Mapping the Galactic disk with the LAMOST and Gaia Red clump sample: I: precise distances, masses, ages and 3D velocities of $\sim$ 140000 red clump stars
Yang Huang, Ralph Schonrich, Huawei Zhang, Yaqian Wu, Bingqiu Chen, Haifeng Wang, Maosheng Xiang, Chun Wang, Haibo Yuan, Xinyi Li, Weixiang Sun, Ji Li, Xiaowei Liu
备注：
16 pages, 19 figures, 3 tables, accepted for publication in ApJS
We present a sample of $\sim$ 140,000 primary red clump (RC) stars of spectral signal-to-noise ratios higher than 20 from the LAMOST Galactic spectroscopic surveys, selected based on their positions in the metallicity-dependent effective temperature--surface gravity and color--metallicity diagrams, supervised by high-quality $Kepler$ asteroseismology data. The stellar masses and ages of those stars are further determined from the LAMOST spectra, using the Kernel Principal Component Analysis method, trained with thousands of RCs in the LAMOST-$Kepler$ fields with accurate asteroseismic mass measurements. The purity and completeness of our primary RC sample are generally higher than 80 per cent. For the mass and age, a variety of tests show typical uncertainties of 15 and 30 per cent, respectively. Using over ten thousand primary RCs with accurate distance measurements from the parallaxes of Gaia DR2, we re-calibrate the $K_{\rm s}$ absolute magnitudes of primary RCs by, for the first time, considering both the metallicity and age dependencies. With the the new calibration, distances are derived for all the primary RCs, with a typical uncertainty of 5--10 per cent, even better than the values yielded by the Gaia parallax measurements for stars beyond 3--4 kpc. The sample covers a significant volume of the Galactic disk of $4 \leq R \leq 16$ kpc, $|Z| \leq 5$ kpc, and $-20 \leq ϕ\leq 50^{\circ}$. Stellar atmospheric parameters, line-of-sight velocities and elemental abundances derived from the LAMOST spectra and proper motions of Gaia DR2 are also provided for the sample stars. Finally, the selection function of the sample is carefully evaluated in the color-magnitude plane for different sky areas. The sample is publicly available.
Red Clump Stars from the LAMOST data I: identification and distance
我们提出了一个样本的约120,000红团候选人选择从LAMOST DR 2目录的基础上的经验分布模型在有效温度与表面重力平面。虽然红团星一般被认为是标准烛光，但它们的绝对星等并不局限在一个狭窄的范围内，而是可能根据它们的初始质量而扩展到超过1等。因此，传统的过于简化的距离估计与固定的光度假设可能会导致系统的偏差有关的初始质量或年龄，这可能会影响研究银河系的演化与红团星。因此，我们采用等时线为基础的方法来估计的绝对星等的红丛星从他们观察到的表面重力，有效温度和金属丰度。我们验证，估计以及删除系统，并提供一个初始的质量/年龄独立的距离估计精度小于10%。
We present an independent examination of the parallax zero-point of the Third Gaia Early Data Release (hereafter EDR3), using the LAMOST primary red clump (PRC) stellar sample. A median parallax offset of around $26 μ$as, slightly larger than that found by examination of distant quasars, is found for both the five- and six-parameter solutions in EDR3, based on samples of over 63,000 and 2000 PRC stars, respectively. Similar to the previous investigation of Lindegren et al., to which we compare our results, the parallax zero-point exhibits clear dependencies on the $G$ magnitudes, colors, and p…
Using a sample of nearly 140,000 primary red clump stars selected from the LAMOST and $Gaia$ surveys, we have identified a large sample of "young" [$α$/Fe]-enhanced stars with stellar ages younger than 6.0 Gyr and [$α$/Fe] ratios greater than 0.15 dex. The stellar ages and [$α$/Fe] ratios are measured from LAMOST spectra, using a machine learning method trained with common stars in the LAMOST-APOGEE fields (for [$α$/Fe]) and in the LAMOST-$Kepler$ fields (for stellar age). The existence of these "young" [$α$/Fe]-enhanced stars is not expected from the classical Galactic chemical evolution mode…
We propose a new model to determine the ages and masses of red giant branch (RGB) stars from the low-resolution large sky area multi-object fiber spectroscopic telescope (LAMOST) spectra. The ages of RGB stars are difficult to determine using classical isochrone fitting techniques in the Hertzsprung-Russell diagram, because isochrones of RGB stars are tightly crowned. With the help of the asteroseismic method, we can determine the masses and ages of RGB stars accurately. Using the ages derived from the asteroseismic method, we train a deep learning model based on DenseNet to calculate the ages…
Although red clump (RC) stars are easy to identify due to their stability of luminosity and color, about 20-50% are actually red giant branch (RGB) stars in the same location on the HR diagram. In this paper, a sample of 210,504 spectra for 184 318 primary RC (PRC) stars from the LAMOST DR7 is identified, which has a purity of higher than 90 percent. The RC and the RGB stars are successfully distinguished through LAMOST spectra(R~1800 and SNR>10) by adopting the XGBoost ensemble learning algorithm, and the secondary RC stars are also removed. The SHapley Additive exPlanations (SHAP) value is u…
In this work, we identify 734 ultracool dwarfs with a spectral type of M6 or later, including one L0. Of this sample, 625 were studied spectroscopically for the first time. All of these ultracool dwarfs are within 360~pc, with a \textit{Gaia} G magnitude brighter than ~19.2 mag. By studying the spectra and checking their stellar parameters (Teff, logg, and [FeH] derived with the LAMOST pipeline, we found their cool red nature and their metallicity to be consistent with the nature of Galactic thin-disk objects. Furthermore, 77 of them show lithium absorption lines at 6708A, further indicating t…
The Comparison of Stellar Atomspheric Parameters between LAMOST and APOGEE databases
比较了LAMOST-DR 2和SDSS-DR 12/APOGEE数据库的温度、重力和金属丰度等恒星参数。据发现，LAMOST数据库提供了一个更好的红团功能比APOGEE数据库中的Teff与logg图。利用这一优势，我们将红团簇星和红巨星分离出来，并尝试分别建立这两组恒星的两个数据集之间的定标关系。结果表明，在温度上有很好的一致性，刻度值接近于一对一的直线，对红团和红巨星分支样品都能建立满意的金属度刻度值[Fe/H]_APO = 1.18 [Fe/H]_APO +0.11，离散度为0.08 dex。在引力方面，两个数据库中的红团簇星没有任何相关性，红巨星刻度周围的散射很大。我们发现红巨星logg散射的两个主要来源。一组是$0.00253*Teff-8.67<logg<2.6 locating at the forbidden region, and the other is the contaminated red clump stars, which could be picked out from the unmatched region where stellar metallicity is not consistent with the position in the Teff versus logg diagram. After excluding stars at th…
Stellar chromospheric activity and age relation from open clusters in the LAMOST Survey
我们在LAMOST巡天中识别了90多个疏散星团的成员星。用Fang et al.（2018）计算了82个疏散星团中1091颗成员星的色球活动指数logR'CaK和83个疏散星团中1118颗成员星的色球活动指数logR' H α。在不同的Teff和[Fe/H]范围内，研究了每个疏散星团的平均logR'CaK，logR' H α与年龄的关系。我们发现CA从logt = 6.70到logt = 8.50开始缓慢下降，然后迅速下降，直到logt = 9.53。对于温度较低的恒星，这种趋势变得更加明显。构造了logR'和logt之间的二次函数，当4000 K < Teff <5500 K时，可用于粗略估计场星年龄，其精度对logR'CaK约为40%，对logR 'H α约为60%。
The puzzle of Li-rich giant is still unsolved, contradicting the prediction of the standard stellar models. Although the exact evolutionary stages play a key role in the knowledge of Li-rich giants, a limited number of Li-rich giants have been taken with high-quality asteroseismic parameters to clearly distinguish the stellar evolutionary stages. Based on the LAMOST Data Release 7 (DR7), we applied a data-driven neural network method to derive the parameters for giant stars, which contain the largest number of Li-rich giants. The red giant stars are classified into three stages of Red Giant Br…
The present work presents our efforts at identifying new mercury-manganese (HgMn/CP3) stars using spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Suitable candidates were searched for among pre-selected early-type spectra from LAMOST DR4 using a modified version of the MKCLASS code that probes several Hg II and Mn II features. The spectra of the resulting 332 candidates were visually inspected. Using parallax data and photometry from Gaia DR2, we investigated magnitudes, distances from the Sun, and the evolutionary status of our sample stars. We al…
Stellar population astrophysics (SPA) with the TNG. Abundance analysis of nearby red giants and red clump stars: combining high resolution spectroscopy and asteroseismology
Context: Precise chemical abundances coupled with reliable ages are key ingredients to understand the chemical history of our Galaxy. Open Clusters (OCs) are useful for this purpose because they provide ages with good precision. Aims: The aim of this work is to investigate the relations of different chemical abundance ratios vs age traced by red clump (RC) stars in OCs. Methods: We analyze a large sample of 209 reliable members in 47 OCs with available high-resolution spectroscopy. We applied a differential line-by-line analysis to provide a comprehensive chemical study of 25 chemical species.…
In this work, we studied the distribution of lithium abundances in giants as a function of stellar mass. We used a sample of 1240 giants common among Kepler photometric and LAMOST medium resolution (R $\approx$ 7500) spectroscopic survey fields. The asteroseismic $Δ$P - $Δν$ diagram is used to define core He-burning red clump giants and red giant branch stars with inert He-core. Li abundances have been derived using spectral synthesis for the entire sample stars. Directly measured values of asteroseismic parameters $Δ$P(or $ΔΠ_1$) and $Δν$ are either taken from the literature or measured in th…
Two Li-rich candidates, TYC 1338-1410-1 and TYC 2825-596-1, were observed with the new high-resolution echelle spectrograph, LAMOST/HRS. Based on the high-resolution and high-signal-to-noise ratio (SNR) spectra, we derived stellar parameters and abundances of 14 important elements for the two candidates. The stellar parameters and lithium abundances indicate that they are Li-rich K-type giants, and they have A(Li)$_\mathrm{NLTE}$ of 1.77 and 2.91 dex, respectively. Our analysis suggests that TYC 1338-1410-1 is likely a red giant branch (RGB) star at the bump stage, while TYC 2825-596-1 is most…
We derive stellar parameters and abundances (`stellar labels') of 40,034 late-B and A-type main-sequence stars extracted from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope Medium Resolution Survey (LAMOST--MRS). The primary selection of our early-type sample was obtained from LAMOST Data Release 7 based on spectral line indices. We employed the Stellar LAbel Machine (SLAM) to derive their spectroscopic stellar parameters, drawing on Kurucz spectral synthesis models with 6000 K $< T_\mathrm{eff} <$ 15,000 K and $-1$ dex $< \mathrm{[M/H]} <$ 1 dex. For a signal-to-noise ratio of …
The formation of the extended thin disc is the most spectacular event of our Galaxy in the past $\sim8$\,Gyr. To unveil this process, obtaining precise and accurate stellar ages for a large sample of stars is essential although challenging. In this work, we present the asteroseismic age determination of 5306 red giant branch stars using \kepler{} and LAMOST data, with a thorough examination of how the age determination is affected by the choice of different temperature scales and stellar models. Thanks to the high precision of the asteroseismic and spectroscopic parameters of our sample stars,…
High-resolution spectroscopic analysis of a large sample of Li-rich giants found by LAMOST
富锂巨星的发现对标准的恒星演化模型提出了新的挑战，为了解决这一问题，近年来随着全球范围内观测的发展，这类天体的数量迅速增加。利用大天区多目标光纤光谱望远镜巡天，报道了44颗新发现的富锂巨星，并得到了高分辨率观测的证实。基于高分辨率、高信噪比的光谱数据，采用光谱合成方法反演大气参数和元素丰度。我们对它们的演化阶段、红外过剩、投影自转速度（v sin i）和恒星星族进行了详细的分析。结果表明：（1）富锂巨星主要集中在红巨星分支凸点、红巨星团和渐近巨星分支的演化状态;（2）其中3颗是快转巨星，没有一颗表现出红外过剩。我们的研究结果表明，锂富集的起源最有可能与恒星内部的额外混合有关，而外部来源可能只做出很小的贡献。此外，不同的富锂事件发生在不同的进化阶段。
Red clump stars (RCs) are useful tracers of distances, extinction, chemical abundances, and Galactic structures and kinematics. Accurate estimation of the RC parameters -- absolute magnitude and intrinsic color -- is the basis for obtaining high-precision RC distances. By combining astrometric data from Gaia, spectroscopic data from APOGEE and LAMOST, and multi-band photometric data from Gaia, APASS, Pan-STARRS1, 2MASS, and WISE surveys, we use the Gaussian process regression to train machine learners to derive the multi-band absolute magnitudes $M_λ$ and intrinsic colors $(λ_1-λ_2)_0$ for eac…
Testing Chemical Tagging with LAMOST: Intrinsic Abundance Dispersion of Subgiant Stars in the Galactic Disk
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿交叉科学研究院）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；Department of Astronomy, Beijing Normal University（北京师范大学天文学系）
Known sources of lithium (Li) in the universe include the big bang, novae, asymptotic giant branch stars, and cosmic ray spallation. During their longer-lived evolutionary phases, stars are not expected to add to the Li budget of the Galaxy, but to largely deplete it. In this context, recent analyses of Li data from GALAH and LAMOST for field red clump (RC) stars have concluded that there is the need for a new production channel of Li, ubiquitous among low-mass stars, and that would be triggered on the upper red giant branch (RGB) or at helium ignition. This is distinct from the "Li-rich giant…
We present observations of ammonia emission lines toward the interstellar filament WB~673 hosting the dense clumps WB~673, WB~668, S233-IR and G173.57+2.43. LTE analysis of the lines allows us to estimate gas kinetic temperature ($\lesssim$ 30~K in all the clumps), number density ($7-17\times10^3$~cm$^{-3}$), and ammonia column density ($\approx 1-1.5\times 10^{15}$~cm$^{-2}$) in the dense clumps. We find signatures of collapse in WB 673 and presence of compact spatially unresolved dense clumps in S233-IR. We reconstruct 1D density and temperature distributions in the clumps and estimate their…
We have performed a search among low mass red giants for finding evidence for merger scenario for triggering He-flash and subsequent Li enhancement. We chose a sample of red giants from GALAH survey with well-measured Li abundances, and near and mid-IR fluxes from 2MASS and WISE surveys, respectively. The sample contains 418 cool red clump giants and 359 upper red giant branch giants. Most of the giants and majority of super Li-rich giants show no IR excess. Only five red clump giants and one RGB giant show IR excess. Notably, of the five red clump giants with IR excess, three are super Li-ric…
Over 4,000 exoplanets have been identified and thousands of candidates are to be confirmed. The relations between the characteristics of these planetary systems and the kinematics, Galactic components, and ages of their host stars have yet to be well explored. Aiming to addressing these questions, we conduct a research project, dubbed as PAST (Planets Across Space and Time). To do this, one of the key steps is to accurately characterize the planet host stars. In this paper, the Paper I of the PAST series, we revisit the kinematic method for classification of Galactic components and extend the …
Stellar ages from [C/N] in giant stars: applicability and limitations
The Australian National University（澳大利亚国立大学）；INAF - Osservatorio di Astrofisica e Scienza dello Spazio（意大利国家天体物理研究所-天文与空间科学观测站）；Università degli Studi di Catania（卡塔尼亚大学）；Università degli Studi di Bologna（博洛尼亚大学）；Vilnius University（维尔纽斯大学）；INAF - Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所-阿切特里天文台）
