## 3. Results## 3.1. Nova Sco 1994Shahbaz et al., Shahbaz et al. (1999) have recently
determined the present stellar masses in Nova Sco 1994 (GRO J1655-40).
They find and
. The mass transfer in Nova Sco 1994
may already have been going on for a long period of time. From the
luminosity and effective temperature of the donor star in this system
one finds, using stellar evolution tracks, that the donor can not have
started out with a mass larger than
at the onset of the X-ray phase van der Hooft et al. 1998. As an
example of combinations of present masses we use
() = (6, 2.5) and (7.75, 3.25).
Assuming conservative mass transfer (
) some possibilities for the system
configuration at the onset of mass transfer are the following
combinations of : (4.5, 4.0, 1.52),
(7.0, 4.0, 1.91) and (7.5, 3.5, 2.31). With these values and Eq. (7)
we find that the present runaway velocity of
106 km s
If we relax the assumption of conservative mass transfer (as is suggested by the observation of jets from Nova Sco), and assuming the lost material drags along three times the specific angular momentum (Pols & Marinus Pols and Marinus (1994)), we calculated the orbits for the first two cases, assuming 0.5 was lost from the system. The resulting system parameters at the onset of the mass transfer then become (5, 4, 1.96) and (7.5, 4, 2.42) for the first two examples. These curves are plotted as dashed lines in Fig. 1. In this case at least 5 and 8 are lost, respectively. ## 3.2. Cygnus X-1For Cygnus X-1 the presently best estimate of the masses of the stellar components is and . Extremes of the allowed masses are given by = (3.9, 11.7) and (15.2, 19.2) respectively Herrero et al. 1995. We assume no orbital evolution since the beginning of the mass transfer phase, because Roche lobe overflow can not have started long ago since the expected mass transfer rates then would be much higher. We use the values of the masses as given above and the present day orbital period of 5.6 days. We also neglect the small eccentricity that the orbit still has. The right hand panel in Fig. 1 shows the resulting allowed range of mass ejected in the formation of the black hole. For a present black hole mass of 3.9 at least 2.6 must have been ejected to produce the observed space velocity. For a black hole of 15.2 at least 6 must have been ejected. ## 3.3. The remaining black hole X-ray transientsTable 1 shows that all the black hole X-ray binaries with low
mass donors have low velocities. As derived by White &
van Paradijs White and van Paradijs (1996), the expected
additional velocity component of these X-ray binaries is of the order
of 20-40 km s
© European Southern Observatory (ESO) 1999 Online publication: December 2, 1999 |