Far‐Ultraviolet Space Telescope Imaging Spectrometer Spectra of the White Dwarf REJ 1032+532. I. Interstellar Line of Sight

Abstract

An 1150-1725 Å echelle spectrum of the hot DA white dwarf REJ 1032+532, recently obtained with the Space Telescope Imaging Spectrometer E140M grating, reveals numerous stellar and interstellar lines. The interstellar column densities and abundances of C, N, O, Si, and S relative to the directly measured H column are determined for this particular line of sight through the local interstellar medium (ISM). An estimate of the electron density, ne=0.11+0.07-0.06, is obtained from the population ratio of the excited to ground state fine-structure levels in C II. This electron volume density is compared with an independent Extreme Ultraviolet Explorer measurement of the total line-of-sight electron column density derived from the ionization state of H and He. A path length of ~10 pc is estimated for the region responsible for the bulk of the ISM absorption. From the observed ISM velocity components, we identify this absorbing component as the local interstellar cloud (LIC) surrounding the solar system. For the LIC we find the abundances of nitrogen, oxygen, and silicon relative to hydrogen to be significantly less than those characteristic of much longer lines of sight through the local ISM. The LIC abundances of these elements are very consistent with the recent determinations of Vidal-Madjar and coworkers for the LIC.