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D. W. Hoard, S. Wachter (CTIO)
We present an analysis of time-resolved, medium resolution (1.5Å) optical (6200--7100Å) spectroscopy of the low mass X-ray binary Sco X-1. The spectra were obtained during 2000 April 07--10 UT on the 1.5-m telescope at Cerro Tololo Inter-American Observatory. A complete orbital cycle of Sco X-1 was sampled in 40 spectra with orbital phase resolution of \approx0.03. In addition to a new radial velocity curve of the H\alpha emission line, we present the first Doppler tomograms of Sco X-1. The H\alpha line profile exhibits several interesting features that have not been seen in previously published spectra of Sco X-1: (1) The main emission component is a strong, narrow peak blue-shifted by \approx -200 km s-1 (quoted velocities are relative to the rest wavelength of H\alpha). This component traces an S-wave as a function of orbital phase in the trailed spectrogram. (2) A narrow absorption feature, reminiscent of an inverse P Cygni profile, is located redward of the H\alpha emission peak, at \approx +150 km s-1. The depth and velocity of this feature vary considerably during the orbit. (3) A broad (\Delta V\approx500 km s-1) wing of H\alpha emission is visible redward of the absorption feature, at \approx +600 km s-1. These three features provide valuable clues about the structure of the disk and accretion flow in Sco X-1.
Cerro Tololo Inter-American Observatory is operated by AURA, Inc.\ under cooperative agreement with the NSF.