Self-consistent Stellar Radial Velocities from LAMOST Medium-resolution Survey DR7

• Published in: The Astrophysical journal. Supplement series Vol. 256; no. 1; pp. 14 - 32
• Main Authors: Zhang, Bo, Li, Jiao, Yang, Fan, Xiong, Jian-Ping, Fu, Jian-Ning, Liu, Chao, Tian, Hao, Li, Yin-Bi, Wang, Jia-Xin, Liang, Cai-Xia, Zhou, Yu-Tao, Zong, Weikai, Yang, Cheng-Qun, Liu, Nian, Hou, Yong-Hui
• Format: Journal Article
• Language: English
• Published: Saskatoon The American Astronomical Society 01.09.2021; IOP Publishing
• Subjects: Algorithms; Astronomy data analysis; Astronomy data reduction; Astrostatistics; Correlation; Cross correlation; Distribution functions; Exposure; Polls & surveys; Radial velocity; Radio spectroscopy; Robust regression; Sky surveys; Spectral resolution; Spectroscopic binary stars; Spectroscopy; Stars; Stellar spectra; Surveys; Time domain analysis
• ISSN: 0067-0049; 1538-4365
• DOI: 10.3847/1538-4365/ac0834

Abstract Radial velocity (RV) is among the most fundamental physical quantities obtainable from stellar spectra and is rather important in the analysis of time-domain phenomena. LAMOST Medium-resolution Survey (MRS) DR7 contains five million single-exposure stellar spectra with spectral resolution R ∼ 7500. However, the temporal variation of the RV zero-points (RVZPs) of the MRS, which makes the RVs from multiple epochs inconsistent, has not been addressed. In this paper, we measure the RVs of 3.8 million single-exposure spectra (for 0.6 million stars) with signal-to-noise ratios (S/N) higher than 5 based on the cross-correlation function method, and propose a robust method to self-consistently determine the RVZPs exposure by exposure for each spectrograph with the help of Gaia DR2 RVs. Such RVZPs are estimated for 3.6 million RVs and can reach a mean precision of ∼0.38 km s −1 . The result of the temporal variation of RVZPs indicates that our algorithm is efficient and necessary before we use the absolute RVs to perform time-domain analyses. Validating the results with APOGEE DR16 shows that our absolute RVs can reach an overall precision of 0.84/0.80 km s −1 in the blue/red arm at 50 < S/N < 100 and of 1.26/1.99 km s −1 at 5 < S/N < 10. The cumulative distribution function of the standard deviations of multiple RVs ( N obs ≥ 8) for 678 standard stars reaches 0.45/0.54, 1.07/1.39, and 1.45/1.86 km s −1 in the blue/red arm at the 50%, 90%, and 95% levels, respectively. Catalogs of the RVs, RVZPs, and selected candidate RV standard stars are available at https://github.com/hypergravity/paperdata .