S18B0012

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 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 RV monitoring observations of S2 with Subaru/IRCS in 2016 resulted in RV uncertainties of 13.6 km/s, demonstrating that 10 km/s accuracy can be achieved in 2018 observations. We request 4 half-night observations in S18B to cover the minimum phase of the RV of S2, especially to determine the mass of the SMBH. 2018 is the first and last opportunity to monitor RV of S2 frequently during the pericenter passage, and 2018 Aug is the last chance to detect the GR effects with Subaru, before the 30-m telescope era.


This document was translated from LATEX by HEVEA.