New estimate of the black hole mass in the binary system MWC 656

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 201, Tutor: Marc Ribó GomisThis work consists of the study of the MWC 656 binary system. It was the first binary system composed of a Be star and a black hole ever found. Black holes orbiting Be star are of great interest in the study of supernova explosions and formation of a binary system composed of a neutron star and a black hole because their merging in nearby galaxies could be detected via gravitational waves. We analysed the radial velocities from the photo-spheric He I absorption lines generated in the Be star and from the He II emission line generated in the accretion disc of the compact object. Two single-line fits and one double line fit are presented. From the single-line fits we observed that the epoch and the argument of periastron correspond to those of a binary system. However, we found di_erent eccentricities: e=0.41±0.08 from the Be star orbit and e=0.09±0.03 from the black hole orbit. In addition, from the double-line fit, fixing e to 0.2, we estimated the mass range of the compact object to be M2 =3.0±7.4M which still implies the presence of a black hole. Furthermore, we calculated that a mass loss of ΔM=(3.6±1.9) M_ in a supernova explosion is enough to explain an eccentricity of 0.2±0.1 and the measured space velocity of the binary system