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Astron. Astrophys. 352, 257-265 (1999)

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Optical observations of three Galactic halo stars: evidence for cloudlets in intermediate- and high-velocity interstellar clouds

N. Lehner 1, K.R. Sembach 2, D.L. Lambert 3, R.S.I. Ryans 1 and F.P. Keenan 1

1 Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast, BT7 1NN, Northern Ireland
2 The John Hopkins University, Department of Physics and Astronomy, Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA
3 Department of Astronomy, The University of Texas at Austin, Austin, TX 78712-1083, USA

Received 29 March 1999 / Accepted 12 October 1999


Very high resolution ([FORMULA]) absorption line measurements of the interstellar CaII K and NaI D lines and medium resolution ([FORMULA]) measurements of the interstellar TiII (3384 Å) line towards three Galactic halo stars are presented. The data have signal-to-noise ratios of [FORMULA]. The sightlines studied clearly show several intermediate-high velocity interstellar clouds with local standard of rest velocities in the range [FORMULA] to -110 km s-1. Two different methods have been used to analyze these data. Line profile fitting allows us to model multiple components for the different high-velocity clouds separated by only a few km s-1. The close proximity of the lines in velocity space indicates that the cloudlets are related. Conversion of the absorption profiles to apparent optical depth profiles also allows us to examine the column densities and their ratios as a function of velocity. Variations in [FORMULA], [FORMULA] and [FORMULA] with cloud velocity are discussed.

Key words: ISM: general – ISM: clouds – ISM: structure – stars: early-type – Galaxy: halo

Send offprint requests to: Nicolas Lehner (N.Lehner@qub.ac.uk)

© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999