Astron. Astrophys. 359, 347-363 (2000)

Foreground and background dust in star cluster directions

C.M. Dutra and E. Bica

Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501-970, RS, Brazil

Received 20 January 2000 / Accepted 13 April 2000

Abstract

This paper compares reddening values E(B-V) derived from the stellar content of 103 old open clusters and 147 globular clusters of the Milky Way with those derived from DIRBE/IRAS 100 µm dust emission in the same directions. Star clusters at show comparable reddening values between the two methods, in agreement with the fact that most of them are located beyond the disk dust layer. For very low galactic latitude lines of sight, differences occur in the sense that DIRBE/IRAS reddening values can be substantially larger, suggesting effects due to the depth distribution of the dust. The differences appear to arise from dust in the background of the clusters consistent with a dust layer where important extinction occurs up to distances from the Plane of 300 pc. For 3 % of the sample a significant background dust contribution might be explained by higher dust clouds. We find evidence that the Milky Way dust lane and higher dust clouds are similar to those of several edge-on spiral galaxies recently studied in detail by means of CCD imaging.

Key words: Galaxy: globular clusters: general Galaxy: open clusters and associations: general ISM: dust, extinction

Send offprint requests to: C.M. Dutra (dutra@if.ufrgs.br)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Overview of dust emission reddening values
  • 2.1. Comparison with reddening values from JHK photometry for nearby dark clouds
  • 2.2. Dust layer height from nearby dark clouds
• 3. Reddening values in star cluster directions
  • 3.1. Globular clusters
  • 3.2. Old open clusters
• 4. Discussion
  • 4.1. E(B-V): possibility of background reddening
  • 4.2. Directions of some reddened young open clusters
  • 4.3. Reddening in the Sagittarius dwarf direction
  • 4.4. Evidence for dark clouds with pc
• 5. Concluding remarks
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 30, 2000
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