S18A0011abst
S18A0011
Stars orbiting the Galactic supermassive black hole (SMBH) experience strong gravity by the SMBH, which makes general relativistic (GR) effects potentially detectable. Particularly crucial to our understanding of the properties and the environment of the Galactic SMBH is the time evolution of the radial velocity (RV) of the star S2, because it is the best probe to detect the GR effects. Our GR calculations of the S2 motions show that if we measure the RV of S2 at the peak and periapsis phases with an uncertainty of ≈ 10 km/s, we can reach the following scientific goals: First detection of the GR effects; Determination of the mass of, and the distance to the SMBH with unprecedented precision; Test of GR as a gravity theory of the SMBH; and Measurement of the extended dark mass component around the SMBH. Our past RV monitoring observations of S2 with Subaru/IRCS from 2014 to 2016 resulted in RV uncertainties of 13−17 km/s, demonstrating that 10 km/s accuracy can be achieved in 2018 intensive monitoring observations. We request 15 nights in S18A to cover the RV peak and the periapsis of S2, to accomplish the above scientific goals. 2018 is the last chance to detect the GR effects of the SMBH with Subaru, and this will be a milestone for SMBH spin measurements with TMT.
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