On the masses of the components of the V1387 Aql/GRS1915+105 binary system

Abstract

V1387 Aql (the optical companion to the microquasar GRS1915+105) is a low mass giant. Such star consists of a degenerate, nearly isothermal helium core and a hydrogen rich envelope. Both components are separated by an hydrogen burning shell. The structure of such an object is relatively simple and easy to model. Making use of the observational values of the luminosity and of the radius of V1387 Aql, we determined the mass of this star as equal 0.28+-0.02 solar masses. This determination is relatively precise thanks to high sensitivity of the luminosity of such structure to the mass of the helium core and high sensitivity of its radius to the mass of the envelope. The estimate does not depend on the knowledge of the distance to the system (which is not precisely known). The main source of the uncertainty of my estimate is uncertainty of the effective temperature of V1387 Aql. When the effective temperature will be known more accurately, the mass of V1387 Aql could be determined even more precisely.