Deuterium toward the WD0621-376 sight line: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission

TL;DR

This study uses FUSE observations of the WD0621-376 white dwarf to measure interstellar deuterium and other element ratios, providing insights into the local interstellar medium's composition and ionization state.

Contribution

First measurement of D/O and D/H ratios along the WD0621-376 sight line using FUSE data, enhancing understanding of interstellar deuterium distribution.

Findings

D/O ratio is approximately 3.9 x 10^-2

D/H ratio is about 1.3 x 10^-5

The sight line is partially ionized with nitrogen ionization fraction > 0.23

Abstract

Far Ultraviolet Spectroscopic Explorer observations are presented for WD0621-376, a DA white dwarf star in the local interstellar medium (LISM) at a distance of about 78 pc. The data have a signal-to-noise ratio of about 20-40 per 20 km/s resolution element and cover the wavelength range 905-1187 \AA. LISM absorption is detected in the lines of D I, C II, C II*, C III, N I, N II, N III, O I, Ar I, and Fe II. This sight line is partially ionized, with an ionized nitrogen fraction of > 0.23. We determine the ratio $D/O = (3.9 \pm ^{1.3}_{1.0})\times 10^{-2}$ (2$\sigma$). Assuming a standard interstellar oxygen abundance, we derive ${\rm D/H} \approx 1. 3 \times 10^{-5}$. Using the value of N(H I) derived from EUVE data gives a similar D/H ratio. The D I/N I ratio is $(3.3 \pm ^{1.0}_{0.8})\times 10^{-1}$ (2$\sigma$).