arXiv subjects

Haining Li

Publications and source records attributed to Haining Li.

At least 19 recordsLinked to original sources

arXiv2026

Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. IV. Heavy Element Enhanced Stars

We perform a homogeneous analysis of 82 heavy-element-enhanced metal-poor stars from the\\ LAMOST/Subaru sample, including 64 $r$-process-enhanced stars, 2 limited-$r$ stars, and 16 stars exhibiting significant or moderate carbon enhancement (comprising 9 $s$-process-enhanced, 2 $r$-process-enhanced, 2 $r$/$s$, and 3 $r$+$s$ stars). Systematic differences in $\mathrm{[X/Eu]}$ between $r$-I and $r$-II stars, together with their distinct dynamical properties, suggest that $r$-II stars likely formed in low-mass dwarf galaxies where contamination from additional nucleosynthetic channels was minimal. We have also discovered a number of peculiar objects. We identify an extremely metal-poor $r$-II star, J1158+0734 ($\mathrm{[Fe/H]}$ = -2.93), whose enhanced Zn abundance ($\mathrm{[Zn/Fe]}$ = +0.67) is best explained by yields from a high-energy, massive core-collapse supernova. The surface abundances of $s$-process-enhanced stars exhibit pronounced dispersion, consistent with enrichment from AGB progenitors with diverse properties. Notably, one star, J2256+0215, reveals compelling evidence for additional evolutionary mixing, as indicated by its unusually low carbon abundance ($\mathrm{[C/Fe]}$ = +0.08) and extremely low $^{12}$C/$^{13}$C ratio of 2.33. Additionally, we identify 3 $r$+$s$ stars whose abundance patterns reveal combined contributions from both the $r$- and $s$-processes. We further propose a modified diagnostic scheme for the identification of CEMP-$r$+$s$ stars, defined as: -0.2 $\leqslant$ $\mathrm{[La/Nd]}$ $\leqslant$ 0.2 and -0.5 $\leqslant$ $\mathrm{[Eu/Nd]}$ $\leqslant$ 0.0.

astro-ph.SR↗

arXiv2026

Impact of Gaia-Sausage-Enceladus Debris on Milky Way Escape-velocity Estimates in TNG50

The escape velocity is a key probe of the Milky Way (MW) potential, but standard estimates can be biased by unrelaxed substructures. Using MW analogs from the TNG50 cosmological simulation, we investigate the impact of the dominant, highly radial Gaia-Sausage-Enceladus (GSE) debris on escape-velocity measurements. We introduce an adaptive selection strategy that balances statistical reliability with sample size to identify the power-law decline regime of the local halo velocity distribution. Applying this strategy to 16 MW analogs with prominent GSE-like structures and continuous high-velocity tails, we find that retaining GSE-like stars yields a systematic underestimate, with a recovery fraction of $97.5^{+2.1}_{-2.9}\%$, while removing GSE-like stars alone increases the recovery fraction to $99.4^{+2.1}_{-2.5}\%$. The $\sim 2\%$ underestimation of the escape velocity corresponds to an $\sim 6\%$ underestimation of the total mass. This improvement persists in LAMOST-like magnitude and footprint selection. GSE-like debris is therefore a key contributor to the systematic underestimation of escape-velocity measurements, with direct implications for the inferred MW mass.

astro-ph.GA↗

arXiv2026

A $\wedge$-like metallicity profile in the disk of the Sagittarius dwarf galaxy

Unveiling the properties of the progenitors that formed the tidal structures of the Milky Way (MW) is essential for exploring the MW's assembly history. Such studies further afford a unique opportunity to dissect the formation and evolution of dwarf galaxies by contrasting surviving and disrupted systems. However, reconstructing the intrinsic structure of progenitors solely from the positions and velocities of their tidal debris remains a formidable challenge. Here, we decode the chemo-kinematic signatures embedded in the stellar streams of the Sagittarius (Sgr) dwarf galaxy through N-body simulations. Our simulation reproduces a vertical metallicity gradient in the Sgr streams. We show that this feature is naturally explained if the stream originated from a disk component with a $\wedge$-like metallicity profile. Remarkably, similar metallicity profiles are identified in MaNGA survey data for a few (3/217) field dwarf galaxies, suggesting this feature is rare but not unique to Sgr. The vertical metallicity gradient of stellar streams preserves extra detailed galactic fossil records, enabling quantitative reconstruction of the peculiar structure of the satellite galaxy. The similar metallicity profiles of Sgr and MW raise the question of a possible special coevolution.

astro-ph.GA↗

arXiv2026

Nitrogen-Loud Quasars from the Dark Energy Spectroscopic Instrument. II. Broad-Line Region Metallicity and Relative Nitrogen Enrichment

Whether the unusually strong nitrogen emission in nitrogen-loud (N-loud) quasars reflects high overall metallicity, enhanced nitrogen abundance relative to other elements, or both has long been debated. We analyze the broad-line region (BLR) abundances of 121 N-loud quasars at $2.13 \leq z \leq 3.90$ selected from the Dark Energy Spectroscopic Instrument Data Release 1 and construct a control sample of normal quasars matched in redshift, continuum luminosity, and virial black hole mass. Within the N-loud sample, metallicities inferred from N V/C IV span $\sim 3$-$50\,Z_\odot$ and are systematically higher than those inferred from the nitrogen-independent (Si IV+O IV])/C IV and Al III/C IV diagnostics, which agree closely and mainly span $\sim 1$-$20\,Z_\odot$. Compared with the matched controls, the N-loud quasars show systematically higher metallicities in both N V/C IV and (Si IV+O IV])/C IV, with median values approximately three times those of the controls. Notably, the discrepancy between the metallicities inferred from N V/C IV and (Si IV+O IV])/C IV becomes more pronounced toward the high-metallicity end of the N-loud sample, suggesting additional nitrogen enrichment beyond the overall metal enrichment. Together, these results indicate that N-loud quasars have both high overall BLR metallicity and enhanced relative nitrogen abundance, suggesting that relative nitrogen abundance is at least partially decoupled from overall metallicity. N-loud quasars therefore provide a high-metallicity laboratory for understanding how nuclear environments can produce unusual abundance patterns and offer a complementary view of how nitrogen enrichment arises across cosmic time.

astro-ph.GA↗

arXiv2026

Nitrogen-Loud Quasars from the Dark Energy Spectroscopic Instrument. I. Sample Selection and Basic Properties

We present the largest sample to date of nitrogen-loud (N-loud) quasars with strong broad N IV] $\lambda1486$ and/or N III] $\lambda1750$ emission lines over the redshift range $1.6 < z < 4.3$, selected from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. The final sample contains 1,993 N-loud quasars, corresponding to about 1.2% of the parent quasar sample. The $L_{1450}$ distribution of the N-loud quasars is broadly similar to that of the DESI parent sample, but their redshift distribution is distinct, with a stronger concentration around $z \sim 2.5$--3. Their composite spectrum displays a broadly similar UV continuum shape to that of the parent quasars, while showing significantly enhanced broad nitrogen emission features, including N V, N IV], and N III]. Other metal emission features also show a moderate enhancement. Relative to a control sample matched in redshift and UV continuum luminosity, the N-loud quasars show systematically narrower broad C IV and Mg II emission lines, lower single-epoch virial black hole masses, and higher Eddington ratios, suggesting that N-loud quasars may preferentially appear during a relatively rapid black hole accretion phase. The radio-loud fraction is 10.1%, with the highest fraction among objects exhibiting both N III] and N IV] emission. The catalog provides a statistical baseline for future studies of nitrogen enhancement and its physical origin.

astro-ph.GA↗

arXiv2026

Probabilistic Stellar Age Estimation for Gaia XP Stars with NGBoost

Stellar age is a fundamental quantity for Galactic archaeology, but reliable age estimation for large stellar samples remains challenging. In this work, we develop an uncertainty aware NGBoost framework for stellar age estimation using Gaia XP-derived atmospheric parameters and chemical abundances. Different from the standard NGBoost model, we modify the loss function by incorporating the uncertainties of the training age labels. We further use a Monte Carlo strategy to quantify the influence of input-feature uncertainties on the predicted ages. The resulting model provides age estimates together with uncertainty estimates. Applying this framework to Gaia XP stars, we construct a stellar age catalog containing 15,175,107 stars.

astro-ph.SR↗

arXiv2026

A Systematic NLTE Study of Very Metal-Poor Stars with Metallicity Down to $-4.3$ dex. II. Lithium Abundance and New Insight to the Lithium Plateau

Metal-poor stars are crucially important for understanding the early Galaxy, first stars, and the Universe. In this series of papers, we present a homogeneous non-local thermodynamic equilibrium (NLTE) abundances analysis of 12 elements for 103 very/extremely metal-poor (VMP/EMP) stars with metallicity down to $-4.3$ dex. The sample was selected from the LAMOST survey and observed by the high-resolution spectroscopy of Subaru. In this paper, we present the NLTE abundances and evolution of lithium in these stars. We report different lithium behaviors corresponding to different evolutionary stages and their signatures: 1) The Spite Plateau shows a slightly positive slope, indicating increasing lithium abundance with increasing metallicity. Most significantly, it appears to extend to lower metallicities as previously suggested, calling into question the reality of the so-called 'meltdown' at low metallicity; 2) We confirm a lithium plateau for lower red giant branch (LRGB) stars with A(Li) $= 1.13$ dex in our sample, while lithium abundance drops rapidly to A(Li)$<0.5$ as stars continue to evolve to higher stage. 3) We identify four Li-rich stars in our sample across different evolutionary stages, showing complex and multiple lithium production mechanisms in VMP/EMP stars. These findings suggest that early Galactic lithium enrichment results from a complex interplay between depletion and production processes.

astro-ph.SR↗

arXiv2026

Milky Way Dynamics Favor Dark Matter over Modified Gravity Models

Modified gravity theories such as Modified Newtonian Dynamics (MOND) and Scalar-Tensor-Vector Gravity (STVG) have been proposed as alternatives to dark matter, but decisive tests have been hindered by degeneracies between baryonic structure and gravitational laws. Here we break this degeneracy using independent, high-precision constraints: the Milky Way radial rotation curve, vertical phase-space spirals from Gaia, and a broken-exponential stellar disk. A joint reconstruction of the radial and vertical gravitational fields reveals a structural inconsistency in modified gravity -- no model can simultaneously reproduce both observations. Our results strongly disfavor MOND at $>13σ$ and STVG at $>4σ$. In contrast, dark matter halo models naturally explain the observations, providing a self-consistent test of gravity on galactic scales.

astro-ph.GA↗

arXiv2026

Technical Report: A Hierarchical Dynamically Weighting Deep Reinforcement Learning Method for Multi-UAV Multi-Task Coordination

This paper investigates the multi-UAV multi-task coordination problem in infrastructure-less emergency scenarios, where UAVs collaboratively are required to jointly perform aerial image acquisition and ground-user communication. To tackle the challenge of balancing heterogeneous tasks within dynamic environments, we propose a hierarchical dynamic weighting Deep Reinforcement Learning (DRL) framework. Specifically, an episode-level module is introduced to capture global task preferences, while a step-level module adaptively adjusts the objective weights according to real-time system conditions. By integrating global and instantaneous weights, the proposed framework improves decision stability and responsiveness during task execution. Simulation results demonstrate that the proposed method achieves faster convergence, more stable training, and higher task completion efficiency than conventional works.

cs.NI↗

arXiv2026

The Stellar Abundances and Galactic Evolution Survey (SAGES). V. The First Data Release of the DDO51 Band

We present the first public data release of DDO51 band from the Stellar Abundances and Galactic Evolution Survey (SAGES), based on Nanshan One-meter Wide-field Telescope (NOWT) observations obtained between 2023 September and 2024 January. This release initiates the DDO51-band component of the survey, covering $\sim$ 2,500 deg$^2$ of the northern sky and including more than 10 million sources. The DDO51 filter is centered near the \ion{Mg}{1}~$b$ triplet and the adjacent MgH feature, offering sensitivity to stellar surface gravity. The data reduction pipeline incorporates an improved astrometric solution anchored to Gaia DR3 and a photometric calibration strategy tied to synthetic photometry from Gaia XP spectra. These procedures yield a point-source depth of $\sim$18.9 mag at S/N$\sim$10 and an internal photometric precision $\approx$6-7 mmag at the bright end. A preliminary color--color analysis using Gaia broadband photometry confirms the expected sensitivity of the DDO51 band to stellar surface gravity, demonstrating a clear photometric separation between dwarf and giant sequences for late-type stars. This dataset, when combined with existing SAGES photometry in other bands, provides a crucial tool for disentangling the substructures of the Milky Way. All data products from this release upon publication will be available.

astro-ph.SR↗

arXiv2026

The Spectroscopic and Photometric Study of a Star Cluster Sample in Andromeda Halo

Halo star clusters serve as vital tracers for the formation and evolution of the Andromeda galaxy. In this work, we present physical parameters for 29 M31 halo star clusters, derived from a combination of spectroscopic and photometric data. Low-resolution spectra were acquired using the BFOSC spectrograph on the NAOC Xinglong 2.16-m telescope. For the photometric analysis, we utilized uSC and vSAGE bands from the SAGE survey, complemented by archival data from GALEX(NUV, FUV), PAN-STARRS(grizy) and the 2MASS(JHK). Ages and metallicities were determined via ULySS (Vazdekis et al. and pegase-hr) SSP model and the Bruzual & Charlot (2003) (BC03) stellar population synthesis models. The derived parameters show good agreement with literature values. Notably, for three of these clusters, this study represents the first combined photometric and spectroscopic analysis.

astro-ph.GA↗

arXiv2026

Proton-rich production of lanthanides: the $νi$ process

The astrophysical origin of the lanthanides is an open question in nuclear astrophysics. Besides the widely studied $s$, $i$, and $r$ processes in moderately-to-strongly neutron-rich environments, an intriguing alternative site for lanthanide production could in fact be robustly $\textit{proton-rich}$ matter outflows from core-collapse supernovae under specific conditions -- in particular, high-entropy winds with enhanced neutrino luminosity and fast dynamical timescales. In this environment, excess protons present after charged particle reactions have ceased can continue to be converted to neutrons by (anti-)neutrino interactions, producing a neutron capture reaction flow up to A~200. This scenario, christened the $νi$ process in a recent paper, has previously been discussed as a possibility. Here, we examine the prospects for $νi$ process through the lens of stellar abundance patterns, bolometric lightcurves, and galactic chemical evolution models, with a particular focus on hypernovae as candidate sites. We identify specific lanthanide signatures for which the $νi$ process can provide a credible alternative to $r$/$i$ processes.

astro-ph.HE↗

arXiv2026

HR-GO II: chemical abundances of low-$E$ retrograde dynamically-tagged-groups: Revealing Thamnos as a very metal-poor substructure

Milky Way halo substructures identified in dynamical space are known to suffer from contamination from the Milky Way in-situ stars, which makes their accreted origins uncertain. We present detailed chemical abundances of 35 stars belonging to two sets of dynamically tagged groups, Rg8 and Rg9, to investigate their accreted nature. Both groups are composed of stars with low orbital energy and very retrograde orbits. We find that Rg8 and Rg9 are chemically indistinguishable across all elements, from C to Eu, strongly indicating that they belong to the same structure. The iron-abundance distribution of this low-$E$ retrograde group has a prominent peak at [Fe/H] $\approx-2.1$, revealing that its main population is very metal-poor, and a secondary peak at [Fe/H] $\approx-1.5$, very likely due to contamination from Milky Way in-situ stars. These groups also heavily overlap with the Thamnos substructure in dynamical space, and we thus use them to investigate the chemical properties of Thamnos. The dominant, low-metallicity population provides strong evidence for the ex-situ origin of Thamnos, as well as its very metal-poor nature. We do not see any evidence of an $α$ knee in our sample, which is consistent with previous studies. Comparison with the Cetus-Palca stream in the chemical space shows similar abundance distributions, and thus it suggests that the Thamnos progenitor dwarf galaxy had a truncated star formation history due to its early merger with the Milky Way.

astro-ph.GA↗

arXiv2025

Milky Way Mass Through Escape Velocity Curve from LAMOST K Giants

Escape velocity has long been used to constrain the mass of the Dark Matter (DM) halo in the Milky Way (MW). Here we present a study of the escape velocity curve using a sample of high-velocity K giants with full 6D phase-space information and relatively good quality, selected from LAMOST DR8 and cross-matched with Gaia DR3. To expand the high-velocity stars to larger distances, we used radius-dependent criteria of total velocity, that is, $v_{\rm GC}>300\;\rm{km s^{-1}}$ for the solar neighborhood; $v_{\rm GC}>v_{\rm min}\sim0.6\times v_{\rm esc}(r_{\rm GC})$ for outer region. We also selected halo stars based on $v_ϕ-{\rm [Fe/H]}$ information to ensure that the sample is isotropic. We modeled the velocity distribution with traditional power-law models to determine the escape velocity in each radial bin. For the first time, we have directly measured a relatively continuous escape velocity curve that can extend to Galactocentric radii of $\sim 50$ kpc, finding a decline in agreement with previous studies. The escape velocity at the solar position yielded by our measurements is $523.74^{+12.83}_{-13.47}\;\rm{km s^{-1}}$. Combined with the local circular velocity, we estimated the mass of the MW assuming a Navarro-Frenk-White DM profile, which resulted in a total mass of $M_{200,\;\rm{total}}=0.90_{-0.07}^{+0.06}\times 10^{12}\;M_{\odot}$, with a concentration of $c_{200}=13.47_{-1.70}^{+1.85}$. The small uncertainty implies that including the escape velocities beyond the solar neighborhood can result in a more precise mass estimate. Our derived MW mass is consistent with some recent studies using the escape velocity as well as other tracers, which may support a lower mass of the DM halo than in the past.

astro-ph.GA↗

arXiv2025

Where are the Population III star relics in the simulated Milky Way analogues?

Using 6 Milky Way analogues with two different numerical resolutions from the Auriga simulation, we investigate the total mass, spatial distribution and kinematics of the Population III star relics in the Milky Way analogues at $z=0$. These relics (primarily second generation stars) formed over a wide redshift range, from about $z=22$ to $z=4$, with an average formation redshift of $z \sim 10.0$, and comprise about $2\times10^{-5}$ of the entire galactic stellar population. The disk and bulge components host only a small fraction of these relics, contributing less than $12$ percent in total. The stellar halo, in particular the outer stellar halo of which galactic radius $r>30$ kpc, hosts the largest fraction (about 46 percent on average), with an average of one relic star for per $4,000$ to $10,000$ stars, making it a promising region for observational searches. Additionally, around $18$ percent of the Population III star relics are found in satellite galaxies, with smaller and older satellite galaxies tending to contain a higher proportion of these stars. Thus, low-mass and early-formed satellite galaxies are also ideal targets for finding such relics, although some satellite galaxies may lack them entirely. The spatial distribution and kinematics of these stars show good numerical convergence across different simulation resolutions. Our results provide valuable guidance for searches of the Population III star relics and offer insights for interpreting findings from ongoing and future stellar archaeology surveys.

astro-ph.GA↗

arXiv2025

Abundance Pattern Fitting with Bayesian Inference: Constraining First Stars' Properties and Their Explosion Mechanism with Extremely Metal-poor Stars

The abundance patterns of extremely metal-poor stars preserve a fossil record of the Universe's earliest chemical enrichment by the supernova explosions from the evolution of first generation of stars, also referred to as Population III (or Pop III). By applying Bayesian inference to the analysis of abundance patterns of these ancient stars, this study presents a systematic investigation into the properties and explosion mechanism of Pop III stars. We apply NLTE corrections to enhance the reliability of abundance measurements, which significantly reduces the discrepancies in abundances between observations and theoretical yields for odd-Z elements, such as Na and Al. Our Bayesian framework also enables the incorporation of explodability and effectively mitigates biases introduced by varying resolutions across different supernova model grids. In addition to confirming a top-heavy ($α=0.54$) initial mass function for massive Pop III stars, we derive a robust mass--energy relation ($E\propto M^2$) of the first supernovae. These findings demonstrate that stellar abundance analysis provides a powerful and independent approach for probing early supernova physics and the fundamental nature of the first stars.

astro-ph.SR↗

arXiv2025

Introduction to the Chinese Space Station Survey Telescope (CSST)

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.

astro-ph.IM↗

arXiv2025

The Stellar Abundances and Galactic Evolution Survey (SAGES). IV. Surface Gravity Estimation and Giant-Dwarf Separation with the DDO51 Filter

Reliable estimation of stellar surface gravity (log $g$) for a large sample is crucial for evaluating stellar evolution models and understanding galactic structure; However, it is not easy to accomplish due to the difficulty in gathering a large spectroscopic data set. Photometric sky survey using a specific filter, on the other hand, can play a substantial role in the assessment of log $g$. The Stellar Abundances and Galactic Evolution Survey (SAGES) utilizes eight filters to provide accurate stellar parameters for $\sim10^{7}$ stars, with its DDO51 intermediate-band filter specifically designed for robust log $g$ determination. In this work, the observed SAGES $u_{\rm SC}$ and $v_{\rm SAGES}$ photometry, the synthetic photometry in $g$, $r$, $i$, and DDO51 bands derived from \textit{Gaia} XP spectra are employed to investigate the importance of the DDO51 filter in the determination of log $g$. We applied machine-learning-based extinction correction and employed XGBoost models, trained on stellar parameters from LAMOST, to predict log $g$ using photometric data. By comparing model predicted log $g$ with LAMOST values, we find that including DDO51 filter improve the accuracies of log $g$ estimates by 21.0\% (from 0.224\,dex to 0.177\,dex) overall, and by 26.5\% (from 0.302\,dex to 0.222\,dex ) for GK-type stars, as compared to those obtained without DDO51. The DDO51 filter is also validated to be particularly effective for metal-poor stars ([Fe/H]$<$-1.0), where it significantly mitigates systematic biases. Our findings highlight the diagnostic power of the SAGES DDO51 filter, providing enhanced stellar characterization vital for future in-depth studies of the Milky Way.

astro-ph.SR↗