High-resolution optical and infrared spectroscopic observations of Cir X-1 |
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| Authors: | Helen M Johnston Robert Fender Kinwah Wu |
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| Institution: | Anglo-Australian Observatory, PO Box 296, Epping NSW 1710, Australia; Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, the Netherlands; Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, NSW 2006, Australia |
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| Abstract: | We present new optical and infrared (IR) observations of Cir X-1 taken near apastron. Both sets of spectra show asymmetric emission lines. Archival optical observations show that an asymmetric H α emission line has been in evidence for the past 20 years, although the shape of the line has changed significantly. We present an eccentric ( e ∼0.7–0.9) low-mass binary model, where the system consists of a neutron star orbiting around a (sub)giant companion star of 3–5 M⊙. We suggest that the broad components of the emission lines arise in a high-velocity, optically thick flow near the neutron star, while the narrow components of the optical and the IR lines arise near the companion star and a heated ejecta shell surrounding the binary respectively. In this model, the velocity of the narrow component reflects the space velocity of the binary; the implied radial velocity (+430 km s−1 after correcting for Galactic rotation) is the highest velocity known for an X-ray binary. |
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| Keywords: | binaries: spectroscopic stars: individual: Cir X-1 X-rays: stars |
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