Secular and orbital variability of Cir X-1 observed in optical spectra

Details Secular and orbital variability of Cir X-1 observed in optical spectra Secular and orbital variability of Cir X-1 observed in optical spectra

2001-09-11

arxiv.org/abs/astro-ph/0109180v1

Mon.Not.Roy.Astron.Soc. 328 (2001) 1193

Astronomy and Astrophysics

Astrophysics

8 pages, to be published in MNRAS

Scientific paper

10.1046/j.1365-8711.2001.04963.x

We have observed variations in the optical emission lines from the X-ray binary Circinus X-1. These variations may be attributed both to orbital variations and to long term secular changes in line strength. We have detected double-peaked H-alpha emission lines on two occasions, providing the first direct evidence for an accretion disk in the system. The separation of the peaks was different on the two occasions, suggesting that the disk might have a different size. The equivalent width of the emission lines dropped by more than a factor of three between 1999 and 2000; this continues the trend seen in earlier data, so that the H-alpha equivalent width has now declined by a factor of twenty since 1976. The emission lines do not appear to show signature of orbital motion, except for the data taken near phase 0, which show a significant velocity shift. We have observed an absorption component to the He I lines on one occasion. We suggest that, unlike the P Cygni profiles seen in X-ray spectra, this absorption does not arise in the accelerating zone of a radiatively driven wind. Instead, the absorption arises in material previously ejected from the system. It was only seen on this one occasion because the strength of the emission line had dropped dramatically.

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