Discussion

Our radial velocities needed to be shifted in phase by -0.06 in order to coincide with the sinusoid curve derived by Shahbaz et al. (1999) who, in turn, needed to shift their radial velocities by -0.05 with respect to the orbital ephemeris of van der Hooft et al. (1998). This suggests that the orbital period needs to be refined which we cannot do with such a limited dataset. There is the possibility that a deviation from the radial velocity curve exists at orbital phase 0.6. Future observations at this orbital phase would be valuable to see if this is indeed the case in quiescence.

We have used Kurucz model spectra to measure the rotational velocity, effective temperature and metallicity of the companion star in GRO J16550-40. Our value of is consistent with Shahbaz et al. (1999) and Israelian et al. (1999). This rotational velocity leads to a companion star mass M₂ = 2.76 1.79 M (1) and compact object mass of M₁ = 7.91 3.79 M (1), also consistent with the literature and strengthening the evidence that this is a black hole.

© Copyright Astronomical Society of Australia 1997