Showing 1–50 of 475 results for author: Caballero, A

Early Exploration of the Scientific Discovery Space for the Habitable Worlds Observatory

Authors: Courtney D. Dressing, Danica Adams, Evelyne Alecian, Gagandeep Anand, Giada Arney, Sarah Gomes Aroucha Barbosa, Martin Barstow, Joanna K. Barstow, Rachael L. Beaton, Eduardo Bendek, Svetlana Berdyugina, Julie Biedermann, Sarah Blunt, Sanchayeeta Borthakur, Kara Brugman, Joseph N. Burchett, Eric Burns, Jenna M. Cann, Ludmila Carone, Cody A. Carr, Richard Cartwright, Renyue Cen, Jean-yves Chaufray, Pin Chen, Lígia F Coelho , et al. (302 additional authors not shown)

Abstract: The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Techn… ▽ More The Habitable Worlds Observatory (HWO) is a future NASA flagship mission concept identified by the Astro2020 Decadal Survey as the highest priority for large space missions. HWO should conduct "transformative astrophysics" and search for biosignatures in the atmospheres of approximately 25 potentially Earth-like planets. To further the early-stage development of HWO, NASA formed the Science, Technology, Architecture Review Team (START). In turn, START invited the scientific community to join working groups to explore the potential discovery space. In this paper, we present 70 science cases that resulted from this process. The cases address four scientific pillars: growth of galaxies (15 cases), evolution of the elements (13 cases), solar systems in context (32 cases), and living worlds (10 cases). Combined, they would address 27 of the 30 science questions and discovery areas identified by Astro2020. The 140 observing programs needed for the 70 investigations encompass a rich variety of spectroscopic (for 87% of science cases) and photometric (for 30%) observations extending from the UV to the NIR. Additionally, high-contrast and polarimetric capabilities would be needed for 34% and 27% of science cases, respectively. Access to UV wavelengths is critical: 83% of science cases need data at wavelengths <400 nm, and 26% extend to <100 nm. In the NIR, 26% of science cases need observations at wavelengths >=2000 nm. Pursuing the full portfolio of science would also necessitate precise astrometry for planet mass measurement, rapid response capabilities, a large instantaneous field of regard, non-sidereal tracking, saturation mitigation strategies, and high dynamic range. △ Less

Submitted 11 August, 2026; originally announced August 2026.

Comments: 215 pages, 18 figures, 16 tables. This to-be-submitted manuscript summarizes and synthesizes science cases developed by the Habitable Worlds Observatory START and science working groups. See Table 1 for a roadmap, Table 5 for a list of science cases, Figure 11 for a visualization of common observational needs, Figure 16 for connections to Astro2020, and Tables 6-15 (after conclusions) for details

Signal selection and model-independent extraction of pionless charged-current muon neutrino cross section using double-differential kinematic imbalance observables on carbon and oxygen with the T2K experiment

Authors: K. Abe, S. Abe, H. Adhikary, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Asami, Y. Asaoka, Y. Ashida, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak , et al. (380 additional authors not shown)

Abstract: We present the first joint measurement of muon neutrino CC$0πNp$ interactions on carbon and oxygen targets, in two double-differential kinematic imbalance (KI) observable spaces, $δp_{T}$-$δα_{T}$ and $p_{N}$-$\cosθ_μ$. The measurement employs the ND280 detector of the T2K experiment and includes a detailed description of the event selection used to define signal and control regions, the evaluatio… ▽ More We present the first joint measurement of muon neutrino CC$0πNp$ interactions on carbon and oxygen targets, in two double-differential kinematic imbalance (KI) observable spaces, $δp_{T}$-$δα_{T}$ and $p_{N}$-$\cosθ_μ$. The measurement employs the ND280 detector of the T2K experiment and includes a detailed description of the event selection used to define signal and control regions, the evaluation of systematic uncertainties, and the signal extraction procedure, together with validation studies supporting a robust cross-section measurement. The results of this analysis indicate that current neutrino-nucleus interaction models do not adequately describe the data, and demonstrate the strong discriminating power of KI observables. This measurement highlights the need for improved theoretical nuclear modeling within neutrino interaction generators to achieve increased precision in neutrino oscillation measurements. △ Less

Submitted 12 July, 2026; originally announced July 2026.

First double-differential measurement of pionless charged-current muon neutrino interactions using kinematic imbalance observables on carbon and oxygen with the T2K experiment

Authors: K. Abe, S. Abe, H. Adhikary, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Asami, Y. Asaoka, Y. Ashida, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak , et al. (380 additional authors not shown)

Abstract: We report the first measurement of muon-neutrino charged-current cross section as a function of kinematic imbalance (KI) observables on oxygen with no pions and at least one proton in the final state, using the T2K ND280 detector. The cross section is extracted simultaneously for carbon and oxygen targets and double-differentially as a function of several KI observables, providing new insight into… ▽ More We report the first measurement of muon-neutrino charged-current cross section as a function of kinematic imbalance (KI) observables on oxygen with no pions and at least one proton in the final state, using the T2K ND280 detector. The cross section is extracted simultaneously for carbon and oxygen targets and double-differentially as a function of several KI observables, providing new insight into the modeling of nuclear effects. This joint measurement offers direct sensitivity to the correlations between two targets, a key ingredient for reducing systematic uncertainties in neutrino oscillation experiments that employ multiple target nuclei, such as T2K and Hyper-Kamiokande. Comparisons with predictions from widely used neutrino event generators show that none of the models fully describe the data across all regions of measured phase space. These results highlight possible directions where improvements in neutrino-nucleus interaction modeling are needed for current and future neutrino oscillation experiments. △ Less

Submitted 14 July, 2026; v1 submitted 12 July, 2026; originally announced July 2026.

Comments: Added cross reference to arXiv:2607.10644

Constraining Neutrino Interaction Uncertainties for Neutrino Oscillation Measurements at the T2K Experiment

Authors: K. Abe, S. Abe, H. Adhikary, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Asami, Y. Asaoka, Y. Ashida, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak , et al. (417 additional authors not shown)

Abstract: In the context of neutrino oscillation measurements from the T2K experiment, the off-axis near detector ND280 plays a crucial role in constraining the incoming neutrino flux and neutrino-nucleus interaction cross sections. The result is a robust control over systematic uncertainties in the fit of neutrino oscillation parameters to the data at the T2K far detector, Super-Kamiokande. This paper deta… ▽ More In the context of neutrino oscillation measurements from the T2K experiment, the off-axis near detector ND280 plays a crucial role in constraining the incoming neutrino flux and neutrino-nucleus interaction cross sections. The result is a robust control over systematic uncertainties in the fit of neutrino oscillation parameters to the data at the T2K far detector, Super-Kamiokande. This paper details the methodology and results of these constraints in the context of the latest neutrino oscillation analysis from T2K. It describes how a new neutrino cross-section model and refined flux prediction are parameterized and fit to data in new ND280 event selections. Additionally, this work reports the results of extensive robustness studies, including fits with alternative interaction models, consistency checks against publicly available cross-section measurements, and \textit{p}-value evaluations, to demonstrate the reliability and robustness of our methodology. Finally, we present a sensitivity study demonstrating that the upgraded ND280, with improved acceptance and a lower hadron threshold, may enhance future constraints and further reduce systematic uncertainties in oscillation measurements. △ Less

Submitted 11 June, 2026; originally announced June 2026.

A Critical UV Legacy: A Hubble Roadmap for HWO Science Readiness

Authors: Sarah Peacock, Aiden S. Zelakewicz, Lisa Kaltenegger, Breanna A. Binder, José A. Caballero, Lía Corrales, Kevin France, Cynthia Froning, Eric Mamajek, Seth Redfield, Tyler Richey-Yowell, Keighley Rockcliffe, Edward Schwieterman, Riccardo Spinelli, Noah Tuchow, David Wilson, Allison Youngblood

Abstract: The Habitable Worlds Observatory (HWO) will provide the first opportunity to directly image and spectrally characterize terrestrial exoplanets in the habitable zones of nearby stars. Maximizing its scientific return requires a comprehensive understanding of the high-energy radiation environments of target stars, which shape planetary atmospheres and govern the production, destruction, and detectab… ▽ More The Habitable Worlds Observatory (HWO) will provide the first opportunity to directly image and spectrally characterize terrestrial exoplanets in the habitable zones of nearby stars. Maximizing its scientific return requires a comprehensive understanding of the high-energy radiation environments of target stars, which shape planetary atmospheres and govern the production, destruction, and detectability of biosignatures. Ultraviolet (UV) radiation plays a particularly critical role in atmospheric chemistry. Far-ultraviolet (FUV) and near-ultraviolet (NUV) photons regulate key photochemical pathways, influence ozone stability, and drive the formation of prebiotic molecules. However, the majority of high-priority HWO target stars lack high-quality UV observations. Existing datasets are sparse, heterogeneous, or limited by calibration uncertainties, and no comparable UV observatory is expected for at least 5-10 years (with UVEX offering more limited spectral resolution, wavelength coverage, and sensitivity). The Hubble Space Telescope (HST) remains the only observatory capable of acquiring high-resolution FUV and NUV spectra for these targets over the next 10-15 years. We therefore advocate for a coordinated HST program to systematically obtain UV spectra of high-priority HWO targets, ideally in conjunction with X-ray observations. This effort is essential for enabling accurate target prioritization, constraining stellar radiation environments, and ensuring robust interpretation of future HWO observations. △ Less

Submitted 3 June, 2026; originally announced June 2026.

Comments: Building a Roadmap for Hubble science into the 2030s White Paper, 5 pages

HWO Target Stars and Systems: Activity and Rotation Catalog (ARC) of Potential Target Stars for the Habitable Worlds Observatory

Authors: Tara Fetherolf, Arvind F. Gupta, Elisabeth R. Newton, Andrea P. Buccino, Jennifer A. Burt, Jose A. Caballero, Sebastian Carrazco-Gaxiola, Mariela C. Vieytes, Natalie R. Hinkel, Eric E. Mamajek

Abstract: A major goal of the Habitable Worlds Observatory (HWO) is to precisely characterize exoplanets and their atmospheres. However, magnetic activity from an exoplanet's host star can complicate measurements of both the stellar and planetary properties, and stellar activity can be an important factor in our interpretation of the evolutionary history of an exoplanet. In this work, we assess the extent t… ▽ More A major goal of the Habitable Worlds Observatory (HWO) is to precisely characterize exoplanets and their atmospheres. However, magnetic activity from an exoplanet's host star can complicate measurements of both the stellar and planetary properties, and stellar activity can be an important factor in our interpretation of the evolutionary history of an exoplanet. In this work, we assess the extent to which magnetic activity has been characterized for potential HWO target stars by collating archival measurements of relevant observables as published in a broad range of photometric and spectroscopic datasets. We describe our data collection strategy, provide an overview of currently known activity and rotation properties in the Activity and Rotation Catalog (ARC) for potential HWO target stars, and briefly review known relationships between stellar inclination, rotation, activity, and age. Overall, we find that stellar activity (S-index and R'HK) and rotation (v sin i and Prot) properties have been measured for at least 70% systems that are currently of high interest as potential HWO atmospheric characterization targets. However, stellar activity is temporal in nature, such that activity properties should be regularly monitored in order to remain up-to-date for informing future observations. In particular, we find that stellar activity cycles are measured for fewer than 20% of high interest potential HWO target stars. Measuring a star's activity cycle is critical for anticipating times when higher levels of magnetic activity may occur during planned HWO observations, which may interfere with measuring precise exoplanet atmospheric characteristics. △ Less

Submitted 20 July, 2026; v1 submitted 21 May, 2026; originally announced May 2026.

Comments: 29 pages, 11 figures, accepted to PASP, catalog available on GitHub: https://github.com/ernewton/TSS_ARC

Spinning out of focus: The challenge of rotational line broadening in exoplanet reflection spectroscopy

Authors: T. O. Winterhalder, K. Molaverdikhani, D. Cont, F. Yan, E. Nagel, A. Kaminski, L. Nortmann, P. J. Amado, V. J. S. Béjar, G. Bergond, J. A. Caballero, S. Czesla, Th. Henning, G. Morello, D. Montes, E. Palle, A. Quirrenbach, A. Reiners, I. Ribas, A. Schweitzer

Abstract: Detecting light reflected off the dayside of an exoplanet in high-resolution spectroscopic data has proved to be a notoriously difficult endeavour. Despite several attempts, the faint signal has yet to be detected. We present a new effort at finding reflection signatures and show how a strong rotational broadening of the reflected spectrum can complicate this objective. We introduce a new figure o… ▽ More Detecting light reflected off the dayside of an exoplanet in high-resolution spectroscopic data has proved to be a notoriously difficult endeavour. Despite several attempts, the faint signal has yet to be detected. We present a new effort at finding reflection signatures and show how a strong rotational broadening of the reflected spectrum can complicate this objective. We introduce a new figure of merit that quantifies the favourability of different systems for a reflection study, the reflection spectroscopy metric. Applying this metric, we identify the KELT-9 system, which features a highly misaligned, rapidly rotating host star, as the target for a case study based on a spectroscopic time series obtained by CARMENES. We also perform an injection-recovery test to determine the detectability of the signal in our data and demonstrate its sensitivity to rotational line broadening. The search for a genuine reflection signal in our data resulted in a non-detection. The injection-recovery test puts this finding into context by revealing the critical importance of taking rotational broadening into account when dealing with systems featuring rapidly rotating stars and large spin-orbit misalignments. The case study presented here underscores the need to incorporate stellar rotation and spin-orbit misalignment into assessments of a given planet's favourability to reflection studies. △ Less

Submitted 15 May, 2026; originally announced May 2026.

Comments: Accepted for publication in Astronomy and Astrophysics

Orbital motion and dynamical mass of the complex periodic variable binary system 2MASS J05082729-2101444

Authors: S. Curiel, G. N. Ortiz-León, V. J. S. Béjar, D. Viganò, J. M. Girart, S. Kaur, Y. Shan, F. Murgas, M. Zechmeister, P. J. Amado, J. A. Caballero, Th. Henning, E. Ilin, D. Montes, J. C. Morales, Ó. Morata, M. Pérez-Torres, A. Quirrenbach, A. Reiners, I. Ribas, Á. Sánchez-Monge, A. Schweitzer, J. I. Vico Linares, M., R. Zapatero Osorio

Abstract: We used very long baseline interferometry to constrain the orbit of the binary system 2MASS J05082729-2101444. We observed the system with the VLBA in three epochs at a frequency of 4.85 GHz, which provides an angular resolution of about 3 mas. We combined the three radio astrometric observations, 119 RVs (60 VIS and 59 NIR) obtained with the CARMENES high-resolution spectrograph over a period of… ▽ More We used very long baseline interferometry to constrain the orbit of the binary system 2MASS J05082729-2101444. We observed the system with the VLBA in three epochs at a frequency of 4.85 GHz, which provides an angular resolution of about 3 mas. We combined the three radio astrometric observations, 119 RVs (60 VIS and 59 NIR) obtained with the CARMENES high-resolution spectrograph over a period of 8.1 years, and a relative astrometric measurement of an archival H-band Keck NIRC adaptive optics image to fit the orbital motion of the binary system. The VLBA observations resolved the binary system and show emission from both stellar components, with similar flux-density levels (0.34-0.67 mJy), and showing slight temporal flux variations. The emission appears quiescent, with no significant circular polarization, and with no flare events. We obtained an orbital motion fit of the binary system, which shows an eccentric orbit (e = 0.71), an orbital period of 2.19 yr, and a semimajor axis of 26.964 mas (1.3 au). The VLBA observations made it possible to resolve the binary system and identify both stars as radio-loud sources. The combined fit shows that 2M0508-21 is an M-dwarf binary with a total dynamical mass of $0.459\pm0.007$ M$_{\odot}$, assuming Gaia's parallax. This mass is slightly higher than those estimated from the luminosity and theoretical evolutionary models. The upper limit of the circular polarization at 4.85 GHz ($\lesssim$10\%), the persistence of the quiescent emission, and the relatively low brightness temperatures are consistent with a gyro-synchrotron or synchrotron origin of the radio emission. Further VLBA observations are needed to obtain the individual masses of the stars, as well as to verify Gaia's parallax of the system. A complete characterization of the system will help improve evolutionary models for young objects at the substellar boundary. △ Less

Submitted 27 May, 2026; v1 submitted 5 May, 2026; originally announced May 2026.

Comments: 12 pages, 8 figures, 2 tables. Accepted in A&A

Characterisation of all known multiple stellar systems within 10 pc

Authors: J. González-Payo, J. A. Caballero, C. Cifuentes, M. Cortés-Contreras, F. Rica

Abstract: The study of stellar multiplicity offers important constraints on the structure of the Galaxy as well as stellar and planet formation and evolution. Focusing on the most immediate solar neighbourhood benefits from obtaining both complete and accurate data for reliable statistics. Our goal is to describe the solar neighbourhood within 10 pc in terms of multiplicity by evaluating the angular and phy… ▽ More The study of stellar multiplicity offers important constraints on the structure of the Galaxy as well as stellar and planet formation and evolution. Focusing on the most immediate solar neighbourhood benefits from obtaining both complete and accurate data for reliable statistics. Our goal is to describe the solar neighbourhood within 10 pc in terms of multiplicity by evaluating the angular and physical separations, masses, and orbital periods of the systems from the most complete volume-limited sample. We carried out a comprehensive data compilation from the Washington Double Star catalogue and the literature of all known multiple systems at any separation range, and completed this information with a common proper motion and parallax search with Gaia DR3 data. We also used public astrometric and radial-velocity data to compute orbital solutions of seven pairs. From a sample of 424 stars and brown dwarfs within 10 pc we identified 215 of them in 92 systems in double (68), triple (19), quadruple (3), and quintuple (2) configurations. All except eight pairs have been resolved. Their orbital periods range over ten orders of magnitude from about one day to millions of years. We measured precise mass and companion star fractions at different mass intervals. The multiplicity fraction smoothly decreases from 41+-11% for stars with M >= 0.50 Msun to 9.3+-7.4% for stars and brown dwarfs with M <= 0.10 Msun. △ Less

Submitted 29 April, 2026; originally announced May 2026.

Comments: 33 pages including 3 annexes. Accepted in Monthly Notices of the Royal Astronomical Society

Report number: MN-26-0529-P

Non-radial pulsations of gravitationally coupled two-fluid neutron stars in general relativity

Authors: Ankit Kumar, Daniel A. Caballero, Hajime Sotani, Nicolás Yunes

Abstract: Non-radial oscillations of neutron stars provide a powerful probe of stellar structure and relativistic gravity, but a fully general relativistic treatment for gravitationally coupled two-fluid stars with independently conserved currents has so far been lacking. In this work, we develop a fully relativistic framework for polar perturbations of gravitationally coupled two-fluid neutron stars, assum… ▽ More Non-radial oscillations of neutron stars provide a powerful probe of stellar structure and relativistic gravity, but a fully general relativistic treatment for gravitationally coupled two-fluid stars with independently conserved currents has so far been lacking. In this work, we develop a fully relativistic framework for polar perturbations of gravitationally coupled two-fluid neutron stars, assuming that the two fluids interact only through the common spacetime and are not coupled by entrainment or direct microphysical interactions. We derive the coupled linear perturbation equations governing the metric and both fluid components, and complete the formulation by establishing the regularity, surface, and exterior matching conditions required for a well-posed oscillation eigenvalue problem. We then implement the resulting system numerically and compute representative polar mode spectra for gravitationally coupled two-fluid stellar models. This implementation provides a practical way to address mode identification in gravitationally coupled two-fluid stars, allowing the fundamental ($\mathsf{f}$) and pressure ($\mathsf{p}$) mode branches of the spectrum to be classified according to their dominant inner- or outer-fluid character through the associated eigenfunctions and their node structure. The formalism developed here provides a foundation for extending relativistic asteroseismology to multi-fluid compact stars and for exploring their potential gravitational-wave signatures in a fully general relativistic setting. △ Less

Submitted 4 May, 2026; originally announced May 2026.

Charged-Current Neutrino-Induced Single-Pion Production in the Superscaling Approach and Relativistic Distorted-Wave Impulse Approximation

Authors: Jesus Gonzalez-Rosa, Alexis Nikolakopoulos, Maria B. Barbaro, Juan A. Caballero, Raúl González-Jiménez, Guillermo D. Megias

Abstract: In this work, we present a detailed comparison of the SuSAv2 (SuperScaling Approach version 2) and RDWIA (Relativistic Distorted-Wave Impulse Approximation) models with measurements of charged-current neutrino-induced single-pion production from different experiments (T2K, MINERvA and MiniBooNE), studying the differences between the two theoretical descriptions. The neutrino energy range in these… ▽ More In this work, we present a detailed comparison of the SuSAv2 (SuperScaling Approach version 2) and RDWIA (Relativistic Distorted-Wave Impulse Approximation) models with measurements of charged-current neutrino-induced single-pion production from different experiments (T2K, MINERvA and MiniBooNE), studying the differences between the two theoretical descriptions. The neutrino energy range in these experiments spans from hundreds of MeV to roughly 20 GeV, and the nuclear targets are mainly composed of $^{12}$C. The SuSAv2 model uses the single-nucleon inelastic structure functions from the ANL-Osaka DCC model, which allows for a separation of pion production channels, distinguishing between the $π^+$, $π^-$ and $π^0$ final states. In the RDWIA approach, the Hybrid model developed by the Ghent group is used for the description of the boson-pion-nucleon vertex. △ Less

Submitted 22 April, 2026; originally announced April 2026.

Comments: 20 pages, 15 figures, 2 tables. Version accepted for publication in Universe

Journal ref: Universe 2026, 12(5), 121

Dirac-Bergmann analysis of SW-mapped non-commutative $U(1)$ electrodynamics with external currents

Authors: J. Manuel Cabrera, A. G. Andarcia Caballero, J. M. Paulin Fuentes

Abstract: Non-commutative electrodynamics obtained through the Seiberg-Witten map ceases to have equivalent action-level and equation-level realizations once fixed external currents are introduced, and in the action-level construction associated with the Banerjee current map the canonical location of this source-induced obstruction has remained unclear. Working in the full phase space and treating the curre… ▽ More Non-commutative electrodynamics obtained through the Seiberg-Witten map ceases to have equivalent action-level and equation-level realizations once fixed external currents are introduced, and in the action-level construction associated with the Banerjee current map the canonical location of this source-induced obstruction has remained unclear. Working in the full phase space and treating the current as prescribed and non-dynamical, we apply the Dirac-Bergmann algorithm without imposing current conservation as an external condition. The preservation of the Gauss-type secondary constraint produces a third-stage candidate whose phase-space expression is shown to be algebraically identical, at first order in the non-commutativity parameter and for purely space-space non-commutativity, to the canonical pullback of the divergence of the mapped Euler-Lagrange equations. This identity locates the source-compatibility obstruction directly within the Dirac chain. For generic inhomogeneous sources, the next consistency step feeds this object back into the primary multiplier through a source-dependent kernel, so the chain closes by multiplier fixing rather than by the generic appearance of a quaternary constraint. Reduced-phase-space results, including the gauge generator, Dirac brackets and degree-of-freedom count, are obtained only in a restricted sufficient first-class subcase; no broader claim is made for arbitrary source profiles. △ Less

Submitted 20 April, 2026; v1 submitted 17 April, 2026; originally announced April 2026.

Comments: 21 pages, 0 figures

The CARMENES search for exoplanets around M dwarfs. A homogeneous catalogue of projected rotational velocities accounting for limb-darkening

Authors: R. Varas, G. Morello, M. Zechmeister, P. J. Amado, F. J. Pozuelos, J. A. Caballero, A. Claret, C. Cifuentes, R. Morales, A. Quirrenbach, A. Reiners, I. Ribas, V. J. S. Béjar, M. Cortés-Contreras, A. P. Hatzes, Th. Henning, I. Hermelo, H. L. Ruh, A. Schweitzer, H. M. Tabernero, M. R. Zapatero Osorio

Abstract: Stellar rotation is closely linked to both age and magnetic activity. Through gyrochronology, it provides a means to estimate stellar ages and trace the evolution of planetary systems, and it is also crucial to constrain and correct stellar activity effects for robust exoplanet detection and characterisation. CARMENES is a dual-channel, high-resolution (R > 80000) spectrograph that has been highly… ▽ More Stellar rotation is closely linked to both age and magnetic activity. Through gyrochronology, it provides a means to estimate stellar ages and trace the evolution of planetary systems, and it is also crucial to constrain and correct stellar activity effects for robust exoplanet detection and characterisation. CARMENES is a dual-channel, high-resolution (R > 80000) spectrograph that has been highly successful in detecting exoplanets around M-dwarf stars using the radial-velocity technique, and it also enables precise measurements of the projected rotational velocity (vsini) from spectral line broadening. We present an oversampled convolution method incorporating a realistic limb-darkening model to determine vsini from CARMENES spectra by comparing observed spectra with that of a template star. The advantages over existing methods in the literature have been assessed using high-resolution synthetic spectra spanning effective temperatures of 2500-4000 K and projected rotational velocities of up to 50 km/s. Applied to 392 M dwarfs observed with CARMENES, our method yields vsini measurements (or upper limits at 2 km/s) with a median relative uncertainty of 6.8%, substantially smaller than the 15.4% reported in the literature. This work provides the largest uniform catalogue of vsini measurements for M dwarfs, including significantly updated values for several targets, along with 36 new targets. △ Less

Submitted 16 April, 2026; originally announced April 2026.

Comments: 12 pages, 16 figures, 4 tables. Accepted for publication in A&A

Journal ref: A&A 709, A244 (2026)

Constraining an exoplanets magnetic field using star-planet interactions

Authors: D. Revilla, P. J. Amado, R. Luque, P. Schöfer, A. F. Lanza, A. Binnenfeld, J. A. Caballero, A. P. Hatzes, G. W. Henry, S. V. Jeffers, S. Kaur, E. Pallé, L. Peña-Moñino, M. Pérez-Torres, A. Quirrenbach, A. Reiners, I. Ribas, D. Viganò, M. R. Zapatero Osorio, S. Zucker

Abstract: Theory predicts that a planet with a sufficiently strong magnetic field orbiting close to its host star could induce star-planet magnetic interactions. This is potentially observable as an optical or radio signal synchronised with the orbital period. We analyze 18 years of high-resolution optical spectroscopy of GJ 436, a low mass star orbited by a Neptune-sized exoplanet in a polar eccentric orbi… ▽ More Theory predicts that a planet with a sufficiently strong magnetic field orbiting close to its host star could induce star-planet magnetic interactions. This is potentially observable as an optical or radio signal synchronised with the orbital period. We analyze 18 years of high-resolution optical spectroscopy of GJ 436, a low mass star orbited by a Neptune-sized exoplanet in a polar eccentric orbit. Stellar activity indicators show enhancements at a period corresponding to the exoplanet orbit, modulated by stellar rotation, and the star's 8-year magnetic cycle. We interpret this as a signal of star-planet magnetic interaction. Using a geometric model, we reproduce these periods if GJ 436 b has a magnetic field strength of 6 to 110 Gauss. △ Less

Submitted 24 June, 2026; v1 submitted 8 April, 2026; originally announced April 2026.

Comments: 39 pages, 19 figures, 3 tables. Sent to journal on 16/12/2024

On spectral stability for self-adjoint extensions

Authors: Mario Alberto Ruiz Caballero

Abstract: We prove that given a symmetric completely non-selfadjoint operator $B$ with finite deficiency indices $(n,n)$ on a Hilbert space and a boundary triplet $\left(\mathbb{C}^{n},Γ_{1},Γ_{2}\right)$ for $B^{*}$, the set of points in the spectrum of $A_{1}$ (the self-adjoint extension with domain $Ker\;Γ_{1}$) which are not eigenvalues of maximum multiplicity for any self-adjoint extension of $B$ disjo… ▽ More We prove that given a symmetric completely non-selfadjoint operator $B$ with finite deficiency indices $(n,n)$ on a Hilbert space and a boundary triplet $\left(\mathbb{C}^{n},Γ_{1},Γ_{2}\right)$ for $B^{*}$, the set of points in the spectrum of $A_{1}$ (the self-adjoint extension with domain $Ker\;Γ_{1}$) which are not eigenvalues of maximum multiplicity for any self-adjoint extension of $B$ disjoint of $A_{1}$, is a dense $\textit{G}_δ$ set in $σ(A_{1})$. Furthermore, a proof of a Malamud's theorem that generalizes a well-known result of the Aronszajn-Donoghue theory on the characterization of eigenvalues is offered. △ Less

Submitted 17 March, 2026; originally announced March 2026.

MSC Class: 47B02; 47B25; 47A55; 47A10

Characterization of two new transiting sub-Neptunes and a terrestrial planet around M-dwarf hosts

Authors: E. Poultourtzidis, G. Lacedelli, E. Pallé, I. Carleo, C. Magliano, S. Geraldía-González, J. A. Caballero, G. Morello, J. Orell-Miquel, H. M. Tabernero, F. Murgas, G. Covone, F. J. Pozuelos, P. J. Amado, V. J. S. Béjar, S. Chairetas, C. Cifuentes, D. R. Ciardi, K. A. Collins, I. J. M. Crossfield, E. Esparza-Borges, G. Fernández-Rodríguez, A. Fukui, Y. Hayashi, A. P. Hatzes , et al. (27 additional authors not shown)

Abstract: We report the confirmation of three transiting exoplanets orbiting TOI-1243 (LSPM~J0902+7138), TOI-4529 (G~2--21), and TOI-5388 (Wolf~346) that were initially detected by TESS through ground-based photometry and radial velocity follow-up measurements with CARMENES. The planets present short orbital periods of $4.65$, $5.88$, and $2.59$ days, and they orbit early-M dwarfs (M2.0V, M1.5V, and M3.0V,… ▽ More We report the confirmation of three transiting exoplanets orbiting TOI-1243 (LSPM~J0902+7138), TOI-4529 (G~2--21), and TOI-5388 (Wolf~346) that were initially detected by TESS through ground-based photometry and radial velocity follow-up measurements with CARMENES. The planets present short orbital periods of $4.65$, $5.88$, and $2.59$ days, and they orbit early-M dwarfs (M2.0V, M1.5V, and M3.0V, respectively). We were able to precisely determine the radius of all three planets with a precision of $< 7\, \%$, the mass of TOI-1243 b with a precision of $19\, \%$, and upper mass limits for TOI-4529 b and TOI-5388 b. The radius of TOI-1243 b is $2.33\pm0.12\, {R_{\oplus}}$, its mass is $7.7 \pm 1.5\,{M_{\oplus}}$, and the mean density is $0.61 \pm 0.15 \, {ρ_\oplus}$. The radius of TOI-4529 b is $1.77 ^{+0.09}_{-0.08} \, {R_{\oplus}}$, the $3 σ$ upper mass limit is $4.9 \, {M_{\oplus}}$, and the $3 σ$ upper density limit is $0.88\, {ρ_\oplus}$. The third planet, TOI-5388 b, is Earth-sized with a radius of $0.99 ^{+0.07}_{-0.06} \, {R_{\oplus}}$, a $3 σ$ upper mass limit of $2.2 \, {M_{\oplus}}$, and a $3 σ$ upper density limit of $2.2\, {ρ_\oplus}$. While TOI-5388 b is most probably rocky, given its Earth-like radius, TOI-1243 b and TOI-4529 b are located in a highly degenerate region in the mass-radius space. TOI-4529 b appears to lean toward a water-world composition. TOI-1243 b has enough mass to host a significant H-He envelope, although a water-world and pure rocky compositions are also consistent with the data. Our analysis indicates that future atmospheric observations using JWST can aid in determining their real composition. The sample of small planets around M dwarfs is widely used to understand planet formation and composition theories, and our study adds three planets to this sample. △ Less

Submitted 12 January, 2026; originally announced January 2026.

Comments: 21 pages, 15 figures. Accepted for publication in A&A

Paving the Road to the Habitable Worlds Observatory with High-Resolution Imaging I: New and Archival Speckle Observations of Potential HWO Target Stars

Authors: Zachary D. Hartman, Catherine A. Clark, Michael B. Lund, Kathryn V. Lester, José A. Caballero, Steve B. Howell, David Ciardi, Sarah Deveny, Mark E. Everett, Elise Furlan, Venu Kalari, Colin Littlefield, Andrew W. Stephens, Jennifer A. Burt, Guillaume Huber, Rachel Matson, Eric E. Mamajek, Noah Tuchow

Abstract: One of the key goals of the Habitable Worlds Observatory (HWO) is to directly image about 25 potentially habitable exoplanets and determine their properties. This challenge will require a large survey of nearby, bright stars -- ~100 according to the Astro2020 Decadel Survey. To ensure the success of the mission and to help guide design decisions, the stellar multiplicity of the target stars must b… ▽ More One of the key goals of the Habitable Worlds Observatory (HWO) is to directly image about 25 potentially habitable exoplanets and determine their properties. This challenge will require a large survey of nearby, bright stars -- ~100 according to the Astro2020 Decadel Survey. To ensure the success of the mission and to help guide design decisions, the stellar multiplicity of the target stars must be well-understood. To this end, we present optical speckle imaging of stars in the NASA Exoplanet Exploration Program (ExEP) provisional HWO star list, which is currently the Tier 1 target list for the HWO Target Stars and Systems Sub-Working Group. We obtained new observations using `Alopeke and Zorro at Gemini Observatory and queried the Exoplanet Follow-up Observing Program Archive for archival observations, resulting in speckle imaging data for 80 of the 164 stars. We confirmed one candidate companion detected previously by Gaia (HD 90089) and obtained an ambiguous detection of a known companion (HD 212330). To examine our sensitivity to companions, we simulated stellar companions down to ~0.1 $M_{\odot}$ for each target and found that 75%-85% would be detected in our speckle images; the remaining simulated companions are either too faint or too close-in, and will require follow-up using other methods such as long-term spectroscopic measurements and space-based techniques. This work represents a first step towards surveying potential HWO targets for close-in stellar companions and helping to inform the target selection process for the HWO direct-imaging survey, bringing us closer towards the discovery of potential habitable worlds. △ Less

Submitted 8 January, 2026; originally announced January 2026.

Comments: 26 pages, 9 figures, Accepted for publication in ApJ

Elemental abundance pattern and temperature inversion on the dayside of HAT-P-70b observed with CARMENES and PEPSI

Authors: B. Guo, F. Yan, Th. Henning, L. Nortmann, M. Stangret, D. Cont, E. Pallé, D. Shulyak, K. G. Strassmeier, I. Ilyin, F. Lesjak, A. Reiners, S. Liu, K. Molaverdikhani, G. Scandariato, E. Keles, J. A. Caballero, P. J. Amado, A. Quirrenbach, I. Ribas, S. Góngora, A. P. Hatzes, M. López-Puertas, D. Montes, K. Poppenhaeger , et al. (3 additional authors not shown)

Abstract: Ground-based high-resolution spectroscopy has identified various chemical species in the atmospheres of ultra-hot Jupiters, including neutral and ionized metals, providing key insights into planet formation through refractory element abundances. We observed the dayside thermal emission spectrum of the UHJ HAT-P-70b using the high-resolution spectrographs CARMENES and PEPSI. Through cross-correlati… ▽ More Ground-based high-resolution spectroscopy has identified various chemical species in the atmospheres of ultra-hot Jupiters, including neutral and ionized metals, providing key insights into planet formation through refractory element abundances. We observed the dayside thermal emission spectrum of the UHJ HAT-P-70b using the high-resolution spectrographs CARMENES and PEPSI. Through cross-correlation analysis, we detect emission signals of Al i, AlH, Ca ii, Cr i, Fe i, Fe ii, Mg i, Mn i, and Ti i, marking the first detection of Al i and AlH in an exoplanetary atmosphere. Tentative signals of C i, Ca i, Na i, NaH, and Ni i are also identified. These detections enable atmospheric retrievals to constrain the thermal profile and elemental abundances of the planet's dayside hemisphere. The retrieved temperature-pressure profile reveals a strong thermal inversion. The chemical free retrieval yields a metallicity of [Fe/H] = 0.38(+0.74/-1.11), while the chemical equilibrium retrieval gives [Fe/H] = 0.23(+1.08/-0.98), both consistent with solar metallicity. We also tentatively find an enhanced abundance of Ni, possibly due to the accretion of Ni-rich planetesimals during formation. On the other hand, elements with condensation temperatures above 1400 K (e.g., Ca, Ti, and V) appear slightly depleted, which may be caused by nightside cold trapping. However, Al, with the highest condensation temperature at 1653K, displays a solar like abundance, which might reflect the formation-related enrichment of Al. Our retrieval indicates extremely high volume mixing ratios of metal ions (Fe ii and Ca ii), which are significantly inconsistent with predictions from chemical equilibrium models. This disequilibrium suggests that the atmosphere is likely undergoing significant hydrodynamic escaping, which enhances the atmospheric density at high altitudes where the ionic lines are formed. △ Less

Submitted 24 December, 2025; originally announced December 2025.

Comments: 18 pages, 15 figures. Accepted for publication in A&A

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

Revisiting the atmosphere of HAT-P-70b with CARMENES high-resolution transmission spectroscopy

Authors: Tianjun Gan, Jaume Orell-Miquel, Fei Yan, Lisa Nortmann, Jorge Sanz-Forcada, Enric Pallé, Shude Mao, Pedro J. Amado, José A. Caballero, Stefan Cikota, David Cont, Artie P. Hatzes, Thomas Henning, Fabio Lesjak, Manuel López-Puertas, David Montes, Juan Carlos Morales, Alberto Peláez-Torres, Andreas Quirrenbach, Ansgar Reiners, Ignasi Ribas, Andreas Schweitzer

Abstract: Owing to hot and inflated envelopes that facilitate atmospheric studies, ultra-hot Jupiters (UHJs) have attracted much attention. Significant progress has been achieved, from enlarging the sample size to broadening the studies to encompass diverse stellar types and ages. Here, we present a transmission spectroscopy study of HAT-P-70b, an UHJ orbiting a young A-type star, through high-resolution ob… ▽ More Owing to hot and inflated envelopes that facilitate atmospheric studies, ultra-hot Jupiters (UHJs) have attracted much attention. Significant progress has been achieved, from enlarging the sample size to broadening the studies to encompass diverse stellar types and ages. Here, we present a transmission spectroscopy study of HAT-P-70b, an UHJ orbiting a young A-type star, through high-resolution observations with CARMENES at the 3.5m Calar Alto telescope. By using the line-by-line technique, we confirm the previous detections of Ha, Na I, and Ca II, report a new tentative detection of K I, and impose an upper limit on the He triplet absorption. Through cross-correlation analysis, we identify the Ca II and Fe I absorptions, both blue-shifted by approximately 5 km/s, indicating a day-to-night side atmospheric wind. Additionally, we find a new tentative detection of K I. We do not see any significant atmospheric molecular signal in the near-infrared data. Putting HAT-P-70b in the context of UHJs from the literature, it turns out that (1) Ha absorption is more common on gas giants orbiting stars younger than 1 Gyr, with a relative detection probability of $P_{\rm Age<1\,Gyr}({\rm Ha})/P_{\rm Age\geq1\,Gyr}({\rm Ha})\sim 3$; (2) any UHJ is likely to exhibit Fe I absorption if it has Ca II. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Comments: 19 pages, 11 figures, 3 tables, accepted for publication in AJ

Tighter constraints on the atmosphere of GJ 436 b from combined high-resolution CARMENES and CRIRES$^+$ observations

Authors: A. Peláez-Torres, A. Sánchez-López, L. Nortmann, M. López-Puertas, E. González-Álvarez, H. M. Tabernero, C. Jiang, D. Revilla, G. Morello, J. Orell-Miquel, E. Pallé, P. J. Amado, J. A. Caballero, I. Ribas, A. Reiners, A. Quirrenbach, D. Cont, S. Dreizler, A. Fernández-Martín, A. P. Hatzes, Th. Henning, F. Lesjak, D. Montes, A. Schweizer, T. Trifonov , et al. (1 additional authors not shown)

Abstract: We aim to study the atmospheric properties of the warm Neptune GJ 436 b by combining a set of five transit events observed with the CARMENES spectrograph with one transit from CRIRES$^+$ so as to provide the most constrained results possible at high resolution. We removed telluric and stellar signals from the data using SysRem and potential planetary signals were investigated using the cross-corre… ▽ More We aim to study the atmospheric properties of the warm Neptune GJ 436 b by combining a set of five transit events observed with the CARMENES spectrograph with one transit from CRIRES$^+$ so as to provide the most constrained results possible at high resolution. We removed telluric and stellar signals from the data using SysRem and potential planetary signals were investigated using the cross-correlation technique. Following standard procedures for undetected species, we performed injection recovery tests and Bayesian retrievals to place constraints on the detectability of the main near-infrared absorbers. In addition, we simulated ELT/ANDES observations by computing end-to-end in silico datasets with EXoPLORE. No molecular signals were detected in the atmosphere of GJ 436 b, which is consistent with previous studies. Combined CARMENES-CRIRES$^+$ injection-recovery and Bayesian retrieval analyses show that the atmosphere is likely covered by high-altitude clouds ($\sim$ $1$ mbar) at low and intermediate metallicities or, alternatively, is very metal-rich ($\gtrsim$ $900\times$ solar), which would suppress spectral features without invoking clouds. Simulations of ELT/ANDES observations suggest a boost by nearly an order of magnitude to the upper limit in the photon-limited regime, reaching $0.1$ mbar at $10$-$300\times$ solar metallicities. The joint analysis of all useful transit observations from CARMENES and CRIRES$^+$ provides the most stringent constraints to date on the atmospheric properties of GJ 436 b. Complementary CCF-based and retrieval approaches consistently indicate that the atmosphere is either cloudy or highly metal enriched. Any weak near-infrared absorption lines, if present, are likely to be below current detection limits. However, according to our simulations, these features may be revealed with ELT/ANDES even in single-transit observations. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Journal ref: A&A 705, A256 (2026)

Upper limits on atmospheric abundances of KELT-11b and WASP-69b from a retrieval approach

Authors: F. Lesjak, L. Nortmann, D. Cont, P. J. Amado, M. Azzaro, J. A. Caballero, S. Czesla, A. Hatzes, Th. Henning, M. López-Puertas, K. Molaverdikhani, D. Montes, J. Orell-Miquel, E. Pallé, A. Peláez-Torres, A. Quirrenbach, A. Reiners, I. Ribas, A. Sánchez-López, A. Schweitzer, F. Yan

Abstract: WASP-69b and KELT-11b are two low-density hot Jupiters, which are expected to show strong atmospheric features in their transmission spectra. Such features offer valuable insights into the chemical composition, thermal structure, and cloud properties of exoplanet atmospheres. High-resolution spectroscopic observations can be used to study the line-forming regions in exoplanet atmospheres and poten… ▽ More WASP-69b and KELT-11b are two low-density hot Jupiters, which are expected to show strong atmospheric features in their transmission spectra. Such features offer valuable insights into the chemical composition, thermal structure, and cloud properties of exoplanet atmospheres. High-resolution spectroscopic observations can be used to study the line-forming regions in exoplanet atmospheres and potentially detect signals despite the presence of clouds. We aimed to detect various molecular species and constrain the chemical abundances and cloud deck pressures using high-resolution spectroscopy. We observed multiple transits of these planets with CARMENES and applied the cross-correlation method to detect atmospheric signatures. Further, we used an injection-recovery approach and retrievals to place constraints on the atmospheric properties. We detected a tentative H$_2$O signal for KELT-11b but not for WASP-69b, and searches for other molecules such as H$_2$S and CH$_4$ resulted in non-detections for both planets. By investigating the signal strength of injected synthetic models, we constrained which atmospheric abundances and cloud deck pressures are consistent with our cross-correlation results. In addition, we show that a retrieval-based approach leads to similar constraints of these parameters. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Comments: Accepted for publication in Astronomy & Astrophysics, 18 pages, 17 figures

The CARMENES search for exoplanets around M dwarfs : Understanding the wavelength dependence of radial velocity measurements

Authors: S. V. Jeffers, J. R. Barnes, P. Schöfer, S. Reffert, V. J. S. Béjar, A. Quirrenbach, A. Reiners, Y. Shan, M. R. Zapatero Osorio, B. Fuhrmeister, P. J. Amado, J. A. Caballero, I. Ribas, C. Cardona Guillén, F. Del Sordo, M. Fernández, A. García-López, A. Guijarro, A. P. Hatzes, M. Lafarga, N. Lodieu, M. Kürster, K. Molaverdikhani, D. Montes, J. C. Morales

Abstract: Context. Current exoplanet surveys are focused on detecting small exoplanets orbiting in the liquid-water habitable zones of their host stars. Despite the recent significant advancements in instrumental developments, the current limitation in detecting these exoplanets is the intrinsic variability of the host star itself. Aims. Our aim is to use the full CARMENES guaranteed time observations (GTO)… ▽ More Context. Current exoplanet surveys are focused on detecting small exoplanets orbiting in the liquid-water habitable zones of their host stars. Despite the recent significant advancements in instrumental developments, the current limitation in detecting these exoplanets is the intrinsic variability of the host star itself. Aims. Our aim is to use the full CARMENES guaranteed time observations (GTO) data set spanning more than 8 years of observations of over 350 stars to investigate the wavelength dependence of high-precision radial velocities (RV), as stellar activity features should exhibit a wavelength dependence while the RV variation due to an orbiting planet will be wavelength independent. Methods. We use the chromatic index (CRX) to quantify the slope of the measured RVs as a function of logarithmic wavelength. We investigate the dependence of the CRX in the full CARMENES GTO sample on 24 stellar activity indices in the visible and near-infrared channels of the CARMENES spectrograph and each star's stellar parameters. We also present an updated convective turnover time scaling for the calculation of the stellar Rossby number for M dwarfs. Results. Our results show that approximately 17\% of GTO stars show a strong or a moderate correlation between CRX and RV. We can improve the measured RVs by a factor of up to nearly 4 in rms by subtracting the RV predicted by the CRX-RV correlation from the measured RVs. Mid M dwarfs with moderate rotational velocities, moderate CRX-gradients and quasi-stable activity features have the best rms improvement factors. Conclusions. We conclude that the CRX is a powerful diagnostic in mitigation of stellar activity and the search for low mass rocky planets. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Comments: published in A&A

Journal ref: 2025A&A...696A..27J

Joint neutrino oscillation analysis from the T2K and NOvA experiments

Authors: NOvA, T2K Collaborations, :, K. Abe, S. Abe, S. Abubakar, M. A. Acero, B. Acharya, P. Adamson, H. Adhkary, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, N. Anfimov, L. Anthony, A. Antoshkin, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, E. Arrieta-Diaz, Y. Ashida, L. Asquith , et al. (577 additional authors not shown)

Abstract: The landmark discovery that neutrinos have mass and can change type (or "flavor") as they propagate -- a process called neutrino oscillation -- has opened up a rich array of theoretical and experimental questions being actively pursued today. Neutrino oscillation remains the most powerful experimental tool for addressing many of these questions, including whether neutrinos violate charge-parity (C… ▽ More The landmark discovery that neutrinos have mass and can change type (or "flavor") as they propagate -- a process called neutrino oscillation -- has opened up a rich array of theoretical and experimental questions being actively pursued today. Neutrino oscillation remains the most powerful experimental tool for addressing many of these questions, including whether neutrinos violate charge-parity (CP) symmetry, which has possible connections to the unexplained preponderance of matter over antimatter in the universe. Oscillation measurements also probe the mass-squared differences between the different neutrino mass states ($Δm^2$), whether there are two light states and a heavier one (normal ordering) or vice versa (inverted ordering), and the structure of neutrino mass and flavor mixing. Here, we carry out the first joint analysis of data sets from NOvA and T2K, the two currently operating long-baseline neutrino oscillation experiments (hundreds of kilometers of neutrino travel distance), taking advantage of our complementary experimental designs and setting new constraints on several neutrino sector parameters. This analysis provides new precision on the $Δm^2_{32}$ mass difference, finding $2.43^{+0.04}_{-0.03}\ \left(-2.48^{+0.03}_{-0.04}\right)\times 10^{-3}~\mathrm{eV}^2$ in the normal (inverted) ordering, as well as a $3σ$ interval on $δ_{\rm CP}$ of $[-1.38π,\ 0.30π]$ $\left([-0.92π,\ -0.04π]\right)$ in the normal (inverted) ordering. The data show no strong preference for either mass ordering, but notably if inverted ordering were assumed true within the three-flavor mixing paradigm, then our results would provide evidence of CP symmetry violation in the lepton sector. △ Less

Submitted 24 October, 2025; v1 submitted 22 October, 2025; originally announced October 2025.

Comments: 25 pages, 13 figures

Journal ref: Nature 646, 818-824 (2025)

Interface States in Space-Time Photonic Crystals: Topological Origin, Propagation and Amplification

Authors: Alejandro Caballero, Thomas F. Allard, Paloma A. Huidobro

Abstract: Studying the topology of spatiotemporal media poses a fundamental challenge: their remarkable properties stem from breaking spatial and temporal symmetries, yet this same breaking obscures their topological characterization. Here, we show that space-time symmetries persist in crystals with travelling-wave modulations whose velocities can be either lower (subluminal) or higher (superluminal) than t… ▽ More Studying the topology of spatiotemporal media poses a fundamental challenge: their remarkable properties stem from breaking spatial and temporal symmetries, yet this same breaking obscures their topological characterization. Here, we show that space-time symmetries persist in crystals with travelling-wave modulations whose velocities can be either lower (subluminal) or higher (superluminal) than the speed of light, enabling the study of their topological properties and the prediction of spatiotemporal interface states. For each modulation regime, we use a Lorentz transformation to a frame in which the modulation depends on only one of the transformed variables. Then, we identify a conserved joint parity-time-reversal symmetry in the new variables that enforces the quantization of a spatiotemporal Zak phase, elevating it to a $\mathbb{Z}_2$ topological invariant. Finally, we calculate the associated interface states and uncover unique features arising from time-varying effects, including selective directional amplification, propagation along subluminal and superluminal boundaries, frequency- and momentum-converted replicas, and broadband amplification even in the absence of momentum gaps. Our framework holds for spatiotemporal modulations of any velocity, unifying a wide class of systems that includes photonic time crystals, and clarifying their topological origin. △ Less

Submitted 26 February, 2026; v1 submitted 21 October, 2025; originally announced October 2025.

Comments: 17 pages, 6 figures

A planetary system with a sub-Neptune planet in the habitable zone of TOI-2093

Authors: J. Sanz-Forcada, E. González-Álvarez, M. R. Zapatero Osorio, J. A. Caballero, V. J. S. Béjar, E. Herrero, C. Rodríguez-López, K. R. Sreenivas, L. Tal-Or, S. Vanaverbeke, A. P. Hatzes, R. Luque, E. Nagel, F. J. Pozuelos, D. Rapetti, A. Quirrenbach, P. J. Amado, M. Blazek, I. Carleo, D. Ciardi, C. Cifuentes, K. Collins, Th. Henning, D. W. Latham, J. Lillo-Box , et al. (11 additional authors not shown)

Abstract: Aims. We aim to confirm and measure the mass of the transiting planet candidate around the K5V star TOI-2093, previously announced by the Transiting Exoplanet Survey Satellite (TESS) project. Methods. We combined photometric data from 32 sectors between 2019 and 2024 with 86 radial velocity measurements obtained with the CARMENES spectrograph over a period of 2.4 years, along with a series of grou… ▽ More Aims. We aim to confirm and measure the mass of the transiting planet candidate around the K5V star TOI-2093, previously announced by the Transiting Exoplanet Survey Satellite (TESS) project. Methods. We combined photometric data from 32 sectors between 2019 and 2024 with 86 radial velocity measurements obtained with the CARMENES spectrograph over a period of 2.4 years, along with a series of ground-based, broadband photometric monitoring campaigns to characterize the host star and the transiting planet candidate, as well as to search for additional planets in the system. Our data indicate that TOI-2093 is a main-sequence star located at a distance of 83 pc, with solar metallicity, and a rotation period of 43.8 +- 1.8 d. Results. We have confirmed the planetary nature of the TESS transiting planet candidate, named TOI-2093 c, through the detection of its Keplerian signal in the spectroscopic data. We measured a planetary radius of 2.30 +- 0.12 Rearth, a Neptune-like mass of 15.8 +- 3.7 Mearth, and an orbital period of 53.81149 +- 0.00017 d. This makes TOI-2093 c the smallest exoplanet known in the habitable zone of a main-sequence FGK star. Given its size and relatively high density, TOI-2093 c belongs to a class of planets with no analog in the Solar System. In addition, the CARMENES data revealed the presence of a second planet candidate with a minimum mass of 10.6 +- 2.5 Mearth and an orbital period of 12.836 +- 0.021 d. This inner planet, which we designated TOI-2093 b, shows no detectable photometric transit in the TESS light curves. The orbital planes of the two planets are misaligned by more than 1.6 deg despite the near 4:1 mean-motion resonance of their orbital periods. △ Less

Submitted 30 September, 2025; originally announced October 2025.

Comments: Accepted by A&A. 12 pages, 7 figures, 5 tables in the main body (20 pages, 19 figures, 9 tables including appendices)

Improving radial velocity precision with CARMENES-PLUS:An upgrade of the near-infrared spectrograph cooling system

Authors: R. Varas, R. Calvo-Ortega, P. J. Amado, S. Becerril, H. Ruh, M. Azzaro, L. Hernandez, H. Magan-Madinabeitia, S. Reinhart, D. Maroto-Fernandez, J. Helmling, A. L. Huelmo, D. Benitez, J. F. Lopez, M. Pineda, J. A. Garcia, J. Garcia de la Fuente, J. Marin, F. Hernandez, J. Aceituno, J. A. Caballero, A. Kaminski, R. J. Mathar, A. Quirrenbach, A. Reiners , et al. (3 additional authors not shown)

Abstract: CARMENES is a dual-channel high-resolution spectrograph at the 3.5 m Calar Alto telescope designed to detect low-mass planets around late-type dwarfs by measuring their radial velocities (RVs). High thermal stability in both the visible (VIS) and near infrared channels is essential to achieve the precision required for these measurements. In particular, stabilising the NIR channel to the millikelv… ▽ More CARMENES is a dual-channel high-resolution spectrograph at the 3.5 m Calar Alto telescope designed to detect low-mass planets around late-type dwarfs by measuring their radial velocities (RVs). High thermal stability in both the visible (VIS) and near infrared channels is essential to achieve the precision required for these measurements. In particular, stabilising the NIR channel to the millikelvin level, which operates at cryogenic temperatures (140 K), poses significant engineering challenges.The CARMENES-PLUS project was initiated to improve the instruments intrinsic RV precision. In this article, we focus on the thermal stability improvements made to the NIR channels cooling system. The NIR cooling system was originally conceived to operate with a discontinuous flow of cryogenic nitrogen gas. As part of CARMENES-PLUS, this was upgraded to a continuous flow configuration. Additional changes included the installation of an automatic vacuum system, a proportional control valve, and a pressure regulation system. These upgrades were designed to reduce thermal fluctuations and enhance long-term stability. The implemented upgrades significantly improved the intrinsic RV precision of the NIR channel. We quantified this improvement using Fabry Perot calibration spectra, obtaining an intrinsic RV precision of 0.67 ms after the interventions, an improvement of nearly 2 ms . We also assessed the stability of the nightly zero points, finding a reduced scatter of 3.9 ms post upgrade, compared to 6.1 ms before. For a sample of slowly rotating stars (vsin i below 2 kms), the median scatter decreased from 8.8 ms to 6.7 ms after the upgrades. These results demonstrate that the thermal control upgrades introduced in CARMENES PLUS have enhanced the NIR channels RV performance, bringing it closer to the VIS channels stability and reinforcing CARMENES capabilities for exoplanet detection around M dwarfs. △ Less

Submitted 16 April, 2026; v1 submitted 22 September, 2025; originally announced September 2025.

Algebraic treatment of alpha-cluster nuclei

Authors: Roelof Bijker, Omar Alejandro Díaz Caballero

Abstract: In this contribution we review the algebraic cluster model (ACM) for $α$-cluster nuclei with $A=4k$ nucleons and its extension to the cluster shell model (CSM) for $A=4k+x$ nuclei. Particular attention is paid to the question to what extent the $α$-cluster structure survives under the addition of extra nucleons. As an example, we discuss the properties of $^{12}$C and $^{13}$C. In this contribution we review the algebraic cluster model (ACM) for $α$-cluster nuclei with $A=4k$ nucleons and its extension to the cluster shell model (CSM) for $A=4k+x$ nuclei. Particular attention is paid to the question to what extent the $α$-cluster structure survives under the addition of extra nucleons. As an example, we discuss the properties of $^{12}$C and $^{13}$C. △ Less

Submitted 11 September, 2025; originally announced September 2025.

Comments: 8 pages, 7 figures, 1 table, to be published in EPJ Web of Conferences, Proceedings of 14th Spring Seminar on Nuclear Physics: Cutting-edge developments in Nuclear Structure Physics, May 19-23, Ischia, Italy

HWO Target Stars and Systems: A Survey of Archival UV and X-ray Data

Authors: Sarah Peacock, David J. Wilson, Tyler Richey-Yowell, Noah W. Tuchow, Kevin France, José A. Caballero, Riccardo Spinelli, Lía Corrales, Aiden S. Zelakiewicz, Seth Redfield, Keighley Rockcliffe, Allison Youngblood, Cynthia S. Froning, Girish M. Duvvuri, Breanna A. Binder, Natalie R. Hinkel, Eric E. Mamajek

Abstract: We assess archival high-energy data for key stars on the Habitable Worlds Observatory (HWO) Target Stars and Systems 2025 list, as stellar radiation is critical to shaping and interpreting planetary atmospheres. Using a sample of 98 nearby stars (HWO Tier 1 targets), we compile and evaluate X-ray and ultraviolet (UV) data from archival eROSITA, Chandra, XMM-Newton, ROSAT, EUVE, Swift, FUSE, IUE, G… ▽ More We assess archival high-energy data for key stars on the Habitable Worlds Observatory (HWO) Target Stars and Systems 2025 list, as stellar radiation is critical to shaping and interpreting planetary atmospheres. Using a sample of 98 nearby stars (HWO Tier 1 targets), we compile and evaluate X-ray and ultraviolet (UV) data from archival eROSITA, Chandra, XMM-Newton, ROSAT, EUVE, Swift, FUSE, IUE, GALEX, and HST. We examine spectral and temporal coverage, assess data quality, and identify major gaps. UV data are moderately available, with most coverage coming from near-UV spectra from IUE. Far fewer stars have far-UV spectra, especially from HST. In the X-ray regime, some stars have high-quality spectra, while others are limited to shallow detections or broad-band photometry. A small fraction of the sample has both X-ray and UV spectra of sufficient quality to support full spectral energy distribution modeling. Truly comprehensive coverage across X-ray, extreme-UV, and both UV bands remains extremely rare. Most datasets are single-epoch, limiting assessments of variability and flares - key factors in atmospheric photochemistry and escape. Moreover, the lack of simultaneous or contemporaneous observations across bands adds further uncertainty. Our findings underscore the need for new space-based missions and coordinated multiwavelength campaigns, ideally with overlapping coverage, to improve stellar characterization for HWO. As several key observatories age and face potential decommissioning, there is a narrow window of opportunity to secure these critical data. Investing in this effort now will directly support the science goals of HWO and enhance future studies of planetary habitability. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Comments: 32 pages, 13 Figures, 6 Tables, accepted to AJ

Discovery of a transiting hot water-world candidate orbiting Ross 176 with TESS and CARMENES

Authors: S. Geraldía-González, J. Orell-Miquel, E. Pallé, F. Murgas, G. Lacedelli, V. J. S. Béjar, J. A. Caballero, C. Duque-Arribas, J. Lillo-Box, D. Montes, G. Morello, E. Nagel, A. Schweitzer, H. M. Tabernero, Y. Calatayud-Borras, C. Cifuentes, G. Fernández-Rodríguez, A. Fukui, J. de Leon, N. Lodieu, R. Luque, M. Mori, N. Narita, H. Parviainen, E. Poultourtzidis , et al. (8 additional authors not shown)

Abstract: The case of Ross 176 is a late K-type star that hosts a promising water-world candidate planet. The star has a radius of $R_*$=0.569$\pm$0.020$R_{\odot}$ and a mass of $M_{\star}$ = 0.577 $\pm$ 0.024 $M_{\odot}$. We constrained the planetary mass using spectroscopic data from CARMENES, an instrument that has already played a major role in confirming the planetary nature of the transit signal detec… ▽ More The case of Ross 176 is a late K-type star that hosts a promising water-world candidate planet. The star has a radius of $R_*$=0.569$\pm$0.020$R_{\odot}$ and a mass of $M_{\star}$ = 0.577 $\pm$ 0.024 $M_{\odot}$. We constrained the planetary mass using spectroscopic data from CARMENES, an instrument that has already played a major role in confirming the planetary nature of the transit signal detected by TESS. We used Gaussian Processes (GP) to improve the analysis because the host star has a relatively strong activity that affects the radial velocity dataset. In addition, we applied a GP to the TESS light curves to reduce the correlated noise in the detrended dataset. The stellar activity indicators show a strong signal that is related to the stellar rotation period of $\sim$ 32 days. This stellar activity signal was also confirmed on the TESS light curves. Ross 176b is an inner hot transiting planet with a low-eccentricity orbit of $e = 0.25 \pm 0.04$, an orbital period of $P \sim 5$ days, and an equilibrium temperature of $T_{eq}\sim 682K$. With a radius of $R_p = 1.84\pm0.08R_{\oplus}$ (4% precision), a mass of $M_p = 4.57^{+0.89}_{-0.93} M_{\oplus}$ (20% precision), and a mean density of $ρ_p = 4.03^{+0.49}_{-0.81} g cm^{-3}$, the composition of Ross 176b might be consistent with a water-world scenario. Moreover, Ross 176b is a promising target for atmospheric characterization, which might lead to more information on the existence, formation and composition of water worlds. This detection increases the sample of planets orbiting K-type stars. This sample is valuable for investigating the valley of planets with small radii around this type of star. This study also shows that the dual detection of space- and ground-based telescopes is efficient for confirm new planets. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: Accepted for publication in A&A. 16 pages. 13 figures

The CARMENES search for exoplanets around M dwarfs. Revisiting the GJ 317, GJ 463, and GJ 3512 systems and two newly discovered planets orbiting GJ 9773 and GJ 508.2

Authors: J. C. Morales, I. Ribas, S. Reffert, M. Perger, S. Dreizler, G. Anglada-Escudé, V. J. S. Béjar, E. Herrero, J. Kemmer, M. Kuzuhara, M. Lafarga, J. H. Livingston, F. Murgas, B. B. Ogunwale, L. Tal-Or, T. Trifonov, S. Vanaverbeke, P. J. Amado, A. Quirrenbach, A. Reiners, J. A. Caballero, J. F. Agüí Fernández, J. Banegas, P. Chaturvedi, S. Dufoer , et al. (11 additional authors not shown)

Abstract: Surveys for exoplanets indicate that the occurrence rate of gas giant planets orbiting late-type stars in orbits with periods shorter than 1000 days is lower than in the case of Sun-like stars. This is in agreement with planet formation models based on the core or pebble accretion paradigm. The CARMENES exoplanet survey has been conducting radial-velocity observations of several targets that show… ▽ More Surveys for exoplanets indicate that the occurrence rate of gas giant planets orbiting late-type stars in orbits with periods shorter than 1000 days is lower than in the case of Sun-like stars. This is in agreement with planet formation models based on the core or pebble accretion paradigm. The CARMENES exoplanet survey has been conducting radial-velocity observations of several targets that show long-period trends or modulations that are consistent with the presence of giant planets at large orbital separations. We present an analysis of five such systems that were monitored with the CARMENES spectrograph, as well as with the IRD spectrograph. In addition, we used archival data to improve the orbital parameters of the planetary systems. We improve the parameters of three previously known planets orbiting the M dwarfs GJ 317, GJ 463, and GJ 3512. We also determine the orbital parameters and minimum mass of the planet GJ 3512 c, for which only lower limits had been given previously. Furthermore, we present the discovery of two new giant planets orbiting the stars GJ 9733 and GJ 508.2, although for the second one only lower limits to the orbital properties can be determined. The new planet discoveries add to the short list of known giant planets orbiting M-dwarf stars with subsolar metallicity at long orbital periods above 2000 days. These results reveal that giant planets appear to form more frequently in wide orbits than in close-in orbits around low-mass and lower metallicity stars. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: 32 pages (including appendix with radial velocity time series), 16 figures, 14 tables. Accepted for publication in A&A

High-resolution Ultraviolet-to-nearinfrared Characterization of Exoplanet Atmospheres

Authors: Patricio E. Cubillos, Matteo Brogi, Antonio García Muñoz, Luca Fossati, Sudeshna Boro Saikia, Vincent Bourrier, Jose A. Caballero, Juan Cabrera, Andrea Chiavassa, Andrzej Fludra, Leonardos Gkouvelis, John Lee Grenfell, Manuel Guedel, Alvaro Labiano, Monika Lendl, Donna Rodgers-Lee, Arnaud Salvador, Ilane Schroetter, Antoine Strugarek, Benjamin Taysum, Aline Vidotto, Thomas G. Wilson

Abstract: The Habitable Worlds Observatory (HWO) offers a unique opportunity to revolutionize our understanding of planetary formation and evolution. The goal of this Science Case Development Document (SCDD) is to investigate the physical and chemical processes that shape the composition and atmospheric mass loss in exoplanets. We review the key observables currently known as diagnostics of mass loss via tr… ▽ More The Habitable Worlds Observatory (HWO) offers a unique opportunity to revolutionize our understanding of planetary formation and evolution. The goal of this Science Case Development Document (SCDD) is to investigate the physical and chemical processes that shape the composition and atmospheric mass loss in exoplanets. We review the key observables currently known as diagnostics of mass loss via transit observations, i.e., absorption lines of escaping hydrogen (Lyman-alpha), helium, and metals (Fe, Mg, C, O). We also explore the challenges to infer planetary formation processes based on atmospheric composition characterization. HWO could enable a broad, continuous coverage from far-ultraviolet to near-infrared spectroscopy (~100--1600 nm) at high resolution (R > 60, 000), which is essential to make these measurements, disentangle their planetary origin from stellar activity, and ultimately, contextualize the escape rates by simultaneously characterizing the composition, cloud predominance, and thermal structure of exoplanet atmospheres. △ Less

Submitted 3 July, 2025; originally announced July 2025.

Comments: Science Case Development Document for the Habitable Worlds Observatory. Comments and endorsements (by Aug 15, 2025) welcomed at patricio.cubillos@oeaw.ac.at

Testing T2K's Bayesian constraints with priors in alternate parameterisations

Authors: The T2K Collaboration, K. Abe, S. Abe, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Ashida, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak, N. Baudis, V. Berardi , et al. (379 additional authors not shown)

Abstract: Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (a… ▽ More Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (as given by the Jarlskog invariant) are robust under the choices of prior considered in the analysis. On the other hand, the degree of octant preference for the atmospheric angle depends on which symmetry has been privileged. △ Less

Submitted 2 July, 2025; originally announced July 2025.

Journal ref: Eur.Phys.J.C 85 (2025) 12, 1414

Detecting and characterising the magnetic field of exoplanets

Authors: A. Strugarek, S. V. Berdyugina, V. Bourrier, J. A. Caballero, J. J. Chebly, R. Fares, A. Fludra, L. Fossati, A. García Muñoz, L. Gkouvelis, C. Gourvès, J. L. Grenfell, R. D. Kavanagh, K. G. Kislyakova, L. Lamy, A. F. Lanza, C. Moutou, D. Nandy, C. Neiner, A. Oklopčić, A. Paul, V. Réville, D. Rodgers-Lee, E. L. Shkolnik, J. D. Turner , et al. (3 additional authors not shown)

Abstract: Magnetic fields play a crucial role in planetary evolution and habitability. While the intrinsic magnetic fields of solar system planets are relatively well understood, the magnetic properties of exoplanets remain largely unconstrained, despite their potential ubiquity. Detecting exoplanetary magnetic fields is essential to advancing our understanding of planetary habitability beyond the solar sys… ▽ More Magnetic fields play a crucial role in planetary evolution and habitability. While the intrinsic magnetic fields of solar system planets are relatively well understood, the magnetic properties of exoplanets remain largely unconstrained, despite their potential ubiquity. Detecting exoplanetary magnetic fields is essential to advancing our understanding of planetary habitability beyond the solar system. This paper focuses on two promising spectropolarimetric techniques for detecting magnetic fields in hot exoplanets: direct detection through polarization signatures in the He I 1083 nm triplet and indirect detection via star-planet magnetic interactions manifesting as stellar hot spots. The direct method is particularly suited to close-in gas giants, leveraging the Hanle and Zeeman effects to detect low-amplitude magnetic fields. The indirect method can apply to both giant and low-mass planets by identifying magnetic connectivity-induced features in the stellar atmosphere. Although the interpretation of current detections remain tentative, upcoming high-resolution spectropolarimetric capabilities in the UV and near-infrared, particularly with future missions like HWO, promise to enable definitive measurements of exoplanetary magnetic fields. These advancements will open new avenues for probing the magnetic environments of exoplanets and their implications for atmospheric retention and habitability. △ Less

Submitted 2 July, 2025; originally announced July 2025.

Comments: 9 pages, 2 figures, 5 tables, Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology SCDD, to be presented at HWO2025 and submitted to Astronomical Society of the Pacific

On Spectral Stability for Rank One Perturbations

Authors: Mario Alberto Ruiz Caballero, Rafael del Rio

Abstract: Embedded point spectra of rank one singular perturbations of an arbitrary self-adjoint operator A on a Hilbert space H is studied. It is shown that these perturbations can be regarded as self-adjoint extensions of a densely defined closed symmetric operator B with deficiency indices (1; 1). Assuming the deficiency vector of B is cyclic for its self-adjoint extensions, we prove that the spectrum of… ▽ More Embedded point spectra of rank one singular perturbations of an arbitrary self-adjoint operator A on a Hilbert space H is studied. It is shown that these perturbations can be regarded as self-adjoint extensions of a densely defined closed symmetric operator B with deficiency indices (1; 1). Assuming the deficiency vector of B is cyclic for its self-adjoint extensions, we prove that the spectrum of A contains a dense Gδ subset where it is not possible to have eigenvalues for any rank one singular perturbation. Moreover, for a dense Gδ set of rank one singular perturbations of A their eigenvalues are isolated. The approach presented here unifies points of view taken by different authors. △ Less

Submitted 26 June, 2025; originally announced June 2025.

MSC Class: 47B02; 47B25; 47A55; 47A10

The mass of the exo-Venus Gliese 12 b, as revealed by HARPS-N, ESPRESSO, and CARMENES

Authors: Daisy A. Turner, Yoshi Nike Emilia Eschen, Felipe Murgas, Annelies Mortier, Thomas G Wilson, Jorge Fernández Fernández, Nicole Gromek, Giuseppe Morello, Hugo M. Tabernero, Jo Ann Egger, Shreyas Vissapragada, José A. Caballero, Stefan Dreizler, Alix Violet Freckelton, Artie P. Hatzes, Ben Scott Lakeland, Evangelos Nagel, Luca Naponiello, Siegfried Vanaverbeke, Alexander Venner, María Rosa Zapatero Osorio, Pedro J. Amado, Víctor J. S. Béjar, Aldo Stefano Bonomo, Lars A. Buchhave , et al. (38 additional authors not shown)

Abstract: Small temperate planets are prime targets for exoplanet studies due to their possible similarities with the rocky planets in the Solar System. M dwarfs are promising hosts since the planetary signals are within our current detection capabilities. Gliese 12 b is a Venus-sized temperate planet orbiting a quiet M dwarf. We present here the first precise mass measurement of this small exoplanet. We pe… ▽ More Small temperate planets are prime targets for exoplanet studies due to their possible similarities with the rocky planets in the Solar System. M dwarfs are promising hosts since the planetary signals are within our current detection capabilities. Gliese 12 b is a Venus-sized temperate planet orbiting a quiet M dwarf. We present here the first precise mass measurement of this small exoplanet. We performed a detailed analysis using HARPS-N, ESPRESSO, and CARMENES radial velocities, along with new and archival \tess, \cheops, and MuSCAT2/3 photometry data. From fitting the available data, we find that the planet has a radius of $R_\mathrm{p} = 0.93\pm0.06 \,\mathrm{R_\oplus}$ and a mass of $M_\mathrm{p} = 0.95^{+0.29}_{-0.30} \,\mathrm{M_\oplus}$ (a $3.2σ$ measurement of the semi-amplitude $K=0.67\pm0.21\,\mathrm{m\,s^{-1}}$), and is on an orbit with a period of $12.761418^{+0.000060}_{-0.000055}\,\mathrm{d}$. A variety of techniques were utilised to attenuate stellar activity signals. Gliese 12 b has an equilibrium temperature of $T_\mathrm{eq}=317 \pm 8\,\mathrm{K}$, assuming an albedo of zero, and a density consistent with that of Earth and Venus ($ρ_\mathrm{p}=6.4\pm2.4\,\mathrm{g\,cm^{-3}}$). We find that Gliese 12 b has a predominantly rocky interior and simulations indicate that it is unlikely to have retained any of its primordial gaseous envelope. The bulk properties of Gliese 12 b place it in an extremely sparsely populated region of both mass--radius and density--$T_\mathrm{eq}$ parameter space, making it a prime target for follow-up observations, including Lyman-$α$ studies. △ Less

Submitted 3 October, 2025; v1 submitted 25 June, 2025; originally announced June 2025.

Comments: 25 pages, 14 figures; accepted for publication in MNRAS

Neutron Star Radial Perturbations for Causal, Viscous, Relativistic Fluids

Authors: Daniel A. Caballero, Nicolás Yunes

Abstract: Which of the multiple models of causal and stable relativistic viscous fluids that have been developed is best suited to describe neutron stars? The modeling of out-of-equilibrium effects in these relativistic, astrophysical objects must be one with care, as simple Newtonian intuition fails to remain causal. Radial stability of neutron stars is one of the primary conditions for the viability of su… ▽ More Which of the multiple models of causal and stable relativistic viscous fluids that have been developed is best suited to describe neutron stars? The modeling of out-of-equilibrium effects in these relativistic, astrophysical objects must be one with care, as simple Newtonian intuition fails to remain causal. Radial stability of neutron stars is one of the primary conditions for the viability of such out-of-equilibrium models. In this paper, we study radial perturbations of neutron stars for the Eckart, the Bemfica-Disconzi-Noronha-Kovtun, and the Müller-Israel-Stewart fluid models of relativistic viscous fluids. We find that for small viscosity, the three models have the same stability properties: they are always stable to bulk and shear viscosity, but they can be unstable to heat conductivity if certain thermodynamic conditions are violated. For the latter case, we derive a necessary criterion for stability to heat conductivity that applies to all three fluids. Moreover, we show that the additional degrees of freedom introduced by the Bemfica-Disconzi-Noronha-Kovtun and the Müller-Israel-Stewart models force the perturbations to evolve on fast timescales. Specifically, the Bemfica-Disconzi-Noronha-Kovtun model has additional oscillatory perturbations that propagate with the speed of second sound, while the Müller-Israel-Stewart model MIS only exhibits decaying behavior on the fast timescale. This work therefore establishes the first formal results and criteria for radial stability of these three out-of-equiblirium fluid models on the non-trivial, relativistic background of neutron stars. △ Less

Submitted 17 September, 2025; v1 submitted 10 June, 2025; originally announced June 2025.

Comments: 25 pages, 0 figures. Accepted version

Results from the T2K experiment on neutrino mixing including a new far detector $μ$-like sample

Authors: The T2K Collaboration, K. Abe, S. Abe, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Ashida, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak, N. Baudis, V. Berardi , et al. (383 additional authors not shown)

Abstract: We have made improved measurements of three-flavor neutrino mixing with 19.7(16.3)$\times 10^{20}$ protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, as well as new proton and photon-tagged samples at the near detector. Significant improvements have been made to the flux and neutrino interaction model… ▽ More We have made improved measurements of three-flavor neutrino mixing with 19.7(16.3)$\times 10^{20}$ protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, as well as new proton and photon-tagged samples at the near detector. Significant improvements have been made to the flux and neutrino interaction modeling. T2K data continue to prefer the normal mass ordering and upper octant of $\sin^2θ_{23}$ with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of $δ_{\scriptscriptstyle\mathrm{CP}}=-2.18\substack{+1.22 \\ -0.47}$, $\sin^2θ_{23}=0.559\substack{+0.018 \\ -0.078}$ and $Δm^2_{32}=(+2.506\substack{+0.039 \\ -0.052})\times 10^{-3}$ eV$^{2}$. △ Less

Submitted 30 December, 2025; v1 submitted 6 June, 2025; originally announced June 2025.

Comments: Version accepted for publication by PRL

Journal ref: Phys. Rev. Lett. 135, 261801 (2025)

First measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasi-elastic-like interactions using an accelerator neutrino beam

Authors: T2K Collaboration, K. Abe, S. Abe, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, M. Antonova, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Asada, Y. Ashida, N. Babu, G. Barr, D. Barrow, P. Bates, M. Batkiewicz-Kwasniak, V. Berardi, L. Berns, S. Bordoni, S. B. Boyd , et al. (314 additional authors not shown)

Abstract: We report the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasi-elastic-like interactions at the gadolinium-loaded Super-Kamiokande detector using the T2K neutrino beam, which has a peak energy of about 0.6 GeV. A total of 30 neutral-current quasi-elastic-like event candidates were selected from T2K data corresponding to an exposure of $1.76\times10^{20}$ p… ▽ More We report the first measurement of neutron capture multiplicity in neutrino-oxygen neutral-current quasi-elastic-like interactions at the gadolinium-loaded Super-Kamiokande detector using the T2K neutrino beam, which has a peak energy of about 0.6 GeV. A total of 30 neutral-current quasi-elastic-like event candidates were selected from T2K data corresponding to an exposure of $1.76\times10^{20}$ protons on target. The $γ$ ray signals resulting from neutron captures were identified using a neural network. The flux-averaged mean neutron capture multiplicity was measured to be $1.37\pm0.33\text{ (stat.)}$$^{+0.17}_{-0.27}\text{ (syst.)}$, which is compatible within $2.3\,σ$ than predictions obtained using our nominal simulation. We discuss potential sources of systematic uncertainty in the prediction and demonstrate that a significant portion of this discrepancy arises from the modeling of hadron-nucleus interactions in the detector medium. △ Less

Submitted 30 May, 2025; v1 submitted 28 May, 2025; originally announced May 2025.

Comments: 27 pages, 20 figures

A neural network approach to determining photometric metallicities of M-type dwarf stars

Authors: C. Duque-Arribas, H. M. Tabernero, D. Montes, J. A. Caballero, E. Galceran

Abstract: M dwarfs are the most abundant stars in the Galaxy and serve as key targets for stellar and exoplanetary studies. It is particularly challenging to determine their metallicities because their spectra are complex. For this reason, several authors have focused on photometric estimates of the M-dwarf metallicity. Although artificial neural networks have been used in the framework of modern astrophysi… ▽ More M dwarfs are the most abundant stars in the Galaxy and serve as key targets for stellar and exoplanetary studies. It is particularly challenging to determine their metallicities because their spectra are complex. For this reason, several authors have focused on photometric estimates of the M-dwarf metallicity. Although artificial neural networks have been used in the framework of modern astrophysics, their application to a photometric metallicity estimate for M dwarfs remains unexplored. We develop an accurate method for estimating the photometric metallicities of M dwarfs using artificial neural networks to address the limitations of traditional empirical approaches. We trained a neural network on a dataset of M dwarfs with spectroscopically derived metallicities. We used eight absolute magnitudes in the visible and infrared from Gaia, 2MASS, and WISE as input features. Batch normalization and dropout regularization stabilized the training and prevented overfitting. We applied the Monte Carlo dropout technique to obtain more robust predictions. The neural network demonstrated a strong performance in estimating photometric metallicities for M dwarfs in the range of -0.45<[Fe/H]<0.45dex and for spectral types as late as M5.0V. On the test sample, the predictions showed uncertainties down to 0.08dex. This surpasses the accuracy of previous methods. We further validated our results using an additional sample of 46 M dwarfs in wide binary systems with FGK-type primary stars with well-defined metallicities and achieved an excellent predictive performance that surpassed the 0.1dex error threshold. This study introduces a ML-based framework for estimating the photometric metallicities of M dwarfs and provides a scalable data-driven solution for analyzing large photometric surveys. The results outline the potential of artificial neural networks to enhance the determination of stellar parameters. △ Less

Submitted 22 May, 2025; originally announced May 2025.

Comments: Accepted for publication in A&A

First Measurement of the Electron Neutrino Charged-Current Pion Production Cross Section on Carbon with the T2K Near Detector

Authors: K. Abe, S. Abe, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak, N. Baudis, V. Berardi, L. Berns, S. Bhattacharjee , et al. (371 additional authors not shown)

Abstract: The T2K Collaboration presents the first measurement of electron neutrino-induced charged-current pion production on carbon in a restricted kinematical phase space. This is performed using data from the 2.5$^°$ off-axis near detector, ND280. The differential cross sections with respect to the outgoing electron and pion kinematics, in addition to the total flux-integrated cross section, are obtai… ▽ More The T2K Collaboration presents the first measurement of electron neutrino-induced charged-current pion production on carbon in a restricted kinematical phase space. This is performed using data from the 2.5$^°$ off-axis near detector, ND280. The differential cross sections with respect to the outgoing electron and pion kinematics, in addition to the total flux-integrated cross section, are obtained. Comparisons between the measured and predicted cross section results using the Neut, Genie and NuWro Monte Carlo event generators are presented. The measured total flux-integrated cross section is [2.52 $\pm$ 0.52 (stat) $\pm$ 0.30 (sys)] x $10^{-39}$ cm$^2$ nucleon$^{-1}$, which is lower than the event generator predictions. △ Less

Submitted 1 May, 2025; originally announced May 2025.

Comments: 8 pages, 2 figures. Data release: https://zenodo.org/records/15316318

Retrieving day- and nightside atmospheric properties of the ultra-hot Jupiter TOI-2109b. Detection of Fe and CO emission lines and evidence for inefficient heat transport

Authors: D. Cont, L. Nortmann, F. Lesjak, F. Yan, D. Shulyak, A. Lavail, M. Stangret, E. Pallé, P. J. Amado, J. A. Caballero, A. Hatzes, Th. Henning, N. Piskunov, A. Quirrenbach, A. Reiners, I. Ribas, J. F. Agüí Fernández, C. Akın, L. Boldt-Christmas, P. Chaturvedi, S. Czesla, A. Hahlin, K. Heng, O. Kochukhov, T. Marquart , et al. (10 additional authors not shown)

Abstract: The ultra-hot Jupiter (UHJ) TOI-2109b marks the lower edge of the equilibrium temperature gap between 3500 K and 4500 K, an unexplored thermal regime that separates KELT-9b, the hottest planet yet discovered, from all other currently known gas giants. To study the structure of TOI-2109b's atmosphere, we obtained high-resolution emission spectra of both the planetary day- and nightsides with CARMEN… ▽ More The ultra-hot Jupiter (UHJ) TOI-2109b marks the lower edge of the equilibrium temperature gap between 3500 K and 4500 K, an unexplored thermal regime that separates KELT-9b, the hottest planet yet discovered, from all other currently known gas giants. To study the structure of TOI-2109b's atmosphere, we obtained high-resolution emission spectra of both the planetary day- and nightsides with CARMENES and CRIRES$^+$. By applying the cross-correlation technique, we identified the emission signatures of Fe I and CO, as well as a thermal inversion layer in the dayside atmosphere; no significant H$_2$O signal was detected from the dayside. None of the analyzed species were detectable from the nightside atmosphere. We applied a Bayesian retrieval framework that combines high-resolution spectroscopy with photometric measurements to constrain the dayside atmospheric parameters and derive upper limits for the nightside hemisphere. The dayside thermal inversion extends from 3200 K to 4600 K, with an atmospheric metallicity consistent with that of the host star (0.36 dex). Only weak constraints could be placed on the C/O ratio ($>$ 0.15). The retrieved spectral line broadening is consistent with tidally locked rotation, indicating the absence of strong dynamical processes. An upper temperature limit of 2400 K and a maximum atmospheric temperature gradient of 700 K/log bar could be derived for the nightside. Comparison of the retrieved dayside T-p profile with theoretical models, the absence of strong atmospheric dynamics, and significant differences in the thermal constraints between the day- and nightside hemispheres suggest a limited heat transport efficiency across the planetary atmosphere. Overall, our results place TOI-2109b in a transitional regime between the UHJs below the thermal gap, which show both CO and H$_2$O emission lines, and KELT-9b, where molecular features are largely absent. △ Less

Submitted 22 April, 2025; originally announced April 2025.

Comments: Accepted for publication in A&A

The CARMENES search for exoplanets around M dwarfs. Cluster analysis of signals from spectral activity indicators to search for shared periods

Authors: J. Kemmer, M. Lafarga, B. Fuhrmeister, Y. Shan, P. Schöfer, S. V. Jeffers, J. A. Caballero, A. Quirrenbach, P. J. Amado, A. Reiners, I. Ribas, V. J. S. Béjar, F. Del Sordo, A. P. Hatzes, Th. Henning, I. Hermelo, A. Kaminski, D. Montes, J. C. Morales, S. Reffert

Abstract: A multitude of spectral activity indicators are routinely computed nowadays from the spectra generated as part of planet-hunting radial velocity surveys. Searching for shared periods among them can help to robustly identify astrophysical quantities of interest, such as the stellar rotation period. However, this identification can be complicated due to the fact that many different peaks occurring i… ▽ More A multitude of spectral activity indicators are routinely computed nowadays from the spectra generated as part of planet-hunting radial velocity surveys. Searching for shared periods among them can help to robustly identify astrophysical quantities of interest, such as the stellar rotation period. However, this identification can be complicated due to the fact that many different peaks occurring in the periodograms. This is especially true in the presence of aliasing and spurious signals caused by environmental influences affecting the instrument. Our goal is to test a clustering algorithm to find signals with the same periodicity, (i.e. with the stellar rotation period) in the periodograms of a large number of activity indicators. On this basis, we have looked to evaluate the correlations between activity indicators and fundamental stellar parameters. We used generalised Lomb-Scargle periodograms to find periodic signals in 24 activity indicators, spanning the VIS and NIR channels of the CARMENES spectrograph. Common periods were subsequently determined by a machine learning algorithm for density-based spatial clustering of applications with noise (DBSCAN). The clustering analysis of the signals apparent in the spectral activity indicators is a powerful tool for the detection of stellar rotation periods. It is straightforward to implement and can be easily automated, so that large data sets can be analysed. For a sample of 136 stars, we were able to recover the stellar rotation period in a total of 59 cases, including 3 with a previously unknown rotation period. In addition, we analysed spurious signals frequently occurring at the period of one year and its integer fractions, concluding that they are likely aliases of one underlying signal. Furthermore, we reproduced the results of several previous studies on the relationships between activity indicators and the stellar characteristics. △ Less

Submitted 11 April, 2025; originally announced April 2025.

Comments: 33 pages (16 pages main text), 14 figures, accepted for publication in Astronomy & Astrophysics

The CARMENES search for exoplanets around M dwarfs. Occurrence rates of Earth-like planets around very low-mass stars

Authors: A. Kaminski, S. Sabotta, J. Kemmer, P. Chaturvedi, R. Burn, J. C. Morales, J. A. Caballero, I. Ribas, A. Reiners, A. Quirrenbach, P. J. Amado, V. J. S. Béjar, S. Dreizler, E. W. Guenther, A. P. Hatzes, Th. Henning, M. Kürster, D. Montes, E. Nagel, E. Pallé, V. Pinter, S. Reffert, M. Schlecker, Y. Shan, T. Trifonov , et al. (2 additional authors not shown)

Abstract: Aims: Previous estimates of planet occurrence rates in the CARMENES survey indicated increased numbers of planets on short orbits for M dwarfs with masses below 0.34\,M$_\odot$. Here we focused on the lowest-mass stars in the survey, comprising 15 inactive targets with masses under 0.16\,M$_\odot$. Methods: To correct for detection biases, we determined detection sensitivity maps for individual… ▽ More Aims: Previous estimates of planet occurrence rates in the CARMENES survey indicated increased numbers of planets on short orbits for M dwarfs with masses below 0.34\,M$_\odot$. Here we focused on the lowest-mass stars in the survey, comprising 15 inactive targets with masses under 0.16\,M$_\odot$. Methods: To correct for detection biases, we determined detection sensitivity maps for individual targets and the entire sample. Using Monte Carlo simulations, we estimated planet occurrence rates for orbital periods of 1\,d to 100\,d and minimum masses from 0.5\,M$_\oplus$ to 10\,M$_\oplus$. Results: The radial velocity (RV) data from CARMENES reveal four new planets around three stars in our sample, namely G~268--110\,b, G~261--6\,b, and G~192--15\,b and c. All three b planets have minimum masses of 1.03--1.52\,M$_\oplus$ and orbital periods of 1.43--5.45\,d, while G~192--15\,c is a 14.3\,M$_\oplus$ planet on a wide, eccentric orbit with $P \approx 1218$\,d and $e \approx 0.68$. Our occurrence rates suggest considerable dependencies with respect to stellar masses. For planets below 3\,M$_\oplus$ we found rates consistent with one planet per star across all investigated periods, but the rates decrease almost by an order of magnitude for larger planet masses up to 10\,M$_\oplus$. Compared to previous studies, low-mass stars tend to harbor more planets with $P <10$\,d. We also demonstrate that synthetic planet populations based on the standard core accretion scenario predict slightly more massive planets on wider orbits than observed. Conclusions: Our findings confirm that planet occurrence rates vary with stellar masses even among M dwarfs, as we found more planets with lower masses and on shorter orbits in our subsample of very low-mass stars compared to more massive M dwarfs. Therefore, we emphasize the need for additional differentiation in future studies. △ Less

Submitted 8 April, 2025; v1 submitted 4 April, 2025; originally announced April 2025.

Comments: Number of pages: 25; number of figures: 23 (12 in main + 11 in appendix). Accepted in A&A; DOI (pending): 10.1051/0004-6361/202453381 (Volume 696, Article number A101)

First differential measurement of the single $\mathbfπ^+$ production cross section in neutrino neutral-current scattering

Authors: K. Abe, S. Abe, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Ashida, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak, N. Baudis, V. Berardi, L. Berns , et al. (357 additional authors not shown)

Abstract: Since its first observation in the 1970s, neutrino-induced neutral-current single positive pion production (NC1$π^+$) has remained an elusive and poorly understood interaction channel. This process is a significant background in neutrino oscillation experiments and studying it further is critical for the physics program of next-generation accelerator-based neutrino oscillation experiments. In this… ▽ More Since its first observation in the 1970s, neutrino-induced neutral-current single positive pion production (NC1$π^+$) has remained an elusive and poorly understood interaction channel. This process is a significant background in neutrino oscillation experiments and studying it further is critical for the physics program of next-generation accelerator-based neutrino oscillation experiments. In this Letter we present the first double-differential cross-section measurement of NC1$π^+$ interactions using data from the ND280 detector of the T2K experiment collected in $ν$-beam mode. The measured flux-averaged integrated cross-section is $ σ= (6.07 \pm 1.22 )\times 10^{-41} \,\, \text{cm}^2/\text{nucleon}$. We compare the results on a hydrocarbon target to the predictions of several neutrino interaction generators and final-state interaction models. While model predictions agree with the differential results, the data shows a weak preference for a cross-section normalization approximately 30\% higher than predicted by most models studied in this Letter. △ Less

Submitted 1 July, 2025; v1 submitted 9 March, 2025; originally announced March 2025.

Signal selection and model-independent extraction of the neutrino neutral-current single $π^+$ cross section with the T2K experiment

Authors: K. Abe, S. Abe, R. Akutsu, H. Alarakia-Charles, Y. I. Alj Hakim, S. Alonso Monsalve, L. Anthony, S. Aoki, K. A. Apte, T. Arai, T. Arihara, S. Arimoto, Y. Ashida, E. T. Atkin, N. Babu, V. Baranov, G. J. Barker, G. Barr, D. Barrow, P. Bates, L. Bathe-Peters, M. Batkiewicz-Kwasniak, N. Baudis, V. Berardi, L. Berns , et al. (357 additional authors not shown)

Abstract: This article presents a study of single $π^+$ production in neutrino neutral-current interactions (NC1$π^+$) using the FGD1 hydrocarbon target of the ND280 detector of the T2K experiment. We report the largest sample of such events selected by any experiment, providing the first new data for this channel in over four decades and the first using a sub-GeV neutrino flux. The signal selection strateg… ▽ More This article presents a study of single $π^+$ production in neutrino neutral-current interactions (NC1$π^+$) using the FGD1 hydrocarbon target of the ND280 detector of the T2K experiment. We report the largest sample of such events selected by any experiment, providing the first new data for this channel in over four decades and the first using a sub-GeV neutrino flux. The signal selection strategy and its performance are detailed together with validations of a robust cross section extraction methodology. The measured flux-averaged integrated cross-section is $ σ= (6.07 \pm 1.22 )\times 10^{-41} \,\, \text{cm}^2/\text{nucleon}$, 1.3~$σ~$ above the NEUT v5.4.0 expectation. △ Less

Submitted 1 July, 2025; v1 submitted 9 March, 2025; originally announced March 2025.

CARMENES as an Instrument for Exoplanet Research

Authors: José A. Caballero, Walter Seifert, Andreas Quirrenbach, Pedro J. Amado, Ignasi Ribas, Ansgar Reiners

Abstract: CARMENES stands for Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs. CARMENES took six years from a concept to the start of operations, and a couple more years of initial data collection until the first science publication, but now is revolutionising our knowledge on exoplanets and their stars in our immediate vicinity. Here we des… ▽ More CARMENES stands for Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs. CARMENES took six years from a concept to the start of operations, and a couple more years of initial data collection until the first science publication, but now is revolutionising our knowledge on exoplanets and their stars in our immediate vicinity. Here we describe what CARMENES is: (i) an ultra-stabilised two-channel spectrograph at an almost dedicated 3.5 m telescope in southern Spain that covers in high spectral resolution and without big gaps from 0.52 mum to 1.71 mum; (ii) a science project aimed at comprehensively searching for and studying planetary systems with nearby, bright, M-dwarf hosts, but that also investigates transiting planets around other stars; and (iii) the German-Spanish consortium that designed and built the instrument and that has operated it under guaranteed and legacy time observations. △ Less

Submitted 7 March, 2025; originally announced March 2025.

Comments: To be published in: Handbook of Exoplanets, 2nd edition, Hans Deeg and Juan Antonio Belmonte (eds. in chief), Springer International Publishing AG, part of Springer Nature. The corresponding images in full size can be downloaded at this link: https://carmenes.caha.es/ext/instrument/CARMENES_Handbook_Caballero_Figs.pdf (massive file)

Connection between planetary He I $λ$10830 Å absorption and extreme-ultraviolet emission of planet-host stars

Authors: J. Sanz-Forcada, M. López-Puertas, M. Lampón, S. Czesla, L. Nortmann, J. A. Caballero, M. R. Zapatero Osorio, P. J. Amado, F. Murgas, J. Orell-Miquel, E. Pallé, A. Quirrenbach, A. Reiners, I. Ribas, A. Sánchez-López, E. Solano

Abstract: Context. The detection of the He I 10830 A triplet in exoplanet atmospheres has opened a new window for probing planetary properties, including atmospheric escape. Unlike Lyman alpha, the triplet is less affected by ISM absorption. Sufficient XUV stellar irradiation may trigger the formation of the He I triplet via photoionization and posterior recombination processes in the planet atmospheres. On… ▽ More Context. The detection of the He I 10830 A triplet in exoplanet atmospheres has opened a new window for probing planetary properties, including atmospheric escape. Unlike Lyman alpha, the triplet is less affected by ISM absorption. Sufficient XUV stellar irradiation may trigger the formation of the He I triplet via photoionization and posterior recombination processes in the planet atmospheres. Only a weak trend between stellar XUV and the planetary He I strength has been observed so far. Aims. We aim to confirm this mechanism for producing the He I absorption in exoplanetary atmospheres by examining a sample of planetary systems. Methods. We obtained homogeneous measurements of the planetary He I line EW and consistently computed the stellar XUV ionizing irradiation. We first derived new coronal models for the planet-host stars. We used updated data from the X-exoplanets database, archival X-ray spectra of M-type stars (including AU Mic and Proxima Cen), and new XMM-Newton X-ray data obtained for the CARMENES project. These data were complemented at longer wavelengths with publicly available HST, FUSE, and EUVE spectra. A total of 75 stars are carefully analyzed to obtain a new calibration between X-ray and EUV emission. Results. Two distinct relationships between stellar X-ray emission (5-100 A) and EUV_H (100-920 A) or EUV_He (100-504 A) radiation are obtained to scale the emission from late-type stellar coronae. A total of 48 systems with reported planetary He I 10830 A studies, exhibit a robust relationship between the planetary He I feature and the ionizing XUV_He received by the planet, corrected by stellar and planetary radii, and the planet's gravitational potential. Some outliers could be explained by a different atmospheric composition or the lack of planetary gaseous atmospheres. This relation may be used to predict the He I 10830 A absorption in exoplanet atmospheres. △ Less

Submitted 30 January, 2025; v1 submitted 7 January, 2025; originally announced January 2025.

Comments: Accepted by A&A. 12 pages, 5 figures in the main body (42 pages, 22 figures, 21 tables including appendices)

Journal ref: A&A, 693, A285 (2025)

Multi-Epoch precise photometry from the ground: MUDEHaR, magnetic stars and everything around

Authors: G. Holgado, J. Maíz Apellániz, J. A. Caballero

Abstract: MUDEHaR is an on-going multi-epoch photometric survey with two narrow filters in H$α$ and the calcium triplet window that uses the T80Cam wide-field imager at the JAST/T80 telescope at Spanish Javalambre astronomical observatory. It is obtaining 100 epochs/year per field for 20 fields in the Galactic disk, each of 2\,deg$^2$, for a total of 40\,deg$^2$. Focused on stellar clusters and HII regions… ▽ More MUDEHaR is an on-going multi-epoch photometric survey with two narrow filters in H$α$ and the calcium triplet window that uses the T80Cam wide-field imager at the JAST/T80 telescope at Spanish Javalambre astronomical observatory. It is obtaining 100 epochs/year per field for 20 fields in the Galactic disk, each of 2\,deg$^2$, for a total of 40\,deg$^2$. Focused on stellar clusters and HII regions including bright stars, its main objective is to detect tens of thousands OB stars that present emission variability in H$α$ on days-months-years scale. The observed targets include magnetic massive stars, pulsating stars, and all kinds of variable stars. Among our driving scientific objectives of MUDEHaR observations is to identify potential magnetic candidates in massive stars. Only 10--20\,\% of OB stars display a measurable magnetic field, and its origin is still in debate. We outline here the multi-step process involved in identifying OB magnetic stars, highlighting the significance of MUDEHaR observations in this process. △ Less

Submitted 29 December, 2024; originally announced December 2024.

Comments: 11 pages, 5 figures. To appear in the edition of the Central European Astrophysical Bulletin dedicated to the proceedings of the Hvar Stellar Meeting 2023

Analysis of NOvA and MicroBooNE charged-current inclusive neutrino measurements within the SuSAv2 framework

Authors: J. Gonzalez-Rosa, G. D. Megias, J. A. Caballero, M. B. Barbaro

Abstract: In this work we compare the SuSAv2 model, based on the superscaling phenomenon and the relativistic mean field theory, with charged-current inclusive neutrino cross sections from the NOvA and MicroBooNE experiments, whose targets are composed primarily by 12 C and 40 Ar, respectively. The neutrino energy in these experiments covers a kinematic range from tens of MeV to roughly 20 GeV. Thus, we con… ▽ More In this work we compare the SuSAv2 model, based on the superscaling phenomenon and the relativistic mean field theory, with charged-current inclusive neutrino cross sections from the NOvA and MicroBooNE experiments, whose targets are composed primarily by 12 C and 40 Ar, respectively. The neutrino energy in these experiments covers a kinematic range from tens of MeV to roughly 20 GeV. Thus, we consider the different reaction mechanisms that contribute significantly to these kinematics, namely quasielastic, two-particle two-hole meson exchange currents, resonances and deep inelastic scattering contributions. △ Less

Submitted 23 December, 2024; originally announced December 2024.

Comments: Article submitted to Phys. Rev. D