High-resolution interstellar and stellar line profiles of stars in the globular cluster M22

Abstract

Summary High-resolution (˜5 km s−1 FWHM) spectra have been obtained for stars in the globular cluster M22 using the University College London echelle spectrograph (UCLES) at the coudé focus of the AAT. The prime objective was a study of the fine-scale spatial structure of the line-of-sight gas through observations of the Na D lines. Essentially the gas towards the cluster at distance ˜ 6 kpc is concentrated in two components at the approximate velocities (LSR) of + 6 and + 37 km s−1. The lower velocity material is likely to be part of a nearby H I cloud, first mapped in the radio region, in which case the spatial sampling in the present study has a scale < 0.3 pc. The higher velocity gas varies from a single component to a multiple component structure over the angular extent of the cluster. The distance to this material is less certain but it may be associated with the Sagittarius arm. New observations are presented also for the stellar Hα and Na D lines. Time variability of Hα emission and Na D line asymmetry are detected for two stars. The present data are in qualitative agreement with models for mass loss occurring in expanding, circumstellar envelopes.