S19A0023abst
S19A0023
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 ≈ 15 km/s, we can reach the following scientific goals: Significant detection of the GR effects; Determination of the mass of, and the distance to the SMBH with unprecedented precision; and Measurement of the extended dark mass component around the SMBH. Our RV monitoring observations of S2 with Subaru/IRCS in 2017 resulted in RV uncertainties of ≈ 16.0 km/s, which is one of the best accuracies ever obtained. We request 3 monitoring observation runs from April to June 2019, to follow the decline phase of the GR effects from Sgr A*, and to determine the RV bottom to understand the extended mass around the SMBH. 2019 is the last opportunity to detect the GR effects with 8-10 m class telescopes, before the 30-m telescope era. (This is a follow-up project of our 2018 Intensive Program.)
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