Rapid optical spectroscopy of X-ray binaries with Keck II

Abstract

The large collecting area of 4+ metre class telescopes allows atronomers to observe bright objects on faster timescales than previously possible. In order to exploit this capability, we designed a novel read-out mode for use on the 10-m Keck-II telescope on Mauna Kea, Hawaii. This took the form of a continuous read-out mode, enabling us to obtain a target spectrum between 3500 and 8500 Å, with a dispersion of ~2.5 Å/pix, every *70 milliseconds*. I present results from 5 nights of observations of Interacting Binaries, using this novel data acquisition system in July 1998. During the run we obtained more than 1.2 million optical spectra, many of which were simultaneous with pointed RXTE observations. This fast spectroscopic capability has allowed us to explore regimes previously only accessible with broadband instruments. I will concentrate on results from the coordinated Keck/RXTE observations, which have revealed interesting correlated variability on timescales from seconds to days. I will also show the results of a spectroscopic-timing analysis of QPOs in Hercules X-1, which shows evidence for the decay of individual blobs of material orbiting the neutron star.