Radial velocity measurements of an orbiting star around Sgr A*

PASJ: Publications of the Astronomical Society of Japan

Takahashi, Masaaki¹  Tamura, Motohide²  Omiya, Masashi²  Najarro, Francisco³  Saida, Hiromi⁴  Schödel, Rainer⁵  Hamano, Satoshi⁶  Nagata, Tetsuya⁷  Nishiyama, Shogo⁸  Nagatomo, Schun⁸  Takamori, Yohsuke⁹  Takahashi, Mizuki^1,10  Gorin, Haruka^1,11 

[1] Aichi University of Education, 1 Hirosawa, Igaya-cho, Kariya, Aichi 448-8542, Japan;Astrobiology Center, NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan;Centro de Astrobiología (CSIC/INTA), Carretera de Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain;Daido University, 10-3 Takiharu-cho, Minami-ku, Nagoya, Aichi 457-8530, Japan;Instituto de Astrofísica de Andalucía (IAA)-CSIC, Apartado 3004, 18008 Granada, Spain;Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto, Kyoto 603-8555, Japan;Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto, Kyoto 606-8502, Japan;Miyagi University of Education, 149 Aramaki-aza-Aoba, Aobaku, Sendai, Miyagi 980-0845, Japan;National Institute of Technology, Wakayama College, 77 Noshima, Nada-cho, Gobo, Wakayama 644-0023, Japan;The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;Tohoku University, 6-3 Aramaki Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan

关键词: Galaxy: center;    black hole physics;    relativistic processes;    instrumentation: spectrographs;    techniques: radial velocities;   

DOI  :  10.1093/pasj/psy067

学科分类：天文学(综合)

来源: Oxford University Press

【 摘 要 】

During the next closest approach of the orbiting star S2/S0-2 to the Galactic supermassive black hole (SMBH), it is estimated that radial velocity (RV) measurements with an uncertainty of a few 10 km s−1 will allow us to detect post-Newtonian effects throughout 2018. To evaluate the best achievable uncertainty in RV and its stability, we carried out near-infrared, high-resolution (R ∼ 20000) spectroscopic monitoring observations of S2 using the Subaru telescope and its near-infrared spectrograph IRCS from 2014 to 2016. Br-γ absorption lines have been detected in the 2015 and 2016 spectra, but have not been clearly detected in the 2014 spectrum. The detected Br-γ absorption lines are used to determine the RVs of S2. The statistical uncertainties are derived using the jackknife analysis, and spectra combined from divided subdata sets. The wavelength calibrations in our three-year monitoring are stable: short-term (hours to days) uncertainties in RVs are ≲ 0.5 km s−1, and the long-term (three years) uncertainty is 1.2 km s−1. We thoroughly analyzed possible sources of systematic uncertainties, such as the incomplete subtraction of OH skylines. The relevant uncertainties are estimated to be less than several km s−1. The final results using the Br-γ line are 877 ± 25 km s−1 in 2015, and 1109 ± 14 km s−1 in 2016. When we use two He i lines at 2.113 μm in addition to Br-γ, the mean RV and its standard error are 1114 km s−1 and 5 km s−1, respectively, in 2016. However, we have found a larger scatter around the expected RV curve with the best-fitting orbiting parameters of S2, implying additional uncertainties not yet considered. The difference between the RVs estimated by Newtonian mechanics and general relativity will reach about 200 km s−1 near the next pericenter passage in 2018. Therefore, in addition to astrometric and spectroscopic data obtained with other telescopes, RV measurements with Subaru in 2018 will form important data sets with which to detect general relativistic effects from the SMBH.

【 授权许可】

CC BY