SHRINKING DISK IN V926 SCO
Abstract
We present phase-resolved spectroscopic observations of the low-mass X-ray binary V926sco, composed of a neutron star and a late-type secondary. The data were obtained using IMACS on the 6.5m Walter Baade telescope at Las Campanas Observatory. A full orbital period (4.65 hr) was obtained in June 2010, in addition to two partial periods in June 2011. Consistent with previous work, spectral lines in the spectrum of V926Sco include lines from H and He, as well as the Bowen blend of NIII and CIII fluorescence. Modulation tomograms using the strongest lines show that the inner disk velocities are significantly lower than those we have observed in black holes in quiescence (Neilsen et al. 2008; Calvelo et al 2009). The velocities are slightly lower than those observed in V926 Sco in 2003 (Casares et. al. 2006), suggesting that the inner radius of the disk has expanded since their observations: this is consistent with RXTE/ASM lightcurves of the object, which show that it has become less bright during that time. In H alpha we see emission concentrated on one side of the disk similar to that observed by Casares et. al. in HeII and interpreted by them as due to an extended disk bulge. We also find that the centre of the disk is offset from the neutron star's center of mass; we can correct this effect by adjusting the mass ratio to 0.1 which is well within the 0.05 -0.41 range suggested by Casares.
- Publication:
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American Astronomical Society Meeting Abstracts #219
- Pub Date:
- January 2012
- Bibcode:
- 2012AAS...21943307C