A search for interstellar absorptions towards Sgr dSph

¹ Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Trieste, via Tiepolo 11 34131 Trieste, Italy e-mail: monai@ts.astro.it
² European Southern Observatory, Casilla 19001, Santiago, Chile
³ Università di Roma 2 “Tor Vergata”, via della Ricerca Scientifica, Rome, Italy

Received: 6 October 2004
Accepted: 3 December 2004

Abstract

We searched for Na I D1, D2 interstellar absorption lines towards 12 giant stars of the Sgr dwarf spheroidal and 3 stars of the associated globular cluster Terzan 7, observed at high resolution with the UVES spectrograph at the 8.2 m Kueyen VLT telescope. These stars are not an ideal background source for the analysis of interstellar (IS) absorption lines since they have been observed in the framework of a stellar abundances study. However they are sufficiently luminous to allow a decent S/N ratio at a resolution of about 43 000, i.e.  7 , which allows an exploratory study. We detected two distinct groups of IS absorptions, a “local” group, with radial velocities ranging from -43  to 50 , and a high velocity group with radial velocities ranging from 150 km s^-1 to 165 km s^-1. Likely the high velocity components are due to gas falling on the Sgr dSph since they have been observed only in 2 stars which are separated by only 15 in the sky. We argue that the observations suggest a stripping of gas due to the passage of Sgr through the Galactic disc.