arXiv subjects

Mingfeng Qin

Publications and source records attributed to Mingfeng Qin.

10 recordsLinked to original sources

arXiv2026

Statistical evidence for linear combination frequencies in {\gamma} Doradus stars being nonlinear resonant modes

The quest for the origin of linear combination frequencies in pulsating stars is critical for mode identification and subsequent seismic modeling. Hybrid {\gamma} Doradus (Dor) stars provide a crucial testbed for such investigations due to their rich frequency content in both gravity (g) and pressure (p) modes. Here, we performed a comprehensive survey of 608 Kepler {\gamma} Dor stars, detecting 81,265 frequencies, and identifying 1,895 harmonics and 45,968 combinations involving two parent frequencies. Our results suggest that the proportion of linear combinations increases with the frequency number in each {\gamma} Dor star, leveling off at approximately 75%. The majority of the parent-to-child amplitude ratios are distributed between 100 and 10,000, peaking between 2,000 and 4,000. Moreover, the amplitude ratios, involving two g-mode parents, are found to escalate with increasing combination frequency. These values are at least an order of magnitude higher than those predicted by nonlinearity distortion of the light curve, whereas they align well with those of nonlinear resonant coupling. Our findings suggest that a significant portion of combination frequencies are likely intrinsic modes under resonant conditions rather than products of surface geometric distortions, offering new insights that warrant systematic investigations across other types of pulsating star.

astro-ph.SR↗

arXiv2026

Missing pairs in open cluster catalogs

Open clusters (OCs) in our Galaxy can be found in pairs, possibly forming physical binaries, or in groups. These objects offer unique insights into the process of star formation and testify to the dynamical interactions at local and galactic scales. Therefore, building as complete a census as possible is a valuable endeavor. This work is aimed at identifying and characterizing new OC pair candidates that had been overlooked in previous studies. Two recent comprehensive catalogs were cross-matched to identify OCs in the first catalog that had been missing from the second one. From this list, counterparts in the second catalog were searched within a 3D distance of 50 pc. Candidate pairs were then selected by applying constraints on the tangential velocity (TV) difference. An orbital integration was performed to assess gravitational binding. The similarity in terms of the radial velocity (RV) and age was evaluated. We identified seven isolated binary cluster candidates, comprising two likely bound systems with stable orbits over 100 Myr; two pairs with a possible common origin but lacking RV confirmation; and three pairs with significant velocity discrepancies, suggesting they are unbound or in transitional states. We also identified six cluster group candidates, while refining the membership of known complexes such as UBC\_672 and NGC\_1977, and discovering a new group around FSR\_0198. Notably, the UBC\_392 group exhibits coherent proper motions but inconsistent RVs and large age spreads, indicating that it is not gravitationally bound. Additionally, we reconciled 15 clusters with discrepant nomenclature between the two catalogs. Multi-catalog integration combined with kinematic and dynamical validation is essential for establishing a complete census of Galactic cluster pairs.

astro-ph.GA↗

arXiv2026

Precise parameter determination of the open cluster NGC 1647 via asteroseismology of p-mode pulsators

Asteroseismology of member pulsators provides a robust physical constraint on cluster parameters by linking internal stellar structures to the global properties of the host cluster. However, the parameters of NGC 1647 remains poorly constrained due to limited investigation, a situation that cluster asteroseismology can significantly refine. In this study, we identified 271 high confidential cluster members in NGC 1647, using HDBSCAN clustering with radial-velocity validation. Its initial age is determined in the range of 1250-280 Myr, derived from isochrone fitting based on multi-survey metallicities extinction-corrected Gaia photometry. Among the members, we found 96 periodic variables from TESS and K2 photometry, including nine p-mode pulsators (five {\delta} Sct and four hybrid {\delta} Sct-{\gamma} Dor stars). Assuming a common cluster age and initial chemical composition, joint asteroseismic modeling is performed based on measured large frequency separations and individual mode frequencies. This yields a metallicity of [Fe/H] = -0.08+0.04-0.01, well consistent with the spectroscopic determinations, and a seismic age of 178+11-9 Myr, more precise than isochrone-based estimates. This work shows the diagnostic potential of {\delta} Sct asteroseismology in young open clusters and establishes a high-precision benchmark for future studies of NGC 1647 and other open clusters.

astro-ph.SR↗

arXiv2026

The morphological stability of open clusters: a new 2D perspective

Open clusters (OCs) usually evolve gradually as the number of their members changes, which can be manifested in their morphological characteristics. We aim to investigate the morphological stability of 1,490 OCs and further explore the potential change of morphological stability of the OCs at different spatial positions, using the OC catalog from the literature. We define for the first time a new morphological stability parameter Ncore/Nouter, a ratio of member numbers between cluster core and outer areas within tidal radii, which has a significant positive correlation against N, with a slope of 1.140$\pm$0.039, significantly steeper than the 0.720$\pm$0.026 measured for Score/Souter. This demonstrates that the stellar density in the core is a more sensitive tracer for morphological stability than geometry. Spatially, the radial sample OCs have larger slopes of Ncore/Nouter and Score/Souter against N, with 1.083$\pm$0.116 and 0.733$\pm$0.080, respectively, whereas those in the tangential direction 1.013$\pm$0.110 and 0.529$\pm$0.075, respectively, which means that the impact on sample OCs from tidal forces directed toward the Galactic center is possibly stronger than that from the shear force caused by the differential rotation of the Galactic disk. Besides, the sample OCs younger than 30 Myr display a shallow slope of 0.751$\pm$0.166, with those older than 800 Myr (1.442$\pm$0.128), reflecting that young OCs likely endure both internal disruptions, such as early dynamical heating weakening core binding and more severe external disturbances, compared to older OCs.

astro-ph.GA↗

arXiv2025

Phase II of the LAMOST-Kepler/K2 Survey. II. Time Domain of Medium-resolution Spectroscopic Observations from 2018 to 2023

The LAMOST-Kepler/K2 Medium-Resolution Spectroscopic Survey (LK-MRS) conducted time-domain medium-resolution spectroscopic observations of 20 LAMOST plates in the Kepler and K2 fields from 2018 to 2023, a phase designated as LK-MRS-I. A catalog of stellar parameters for a total of 36,588 stars, derived from the spectra collected during these five years, including the effective temperature, the surface gravity, the metallicity, the {\alpha}-element abundance, the radial velocity, and v sin i of the target stars, is released, together with the weighted averages and uncertainties. At S/N = 10, the measurement uncertainties are 120 K, 0.18 dex, 0.13 dex, 0.08 dex, 1.9 km/s, and 4.0 km/s for the above parameters, respectively. Comparisons with the parameters provided by the APOGEE and GALAH surveys validate the effective temperature and surface gravity measurements, showing minor discrepancies in metallicity and {\alpha}-element abundance values. We identified some peculiar star candidates, including 764 metal-poor stars, 174 very metal-poor stars, and 30 high-velocity stars. Moreover, we found 2,333 stars whose radial velocity seems to be variable. Using Kepler/K2 or TESS photometric data, we confirmed 371 periodic variable stars among the radial velocity variable candidates and classified their variability types. LK-MRS-I provides spectroscopic data being useful for studies of the Kepler and K2 fields. The LK-MRS project will continue collecting time-domain medium-resolution spectra for target stars during the third phase of LAMOST surveys, providing data to support further scientific research.

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arXiv2025

Precise Asteroseismology of the High-amplitude Delta Scuti Star EH Librae, an AE UMa Analogue in the Hertzsprung Gap

A subclass of intermediate mass variables Delta Scuti stars, known as High-amplitude Delta Scuti (HADS) stars, exhibits pronounced radial pulsations with high amplitudes. The ground-based and space-based observations of the HADS star EH Lib are used to help making asteroseismological analysis of this pulsating star. Following the reduction of the light curves, the frequency analysis reveals the fundamental frequency as $f_0=11.3105$ c day$^{-1}$ and two more significant frequencies $f_1$ and $f_2$, in addition to the harmonics of $f_0$ and a linear combination. The period change rate is determined as $(1/P_0)(dP_0/dt)=(5.4\pm0.5)\times10^{-9}$ yr$^{-1}$ derived from an O-C diagram, which is constructed from 342 times of maximum light spanning over 70 years. Using these observational constraints, along with the metallicity reported in the literature, we construct theoretical models using the stellar evolution code MESA and calculate the theoretical frequencies of the eigen modes using the oscillation code GYRE. The appropriate models are selected by matching both $f_0$ and $(1/P_0)(dP_0/dt)$ within their respective uncertainties. The results indicate that the observed period change of EH Lib can be attributed to stellar evolutionary effects. The stellar parameters of EH Lib are derived as: the mass of $1.715\pm0.065$ M$_{\odot}$, the luminosity of log $(L/L_{\odot})=1.38\pm0.06$, and the age of $(1.14\pm0.13)\times10^{9}$ years. EH Lib is classified as a single-mode HADS star, locating currently in the Hertzsprung gap, with a helium core and a hydrogen-burning shell. This work expands the asteroseismological sample of HADS stars and establishes a foundation for future investigations into their commonalities and specific properties, thereby advancing our understanding of these variables.

astro-ph.SR↗

arXiv2024

An In-depth Investigation of the Primordial Cluster Pair ASCC 19 and ASCC 21

Utilizing \texttt{Gaia} data from the literature, we report a new young ($\sim$8.9~Myr) cluster pair, ASCC~19 and ASCC~21, located near the Orion star-forming complex. The clusters are separated by a 3D distance of ~27.00~$\pm$~7.51~pc. Both clusters share a common age (Log(age)~=~6.95~$\pm$~0.05), similar radial velocities ($R_{v}$~=~21.34~$\pm$~4.47~km s$^{-1}$ for ASCC~19 and $R_{v}$~=~20.05~$\pm$~3.86~km s$^{-1}$ for ASCC~21), and comparable metallicities ([Fe/H]~=~$-$0.14~$\pm$~0.25~dex for ASCC~19 and [Fe/H]~=~$-$0.12~$\pm$~0.04~dex for ASCC~21, from LAMOST-DR11). These similarities suggest that the clusters likely originated from the fragmentation of the same molecular cloud, forming a primordial cluster pair. Furthermore, the formation of the two clusters is attributed to the coalescence of multiple subclusters, as inferred from the distribution analysis between metal abundances and distances to clusters' centers. Neither cluster shows significant mass segregation. Their members with radial velocities exceeding 100~km s$^{-1}$ are young variables. Additionally, a tidal interaction between the clusters is observed. Comparisons of the Roche radius with tidal radii, and velocity difference with orbital velocity, suggest that the pair is an unbound system, that is, a double cluster. Finally, orbital motion simulations show that the clusters will not merge into a single system.

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arXiv2023

A detection of the layered structure of nearby open clusters

We applied the newly developed rose diagram overlay method to detect the layered structure of 88 nearby open clusters ($\leq$500~pc) on the three projections after the distance correction of their member stars, based on the catalog in literature. The results show that with the rose diagram overlay method, a total of 74 clusters in our sample have a layered structure, while the remaining clusters are without a clear layered structure. We for the first time defined the layered structure parameters for the sample clusters. Meanwhile, we found that the layered circle core area ($s$) has a strong positive correlation with the number of cluster members, while the kernel instability index ($\eta$) has a strong negative correlation with the number of cluster members. Our study provides a novel perspective for the detection of the layered structure of open clusters.

astro-ph.GA↗

arXiv2022

A Low-speed Intruder Star in Hyades: A Temporary Residence

We hereby report a low-speed (about~21~km$\cdot$~s$^{-1}$ with respect to the Sun) intruder member in the Hyades cluster based on the data in the literature. The results show that the star is a non-native member star for the Hyades, with its radial velocity being smaller than the radial velocity of the Hyades cluster, even exceeding the standard deviation of the radial velocity of the cluster by a factor of 9. Furthermore, by analyzing and comparing the orbits of this star and its host, it may have intruded into its host in the past 2~Myr. If the star's current motion orbit remains unchanged, it may leave its host in the next 2~Myr. This implies that the intruder star may be temporarily residing in the cluster. This study presents the first observational evidence of a star intrusion into a cluster, which suggests that more evidence may be found.

astro-ph.SR↗

arXiv2022

Searching for Variable Stars in the Open Cluster NGC 2355 and Its Surrounding Region

We have investigated the variable stars in the field surrounding NGC 2355 based on the time-series photometric observation data. More than 3000 CCD frames were obtained in the V band spread over 13 nights with the Nanshan One-meter Wide-field Telescope. We have detected 88 variable stars, containing 72 new variable stars and 16 known variable stars. By analyzing these light curves, we classified the variable stars as follows: 26 eclipsing binaries, 52 pulsating stars, 4 rotating variables, and 6 unclear type variable stars for which their periods are much longer than the time baseline chosen. Employing Gaia DR2 parallax, kinematics, and photometry, the cluster membership of these variable stars were also analyzed for NGC 2355. In addition to the 11 variable members reported by Cantat-Gaudin et al. (2018), we identify 4 more variable member candidates located at the outer region of NGC 2355 and showed homogeneity in space positions and kinematic properties with the cluster members. The main physical parameters of NGC 2355 estimated from the two-color and color-magnitude diagrams are log(age/yr) = 8.9, E(B - V) = 0.24 mag, and [Fe/H] = - 0.07 dex.

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