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Lithium is a fragile but crucial chemical element in the universe, exhibits interesting and complex behaviors. Thanks to the massive spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) medium-resolution survey (MRS), we can investigate the lithium abundances in a large and diverse sample of stars, which could bring vital help to study the origin and evolution of lithium. In this work, we use the Li 6,707.8 {\AA} line to derive the lithium abundance through a template-matching method. A catalog of precise lithium abundance is presented for 795,384 spectra corresponding to 455,752 stars from the LAMOST MRS Data Release (DR) 9. Comparing our results with those of external high-resolution references we find a good consistency with a typical deviation of {\sigma} A(Li) ~ 0.2 dex. We also analyze the internal errors using stars that have multiple LAMOST MRS observations, which will reach as low as 0.1 dex when the signal-to-noise ratio (S/N) of the spectra > 20. Besides, our result indicates that a small fraction of giant stars still exhibit surprisingly high amount of lithium contents, and 967 stars are identified as Li-rich giants with A(Li) > 1.5 dex, accounting for ~ 2.6% of our samples. If one takes into account the fact that nearly all stars deplete lithium during the main sequence, then the fraction of Li-rich stars may exceed 2.6% much. This new catalog covers a wide range of stellar evolutionary stages from pre-main sequence to giants, and will provide help to the further study of the chemical evolution of lithium., Comment: 16 pages, 9 figures, 2 tables. Accepted for publication in ApJS

The unexpected discovery of hot Jupiters challenged the classical theory of planet formation inspired by our solar system. Until now, the origin and evolution of hot Jupiters are still uncertain. Determining their age distribution and temporal evolution can provide more clues into the mechanism of their formation and subsequent evolution. Using a sample of 383 giant planets around Sun-like stars collected from the kinematic catalogs of the Planets Across Space and Time (PAST) project, we find that hot Jupiters are preferentially hosted by relatively younger stars in the Galactic thin disk. We subsequently find that the frequency of hot Jupiters declines with age. In contrast, the frequency of warm/cold Jupiters shows no significant dependence on age. Such a trend is expected from the tidal evolution of hot Jupiters' orbits, and our result offers supporting evidence using a large sample. We also perform a joint analysis on the planet frequencies in the stellar age-metallicity plane. The result suggests that the frequencies of hot Jupiters and warm/cold Jupiters, after removing the age dependence are both correlated with stellar metallicities. Moreover, we show that the above correlations can explain the bulk of the discrepancy in hot Jupiter frequencies inferred from the transit and radial velocity (RV) surveys, given that RV targets tend to be more metal-rich and younger than transits., Comment: Published in PNAS; 7 pages, 5 figures in the main text; 17 pages, 29 figures, 5 tables in the supporting information

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Low Resolution Spectroscopic Survey (LRS) provides massive spectroscopic data of M-type stars, and the derived stellar parameters could bring vital help to various studies. We adopt the ULySS package to perform $\chi^2$ minimization with model spectra generated from the MILES interpolator, and determine the stellar atmospheric parameters for the M-type stars from LAMOST LRS Data Release (DR) 8. Comparison with the stellar parameters from APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP) suggests that most of our results have good consistency. For M dwarfs, we achieve dispersions better than 74 K, 0.19 dex and 0.16 dex for $T_{\rm eff}$, $\log{g}$ and [Fe/H], while for M giants, the internal uncertainties are 58 K, 0.32 dex and 0.26 dex, respectively. Compared to ASPCAP we also find a systematic underestimation of $\Delta {T_{\rm eff}} =$ $-$176 K for M dwarfs, and a systematic overestimation of $\Delta {\log{g}} =$ 0.30 dex for M giants. However, such differences are less significant when we make comparison with common stars from other literature, which indicates that systematic biases exist in the difference of ASPCAP and other measurements. A catalog of 763,136 spectra corresponding to 616,314 M-type stars with derived stellar parameters is presented. We determine the stellar parameters for stars with $T_{\rm eff}$ higher than 2,900 K, with $\log{g}$ from -0.24 dex to 5.9 dex. The typical precisions are 45 K, 0.25 dex and 0.22 dex, for $T_{\rm eff}$, $\log{g}$ and [Fe/H], respectively, which are estimated from the duplicate observations of the same stars., Comment: 21 pages, 20 figures, 3 tables, accepted for publication in The Astrophysical Journal Supplement Series

The Kepler telescope has discovered over 4,000 planets (candidates) by searching ? 200,000 stars over a wide range of distance (order of kpc) in our Galaxy. Characterizing the kinematic properties (e.g., Galactic component membership and kinematic age) of these Kepler targets (including the planet (candidate) hosts) is the first step towards studying Kepler planets in the Galactic context, which will reveal fresh insights into planet formation and evolution. In this paper, the second part of the Planets Across the Space and Time (PAST) series, by combining the data from LAMOST and Gaia and then applying the revised kinematic methods from PAST I, we present a catalog of kinematic properties(i.e., Galactic positions, velocities, and the relative membership probabilities among the thin disk, thick disk, Hercules stream, and the halo) as well as other basic stellar parameters for 35,835 Kepler stars. Further analyses of the LAMOST-Gaia-Kepler catalog demonstrate that our derived kinematic age reveals the expected stellar activity-age trend. Furthermore, we find that the fraction of thin(thick) disk stars increases (decreases) with the transiting planet multiplicity (Np = 0, 1, 2 and 3+) and the kinematic age decreases with Np, which could be a consequence of the dynamical evolution of planetary architecture with age. The LAMOST-Gaia-Kepler catalog will be useful for future studies on the correlations between the exoplanet distributions and the stellar Galactic environments as well as ages., Comment: Accepted for publication in Astronomical Journal, 19 pages, 9 figures, 5 tables. The full data of the LAMOST-Gaia-Kepler kinematic catalog (Table 3) will be published with the journal. If you need to use the data, please contact us via the email (jwxie@nju.edu.cn, dg1826003@smail.nju.edu.cn)

Standard stellar evolution model predicts a severe depletion of lithium (Li) abundance during the first dredge-up process (FDU). Yet a small fraction of giant stars are still found to preserve a considerable amount of Li in their atmospheres after FDU. Those giants are usually identified as Li-rich by a widely used criterion, A(Li) $ > 1.5$\,{\it dex}. A large number of works dedicated to search for and investigate this minority of the giant family, and the amount of Li-rich giants has been largely expanded, especially in the era of big data. In this paper, we present a catalog of Li-rich giants found from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey with Li abundances derived from a template matching method developed for LAMOST low-resolution spectra. The catalog contains $10,535$ Li-rich giants with Li abundances from $\sim 1.5$\,{\it dex} to $\sim 4.9$\,{\it dex}. We also confirm that the ratio of Li-rich phenomenon among giant stars is about one percent, or for a more expression, $1.29\%$ from our statistically important sample. This is the largest Li-rich giant sample ever reported to date, which significantly exceeds amount of all the reported Li-rich giants combined. The catalog will help the community to better understand the Li-rich phenomenon in giant stars., Comment: 16 pages, 11 figures