G.-C. Liu1 , Y. Huang2,9 , H.-W. Zhang3,4 , M.-S. Xiang5 , J.-J. Ren6 , B.-Q. Chen2 , H.-B. Yuan7 , C. Wang3 , Y. Yang2 , Z.-J. Tian8 , F. Wang3,4 , and X.-W. Liu2,9 

1 Center for Astronomy and Space Sciences, China Three Gorges University, Yichang 443002, People’s Republic of China 2 South-Western Institute For Astronomy Research, Yunnan University, Kunming 650500, People’s Republic of China; yanghuang@ynu.edu.cn, x.liu@ynu.edu.cn 3 Department of Astronomy, Peking University, Beijing 100871, People’s Republic of China 4 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People’s Republic of China 5 Max-Planck Institute for Astronomy, Königstuhl, D-69117, Heidelberg, Germany 6 National Astronomical Observatories, Chinese Academy of Science, Beijing 100012, People’s Republic of China 7 Department of Astronomy, Beijing Normal University, Beijing 100875, People’s Republic of China 8 Department of Astronomy, Yunnan University, Kunming 650500, People’s Republic of China Received 2019 August 28; revised 2020 January 31; accepted 2020 February 3; published 2020 April 7

Abstract 

We present a catalog of 5290 RR Lyrae stars (RRLs) with metallicities estimated from spectra of the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) and the Sloan Extension for Galactic Understanding and Exploration (SEGUE) surveys. Nearly 70% of them (3642 objects) also have systemic radial velocities measured. Given the pulsating nature of RRLs, metallicity estimates are based on spectra of individual exposures that have been matched with their synthetic templates. The systemic radial velocities are measured by fifitting the observed velocity as a function of phase assuming an empirical pulsating velocity template curve. Various tests show that our analyses yield metallicities with a typical precision of 0.20 dex and systemic radial velocities with uncertainties ranging from 5 to 21 km s−1 (depending on the number of radial-velocity measurements available for a given star). Based on the well-calibrated near-infrared PMW1Z or PM Z Ks , and MV–[Fe/H] relations, precise distances are derived for these RRLs. Finally, we include Gaia DR2 proper motions in our catalog. The catalog should be very useful for various Galactic studies, especially of the Galactic halo. Unifified Astronomy Thesaurus concepts: RR Lyrae variable stars (1410); Galaxy abundances (574); Chemical abundances (224); Galaxy structure (622); Milky Way stellar halo (1060) Supporting material: machine-readable table。

1.Introduction 

Probing the Galactic structure is important for understanding the assemblage history of the Milky Way as well as galaxies in general. The Milky Way halo contains some of the oldest stars and structures found in our Galaxy, and thus provides information of the earliest stage of the evolution of our Galaxy. Despite its crucial importance, our knowledge of the stellar halo is still far from complete, partly due to the lack of large samples of halo tracers to probe its properties. Previously, the main halo tracers employed included blue horizontal branch (BHB) stars (e.g., Xue et al. 2008; Deason et al. 2011, 2014; Das et al. 2016), K giants (e.g., Xue et al. 2015; Xu et al. 2018), near-main-sequence turnoff stars (nMSTO) (e.g., Sesar et al. 2011; Pila-Diez et al. 2015) and RR Lyrae stars (RRLs; e.g., Watkins et al. 2009). The available number of BHB stars is small since they are diffificult to identify; distance estimation of K giants is not easy considering that their intrinsic luminosities vary by two orders of magnitude (depending on stellar age and metallicity); and the luminosities of nMSTO are not high enough to be useful for probing the distant outer halo of the Galaxy. Compared to the other tracers, RRLs are ideal for studying halo properties. First, RRLs are old (>9 Gyr), low-mass metalpoor stars that reside in the instability strip of the horizontal branch (HB) and thus represent a fair sample of the halo populations (Smith 2004). Second, their well defifined period– luminosity relation makes them good standard candles, allowing one to accurately map out the 3D structure of the halo......

原文下载：Probing the Galactic Halo with RR Lyrae Stars. I. The Catalog.pdf