We present a detailed reanalysis of the atmospheric properties of WASP-19b, an ultra-hot Jupiter (1.14 M Jup, 1.41 R Jup) orbiting an active Sun-like star every 0.79 day. We reanalyze a transit and secondary eclipse of WASP-19b observed by the Hubble Space Telescope's Wide Field Camera 3 spectrograph (1.1 - 1.7 microns). When combined with Spitzer photometry at longer wavelengths, our analyses indicate the presence of water absorption features in both the planet's transmission and emission spectra, consistent with results from previously published studies. We jointly fit WASP-19b's dayside emission and transmission spectra with a retrieval model in order to constrain its atmospheric composition, and explore the effect of stellar activity on its transmission spectrum in greater depth. We also compare our dayside emission spectrum to predictions from a general circulation model, and conclude that magnetic drag appears to be relatively unimportant in shaping WASP-19b's atmospheric circulation. Lastly, we compare the size of WASP-19b's dayside water absorption feature to the population of hot Jupiters with similar measurements, and show that it is located in the transitional irradiation regime where temperature inversions first begin to emerge. As in previous studies, we find that the current observations provide relatively weak constraints on this planet's atmospheric properties. These constraints could be significantly improved by the addition of spectroscopically resolved observations at longer wavelengths with JWST/NIRSpec PRISM.

Recent claims of biosignature gases in sub-Neptune atmospheres have renewed interest in water-rich sub-Neptunes with surface oceans, often referred to as Hycean planets. These planets are hypothesized to form beyond the snow line, accreting large amounts of H$_2$O (>10 wt%) before migrating inward. However, current interior models often neglect chemical equilibration between primordial atmospheres and molten interiors. Here, we compute global chemical equilibrium states for a synthetic population of sub-Neptunes with magma oceans. Although many initially accrete 5-30 wt% water, interior-atmosphere interactions destroy most of it, reducing final H$_2$O mass fractions to below 1.5 wt%. As a result, none meet the threshold for Hycean planets. Despite that, we find H$_2$O-dominated atmospheres exclusively on planets that accreted the least ice. These planets form inside the snow line, are depleted in carbon and hydrogen, and develop small envelopes with envelope mass fractions below 1%, dominated by endogenic water. In contrast, planets formed beyond the snow line accrete more volatiles, but their water is largely converted to H$_2$ gas or sequestered into the interior, resulting in low atmospheric H$_2$O mass fractions. Most H$_2$O-rich envelopes are also fully miscible with H$_2$, making a separate water layer unlikely. Our results topple the conventional link between ice accretion and water-rich atmospheres, showing instead that H$_2$O-dominated envelopes emerge through chemical equilibration in hydrogen-poor planets formed inside the snow line.

We present high-resolution (0.13"-0.23") NOEMA observations of the dust continuum emission at 1.1 mm (rest-frame 220 micron) and JWST/NIRCam and MIRI imaging of the z=4.055 starburst galaxy GN20. The sensitive NOEMA imaging at 1.6 kpc resolution reveals extended dust emission, ~14 kpc in diameter (r_e~2.5 kpc, b/a=0.5), that is centrally asymmetric and clumpy. The dust emission is as extended as the stellar emission and the molecular gas traced by CO(2-1), with a common center, and is brightest in the strongly-obscured nuclear part of the galaxy. Approximately one-third of the total dust emission emerges from the nucleus and the most prominent clump to the south, and (only) 60% from the central 3.5x1.5 kpc (0.5"-0.2"), implying that the starburst is very extended. The combined JWST and NOEMA morphology suggests GN20 experienced a recent interaction or merger, likely invigorating the starburst. The radial surface brightness profiles of the molecular gas and near-IR stellar emission are similar, while in contrast, the dust emission appears significantly more concentrated. Through self-consistent radiative transfer modeling of the integrated and resolved CO and dust emission, we derive an $M_{mol}=2.9^{+0.4}_{-0.3}\times10^{11}$ Msun with $\alpha_{CO}=2.8^{+0.5}_{-0.3}$. We find that the extended dust implies a lower global dust optical depth than previously reported, but a high dust mass of $M_{dust}=5.7^{+0.8}_{-0.6}\times 10^{9}$ Msun and gas-to-dust ratio of ~50. Furthermore, we show the distinct apparent radial profiles of the gas and dust can be explained purely by radiative transfer effects and the observations are consistent with the gas and dust mass being similarly distributed throughout the starburst. The latter highlights the importance of accounting for radiative transfer effects when comparing molecular gas and dust distributions from different tracers.

Understanding the formation and evolutionary history of the Milky Way requires detailed mapping of its stellar components, which preserve fossil records of the Galaxy's assembly through cosmic time. RR Lyrae stars are particularly well-suited for this endeavor, as they are old, standard candle variables that probe the Galaxy's earliest formation epochs. In this work, we employ a hierarchical Bayesian Gaussian Mixture Model (GMM) to characterize the three-dimensional density distribution of RR Lyrae stars in the Milky Way. This approach provides a flexible framework for modeling complex stellar distributions, particularly in the inner Galaxy where the bulge, disk, and halo components overlap. Our analysis reveals that the inner Galaxy is dominated by a distinct prolate stellar population with axis ratio $q$=1.30. Consistent with previous work, we find the halo follows a $r^{-4}$ power-law profile that flattens within 12 kpc of the Galactic center. We also confirm the halo is oblate ($q$=0.62) with a tilt angle of $12.22^{\circ}$. We report for the first time that this tilt aligns the halo major axis in the direction of the Sagittarius dwarf galaxy. These results establish GMMs as an effective and flexible tool for modeling Galactic structure and provide new constraints on the distribution of old stars in the inner Galaxy.

Hot Jupiters (HJs) are $2-3\times$ less common around early M dwarfs than around AFGK stars, suggesting that HJs may form and/or migrate via distinct pathways around different types of stars. One source of insight into HJ formation mechanisms is to trace their dynamical histories through measurements of host stellar obliquities via the Rossiter-McLaughlin (RM) effect. Here we present measurements of the RM effect for the HJs TOI-3714 b and TOI-5293 A b using the Gemini-North/MAROON-X spectrograph. Our measurements represent just the second and third hot Jupiters around M dwarfs (HJMD) with a detection of the RM effect. We find that both systems are well-aligned with sky-projected obliquities of $\lambda = 21^{+14}_{-11}$$\mathrm{^{\circ}}$ and $-12^{+19}_{-14}$$\mathrm{^{\circ}}$ and deprojected obliquities of $\psi = 26^{+11}_{-10}$$\mathrm{^{\circ}}$ and $24^{+11}_{-10}$$\mathrm{^{\circ}}$ for TOI-3714 and TOI-5293 A, respectively. Both stars are in wide binary systems. We refine the stellar parameters by decontaminating their unresolved $K_s$-band photometry and constrain the binary orbits using Gaia DR3 astrometry. We find that the minimum mutual inclination of the planet and binary companion in the TOI-5293 system is sufficiently large to drive Kozai-Lidov (KL) migration while the result for TOI-3714 is inconclusive. We present a population-level analysis of HJs around AFGK versus early M dwarfs and argue that KL migration is more efficient around the latter, which is expected to produce misaligned stellar obliquities in HJMD systems in the absence of efficient tidal damping. The emerging population of well-aligned HJMD hosts supports the expectation that M dwarfs, with their deep convective envelopes, do efficiently dampen misaligned obliquities.

We present a new, all-sky quasar catalog, Quaia, that samples the largest comoving volume of any existing spectroscopic quasar sample. The catalog draws on the 6,649,162 quasar candidates identified by the Gaia mission that have redshift estimates from the space observatory's low-resolution BP/RP spectra. This initial sample is highly homogeneous and complete, but has low purity, and 18% of even the bright (G<20.0) confirmed quasars have discrepant redshift estimates (|\Delta z/(1+z)|>0.2) compared to those from the Sloan Digital Sky Survey (SDSS). In this work, we combine the Gaia candidates with unWISE infrared data (based on the Wide-field Infrared Survey Explorer survey) to construct a catalog useful for cosmological and astrophysical quasar studies. We apply cuts based on proper motions and Gaia and unWISE colors, reducing the number of contaminants by $\sim$4$\times$. We improve the redshifts by training a $k$-nearest neighbors model on SDSS redshifts, and achieve estimates on the G<20.0 sample with only 6% (10%) catastrophic errors with |\Delta z/(1+z)|>0.2 ($0.1$), a reduction of $\sim$3$\times$ ($\sim$2$\times$) compared to the Gaia redshifts. The final catalog has 1,295,502 quasars with G<20.5, and 755,850 candidates in an even cleaner G<20.0 sample, with accompanying rigorous selection function models. We compare Quaia to existing quasar catalogs, showing that its large effective volume makes it a highly competitive sample for cosmological large-scale structure analyses. The catalog is publicly available at this https URL.

The Gaia Galactic survey mission is designed and optimized to obtain astrometry, photometry, and spectroscopy of nearly two billion stars in our Galaxy. Yet as an all-sky multi-epoch survey, Gaia also observes several million extragalactic objects down to a magnitude of G~21 mag. Due to the nature of the Gaia onboard selection algorithms, these are mostly point-source-like objects. Using data provided by the satellite, we have identified quasar and galaxy candidates via supervised machine learning methods, and estimate their redshifts using the low resolution BP/RP spectra. We further characterise the surface brightness profiles of host galaxies of quasars and of galaxies from pre-defined input lists. Here we give an overview of the processing of extragalactic objects, describe the data products in Gaia DR3, and analyse their properties. Two integrated tables contain the main results for a high completeness, but low purity (50-70%), set of 6.6 million candidate quasars and 4.8 million candidate galaxies. We provide queries that select purer sub-samples of these containing 1.9 million probable quasars and 2.9 million probable galaxies (both 95% purity). We also use high quality BP/RP spectra of 43 thousand high probability quasars over the redshift range 0.05-4.36 to construct a composite quasar spectrum spanning restframe wavelengths from 72-100 nm.

The low equilibrium temperatures of temperate sub-Neptunes lead to extremely long chemical timescales in their upper atmospheres, causing the abundances of chemical species to be strongly shaped by atmospheric transport. Here, we used a three-dimensional (3D) general circulation model involving a passive tracer to investigate the atmospheric circulation and 3D transport of temperate gas-rich sub-Neptunes, using K2-18b as an example. We model K2-18b as a synchronous or asynchronous rotator, exploring spin-orbit resonances (SOR) of 2:1, 6:1, and 10:1. We find that the strong absorption of CO$_2$ and CH$_4$ induces a detached convective zone between 1 and 5 bar, resulting in strong vertical mixing at these levels. The upper atmosphere is dominated by eastward winds (an equatorial superrotating jet present in all simulations), leading to warmer evening terminators and approximately 20% higher passive tracer mass mixing ratios compared to the morning terminators. Rotation rates have minimal impact on the strength of global mean vertical mixing, but significantly influence the latitudinal distribution of passive tracers. For synchronous, 2:1 SOR, and 6:1 SOR simulations, passive tracers are more abundant in the upwelling branches at latitudes within 60$^\circ$, while for the 10:1 SOR simulation, strong transient eddies at high latitudes (>70$^\circ$) between 0.1 to 1 bar can transport passive tracers upward from the deep atmosphere, making them more abundant there, despite their alignment with the downwelling branch of the large-scale circulation. This study focuses on the atmospheric dynamics and its influence on passive tracer transport, while a follow-up paper will incorporate active chemical species.

Periodic variability in active galactic nuclei (AGN) light curves has been proposed as a signature of close supermassive black hole (SMBH) binaries. Recently, 181 candidate SMBH binaries were identified in Gaia DR3 based on periodicity in their $\sim$1000-day light curves. By supplementing Gaia photometry with longer-baseline light curves from the Zwicky Transient Facility (ZTF) and the Catalina Real Time Transient Survey (CRTS), we test whether the reported periodic signals persist beyond the Gaia DR3 time window. We find that in all 116 cases with available ZTF data, the Gaia-inferred periodic model fails to predict subsequent variability, which appears stochastic rather than periodic. The periodic candidates thus overwhelmingly appear to be false positives; red noise contamination appears to be the primary source of false detections. We conclude that truly periodic AGN are exceedingly rare, with at most a few in $10^6$ AGN exhibiting stable periodicity on 100 to 1000 day timescales. Models predict that the Gaia AGN light curve sample should contain dozens of true SMBH binaries with periods within the observational baseline, so the lack of strictly periodic light curves in the sample suggests that most short-period binary AGN do not have light curves dominated by simple periodicity.

The canonical formation of second-generation (G2) stars in globular clusters (GCs) from gas enriched and ejected by G1 (primordial) polluters faces substantial challenges, i.e. (i) a mass-budget problem and (ii) uncertainty in the source(s) of the abundance anomaly of light elements (AALE) in G2 stars. The merger of G1 low-mass main-sequence (MS) binaries can overcome (i), but its ability to result in AALE is omitted. We provide evidence of the merger process to explain AALE by relying on highly probable merger remnants in the Galactic disk. We focus on carbon-deficient red-clump giants with low mass of 1.0 M_{\sun} < M $\lesssim$ 2.0 M_{\sun} and hot He-intermediate subdwarfs of supersolar metallicity, both manifesting G2-like AALE incompatible with GC origin. The origin of such rare core He-burning stars as the mergers of [MS star (MSS)]+[helium white dwarf (HeWD)] binaries, evolved from low-mass high-mass ratio (MSS+MSS) ones, is supported by models evolving to either horizontal branch (HB) stars or He subdwarfs via the red giant branch (RGB). Such binaries in the GC NGC 362 contain very young ($\sim$ 4 Myr) extremely low-mass HeWDs, in contrast to much older ($\sim 100$ times) counterparts in open clusters. This agrees with the impact of GC environment on the lifetime of hard binaries: (MSS+HeWD) systems merge there soon after arising from (MSS+MSS) binaries that underwent the common-envelope stage of evolution. From the number and lifetime of the (MSS+HeWD) binaries uncovered in NGC 362, the expected fraction of their progeny RGB G2 stars is estimated to be $\lesssim$10\%. The field merger remnants with G2-like AALE support the merger nature of at least a fraction of G2 stars in GCs. The specific channel [(MSS+MSS) - (MSS+HeWD) - merger product] supported by observations and models is tentatively identified as the channel of formation of the extreme G2 RGB component in GCs.

LTT-9779 b is an ultra-hot Neptune (Rp ~ 4.7 Re, Mp ~ 29 Me) orbiting its Sun-like host star in just 19 hours, placing it deep within the "hot Neptune desert," where Neptunian planets are seldom found. We present new JWST NIRSpec G395H phase-curve observations that probe its atmospheric composition in unprecedented detail. At near-infrared wavelengths, which penetrate the high-altitude clouds inferred from previous NIRISS/SOSS spectra, thermal emission reveals a carbon-rich atmosphere with opacity dominated by carbon monoxide (CO) and carbon dioxide (CO2). Both species are detected at all orbital phases, with retrieved mixing ratios of 10^-1 for CO and 10^-4 for CO2, indicating a globally well-mixed reservoir of carbon-bearing gases. We also moderately detect water vapor (H2O) and tentatively detect sulfur dioxide (SO2), providing insight into its chemistry and possible photochemical production under intense stellar irradiation. From these detections we infer a carbon-to-oxygen ratio near unity (C/O ~ 1) and a metallicity exceeding 500X Solar, consistent with equilibrium chemistry predictions for high-temperature atmospheres. This enrichment raises the mean molecular weight, reducing atmospheric escape, and likely helps LTT-9779 b retain a substantial atmosphere despite extreme irradiation. Our findings show that LTT-9779 b survives where few planets can, maintaining a carbon-rich atmosphere in a region where hot Neptune-class worlds are expected to evaporate. This makes LTT-9779 b a valuable laboratory for studying atmospheric escape and chemical processes under extreme conditions, offering new insight into the survival of planets in the hot Neptune desert.

We present observations and detailed modeling of a protoplanetary disk around the T Tauri star, V1098 Sco. Millimeter wavelength data from the Atacama Large Millimeter Array (ALMA) show a ring of large dust grains with a central cavity that is filled with molecular gas. Near-infrared data with the Very Large Telescope (VLT) detect the scattered starlight from the disk surface and reveal a large shadow that extends over it's entire southern half. We model the ALMA continuum and line data to determine the outer disk geometry and the central stellar mass. Using radiative transfer models, we demonstrate that a misaligned inner disk, tilted in both inclination and position angle with respect to the outer disk, can reproduce the salient scattered light features seen with the VLT. Applying an image threshold algorithm to compare disk morphologies and training a neural network on a set of high signal-to-noise models, we forward model the data and determine the inner disk geometry. We find that the rotation axes of the inner and outer disks are misaligned by 38 degrees and constrain the mass and location of a perturbing planetary or substellar companion. The technique of simulation based inference that is illustrated here is broadly applicable for radiative transfer modeling of other objects.

As the statistical precision of cosmological measurements increases, the accuracy of the theoretical description of these measurements needs to increase correspondingly in order to infer the underlying cosmology that governs the Universe. To this end, we have created the Cosmology Likelihood for Observables in Euclid (CLOE), which is a novel cosmological parameter inference pipeline developed within the Euclid Consortium to translate measurements and covariances into cosmological parameter constraints. In this first in a series of six papers, we describe the theoretical recipe of this code for the Euclid primary probes. These probes are composed of the photometric 3x2pt observables of cosmic shear, galaxy-galaxy lensing, and galaxy clustering, along with spectroscopic galaxy clustering. We provide this description in both Fourier and configuration space for standard and extended summary statistics, including the wide range of systematic uncertainties that affect them. This includes systematic uncertainties such as intrinsic galaxy alignments, baryonic feedback, photometric and spectroscopic redshift uncertainties, shear calibration uncertainties, sample impurities, photometric and spectroscopic galaxy biases, as well as magnification bias. The theoretical descriptions are further able to accommodate both Gaussian and non-Gaussian likelihoods and extended cosmologies with non-zero curvature, massive neutrinos, evolving dark energy, and simple forms of modified gravity. These theoretical descriptions that underpin CLOE will form a crucial component in revealing the true nature of the Universe with next-generation cosmological surveys such as Euclid.

Rocky exoplanet characterization has been a top priority for early James Webb Space Telescope (JWST) science operations. Several milestones have been achieved, including the most precise rocky planet transmission spectra measured to date, and the first detection of thermal emission for rocky worlds below 800 Kelvin. Despite these advances, no atmospheres have been definitively detected. Several transmission spectra show tentative evidence for molecular absorption features, but these hints are marginally significant and the spectra may be affected by stellar contamination. Features from many plausible atmospheres, including those dominated by oxygen, nitrogen, and carbon dioxide, are below the current noise level. Meanwhile, the emerging picture from thermal emission spectra is that the planets have hot daysides, consistent with either a bare rock composition or low surface pressure atmospheres (< 10 bar). Higher surface pressures and high carbon dioxide abundances are generally ruled out, assuming cloud-free atmosphere models. The absence of strong CO$_2$ features hints at a limited initial volatile inventory or rapid atmospheric escape during the planets' early lifetimes. Taken together, these results motivate a push towards higher precision data, as well as observations of cooler planets that may be more likely to retain atmospheres. As a goal for future transmission spectroscopy, we suggest a "five scale height challenge," to achieve the precision necessary to detect CO$_2$ features in nitrogen-rich atmospheres. Detecting rocky planet atmospheres remains challenging, but with JWST's excellent performance and a continuing investment of telescope time, we are optimistic these uncharted atmospheres will be detected in coming years.

Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array (JVLA) have revealed many dust rings in protoplanetary disks, often interpreted as dust traps at gas pressure bumps. Previous studies have typically modeled these rings by assuming a single dust species in drift-diffusion equilibrium, neglecting dust size evolution resulting from coagulation and fragmentation. In this work, we perform numerical simulations that incorporate both dust-gas dynamics (drift and diffusion) and dust size evolution. Our results show that the radial distributions of different dust species (up to the fragmentation limit) are nearly identical in the dust ring, as dust growth dominates over drift and diffusion (e.g., with a typical dust-to-gas ratio of $\epsilon \sim 10^{-2}$). Building on this finding, we develop a comprehensive, self-consistent analytical theory that describes the dust ring structure while explicitly accounting for size evolution effects. Our model provides a unified framework for interpreting multi-wavelength observations by linking the physical dust distribution to the observed ring properties, thus laying the foundation for future observational modeling.