Table of contents for issue 3, volume 169, The Astronomical Journal

As demonstrated with the Sloan Digital Sky Survey (SDSS), Pan-STARRS, and most recently with Gaia data, broadband near-UV to near-IR stellar photometry can be used to estimate distance, metallicity, and interstellar dust extinction along the line of sight for stars in the Galaxy. Anticipating photometric catalogs with tens of billions of stars from Rubin's Legacy Survey of Space and Time (LSST), we present a Bayesian model and pipeline that build on previous work and can handle LSST-sized datasets. Likelihood computations utilize MIST/Dartmouth isochrones and priors are derived from TRILEGAL-based simulated LSST catalogs from P. Dal Tio et al. The computation speed is about 10 ms per star on a single core for both optimized grid search and Markov Chain Monte Carlo methods; we show in a companion paper by K. Mrakovčić et al. how to utilize neural networks to accelerate this performance by up to an order of magnitude. We validate our pipeline, named PhotoD (in analogy with photo-z, photometric redshifts of galaxies) using both simulated catalogs and SDSS, DECam, and Gaia photometry. We intend to make LSST-based value-added PhotoD catalogs publicly available via the Rubin Science Platform with every LSST data release.

Suspended dust is a vital component of Martian climatic system and its temporal-spatial variation can influence the recession of the South Polar Seasonal Cap (SPSC). However, dust activity varies across different stages and years, affecting the SPSC recession process differently. Continuous observations of SPSC/South Polar Residual Cap (SPRC) across several Martian years, alongside segmented analyses of annual dust activity, will provide new insights into the climate conditions of Martian south polar region. Here, we performed a combined analysis on the extents of SPSC from MY28-MY31 and MY36, together with the concurrent Martian atmospheric optical thickness, to assess the influence of dust activity at various recession time steps. Results show that dust activity peaks in both spring and summer can impact the SPSC/SPRC recession. The recession process is accelerated if the dust activity peak occurs earlier. If the timing of the peak dust activity is identical, the intensity of the dust activity influences the recession. Specific regions, such as the “Cryptic Region” and the Mountains of Mitchel, respond uniquely to dust activity. Higher dust intensity slows the recession of the Cryptic Region, while the SPSC in the Mountains of Mitchel area shows variability in recession timing based on local dust activity intensity. This research provides observational constraints that enhance our understanding of Martian atmospheric circulation and can potentially aid the future development of polar dust activity models.

Modern telescopes generate catalogs of millions of objects with the potential for new scientific discoveries, but this is beyond what can be examined visually. Here we introduce ASTRONOMALY: PROTEGE, an extension of the general-purpose machine-learning-based active anomaly detection framework ASTRONOMALY. PROTEGE is designed to provide well-selected recommendations for visual inspection, based on a small amount of optimized human labeling. The resulting sample contains rare or unusual sources that are simultaneously as diverse as the human trainer chooses and of scientific interest to them. We train PROTEGE on images from the MeerKAT Galaxy Cluster Legacy Survey, leveraging the self-supervised deep learning algorithm Bootstrap Your Own Latent to find a low-dimensional representation of the radio galaxy cutouts. By operating in this feature space, PROTEGE is able to recommend interesting sources with completely different morphologies in image space to those it has been trained on. This provides important advantages over similarity searches, which can only find more examples of known sources, or blind anomaly detection, which selects unusual but not necessarily scientifically interesting sources. Using an evaluation subset, we show that, with minimal training, PROTEGE provides excellent recommendations and find that it is even able to recommend sources that the authors missed. We briefly highlight some of PROTEGE's top recommendations, which include X- and circular-shaped sources, filamentary structures, and one-sided structures. These results illustrate the power of an optimized human-machine collaboration, such as PROTEGE, to make unexpected discoveries in samples beyond human-accessible scales.

Developing algorithms to search through data efficiently is a challenging part of searching for signs of technology beyond our solar system. We have built a digital signal processing system and computer cluster on the backend of the Karl G. Jansky Very Large Array (VLA) in New Mexico in order to search for signals throughout the Galaxy consistent with our understanding of artificial radio emissions. In our first paper, we described the system design and software pipelines. In this paper, we describe a postprocessing pipeline to identify persistent sources of interference, filter out false positives, and search for signals not immediately identifiable as anthropogenic radio frequency interference during the VLA Sky Survey. As of 2024 September 1, the Commensal Open-source Multi-mode Interferometric Cluster had observed more than 950,000 unique pointings. This paper presents the strategy we employ when commensally observing during the VLA Sky Survey and a postprocessing strategy for the data collected during the survey. To test this postprocessing pipeline, we searched toward 511 stars from the Gaia catalog with coherent beams. This represents about 30 minutes of observation during the VLA Sky Survey, where we typically observe about 2000 sources hr^–1 in the coherent beamforming mode. We did not detect any unidentifiable signals, setting isotropic power limits ranging from 10¹¹ to 10¹⁶ W.

Equipping sensors on the lunar surface would enable the capture of Earth’s outgoing longwave radiation (OLR) from nearly an entire hemisphere. However, the Earth’s nonsphericity would profoundly impact the observational solid angle, thereby influencing the disk-integrated Earth OLR estimation. This study analyzes the impact of the Earth’s ellipsoidal shape on the OLR estimation by examining the effects of the observational solid angle. In particular, an expansion-series-based method is proposed for calculating the observational solid angle, avoiding complex numerical integration. Three critical issues are analyzed. (1) Comparing the observational solid angles calculated by using an Earth ellipsoidal model versus those obtained by adjusting the Earth’s radius. We find that adjusting the Earth’s radius can approximate the results based on an Earth ellipsoidal model, offering insights into parameterizing the observational solid angle. (2) Parameterizing the observational solid angle through series expansion, which is validated by comparing the associated results to those from numerical integrations. The observational solid angle is parameterized into two components: one is attributable to a variable Earth radius and another is related to the nadir point’s latitude and the Earth–Moon distance. (3) Guiding parameter selection for observational solid angle estimation. These findings enhance our understanding of disk-integrated Earth OLR estimates and provide a unique tool for establishing benchmarks for the Earth samples needed in the study of habitable planets, thereby contributing to sustainable development.

Joint analysis of position measurements and radial velocities of six triple stellar systems is conducted to determine their inner and/or outer orbits. Accumulation of such data is needed to study the architecture of stellar hierarchies and its relation to the formation mechanisms. The inner periods in the six systems (HIP 11783, 64836, 72423, 84720, 89234, and 105404) range from 0.5 days to 44 yr. The shortest outer period of 3.34 yr is found in the compact triple HIP 105404 (BS Ind). The resolved triple system HIP 64836 has comparable inner and outer periods (5 and 30 yr), placing it near the limit of dynamical stability, while its quasi-circular and coplanar orbits suggest a 1:6 mean motion resonance. The periods in HIP 89234 (44 and ~450 yr) are also comparable, but the mutual orbit inclination is large, 54°. Masses of the components are estimated and each system is discussed individually.

Terrestrial planets in the habitable zone (HZ) of Sun-like stars are priority targets for detection and observation by the next generation of space telescopes. Earth's long-term habitability may have been tied to the geological carbon cycle, a process critically facilitated by plate tectonics. In the modern Earth, plate motion corresponds to a mantle convection regime called mobile lid. The alternate, stagnant-lid regime is found on Mars and Venus, which may have lacked strong enough weathering feedback to sustain surface liquid water over geological timescales if initially present. Constraining observational strategies able to infer the most common regime in terrestrial exoplanets requires quantitative predictions of the atmospheric composition of planets in either regime. We use end-member models of volcanic outgassing and crust weathering for the stagnant- and mobile-lid convection regimes, which we couple to models of atmospheric chemistry and climate and ocean chemistry to simulate the atmospheric evolution of these worlds in the HZ. In our simulations under the two alternate regimes, we find that the fraction of planets possessing climates consistent with surface liquid water is virtually the same. Despite this unexpected similarity, we predict that a mission capable of detecting atmospheric CO₂ abundance above 0.1 bar in 25 terrestrial exoplanets is extremely likely (≥95% of samples) to infer the dominant interior convection regime in that sample with strong evidence (10:1 odds). This offers guidance for the specifications of the Habitable Worlds Observatory NASA concept mission and other future missions capable of probing samples of habitable exoplanets.

The composition inside a comet nuclear can be detected through the molecular rotational emission lines at millimeter or submillimeter wavelengths. We observed a long-period comet C/2022 E3 (ZTF) using the Purple Mountain Observatory 13.7 m radio telescope at 3.4 mm during mid January and early February in 2023. From the observed spectra, the hydrogen cyanide (HCN)(J = 1–0) spectra lines was detected. The mean production rate of HCN is (8.30 ± 1.14) × 10²⁵ molec. ​s⁻¹ in mid January and (3.91 ± 0.84) × 10²⁵ molec. ​​​s⁻¹ in early February. we also estimated the upper limit of the production rate of HCO+. We obtained the abundance of HCN relative to water, (0.13 ± 0.02)% in mid January when C/2022 E3 (ZTF) got close to the Sun at 1.11 au, and (0.13 ± 0.03)% in early February at 1.16 au. Our conclusion leans toward E3 being similar to most comets, with the abundance of HCN remaining stable during our two observation periods.

We obtained new spectra of Kepler-34 and Kepler-35 with Keck-HIRES—nearly a decade after these systems were originally characterized with this spectrograph and other instruments—to search for radial velocity (RV) trends from a potential third stellar-mass companion at long periods. For Kepler-34, we rule out coplanar stellar masses as low as 0.12M_⊙ at an orbital period of  ≲52 yr. For Kepler-35, we rule out stellar masses of 0.13M_⊙ at orbital periods of  ≲55 yr. Highly stable, extreme precision RV instruments, as well as improved methodologies in characterizing double-lined spectroscopic binaries that come with these new instruments, will provide an opportunity to push these mass limits lower in the future.

Luminous blue variables (LBVs) are enigmatic, evolved, massive stars. Their variability has been observed to be episodic with large eruptions, along with variations on timescales of days to decades. We have extracted light curves of 37 LBVs from the first 4 yr of the TESS mission. These light curves provide two years of photometric time series for stars in the LMC, with several months of data for Galactic or SMC targets. We analyze the Fourier properties of the stellar light curves to determine their characteristic frequencies and red noise amplitudes, comparing them to mass-loss parameters through Hα strength, and in the case of the LMC stars, B − V color and luminosity as estimated by their apparent g magnitudes. We confirm the absence of correlation between any of the Fourier parameters and stellar parameters, implying that there is no trend in how these stars vary as measured with these photometric data, which may point toward these stars being an extension to the supergiant α Cygni variables and not a unique class of object with regards to their short-term variations.

Since the advent of Gaia catalog, positional precision of a ground-based telescope can be greatly improved by correction of more subtle errors, including positional biases induced by atmospheric turbulence, and some instrumental factors such as geometric distortion and the charge transfer efficiency. In our previous work, the correlation of positional precision as a function of two objects’ separation is studied and found to be effectively modeled by a sigmoidal function, which provides a good description of this rule. Based on our understanding of the physics of the precision premium, we further refine the astrometric approach in this paper, which determines a target's position in a small region through a weighting scheme. Based on the reductions of the observations of several open clusters and Himalia, Jupiter's largest irregular satellite, the refined approach has demonstrated substantial improvements in positional precision, particularly in scenarios where a sufficient number of reference stars are present in dense fields. We suspect that the contributing factor might be the refined approach's ability to mitigate not only turbulence effects but instrumental effects as well, prevalent among closely spaced star images, given that the approach focuses on localized measurements within a confined area.

Reconstructing the signal from measured visibilities in radio interferometry is an ill-posed inverse problem. In this paper, we present a novel radio-interferometric imaging method based on the wavelet tight frame aimed at efficiently obtaining an accurate solution. In our approach, the signal is sparsely represented by the directional tensor product complex tight framelets, which can effectively capture the texture and shape features of the images. To enhance computational efficiency, we employ the projected fast iterative soft-thresholding algorithm for solving the l₁-norm minimization problem. Several simulation experiments are carried out to verify the effectiveness and performance of the proposed method.

We present an analysis of adaptive optics images from the Keck I telescope of the microlensing event MOA-2011-BLG-262. The original discovery paper by Bennett et al. reports two possibilities for the lens system: a nearby gas giant lens with an exomoon companion or a very low-mass star with a planetary companion in the Galactic bulge. The ∼10 yr baseline between the microlensing event and the Keck follow-up observations allows us to detect the faint candidate lens host (star) at K = 22.3 mag and confirm the distant lens system interpretation. The combination of the host star brightness and light curve parameters yields host star and planet masses of M_host = 0.19 ± 0.03 M_⊙ and m_p = 28.92 ± 4.75 M_⊕ at a distance of D_L = 7.49 ± 0.91 kpc. We perform a multiepoch cross reference to Gaia Data Release 3 and measure a transverse velocity for the candidate lens system of v_L = 541.31 ± 65.75 km s⁻¹. We conclude this event consists of the highest-velocity exoplanet system detected to date, and also the lowest-mass microlensing host star with a confirmed mass measurement. The high-velocity nature of the lens system can be definitively confirmed with an additional epoch of high-resolution imaging at any time now. The methods outlined in this work demonstrate that the Roman Galactic Exoplanet Survey will be able to securely measure low-mass host stars in the bulge.

The inflated radii of hot Jupiters have been explored by various theoretical mechanisms. By connecting planetary thermal evolution models with the observed properties of hot Jupiters using hierarchical Bayesian models, a theoretical parameter called the heating efficiency has been introduced to describe the heating of the interiors of these planets. Previous studies have shown that the marginal distribution of this heating-efficiency parameter has a single-peak distribution along the planetary equilibrium temperature (T_eq). Since the observed properties of hot Jupiters are the foundation of these Bayesian inference models, there must be a corresponding feature in the observed data that leads to the inferred single-peak distribution of the heating efficiency. This study aims to find the underlying cause of the single-peak heating-efficiency distribution without relying on specific theoretical models. By analyzing the relationships between different observed physical properties, we obtain a similar single-peak distribution of the radius expansion efficiency of hot Jupiters along T_eq, which can be explained by the correlation with the stellar effective temperature. However, a detailed investigation suggests that this single-peak distribution is actually the result of straightforward physical processes. Specifically, the increase in heating efficiency can be attributed to the increase in incident stellar flux, while the decrease in heating efficiency can be attributed to the rise in the gravitational binding energy associated with the increase in planetary mass.

We present a comparison of observed polycyclic aromatic hydrocarbon (PAH) feature ratios in 19 nearby galaxies with a grid of theoretical expectations for near- and mid-infrared dust emission. The PAH feature ratios are drawn from Cycle 1 JWST observations and are measured for 7224 stellar clusters and 29,176 stellar associations for which we have robust ages and mass estimates from Hubble Space Telescope five-band photometry. Though there are galaxy-to-galaxy variations, the observed PAH feature ratios largely agree with the theoretical models, particularly those that are skewed toward more ionized and larger PAH size distributions. For each galaxy we also extract PAH feature ratios for 200 pc wide circular regions in the diffuse interstellar medium, which serve as a noncluster/association control sample. Compared to what we find for stellar clusters and associations, the 3.3 μm/7.7 μm and 3.3 μm/11.3 μm ratios from the diffuse interstellar medium are ∼0.10–0.15 dex smaller. When the observed PAH feature ratios are compared to the radiation field hardness as probed by the [O iii]/Hβ ratio, we find anticorrelations for nearly all galaxies in the sample. These results together suggest that the PAH feature ratios are driven by the shape and intensity of the radiation field and that the smallest PAHs—observed via JWST F335M imaging—are increasingly “processed” or destroyed in regions with the most intense and hard radiation fields.

One of the most prolific methods of studying exoplanet atmospheres is transmission spectroscopy, which measures the difference between the depth of an exoplanet's transit signal at various wavelengths and attempts to correlate the depth changes to potential features in the exoplanet's atmosphere. Here we present reconnaissance observations of 21 exoplanet atmospheres measured with the Exoplanet Transmission Spectroscopy Imager (ETSI), a recently deployed spectrophotometer on the McDonald Observatory Otto Struve 2.1 m telescope. ETSI measurements are mostly free of systematics through the use of a novel observing technique called common-path multiband imaging (CMI), which has been shown to achieve photometric color precision on par with space-based observations (300 ppm or 0.03%). This work also describes the various statistical tests performed on the data to evaluate the efficacy of the CMI method and the ETSI instrument in combination. We find that none of the eight comparisons of exoplanet atmospheres measured with ETSI and other observatories (including the Hubble Space Telescope) provide evidence that the spectra are statistically dissimilar. These results suggest that ETSI can provide initial transmission spectroscopy observations for a fraction of the observational and monetary overhead previously required to detect an exoplanet's atmosphere. Ultimately these reconnaissance observations increase the number of planets with transmission spectroscopy measurements by ~10% and provide an immediate prioritization of 21 exoplanets for future follow-up with more precious observatories, such as the James Webb Space Telescope. The reconnaissance spectra are available through the Filtergraph visualization portal at the URL https://filtergraph.com/etsi/.

Ground-based high-resolution cross-correlation spectroscopy (HRCCS; R ≳ 15,000) is a powerful complement to space-based studies of exoplanet atmospheres. By resolving individual spectral lines, HRCCS can precisely measure chemical abundance ratios, directly constrain atmospheric dynamics, and robustly probe multidimensional physics. But the subtleties of HRCCS data sets—e.g., the lack of exoplanetary spectra visible by eye and the statistically complex process of telluric removal—can make interpreting them difficult. In this work, we seek to clarify the uncertainty budget of HRCCS with a forward-modeling approach. We present an HRCCS observation simulator, scope,⁵that incorporates spectral contributions from the exoplanet, star, tellurics, and instrument. This tool allows us to control the underlying data set, enabling controlled experimentation with complex HRCCS methods. Simulating a fiducial hot Jupiter data set (WASP-77Ab emission with IGRINS), we first confirm via multiple tests that the commonly used principal component analysis does not bias the planetary signal when few components are used. Furthermore, we demonstrate that mildly varying tellurics and moderate wavelength solution errors induce only mild decreases in HRCCS detection significance. However, limiting-case, strongly varying tellurics can bias the retrieved velocities and gas abundances. Additionally, in the low signal-to-noise ratio limit, constraints on gas abundances become highly non-Gaussian. Our investigation of the uncertainties and potential biases inherent in HRCCS data analysis enables greater confidence in scientific results from this maturing method.

The SKYSURF project constrained extragalactic background light and diffuse light (DL) with the vast archive of Hubble Space Telescope (HST) images. Thermal emission from HST itself introduces an additional uncertain background and hinders accurate measurement of the DL level. Here, we use archival Wide Field Camera 3 (WFC3)/IR engineering data to investigate and model changes in the temperature of various components in HSTs optical path as a function of time (solar cycle) and time of the year (Earth–Sun distance). We also specifically investigate changes in temperature with HST's orbital phase and time since Earth occultation. We investigate possible correlations between HST component temperature and year, and temperature and month. The thermal background changes by less than one Kelvin in the WFC3 pickoff mirror, one of the most important contributors to the thermal background. We model these data to describe the impact that orbital phase, year, and time of year have on the HST and WFC3 component temperatures, and use this to derive the impact on the thermal dark signal and the resulting DL measurements. Based on this improved modeling, we provide new upper limits on the level of DL of 21, 32, and 25 nW m⁻² sr⁻¹ for F125W, F140W, and F160W. Additionally, by accounting for all known sources of measurement uncertainty, we report lower limits on the level of DL of 12, 20, and 2 nW m⁻² sr⁻¹ for F125W, F140W, and F160W.

We observed the planet-hosting system PDS 70 with the James Webb Interferometer, JWST's aperture masking interferometric mode within NIRISS. Observing with the F480M filter centered at 4.8 μm, we simultaneously fit geometrical models to the outer disk and the two known planetary companions. We redetect the protoplanets PDS 70 b and c at a signal-to-noise ratio (SNR) of 14.7 and 7.0, respectively. Our photometry of both PDS 70 b and c provides tentative evidence of mid-IR circumplanetary disk emission through fitting spectral energy distribution models to these new measurements and those found in the literature. We also newly detect emission within the disk gap at an SNR of ~4, a position angle of °, and an unconstrained separation within ~200 mas. Follow-up observations will be needed to determine the nature of this emission. We place a 5σ upper limit of 208 ± 10 μJy on the flux of the candidate PDS 70 d at 4.8 μm, which indicates that if the previously observed emission at shorter wavelengths is due to a planet, this putative planet has a different atmospheric composition than PDS 70 b or c. Finally, we place upper limits on emission from any additional planets in the disk gap. We find an azimuthally averaged 5σ contrast upper limit >7 mag at separations greater than 110 mas. These are the deepest limits to date within ~250 mas at 4.8 μm and the first space-based interferometric observations of this system.

This study investigates the structural parameters of the thin-disk population by analyzing the spatial distribution of evolved stars in the solar neighborhood. From the Gaia Data Release 3 database, about 39.1 million stars within 1 kpc and with relative parallax errors σ_ϖ/ϖ ≤ 0.10 were selected. The photometric data was corrected for extinction using a Galactic dust map. The sample was refined by considering the color–magnitude region associated with evolved stars, applying a stricter parallax error limit of σ_ϖ/ϖ ≤ 0.02, and yielding 671,600 stars. The star sample was divided into 36 regions based on their Galactic coordinates, with evolved stars in the absolute magnitude range of −1 < M_G (mag) ≤ 4 further split into five one-unit magnitude intervals. This led to 180 subgroups whose space-density profiles were modeled using a single-component Galaxy model. The analysis shows that the space densities are in agreement with the literature and that the scale heights vary with 200 < H (pc) < 600 interval to their absolute magnitudes. Red clump stars in the solar neighborhood were also estimated to have a scale height of 295 ± 10 pc. These findings indicate that evolved stars with bright absolute magnitudes originate from the evolution of the early spectral-type stars with short scale height, while fainter ones come from the evolution of the intermediate spectral-type stars with large scale height, suggesting that variations in scale height reflect the contribution of Galactic evolution processes.

With the development of wide-field surveys, a large amount of data on short-period W UMa contact binaries have been obtained. Continuous and uninterrupted light curves as well as high-resolution spectroscopic data are crucial in determining the absolute physical parameters. Targets with both TMTS light curves and LAMOST medium-resolution spectra were selected. The absolute physical parameters were inferred with the W-D code for 10 systems, all of them are W-type shallow or medium contact binaries. The O’Connell effect observed in the light curves can be explained by adding a spot on the primary or secondary component in the models. According to O − C analysis, the orbital periods exhibit a long-term increasing or decreasing trend, among which J0132, J1300, and J1402 show periodic variations that may be attributed to the presence of a third body or magnetic activity cycles. Spectral subtraction analysis revealed that the equivalent width of Hα indicates strong magnetic activity in J0047, J0305, J0638, and J1402. Among the 10 selected binary systems, except for J0132 and J0913, the more massive components are found to be main-sequence stars while the less massive components have evolved off the main sequence. In J0132, both components are in the main sequence, whereas both components of J0913 lie above the terminal-age main sequence. Based on the relationship between orbital angular momentum and total mass for these two systems, as well as their low fill-out factors, it is possible that these two systems are newly formed contact binaries, having recently evolved from the detached configuration.

Asymptotic giant branch (AGB) stars are the primary source of dust and complex molecules in the interstellar medium. The determination of outflow parameters is often hindered by the unknown geometry of the circumstellar environment, creating a demand for high-angular resolution observations. We use our near-infrared spectra and photometry of the carbon AGB star V Cyg, along with literature data, to construct its spectral energy distribution over a wide range of wavelengths. The dust envelope responsible for the infrared excess was also resolved in scattered polarized light at angular scales of 50–80 mas using differential speckle polarimetry. We present an interpretation of the thermal and scattered radiation of the dust using models of a spherical dusty outflow (M_dust = 5.3 × 10⁻⁷M_⊙) and an inclined equatorial density enhancement, either in the form of a disk (M_dust = 7.6 × 10⁻³M_⊕) or a torus (M_dust = 5.7 × 10⁻³M_⊕), which material is concentrated at stellocentric distances less than 25 au. The dust material consists of amorphous carbon and SiC, with 84% of the dust being amorphous carbon. Dust particle radii range from 5 to 950 nm and follow a power law with an exponent of −3.5. Modeling the envelope allowed us to improve the accuracy of stellar luminosity estimations: 21,000L_⊙ and 8300L_⊙ at maximum and minimum brightness, respectively. The relation between the disk and the high water content in the envelope is also discussed.

While both observations and theories demonstrate that protoplanetary disks are not expected to live much longer than ∼10 Myr, several examples of prolonged disks have been observed in the past. In this work, we perform a systematic search for aged young stellar objects still surrounded by protoplanetary disks in the M-star catalog from the LAMOST archive. We identify 14 sources older than 10 Myr, still surrounded by protoplanetary disks and with ongoing accretion activities, significantly improving the census of the category known as the Peter Pan disks. The stellar parameters, variability, and accretion properties of these objects, as well as their spatial distribution, are investigated. Nearly all of these objects are distributed far away from nearby associations and star-forming regions but show evidence of being members of open clusters. Investigating the correlation between mass accretion rates and stellar masses, we find that these long-lived disks accrete at systematically lower levels, compared to their younger counterparts with similar stellar masses. Studying the evolution of mass accretion rates with stellar ages, we find that these aged disks follow a similar trend to young ones.

We present two transit observations of the ∼520 K, 1.85 R_⊕, 4.0 M_⊕ super-Earth TOI-776 b with JWST NIRSpec/G395H, resulting in a 2.8–5.2 μm transmission spectrum. Producing reductions using the ExoTiC-JEDI and Eureka! pipelines, we obtain a median transit depth precision of 34 ppm for both visits and both reductions in spectroscopic channels 30 pixels wide (∼0.02 μm). We find that our independent reductions produce consistent transmission spectra; however, each visit shows differing overall structure. For both reductions, a flat line is preferred for Visit 1 while a flat line with an offset between the NRS1 and NRS2 detectors is preferred for Visit 2; however, we are able to correct for this offset during our modeling analysis following methods outlined in previous works. Using PICASO forward models, we can rule out metallicities up to at least 100× solar with an opaque pressure of 10⁻³ bars to ≥3σ in all cases; however, the exact lower limit varies between the visits, with Visit 1 ruling out ≲100× solar while the lower limits for Visit 2 extend beyond ∼350× solar. Our results add to the growing list of super-Earth atmospheric constraints by JWST, which provide critical insight into the diversity and challenges of characterizing terrestrial planets.

How the environment of the host galaxy affects the formation of multiple populations (MPs) in globular clusters (GCs) is one of the outstanding questions in near-field cosmology. To understand the true nature of the old GC MPs in the Large Magellanic Cloud (LMC), we study the Ca–CN–CH photometry of the old metal-poor LMC GC NGC 2257. We find the predominantly first-generation-dominated populational number ratio of n(FG):n(SG) = 61:39(±4), where FG and SG denote the first and second generations, respectively. Both the FG and SG have similar cumulative radial distributions, consistent with the idea that NGC 2257 is dynamically old. We obtain [Fe/H]_hk = −1.78 ± 0.00 dex(σ = 0.05 dex), and our metallicity is ∼0.2 dex larger than that from the high-resolution spectroscopy by others, due to their significantly lower temperatures by ∼−200 K. The NGC 2257 FG shows a somewhat larger metallicity variation than the SG, the first detection of such a phenomenon in an old LMC GC, similar to Galactic GCs with MPs, strongly suggesting that it is a general characteristic of GCs with MPs. Interestingly, the NGC 2257 SG does not show a helium enhancement compared to the FG. Our results for the Galactic normal GCs exhibit that the degree of carbon and nitrogen variations is tightly correlated with the GC mass, while NGC 2257 exhibits slightly smaller variations in its mass. We show that old LMC GCs follow the same trends as the Galactic normal GCs in the ΔW_{CF336W,F438W,F814W}, N_FG/N_tot, and domains. Our result indicates that the environment of the host galaxy did not play a major role in the formation and evolution of GC MPs.

Because of the continuous variations in mass, metallicity, and opacity, dwarf stars are distributed along the main sequence on optical and near-IR color–magnitude diagrams following a smooth polynomial. In this study, utilizing a catalog of crossmatched Galaxy Evolution Explorer (GALEX) and Gaia sources, we identify two distinct populations of M dwarfs in the near-UV (NUV) band on the M_NUV versus M_G diagram. We also reveal a pronounced increase in the number of stars exhibiting high NUV fluxes near the spectral type M2 or M_G ~ 9.4, coinciding with the H₂ formation in the atmosphere that improves the energy transportation at the surface. This suggests that certain yet-to-be-understood stellar mechanisms drive heightened activity in the NUV band around the effective temperatures of M2 and later types of M dwarfs. Through examination of archival Hubble Space Telescope spectra, we show that Fe ii line forests at ~2400 Å and 2800 Å dominate the spectral features in the GALEX NUV bandpass, contributing to the observed excess fluxes at a given mass between the two populations. Additionally, our investigation indicates that fast rotators and young stars likely increase in brightness in the NUV band, but not all stars with bright NUV fluxes are fast rotators or young stars.

The Pleiades is the most prominent open star cluster visible from Earth and an important benchmark for simple stellar populations unified by common origin, age, and distance. Binary stars are its essential ingredient, yet their contribution remains uncertain due to heavy observational biases. A resolved multiplicity survey was conducted for a magnitude-limited G < 15^mag sample of 423 potential cluster members, including sources with poorly fitted astrometric solutions in Gaia DR3. Speckle interferometric observations at the 2.5 m telescope of the Sternberg Astronomical Institute, Moscow State University observatory were combined with Gaia data, enabling the identification of 61 resolved binary or multiple systems within the 004–10″ (5–1350 au) separation range. With speckle observations, we discovered 21 components in 20 systems. The existence of a Merope (23 Tau) companion is confirmed after several previous unsuccessful attempts. We show that the Gaia multipeak fraction is a strong predictor of subarcsecond multiplicity, as all sources with ipd_frac_multi_peak > 4% are successfully resolved. We found that 10% of Pleiades stars have a companion with a mass ratio q > 0.5 within the projected separation of 27 < s < 1350 au, and confirm a deficit of wide binaries with s > 300 au. An observed dearth of wide pairs with a large mass ratio (q > 0.55) may imprint the transition from hard to soft binaries regime at the early stages of cluster evolution. The total binary fraction for q > 0.5 systems is extrapolated to be around 25%.

The detection of celestial objects in ground-based wide-field optical telescope images serves as the foundational step for subsequent celestial analysis tasks. Existing methods for astronomical target detection have not addressed the challenges posed by a high dynamic range, faintness of targets, and an inaccurate supervision map. This paper presents a faint celestial target detection framework named the Celestial Densely Nested Network (CDN-Net). First, a hierarchical bit-depth decomposition strategy is designed to address high dynamic range astronomical FITS images, ensuring effective representation of faint targets. Second, a densely nested hierarchical network is introduced to extract high-resolution features of these faint astronomical targets. Lastly, a soft segmentation map, along with the corresponding loss, is proposed to guide the network’s focus toward faint targets. Experiments were conducted on both simulated and real data sets, separately comprising 2560 images and 24,087 images, respectively, to evaluate the performance of CDN-Net. Compared to six existing methods, CDN-Net achieves superior precision, recall, and F1 score, especially for faint targets with signal-to-noise ratios below 3. Additionally, comparisons with star catalogs validate the effectiveness of CDN-Net. The code for this work is available at https://github.com/AeroFirefly/CDN-Net.

We present the discovery and characterization of a sub-Saturn exoplanet, TOI-6038 A b, using the PARAS-2 spectrograph. The planet orbits a bright (m_V = 9.9), metal-rich late F-type star, TOI-6038 A, with T_eff = 6110 ± 100 K, , and dex. The system also contains a wide-orbit binary companion, TOI-6038 B, an early K-type star at a projected separation of ≈3217 au. We combined radial velocity data from PARAS-2 with photometric data from the Transiting Exoplanet Survey Satellite for joint modeling. TOI-6038 A b has a mass of and a radius of , orbiting in a circular orbit with a period of days. Internal structure modeling suggests that ≈74% of the planet's mass is composed of dense materials, such as rock and iron, forming a core, while the remaining mass consists of a low-density H/He envelope. TOI-6038 A b lies at the transition regime between the recently identified Neptunian ridge and savanna. Having a density of , TOI-6038 A b is compatible with the population of dense ridge planets (ρ_P ≃ 1.5–2.0 g cm⁻³), which have been proposed to have reached their close-in locations through high-eccentricity tidal migration (HEM). First-order estimates suggest that the secular perturbations induced by TOI-6038 B may be insufficient to drive the HEM of TOI-6038 A b. Therefore, it is not clear whether HEM driven by a still undetected companion or early disk-driven migration brought TOI-6038 A b to its present-day close-in orbit. Interestingly, its bright host star makes TOI-6038 A b a prime target for atmospheric escape and orbital architecture observations, which will help us to better understand its overall evolution.

We present starkiller, an open-source Python package for forward-modeling flux retrieval from integral field unit (IFU) spectrograph data cubes. starkiller simultaneously provides stellar spectral classification, relative velocity, and line-of-sight extinction for all sources in a catalog, alongside a source-subtracted data cube. It performs synthetic difference imaging by simulating all catalog sources in the field of view, using the catalog for positions and fluxes to scale stellar models, independent of the data cube. This differencing method is particularly powerful for subtracting both point sources and trailed or even streaked sources from extended astronomical objects. We demonstrate starkiller's effectiveness in improving observations of extended sources in dense stellar fields for Very Large Telescope (VLT)/Multi Unit Spectroscopic Explorer (MUSE) observations of comets, asteroids, and nebulae. We also show that starkiller can treat satellite-impacted VLT/MUSE observations. The package could be applied to tasks as varied as dust extinction in clusters and stellar variability; the stellar modeling using Gaia fluxes is provided as a standalone function. The techniques can be expanded to imagers and to other IFUs.

This paper presents a classification framework for the architectures of planetary systems based on a complete survey of the confirmed exoplanet population. With nearly 6000 confirmed exoplanets discovered, including more than 300 multiplanet systems with N ≥ 3 planets, the current observational sample has reached a point where it is both feasible and useful to build a classification system that divides the observed population into meaningful categories. This framework provides a criterion for splitting planetary systems into inner and outer regimes, then further dividing inner systems into dynamical classes. The resulting categories include “peas-in-a-pod systems,” with uniformly small planets, and “warm-Jupiter systems,” with a mix of large and small planets, as well as “closely spaced systems” and “gapped systems,” with further subdivisions based on the locations of gaps and other features. These categories can classify nearly all of the confirmed N ≥ 3 systems with minimal ambiguity. We qualitatively examine the relative prevalence of each type of system, subject to observational selection effects, as well as other notable features, such as the presence of hot Jupiters. A small number of outlier systems are also discussed. Potential additional classes of systems yet to be discovered are proposed.

The PHANGS project is assembling a comprehensive, multiwavelength data set of nearby (∼5–20 Mpc), massive star-forming galaxies to enable multiphase, multiscale investigations into the processes that drive star formation and galaxy evolution. To date, large survey programs have provided molecular gas (CO) cubes with the Atacama Large Millimeter/submillimeter Array, optical integral field unit (IFU) spectroscopy with the Very Large Telescope/Multi-Unit Spectroscopic Explorer (MUSE), high-resolution near-ultraviolet–optical imaging in five broadband filters with Hubble Space Telescope (HST), and infrared imaging in NIRCAM+MIRI filters with JWST. Here we present PHANGS-HST-Hα, which has obtained high-resolution (∼2–10 pc), narrowband imaging in the F658N or F657N filters with the HST/WFC3 camera of the warm ionized gas in the first 19 nearby galaxies observed in common by all four of the PHANGS large programs. We summarize our data reduction process, with a detailed discussion of the production of flux-calibrated, Milky Way extinction-corrected, continuum-subtracted Hα maps. PHANGS-MUSE IFU spectroscopy data are used to background-subtract the HST-Hα maps and to determine the [N ii] correction factors for each galaxy. We describe our public data products (the data released as part of this work include the reduced drizzled narrowband images and the flux-calibrated, continuum-subtracted Hα maps for each galaxy; these images are available for download via MAST at https://archive.stsci.edu/hlsp/phangs.html, as well as at the Canadian Astronomy Data Centre as part of the PHANGS archive at https://www.canfar.net/storage/vault/list/phangs/RELEASES) and highlight a few key science cases enabled by the PHANGS-HST-Hα observations.

The accuracy of photometric calibration has gradually become a limiting factor in various fields of astronomy, limiting the scientific output of a host of research. Calibration using artificial light sources in low Earth orbit remains largely unexplored. Here, we demonstrate that photometric calibration using light sources in low Earth orbit is a viable and competitive alternative/complement to current calibration techniques, and explore the associated ideas and basic theory. We present the publicly available Python code Streaktools as a means to simulate and perform photometric calibration using real and simulated light streaks. Using Streaktools, we perform “pill” aperture photometry on 131 simulated streaks, and Markov chain Monte Carlo based point-spread-function (PSF) model-fitting photometry on 425 simulated streaks in an attempt to recover the magnitude zeropoint of a real exposure of the Dark Energy Camera instrument on the Blanco 4 m telescope. Our results show that calibration using pill photometry is too inaccurate to be useful, but that PSF photometry is able to produce unbiased and accurate (1σ error = 3.4 mmag) estimates of the zeropoint of a real image in a realistic scenario, with a reasonable light source. This demonstrates that light-streak photometry is a promising alternative and complement to established techniques, which should be explored and tested further.

We reanalyze VLT/SPHERE-IRDIS K- and H-band sparse aperture masking interferometry data of the transition disk HD 100546 observed in 2018 and 2021, respectively. We fit geometrical models to the closure phases extracted from both datasets. We compare three model classes: a forward scattering disk, a forward scattering disk plus an arbitrary asymmetric disk feature, and a forward scattering disk plus an unresolved point source in the disk gap. We find that the forward scattering disk plus point-source model is the best representation of the data. We find that this point-source candidate moved from a position of sep. = mas, P.A. = degrees to a sep. = mas, P.A. = degrees between 2018 and 2021. Both of these positions are well within the ~13 au (~120 mas) disk gap, favouring the point-source interpretation. We explore the orbital parameter space that is consistent with the measured relative astrometry. We find orbits either with a similar orientation to the outer disk, with a high eccentricity e ≿ 0.65, or orbits with a large relative inclination (∼60°) to the outer disk, and any eccentricity. Despite the significance of the observed point-source signal, follow-up observations will be necessary to conclusively determine its nature.

M dwarf stars comprise 70%–80% of the galaxy's stars and host most of its rocky planets. They also differ from Sunlike stars in that they are “active” for billions of years or more: rotating quickly, flaring often, and emitting large amounts of UV and X-ray light. The effects of stellar activity upon both photometry and spectroscopy make their exoplanets more difficult to detect. While activity signals such as flaring and stellar rotation can be more readily modeled or removed from photometry, the contribution of unresolved stellar activity to transit sensitivity is harder to quantify. We investigate the difference in the detectability of planetary transits around a sample of M dwarfs observed by NASA's Transiting Exoplanet Survey Satellite (TESS) Mission, characterized by a common stellar radius, effective temperature, and TESS magnitude. Our sample is classified as either “active” or “inactive” based upon the presence of Hα in emission. After removing more readily identifiable signatures of activity: stellar rotation and large flares, we perform an injection-and-recovery analysis of transits for each star. We extract detection sensitivity as a function of planetary radius and orbital period for each star. Then, we produce averaged sensitivity maps for the “active” stars and the “inactive” stars, for the sake of comparison. We quantify the extent to which signal-to-noise ratio is degraded for transit detection, when comparing an active star to an inactive star of the same temperature and apparent brightness. We aim for these sensitivity maps to be useful to the exoplanet community in future M dwarf occurrence-rate studies.

We present the deepest color–magnitude diagram (CMD) for NGC 205 in the F606W (≈V) and F814W (≈I) filters. Our archival Hubble Space Telescope/Advanced Camera for Surveys field is centered ∼38 northwest of the galaxy's center. The CMD shows the canonical features of a predominantly intermediate-to-old age stellar population. Among other features, the CMD reveals a prominent red clump as well as a blue horizontal branch. Notably absent is any significant signature of a young main sequence typically produced by a stellar population with an age less than a few Gyr. From the magnitude of the red-giant-branch tip, we derive a distance modulus of (m − M)_o = 24.66 ± 0.05. When compared with α-enhanced theoretical isochrones, the color distribution of the red giant branch stars yields a peak metallicity value of [Fe/H] = −0.51 ± 0.10. Our photometry also reveals a sample of 479 RR Lyrae variable stars (443 ab-type and 36 c-type). Utilizing equations that relate the periods and amplitudes to the metallicities of these stars, we find a mean 〈[Fe/H]〉 = −1.45 ± 0.02 on the Zinn & West scale for the purely old stellar population in NGC 205. The quoted uncertainty represents the standard error of the mean abundance value is consistent with that of the six genuine old globular clusters in NGC 205.

The mass accretion rates of young stellar objects (YSOs) are key to understanding how stars form, how their circumstellar disks evolve, and even how planets form. We develop a Bayesian framework to determine the accretion rates of a sample of 15 YSOs using archival data from the VIRUS spectrograph (R ∼ 800, 3500–5500 Å) on the Hobby–Eberly Telescope. We are publicly releasing our developed tool, dubbed nuts-for-ysos, as a Python package, which can also be applied to other spectroscopic data sets (https://github.com/laurenwillett/nuts-for-ysos). The nuts-for-ysos code fits a simple accretion model to the near-UV and optical continuum of each VIRUS spectrum. Our Bayesian approach aims to identify correlations between model parameters using the No U-Turn Sampler (NUTS). Moreover, this approach self-consistently incorporates all parameter uncertainties, allowing for a thorough estimation of the probability distribution for accretion rate not accomplished in previous works. Using nuts-for-ysos, we derive accretion rates of each YSO. We then verify the reliability of our method by comparing to results separately derived from only the spectral emission lines, and to results from earlier studies of the Lupus, Chamaeleon I, and NGC 1333 regions. Finally, we discuss what qualitative trends, covariances, and degeneracies were found among model parameters. The technique developed in this paper is a useful improvement that can be applied in the future to larger samples of YSOs observed by VIRUS or other spectrographs.

We report the search of RR Lyrae in the vicinity of a newly discovered ultrafaint dwarf galaxy, Aquarius III. Based on the known RR Lyrae catalogs and gri-band light curves retrieved from public archives, we identified a RR Lyrae with distance, metallicity, and proper motion consistent with Aquarius III. Therefore, this RR Lyrae is the first variable star identified to be associated with Aquarius III, despite its projected distance is more than 15 times the half-light radius of Aquarius III. On the other hand, a dedicated time-series monitoring of the central part of Aquarius III, out to a projected radius of approximately four half-light radius, revealed there is no RR Lyrae in this region. We ran a set of synthetic color–magnitude diagrams with properties similar to Aquarius III, and found a nonnegligible probability that Aquarius III could have (at least one) RR Lyrae. We have also identified a RR Lyrae candidate but most likely it is a background halo star.

The Dark Energy Spectroscopic Instrument (DESI) cosmology survey includes a Bright Galaxy Survey (BGS), which will yield spectra for over 10 million bright galaxies (r < 20.2 AB mag). The resulting sample will be valuable for both cosmological and astrophysical studies. However, the star/galaxy separation criterion implemented in the nominal BGS target selection algorithm excludes quasar host galaxies in addition to bona fide stars. While this excluded population is comparatively rare (∼3–4 per square degrees), it may hold interesting clues regarding galaxy and quasar physics. Therefore, we present a target selection strategy that was implemented to recover these missing active galactic nuclei (AGN) from the BGS sample. The design of the selection criteria was both motivated and confirmed using spectroscopy. The resulting BGS-AGN sample is uniformly distributed over the entire DESI footprint. According to DESI survey validation data, the sample comprises 93% quasi-stellar objects (QSOs), 3% narrow-line AGN or blazars with a galaxy contamination rate of 2%, and a stellar contamination rate of 2%. Peaking around redshift z = 0.5, the BGS-AGN sample is intermediary between quasars from the rest of the BGS and those from the DESI QSO sample in terms of redshifts and AGN luminosities. The stacked spectrum is nearly identical to that of the DESI QSO targets, confirming that the sample is dominated by quasars. We highlight interesting small populations reaching z > 2, which are either faint quasars with nearby projected companions or very bright quasars with strong absorption features including the Lyα forest, metal absorbers, and/or broad absorption lines.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has been fully operational since 2020 January 11. We present a comprehensive analysis of the beam structure for each of the 19 feed horns on FAST's L-band receiver across the Stokes I, Q, U, and V parameters. Using an on-the-fly mapping pattern, we conducted simultaneous sky mapping using all 19 beams directed toward polarization calibrators J1407+2827 and J0854+2006 from 2020 to 2022. Electromagnetic simulations were also performed to model the telescope's beam patterns in all Stokes parameters. Our findings reveal a symmetrical Gaussian pattern in the Stokes I parameter of the central beam without strong sidelobes, while the off-center beams exhibit significant asymmetrical shapes that can be fitted using a combination of log-normal and Gaussian distributions. The inner beams have higher relative beam efficiencies and smaller beam sizes compared to those of the outer beams. The sidelobes of the inner beams contribute approximately 2% of the total flux in the main lobe, increasing to 5% for outer beams, with a peak at 6.8%. In Stokes U, a distinct four-lobed cloverleaf beam squash structure is observed, with similar intensity levels in both inner and outer beams. In Stokes V, a two-lobed beam squint structure is observed in the central beam, along with a secondary eight-lobed structure. The highest squint peak in Stokes V is about 0.3% of the Stokes I in the outer beams. These results align closely with the simulations, providing valuable insights for the design of radio multibeam observations.

Traditional microlensing event vetting methods require highly trained human experts, and the process is both complex and time consuming. This reliance on manual inspection often leads to inefficiencies and constrains the ability to scale for widespread exoplanet detection, ultimately hindering discovery rates. To address the limits of traditional microlensing event vetting, we have developed LensNet, a machine learning pipeline specifically designed to distinguish legitimate microlensing events from false positives caused by instrumental artifacts, such as pixel bleed trails and diffraction spikes. Our system operates in conjunction with a preliminary algorithm that detects increasing trends in flux. These flagged instances are then passed to LensNet for further classification, allowing for timely alerts and follow-up observations. Tailored for the multiobservatory setup of the Korea Microlensing Telescope Network and trained on a rich data set of manually classified events, LensNet is optimized for early detection and warning of microlensing occurrences, enabling astronomers to organize follow-up observations promptly. The internal model of the pipeline employs a multibranch Recurrent Neural Network architecture that evaluates time-series flux data with contextual information, including sky background, the full width at half-maximum of the target star, flux errors, point-spread function quality flags, and air mass for each observation. We demonstrate a classification accuracy above 87.5% and anticipate further improvements as we expand our training set and continue to refine the algorithm.

The optical star in the T Tauri triple system is the prototype of young Sun-like stars in our galaxy. This complex and dynamic system has evidence for misaligned disks and outflows, and molecular material in a circumbinary ring that obscures the southern infrared binary, T Tau South. Observations by members of the American Association of Variable Star Observers show that T Tau North, the optical star, has dimmed by up to  ∼2 mag in the visual over the course of the past decade. The dimming across the B, V, R, and I bands has a color character typical of changes in interstellar medium extinction, suggesting an increase in obscuration along the line of sight to T Tau North. Material associated with the circumbinary ring around T Tau South has been predicted to occult the optical star via wide-scale orbital motion of the system. Through analysis of the geometrical configuration and motion of dust structures in the system, it seems that a great dimming of T Tau North by line-of-sight material associated with the T Tau South binary has, in fact, begun. Based on the extent and motion of the circumbinary ring material associated with the southern binary, T Tau North will likely experience dimming events for decades to come and may disappear entirely from the optical sky as the densest midplane region of the ring traverses our line of sight.

In this study, we explore the characteristics of bulk flow across various redshift ranges within the frameworks of f(R) gravity, perturbed f(R) gravity, and perturbed f(R) gravity coupled with neutrinos. Our investigation reveals profound insights into large-scale cosmic flows and their interactions with major cosmic structures, such as the Sloan Great Wall (SGW) and the King Ghidorah Supercluster (KGSc). We find that incorporating neutrinos into the perturbed f(R) gravity model results in a substantial increase in bulk flow velocities across all redshifts, with notable enhancements in the higher redshift ranges, where velocities can exceed 3000 km s⁻¹ in the 0.8 < z < 1.4 range. Moreover, the direction of the bulk flow in this model closely aligns with the dark energy dipole, especially at redshifts z > 0.4, showing near-perfect congruence with cosmic superclusters. This suggests a significant interaction between neutrinos and cosmic structures, influencing cosmic acceleration. At lower redshifts, such as 0.1 < z < 0.2, the bulk flow aligns with the SGW, while in the 0.4 < z < 0.6 range it aligns with the KGSc. In the low redshift range 0.001 < z < 0.016, although velocities are lower, neutrinos still subtly increase the bulk flow velocity and maintain alignment with nearby cosmic structures, such as the Local Supercluster. Our results underscore the critical role of neutrinos in shaping cosmic flows and offer new insights into the interplay between dark energy, neutrinos, and modified gravity models. Future research should delve deeper into these interactions to elucidate the mechanisms influencing large-scale cosmic structures.

In the I-band color–magnitude diagrams of resolved nearby galaxies, the reddest asymptotic giant branch (AGB) stars form a previously unremarked-upon, but nevertheless distinct and easily identified population of high-luminosity stars. Hereafter we refer to this population as being comprised of I-band AGB (IAGB) stars. Identifying these stars in the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and in NGC 4258 (for all three of which there are published geometric distances) we find that the marginalized luminosity functions are each well approximated by single-peaked Gaussians, having 1σ dispersions of  ±0.22 mag,  ±0.25 mag and  ±0.24 mag, respectively. The zero points for the modal I-band absolute magnitudes of IAGB stars are found to be M_I = −4.49 ± 0.003 mag (stat) in the LMC (4204 stars), M_I = −4.67 ± 0.008 mag (stat), for the SMC sample (916 stars), and M_I = −4.78 ± 0.030 mag (stat) for NGC 4258 (62 stars). A global average over these three independent calibrations of the IAGB zero-point (weighted inversely by squares of their systematic errors) gives  〈M_I〉 = −4.65 ± 0.119 mag (stat)  ±  0.025 (sys). In Paper II we will show the results of applying the IAGB Method to 92 galaxies additional galaxies resolved by Hubble Space Telescope, reaching out to distances just short of 10 Mpc.

Brown dwarfs lack nuclear fusion and cool with time; the coldest known have an effective temperature below 500 K, and are known as Y dwarfs. We present a James Webb Space Telescope (JWST) photometric data set of Y dwarfs: 23 were imaged in wide-field mode, 20 using NIRCam with the F150W and F480M filters, and three using NIRISS with the F480M filter. We present an F480M versus F150W – F480M color–magnitude diagram for our sample, and other brown dwarfs with F150W and F480M colors synthesized from JWST spectra by S. A. Beiler et al. For one target, WISEA J083011.95+283716.0, its detection in the near-infrared confirms it as one of the reddest Y dwarfs known, with F150W – F480M = 9.62 mag. We provide its updated parallax and proper motion. One of the Beiler et al. Y dwarfs, CWISEP J104756.81+545741.6, is unusually blue, consistent with strong CO absorption seen in its spectrum, which the F480M filter is particularly sensitive to. The strong CO and the kinematics of the object suggest it may be very low mass and young. We update the resolved photometry for the close binary system WISE J033605.05–014350.4 AB, and find that the secondary is almost as cold as WISE 085510.83–071442.5, with T_eff ≲ 300 K, however the F150W – F480M color is significantly bluer, possibly suggesting the presence of water clouds. Astrometry is measured at the JWST epoch for the sample which is consistent with parallax and proper motion values reported by J. D. Kirkpatrick et al. and F. Marocco et al.

Stellar light curves from edge-on double white dwarf (DWD) systems have periodic lensing/eclipsing signals at times of alignment between the two components as seen by the observer. Here, we study the characterization and detection of these signals. In common DWDs, the Einstein radii have similar orders of magnitude to the radii of the white dwarfs (WDs), and the projected source and lens radii normalized to the Einstein radius (ρ_⋆ and ρ_l) are ∼1. Both of them are reduced with the orbital period and the lens mass. If ρ_l ≃ 1 the lensing-induced minor image is always blocked by the lens, which results in lower magnification factors. If ρ_l ≲ 1, and in transit events, the finite-lens effects decrease the light curves’ width. When ρ_l ≳ 1 (which happens for close DWDs consisting of a low-mass WD and a massive one) deep or complete eclipses dominate over lensing effects. The self-lensing signals are maximal for massive DWDs in wide orbits. We study the detectability of lensing/eclipsing signals in edge-on DWDs in observations by NASA’s Transiting Exoplanet Survey Satellite (TESS), the Vera Rubin Observatory Large Synoptic Survey Telescope (LSST), and the Nancy Grace Roman Space Telescope. We simulate stellar light curves due to edge-on DWDs and generate synthetic data points based on their observing strategies. Detection efficiency is maximal for extremely low-mass WDs in close orbits, and the numbers of DWDs within 100 pc and an observing cone with detectable lensing/eclipsing signals in one observing window of 27.4 days for TESS and 62 days for Roman are ∼1 and <1, respectively. Detecting these signals by LSST is barely possible because of its long cadence.

This work aims at providing fundamental general tools for the analysis of water spectra as observed in protoplanetary disks with JWST-MIRI. We analyze 25 high-quality spectra from the JDISC Survey reduced with asteroid calibrators as presented in K. M. Pontoppidan et al. (2024). First, we present a spectral atlas to illustrate the clustering of H₂O transitions from different upper-level energies (E_u) and identify single (unblended) transitions that provide the most reliable measurements. With that, we demonstrate two important excitation effects: the opacity saturation of ortho-para line pairs that overlap, and the subthermal excitation of excitation of v = 1–1 lines scattered across the v = 0–0 rotational band. Second, we define a shorter list of fundamental lines spanning E_u =  1500–6000 K to develop simple line-ratio diagnostic diagrams for the radial temperature distribution of water in inner disks, which are interpreted using discrete temperature components and power-law radial gradients. Third, we report the detection of disk-rotation Doppler broadening of molecular lines, which confirms the radial distribution of water emission including, for the first time, the radially extended ≈170–220 K reservoir close to the snowline. The combination of measured line ratios and broadening suggests that drift-dominated disks have shallower temperature gradients with an extended cooler disk surface enriched by ice sublimation. We also report the first detection of an H₂O-rich inner disk wind from narrow blueshifted absorption in the ro-vibrational lines. We summarize these findings and tools into a general recipe to make the study of water in planet-forming regions reliable, effective, and sustainable for samples of >100 disks.

We present the discovery and characterization of TOI-4364b, a young mini-Neptune in the tidal tails of the Hyades cluster, identified through TESS transit observations and ground-based follow-up photometry. The planet orbits a bright M dwarf (K = 9.1 mag) at a distance of 44 pc, with an orbital period of 5.42 days and an equilibrium temperature of K. The host star's well-constrained age of 710 Myr makes TOI-4364b an exceptional target for studying early planetary evolution around low-mass stars. We determined a planetary radius of , indicating that this planet is situated near the upper edge of the radius valley. This suggests that the planet retains a modest H/He envelope. As a result, TOI-4364b provides a unique opportunity to explore the transition between rocky super-Earths and gas-rich mini-Neptunes at the early stages of evolution. Its radius, which may still evolve as a result of ongoing atmospheric cooling, contraction, and photoevaporation, further enhances its significance for understanding planetary development. Furthermore, TOI-4364b’s moderately high transmission spectroscopy metric of 44.2 positions it as a viable candidate for atmospheric characterization with instruments such as JWST. This target has the potential to offer crucial insights into atmospheric retention and loss in young planetary systems.

The radial velocity catalog from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) is unique in its simultaneously large volume and high precision as a result of its decade-long survey duration, multiplexing (600 fibers), and spectral resolution of R ∼ 22,500. However, previous data reductions of APOGEE have not fully realized the potential radial velocity (RV) precision of the instrument. Here we present an RV catalog based on a new reduction of all 2.6 million visits of APOGEE DR17 and validate it against improved estimates for the theoretical RV performance. The core ideas of the new reduction are the simultaneous modeling of all components in the spectra, rather than a separate subtraction of point estimates for the sky, and a marginalization over stellar types, rather than a grid search for an optimum. We show that this catalog, when restricted to RVs measured with the same fiber, achieves noise-limited precision down to 30 m s⁻¹ and delivers well-calibrated uncertainties. We also introduce a general method for calibrating fiber-to-fiber constant RV offsets and demonstrate its importance for high RV precision work in multifiber spectrographs. After calibration, we achieve 47 m s⁻¹ RV precision on the combined catalog with RVs measured with different fibers. This degradation in precision relative to measurements with only a single fiber suggests that refining line spread function models should be a focus in the Sloan Digital Sky Survey V to improve the fiber-unified RV catalog.

The existence of high-α stars with inferred ages <6 Gyr has been confirmed recently with large spectroscopic and photometric surveys. However, stellar mergers or binary interactions can induce properties associated with young ages, such as high mass, rapid rotation, or high activity, even in old populations. Literature studies have confirmed that at least some of these apparently young stars are old merger products. However, none have ruled out the possibility of genuinely young high-α stars. Because cool GKM dwarfs spin down, rapid rotation can be used to indicate youth. In this paper, we provide strong evidence that truly young high-α stars exist by studying high-α rotators in the Kepler and K2 field with abundance measurements from GALAH and APOGEE. After excluding close binaries using radial velocity (RV) measurements from Gaia DR3 and multiepoch RVs from APOGEE, we find a total of 32 high-α rapid rotators with periods ∼10–30 days, 14 of which have lithium measurements from GALAH, indicating that they have not gone through past mass transfer or stellar merger events. We identify 10 young high-α candidates with no signs of merger-induced mixing or close companions. One clear example is a G dwarf with a measurable rotation and an age of <5 Gyr that is likely a single star with multiple RV measurements from APOGEE, has significant lithium detection from GALAH (A(Li) = 1.79), and has no signs of planet engulfment.

The ExoEcho project is designed to study the photodynamics of exoplanets by leveraging high-precision transit timing data from ground- and space-based telescopes. Some exoplanets are experiencing orbital decay, and transit timing variation (TTV) is a useful technique to study their orbital period variations. In this study, we have obtained transit middle-time data from the Hubble Space Telescope observations for 37 short-period exoplanets, most of which are hot Jupiters. To search for potential long- and short-term orbital period variations within the sample, we conduct TTV model fitting using both linear and quadratic ephemeris models. Our analysis identifies two hot Jupiters experiencing strong periodic decays. Given the old age of the host stars of the hot Jupiter population, our findings call for a scenario where HJs are continuously being destructed and created. Our study demonstrates the importance of incorporating high-precision transit timing data to TTV study in the future.

We present microlux, which is a Jax-based code that can compute the binary microlensing light curve and its derivatives both efficiently and accurately. The key feature of microlux is the implementation of a modified version of the adaptive sampling algorithm that was originally proposed by V. Bozza to account for the finite-source effect most efficiently. The efficiency and accuracy of microlux have been verified across the relevant parameter space for binary microlensing. As a differentiable code, microlux makes it possible to apply gradient-based algorithms to the search and posterior estimation of the microlensing modeling. As an example, we use microlux to model a real microlensing event and infer the model posterior via both Fisher information matrix and Hamiltonian Monte Carlo, neither of which would have been possible without access to accurate model gradients.

Biosignature detection in the atmospheres of Earth-like exoplanets is one of the most significant and ambitious goals for astronomy, astrobiology, and humanity. Molecular oxygen is among the strongest indicators of life on Earth, but it will be extremely difficult to detect via transmission spectroscopy. We used the Bioverse statistical framework to assess the ability to probe Earth-like O₂ levels on hypothetical nearby habitable zone exo-Earth candidates (EECs) using direct imaging and high-resolution spectroscopy on the Giant Magellan Telescope (GMT) and the Extremely Large Telescope (ELT). Assuming continued improvement in instruments and data processing, our analysis highlights the best-case scenarios. Earth-like O₂ levels could be probed on up to ∼7 and ∼19 EECs orbiting bright M dwarfs within 20 pc in a hypothetical 10 yr survey on the GMT and ELT, respectively. Four known super-Earth candidates, including Proxima Centauri b, could be probed for O₂ within about 1 week of observations on the ELT and a few months on the GMT. We also assessed the ability of the ELT to test the habitable zone oxygen hypothesis—that habitable zone Earth-sized planets are more likely to have O₂—within a 10 yr survey using Bioverse. Testing this hypothesis requires either ∼one-half of the EECs to have O₂ or ∼one-third if η_⊕ is large. A Northern Hemisphere large-aperture telescope, such as the Thirty Meter Telescope, would expand the target star pool by about 25%, reduce the time to probe biosignatures on individual targets, and provide an additional independent check on potential biosignature detections.

We present equivalent widths, improved model atmosphere parameters, and revised abundances for 14 species of 11 elements derived from high-resolution optical spectroscopy of 311 metal-poor stars. All of these stars had their parameters previously published by Roederer et al. We use color–T_eff relationships calibrated for Gaia and 2MASS photometry to calculate improved effective temperatures (T_eff). We calculate log of surface gravity (log g) values using measurements derived from Gaia parallaxes and other fundamental stellar properties. We perform a standard LTE abundance analysis using MARCS model atmospheres and the MOOG line analysis software to rederive microturbulence velocity parameters, metallicities, and abundances based on O i, Na i, Mg i, Si i, K i, Ca i, Ti i, Ti ii, Cr i, Cr ii, Fe i, Fe ii, Ni i, and Zn i lines using previously measured equivalent widths. On average, the new T_eff values are 310 K warmer, the new log g values are higher by 0.64 dex, and the new [Fe/H] values are higher by 0.26 dex. We apply NLTE corrections to the abundances derived from O i, Na i, Mg i, Si i, K i, Fe i, and Fe ii lines. Our sample contains 6 stars with [Fe/H] < −3.5, 28 stars with [Fe/H] < −3.0, and 113 stars with [Fe/H] < −2.5. Our revised abundances for these 311 stars are now in better agreement with those derived by previous studies of smaller samples of metal-poor stars in the Milky Way.

Active galactic nuclei (AGNs) observed with the very long baseline interferometry (VLBI) technique are used as fiducial references on the sky to precisely measure the shape and orientation of the Earth. Their positions form a celestial reference frame that plays an important role in both astronomy and geodesy. This study investigates the accuracy and stability of the positions of the AGNs that are measured by simultaneous VLBI observations at 3.3, 5.5, 6.6, and 10.5 GHz. Based on position time series from dedicated geodetic solutions, we characterize the observed source position variations and identify the possible factors causing such variations. We find that the primary contributor is source structure for sources above 20° decl., while the sensitivity of the observations to the decl. coordinate predominates for sources below 20° decl. The position time series are further explored to derive more realistic uncertainties for the quad-band positions. Significant position offsets with respect to the positions at 2.2/8.6 GHz are found for 15% of the sources. For 6% of the sources, the offsets are larger than 0.8 mas. The source structure may be divided into two parts: the invisible structure (within the beam size) and the visible structure (on larger scales). The latter causes closure delays enlarging postfit delay residuals in geodetic solutions, whereas the former causes source position changes. Such position changes will contribute significantly to the offsets between radio and optical positions. Overall, this work highlights the necessity to have a specific quad-band catalog for processing operational quad-band observations.

Spectroscopic observations of various tracers in nearby galaxies, such as Andromeda (M31), play a crucial role in identifying and classifying individual stellar populations and nebular objects, thereby enhancing our understanding of galactic composition, environment, and dynamics, as well as stellar evolution. While the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey of M31 has produced extensive data sets, a comprehensive catalog of emission-line nebulae, star clusters, and supergiants is yet to be completed. In this paper, we present a final catalog of 384 emission-line nebulae, 380 star clusters, and 375 supergiants and candidates in M31, as carefully selected and identified from the LAMOST spectroscopic database. These objects were classified using a random forest algorithm, followed by thorough visual examinations of their spectral characteristics, as well as morphologies revealed by archive images. For emission-line nebulae, we measured radial velocities and relative fluxes of emission lines, enabling further classification of planetary nebulae and H ii regions. Additionally, we identified 245 emission-line nebulae in M33. This work lays the data foundation for the study of M31 and offers valuable tracers to investigate M31’s structure and evolution.

We present an atmospheric characterization and orbital analysis of HD 206893 B, an exceptionally red, L/T-transition substellar companion in a multiplanetary system, via Keck Planet Imager and Characterizer (KPIC) high-resolution (R ∼ 35,000) K-band spectroscopy. Using PHOENIX atmospheric models in a forward-model framework that fits the spectrum of the companion and diffracted starlight simultaneously, we detect HD 206893 B at >8σ significance via cross correlation in two epochs. We find an effective temperature for the companion of 1634 K and a of 4.55. Only accounting for statistical uncertainties, we measure the carbon-oxygen ratio (C/O) of this companion to be 0.57 ± 0.02, or near-solar while assuming solar metallicity. The C/O ratio we measure fits the tentative trend of >4 M_Jup companions having near-solar C/O ratios while less massive companions have greater-than-solar C/O ratios. Using substellar evolution models, we find an age of 112 Myr, a mass of 22.7 M_Jup, and a radius of 1.11 ± 0.03 R_Jup for this companion. We also use KPIC radial velocity data to fit the orbit of HD 206893 B and analyze the orbital stability of this system. We find that the orbital stability is relatively independent of the mass of HD 206893 B, and favors an orbital configuration where B and its interior planetary companion, HD 206893 c, are coplanar. The measured C/O ratio coupled with the current architecture of the system cannot rule out the core accretion scenario, nor the disk fragmentation scenario regarding the formation pathway of HD 206893 B.

The Multi-Object MKID Optical Spectrometer (MOMOS) is a proposed visible wavelength spectrograph that uses microwave kinetic inductance detectors (MKIDs) targeting an initial resolving power of 3500 for up to five fiber inputs. With their modest wavelength-resolving abilities, MKIDs take the place of both the cross disperser and detector in the spectrograph. MKIDs lack read noise and dark current enabling noiseless post-observation rebinning and characterization of faint objects, as well as time-resolved photon-counting spectroscopy. This work presents a MOMOS simulator customizable for different MOMOS configurations. Treating simulator products as inputs, an algorithm was developed and implemented in the MOMOS data reduction package to calibrate and extract spectra.

HL Tau is one of the most well-studied Class I young stellar objects (YSOs), including frequent observations at near- and mid-infrared, (sub)millimeter, and X-ray wavelengths. We present the results of an X-ray variability monitoring campaign with XMM-Newton in 2020 and X-ray grating spectroscopy from Chandra/HETGS in 2018. We find that the X-ray spectrum of HL Tau is consistently hot (with characteristic plasma temperatures T ≳ 30 MK) over 31 epochs spanning 20 yr, which is consistent in temperature with most Class I YSOs. The high-resolution HETG spectrum indicates the presence of some cooler plasma. We characterize the variability of the star across the 31 observations and find a subset of observations with significant variability on a ∼21-day timescale in the observed count rate and flux. We discuss the possible origins of this variability and identify further observations that would better constrain the nature of the changes.

A new set of stellar spectral models is generated from nonlocal thermodynamic equilibrium metal line-blanketed model atmospheres of T. Lanz & I. Hubeny. The new libraries present spectra in the effective temperature range from 15,000 to 55,000 K, for 8 metallicities, Z/Z_⊙ = 2, 1, 0.5, 0.2, 0.1, 0.0032, 0.02, and 0.01; all of them for three microturbulent velocities, v_turb = 2, 5, and 10 km s⁻¹; between 200 Å and 32 μm, and with resolution R = 100,000. The wavelength range supports ground-based optical/NIR, Hubble Space Telescope UV to NIR, as well as JWST NIR/MIR wavelength ranges fully. All models have the same vacuum wavelength scale with 739,791 sample points.

A transiting planet was recently discovered around a star in the Taurus star-forming region, IRAS 04125+2902, making it one of the youngest known planets. The discovery paper cited two age estimates for IRAS 04125+2902, one based on a comparison to two sets of model isochrones in the Hertzsprung–Russell diagram and a second age reported by an earlier study for a putative population in Taurus that includes IRAS 04125+2902 (D4-North). However, the model isochrones in question differ significantly for most temperatures and luminosities of young low-mass stars, and do not reproduce the observed sequences for the TW Hya and 32 Ori associations (10 and 21 Myr). Meanwhile, as found in my previous work, D4-North is a collection of field stars and fragments of several distinct Taurus groups and older associations, so its quoted age is not meaningful. The true parent population for IRAS 04125+2902 is a small group that is ∼35 pc behind the L1495 and B209 clouds (B209N). I have analyzed the age of B209N through a comparison to TW Hya and 32 Ori. The M-star sequences in the latter two associations have the same shapes, but the sequence for B209N is flatter, indicating that >M4 stars at ages of <10 Myr fade more quickly than stars at earlier types and older ages. For the one member of B209N that is earlier than M4 (IRAS 04125+2902), I estimate an age of 3.0 ± 0.4 Myr based on its offsets from TW Hya and 32 Ori, which by happenstance is similar to the value derived through the comparison to model isochrones.

The initial stellar carbon-to-oxygen (C/O) ratio can have a large impact on the resulting condensed species present in the protoplanetary disk and, hence, the composition of the bodies and planets that form. The observed C/Os of stars can vary from 0.1–1. We use a sequential dust condensation model to examine the impact of the C/O on the composition of solids around a solar-like star. We utilize this model in a focused examination of the impact of varying the initial stellar C/O to isolate the effects of the C/O in the context of solar-like stars. We describe three different system types in our findings. The solar system falls into the silicate-dominant, low-C/O systems which end at a stellar C/O somewhere between 0.52 and 0.6. At C/Os between about 0.6 and 0.9, we have intermediate systems. Intermediate systems show a decrease in silicates while carbides begin to become significant. Carbide-dominant systems begin around a C/O of 0.9. Carbide-dominant systems exhibit high carbide surface densities at inner radii with comparable levels of carbides and silicates at outer radii. Our models show that changes between C/O = 0.8 and C/O = 1 are more significant than previous studies, that carbon can exceed 80% of the condensed mass, and that carbon condensation can be significant at radii up to 6 au.

To reveal the origin of the mini-starbursts in the Milky Way, we carried out large-scale CO observations toward the RCW 106 giant molecular cloud (GMC) complex using the NANTEN2 4 m radio telescope operated by Nagoya University. We also analyzed the Mopra Southern Galactic Plane CO survey and Herschel infrared continuum archival data. The RCW 106 GMC complex contains the radial velocity components of −68 km s⁻¹ and −50 km s⁻¹ reported by H. Nguyen et al. (2015). Focusing on the RCW 106 East and West region with the massive star formation having the bright infrared dust emission, we found that these regions have three different velocity components with ∼10 km s⁻¹ differences. The two out of three velocity components show morphological correspondence with the infrared cold dust emission and connect with the bridge feature on a position–velocity diagram. Therefore, two molecular clouds with ∼10 km s⁻¹ differences are likely to be physically associated with massive star-forming regions in the GMC complex. Based on these observational results, we argue that mini-starbursts and massive star/cluster formation in the RCW 106 GMC complex are induced by supersonic cloud–cloud collisions in an agglomerate of molecular gas on the Scutum–Centaurus arm.

Gl 229 is a well-known system hosting the first confirmed brown dwarf (BD), Gl 229 B, discovered in 1995. Subsequent radial velocity (RV) follow-up of the star unveiled, in 2014, an exoplanet on a 471 days orbit with a minimum mass of  ∼32 M_⊕. In 2020, a second exoplanet with a 122 days orbital period and a minimum mass of approximately 7 M_⊕ was reported. With its BD, now a known binary, and two exoplanets, Gl 229 has been deemed one of the most diverse systems and has sparked discussions regarding the different formation mechanisms that could have taken place around this star. This work presents a new analysis of the publicly available Gl 229 High Accuracy Radial Velocity Planet Searcher data reduced with the line-by-line precision RV algorithm resistant to spectral outliers. We find strong evidence for stellar activity impacting RV measurements. Stellar activity-induced RVs were modelled with a Gaussian process trained on the activity indicator provided by the algorithm, revealing the star's rotation period at 28.9 ± 1.6 days. We show that systematic errors and stellar activity are the most likely cause of the previously reported exoplanet signals. Our analysis provides a 3σ upper limit of 9.1 M_⊕ for a planet in the system's habitable zone except for the periods close to the star's rotation period, where stellar activity worsens the limit to around 15 M_⊕.

Astrometric measurements are significantly challenged by the relative motion between the point source and the telescope, primarily due to the difficulty in accurately determining the position of the point source at the mid-exposure moment. Especially when the trail is irregular in shape or results from nonuniform relative motion, determining the centroid of such a trail becomes significantly more challenging. To address this issue, a new centroiding algorithm for point-source trails has been developed. This algorithm employs a piecewise linear model to approximate the irregular trajectory of a point source. An estimated intensity distribution of the trail is constructed by integrating the point-spread function with the approximated trajectory. The cost function is defined as the difference between the estimated and observed trail intensity distributions, with an added smoothness constraint term. Optimizing this cost function yields a refined trajectory fit. A coarse-to-fine iterative approach is used to progressively converge on the true trajectory of the point source, ultimately determining both the trail’s centroid and the trajectory of the point source. The efficacy of the algorithm is validated using synthetic images. Furthermore, this technique is applied to Cassini Imaging Science Subsystem images of several inner Saturnian satellites, successfully processing 267 astrometric observations. The results demonstrate the effectiveness of the algorithm in real astronomical applications.

We present a MIRI-MRS spectrum of the high-inclination protoplanetary disk around the solar-mass (K0) star MY Lup, obtained as part of the JWST Disk Infrared Spectral Chemistry Survey (JDISCS). The spectrum shows an unusually weak water emission spectrum for a disk around a star of its spectral type, but strong emission from CO₂, HCN, and isotopologues of both molecules. This includes the first ever detection of C¹⁸O¹⁶O and H¹³CN in an inner disk, as well as tentative detections of C¹⁷O¹⁶O and HC¹⁵N. Slab modeling provides the molecular temperatures, column densities, and emitting areas of the detected molecules. The emitting molecular gas is cold compared to that of other observed protoplanetary disk spectra. We estimate the isotopologue ratios of CO₂ and HCN, albeit with significant uncertainty. We suggest that the unusual spectrum of MY Lup arises from a combination of inner-disk clearing, which removes emission from warm water, and its nearly edge-on inclination, which enhances line-of-sight column densities, although unusual chemistry may also be required. MY Lup’s spectrum highlights the potential to detect and measure trace isotopologues to study isotopic fractionation in protoplanetary disks; observations at higher spectral resolving power are needed to constrain the isotopologue ratios to greater precision.

The upcoming all-sky infrared spectrophotometric SPHEREx mission is set to provide spatially resolved stellar mass maps of nearby galaxies, offering more detailed insights than integrated light observations. In this study, we develop a strategy for estimating stellar mass using SPHEREx by examining the dependence on different stellar population synthesis (SPS) models and proposing new scaling relations based on simulated SPHEREx data. We estimate the resolved stellar masses of 19 nearby late-type galaxies from the PHANGS-MUSE survey, treating these as fiducial masses. By testing four SPS models covering infrared wavelengths, i.e., E-MILES, Bruzual & Charlot (BC03), Charlot & Bruzual (CB19), and FSPS, we find systematic differences in mass-to-light ratios at 3.6 μm (M_*/L_{3.6 μm}) among the SPS models. In particular, BC03 and CB19 yield mass-to-light ratios on average  ∼0.2−0.3 dex lower than those from E-MILES and FSPS. These mass-to-light ratios strongly correlate with stellar age, indicating a significant impact of young stellar populations on stellar mass measurements. Our analysis, incorporating fiducial masses and simulated SPHEREx data, identifies the 1.6 μm band as the optimal wavelength for stellar mass estimation, with the lowest scatter (0.15−0.20 dex) of the stellar mass. This scatter can be further reduced to 0.10−0.12 dex across all SPS models by incorporating optical and SPHEREx colors. These results can provide guidance for measuring the stellar masses of the numerous nearby galaxies that SPHEREx will survey.

We present new color–ϒ_* (mass-to-light ratio) models to convert Wide-field Infrared Survey Explorer W1 fluxes into stellar masses. We outline a range of possible star formation histories and chemical evolution scenarios to explore the confidence limits of stellar population models on the value of ϒ_*. We conclude that the greatest uncertainties (around 0.1 dex in ϒ_*) occur for the bluest galaxies with the strongest variation in recent star formation. For high-mass galaxies, the greatest uncertainty arises from the proper treatment of bulge–disk separation in which to apply different ϒ_* relations appropriate for those differing underlying stellar populations. We compare our deduced stellar masses with those deduced from Spitzer Space Telescope 3.6 μm fluxes and stellar mass estimates in the literature using optical photometry and different ϒ_* modeling. We find the correspondence to be excellent, arguing that rest-frame near-IR photometry is still more advantageous than other wavelengths.

We present the discovery of a low-density planet orbiting the high-metallicity early M-dwarf TOI-5688 A b. This planet was characterized as part of the search for transiting giant planets (R ≳ 8 R_⊕) through the Searching for Giant Exoplanets around M-dwarf Stars (GEMS) survey. The planet was discovered with the Transiting Exoplanet Survey Satellite, and characterized with ground-based transits from Red Buttes Observatory, the Table Mountain Observatory of Pomona College, and radial velocity (RV) measurements with the Habitable-Zone Planet Finder on the 10 m Hobby Eberly Telescope and NEID on the WIYN 3.5 m telescope. From the joint fit of transit and RV data, we measure a planetary mass and radius of 124 ± 24 M_⊕ (0.39 ± 0.07 M_J) and 10.4 ± 0.7 R_⊕ (0.92 ± 0.06 R_J), respectively. The spectroscopic and photometric analysis of the host star TOI-5688 A shows that it is a metal-rich ([Fe/H] = 0.47 ± 0.16 dex) M2V star, favoring the core-accretion formation pathway as the likely formation scenario for this planet. Additionally, Gaia astrometry suggests the presence of a wide-separation binary companion, TOI-5688 B, which has a projected separation of ~5″ (1110 au) and is an M4V, making TOI-5688 A b part of the growing number of GEMS in wide-separation binary systems.

We present high-resolution near-ultraviolet (NUV) and far-ultraviolet (FUV) deep imaging of the field around the Seyfert galaxy IC 4329A based on five observations performed with the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat. The long exposures of 82.9 ks in the NUV (N245M; λ_mean = 2447 Å; Δλ = 270 Å) and 92.2 ks in the FUV (F154W; λ_mean = 1541 Å; Δλ = 380 Å) bands constitute the deepest observations with 5σ detection limits of AB magnitudes m_NUV = 26.2 and m_FUV = 25.7. Leveraging UVIT's excellent angular resolution (FWHM ∼ 1.2″-1.8″, we performed a detailed analysis of the IC 4329A field and detected (above the 5σ significance level) a total of 4437 and 456 sources in the NUV and FUV bands, respectively. A large number of these detected sources were previously unknown. We performed astrometry and photometry on all detected sources. By cross-matching our catalog with the Gaia-DR3 and XMM-Newton DR12 catalogs, we found 651 optical and 97 X-ray counterparts of our sources. Additionally, we explored the UV variability of point sources, identifying 28 NUV sources as variable with a significance above the 2.5σ level. Of these, only three sources exhibited variability in the FUV band. Utilizing the NUV and Gaia fluxes, we determined that two previously cataloged white dwarf candidates are misclassified. Furthermore, we highlight galaxies with atypical morphology, including ring-like structures, multiple compact central sources, bifurcating spiral arms, and so on. Follow-up optical spectroscopy and multiwavelength observations are imperative to further investigate the nature of the sources within this field.

A significant fraction of hot Jupiters have orbital axes misaligned with their host stars’ spin axes. The large stellar obliquities of these giants have long been considered potential signatures of high-eccentricity migration, which is expected to clear out any nearby planetary companions. This scenario requires that only isolated hot Jupiters be spin–orbit misaligned while those with nearby companions, which must have more quiescent histories, maintain low-obliquity orbits, assuming they formed aligned within their primordial protoplanetary disks. Investigations of this stellar obliquity–companionship connection, however, have been severely limited by the lack of hot Jupiters found in compact multiplanet systems. Here, we present the sky-projected stellar obliquity (λ) of a hot Jupiter with a nearby inner companion recently discovered by NASA's Transiting Exoplanet Survey Satellite: TOI-5143c. Specifically, we utilize the Doppler shadow caused by the planet's transit, enabled by the Rossiter–McLaughlin (RM) effect, to find that the planet is aligned with . Of the exoplanets with RM measurements, TOI-5143c becomes just the third hot Jupiter with a nearby companion, and is part of the 19th compact multiplanet single-star system, with an RM measurement. The spin–orbit alignment of these 19 systems provides strong support for primordial alignment, and thus implies that large obliquities are gained primarily due to postdisk dynamical interactions such as those inherent to high-eccentricity migration. As such, the observed spin–orbit alignment of hot Jupiters with nearby companions affirms that some fraction of these giants instead has quiescent origins.