Abstract Blue straggler stars (BSSs) are believed to form through mass transfer in binary systems or stellar collisions. The reported presence of double BSS sequences in some globular clusters (GCs) has been interpreted as evidence that these two formation channels produce distinct sequences in color–magnitude diagrams. We reassess this claim using Hubble Space Telescope (HST) UV Globular Cluster Survey photometry of 56 Galactic GCs. We used the Hartigan dip test to test bimodality, and Akaike model comparison to test whether BSS distance distributions are better described by a mixture of two unskewed Gaussians or a skewed unimodal Gaussian model. We find no strong statistical evidence for bimodality: no cluster yields a dip test p -value below 0.15, and the Akaike model comparison favors the skewed unimodal model in 94 out of 112 cases. We reexamine NGC 7099 (M30), the prototypical case of a double BSS sequence, using three reductions of HST data. We find bimodality is detected at p = 4 × 10 −3 , versus the originally reported p ∼ 10 −5 , in the original photometry. The observed uncertainties derived from the subgiant branch widths are comparable to the suggested separation between the proposed BSS sequences, making the detection of statistically significant bimodality challenging. Our results suggest that the dip between two BSS sequences in the M30 photometry is a coincidence, and that later bifurcation claims can be explained as skew in the BSS color distribution, rather than two separate distributions.

Abstract We present a ground-based time-series photometric study of stellar variability in four intermediate- to old-age open clusters—NGC 2192, NGC 2266, NGC 2509, and IC 1369—based on high-cadence Cousins R -band observations obtained with the 0.6 m VASISTHA telescope at the IERCOO observatory. The monitoring campaign comprises more than ∼34 hr of time-series data, providing sensitivity to short-period variability on timescales of ∼0.02–2 days. We identified between 190 and 290 probable members in each cluster using a Gaussian mixture model. Structural parameters were derived from radial density profiles fitted with King models. Fundamental parameters were further constrained using color–magnitude diagram analysis with PARSEC isochrones, yielding ages of ∼0.3–1.6 Gyr and distances of ∼2.5–3.9 kpc. From the time-series photometry, we identify four new variable stars and seven previously uncharacterized periodic variables, including δ Scuti and γ Doradus pulsators, as well as rotational variables. The detected variables exhibit periods between ∼0.12 and 0.90 days, with R -band amplitudes ranging from 0.01 to 0.20 mag. Periods were determined using Lomb–Scargle analysis of calibrated light curves. For a subset of variables, spectral energy distribution fitting was performed to derive effective temperatures (∼4300–10,000 K), radii (∼1.3–46 R ⊙ ), and luminosities (∼2–100 L ⊙ ), enabling reliable placement on the Hertzsprung–Russell diagram. We present PHOEBE light-curve modelling of the W UMa-type eclipsing binary Gaia DR3 2164531610149292288 in IC 1369, deriving its physical parameters and providing the first detailed characterization beyond its previously reported variability. These results demonstrate that combining dense-cadence ground-based observations with Gaia astrometry provides a reliable approach for identifying and characterizing variable stars in open clusters.

Abstract The Sagittarius dwarf spheroidal galaxy (Sgr dSph) provides us with the unique opportunity to study an ongoing Galactic cannibalistic event between our Milky Way (MW) Galaxy and a satellite dwarf galaxy. Understanding this event crucially requires memberships and high-precision metallicities. Here, we present the first major membership star catalog of the Sgr dwarf core (≈140,000 sources) and Messier 54 (M54; ≈2000 sources) with positions, proper motions, and parallaxes from the third Gaia data release (DR3), supplemented with metallicities from the Apache Point Observatory Galactic Evolution Experiment (or APOGEE). We initially isolate the Sgr dwarf core and M54 spatially from prior literature positions. Using evolutionary subsamples separated within a color–magnitude diagram, we analyze the substructures of the Sgr core and infer its positional relationship with M54 within 5D phase space. A sample of MW stars from a similar Galactic latitude were used to identify contaminants and separate member stars from the core of the Sgr dSph and M54 using a Gaussian mixture model. We present the derived proper motions, parallaxes, and metallicities for these evolutionary subsamples and demonstrate the precision of our sample using red clump (RC) standard candles. We find distance moduli for the Sgr core and M54 of ( m − M ) 0 = 16.95 8 − 0.044 + 0.044 mag and ( m − M ) 0 = 16.9 4 − 0.056 + 0.047 mag, corresponding to heliocentric distances of d = 24.63 5 − 0.49 + 0.49 kpc and d = 24.45 2 − 0.602 + 0.537 kpc, respectively. Using RC distance analysis, our results imply that there is no separation between the Sgr core and M54. Finally, we describe the metallicity distributions of the evolved stars within these two systems, finding evidence for the infall scenario.

Ultra-faint dwarf galaxies (UFDs) are among the oldest and most metal-poor stellar systems in the Universe. Their metallicity distribution encodes the fossil record of the earliest star formation, feedback, and chemical enrichment, providing crucial tests of models of the first stars, galaxy assembly, and dark matter halos. However, due to their faint luminosities and the limited number of bright giants, spectroscopic studies of UFDs typically probe only small stellar samples. Here, we present an analysis of multi-epoch Hubble Space Telescope and James Webb Space Telescope observations of the UFD Boötes I. Using a deep color–magnitude diagram in the F606W and F322W2 bands, extending from the subgiant branch to the M dwarfs, and stellar proper motions to identify likely members, we obtained an unprecedentedly clean census of the system. The exquisite quality of the diagram, combined with the sensitivity of M-dwarf colors to metallicity, allowed us to constrain the metallicity distribution in a large stellar sample. As a first step, we then exploited the metallicity sensitivity of M-dwarf colors to derive the metallicity distribution function. We find that most of the stars ∼85% have [Fe/H] < −2, and that roughly ∼17% have [Fe/H] < − 3. Then, we derived the binary fraction in Boötes I. This is crucial since binaries can bias kinematic mass estimates, affect stellar population analyzes, and shape the photometric signatures used to infer metallicity. We find that 20 ± 2% of stellar systems in Boötes I are binaries with mass ratios larger than 0.4, corresponding to a total binary fraction of ∼30%. This value is comparable to the binary fractions observed in globular clusters of similar stellar mass, suggesting that the presence of dark matter does not significantly affect the binary properties of Boötes I.

A significant fraction of stars in both the Galactic field and stellar clusters belong to binary systems. Understanding their properties is therefore fundamental for a comprehensive picture of stellar structure, stellar evolution, and cluster dynamics. Despite extensive work on binaries in clusters, key questions remain open, particularly concerning photometric binaries among low-mass stars. While the binary fraction among field stars shows a strong dependence on stellar mass, studies of star clusters have so far suggested an approximately constant fraction across the limited mass range explored. Moreover, the mass function (MF) of very low-mass stars remains poorly constrained in clusters older than a few hundred million years. In this work, we used deep Hubble Space Telescope imaging of the intermediate-age open cluster NGC 2158 to investigate its binary population and derive the luminosity and MFs down to ∼0.14 M ⊙ . This dataset enables the first detailed study of binaries in this cluster. We obtained a global binary fraction of 38%, which is consistent with that observed in other open clusters, and detected a clear mass dependence: the fraction decreases from ∼52% at 1.0 M ⊙ to ∼11% at 0.2 M ⊙ . This trend mirrors that seen in the Galactic field, which suggests that binaries in NGC 2158 and field populations share similar properties. The MF of NGC 2158 is best described by three regimes: high-mass stars ( α = −2.49 ± 0.19), low-mass stars ( α = −1.11 ± 0.09), and very low-mass stars ( α = −0.08 ± 0.07). The slope change near 1.0 M ⊙ agrees with recent open cluster surveys, although we find a deficit of stars at the lowest masses ( M ≲ 0.3 M ⊙ ). Finally, we identify a discontinuity in the main sequence around M ∼ 0.3 M ⊙ . We explore the possibility that this feature traces the 3 He-driven instability predicted by stellar models, analogous to the ‘Jao Gap’ observed in the colour–magnitude diagram of nearby field stars.

Context . The Milky Way’s nuclear star cluster (NSC) offers a unique laboratory for studying the formation and evolution of dense stellar systems around a supermassive black hole. Previous work suggests that most stars in the NSC are old; however, the detailed age and metallicity distributions remain uncertain. Aims . We aim to constrain the star formation history (SFH) and metallicity of a poorly explored region of the NSC located about 3 pc from Sagittarius A*. Methods . We analysed NACO/VLT observations in the intermediate-band filter centred at 2.24 μm, complemented by H -band imaging, and constructed colour–magnitude diagrams and completeness-corrected K -band luminosity functions. We clearly identified the red clump and red giant branch bumps. The SFH was derived by fitting cumulative luminosity functions with theoretical models from MIST, PARSEC, and BaSTI, which spans a wide range of ages and metallicities, and by employing Monte Carlo sampling to estimate uncertainties. We also constrained the metallicity of the stellar population, further refined by spectroscopic data from the literature. Results . The NSC stellar population is predominantly old and metal-rich, with 75.6 ± 9.5% of the stellar mass formed ≳10 Gyr ago and a median metallicity of [M/H] ~ +0.35. Significant contributions come from an intermediate-age population around 2–3 Gyr (20.8 ± 8.7%), while minor components appear at ~400 Myr (0.9 ± 0.8%) and 20 Myr (3.6 ± 1.4%), the latter representing a small but non-negligible young population. Systematic uncertainties related to stellar evolution models, binning, photometric range, unresolved binaries, and filter selection are considered. Conclusions . Our findings indicate that the NSC formed predominantly in an early episode, with a substantial contribution from a star formation episode 2–3 Gyr ago and minor younger components. The metallicity estimates are consistent with spectroscopic measurements, and the results agree with the stellar population properties of the inner NSC and the inner nuclear stellar disc, providing useful constraints on the transition between these two structures.

Abstract Using Hubble Space Telescope (HST) imaging, we searched for candidate magnetically active binary (AB) counterparts to low-luminosity Chandra X-ray sources in the globular cluster 47 Tucanae (NGC 104). We consider the catalog of 300 Chandra sources within the half-light radius of 47 Tuc compiled by C. O. Heinke et al. (2005). The 10-band HST imaging used to identify these sources spans the range from 275–658 nm. We generated a cross-matched catalog of objects detected by photometric reductions. We used this catalog to search for counterparts within Chandra source error circles using color–magnitude diagrams and a color–color plot. We found 88 likely ABs that lie primarily in the binary sequence region above the main sequence, 10 possible ABs within this region, 12 sub-subgiants, three subgiants, six blue stragglers, and two yellow stragglers. Of these 121 proposed counterparts, 67 are newly identified. One of the ABs appears to be a pre-cataclysmic variable. Our analysis of the spatial distribution of these proposed counterparts indicates that they are significantly more centrally concentrated than the main-sequence turnoff stars. The inferred characteristic mass for these objects is 1.3 ± 0.1 M ⊙ . A comparison of the numbers of X-ray detected ABs above L X = 10 30 erg s −1 in four globular clusters indicates that their relative numbers can be approximately predicted by the mass and binary fractions of each cluster, suggesting that ABs are a primordial population.

Abstract The presence (and nature) of variations in the stellar initial mass function (IMF) at substantially subsolar masses and metallicities ( m < 0.5 M ⊙ and [M/H] ≲ −1, respectively) remains poorly constrained. Predictions from simulations vary widely, while observationally, resolved star studies of ultrafaint dwarf (UFD) galaxies suffer from small sample sizes and background galaxy contamination due to low projected stellar densities. As an alternative metal-poor target, we measure the IMF from resolved stars toward a carefully selected field in the Small Magellanic Cloud, leveraging a plethora of independent constraints on the target field stellar population including distributions of distance, age, and metallicity. We resolve >15,000 stars down to 0.16 M ⊙ within a single pointing of NIRCam on board JWST, using an observing strategy that minimizes contamination from point-source-like background galaxies. We explore three different functional forms of the IMF, forward modeling observed color–magnitude diagrams and luminosity functions. We find a best-fit single power law IMF slope of α = −1.61 − 0.03 + 0.03 , consistent with UFDs probed down to similar limiting masses. Fitting a broken power-law IMF, we find low- and high-mass slopes of α 1 = −1.44 − 0.04 + 0.04 and α 2 = −2.17 − 0.11 + 0.11 , respectively, consistent with solar neighborhood values. Assuming a lognormal IMF, we find a characteristic mass and lognormal width of m c = 0.1 2 − 0.03 + 0.03 M ⊙ and σ = 0.61 − 0.06 + 0.07 M ⊙ , respectively, allowing for characteristic masses lower than local values as seen in some simulations as well as low-metallicity Galactic clusters. Lastly, we quantify the impact of assumptions required in our analysis and discuss potential future improvements.

Abstract Observations show that multiple stellar populations (MPs) are ubiquitous in globular clusters. The Hubble Space Telescope (HST) has been a pivotal tool for previous photometric studies of MPs. The Chinese Space Station Survey Telescope (CSST) is a 2 m telescope scheduled for launch. One of its imaging instruments, the Survey Camera (SC), combines ultraviolet sensitivity comparable to that of HST with a significantly larger field of view, making it well-suited for conducting large-scale photometric surveys of MPs within extensive stellar stream structures. In this work, we perform mock observations of the stellar stream Palomar 5 to assess the feasibility of detecting MPs with the CSST/SC. The results indicate that the CSST/SC cannot resolve MPs in stellar streams at distances comparable to Palomar 5 (≳20 kpc) with one or 10 150 s exposures. This fundamental limitation arises from the absence of the precise proper motions required to disentangle stream members. We estimate that successful resolution would require the target stream to be ≲8 kpc under a 150 s exposure. Furthermore, using theoretical color–magnitude diagrams, we find that the CSST/SC g band provides an optimal balance between contamination rate and completeness rate for member identification in the cluster’s core. However, this approach fails in the stream due to severe field star contamination. Therefore, future CSST observations of Palomar 5 and its tidal tails will employ multiple epochs across several bands to obtain the deep photometry and proper motion data for a definitive MP analysis.

ABSTRACT The stellar initial mass function (IMF) is among the most fundamental distributions in astrophysics, defined as the mass spectrum of stars produced in a single star-formation event. Even in the solar neighbourhood, where measurements can be conducted via star counting, disentangling the IMF from observational effects remains challenging. In this work, we introduce a new parametrization of the stellar IMF in the 100-pc solar neighbourhood, leveraging the high-precision astrometric and photometric data from Gaia DR3: we model the colour–magnitude diagram of the field star population while accounting for observational uncertainties, Malmquist bias, Lutz–Kelker bias, variations in the mass–luminosity relation arising from metallicity differences and the effects of unresolved binaries. In particular, we synthesize the binary population with a process imitating the dynamical evolution observed in star clusters to enforce that all components are drawn from the same IMF, while simultaneously recovering the observed present-day mass-ratio distribution. We determine an averaged stellar IMF over $0.25\lt m\lt 1.0~{\rm M}_{\odot }$ that aligns with canonical IMFs but achieves significantly tighter constraints: $\alpha _1=0.75^{+0.06}_{-0.04}$, $\alpha _2=2.07^{+0.04}_{-0.03}$, and a break point at $m_{\mathrm{break}}=0.40^{+0.01}_{-0.01}$ $\mathrm{{\rm M}_{\odot }}$. Our inference also yields an averaged binary fraction over $0.25\lt m\lt 1.0~{\rm M}_{\odot }$ of approximately 26 per cent, and constrains the Gaia Data Release 3 angular resolution to $1.11^{+0.11}_{-0.08}$ arcsec. We also provide the $\xi$-parameter for our IMF, which is $0.5070_{-0.0096}^{+0.0068}$, to facilitate direct comparison with other IMF determinations.

Abstract The ∼200,000 stars observed by the Kepler mission have provided unprecedented constraints across astrophysics. With the advent of modern spectroscopic and photometric surveys, new limits in stellar characterizations are within reach. In this work, we report a compilation of atmospheric parameters ( T eff , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo>(</mml:mo> <mml:mi>g</mml:mi> <mml:mo>)</mml:mo> </mml:math> , and [M/H]) for the Kepler stars by crossmatching with several spectroscopic and spectro-photometric surveys. We use these to calculate bolometric corrections, which combined with color–magnitude diagram information from Gaia yield self-consistent luminosities on a survey-by-survey basis. These properties will aid in future explorations of Kepler data toward new astrophysical insights. We make our catalog publicly available online in Zenodo (doi: 10.5281/zenodo.18620911 ).

Abstract The supernova remnant (SNR) S147 contains the pulsar PSR J0538+2817 and a likely unbound binary companion, HD 37424. It is the only good Galactic candidate for a binary unbound by a core-collapse supernova. Using Gaia DR3 parallaxes and photometry, we select the stars local to SNR S147 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ϖ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> <mml:mn>147</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.7</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.04</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mspace width="0.1em"/> <mml:mtext>mas</mml:mtext> <mml:mspace width="0.1em"/> </mml:math> ) in a cylinder with a projected radius of 100 pc and a parallax range of 0.614 &lt; ϖ &lt; 0.787 mas (a length of ≃360 pc). We individually model the most luminous of these stars. The two most luminous single stars are the unbound binary companion, HD 37424, and HD 37367, with estimated masses of (13.51 ± 0.05) M ⊙ and (14.30 ± 0.09) M ⊙ , respectively. The two most luminous binary systems are the spectroscopic binary HD 37366 and the eclipsing binary ET Tau, which have primary masses of (20.9 ± 0.12) and (16.7 ± 0.09) M ⊙ , respectively. We model the Gaia color–magnitude diagram of this local stellar population using both single stars and a model consisting of noninteracting binaries using solar metallicity PARSEC v2.0 isochrones. For both models, the estimated age distributions of the 439 M G &lt; 0 mag stars favor a high-mass progenitor of 21.5–41.1 M ⊙ for the supernova.

ABSTRACT Y dwarfs represent the coldest class of brown dwarfs, with effective temperatures below 500 K, and provide unique analogues to cold giant exoplanets. We present a large compilation of uniform nearinfrared photometry from the Hubble Space Telescope for 21 Y-dwarfs across multiple WFC3/IR filters, including the F105W, F125W, and F160W bands. We employed refined Point Spread Function fitting and calibration procedures to reach photometric uncertainties at the 0.02–0.05 mag level for most targets. Combined with precise parallax measurements, our data reveal well-defined Y-dwarf sequences in near-infrared colour–magnitude diagrams, observed with a markedly improved tightness. Known photometric trends emerge with minimal scatter, including the continuous redward progression in F125W–F160W with decreasing temperature, and the blueward trend in F105W–F125W with possible hints of a reversal around 350 K. Comparisons to the ATMO, Sonora Elf Owl, and Lacy &amp; Burrows atmospheric models highlight systematic discrepancies, in particular F105W–F125W and F105W–F160W colours predicted to be too red. Low-metallicity grids provide the best fits to the global Y-dwarf population, although closer inspection across wavelengths shows that these preferences likely reflect compensating effects in missing or incomplete physics rather than true population level abundances. While some atmospheric diversity is expected among Y dwarfs, their tight observational sequences and systematic offsets from model predictions reveal that key physical and chemical processes remain inadequately captured in current grids. Our results underscore the importance of high precision, internally consistent data sets in robustly tracing the Y-dwarf cooling sequence and providing the empirical constraints needed to advance theoretical models at the lowest temperatures.

Abstract We present a detailed analysis of the long-term photometric and spectroscopic evolution of V1180 Cas over a decade, aiming to identify the dominant mechanisms behind its variability. We combine multiband light curves from 1999 to 2025 with over 30 epochs of optical to near-infrared (NIR) spectroscopy (0.5–2.5 μ m), analyzing variability patterns, color behavior, and emission line diagnostics. We investigate the temporal evolution of accretion and outflow indicators and their correlation with photometric states. The light curve reveals a transition from sporadic early dimming events to a quasi-periodic pattern since 2018, with 11 major dips showing asymmetry and stochastic substructure. Color–magnitude diagrams show classic UXor-like blueing during deep minima, while NIR and mid-infrared color changes indicate thermal evolution of the disk. Spectroscopic analysis reveals persistent hydrogen, Ca II , He I , and forbidden line emission. Accretion diagnostics track photometric variability, and forbidden lines often intensify during dips, implying a physical link between extinction and outflows. Estimated accretion rates range from ∼10 −8 to 10 −7 M ⊙ yr −1 ; the outflow rate and density diagnostics are consistent with disk winds and shock-excited jets. V1180 Cas demonstrates dual-mode variability driven by both variable circumstellar extinction and episodic accretion events. The hybrid UXor/EXor behavior, combined with evolving disk signatures and persistent outflows, suggests a young stellar object undergoing coupled accretion–extinction–outflow evolution. Continued monitoring will be essential to fully resolve the physical processes shaping its variability.

Abstract An understanding of the assembly history of the complex star cluster Omega Centauri has long been sought after, with many studies separating the stars on the color–magnitude diagram into multiple groupings across small magnitude ranges. Utilizing the oMEGACat combined astro-photometric and spectroscopic data set, we parse 14 subpopulations from the upper red giant branch to below the main-sequence turnoff. We combine our results with previous works to estimate the age and age spread of each population. We find that the chemically enhanced (P2) populations are all ∼1 Gyr younger (∼11.6 Gyr old) and have significantly higher intrinsic age spreads (0.6 Gyr) than the primordial (P1) populations (∼12.6 Gyr old, 0.3 Gyr spread), with the intermediate (Im) populations falling in between the two. Additionally, we connect for the first time the chromosome diagram to the two-stream age–metallicity relation, allowing us to link the P1 and P2 stars to the distinct star formation tracks, proposed to be in situ and ex situ contributions to the cluster’s assembly. Our results are consistent with some suggested formation models and rule out others, but no current model can explain all observed features of the subpopulations.

Abstract In this work, we present a detailed asteroseismological analysis of Wide Field Survey Telescope (WFST) J053009.62+594557.0, a newly discovered faint pulsating white dwarf by the WFST with a Gaia G magnitude of 19.13. Analysis of two nights of high-precision WFST g- band photometry reveals three significant pulsation frequencies with high signal-to-noise ratios. Follow-up P200/DBSP spectroscopy classifies the object as a DA white dwarf with T eff = 11,609 ± 605 K and M = 0.63 ± 0.22 M ⊙ . To probe its internal structure, we construct asteroseismological models with the White Dwarf Evolution Code (WDEC) . After exploring sufficient matching models, best-fitting solutions yield T eff = 11, 850 ± 10 K and M = 0.600 ± 0.005 M ⊙ , consistent with independent constraints from Gaia color–magnitude diagram, Gaia XP spectrum, P200 spectral fitting, SED fitting, and Gaia parallax. It is shown that the asteroseismological distance agrees with the Gaia parallax to 1.45%.

Abstract An increasing number of discoveries of isolated and quenched dwarf galaxies are challenging the idea that the present-day local environment of low-mass systems is the main determinant of their quenching. We present new Hubble Space Telescope (HST) data of one such system, the dwarf galaxy Canes Venatici C (CVnC). CVnC is a low-mass ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.2</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>6</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="1em"/> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> ) galaxy with a Tip of the Red Giant Branch distance of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>8.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.32</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.47</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> Mpc determined from the resolved stars in the HST imaging, which we also use to derive CVnC’s structural parameters. CVnC’s distance places CVnC in the Local Volume and in an isolated environment with the most tidally influential L ⋆ galaxy &gt; 5 R vir away. Additional constraints from the HST color–magnitude diagram, archival far-ultraviolet, and neutral hydrogen (H i ) data show that CVnC is quenched, with no evidence of star formation in the last 100 Myr and no detectable gas (M H i &lt; 1.5 × 10 6 M ⊙ ). Circumstantial evidence suggests that CVnC may have quenched via past interactions with the L ⋆ galaxy NGC 4631 ( L K = 10 10.4 L ⊙ ), and was possibly sent on an extreme backsplash orbit by the tidal dissolution of a subhalo group. However, other quenching mechanisms—such as stripping via the cosmic web—cannot be ruled out. CVnC adds to the growing number of quenched dwarf galaxies in underdense environments, a population that will be critical to defining the mass and environment regimes in which different quenching mechanisms operate.

Context . While large samples of nearby M dwarfs are becoming available, it is usually difficult to estimate some intrinsic physical parameters for isolated field M dwarfs, especially their ages, radii, and masses. These parameters can be estimated through a comparison with model stellar isochrones and/or by studying eclipsing binary systems. Aims . Our goal is to gather and analyze a large sample of variable M dwarfs that are members of nearby young open clusters and have known reddenings, distances, ages, and metallicities. This distilled sample would be useful for the comparison with theoretical models and also for the identification of eclipsing binaries with substellar companions (brown dwarfs or giant planets) for future follow-up. Methods . We selected two dozen benchmark young and nearby open clusters (mostly with 40 &lt; age &lt; 132 Myr and 400 &lt; D &lt; 700 pc, respectively). We then combined the optical data from Gaia Data Release 3 (DR3) with near-IR JHK s −band photometry from the VISTA Variables in the Vía Láctea eXtended survey (VVVX) for these target clusters using the proper motions in order to select members within the cluster radii. Gaia and VVVX both provide a wide areal coverage that is ideally suited for mapping these nearby clusters, which are extended on the sky. We then produced optical and near-IR color–magnitude and color-color diagrams and applied appropriate color cuts to choose the M-type dwarfs at the end of the main sequence. The reddening and extinction for all clusters were estimated using the J − K s color distributions of the cluster M dwarfs. We also compared them with the PARSEC theoretical isochrones adjusted to the respective cluster metallicities, ages, extinctions, and distances. Results . Finally, we selected variable M stars according to Gaia DR3 (using phot_variable_flag=VARIABLE) and present a catalog of 318 variable M-dwarf star members of two dozen young nearby Galactic open clusters. The cross-validation with the Gaia DR3 parallaxes supports the cluster membership for all these sources. We also present a few examples to validate the sample of variable cluster M dwarfs. Conclusions . This well-characterized catalog of M-dwarf members of benchmark open clusters not only constitutes a prime sample to search for transiting substellar companions, but also offers a training dataset for machine-learning applications aimed at selecting future similar targets.

Context . Some Galactic open clusters may form in binary or multiple systems. Binary clusters provide direct constraints on the clustered star-formation process, the gravitational potential of the Galactic disk, and the internal dynamical evolution of star clusters. However, only dozens of gravitationally bound binary clusters have been firmly recognized so far. Aims . As a part of the Dali Binary Cluster Project (DL-BCP), we searched for the wide binary open clusters (WBOCs) in the Milky Way using the data from Gaia Data Release 3 (Gaia DR3), and derived their fundamental astrophysical parameters and possible orbital evolution. Methods . We started from a Gaia-based open cluster catalog of 7167 clusters, and selected cluster pairs with separations of less than 100 pc and larger than the sum of the radii of sub-clusters at first. Then we checked whether the sub-clusters of every pair are gravitationally bound. Gravitationally bound pairs with two gravitationally bound sub-clusters are regarded as WBOCs. The ages, reddenings, and metallicities of their sub-clusters were re-derived by isochrone fitting in the ( G BP – G RP ) versus G color–magnitude diagram. Three-dimensional orbits were integrated in a three-component axisymmetric Galactic potential for the following 500 Myr and for the period before now. Results . We finally identified four new WBOCs and two known WBOCs. Two certain primordial binary open clusters (PBOCs) were found and studied. The cluster masses of these WBOCs range from 131.13 M ⊙ to 1155.86 M ⊙ . Age differences between the two components are ≤40 Myr for all of these WBOCs, and their separations vary from 20 to near 100 pc. The result enlarges the currently known BOC sample and provides a uniform set of fundamental parameters and orbital analysis for six WBOCs.

Context. One of the most remarkable and unexpected results of the James Webb Space Telescope is the discovery of a population of compact red galaxies: the so-called little red dots (LRDs). The existence of these galaxies raises many questions, including that of their nature and origin, as well as that of their evolution. Indeed, these compact red sources exhibit a pronounced decline in number density by nearly two orders of magnitude from z = 6 to z = 3. Aims. In this paper, we investigate the possible evolution of this galaxy population at a lower redshift. To this end, we have identified a sample of candidates in the CEERS images that could represent the descendants of LRDs by assuming a single evolutionary path: the development of a blue star-forming outskirt while retaining a inner red core. Methods. Our color–magnitude selection identifies red galaxies as red as LRDs at z &lt; 4, defined by a compact, red, inner region and blue outskirts. The red core is associated with the LRD population, while the blue periphery traces recently formed young stars. Morphological properties were derived by fitting single Sérsic profiles, while other physical quantities were obtained through spectral energy distribution (SED) fitting, assuming a stellar-only model for both the inner region and the outskirts. Results. The selected galaxies are likely “post-LRDs” galaxies, showing similar properties to LRDs under a stellar-only model: stellar masses of M * ≈ 10 10 M ⊙ , central densities Σ * ≈ 10 11 M ⊙ kpc −2 , similar rest-frame red colors, and a ∼1 kpc offset below the size–mass relation. Their number density at z = 3 ± 0.5 (10 −4.15 Mpc −3 ) matches that of LRDs at 5 &lt; z &lt; 7, supporting an evolutionary connection. We find a strong redshift-dependent increase in both outskirts’ mass fraction and galaxy size, from ∼250 pc at z = 5 to ∼600 pc at z = 3, indicating overall stellar growth. Meanwhile, the core remains as red and as massive, but the characteristic V shaped SED fades as the extended star-forming envelope becomes dominant. Conclusions. These findings support an evolutionary scenario in which LRDs gradually acquire an extended stellar component over cosmic time by cold accretion. This growth affects the initial LRD state in two key ways: the physical size increases and the characteristic V shaped SED in the core becomes less distinct and disappears. As a result, the original selection criteria based on both of them can no longer identify this population as it evolves, providing an explanation for their observed decline in number density.