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Paper: Time-resolved optical spectroscopy of Sco X--1
Volume: 261, The Physics of Cataclysmic Variables and Related Objects
Page: 569
Authors: Wachter, S.; Hoard, D. W.; Johnson, B. D.
Abstract: We obtained time-resolved, medium resolution (~1.5 Å) optical (6200--7100 Å) spectra of the low mass X-ray binary (LMXB) Sco X--1 during 2000 April 7--10 on the CTIO 1.5m telescope. In addition to the well-known Hα emission line, our observations showed an absorption feature near Hα. Absorption lines in active LMXBs are very rare and, to our knowledge, have never been seen in Sco X--1. The absorption feature is shallow, centered redward of the emission line, and possibly varies in depth and/or velocity during the orbit. We repeated our observations of Sco X--1 with the identical instrument setup during 2001 June 15--18, with the addition of simultaneous BV I photometry on the CTIO 0.9m telescope. We find that the Hα absorption feature only appears when Sco X--1 is in the bright (B < 12.8) state.
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