Atmospheric Modelling of the Companion Star in GRO J1655-40

We have measured the rotational velocity of the companion star to be v_rot sin i = 80 ± 10 km s^-1 (1σ) by fitting Kurucz model spectra to our observed spectrum of the black-hole candidate GRO J1655-40. From this we have calculated q = 0.31 ± 0.08, the mass of the compact object to be M₁ = 7.91 ± 3.79 Msolar (1σ) and for the companion star M₂ = 2.76 ± 1.79 Msolar (1σ), which is consistent with previous studies. We have also determined T_eff = 6500 ± 50 K and [Fe/H] = -0.5^+0.15_-0.10.