Astronomers are debating whether the plentiful "sub-Neptune" exoplanets -- worlds a bit larger than Earth but smaller than Neptune -- are predominantly rocky planets, water-rich "ocean worlds," or gas-enshrouded mini-Neptunes. This question is crucial because such sub-Neptune-sized planets are among the most common in our galaxy, yet we have no analog in our own solar system, making them a key to understanding planet formation and diversity. It also directly impacts the search for habitable worlds: larger-than-Earth planets with solid surfaces or oceans could support life, whereas gas-rich mini-Neptunes likely cannot. However, distinguishing these types using only a planet's mass and radius is very challenging, because different compositions can produce similar densities, leaving a world's nature ambiguous with current data. The proposed Habitable Worlds Observatory (HWO), a future NASA flagship telescope, offers a solution. HWO could directly image and spectroscopically analyze starlight reflected from 50~100 sub-Neptunes around nearby stars, aiming to reveal their atmospheric compositions and potential surfaces. Using visible and near-infrared spectroscopy along with sensitive polarimetry, HWO would detect atmospheric gases (such as water vapor, methane, and carbon dioxide) and search for telltale surface signatures, including rock absorption features and the characteristic reflectivity patterns of oceans. By analyzing these signals, we could determine whether sub-Neptunes are large rocky planets or water worlds rather than gas-dominated mini-Neptunes. Crucially, expanding the search beyond Earth-sized planets to include these abundant sub-Neptunes may uncover entirely new classes of potentially habitable worlds, directly advancing HWO's mission to identify and characterize planets that could support life.

We report on the observation and measurement of astrometry, photometry, morphology, and activity of the interstellar object 3I/ATLAS, also designated C/2025 N1 (ATLAS), with the NSF-DOE Vera C. Rubin Observatory. The third interstellar object, comet 3I/ATLAS, was first discovered on UT 2025 July 1. Serendipitously, the Rubin Observatory collected imaging in the area of the sky inhabited by the object during regular commissioning activities. We successfully recovered object detections from Rubin visits spanning UT 2025 June 21 (10 days before discovery) to UT 2025 July 7. Facilitated by Rubin's high resolution and large aperture, we report on the detection of cometary activity as early as June 21st, and observe it throughout. We measure the location and magnitude of the object on 37 Rubin images in r, i, and z bands, with typical precision of about 20 mas (100 mas, systematic) and about 10 mmag, respectively. We use these to derive improved orbit solutions, and to show there is no detectable photometric variability on hourly timescales. We derive a V-band absolute magnitude of H_V = (13.7 +/- 0.2) mag, and an equivalent effective nucleus radius of around (5.6 +/- 0.7) km. These data represent the earliest observations of this object by a large (8-meter class) telescope reported to date, and illustrate the type of measurements (and discoveries) Rubin's Legacy Survey of Space and Time (LSST) will begin to provide once operational later this year.

The Kepler mission, despite its conclusion over a decade ago, continues to offer a rich dataset for uncovering new astrophysical objects and phenomena. In this study, we conducted a comprehensive search for exocometary transit signatures within the Kepler light curves, using a machine learning approach based on a neural network trained on a library of theoretical exocomet transit light curves. By analyzing the light curves of 201,820 stars, we identified candidate events through the neural network and subjected the output to filtering and visual inspection to mitigate false positives. Our results are presented into three catalogs of increasing ambiguity. The first-tier catalog includes 17 high-confidence exocometary transit events, comprising 7 previously reported events and 10 newly identified ones, each associated with a different host star. The second-tier catalog lists 30 lower-confidence events that remain consistent with possible exocometary transits. The third-tier catalog consists of 49 more symmetric photometric events that could be either exocometary transits, exoplanet mono-transits, or false positives due to eclipsing binaries mimicking transits. Contrary to previous studies, which suggested that the cometary activity was favored by stellar youth, we find a broad age distribution among candidate host stars, including several red giants. This challenges the general idea of a decline in cometary activity with stellar age and underlines the need for further investigation into the temporal evolution of exocometary activity in planetary systems.

The goal of this study is to analyze the photometric properties of Deimos using Mars Express (MEX) observations, to improve the photometric properties and provide new insights into the texture and composition of the surface of Deimos, in preparation for the MMX mission. We analyzed the data obtained by the HRSC and the SRC cameras onboard MEX. The HRSC data, obtained through the use of four filters (blue, green, red, IR), provides 390 to 800 m/px resolution, while the SRC data reach 85 to 300 m/px and cover a wide phase angle range (0.06-138°). We performed the disk-integrated and disk-resolved photometric analysis using the Hapke model. The Deimos surface is dark and predominantly backscattering, with a single-scattering albedo (SSA) value (6.8%-7.5%) comparable to Phobos. The Deimos phase curve shows a strong opposition effect due to shadow-hiding, with negligible coherent backscattering. The amplitude and the half-width of the shadow-hiding opposition surge were found to be 2.14 +/- 0.14 and 0.065 +/- 0.004, respectively. We found a high porosity of 86% at the top-layer surface, consistent with complex-shaped grains or fractal aggregates, suggesting a thick dust layer. We did not observe significant variations of the opposition surge across the surface. A blue unit on Deimos, located on streamers of the equatorial ridge, shows reflectance increases up to 58%, and a spectral slope decrease of 50% in comparison with the average surface. This blue unit may be due to a different texture of the surface between the two units, with finer grain and/or higher porosity. Deimos photometric properties, including SSA, opposition surge, and phase integral, are very similar to Phobos. The presence of a blue unit on Deimos reinforces the idea that the Martian moons have a common origin, making the capture of two different bodies with such similar properties unlikely.

Asteroids with companions constitute an excellent sample for studying the collisional and dynamical evolution of minor planets. The currently known binary population were discovered by different complementary techniques that produce, for the moment, a strongly biased distribution, especially in a range of intermediate asteroid sizes (approximately 20 to 100 km) where both mutual photometric events and high-resolution adaptive optic imaging are poorly efficient. A totally independent technique of binary asteroid discovery, based on astrometry, can help to reveal new binary systems and populate a range of sizes and separations that remain nearly unexplored. In this work, we describe a dedicated period detection method and its results for the Gaia DR3 data set. This method looks for the presence of a periodic signature in the orbit post-fit residuals. After conservative filtering and validation based on statistical and physical criteria, we are able to present a first sample of astrometric binary candidates, to be confirmed by other observation techniques such as photometric light curves and stellar occultations.

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.

The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey has observed 8 different regions of the sky, including sections of the COSMOS, DEEP2, ELAIS, GOODS-N, SDSS and Groth fields using a new photometric system with 20 contiguous ~ $300Å$ filters covering the optical range, combining them with deep $JHKs$ imaging. The observations, carried out with the Calar Alto 3.5m telescope using the wide field (0.25 sq. deg FOV) optical camera LAICA and the NIR instrument Omega-2000, correspond to ~700hrs on-target science images. The photometric system was designed to maximize the effective depth of the survey in terms of accurate spectral-type and photo-zs estimation along with the capability of identification of relatively faint emission lines. Here we present multicolor photometry and photo-zs for ~438k galaxies, detected in synthetic F814W images, complete down to I~24.5 AB, taking into account realistic noise estimates, and correcting by PSF and aperture effects with the ColorPro software. The photometric ZP have been calibrated using stellar transformation equations and refined internally, using a new technique based on the highly robust photometric redshifts measured for emission line galaxies. We calculate photometric redshifts with the BPZ2 code, which includes new empirically calibrated templates and priors. Our photo-zs have a precision of $dz/(1+z_s)=1$ for I<22.5 and 1.4% for 22.5=0.56 for I<22.5 AB and =0.86 for I<24.5 AB. The data presented here covers an effective area of 2.79 sq. deg, split into 14 strips of 58.5'x15.5' and represents ~32 hrs of on-target.

Although triple systems are common, their orbital dynamics and stellar evolution remain poorly understood. We investigated the V1371 Tau system using TESS photometry, multi-epoch spectroscopy, and recent interferometric data, confirming it as a rare triple system consisting of an eclipsing binary orbited by a classical Be star, with a spectral classification of (B1V + B0V) + B0Ve. The eclipsing binary exhibits an orbital period of approximately 34 days, and the Be star orbits the inner pair on a timescale of a few years. Weak H$\alpha$ emission lines suggest the presence of a Keplerian disk with variability on a timescale of months around the Be star, and a nearly constant V/R ratio with no detectable asymmetry variations. Besides the eclipses, frequencies at 0.24 and 0.26 c/d dominate the photometric variability. Higher-frequency signals are present which appear associated with non-radial pulsation. The eclipsing pair ($i \approx 90^\circ$) shows projected rotational velocities of 160 and 200 km s$^{-1}$. The Be star's measured $v \sin i \approx 250$ km s$^{-1}$ implies a critical rotation fraction between 0.44 and 0.76 for plausible inclinations, significantly faster than the eclipsing components. The shallower eclipses in the KELT data compared to TESS suggest a variation in orbital inclination, possibly induced by Kozai-Lidov cycles from the outer Be star. The evolution analysis suggests that all components are massive main-sequence stars, with the secondary star in the eclipsing binary being overluminous. This study emphasizes the complexity of triple systems with Be stars and provides a basis for future research on their formation, evolution, and dynamics.

The early--type galaxy (ETG) mass--size relation has been largely studied to understand how these galaxies have assembled their mass. One key observational result of the last years is that massive galaxies increased their size by a factor of a few at fixed stellar mass from $z\sim2$. Hierarchical models favor minor mergers as a plausible driver of this size growth. Some of these models, predict a significant environmental dependence in the sense that galaxies residing in more massive halos tend to be larger than galaxies in lower mass halos, at fixed stellar mass and redshift. At present, observational results of this environmental dependence have been contradictory. In this paper we revisit this issue in the local Universe, by investigating how the sizes of massive ETGs depend on large-scale environment using an updated and accurate sample of ETGs in different environments - field, group, clusters - from the Sloan Digital Sky Survey DR7. Our analysis does not show any significant environmental dependence of the sizes of central and satellites ETGs at fixed stellar mass at $z\sim0$. The size-mass relation of early-type galaxies at $z\sim0$ seems to be universal, i.e., independent of the mass of the host halo and of the position of the galaxy in that halo (central or satellite). The result is robust to different galaxy selections based on star formation, morphology or central density. In fact, considering our observational errors and the size of the sample, any size ratio larger than $30-40$ between massive galaxies ($log(M_*/M_\odot)>11$) living in clusters and in the field can be ruled out at $3\sigma$ level.

We report the detection of continuous positional and polarization changes of the compact source SgrA* in high states ('flares') of its variable near- infrared emission with the near-infrared GRAVITY-Very Large Telescope Interferometer (VLTI) beam-combining instrument. In three prominent bright flares, the position centroids exhibit clockwise looped motion on the sky, on scales of typically 150 micro-arcseconds over a few tens of minutes, corresponding to about 30% the speed of light. At the same time, the flares exhibit continuous rotation of the polarization angle, with about the same 45(+/-15)-minute period as that of the centroid motions. Modelling with relativistic ray tracing shows that these findings are all consistent with a near face-on, circular orbit of a compact polarized 'hot spot' of infrared synchrotron emission at approximately six to ten times the gravitational radius of a black hole of 4 million solar masses. This corresponds to the region just outside the innermost, stable, prograde circular orbit (ISCO) of a Schwarzschild-Kerr black hole, or near the retrograde ISCO of a highly spun-up Kerr hole. The polarization signature is consistent with orbital motion in a strong poloidal magnetic field.

The origin of the hard, bright X-ray emission that defines the gamma Cas analog class of Be stars remains an outstanding question in Be star literature. This work explores the possibility that the X-ray flux is produced by accretion onto a white dwarf companion. We use three-dimensional smoothed particle hydrodynamics simulations to model the prototype gamma Cas system assuming a white dwarf companion and investigate the accretion of the circumstellar material by the secondary star. We contrast these results to a model for 59 Cyg, a non-gamma Cas Be star system with a stripped companion. We find that the secondary stars in both systems form disk-like accretion structures with Keplerian characteristics, similar to those seen in the Be decretion disks. We also find that white dwarf accretion can produce X-ray fluxes that are consistent with the observed values for gamma Cas, while the predicted X-ray luminosities are significantly lower for the non-degenerate companion in 59 Cyg. In addition, using the three-dimensional radiative transfer code, HDUST, we find that these models produce H-alpha emission consistent with the observations for both gamma Cas and 59 Cyg, and that the predicted polarization degrees across optical and UV wavelengths are at detectable levels. Finally, we discuss the impact that future UV spectropolarimetry missions could have on our understanding of these systems.

We investigate the cosmological constraints that can be expected from measurement of the cross-correlation of galaxies with cosmic voids identified in the Euclid spectroscopic survey, which will include spectroscopic information for tens of millions of galaxies over $15\,000$ deg$^2$ of the sky in the redshift range 0.9\leq z&lt;1.8. We do this using simulated measurements obtained from the Flagship mock catalogue, the official Euclid mock that closely matches the expected properties of the spectroscopic data set. To mitigate anisotropic selection-bias effects, we use a velocity field reconstruction method to remove large-scale redshift-space distortions from the galaxy field before void-finding. This allows us to accurately model contributions to the observed anisotropy of the cross-correlation function arising from galaxy velocities around voids as well as from the Alcock-Paczynski effect, and we study the dependence of constraints on the efficiency of reconstruction. We find that Euclid voids will be able to constrain the ratio of the transverse comoving distance $D_{\rm M}$ and Hubble distance $D_{\rm H}$ to a relative precision of about $0.3\%$, and the growth rate $f\sigma_8$ to a precision of between $5\%$ and $8\%$ in each of four redshift bins covering the full redshift range. In the standard cosmological model, this translates to a statistical uncertainty $\Delta\Omega_\mathrm{m}=\pm0.0028$ on the matter density parameter from voids, better than can be achieved from either Euclid galaxy clustering and weak lensing individually. We also find that voids alone can measure the dark energy equation of state to $6\%$ precision.

We present a first analysis of the dynamics of in-situ globular clusters (GCs) in Milky Way (MW)-like galaxies embedded in fuzzy dark matter (FDM) halos, combining cosmological assembly histories from the TNG50 simulation with dedicated orbital integrations and analytical models. GC populations are initialized with identical distributions in normalized $E$-$L_{z}$ in matched CDM and FDM halos. In a universe dominated by FDM, we identify three distinct regimes for the in-situ GC population depending on the particle mass $m_{22} \equiv m_{\chi}/ 10^{-22}~\mathrm{eV}$. For m_{22} &lt; 7, baryons dominate the inner potential, which remains steep and centrally concentrated, confining GC orbits to a narrow region and producing less massive, more compact systems than in CDM. For $m_{22} \sim 7$, GC properties resemble those in CDM, with similar mass and spatial distributions. For m_{22} &gt; 7, the dark matter becomes both compact and globally dominant, generating a deeper and more extended gravitational potential that supports a wider range of stable GC orbits, resulting in more massive and spatially extended GC systems. Finally, we extend our framework to make predictions for GC populations in alternative DM models, including warm dark matter and self-interacting dark matter, in both MW-like and dwarf galaxies. Our findings demonstrate that in-situ GC systems offer a sensitive and independent probe of the underlying DM physics, opening new avenues for observational constraints with upcoming Euclid.

Context: Investigating the vertical distribution of molecular content in protoplanetary disks remains difficult in most disks mildly inclined along the line of sight. In contrast, edge-on disks provide a direct (tomographic) view of the 2D molecular brightness. Aims: We study the radial and vertical molecular distribution as well as the gas temperature and density by observing the Keplerian edge-on disk surrounding the Flying Saucer, a Class II object located in Ophiuchus. Methods: We use new and archival ALMA data to perform a tomography of $^{12}$CO, $^{13}$CO, C$^{18}$O, CN, HCN, CS, H$_2$CO, c-C$_3$H$_2$, N$_2$D$^+$, DCN and $^{13}$CS. We analyze molecular tomographies and model data using the radiative transfer code DiskFit. Results: We directly measure the altitude above the mid-plane for each observed species. For the first time, we unambiguously demonstrate the presence of a common molecular layer and measure its thickness: most molecules are located at the same altitude versus radius. Beyond CO, as predicted by chemical models, the CN emission traces the upper boundary of the molecular layer, whereas the deuterated species (DCN and N2D+) resides below one scale-height. Our best fits from DiskFit show that most observed transitions in the molecular layer are thermalized because their excitation temperature is the same, around 17-20 K. Conclusions: These long-integration observations clearly reveal a molecular layer predominantly located around 1-2 scale height, at a temperature above the CO freeze-out temperature. The deuterated molecules are closer to the mid-plane and N2D+ may be a good proxy for the CO snowline. Some molecules, such as CN and H2CO, are likely influenced by the disk environment, at least beyond the mm dust disk radius. The direct observation of the molecular stratification opens the door to detailed chemical modeling in this disk which appears representative of T Tauri disks.

The mesosphere of Venus is a critical range of altitudes in which complex temperature variability has been extensively studied by the space mission Venus Express (Vex) during its eight-years mission (2006-2014). Data collected at different epochs and latitudes show evidence of short and medium timescale variability as well as latitudinal differences. Spatial and temporal variability is also predicted in mesospheric and thermosphere terminator models with lower boundary conditions at 70 km near cloud tops. The Venus transit on June 5-6 2012 was the first to occur with a spacecraft in orbit around Venus. It has been shown that sunlight refraction in the mesosphere of Venus is able to provide useful constraints on mesospheric temperatures at the time of the transit. The European Space Agency's Venus Express provided space-based observations of Venus during the transit. Simultaneously, the Venus aureole photometry was observed using ground-based facilities and solar telescopes orbiting Earth (NASA Solar Dynamic Observatory, JAXA HINODE). As the properties of spatial and temporal variability of the mesosphere are still debated, the opportunity of observing it at all latitudes at the same time, offered by the transit, is rather unique. In this first paper, we establish new methods for analyzing the photometry of the so-called aureole that is produced by refraction of the solar light, and we investigate the choice of physical models that best reproduce the observations. We obtain an independent constraint of 4.8 +/- 0.5 km for the aerosol scale height in the upper haze region above 80 km. We show that a full multiple-layer approach is required to adequately reproduce the aureole photometry, which appears to be sensitive to several second-order variations in the vertical refractivity.

Context. Stellar internal magnetic fields have recently been shown to leave a detectable signature on period spacing patterns of gravity modes. Aims. We investigate the effect of the obliquity of a mixed (poloidal and toroidal) dipolar internal fossil magnetic field with respect to the rotation axis on the frequency of gravity modes in rapidly rotating stars. Methods. We use the traditional approximation of rotation to compute non-magnetic modes, and a perturbative treatment of the magnetic field to compute the corresponding frequency shifts. We apply the new formalism to HD 43317, a magnetic, rapidly rotating, slowly pulsating B-type star, whose field has an obliquity angle of about 80°. Results. We find that frequency shifts induced by the magnetic field on high-radial-order gravity modes are larger with increasing obliquity angle, when the magnetic axis is closer to the equatorial region, where these modes are trapped. The maximum value is reached for an obliquity angle of 90°. This trend is observed for all mode geometries. Conclusions. Our results predict that the signature of an internal oblique dipolar magnetic field is detectable using asteroseismology of gravity modes.

The goal of this white paper is to provide a snapshot of the data availability and data needs primarily for the Ariel space mission, but also for related atmospheric studies of exoplanets and brown dwarfs. It covers the following data-related topics: molecular and atomic line lists, line profiles, computed cross-sections and opacities, collision-induced absorption and other continuum data, optical properties of aerosols and surfaces, atmospheric chemistry, UV photodissociation and photoabsorption cross-sections, and standards in the description and format of such data. These data aspects are discussed by addressing the following questions for each topic, based on the experience of the "data-provider" and "data-user" communities: (1) what are the types and sources of currently available data, (2) what work is currently in progress, and (3) what are the current and anticipated data needs. We present a GitHub platform for Ariel-related data, with the goal to provide a go-to place for both data-users and data-providers, for the users to make requests for their data needs and for the data-providers to link to their available data. Our aim throughout the paper is to provide practical information on existing sources of data whether in databases, theoretical, or literature sources.

BeSS is a database containing a catalogue of Be stars and their spectra, set up more than 10 years ago as a collaboration between professional and amateur astronomers. It currently contains over 177000 spectra of 2340 stars, provided by ~150 different observers. Its continuous success has already led to the use of BeSS data in more than 70 scientific papers.

We report measured spectral properties for more than 1000 NEOs, representing>5% of the currently discovered population. Thermal flux detected below 2.5 {\mu}m allows us to make albedo estimates for nearly 50 objects, including two comets. Additional spectral data are reported for more than 350 Mars-crossing asteroids. Most of these measurements were achieved through a collaboration between researchers at the Massachusetts Institute of Technology and the University of Hawaii, with full cooperation of the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. We call this project the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS; myth-neos).