High-velocity interstellar clouds towards the M 15 globular cluster

I. Low resolution optical data

¹ Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast, BT7 1NN, Northern Ireland
² Isaac Newton Group, Apartado de Correos 368, Santa Cruz de La Palma, Tenerife 38780, Canary Islands, Spain
³ The John Hopkins University, Department of Physics and Astronomy, Bloomberg Center, 3400 N. Charles Street, Baltimore MD 21218, U.S.A.

Send offprint request to: N. Lehner

Received: 10 July 1998
Accepted: 13 August 1998

Abstract

We present low resolution interstellar spectra of the CaII K and NaI D lines towards 12 stars in the M 15 globular cluster. These sightlines are used to study the small scale structure of the interstellar medium, over scales of a few arcseconds to a few arcminutes. A high-velocity cloud is detected in the CaII and NaIlines at a LSR velocity of approximately . Tentative velocity and equivalent width variations are observed on scales of a few arcseconds; however, higher resolution data are necessary to quantify the magnitude of these variations. We discuss these observations and their importance for future studies of this high velocity gas at high spectral resolution.