The rotational broadening and the mass of the donor star of GRS 1915+105

Free access article

Issue		A&A Volume 414, Number 2, February I 2004


Page(s)		L13 - L16
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20031754

A&A 414, L13-L16 (2004)
DOI: 10.1051/0004-6361:20031754

Letter

The rotational broadening and the mass of the donor star of GRS 1915+105

E. T. Harlaftis¹ and J. Greiner²

¹ Institute of Space Applications and Remote Sensing, National Observatory of Athens, PO Box 20048, Athens 118 10, Greece
² Max Planck Institute for Extraterrestrial Physics, Giessenbachstr., PF 1312, 85741 Garching, Germany
e-mail: jcg@mpe.mpg.de

(Received 29 September 2003 / Accepted 11 December 2003)

Abstract
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. 2001b). Here, we present further analysis of the same K-band VLT spectra and we derive a rotational broadening of the donor star of $\upsilon \sin \ i=26\pm3$ km s ^-1 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 $q = \frac{M_{\rm d}}{M_{\rm x}} = 0.058\pm0.033$ . This result, combined with ( P, K, i) = (33.5 d, 140 km s ^-1, 66 $^{\circ}$ ) gives a more refined mass estimate for the black hole, $M_{\rm x}=14.0\pm4.4~M_{\odot}$ , than previously estimated, using an inclination of $i=66^{\circ}\pm2^{\circ}$ (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 $M_{\rm d}=0.81\pm0.53~M_{\odot}$ , 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.

Key words: stars: infrared -- stars: X-ray -- black hole physics -- stars: binaries -- stars: individual: GRS 1915+105

Offprint request: E. T. Harlaftis, ehh@space.noa.gr

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