Abstract Quasar samples remain severely incomplete at low Galactic latitudes because of strong extinction and source confusion. We conduct a systematic search for quasars behind the Galactic plane using X-ray sources from the Chandra Source Catalog (CSC), combined with optical data from Gaia Data Release 3 and mid-infrared data from CatWISE2020. Using spectroscopically confirmed quasars and stellar-type objects from datasets including DESI, the Sloan Digital Sky Survey, and LAMOST, we apply a random forest classifier to identify quasar candidates, with stellar contaminants suppressed using Gaia proper-motion constraints. Photometric redshifts are estimated for the candidates using a random forest regression model. Applying this framework to previously unclassified CSC sources, we identify 7570 quasar candidates, including 1060 Galactic plane quasar (GPQ) candidates at ∣ b ∣ < 20°, of which 551 are high-confidence candidates. Relative to the previously known GPQ sample, our selected GPQs reach lower optical and X-ray fluxes, improving sensitivity to low-flux GPQs. In addition, both the GPQ candidates and known GPQs display harder X-ray spectra than the all-sky quasar sample, consistent with increased absorption through the Galactic plane. Pilot spectroscopy confirms two high-confidence GPQ candidates as quasars at spectroscopic redshifts of z = 1.2582 and z = 1.1313, and further spectroscopic follow-up of the GPQ sample is underway. This work substantially improves the census of GPQs and provides a valuable target sample for future spectroscopic follow-up, enabling the use of GPQs to refine the reference frames for astrometry and probe the Milky Way interstellar and circumgalactic media with the absorption features of GPQs.

Abstract Changing-look active galactic nuclei (CL-AGNs) exhibit dramatic spectral variability on unexpectedly short timescales, challenging standard accretion flow models. Despite growing samples, the physical drivers of this extreme variability, and the potential link to host-galaxy properties, remain unknown. Regardless of the underlying mechanism, the transition between AGN-dominated and host-dominated spectra offers a unique opportunity to study relations between AGNs and their hosts within the same objects. We present intermediate-resolution spectroscopy of 23 CL-AGNs identified by the Sloan Digital Sky Survey V (SDSS-V), obtained with the Very Large Telescope/X-shooter and Gemini-N/GMOS. An analysis of the Mg ii λ 2798 emission line observed in the spectra demonstrates that the majority of these sources cannot be driven by variable obscuration. Our CL-AGNs roughly follow the M BH – σ * and M BH – M * relations of inactive galaxies, with a median black hole-to-stellar mass ratio of 0.38 %. We find no evidence that the stellar population properties of our CL-AGNs, including stellar mass, age, young stellar fraction, and star formation rate, differ from those of type 2 AGNs in SDSS. These results suggest that CL-AGNs reside in typical AGN host galaxies and that their extreme variability is likely unrelated to host-galaxy environment, supporting the idea that CL-AGNs are not a distinct population, but rather represent a phase of normal AGN activity. This result, in turn, implies that CL-AGNs can serve as useful probes of the AGN-host connection, providing access to both AGN-dominated and host-dominated spectra of the same systems.

Abstract We present the first statistical census of emission-line variable active galactic nuclei (EVA) at cosmic noon by combining untargeted and deep Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) spectroscopy with multiepoch spectra from the Sloan Digital Sky Survey, DESI, and LAMOST. Anchoring all candidates to a HETDEX spectroscopic epoch and requiring an active galactic nucleus (AGN) classification in either the HETDEX or external epoch(s), we identify a homogeneous sample of 100 EVA at z ∼ 1.5, including 98 that are newly identified. Emission-line variability is selected primarily through statistically significant line-flux changes, supplemented by extensive visual inspections using contemporaneous photometric light curves. The resulting incidence fraction is f EVA ∼ 0.9%. The rest-frame intervals between spectroscopic epochs span ∼1–10 yr, with brightening and dimming events exhibiting statistically indistinguishable characteristic timescales (Δ T ∼ 2.2 and ∼2.6 yr, respectively). A key result is the characterization of the Baldwin effect in the time domain: while many EVA follow the ensemble Baldwin effect (eBeff) between two epochs, a substantial fraction exhibit apparent anti-eBeff responses. Time-resolved spectroscopy of an individual source reveals that the intrinsic equivalent width–luminosity relation is nonstationary, with the line-to-continuum responsivity systematically evolving from stronger to weaker across successive variability cycles; sparse two-epoch sampling of this evolving intrinsic Baldwin evolution naturally produces both eBeff-like and anti-eBeff behaviors. Finally, EVA show no strong preference for extreme Eddington ratios but exhibit a mild tendency toward lower λ Edd values relative to matched control samples, driven primarily by sources observed in their dim states. Together, these results establish a coherent framework for interpreting emission-line variability in AGN at the peak epoch of cosmic black hole growth.

Abstract Unlocking all the physical information encoded in low-resolution spectra poses a significant challenge for astronomical survey analysis. Such a task demands modeling spectra and optimizing astrophysical parameters in high-dimensional space as a consequence of line blending. Here we present PhDLspec —a deep learning framework embedded with physical priors for stellar spectrum modeling and analysis. By imposing differential spectra derived from ab initio stellar atmospheric model calculation on a Transformer framework, PhDLspec can rigorously and precisely model stellar spectra by simultaneously taking into account more than 30 physical parameters at a computational speed hundreds of times faster than ab initio model calculation. With such a flexible stellar modeling approach, PhDLspec can effectively derive ∼30 stellar labels from a low-resolution spectrum using affordable optimization techniques. Application to LAMOST spectra ( R ≲ 1800) yields stellar elemental abundances in good agreement with high-resolution spectroscopic surveys, after essential calibrations to correct systematic biases in elemental abundance estimates using wide binaries and reference high-resolution data sets. We provide a catalog of 25 elemental abundances for 116,611 subgiant stars with precise age estimates. The successful application of PhDLspec to LAMOST spectra for high-dimensional parameter determination sheds light on similar challenges faced by other surveys and disciplines.

Abstract The abundance discrepancy problem refers to the systematic differences observed between chemical abundances derived from collisionally excited lines (CELs) and recombination lines (RLs) of heavy ions. It remains a major unsolved problem in the study of ionized nebulae and is quantified by the abundance discrepancy factor (ADF). In this work, we present a deep integral field spectroscopic data set of the entire Lagoon Nebula (M8), obtained by the Sloan Digital Sky Survey V Local Volume Mapper project, at a spatial resolution of 0.21 pc spaxel −1 . This unique data set allows us, for the first time, to investigate spatially resolved maps of oxygen RL intensities (O ii V1), together with maps of H i RLs, heavy-ion CELs, and dust attenuation across a whole H ii region. We map the electron temperature using CELs and RLs of O 2+ and CELs of N + , and we map the electron density using CELs of S + . We derive CEL-based ionic and elemental oxygen abundances and, for the first time, a spatially resolved map of the RL-based O 2+ abundance in an H ii region. These measurements enable construction of the first spatially resolved ADF(O 2+ ) map of an H ii region and yield a global mean ADF of ∼0.47 ± 0.02 dex. Focusing on the central region of M8, where ionization is dominated by the O-type star Her 36, we find radial variations in the ADF, ranging between ∼0.35 and 0.50 dex. Our findings provide novel constraints on the spatial behavior and origin of the abundance discrepancy in the H ii regions.

Abstract We present an investigation of the rest-frame optical/UV and X-ray properties for a sample of 3027 X-ray selected quasars between 1.5 ≤ z ≤ 3.5 detected in the deepest Spectrum Roentgen Gamma/eROSITA data available and observed by the fifth iteration of the Sloan Digital Sky Survey (SDSS-V). We parametrize the C iv λ1549 emission line to infer the strength of accretion disc winds and perform X-ray spectral fitting. The X-ray spectral properties – namely, the 2 keV monochromatic luminosity (L2 keV) and spectral slope – are not strongly correlated with wind strength. Despite this result, the X-ray selected sample is shifted towards lower C iv blueshifts and higher equivalent widths than the optically selected sample observed in previous SDSS surveys, and matching in optical luminosity, redshift, and Eddington ratio does not reduce these differences. We estimate the far-UV luminosity using the He ii λ1640 line luminosity and define the slopes between this and the 2500 Å monochromatic luminosity (L2500) and L2 keV (αouv and αuvx, respectively) in a similar manner to the familiar αox parameter, which tracks the spectral slope between L2500 and L2 keV. The quantity αouv is more strongly correlated with wind strength in our sample than αox. We show that the correlation between αox and wind strength is driven by the relationship between the optical luminosity and wind strength. Our results are consistent with a radiation line-driven wind, whereby the ionising far-UV photons must not over-ionise the gas. The hard X-ray photons are few enough in number to have a negligible effect on the ionisation state of the material.

ABSTRACT We present a statistical measurement of the transverse coherence of Mg ii $\lambda \lambda 2796,2803$ absorption using a large sample of 9204 absorber-centric quasar sightline pairs from the Sloan Digital Sky Survey. We quantify the probability that an Mg ii absorber detected along one sightline is also present along a nearby sightline, and measure how this coincidence probability varies with projected separation from $\sim$50 kpc to $\sim$1 Mpc. The resulting coincidence curve exhibits a clear two-regime structure: the coincidence probability rises steeply to $\sim$5–8 per cent at separations below $\sim$100 kpc, but declines rapidly beyond this scale and settles into a low plateau of $\sim$1–2 per cent out to $\sim$1 Mpc. A simple geometrical single-halo model reproduces the enhanced probability at $\lesssim$100 kpc, while the large-scale plateau is well explained by the expected contribution from galaxy clustering, confirmed using both photometric galaxy counts and the two-point correlation function. A complementary stacking analysis reveals a significant excess in Mg ii equivalent width in paired sightlines lacking individual detections, implying a coherence scale of $\sim$100–200 kpc for the cool, metal-enriched CGM. Together, these results identify the transition from a halo-dominated coherence regime at small separations to a clustering-dominated regime at large scales, bridging the gap between small-scale lensing constraints and megaparsec-scale absorber clustering studies.

Abstract We present a sample of large double radio sources hosted by spiral galaxies (spiral double radio active galactic nuclei, SDRAGNs). Candidates were initially selected through the Radio Galaxy Zoo project and subsequently refined using Sloan Digital Sky Survey images. The most promising were targeted in the Zoo Gems Hubble Space Telescope (HST) program, yielding images for 36 candidates. We assess the likelihood that each spiral galaxy is the genuine host of the radio emission, finding 15 new high-probability SDRAGNs. The hosts are seen preferentially close to edge-on. SDRAGNs predominantly show type II Fanaroff–Riley (FR II) radio structures and optical pseudobulges. After accounting for sample selection effects, the radio-jet axes lie preferentially near the poles of the galactic disks; we find a constant probability distribution for intrinsic pole–jet angles ϕ < 30°, declining to zero at ϕ = 60°. We have obtained optical spectra for all these newly identified SDRAGNs. Among both previously known and new SDRAGN samples, 8/25 show Seyfert 2 signatures, 6/25 show central star formation, and 5/25 show low-ionization nuclear emission-line region emission strong enough to indicate active galactic nuclei (AGN) activity or shock ionization, broadly similar to radio galaxies in elliptical hosts but with the addition of star formation (diluting or masking weak AGN signatures). SDRAGNs include FR II sources seen at unusually low radio powers, and preferentially occur in significant galaxy overdensities on 1 Mpc scales. Our “false alarms”—systems where HST data show the spiral is not the actual host galaxy—include radio sources seen through large portions of foreground spiral disks, potentially providing useful probes for Faraday rotation studies of disk magnetic fields.

Statistics on tidal disruption events (TDEs) may be contaminated by repeating TDEs (rTDEs), which have been widely discovered in recent years. However, no statistical study has yet examined rTDEs with time intervals longer than 5 years. In addition, the origin of rTDEs remains unclear. We aim to search for rTDEs with time intervals longer than 5 years in a well-defined TDE sample and to estimate the rTDE rate and fraction in the sample. We used a sample of 16 TDEs at z<0.05 from the Zwicky Transient Facility (ZTF) Bright Transient Survey (BTS) to search for flares 5--19 years before the ZTF TDEs using the Catalina Real-time Sky Survey (CRTS) light curves. We analyzed archival multi-band data to distinguish between TDEs and supernovae (SNe) and estimated the expected number of SNe that CRTS could detect in the sample. We identify two rTDE candidates, AT 2019azh and AT 2024pvu, with time intervals of 13.2 and 17.1 years, respectively. The peak luminosities of the CRTS flares are close to those of ZTF flares. For the CRTS flare of AT 2024pvu, we used UV observations from the Galaxy Evolution Explorer (GALEX) near the peak to measure a blackbody temperature of sim19500 K, consistent with TDEs and higher than that of SNe. Moreover, we estimate the expected number of SNe in the sample to be łesssim0.08, and hence the probability that both CRTS flares are SNe is only 0.3%. Therefore, we rule out the possibility that both CRTS flares are SNe and conclude that both are likely TDEs. Using the two rTDEs, we infer that the TDE rate is two to three orders of magnitude higher than the average over 5--19 years prior to TDE detection. Two rTDEs with intervals of ∼2 years in the sample, together with possible rTDEs missed by CRTS, suggest that rTDEs with intervals of $<20$ years may account for 25%--60% of the TDE sample. We interpret rTDEs as repeating partial TDEs. If so, the high fraction of rTDEs suggests that the observed optical TDE rate is overestimated. However, the possibility of independent TDEs cannot be ruled out and requires future observational tests.

Abstract Solar-type stars have been observed to flare at optical wavelengths with energies much higher than is observed for the Sun. To date, no counterparts have been observed at longer wavelengths. We searched the Very Large Array Sky Survey (VLASS) for radio emission associated with a sample of 150 solar-type stars that exhibit superflares in the Transiting Exoplanet Survey Satellite (TESS) data. Counterparts to six of these stars were present in VLASS as transient or highly variable radio sources. One star is detected in all three VLASS epochs, exhibiting an extreme level of apparently persistent radio emission. The engine for this radio emission is unclear, but may be related to accretion, a binary companion, or the presence of large-scale magnetic fields. Two stars show radio emission with a >50% circular polarization fraction, which likely indicates a coherent emission process. Overall, the VLASS-detected stars likely predominantly emit nonthermal, incoherent emission and tend to have higher flare rates and energies than the rest of our TESS sample. This, in addition to the VLASS-detected stars adhering to the Güdel–Benz relation, suggests that the radio emission may be associated with superflares and that the superflare phenomenon on solar-type stars extends to radio wavelengths, tracing particle acceleration. These data provide the first window into the luminosity function of radio superflares for solar-type stars and highlight the need for coordinated, multiwavelength monitoring of such stars to fully illustrate the stellar flare–particle acceleration relation.

Abstract We report Giant Metrewave Radio Telescope (GMRT) H i 21 cm imaging of NGC 4141, the host galaxy of FRB 20250316A at z = 0.0063. Our GMRT H i 21 cm images have spatial resolutions, at z ≈ 0.0063, of ≈0.48–8.0 kpc, and provide evidence for (i) a companion galaxy, LEDA 2582852, to the southwest, (ii) a nearby (27 kpc distant) H i cloud to the southwest, (iii) disturbances in the H i distributions of both NGC 4141 and LEDA 2582852, and (iv) high H i column densities in the southwestern outskirts of NGC 4141. A Sloan Digital Sky Survey spectrum yields a low metallicity and a high star formation rate (SFR) surface density in the southwestern disk of NGC 4141, and an H α -based SFR estimate that is significantly higher than that at the same location from the Galaxy Evolution Explorer near-ultraviolet image, indicating a recent burst of star formation. The total SFR of NGC 4141 is also found to be higher via the H α line than from the 1.4 GHz radio continuum. The above evidence indicates that NGC 4141 has recently (within the last ≈3 Myr) acquired metal-poor gas, via either a merger or accretion, that resulted in the southwestern starburst and that may also have triggered large-scale star-formation activity in NGC 4141, resulting in the formation of the stellar progenitor of FRB 20250316A and the other transients. Our highest-resolution (480 pc) GMRT H i 21 cm image finds no H i 21 cm emission from the location of FRB 20250316A or the nearby star-forming region, suggesting that most of the H i here has been either ionized or converted into the molecular phase. Our nondetection of continuum emission at the location of FRB 20250316A yields the 3 σ upper limit νL 1.38 GHz < 4.4 × 10 34 erg s −1 on the 1.38 GHz radio luminosity of a putative persistent radio source associated with FRB 20250316A, one of the strongest constraints on the radio luminosity of such an associated persistent radio source.

We compare a parameterized quantum kernel (pQK) with a quantum leaky integrate-and-fire (QLIF) neuromorphic computing approach that employs either the Victor–Purpura or van Rossum kernel in a spectral clustering task, as well as the classical radial basis function kernel. To our knowledge, this is the first study to employ quantum neuromorphic leaky integrate-and-fire neurons as kernel generators within a spectral clustering framework and to directly compare them against gate-based quantum fidelity kernels under identical conditions. Performance evaluation includes label-based classification and clustering metrics, as well as optimal number of clusters predictions for each dataset based on an elbow-like curve, as is typically used in K-means clustering. The pQK encodes feature vectors through angle encoding, with rotation angles scaled parametrically. Parameters are optimized through grid search to maximize kernel-target alignment, producing a kernel that reflects distances in the feature space. The quantum neuromorphic approach uses population coding to transform data into spike trains, which are then processed using temporal distance metrics. Kernel matrices are used as input into a classical spectral clustering pipeline prior to performance evaluation. For the synthetic datasets and Iris, the QLIF kernel typically achieves better classification and clustering performance than pQK. However, on higher-dimensional datasets, such as a preprocessed version of the Sloan Digital Sky Survey, pQK performed better, indicating better relative performance compared to QLIF in higher-dimensional regimes.

Abstract We conduct a multiband photometric investigation of LINEAR\,16694484, a low-mass-ratio contact binary system featuring an orbital period of $0.2492762$\,d, close to the theoretical lower limit for contact systems. Utilizing the \textsc{PHOEBE} modeling suite combined with Markov Chain Monte Carlo (MCMC) sampling, we analyze multiband light curves and infer a fill-out factor of $\sim33\%$. Complementarily, analysis of TESS photometric data yields consistent results, confirming the system’s overcontact configuration. The rare combination of such a short orbital period and an extremely low mass ratio ($q \approx 0.11$) renders this system a valuable testbed for probing binary evolution theories. By combining new eclipse timings with archival data from multiple sky surveys, we detect a secular decrease in the orbital period at a rate of \(\dot{P} = dP/dt = -5.11\times10^{-7}\ \text{day}\cdot\text{yr}^{-1}\), most plausibly attributed to mass transfer from the more massive primary component to the less massive secondary. As the system undergoes progressive orbital contraction, the Roche lobe radii are reduced, which intensifies the contact degree and establishes LINEAR\,16694484 as a plausible progenitor of a contact binary merger event.

ABSTRACT Dust in early-type galaxies (ETGs) may originate from internal or external sources. In this paper, we study the stellar populations of particularly dusty ETGs to search for evidence of the dust’s origin. Using the Southern African Large Telescope (SALT), we obtained long-slit optical spectra within the effective radius ($R_\mathrm{ e}$), along the major axis of 15 nearby ETGs, selected from the Galaxy and Mass Assembly (GAMA) and Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) surveys for their high levels of interstellar dust. Using full spectrum fitting and Lick index fitting we analysed their major axis kinematics and stellar population characteristics. We used stellar population models from the newly developed semi-empirical Medium-resolution Isaac Newton Telescope library of empirical spectra (sMILES) library and from the empirical MILES library. Kinematic results show that most of our sample of dusty ETGs are rotationally supported and there are no detectable kinematic discontinuities. 12 of our sample of 15 dusty ETGs show evidence of young/intermediate age stellar population components suggesting ongoing/recent star formation. Using simulations, we show that these recent (≈1 Gyr) populations are not artefacts of the fitting process or data. As a check with a control sample we use stacked Sloan Digital Sky Survey spectra and find that dusty ETGs show a component with intermediate age, whereas non-dusty ETGs do not. Age, metallicity, and $\alpha$-element abundance ratio increase with increasing central velocity dispersion in the SALT spectra, as seen in previous studies of ETGs, but with larger scatter in our sample. Given our stellar population findings, we discuss formation scenarios that might cause or rule out a high dust/molecular gas content.

In the era of time-domain astronomy, automated and efficient data processing is a crucial factor in ensuring astronomical scientific output. With the international collaboration trend in large-scale sky survey projects, data processing algorithms developed through multi-institutional collaboration face challenges in system integration, scheduling capability, extensibility, and traceability. In this work, we employ containerized execution modules to resolve dependency issues in multi-institutional software integration, implement complex workflow orchestration through message queue control modules, including cyclic dependencies, dynamic parallel relationships, and resource/priority-based scheduling. The system also non-intrusively implements the International Virtual Observatory Alliance (IVOA) provenance data model through aspect injection mechanisms, ensuring traceability and reproducibility of data products. In Einstein Probe (EP) data processing, the system has processed over 20,000 general observations, 170,000 FXT observations, and 21,000 VHF and Beidou alerts, supported over 300 agile algorithm updates, and detected more than 17,000 sources and nearly 200 transient events. The system demonstrates excellent generality and portability, smoothly migrating from the single-module LEIA to the 12-module EP, and supporting data fusion for new payload FXT and multiple data transmission links. This workflow management system provides a flexible, extensible, and standardized data processing framework for future large-scale astronomical observation projects, effectively addressing key issues such as multi-institutional collaboration, complex workflow orchestration, and scientific data reproducibility.

Skykatana: A scalable framework to construct sky masks for the Vera Rubin Observatory and large astronomical surveys

Open clusters are vital laboratories for studying stellar dynamics and evolution, with mass segregation—the preferential concentration of massive stars toward cluster cores—serving as a key indicator of internal dynamical processes. This study investigates four open clusters (NGC 7243, NGC 2301, NGC 1528, and NGC 2281; ages 100–650,Myr) using deep multicolor photometry from the Beijing-Arizona-Taiwan-Connecticut (BATC) Sky Survey, combined with Gaia Data Release 3 (DR3), to explore their mass functions and dynamical states. The work seeks to characterize mass segregation patterns across spatial scales to establish its origin (primordial vs. dynamical) and to provide the first conclusive evidence of mass segregation in NGC 2281. Additionally, we analyze how cluster relaxation timescales and evolutionary stages influence their dynamical architectures. Fundamental parameters were derived via Bayesian methods. The tidal radii were determined from the intersection of the observed cumulative mass profiles and theoretical tidal mass curves, and mass functions were analyzed through power-law fits (Φ(m)∝ m^α) performed separately for the inner (bound) and outer (tidal) regions. All clusters exhibit signs of mass segregation. However, only NGC 2281 shows a statistically significant steepening of the mass function slope in its outer tidal region, indicating significant evaporation of low-mass stars and providing the first clear evidence of strong, dynamically evolved mass segregation in this cluster. For NGC 7243, NGC 2301, and NGC 1528, the derived τ values (τ = /t_ Age relax > 3) suggest advanced dynamical evolution, yet their outer regions contain too few stars to robustly confirm the expected steepening of the mass function.

Abstract The fifth-generation Sloan Digital Sky Survey (SDSS-V) is conducting the first all-sky low-resolution spectroscopic survey of the Milky Way’s (MW) stellar halo. We describe the stellar parameter pipeline for the SDSS-V halo survey, which simultaneously models spectra, broadband photometry, and parallaxes to derive stellar parameters, metallicities, alpha abundances, and distances. The resulting Baryon Oscillation Spectroscopic Survey (BOSS)- MINESweeper catalog is validated across a wide range of stellar parameters and metallicities using star clusters and a comparison to high-resolution spectroscopic surveys. We demonstrate several scientific capabilities of this dataset: identifying the most chemically peculiar stars in our Galaxy, discovering and mapping distant halo substructures, and measuring the all-sky dynamics of the MW on the largest scales. The BOSS- MINESweeper catalog for SDSS DR19 is publicly available and will be updated for future data releases.

Abstract AM CVn stars are ultra-compact semi-detached binaries consisting of a white dwarf primary and a hydrogen-depleted secondary. In this paper we present spectroscopic and photometric results of 15 transient sources pre-classified as AM CVn candidates. Our analysis confirms 9 systems of the type AM CVn, 3 hydrogen-rich cataclysmic variables (accreting white dwarfs with near-main-sequence stars for donors) and 3 systems that could be evolved cataclysmic variables. Eight of the AM CVn stars are analysed spectroscopically for the first time, which increases the number of spectroscopically confirmed AM CVns by about 10%. TESS data revealed the orbital period of the AM CVn star ASASSN-20pv to be P orb =27.282 min, which helps to constrain the possible values of its mass ratio. TESS also helped to determine the superhump periods of one AM CVn star (ASASSN-19ct, P sh = 30.94 min) and two cataclysmic variables we classify as WZ Sge stars ( P sh = 90.77 min for ZTF18aaaasnn and P sh =91.6 min for ASASSN-15na).We identified very different abundances in the spectra of the AM CVns binaries ASASSN-15kf and ASASSN-20pv (both P orb ∼ 27.5 min), suggesting different type of donors. Six of the studied AM CVns are X-ray sources, which helped to determine their mass accretion rates. Photometry shows that the duration of all the superoutbursts detected in the AM CVns is consistent with expectations from the disc instability model. Finally, we provide refined criteria for the identification of new systems using all-sky surveys such as LSST.

Abstract We investigate the influence of large-scale cosmic web environments on galaxy quenching using a volume-limited, stellar mass-matched galaxy sample from Data Release 18 from the Sloan Digital Sky Survey. Galaxies are classified as residing in sheets, filaments, or clusters based on the eigenvalues of the tidal tensor derived from the smoothed density field. The quenched fraction increases with stellar mass and is highest in clusters, intermediate in filaments, and lowest in sheets, reflecting the increasing efficiency of environmental quenching with density. A flattening of the quenched fraction beyond log 10 ( M ⋆ / M ⊙ ) ∼ 10.6 across all environments signals a transition from environment-driven to mass-driven quenching. In contrast, the bulge fraction continues to rise beyond this threshold, indicating a decoupling between the suppression of star formation and morphological transformation. At the high-mass end ( log 10 ( M ⋆ / M ⊙ ) ≳ 11.5 ), both quenched and bulge fractions bifurcate, increasing in clusters but declining in sheets, suggesting a divergent evolutionary pathway where massive galaxies in sheets retain cold gas and disk-like morphologies, potentially sustaining or rejuvenating star formation. The fraction of active galactic nuclei (AGN) also increases with stellar mass and is somewhat higher in sheets than in clusters, indicating enhanced AGN activity in low-density, gas-rich environments. The high-mass trends are independently corroborated by our analysis of specific star formation rate, ( u − r ) colour, concentration index, and D4000 in the stellar mass–density plane, which show that massive galaxies in sheets remain bluer, younger, more star-forming, and structurally less evolved than their cluster counterparts. Our results highlight the cosmic web as an active driver of galaxy evolution.