Planetary nebulae (PNe) trace the late evolution of low-to-intermediate-mass stars, yet the masses of their progenitors are rarely measured directly. Here we present a PN physically associated with a young star cluster in M31, providing an unprecedented extragalactic empirical anchor in the poorly constrained high-mass regime of PN progenitors. High-resolution Hubble Space Telescope imaging shows that the nebula lies near the cluster center, and spectral decomposition of the blended cluster-plus-nebula spectrum yields consistent stellar and nebular radial velocities, strongly supporting a physical association. Isochrone fitting to the color-magnitude diagram indicates a cluster age of similar to 90 Myr and a near-solar metallicity, implying a progenitor initial mass of 5.66-0.37+0.42M circle dot . This value is among the highest empirical progenitor-mass constraints yet reported for any PN and approaches the lower boundary of the super-asymptotic giant branch (super-AGB) regime. We further find that the nebula is strongly nitrogen-enhanced, with an N/O ratio similar to 7 times the solar value, broadly consistent with hot bottom burning in a relatively massive AGB progenitor. This system therefore provides a rare opportunity to test PN formation and nucleosynthesis at the high-mass end of the PN progenitor distribution.

Cepheids are fundamental distance indicators, playing a crucial role not only in the cosmic distance ladder but also in mapping the structure, kinematics, and extinction properties of the Milky Way. Using high-precision photometry and parallaxes from Gaia Data Release 3, we identify a significant anticorrelation between the G-band extinction coefficient and reddening for Galactic Cepheids, quantified as RG = 1.918 +/- 0.060 - (0.106 +/- 0.022) E(GBP - GRP). We propose that this anticorrelation arises from the combination of the nonlinear effects inherent to the broad Gaia bands and the RV variations caused by the diverse interstellar medium. Adopting a fixed RG would not only lead to an overestimation of the metallicity dependence of Cepheid luminosities but also systematically underestimate the distances to highly reddened Cepheids. Moreover, the strong reddening dependence of RG makes the Wesenheit function based on it unsuitable for highly reddened Cepheids, since the definition of Wesenheit magnitudes requires a fixed extinction coefficient. In contrast, infrared-based distances, being less affected by nonlinear effects and insensitive to RV, provide the most reliable Cepheid distances at present. This work emphasizes the importance of accurately determining RV for Galactic Cepheids and accounting for nonlinear effects in distance measurements, particularly in the optical bands.

Eclipsing binaries are crucial astrophysical laboratories for studying stellar parameters and evolutionary processes. In this study, we constructed a machine learning-based model for systematic phenomenological classification of eclipsing binaries. We first extracted eclipsing binaries from the ASAS-SN variable star catalog and crossmatched them with TESS targets. The corresponding TESS light curves were processed through a unified pipeline, resulting in a high-quality training set of 9576 eclipsing-binary light curves (2801 EA, 1930 EB, and 4845 EW systems). We designed and trained a fully connected neural network that achieved accuracies of 99.23% and 99.03% on the validation and test sets, respectively, demonstrating excellent performance. Applying the trained neural network to a total of 20,196 TESS eclipsing binaries collected from multiple star catalogs and performing manual visual inspection, we finally obtained 13,376 EA, 2114 EB, and 4706 EW systems. The standardized preprocessing pipeline and high-performance classifier developed in this study provide a reliable tool for the rapid automated classification of massive numbers of eclipsing binaries in future photometric surveys.

The Hubble constant, H_0, links the nearby distance scale to the present cosmic expansion rate. Local distance-ladder measurements now reach percent-level precision and remain more than 5σ higher than the value inferred from cosmic microwave background (CMB) observations in base-ΛCDM, making the reliability of the local ladder a central issue in the Hubble tension. We describe the ladder as a covariance network connecting level-0 geometric anchors, level-1 stellar distance indicators, and level-2 Hubble-flow probes. The Cepheid–Type Ia supernova (SN Ia) route remains the most precise single local ladder, but independent indicators including the tip of the red giant branch (TRGB), J-region asymptotic giant branch (JAGB) stars, Mira variables, surface-brightness fluctuations (SBF), the Tully–Fisher relation, and Type II supernovae (SNe II) now test shared and method-specific systematics. In a compact seven-route covariance summary, combining the Cepheid–SN Ia route with three level-1 alternatives (TRGB, JAGB, and Mira) and three level-2 alternatives (SBF, Tully–Fisher, and SNe II) gives H_0=73.30±0.92 km s^-1 Mpc^-1, still 5.6σ above Planck base-ΛCDM. JWST has already tested Cepheid crowding and is making independent TRGB-based H_0 measurements increasingly feasible. Over the next five years, a reliable one-percent local H_0 requires larger calibrator samples, cross-validated level-1 zero points, explicit covariance propagation, and AI-assisted, reproducible, pre-specified selection criteria for distance-indicator measurements.

Extreme debris disks provide time-domain probes of rocky planet assembly after giant impacts. We compare Spitzer and JWST spectra of the warm debris disk around HD 15407A, obtained 14.95 yr apart. Across 6-25μm, the stellar-subtracted mid-infrared excess declined by 14.0±1.2

Extinction significantly affects open cluster parameters and their use in studies of Galactic structure, yet homogeneous large sample measurements of open cluster extinction properties remain limited. Using Gaia-era open cluster member samples combined with multi-band photometry and stellar parameters, we derive color excesses of member stars and provide the homogeneous characterization of the mean reddening, differential reddening, and color excess ratio (CER) at the cluster scale. Differential reddening increases systematically with mean reddening, with highly reddened clusters near the Galactic plane showing stronger extinction variations. Star-by-star reddening corrections narrow color–magnitude diagram (CMD) sequences in 369 of 435 clusters (85

Using 200,388 red clump stars from LAMOST and APOGEE, we investigate the radial metallicity gradients of the Galactic disk as a function of vertical height and stellar age. The thin disk displays a pronounced negative radial metallicity gradient near the Galactic mid-plane that progressively flattens with increasing |Z|, following Δ[Fe/H]/ΔR = -0.0784 + 0.0776 (1 - exp (- |Z|/1.4244)). The thin disk also exhibits a clear age dependence in radial metallicity gradients, evolving smoothly from a strong gradient regime for young stars to a weak gradient regime for old stars, following Δ[Fe/H]/ΔR = -0.0438 + 0.0233 tanh ((τ - 11.2908)/4.2130). The thick disk shows weakly positive radial metallicity gradients that remain statistically invariant with respect to both vertical height and stellar age, following respectively, Δ[Fe/H]/ΔR = 0.0038 + 0.0009 |Z| and Δ[Fe/H]/ΔR = 0.0146 - 0.0007 τ. These results indicate that the thin disk retains radial metallicity gradients shaped by relatively ordered inside-out growth and long-term secular evolution processes. The thick disk exhibits spatially and temporally homogeneous radial metallicity gradients, supporting a picture in which it formed rapidly during an early phase when the disk was dynamically hot and efficiently mixed, potentially in chaotic mergers of gas-rich systems and/or the turbulent ISM.

Rotationally modulated photometric variability of ultracool dwarfs encodes key information about cloud structure and temperature contrasts. Large homogeneous optical datasets are crucial for linking atmospheric heterogeneity to fundamental parameters such as rotation, mass, and age. We present a search for rotation periods in ultracool dwarfs using Zwicky Transient Facility (ZTF) optical light curves. By propagating the coordinates to the ZTF epoch and applying Lomb-Scargle analysis, we identified 226 periodic variables, including 32 robust detections and 194 tentative cases. Among the robust detections, 12 have no previously published periods, while 20 have literature counterparts, most of which are consistent with the published values. Most robust detections are M dwarfs, reflecting the optical sensitivity limits of ZTF. We find a trend of decreasing periods toward later spectral types in relatively old dwarfs (>100 Myr), suggesting faster rotation for late-M types than for mid-M types. The age-period relation of our sample is broadly consistent with angular-momentum-conservation models at the higher-mass regime of brown dwarfs, consistent with the M-dwarf bias of our catalog. Many additional candidates remain to be confirmed due to sparse sampling or low S/N. Future high-cadence, multiwavelength monitoring and systematic mining of ZTF and upcoming surveys will be crucial for validating these periods, extend sensitivity to later (L/T) types, and better connect rotation with cloud physics across the stellar-substellar boundary.

High-quality, short-cadence photometry from TESS enables the detection of rapid oscillators with unprecedented sensitivity. In this work, we conduct a homogeneous search for high-frequency variability using 20 s cadence light curves from TESS Cycle 7 (Sectors 84-96). From similar to 3.9 & times; 104 light curves, we compute Lomb-Scargle periodograms and select candidates exhibiting at least one significant signal with a false-alarm probability <= 10-4 at frequencies f >= 50 day-1. After excluding previously reported objects and performing pixel-level and light-curve vetting to mitigate contamination, we identify 73 rapid oscillators, including 24 pulsating white dwarfs, 31 hot subdwarfs, and 18 A/F stars. Using an iterative prewhitening procedure, we carry out a detailed frequency analysis for each target and derive the oscillation frequencies and amplitudes. We further investigate the physical origins of the detected frequency content and present statistical characterizations of the rapid-oscillator sample. We highlight one white dwarf and one subdwarf that exhibit clear frequency multiplets consistent with rotational splitting. This work enlarges the sample of rapid oscillators accessible with TESS data and provides a uniformly measured frequency-amplitude catalog, establishing a consistent basis for future asteroseismic and population studies.

Context. The surface brightness–color relation (SBCR) links stellar color to angular diameter and is a key ingredient of geometric distance measurements on the first rung of the cosmic distance ladder. However, previous calibrations based on the red giant branch (RGB) were limited by small samples and did not observably constrain the role of metallicity. Aims. We aim to quantify the metallicity dependence of the SBCR for RGB stars and to test the robustness of the relation using asteroseismic radii, Gaia distances, and atmospheric parameters from APOGEE. Methods. We selected more than 2000 RGB stars from APOKASC-3 to calibrate and validate the SBCR. Johnson V magnitudes were synthesized from Gaia XP spectra and homogenized to widely used SBCR photometric systems, while Ks photometry was taken from 2MASS. Angular diameters derived from asteroseismic radii and Gaia distances (the ARD method) were used to construct the SBCR. We explored three fitting strategies: metallicity-free, metallicity-binned, and global metallicity-dependent relations. Results. Over the range (V − Ks) ≈ 2 − 3, the SBCR shows only a weak metallicity dependence. A change of 1 dex in [Fe/H] modifies the predicted angular diameter by less than 1%, well below the intrinsic scatter of the calibration (∼0.05 mag). This result is consistent with theoretical expectations. Comparison with the interferometric sample reveals a systematic offset of ∼1.5% toward smaller angular diameters in our SBCR predictions, with a mild color dependence. Conclusions. The metallicity effect on the SBCR is small in the color range explored here, but it becomes relevant for sub-percent distance measurements. Our results show that large RGB samples with asteroseismic radii and Gaia distances provide a powerful observational route for SBCR calibration, with clear potential for extensions to cooler and redder giants as the precision and parameter coverage of the input data improve.

We report the discovery of LAMOST J0041+3948, the most luminous post-asymptotic giant-branch (AGB) Type II Cepheid known, located in the Andromeda Giant Stellar Stream. Its spectral energy distribution (SED) exhibits a strong near-infrared excess, indicating the presence of a circumbinary dusty disk and hence binarity. SED fitting yields an effective temperature of Teff=6738-262+234 K and a post-AGB luminosity of log(L/L circle dot)=4.32-0.08+0.07 . Comparison with theoretical evolutionary tracks suggests a similar to 2.0-4.0 M circle dot progenitor when accounting for a possible scattered-light contribution. Zwicky Transient Facility light curves reveal a pulsation period of 89 days that lies close to the period-luminosity relation for long-period RV Tauri stars. Follow-up spectroscopy reveals clear s-process enrichment and signatures consistent with an accretion disk around the companion. The inferred progenitor is significantly younger and more massive than a typical stream member, suggesting that an additional mechanism, such as a stellar merger, is required. We propose a formation channel in which the present post-AGB binary descends from a hierarchical triple system. In this scenario, the inner binary merged after the system was displaced to its current location by the galaxy merger event, and the resulting massive merger remnant subsequently evolved into the extremely luminous post-AGB star observed today.

With the rapid development of time-domain surveys, the availability of large-scale light-curve data offers new opportunities for studying stellar evolution and variable-star classification, while simultaneously posing challenges for feature extraction and modeling. We present StarCLR, a contrastive pretraining framework for large-scale light curves. By constructing positive pairs from partially overlapping subsequences, StarCLR learns robust temporal representations. We pretrain StarCLR on the Transiting Exoplanet Survey Satellite (TESS) dataset and fine-tune it for variable-star classification across three surveys with distinct observational characteristics: TESS (18 types), the Zwicky Transient Facility (ZTF; 11 types), and Gaia (24 types). StarCLR achieves macro-F1 scores of 84.35%, 87.82%, and 92.73%, and micro-F1 scores of 94.46%, 92.83%, and 99.49%, respectively. Compared with LSTM and transformer models trained from scratch, StarCLR performs better on TESS and ZTF, with the largest gains on sparsely sampled ZTF light curves, demonstrating promising generalization. For Gaia, which involves a broader class space, the evaluation is not directly comparable, and performance is likely influenced by astrophysical feature differences, resulting in a more limited contribution from the pretrained backbone. Systematic ablations on embedding design, pooling strategy, and pretraining settings further indicate that the pretrained representations provide performance gains by capturing informative temporal characteristics of light curves. Looking ahead, with standardized datasets and more diverse labeling schemes, the generalization ability of StarCLR can further be enhanced. The inference code and pretrained model weights are made available on GitHub (https://github.com/dj-y/StarCLR-Inference).

Variable stars play a crucial role in advancing knowledge of stellar evolution, Galactic structure, and cosmological distance scales. The advent of massive datasets from modern time-domain surveys (e.g., Zwicky Transient Facility, All-Sky Automated Survey for Supernovae, or Gaia) has made the classification of these stars increasingly complex. Traditional methods depend extensively on manual feature engineering, a process that is both labor-intensive and difficult to scale, thereby impeding timely scientific progress. To address these limitations, we propose a novel classification framework that treats photometric light curves as structured sequences and fine-tunes a pretrained large language model (LLM) for variable star classification with only a small amount of labeled data. We design a unified tokenization scheme that integrates both time-series measurements and physical parameters (period, parallax, and color index) into a single textual prompt, thereby streamlining traditional feature engineering. When evaluated on a multisurvey dataset comprising 19,580 labeled variable stars across nine classes, the optimal model achieves an overall accuracy of 0.98 and a weighted F _1 score of 0.98. We also verify the complementary contributions of each physical parameter through ablation studies. Our study indicates that LLM-based sequence modeling constitutes an accurate, scalable, and flexible alternative to conventional methods, with strong potential for integration into future large-scale classification of variable stars.

We present the SPHEREx Ultracool Dwarf spectrophotometric Atlas (SUDA), a homogeneous sample of 1675 field ultracool dwarfs with continuous 0.75–5 μm spectrophotometry from SPHEREx Quick Release 2 (QR2). Using the SAND and ATMO2020++ atmospheric grids, we derive atmospheric parameters, compute bolometric luminosities (L_ bol), and combine T_eff and radii with evolutionary tracks to estimate masses, ages, and evolutionary log g. For sources at 1700–2500 K, spectroscopic log g is systematically lower than evolutionary log g, with a median offset of ∼1.05 dex, likely driven primarily by cloud-related model uncertainties. We further construct an empirical atlas by binning the measurements in T_eff and evolutionary log g, producing 57 spectrophotometric templates spanning T_eff≃700–3000 K. Molecular indices trace a coherent atmospheric sequence: H_2O and CH_4 indices strengthen toward lower T_eff, while CO and CO_2 indices increase below ∼1500 K and turn over near ∼1000 K. Model comparisons indicate that CO_2 index is more sensitive to metallicity than gravity at T_eff∼800–1200 K. SUDA provides a reference sample linking 0.75–5 μm spectrophotometric morphology to atmospheric and evolutionary trends in ultracool dwarfs.

Dust extinction laws are essential for precision photometry and provide a direct probe of grain properties, but their behaviour in dense molecular clouds remains poorly constrained at high extinction. Using Euclid Quick Data Release 1 (Q1) imaging of the Orion A dark cloud Lynds Dark Nebula 1641 (LDN 1641), we measured the extinction law from the broad Visible Instrument (VIS) band and the Near-Infrared Spectrometer and Photometer (NISP) Y, J, and H bands along sightlines reaching A_V∼ 30 mag towards the cloud core. We derived colour-excess ratios E(λ-H)/E(Y-H) from linear fits to colour–colour diagrams of (λ-H) versus (Y-H) and converted them into relative extinctions, A_λ/A_H. The near-infrared extinction in LDN 1641 is well described by a power law, A_λ∝ λ^-α, with α=1.57 ± 0.06, corresponding to A_ VIS/A_H=4.23 ± 0.24, A_Y/A_H=2.13 ± 0.18, and A_J/A_H=1.47 ± 0.11. We further find significant spatial variations: α changes by up to 27%, with systematically smaller values and therefore flatter extinction curves in higher-extinction regions. This flattening is consistent with an enhanced large-grain population and supports substantial grain growth from the diffuse outskirts to the dense core of a single molecular cloud.

RR Lyrae stars are essential standard candles for distance measurements in the Milky Way and nearby galaxies. Traditional estimates rely on the Period–Absolute Magnitude–Metallicity relation but are limited by uncertainties in metallicity determinations. We present a deep learning approach that directly predicts absolute magnitudes from RRab and RRc light curves, eliminating the need for metallicity estimates. Our model achieves validation precisions of 0.053 mag and 0.036 mag (approximately 2.5% and 1.7% in distance) for individual RRab and RRc stars, respectively. Tests on globular clusters yield typical distance precisions of 1.0% for RRab and 1.7% for RRc stars. For the benchmark systems, combining the RRab- and RRc-based models yields distance moduli of 18.498±0.001stat±0.018sys mag for the Large Magellanic Cloud and 19.564±0.003stat±0.019sys mag for the Sculptor dwarf spheroidal galaxy. These measurements are in excellent agreement with previous results, achieve a distance precision of approximately 1%, and represent a 1.8-fold improvement over traditional RR Lyrae calibration relations. Our approach showcases the ability of AI to directly extract key physical parameters from complex, information-rich light curves, resolve degeneracies, and scale to broader applications

The Chinese Space Station Survey Telescope (CSST) is an upcoming Stage-IV sky survey telescope, distinguished by its large field of view (FoV), high image quality, and multi-band observation capabilities. It can simultaneously conduct precise measurements of the Universe by performing multi-color photometric imaging and slitless spectroscopic surveys. The CSST is equipped with five scientific instruments, i.e., Multi-band Imaging and Slitless Spectroscopy Survey Camera (SC), Multi-Channel Imager (MCI), Integral Field Spectrograph (IFS), Cool Planet Imaging Coronagraph (CPI-C), and THz Spectrometer (TS). Using these instruments, CSST is expected to make significant contributions and discoveries across various astronomical fields, including cosmology, galaxies and active galactic nuclei (AGN), the Milky Way and nearby galaxies, stars, exoplanets, Solar System objects, astrometry, and transients and variable sources. This review aims to provide a comprehensive overview of the CSST instruments, observational capabilities, data products, and scientific potential.

We use a cross-matched sample of 3.7 million stars from Gaia DR3 and LAMOST DR7 to investigate the velocity substructures in the Milky Way disk. The median radial velocity V_R as a function of guiding-center radius R_g exhibits alternating positive and negative stripes, which are strongly correlated with known moving groups. By examining the V_R distribution in the Z–V_Z phase space, we find that the D1, P2, D2, and P3 V_R stripes display clear two-armed spirals. Among the moving groups embedded in these V_R stripes, the Coma Berenices moving group in the P3 stripe exhibits the most pronounced two-armed spiral and serves as the primary contributor to the left arm of the overall P3 spiral. The angular momentum, eccentricities, orbital frequencies, and frequency ratios of its stars are consistent with either the corotation resonance of the spiral arms or the m=4 inner Lindblad resonance of the bar. Test-particle simulations confirm that a bar with a varying pattern speed, together with static or transient spiral arms, can produce such two-armed spirals.

We present a homogeneous HST/ACS F555W/F814W time-series census of variable stars in two M101 disk fields, using a uniform multi-band reduction and reproducible variable-selection workflow for nearby SN-host galaxies. Supplementary archival F555W epochs are used only to refine selected long-period solutions. Candidates are selected with Lomb-Scargle period searches, Fourier light-curve modeling, two-band consistency statistics, artificial-star-test photometric corrections, and mode-aware Cepheid refinement. The final catalog contains 1417 variable-star candidates, including 1102 secure fundamental-mode and 78 secure first-overtone classical Cepheids. Of these secure Cepheids, 420 are newly identified relative to the Shappee Stanek catalog. The catalog also contains luminous candidates outside the classical Cepheid locus. We release the catalog and source-level two-band light curves for studies of Cepheid physics, stellar variability, and distance-scale applications.

Aims: We aim to quantify the metallicity dependence of the SBCR for red giant branch (RGB) stars and to test the robustness of the relation using asteroseismic radii, Gaia distances, and atmospheric parameters from APOGEE. Methods: We selected more than 2,000 RGB stars from APOKASC-3 to calibrate and validate the SBCR. Johnson V magnitudes were synthesized from Gaia XP spectra and homogenized to widely used SBCR photometric systems, while K_s photometry was taken from 2MASS. Angular diameters derived from asteroseismic radii and Gaia distances (ARD) were used to construct the SBCR. We explored three fitting strategies: metallicity-free, metallicity-binned, and global metallicity-dependent relations. Results: Over the range V-K_s=2-3, the SBCR shows only a weak metallicity dependence. A change of 1 dex in [Fe/H] modifies the predicted angular diameter by less than 1