Interstellar Absorption Lines in the Direction of the Cataclysmic Variable SS Cygni1 1Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium, and on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Mikulski Archive for Space Telescopes. STScI is operated by the Association of Universities

Abstract

We present an analysis of interstellar absorption lines in high-resolution optical echelle spectra of SS Cyg obtained during an outburst in 2013 June and in archival Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer data. The Ca ii K and Na i D lines toward SS Cyg are compared with those toward nearby B and A stars in an effort to place constraints on the distance to SS Cyg. We find that the distance constraints are not very robust from this method due to the rather slow increase in neutral gas column density with distance and the scatter in the column densities from one sight line to another. However, the optical absorption-line measurements allow us to derive a precise estimate for the line-of-sight reddening of E(B - V) = 0.020 ± 0.005 mag. Furthermore, our analysis of the absorption lines of O i, Si ii, P ii, and Fe ii seen in the UV spectra yields an estimate of the H i column density and depletion strength in this direction.