Ultraviolet observations of Sirius A and Sirius B with HST-GHRS; An interstellar cloud with a possible low deuterium abundance

TL;DR

This study uses HST-GHRS ultraviolet observations of Sirius A and B to analyze interstellar clouds, detecting a potential low deuterium abundance in one cloud, contributing new insights into local interstellar medium composition.

Contribution

First detailed UV spectral analysis of Sirius A/B with HST-GHRS revealing interstellar cloud structures and deuterium abundance constraints.

Findings

Detected two interstellar clouds, including the LIC.

Measured D/H ratio in one cloud, suggesting a possible low deuterium abundance.

Identified stellar wind and photospheric absorption features in Lyman alpha lines.

Abstract

We present new observations of the binary Sirius A / Sirius B performed with HST-GHRS. Two interstellar clouds are detected on this sightline, one of them being identified as the Local Interstellar Cloud (LIC). The interstellar structure of this sightline is constrained by high spectral resolution data of the species OI, NI, SiII, CII, FeII and MgII. Lyman alpha interstellar lines are also observed toward the two stars. But whereas the deuterium Lyman alpha line is well detected in the LIC with an abundance in agreement with that obtained by Linsky et al. (1993 & 1995), no significant DI line is detected in the other cloud. However, the Lyman alpha lines toward Sirius A and Sirius B are not trivial. An excess of absorption is seen in the blue wing of the Sirius A Lyman alpha line and interpreted as the wind from Sirius A. In its white dwarf companion, an excess in absorption is seen in the red wing and interpreted as the core of the Sirius B photospheric Lyman alpha line. A composite Lyman alpha profile can nonetheless be constructed, and allows one to measure the deuterium abundance in the second cloud 0 < D/H_ISM < 1.6 10^-5, which is marginally in agreement with the Linsky et al. (1993 & 1995) value. This sightline appears consequently as a good candidate for a low D/H_ISM.