Chun-Qian Li

Based on 120 and 20 s cadence TESS light curves from Sectors 1 to 75, we perform an asteroseismic analysis of 221 main-sequence and subgiant solar-like oscillators with ν max ≥ 500 μ Hz , including 51 new detections. Using Markov Chain Monte Carlo fitting and autocorrelation-based methods, we measure the global seismic parameters, the frequency at maximum power ν max and the large frequency separation Δ ν , with median relative uncertainties of 2.29% and 1.78%, respectively. We identify individual oscillation modes ( l = 0, 1, 2) and extract their mode frequencies ν _nl via peak bagging with the open-source Python package S olarlike P eakbagging . By fitting the folded power spectrum and the asymptotic relation, we derive the asymptotic large frequency separation Δ ν _p , the p -mode phase offset ϵ _p , and the small frequency separation δν ₀₂ . We then infer stellar masses, radii, and surface gravities using asteroseismic scaling relations with Δ ν correction factors ( f _{Δ ν} ). This valuable sample of oscillating main-sequence and subgiant stars will broaden our understanding of the stellar fundamental physical processes.

We present a chemodynamical analysis of three hypervelocity stars (HVS) selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope medium-resolution spectroscopic survey and Gaia. The high-resolution follow-up observation was conducted with Subaru, enabling precise stellar atmospheric parameter determination ( T _eff , log g , [Fe/H], and ξ _t ) and detailed abundance measurements for elements Na, Mg, Ca, Ti, Ba, and Eu. Non–local thermodynamic equilibrium corrections were applied for most species. Orbital properties were computed using GalPy , integrating 1000 Monte Carlo realizations of phase-space coordinates backward for 13 Gyr under the Galactic potential. Our results reveal distinct origins of the three objects: J 1436+3537 exhibits low [ α /Fe], and high [Ba/Fe] and [Eu/Fe] ratios, consistent with an accreted origin. Its galactocentric velocity exceeds the Galactic escape velocity; J 1334+1400 shows thick disk-like α -abundances and a bulge-proximal orbit, supporting an in situ ejection; J 1718+2418 displays the typical chemistry and kinematics of the thick disk. This study demonstrates that the HVS formation mechanisms are complex, and coupling chemical abundances with orbital histories is helpful to constrain their origins.

We present a photometric and spectroscopic analysis of the long-period Algol-type eclipsing binary 2MASS J06281154+164439.3 (J0628), based on 1082days of TESS full-frame photometry and 21 LAMOST spectra. The radial-velocity modeling supports a semidetached configuration with a Roche-lobe-filling donor and a mass ratio q ≃ 0.37, adopting the TESS photometric ephemeris ( P = 21.556 days). The H α line exhibits persistent double-peaked emission whose peak separation is nearly constant (Δ V = 334.8 ± 16.2 km s ⁻¹ ) but with variable V / R , indicating a disk-dominated origin with modest nonaxisymmetry. Interpreting Δ V as Keplerian rotation implies an outer emitting radius R _out ≈ 21.4 ± 2.2 R _⊙ (≈0.79 R _L,1 ). To ensure physical self-consistency, we perform a joint forward modeling of the TESS light curve and a representative H α profile using ShellSpec . This unified model uses a physically consistent stream-impact hot spot at the outer edge of the accretion disk to reproduce the out-of-eclipse asymmetry, yielding global parameters of i = 62 . ° 86, a = 57.60 R _⊙ , T _eff,1 = 10,096 K, and T _eff,2 = 4569 K. The joint fit firmly constrains the disk properties to log 10 ρ disk = − 13.37 (cgs), T _disk = 6021 K, R _in = 3.48 R _⊙ , R _out = 26.56 R _⊙ , and v _turb = 49.7 km s ⁻¹ , confirming a stable Roche-lobe-contained Keplerian disk. J0628 is therefore a valuable laboratory for connecting precise binary parameters with phase-resolved disk diagnostics.

Li-rich giants serve as valuable tracers of stellar evolution and surface enrichment processes, for which a statistically large and homogeneous sample is crucial. Using the massive low-resolution ( R ∼ 1800) spectroscopic dataset from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, we systematically search for Li-rich giants by determining their stellar lithium abundances through template matching of the Li i 6708 Å absorption line with a grid of synthetic spectra generated from ATLAS9 model atmospheres. The derived abundances are validated against previous high-resolution studies, showing good consistency with a mean absolute error of about 0.15 dex. Therefore, we adopt a threshold of A (Li) > 1.65 dex to select Li-rich candidates, followed by visual inspection to ensure the reliability of each detection. Eventually, more than 20,000 Li-rich giants are identified, corresponding to approximately 2.5% of all giants in LAMOST DR9. We also investigate the occurrence rate of Li-rich giants in different evolutionary stages. This work presents a large and homogeneous catalog of Li-rich giants derived from the LAMOST low-resolution survey, which provides a reliable and valuable dataset for future studies of stellar evolution and lithium enrichment in evolved stars.

The formation, evolution, and stability of multiple star systems are still open questions in the field of astrophysics. Algol-type binaries are important for obtaining precise physical parameters, investigating the reversal of the mass ratio, and studying the multiplicity of stars. We present a detailed analysis of RW Leo and RT Per with the high-precision time-series radial velocities from the LAMOST-medium-resolution spectroscopic survey and TESS light curves, and we first obtained their absolute parameters. We found that RT Per and RW Leo are post-mass transfer SD2-type semidetached binaries with mass ratios of 0.29 and 0.176, respectively, and the evolved secondary components almost fill their Roche lobe (both ∼99.4%). Moreover, their O − C diagrams show double-cycle oscillations, and the oscillation periods are ∼78 yr and ∼41 yr for RW Leo and ∼247 yr and ∼41 yr for RT Per, respectively. The long-period of them may be caused by the presence of a third body with a mass not less than 0.4 M _⊙ , but we did not detect the third light. For RT Per, our fitting data do not fully cover a complete long-period oscillation (∼247 yr), and longer duration observations are needed to check our results in the future. For the 41 yr oscillations of RW Leo and RT Per, the cyclic magnetic activity from their active secondary components is a probable reason. Besides, after 2451218.604 (HJD), we also discovered that the magnetic activity cycle of RT Per suddenly halved to 20.88 yr because of a possible change in the geometry of the secondary’s magnetic field.

We report the discovery of LAMOST J0041+3948, the most luminous post-asymptotic giant-branch (AGB) Type II Cepheid known, located in the Andromeda Giant Stellar Stream. Its spectral energy distribution (SED) exhibits a strong near-infrared excess, indicating the presence of a circumbinary dusty disk and hence binarity. SED fitting yields an effective temperature of T eff = 673 8 − 262 + 234 K and a post-AGB luminosity of log ( L / L ⊙ ) = 4.3 2 − 0.08 + 0.07 . Comparison with theoretical evolutionary tracks suggests a ∼2.0–4.0 M _⊙ progenitor when accounting for a possible scattered-light contribution. Zwicky Transient Facility light curves reveal a pulsation period of 89 days that lies close to the period–luminosity relation for long-period RV Tauri stars. Follow-up spectroscopy reveals clear s -process enrichment and signatures consistent with an accretion disk around the companion. The inferred progenitor is significantly younger and more massive than a typical stream member, suggesting that an additional mechanism, such as a stellar merger, is required. We propose a formation channel in which the present post-AGB binary descends from a hierarchical triple system. In this scenario, the inner binary merged after the system was displaced to its current location by the galaxy merger event, and the resulting massive merger remnant subsequently evolved into the extremely luminous post-AGB star observed today.

The stellar model is still facing challenges in explaining the origin of low-mass stars and brown dwarfs. Double-lined detached eclipsing binaries with low-mass and similar components play an important astrophysical role in accurately deriving fundamental parameters, investigating stellar properties, and restricting theoretical stellar models of low-mass stars. Using high-precision light curves and Large Sky Area Multi-Object Fiber Spectroscopic Telescope spectra, we first obtained the fundamental parameters of the four detached binaries (NSVS 07453183, V644 Aur, V912 Per, and V1250 Tau). Except for V1250 Tau (q _sp∼ 0.95), the mass ratios of the other three targets are almost equal to 1, which is consistent with the core fragmentation and dynamical capture theories of binary formation. The O − C curves of these systems based on current data exhibit cyclic variations, which is due to the light-travel time effect caused by the presence of a third body. Among them, the third body of V912 Per is likely to be a stellar black hole ( M 3 sin i 3 = 12.57 M ⊙ ) . The O − C diagram of NSVS 07453183 shows double-cycle oscillations, which means that it is perhaps a quadruple system. The third body of NSVS 07453183 is an M3-type main-sequence star based on third light analysis, and the fourth body maybe a brown dwarf. The obtained Hertzsprung–Russell diagram based on the Modules for Experiments in Stellar Astrophysics code suggested that the components of these four targets are main-sequence stars. These four targets will gradually form Algol-type binaries in the future, which are important systems for studying the reversal of the mass ratio.

Whether the presence of planets affects the lithium (Li) abundance of their host stars is still an open question. To investigate the difference in the Li abundance between planet-host stars (HSs) and isolated stars (ISs) with no detected planets, we analyze a large sample of stars with temperatures ranging from 4600 to 6600 K and metallicity ranging from −0.55 to +0.50. The sample consists of 279 HSs whose spectra were taken from the California-Kepler Survey, which followed up planets detected by Kepler, and 171 ISs whose spectra were taken from the Keck archive. The non–local thermodynamic equilibrium (non-LTE) effects were taken into consideration. It is found that the distributions of Li abundances in both the HS and IS groups are generally consistent with each other. This suggests that the presence of Kepler-like planets does not have a significant impact on Li depletion. We also found that the non-LTE corrections cannot be neglected for stars with A(Li) over ∼2.5 dex.

Based on the spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope medium-resolution spectroscopic survey, we select a sample of 88 Li-rich unevolved star candidates. We redetermine their photospheric lithium abundances, A(Li), through the spectral synthesis method, and take the nonlocal thermodynamic equilibrium (NLTE) into account. It is found that there are 62 stars with A(Li) ranging from 3.33 to 4.59 dex. Among them, 23 stars are young stellar objects. There are 33 super Li-rich unevolved stars with A(Li) higher than 3.8 dex, and 24 of them are newly identified. The NLTE corrections for A(Li) are negative, with a maximum value of around 0.5 dex. Our results suggest that the mechanisms such as mass transfer in binary systems, accretion of circumstellar materials, and diffusion processes may contribute to lithium enrichment in their respective samples.