Secular and orbital variability of Cir X-1 observed in optical spectra |
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| Authors: | Helen M Johnston Kinwah Wu Rob Fender Jason G Cullen |
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| Institution: | 1Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, NSW 2006, Australia;2Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT;3Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, the Netherlands |
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| Abstract: | 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 α emission lines on two occasions, providing the first direct evidence for an accretion disc in the system. The separation of the peaks was different on the two occasions, suggesting that the disc 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 α equivalent width has now declined by a factor of 20 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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| Keywords: | binaries: spectroscopic stars: individual: Cir X-1 X-rays: stars |
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