for the Habitable Worlds Observatory (HWO) to directly image and spectroscopically characterize a broad range of gaseous exoplanets with effective temperatures below 400… ▽ More Cool gas giant exoplanets, particularly those with properties similar to those of Jupiter and Saturn, remain poorly characterized due to current observational limitations. This white paper outlines the transformative science case for the Habitable Worlds Observatory (HWO) to directly image and spectroscopically characterize a broad range of gaseous exoplanets with effective temperatures below 400 K. The study focuses on determining key atmospheric properties, including molecular composition, cloud and haze characteristics, and temperature structure, across planets of varying sizes and orbital separations. Leveraging reflected light spectroscopy and polarimetry, HWO will enable comparative planetology of cool gas giants orbiting both solar-type and M-dwarf stars, bridging the observational gap between hot exoplanets and Solar System giants. We present observational requirements and survey strategies necessary to uncover correlations between atmospheric properties and planetary or stellar parameters. This effort will establish critical constraints on planetary formation, cloud microphysics, and the role of photochemistry under diverse irradiation conditions. The unique capabilities of HWO will make it the first facility capable of characterizing true exo-Jupiters in reflected light, thus offering an unprecedented opportunity to place the Solar System in a broader galactic context. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Comments: Habitable Worlds Observatory (HWO) Science Case Development Document (SCDD), presented at the "Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology" conference in July 2025, and to be published in the conference proceedings

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

Journal ref: A&A 707, A134 (2026)

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

Exoplanet climate characterization with transit asymmetries -- A comprehensive population study from the optical to the infrared

Authors: Ludmila Carone, Christiane Helling, Sebastian Gernjak, Hanna Leitner, Tamara Janz

Abstract: Space missions (CHEOPS, JWST, PLATO) facilitate detailed characterization of exoplanets. This work provides a framework to characterize cloud and climate properties of close-in gas giants via transit depth asymmetries from the optical to the infrared (0.33 ...10 $μ$m). The AFGKM ExoRad 3D GCM grid provides gas temperature profiles for an ensemble of 50 tidally locked gaseous planets orbiting div… ▽ More Space missions (CHEOPS, JWST, PLATO) facilitate detailed characterization of exoplanets. This work provides a framework to characterize cloud and climate properties of close-in gas giants via transit depth asymmetries from the optical to the infrared (0.33 ...10 $μ$m). The AFGKM ExoRad 3D GCM grid provides gas temperature profiles for an ensemble of 50 tidally locked gaseous planets orbiting diverse host stars. It is combined with a detailed kinetic cloud formation model. The end result is a set of synthetic transit spectra and evening-to-morning transit asymmetries that span climate regimes: warm (T=800 K ... 1000K), intermediately hot (T=1200 K ... 2000 K) and ultrahot (T =2200 K ... 2600 K). WASP-39b observations suggest iron-free clouds with less abundant cloud condensation nuclei than previously expected. The ensemble study shows that clouds increase transit limb differences due to asymmetries in cloud coverage and by enhancing horizontal differences in the gas temperatures. For hot planets, evening-to-morning differences of up to 150 ppm are suggested in the optical and 100 ppm in the infrared (2-8 micron). For ultra-hot Jupiters, evening-to-morning transit differences are dominated by the morning cloud for a cloud-free evening limb: They are strongly negative in the PLATO band (0.5-1~$μ$m, -500 ppm), moderately negative in the near-infrared (1-1.5~$μ$m, -200 ppm) and moderately positive (+100 ppm) for $λ> 2μ$m. For a partly cloudy evening terminator, the evening-to-morning transit asymmetry is moderately positive in the whole wavelength range. Warm Jupiter planets exhibit negligible transit asymmetries. PLATO and JWST transit asymmetry observations between 1-2 $μ$m are optimal to characterize cloudy planetary atmospheres around K -A stars. JWST observations are most effective for M star planets with transit differences > +500 ppm for 8-10 $μ$m. △ Less

Submitted 24 November, 2025; v1 submitted 3 November, 2025; originally announced November 2025.

Comments: Accepted for publication in A&A, 32 pages, 29 figures (Typos corrected)

Journal ref: A&A 708, A185 (2026)

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

Silicon pinhole strip defects and their impact on ATLAS Inner Tracker HV current measurement

Authors: Anthony Affolder, Kirsten Affolder, Emily Duden, Vitaliy Fadeyev, Cole Helling, David Lynn, Forest Martinez-Mckinney, Peter Phillips, Luise Poley, Tate Sakaguchi, Abdullah Sayed, Stefania Stucci, Alex Wang, Marcus Wong

Abstract: In preparation for the High-Luminsoity LHC (HL-LHC), the ATLAS detector will undergo major detector upgrades, including the replacement of the current Inner Detector with the new all-silicon Inner Tracker (ITk). The ITk consists of a pixel detector close to the beamline surrounded by a large-area strip detector. During detector production, the electrical properties of silicon sensors and readout e… ▽ More In preparation for the High-Luminsoity LHC (HL-LHC), the ATLAS detector will undergo major detector upgrades, including the replacement of the current Inner Detector with the new all-silicon Inner Tracker (ITk). The ITk consists of a pixel detector close to the beamline surrounded by a large-area strip detector. During detector production, the electrical properties of silicon sensors and readout electronics must be characterized through a series of quality control (QC) and quality assurance tests. These tests ensure any defect is captured at the earliest possible stage. One such defect, called a pinhole, occurs when the strip implant and the metal readout electrode are shorted through the intermediary dielectric layer. Notably, the introduction of pinholes during module assembly and pinhole effects on completed modules, especially on leakage current measurement circuitry, have never been studied. In this paper, we investigate the effect of such connections on the sensor leakage current measurements of completed modules and introduce new ways to locate pinholed strips. With minor modifications to testing procedures, such defects are shown not to impede module testing or performance. △ Less

Submitted 10 November, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Limb Asymmetries on WASP-39b: A Multi-GCM Comparison of Chemistry, Clouds, and Hazes

Authors: Maria E. Steinrueck, Arjun B. Savel, Duncan A. Christie, Ludmila Carone, Shang-Min Tsai, Can Akın, Thomas D. Kennedy, Sven Kiefer, David A. Lewis, Emily Rauscher, Dominic Samra, Maria Zamyatina, Kenneth Arnold, Robin Baeyens, Leonardos Gkouvelis, David Haegele, Christiane Helling, Nathan J. Mayne, Diana Powell, Michael T. Roman, Hayley Beltz, Néstor Espinoza, Kevin Heng, Nicolas Iro, Eliza M. -R. Kempton , et al. (5 additional authors not shown)

Abstract: With JWST, observing separate spectra of the morning and evening limbs of hot Jupiters has finally become a reality. The first such observation was reported for WASP-39b, where the evening terminator was observed to have a larger transit radius by about 400 ppm and a stronger 4.3 $μ$m CO$_2$ feature than the morning terminator. Multiple factors, including temperature differences, photo/thermochemi… ▽ More With JWST, observing separate spectra of the morning and evening limbs of hot Jupiters has finally become a reality. The first such observation was reported for WASP-39b, where the evening terminator was observed to have a larger transit radius by about 400 ppm and a stronger 4.3 $μ$m CO$_2$ feature than the morning terminator. Multiple factors, including temperature differences, photo/thermochemistry, clouds and hazes, could cause such limb asymmetries. To interpret these new limb asymmetry observations, a detailed understanding of how the relevant processes affect morning and evening spectra grounded in forward models is needed. Focusing on WASP-39b, we compare simulations from five different general circulation models (GCMs), including one simulating disequilibrium thermochemistry and one with cloud radiative feedback, to the recent WASP-39b limb asymmetry observations. We also post-process the temperature structures of all simulations with a 2D photochemical model and one simulation with a cloud microphysics model. Although the temperatures predicted by the different models vary considerably, the models are remarkably consistent in their predicted morning--evening temperature differences. Several equilibrium-chemistry simulations predict strong methane features in the morning spectrum, not seen in the observations. When including disequilibrium processes, horizontal transport homogenizes methane, and these methane features disappear. However, even after including photochemistry and clouds, our models still cannot reproduce the observed ${\sim}2000$ ppm asymmetry in the CO$_2$ feature. A combination of factors, such as varying metallicity and unexplored parameters in cloud models, may explain the discrepancy, emphasizing the need for future models integrating cloud microphysics and feedback across a broader parameter space. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Comments: submitted to AAS Journals. Supplementary Data available on Zenodo

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

Journal ref: A&A 704, A174 (2025)

Prediction of sulphate hazes in the lower Venus atmosphere

Authors: Peter Woitke, Manuel Scherf, Christiane Helling, Paul B. Rimmer, Martin Ferus, Helmut Lammer, Fabian Weichbold, Kateřina Němečková, Petr Eminger, Jaroslav Kačina, Tereza Constantinou

Abstract: We study the amount, size distribution and material composition of (sub-)mic aerosol particles in the lower Venus atmosphere < 50 km. Our GGchem phase-equilibrium model predicts metal-chloride and metal-fluoride molecules to be present in the gas over the Venus surface in trace concentrations < 2.E-12, in particular FeCl2, NaCl, KCl and SiF4. Using an improved version of the DiffuDrift model devel… ▽ More We study the amount, size distribution and material composition of (sub-)mic aerosol particles in the lower Venus atmosphere < 50 km. Our GGchem phase-equilibrium model predicts metal-chloride and metal-fluoride molecules to be present in the gas over the Venus surface in trace concentrations < 2.E-12, in particular FeCl2, NaCl, KCl and SiF4. Using an improved version of the DiffuDrift model developed by Woitke et al.2020, we find that these molecules deposit to form solid potassium sulphate K2SO4, sodium sulphate Na2SO4, and pyrite FeS2 above about 15.5 km, 9.5 km and 2.4 km, respectively. These heights coincide well with the three potential haze layers found in the Pioneer Venus Large Probe neutral mass spectrometer data by Mogul et al.2023. The particles with radius < 0.3 mic can be dredged up from the ground to reach the sulphuric acid cloud base from below by diffusion. The particle density decreases from ~ 5000/cm3 at ground level to ~100/cm3 at a height of 45 km. Particles larger than about 1 mic are found to stay confined to the ground < 10 km, indicating that the larger, so-called mode 3 particles, if they exist, cannot originate from the surface. All particles are expected to be coated by a thin layer of FeS2, Na2SO4 and K2SO4. We have included the repelling effect of particle charges on the coagulation, without which the model would predict much too steep gradients close to the surface, which is inconsistent with measured opacity data. Our models suggest that the particles must have at least 100 negative charges per micron of particle radius at ground level, and > 50/mic at a height of 45 km. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Comments: 18 pages, accepted by PSJ on 27-Aug-2025

Accelerating exoplanet climate modelling: A machine learning approach to complement 3D GCM grid simulations

Authors: Alexander Plaschzug, Amit Reza, Ludmila Carone, Sebastian Gernjak, Christiane Helling

Abstract: With the development of ever-improving telescopes capable of observing exoplanet atmospheres in greater detail and number, there is a growing demand for enhanced 3D climate models to support and help interpret observational data from space missions like CHEOPS, TESS, JWST, PLATO, and Ariel. However, the computationally intensive and time-consuming nature of general circulation models (GCMs) poses… ▽ More With the development of ever-improving telescopes capable of observing exoplanet atmospheres in greater detail and number, there is a growing demand for enhanced 3D climate models to support and help interpret observational data from space missions like CHEOPS, TESS, JWST, PLATO, and Ariel. However, the computationally intensive and time-consuming nature of general circulation models (GCMs) poses significant challenges in simulating a wide range of exoplanetary atmospheres. This study aims to determine whether machine learning (ML) algorithms can be used to predict the 3D temperature and wind structure of arbitrary tidally-locked gaseous exoplanets in a range of planetary parameters. A new 3D GCM grid with 60 inflated hot Jupiters orbiting A, F, G, K, and M-type host stars modelled with Exorad has been introduced. A dense neural network (DNN) and a decision tree algorithm (XGBoost) are trained on this grid to predict local gas temperatures along with horizontal and vertical winds. To ensure the reliability and quality of the ML model predictions, WASP-121 b, HATS-42 b, NGTS-17 b, WASP-23 b, and NGTS-1 b-like planets, which are all targets for PLATO observation, are selected and modelled with ExoRad and the two ML methods as test cases. The DNN predictions for the gas temperatures are to such a degree that the calculated spectra agree within 32 ppm for all but one planet, for which only one single HCN feature reaches a 100 ppm difference. The developed ML emulators can reliably predict the complete 3D temperature field of an inflated warm to ultra-hot tidally locked Jupiter around A to M-type host stars. It provides a fast tool to complement and extend traditional GCM grids for exoplanet ensemble studies. The quality of the predictions is such that no or minimal effects on the gas phase chemistry, hence on the cloud formation and transmission spectra, are to be expected. △ Less

Submitted 14 August, 2025; originally announced August 2025.

Report number: A157

Journal ref: A&A Volume 706, February 2026

The effect of stellar magnetic activity on measurements of morning and evening asymmetry of planetary terminator

Authors: N. Kostogryz, A. I. Shapiro, L. Carone, L. Gizon, Ch. Helling, S. Kiefer, S. Mercier, S. Seager, S. K. Solanki, Y. Unruh, J. de Wit, V. Witzke

Abstract: Differences in the ingress and egress shapes of transit light curves can indicate morning-evening temperature contrasts on transiting planets. Here, we pinpoint an alternative mechanism that can introduce asymmetries in transit light curves, potentially affecting the accurate determination of morning-evening differences. Small-scale magnetic field concentrations on the surfaces of the host star af… ▽ More Differences in the ingress and egress shapes of transit light curves can indicate morning-evening temperature contrasts on transiting planets. Here, we pinpoint an alternative mechanism that can introduce asymmetries in transit light curves, potentially affecting the accurate determination of morning-evening differences. Small-scale magnetic field concentrations on the surfaces of the host star affect the visibility of stellar limb regions, making them brighter relative to the non-magnetic case. A difference in magnetization between the star's western and eastern limbs can thus create an asymmetry in limb brightness and, consequently, an asymmetry between transit ingress and egress. We model the limb darkening and stellar limb asymmetry in solar-like stars using the 3D radiative MHD code MURaM to simulate magnetized stellar atmospheres and the MPS-ATLAS code to synthesize spectra using ray-by-ray approach. Our results show that ingress-egress depth differences can reach up to 600 ppm for a 10000 ppm transit at 600 nm, depending on the magnetization of the stellar limbs--significantly interfering with planetary signals. Observations of the Sun show that such concentrations are often not accompanied by spots and do not manifest in photometric variability, indicating that even photometrically quiet stars can produce such asymmetries. However, planetary and stellar asymmetries exhibit distinct wavelength dependencies, which we propose to leverage for disentangling them. △ Less

Submitted 22 July, 2025; originally announced July 2025.

Comments: Accepted to Astrophysical Journal Letters

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

Test beam measurements and computer simulations of the ATLAS ITk R2 silicon strip detector

Authors: Jan-Hendrik Arling, Pavol Federic, Yajun He, Cole Michael Helling, Nigel Hessey, Lennart Huth, Geetika Jain, Callan Jessiman, Sebastian Manson, Luise Poley, John Stakely Keller, Jiri Kroll, Jiri Kvasnicka, Radek Privara, Peter Speers, Pavel Tuma

Abstract: The ATLAS Inner Tracker, the future innermost part of the ATLAS detector, is an all-silicon tracker composed of pixel and strip modules, designed to cope with the extreme conditions expected during High-Luminosity LHC runs. Thorough testing of modules during the individual phases of their development is critical to ensure the required performance level of the whole tracker. This document presents… ▽ More The ATLAS Inner Tracker, the future innermost part of the ATLAS detector, is an all-silicon tracker composed of pixel and strip modules, designed to cope with the extreme conditions expected during High-Luminosity LHC runs. Thorough testing of modules during the individual phases of their development is critical to ensure the required performance level of the whole tracker. This document presents results obtained from electron beam measurements of the ATLAS ITk R2 end-cap strip module. Key performance metrics are presented and discussed for both perpendicular and angled beam incidence. Computer simulations of the module were performed in the Allpix-Squared framework and the results were compared to experimental data. △ Less

Submitted 14 July, 2025; v1 submitted 19 June, 2025; originally announced June 2025.

Comments: Accepted for publication in Journal of Instrumentation (JINST). 15 pages, 7 figures, 3 tables

Journal ref: Journal of Instrumentation 20 (2025) P07033

Can thermodynamic equilibrium be established in planet-forming disks?

Authors: Jayatee Kanwar, Peter Woitke, Inga Kamp, Paul Rimmer, Christiane Helling

Abstract: The inner regions of planet-forming disks are warm and dense. The chemical networks used for disk modelling so far were developed for a cold and dilute medium and do not include a complete set of pressure-dependent reactions. The chemical networks developed for planetary atmospheres include such reactions along with the inverse reactions related to the Gibb's free energies of the molecules. The ch… ▽ More The inner regions of planet-forming disks are warm and dense. The chemical networks used for disk modelling so far were developed for a cold and dilute medium and do not include a complete set of pressure-dependent reactions. The chemical networks developed for planetary atmospheres include such reactions along with the inverse reactions related to the Gibb's free energies of the molecules. The chemical networks used for disk modelling are thus incomplete in this respect. We want to study whether thermodynamic equilibrium can be established in a planet-forming disk. We identify the regions in the disk most likely to reach thermodynamic equilibrium and determine the timescale over which this occurs. We employ the theoretical concepts used in exoplanet atmosphere chemistry for the disk modelling with PROtoplanetary DIsk MOdel ({\sc ProDiMo}). We develop a chemical network called CHemistry Assembled from exoplanets and dIsks for Thermodynamic EquilibriA ({\sc ChaiTea}) that is based on the UMIST 2022, STAND, and large DIscANAlysis (DIANA) chemical networks. It consists of 239 species. From the STAND network, we adopt the concept of reversing all gas-phase reactions based on thermodynamic data. We use single-point models for a range of gas densities and gas temperatures to verify that the implemented concepts work and thermodynamic equilibrium is achieved in the absence of cosmic rays and photoreactions including radiative associations and direct recombinations. We then study the impact of photoreactions and cosmic rays that lead to deviations from thermodynamic equilibrium. We explore the chemical relaxation timescales towards thermodynamic equilibrium. Lastly, we study the predicted 2D chemical structure of a typical T\,Tauri disk when using the new {\sc ChaiTea} network instead of the large DIANA standard network, including photorates, cosmic rays, X-rays, and ice.... △ Less

Submitted 19 May, 2025; originally announced May 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)

Quality Concerns Caused by Quality Control -- deformation of silicon strip detector modules in thermal cycling tests

Authors: Richard Salami, Luise Poley, Kirsten Affolder, Tony Affolder, Lukas Bayer, Ben Crick, Emily Duden, Ian George Dyckes, Vitaliy Fadeyev, Anne Fortman, Pavol Federic, Laura Franconi, Matthew Gignac, Shubham Gupta, John Hallford, Cole Helling, Ewan Hill, Miao Hu, Jiri Kroll, Priyanka Kumari, Carlos Lacasta, Madison Levagood, Hanlez Lopez, Len Morelos-Zaragoza, Meny Raviv Moshe , et al. (9 additional authors not shown)

Abstract: The ATLAS experiment at the Large Hadron Collider (LHC) is currently preparing to replace its present Inner Detector (ID) with the upgraded, all-silicon Inner Tracker (ITk) for its High-Luminosity upgrade (HL-LHC). The ITk will consist of a central pixel tracker and the outer strip tracker, consisting of about 19,000 strip detector modules. Each strip module is assembled from up to two sensors, an… ▽ More The ATLAS experiment at the Large Hadron Collider (LHC) is currently preparing to replace its present Inner Detector (ID) with the upgraded, all-silicon Inner Tracker (ITk) for its High-Luminosity upgrade (HL-LHC). The ITk will consist of a central pixel tracker and the outer strip tracker, consisting of about 19,000 strip detector modules. Each strip module is assembled from up to two sensors, and up to five flexes (depending on its geometry) in a series of gluing, wirebonding and quality control steps. During detector operation, modules will be cooled down to temperatures of about -35C (corresponding to the temperature of the support structures on which they will be mounted) after being initially assembled and stored at room temperature. In order to ensure compatibility with the detector's operating temperature range, modules are subjected to thermal cycling as part of their quality control process. Ten cycles between -35C and +40C are performed for each module, with full electrical characterisation tests at each high and low temperature point. As part of an investigation into the stress experienced by modules during cooling, it was observed that modules generally showed a change in module shape before and after thermal cycling. This paper presents a summary of the discovery and understanding of the observed changes, connecting them with excess module stress, as well as the resulting modifications to the module thermal cycling procedure. △ Less

Submitted 4 March, 2025; originally announced March 2025.

Journal ref: JINST 20 P03004 (2025)

Bohmian Mechanics fails to compute multi-time correlations

Authors: Robert C. Helling

Abstract: The violation of Bell type inequalities in quantum systems manifests that quantum states cannot be described by classical probability distributions. Yet, Bohmian mechanics is a realistic, non-local theory of classical particle trajectories that is claimed to be indistinguishable by observations from more traditional approaches to quantum mechanics. We set up a spatial version of the GHZ system wit… ▽ More The violation of Bell type inequalities in quantum systems manifests that quantum states cannot be described by classical probability distributions. Yet, Bohmian mechanics is a realistic, non-local theory of classical particle trajectories that is claimed to be indistinguishable by observations from more traditional approaches to quantum mechanics. We set up a spatial version of the GHZ system with qubits realised as positional observables that demonstrates that the Bohmian theory fails to match predictions of textbook quantum mechanics (and most likely experients) unless enlarged by a microscopic theory of collapse of the wave function after observation. For this discrepancy to occur it is essential that positions at different times do not commute. △ Less

Submitted 25 February, 2025; v1 submitted 20 February, 2025; originally announced February 2025.

Comments: 15 pages, v2: added references

MSC Class: 81P15; 81D40; 81Q65

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)

Grid-based exoplanet atmospheric mass loss predictions through neural network

Authors: Amit Reza, Daria Kubyshkina, Luca Fossati, Christiane Helling

Abstract: The fast and accurate estimation of planetary mass-loss rates is critical for planet population and evolution modelling. We use machine learning (ML) for fast interpolation across an existing large grid of hydrodynamic upper atmosphere models, providing mass-loss rates for any planet inside the grid boundaries with superior accuracy compared to previously published interpolation schemes. We consid… ▽ More The fast and accurate estimation of planetary mass-loss rates is critical for planet population and evolution modelling. We use machine learning (ML) for fast interpolation across an existing large grid of hydrodynamic upper atmosphere models, providing mass-loss rates for any planet inside the grid boundaries with superior accuracy compared to previously published interpolation schemes. We consider an already available grid comprising about 11000 hydrodynamic upper atmosphere models for training and generate an additional grid of about 250 models for testing purposes. We develop the ML interpolation scheme (dubbed "atmospheric Mass Loss INquiry frameworK"; MLink) using a Dense Neural Network, further comparing the results with what was obtained employing classical approaches (e.g. linear interpolation and radial basis function-based regression). Finally, we study the impact of the different interpolation schemes on the evolution of a small sample of carefully selected synthetic planets. MLink provides high-quality interpolation across the entire parameter space by significantly reducing both the number of points with large interpolation errors and the maximum interpolation error compared to previously available schemes. For most cases, evolutionary tracks computed employing MLink and classical schemes lead to comparable planetary parameters at Gyr-timescales. However, particularly for planets close to the top edge of the radius gap, the difference between the predicted planetary radii at a given age of tracks obtained employing MLink and classical interpolation schemes can exceed the typical observational uncertainties. Machine learning can be successfully used to estimate atmospheric mass-loss rates from model grids paving the way to explore future larger and more complex grids of models computed accounting for more physical processes. △ Less

Submitted 3 February, 2025; originally announced February 2025.

Comments: Accepted for publication on A&A

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

Kinetic and photochemical disequilibrium in the potentially carbon-rich atmosphere of the warm-Jupiter WASP-69b

Authors: Nidhi Bangera, Christiane Helling, Gloria Guilluy, Patricio Cubillos, Luca Fossati, Paolo Giacobbe, Paul Rimmer, Daniel Kitzmann

Abstract: High-resolution transmission spectroscopy of the warm gas-giant WASP-69b has revealed the presence of H2O, CO, CH4, NH3, and C2H2 in its atmosphere. This study investigates the impact of vertical diffusion and photochemistry on its atmospheric composition, with a focus on the detected species plus HCN and CO2, to constrain the atmospheric C/O ratio. We utilize non-equilibrium gas-phase simulations… ▽ More High-resolution transmission spectroscopy of the warm gas-giant WASP-69b has revealed the presence of H2O, CO, CH4, NH3, and C2H2 in its atmosphere. This study investigates the impact of vertical diffusion and photochemistry on its atmospheric composition, with a focus on the detected species plus HCN and CO2, to constrain the atmospheric C/O ratio. We utilize non-equilibrium gas-phase simulations to conduct a parameter study for vertical diffusion strength, local gas temperature, and C/O ratio. Our results indicate that a carbon-rich atmosphere enhances CH4 and C2H2 concentrations, while NH3 undergoes chemical conversion into HCN in carbon-rich, high-temperature environments. Consequently, HCN is abundantly produced in such atmospheres, though its strong spectral features remain undetected in WASP-69b. Photochemical production of HCN and C2H2 is highly sensitive to vertical diffusion strength, with weaker diffusion resulting in higher concentrations. Cross-correlation of synthetic spectra with observed data shows that models with C/O=2 best match observations, but models with C/O=0.55 and 0.9 lead to statistically equivalent fits, leaving the C/O ratio unconstrained. We highlight the importance of accurately modeling NH3 quenching at pressures greater than 100 bars. Models for WASP-69b capped at 100 bars bias cross-correlation fits towards carbon-rich values. We suggest that if the atmosphere of WASP-69b is indeed carbon-rich with a solar metallicity, future observations should reveal the presence of HCN. △ Less

Submitted 14 January, 2025; originally announced January 2025.

Comments: 22 pages, 11 figures, accepted for publication in ApJ

The $\texttt{MSG}$ model for cloudy substellar atmospheres: A grid of self-consistent substellar atmosphere models with microphysical cloud formation

Authors: Beatriz Campos Estrada, David A. Lewis, Christiane Helling, Richard A. Booth, Francisco Ardévol Martínez, Uffe G. Jørgensen

Abstract: State-of-the-art JWST observations are unveiling unprecedented views into the atmospheres of substellar objects in the infrared, further highlighting the importance of clouds. Current forward models struggle to fit the silicate clouds absorption feature at ~$10\,μ$m observed in substellar atmospheres. In the MSG model, we aim to couple the MARCS 1D radiative-convective equilibrium atmosphere model… ▽ More State-of-the-art JWST observations are unveiling unprecedented views into the atmospheres of substellar objects in the infrared, further highlighting the importance of clouds. Current forward models struggle to fit the silicate clouds absorption feature at ~$10\,μ$m observed in substellar atmospheres. In the MSG model, we aim to couple the MARCS 1D radiative-convective equilibrium atmosphere model with the 1D kinetic, stationary, non-equilibrium, cloud formation model DRIFT, to create a new grid of self-consistent cloudy substellar atmosphere models with microphysical cloud formation. We aim to test if this new grid is able to reproduce the silicate cloud absorption feature at ~$10\,μ$m. We model substellar atmospheres with effective temperatures in the range 1200-2500 K and with $\log(g)=4.0$. We compute atmospheric structures that self-consistently account for condensate cloud opacities based on microphysical properties. We present an algorithm based on control theory to help converge such self-consistent models. Synthetic atmosphere spectra are computed for each model to explore the observable impact of the cloud microphysics. We additionally explore the impact of choosing different nucleation species (TiO$_2$ or SiO) and the effect of less efficient atmospheric mixing on these spectra. The new MSG cloudy grid using TiO$_2$ nucleation shows spectra which are redder in the near-infrared compared to the currently known population of substellar atmospheres. We find the models with SiO nucleation, and models with reduced mixing efficiency are less red in the near-infrared. The grid is unable to reproduce the silicate features similar to those found in recent JWST observations and Spitzer archival data. We thoroughly discuss further work that may better approximate the impact of convection in cloud-forming regions and steps that may help resolve the silicate cloud feature. △ Less

Submitted 9 January, 2025; originally announced January 2025.

Comments: Accepted for publication in A&A

Journal ref: A&A 694, A275 (2025)

From CO$_2$- to H$_2$O-dominated atmospheres and back -- How mixed outgassing changes the volatile distribution in magma oceans around M dwarf stars

Authors: Ludmila Carone, Rory Barnes, Lena Noack, Katy L. Chubb, Patrick Barth, Bertram Bitsch, Alexander Thamm, Alexander Balduin, Rodolfo Garcia, Christiane Helling

Abstract: We investigate the impact of CO$_2$ on TRAPPIST-1 e, f and g during the magma ocean stage. These potentially habitable rocky planets are currently the most accessible for astronomical observations. A constraint on the volatile budget during the magma ocean stage is a link to planet formation and also needed to judge their habitability. We perform simulations with 1-100 terrestrial oceans (TO) of H… ▽ More We investigate the impact of CO$_2$ on TRAPPIST-1 e, f and g during the magma ocean stage. These potentially habitable rocky planets are currently the most accessible for astronomical observations. A constraint on the volatile budget during the magma ocean stage is a link to planet formation and also needed to judge their habitability. We perform simulations with 1-100 terrestrial oceans (TO) of H$_2$O with and without CO$_2$ and for albedos 0 and 0.75. The CO$_2$ mass is scaled with initial H$_2$O by a constant factor between 0.1 and 1. The magma ocean state of rocky planets begins with a CO$_2$-dominated atmosphere but can evolve into a H$_2$O dominated state, depending on initial conditions. For less than 10 TO initial H$_2$O, the atmosphere tends to desiccate and the evolution may end with a CO$_2$ dominated atmosphere. Otherwise, the final state is a thick (>1000 bar) H$_2$O-CO$_2$ atmosphere. Complete atmosphere desiccation with less than 10 TO initial H$_2$O can be significantly delayed for TRAPPIST-1e and f, when H$_2$O has to diffuse through a CO$_2$ atmosphere to reach the upper atmosphere, where XUV photolysis occurs. As a consequence of CO$_2$ diffusion-limited water loss, the time of mantle solidification for TRAPPIST-1 e, f, and g can be significantly extended compared to a pure H$_2$O evolution by up to 40 Myrs for albedo 0.75 and by up to 200 Mrys for albedo 0. The addition of CO$_2$ further results in a higher water content in the melt during the magma ocean stage. Our compositional model adjusted for the measured metallicity of TRAPPIST-1 yields for the dry inner planets (b, c, d) an iron fraction of 27 wt-%. For TRAPPIST-1 e, this iron fraction would be compatible with a (partly) desiccated evolution scenario and a CO$_2$ atmosphere with surface pressures of a few 100 bar. A comparative study between TRAPPIST-1 e and the inner planets may yield the most insights about formation and evolution scenarios. △ Less

Submitted 13 December, 2024; originally announced December 2024.

Comments: 36 pages, 28 figues, accepted by A&A 9/12/2024

Journal ref: A&A 693, A303 (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

Machine learning-based classification for Single Photon Space Debris Light Curves

Authors: Nadine M. Trummer, Amit Reza, Michael A. Steindorfer, Christiane Helling

Abstract: The growing number of man-made debris in Earth's orbit poses a threat to active satellite missions due to the risk of collision. Characterizing unknown debris is, therefore, of high interest. Light Curves (LCs) are temporal variations of object brightness and have been shown to contain information such as shape, attitude, and rotational state. Since 2015, the Satellite Laser Ranging (SLR) group of… ▽ More The growing number of man-made debris in Earth's orbit poses a threat to active satellite missions due to the risk of collision. Characterizing unknown debris is, therefore, of high interest. Light Curves (LCs) are temporal variations of object brightness and have been shown to contain information such as shape, attitude, and rotational state. Since 2015, the Satellite Laser Ranging (SLR) group of Space Research Institute (IWF) Graz has been building a space debris LC catalogue. The LCs are captured on a Single Photon basis, which sets them apart from CCD-based measurements. In recent years, Machine Learning (ML) models have emerged as a viable technique for analyzing LCs. This work aims to classify Single Photon Space Debris using the ML framework. We have explored LC classification using k-Nearest Neighbour (k-NN), Random Forest (RDF), XGBoost (XGB), and Convolutional Neural Network (CNN) classifiers in order to assess the difference in performance between traditional and deep models. Instead of performing classification on the direct LCs data, we extracted features from the data first using an automated pipeline. We apply our models on three tasks, which are classifying individual objects, objects grouped into families according to origin (e.g., GLONASS satellites), and grouping into general types (e.g., rocket bodies). We successfully classified Space Debris LCs captured on Single Photon basis, obtaining accuracies as high as 90.7%. Further, our experiments show that the classifiers provide better classification accuracy with automated extracted features than other methods. △ Less

Submitted 27 November, 2024; originally announced November 2024.

Journal ref: Acta Astronautica, Volume 226, Part 1, 2025, Pages 542-554

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

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

Under the magnifying glass: A combined 3D model applied to cloudy warm Saturn type exoplanets around M-dwarfs

Authors: Sven Kiefer, Nanna Bach-Møller, Dominic Samra, David A. Lewis, Aaron D. Schneider, Flavia Amadio, Helena Lecoq-Molinos, Ludmila Carone, Leen Decin, Uffe G. Jørgensen, Christiane Helling

Abstract: Warm Saturn type exoplanets orbiting M-dwarfs are particularly suitable for in-depth cloud characterisation through transmission spectroscopy due to their favourable stellar to planetary radius contrast. However, modelling cloud formation consistently within the 3D atmosphere remains computationally challenging. The aim is to explore the combined atmospheric and micro-physical cloud structure, and… ▽ More Warm Saturn type exoplanets orbiting M-dwarfs are particularly suitable for in-depth cloud characterisation through transmission spectroscopy due to their favourable stellar to planetary radius contrast. However, modelling cloud formation consistently within the 3D atmosphere remains computationally challenging. The aim is to explore the combined atmospheric and micro-physical cloud structure, and the kinetic gas-phase chemistry for the warm Saturn HATS0-6b orbiting an M-dwarf. A combined 3D cloudy atmosphere model is constructed by iteratively executing the 3D General Circulation Model (GCM) expeRT/MITgcm and a kinetic cloud formation model, each in its full complexity. Resulting cloud particle number densities, sizes, and compositions are used to derive the local cloud opacity which is then utilised in the next GCM iteration. The disequilibrium H/C/O/N gas-phase chemistry is calculated for each iteration to assess the resulting transmission spectrum in post-processing. The cloud opacity feedback causes a temperature inversion at the sub-stellar point and at the evening terminator at gas pressures higher than 0.01 bar. Furthermore, clouds cool the atmosphere between 0.01 bar and 10 bar, and narrow the equatorial wind jet. The transmission spectrum shows muted gas-phase absorption and a cloud particle silicate feature at approximately 10 micron. The combined atmosphere-cloud model retains the full physical complexity of each component and therefore enables a detailed physical interpretation with JWST NIRSpec and MIRI LRS observational accuracy. The model shows that warm Saturn type exoplanets around M-dwarfs are ideal candidates to search for limb asymmetries in clouds and chemistry, identify cloud particle composition by observing their spectral features, and identify the cloud-induced strong thermal inversion that arises on these planets specifically. △ Less

Submitted 23 October, 2024; originally announced October 2024.

Comments: 21 pages, 15 figures, Accepted by A&A

Journal ref: A&A 692, A222 (2024)

The fixed probe storage ring magnetometer for the Muon g-2 experiment at Fermi National Accelerator Laboratory

Authors: Erik Swanson, Martin Fertl, Alejandro Garcia, Cole Helling, Ronaldo Ortez, Rachel Osofsky, David A. Peterson, Rene Reimann, Matthias W. Smith, Tim D. Van Wechel

Abstract: The goal of the FNAL E989 experiment is to measure the muon magnetic anomaly to unprecedented accuracy and precision at the Fermi National Accelerator Laboratory. To meet this goal, the time and space averaged magnetic environment in the muon storage volume must be known to better than 70 ppb. A new pulsed proton nuclear magnetic resonance (NMR) magnetometer was designed and built at the Universit… ▽ More The goal of the FNAL E989 experiment is to measure the muon magnetic anomaly to unprecedented accuracy and precision at the Fermi National Accelerator Laboratory. To meet this goal, the time and space averaged magnetic environment in the muon storage volume must be known to better than 70 ppb. A new pulsed proton nuclear magnetic resonance (NMR) magnetometer was designed and built at the University of Washington, Seattle to track the temporal stability of the 1.45T magnetic field in the muon storage ring at this precision. It consists of an array of 378 petroleum jelly based NMR probes that are embedded in the walls of muon storage ring vacuum chambers and custom electronics built with readily available modular radio frequency (RF) components. We give NMR probe construction details and describe the functions of the custom electronic subsystems. The excellent performance metrics of the magnetometer are discussed, where after 8 years of operation the median single shot resolution of the array of probes remains at 650 ppb. △ Less

Submitted 7 January, 2025; v1 submitted 10 October, 2024; originally announced October 2024.

Comments: 19 pages, 20 figures

Report number: FERMILAB-PUB-24-0770-V

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)

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)

Why heterogeneous cloud particles matter: Iron-bearing species and cloud particle morphology affects exoplanet transmission spectra

Authors: Sven Kiefer, Dominic Samra, David A. Lewis, Aaron D. Schneider, Michiel Min, Ludmila Carone, Leen Decin, Christiane Helling

Abstract: The possibility of observing spectral features in exoplanet atmospheres with space missions like JWST and ARIEL necessitates the accurate modelling of cloud particle opacities. In exoplanet atmospheres, cloud particles can be made from multiple materials and be considerably chemically heterogeneous. Therefore, assumptions on the morphology of cloud particles are required to calculate their opaciti… ▽ More The possibility of observing spectral features in exoplanet atmospheres with space missions like JWST and ARIEL necessitates the accurate modelling of cloud particle opacities. In exoplanet atmospheres, cloud particles can be made from multiple materials and be considerably chemically heterogeneous. Therefore, assumptions on the morphology of cloud particles are required to calculate their opacities. The aim of this work is to analyse how different approaches to calculate the opacities of heterogeneous cloud particles affect cloud particle optical properties. We calculate cloud particle optical properties using seven different mixing treatments: four effective medium theories (EMTs: Bruggeman, Landau-Lifshitz-Looyenga (LLL), Maxwell-Garnett, and Linear), core-shell, and two homogeneous cloud particle approximations. We study the mixing behaviour of 21 commonly considered cloud particle materials for exoplanets. To analyse the impact on observations, we study the transmission spectra of HATS-6b, WASP-39b, WASP-76b, and WASP-107b.Materials with large refractive indices, like iron-bearing species or carbon, can change the optical properties of cloud particles when they comprise less than 1\% of the total particle volume. The mixing treatment of heterogeneous cloud particles also has an observable effect on transmission spectroscopy. Assuming core-shell or homogeneous cloud particles results in less muting of molecular features and retains the cloud spectral features of the individual cloud particle materials. The predicted transit depth for core-shell and homogeneous cloud particle materials are similar for all planets used in this work. If EMTs are used, cloud spectral features are broader and cloud spectral features of the individual cloud particle materials are not retained. Using LLL leads to less molecular features in transmission spectra compared to Bruggeman. △ Less

Submitted 2 September, 2024; originally announced September 2024.

Comments: 21 pages, 15 figures, Accepted by A&A

Journal ref: A&A 690, A244 (2024)

The dark days are overcast: Iron-bearing clouds on HD 209458 b and WASP-43 b can explain low dayside albedos

Authors: K. L. Chubb, D. Samra, Ch. Helling, L. Carone, D. M. Stam

Abstract: We simulate the geometric albedo spectra of hot Jupiter exoplanets HD 209458 b and WASP-43 b, based on global climate model (GCMs) post-processed with kinetic cloud models. We predict WASP-43 b to be cloudy throughout its dayside, while HD 209458 b has a clear upper atmosphere around the hot sub-solar point, largely due to the inclusion of strong optical absorbers TiO and VO in the GCM for the lat… ▽ More We simulate the geometric albedo spectra of hot Jupiter exoplanets HD 209458 b and WASP-43 b, based on global climate model (GCMs) post-processed with kinetic cloud models. We predict WASP-43 b to be cloudy throughout its dayside, while HD 209458 b has a clear upper atmosphere around the hot sub-solar point, largely due to the inclusion of strong optical absorbers TiO and VO in the GCM for the latter causes a temperature inversion. In both cases our models find low geometric albedos - 0.026 for WASP-43b and 0.028 for HD 209458 b when averaged over the CHEOPS bandpass of 0.35 - 1.1 microns - indicating dark daysides, similar to the low albedos measured by observations. We demonstrate the strong impact of clouds that contain Fe-bearing species on the modelled geometric albedos; without Fe-bearing species forming in the clouds, the albedos of both planets would be much higher (0.518 for WASP-43 b, 1.37 for HD 209458 b). We conclude that a cloudy upper or mid-to-lower atmosphere that contains strongly absorbing Fe-bearing aerosol species, is an alternative to a cloud-free atmosphere in explaining the low dayside albedos of hot Jupiter atmospheres such as HD 209458 b and WASP-43 b. △ Less

Submitted 30 August, 2024; originally announced September 2024.

Comments: Published in MNRAS

Journal ref: MNRAS, 2024, 533, 2, 1503-1524