arXiv subjects

Liu Long

Publications and source records attributed to Liu Long.

7 recordsLinked to original sources

arXiv2026

Host--Non-host Differences in Stellar Chemistry, Activity, and Birth Radius: Hints of Distinct Formation Environments for Earth-like Planets and Sub-Neptunes

Host-star properties provide important clues to planet formation and evolution, yet it remains unclear whether the observed differences between planet-hosting stars and stars without detected planets reflect genuine signatures of planet formation or underlying differences in stellar populations. Using a homogeneous sample of 28,383 Kepler-LAMOST-Gaia dwarf and subgiant stars, including 629 host stars with 865 planets, we compare host stars with age-mass matched non-host stars after correcting for distribution-induced matching biases. Most host-non-host differences disappear when the full planet sample is considered. However, separating planets by radius reveals distinct trends. At the high-abundance end of the [O/Fe], [Mg/Fe], and [Si/Fe] distributions, Earth-like hosts tend to be more O-rich but more Mg-poor and Si-poor than their age-mass matched non-host stars, whereas sub-Neptune hosts tend to show the opposite behavior. Sub-Neptune hosts also tend to exhibit lower chromospheric activity and smaller birth radii than comparable non-host stars. These results suggest that host-non-host differences become apparent primarily after separating planets by size and that Earth-like planets and sub-Neptunes may be associated with distinct formation environments and evolutionary pathways. We also find that hot-Jupiter hosts are tentatively more metal-rich, chromospherically active, and formed at smaller Galactic birth radii than hosts of longer-period Jupiters.

astro-ph.SR↗

arXiv2026

A Randomized PDE Energy driven Iterative Framework for Efficient and Stable PDE Solutions

Efficient and stable solution of partial differential equations (PDEs) is central to scientific and engineering applications, yet existing numerical solvers rely heavily on matrix based discretizations, while learning based methods require costly training and often suffer from limited generalization. In this work, we proposes a PDE energy driven framework that solves PDEs through physically constrained diffusion iterations, without relying on classical matrix based finite element assembly or data driven neural network training. The proposed method evolves arbitrary random initial fields through PDE energy driven implicit iterations combined with Gaussian smoothing, while strictly enforcing boundary conditions at each iteration. The proposed formulation is applied to representative one dimensional Poisson, Heat, and viscous Burgers equations, covering both steady state and transient problems. Numerical results demonstrate stable convergence to the unique physical solution from random initializations, with accurate resolution of sharp gradients and controlled Mean Squared Error (MSE) across a wide range of discretization parameters. Detailed comparisons with analytical solutions indicate that the framework achieves competitive accuracy and stability. Overall, the proposed framework provides a fast, flexible, and physically consistent alternative to traditional numerical solvers, offering a potential pathway for scalable PDE solutions in both research and engineering applications.

cs.LG↗

arXiv2024

Relations of rotation and chromospheric activity to stellar age for FGK dwarfs from Kepler and LAMOST

The empirical relations between rotation period, chromospheric activity, and age can be used to estimate stellar age. To calibrate these relations, we present a catalog, including the masses and ages of 52,321 FGK dwarfs, 47,489 chromospheric activity index $logR^{+}_{HK}$, 6,077 rotation period $P_{rot}$ and variability amplitude $S_{ph}$, based on data from LAMOST DR7, Kepler and Gaia DR3. We find a pronounced correlation among $P_{rot}$, age, and [Fe/H] throughout the main-sequence phase for F dwarfs. However, the decrease of $logR^{+}_{HK}$ over time is not significant except for those with [Fe/H] $<$ $-$0.1. For G dwarfs, both $P_{rot}$ and $logR^{+}_{HK}$ are reliable age probes in the ranges $\sim$ 2-11 Gyr and $\sim$ 2-13 Gyr, respectively. K dwarfs exhibit a prominent decrease in $logR^{+}_{HK}$ within the age range of $\sim$ 3-13 Gyr when the relation of $P_{rot}-\tau$ is invalid. These relations are very important for promptly estimating the age of a vast number of stars, thus serving as a powerful tool in advancing the fields of exoplanet properties, stellar evolution, and Galactic-archaeology.

astro-ph.SR↗

arXiv2024

Detection of Solar-like Oscillations in Sub-giant and Red Giant Stars Using 2-minute Cadence TESS Data

Based on all 2-minute cadence $TESS$ light curves from Sector 1 to 60, we provide a catalog of 8,651 solar-like oscillators, including frequency at maximum power ($\nu_{\rm max}$, with its median precision, $\sigma$=5.39\%), large frequency separation ($\Delta\nu$, $\sigma$=6.22\%), seismically derived masses, radii, and surface gravity. In this sample, we have detected 2,173 new oscillators and added 4,373 new $\Delta\nu$ measurements. Our seismic parameters are consistent with those from $Kepler$, $K2$, and previous $TESS$ data. The median fractional residual in $\nu_{\rm max}$ is $1.63\%$ with a scatter of $14.75\%$, and in $\Delta\nu$ it is $0.11\%$ with a scatter of $10.76\%$. We have detected 476 solar-like oscillators with $\nu_{\rm max}$ exceeding the $Nyquist$ frequency of $Kepler$ long-cadence data during the evolutionary phases of sub-giant and the base of the red-giant branch, which provide a valuable resource for understanding angular momentum transport.

astro-ph.SR↗

arXiv2023

Investigating 16 Open Clusters in the Kepler/K2-Gaia DR3 field. I. Membership, Binary, and Rotation

Using data from the Gaia Data Release 3 (Gaia DR3) and Kepler/K2, we present a catalog of 16 open clusters with ages ranging from 4 to 4000 Myr, which provides detailed information on membership, binary systems, and rotation. We assess the memberships in 5D phase space, and estimate the basic parameters of each cluster. Among the 20,160 members, there are 4,381 stars identified as binary candidates and 49 stars as blue straggler stars. The fraction of binaries vary in each cluster, and the range between 9% to 44%. We obtain the rotation periods of 5,467 members, of which 4,304 are determined in this work. To establish a benchmark for the rotation-age-color relation, we construct color-period diagrams. We find that the rotational features of binaries are similar to that of single stars, while features for binaries are more scattered in the rotation period. Moreover, the morphology of the color-period relationship is already established for Upper Scorpius at the age of 19 Myr, and some stars of varying spectral types (i.e. FG-, K-, and M-type) show different spin-down rates after the age of ~110 Myr. By incorporating the effects of stalled spin-down into our analysis, we develop an empirical rotation-age-color relation, which is valid with ages between 700 - 4000 Myr and colors corresponding to a range of 0.5 < (G_BP-G_RP)0 < 2.5 mag.

astro-ph.GA↗

arXiv2023

Age of FGK Dwarfs Observed with LAMOST and GALAH: Considering the Oxygen Enhancement

Varying oxygen abundance could impact the modeling-inferred ages. This work aims to estimate the ages of dwarfs considering observed oxygen abundance. To characterize 67,503 LAMOST and 4,006 GALAH FGK-type dwarf stars, we construct a grid of stellar models which take into account oxygen abundance as an independent model input. Compared with ages determined with commonly-used $\alpha$-enhanced models, we find a difference of $\sim$9% on average when the observed oxygen abundance is considered. The age differences between the two types of models are correlated to [Fe/H] and [O/$\alpha$], and they are relatively significant on stars with [Fe/H] $\lesssim$ -0.6 dex. Generally, varying 0.2 dex in [O/$\alpha$] will alter the age estimates of metal-rich (-0.2 $<$ [Fe/H] $<$ 0.2) stars by $\sim$10%, and relatively metal-poor (-1 $<$ [Fe/H] $<$ -0.2) stars by $\sim$15%. Of the low-O stars with [Fe/H] $<$ 0.1 dex and [O/$\alpha$] $\sim$ -0.2 dex, many have fractional age differences of $\geq$ 10%, and even reach up to 27%. The fractional age difference of high-O stars with [O/$\alpha$] $\sim$ 0.4 dex reaches up to -33% to -42% at [Fe/H] $\lesssim$ -0.6 dex. We also analyze the chemical properties of these stars. We find a decreasing trend of [Fe/H] with age from 7.5-9 Gyr to 5-6.5 Gyr for the stars from the LAMOST and GALAH. The [O/Fe] of these stars increases with decreasing age from 7.5-9 Gyr to 3-4 Gyr, indicating that the younger population is more O-rich.

astro-ph.SR↗

arXiv2014

Attenuation Correction of L-shell X-ray Fluorescence Computed Tomography Imaging

X-ray Fluorescence Computed Tomography(XFCT) is a prevalent experimental technique which is utilized to investigate the spatial distribution of elements in sample. The sensitivity of L-shell XFCT of some elements is lower than that of K-shell XFCT. However, the image reconstruction for this technique has much more problems than that of transmission tomography, one of which is self-absorption. In the present work, a novel strategy was developed to deal with such problems. But few researches are concerned on attenuation correction of L-shell XFCT that are essential to get accurate reconstructed image. We make use of the known quantities and the unknown elemental concentration of interest to express the unknown attenuation maps. And then the attenuation maps are added in the contribution value of the pixel in MLEM reconstruction method. Results indicate that the relative error is less than 14.1%, which is proved this method can correct L-shell XFCT very well.

physics.ins-det↗