Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-12-15
Astron.Astrophys. 414 (2004) L13-L16
Astronomy and Astrophysics
Astrophysics
4 pages, 1 figure, A&A Letter
Scientific paper
10.1051/0004-6361:20031754
The binary parameters of the microquasar GRS 1915+105 have been determined by the detection of Doppler-shifted 12CO and 13CO lines in its K-band spectrum (Greiner et al., 2001, Nature, 414, 522). Here, we present further analysis of the same K-band VLT spectra and we derive a rotational broadening of the donor star of V sin i=26+-3 km/s from the 12CO/13CO lines. Assuming that the K-type star is tidally locked to the black hole and is filling its Roche-lobe surface, then the implied mass ratio is q = M_d/M_x = 0.058+-0.033. This result, combined with (P, K, i)=(33.5 d, 140 km/s, 66 deg) gives a more refined mass estimate for the black hole, $M_x=14.0+-4.4 M_{\odot}$, than previously estimated, using an inclination of i=66+-2 deg (Fender et al. 1999) as derived from the orientation of the radio jets and a more accurate distance. The mass for the early K-type giant star is $M_d=0.81\pm0.53 M_{\odot}$, consistent with a more evolved stripped-giant donor star in GRS 1915+105 than, for example, the donor star of the prototype black-hole X-ray transient, V404 Cyg which has the longest binary period after GRS 1915+105.
Greiner Jochen
Harlaftis Emilios T.
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