Astron. Astrophys. 364, 712-722 (2000)

Optical observations of the Draco molecular cloud

I. Catalog of B and V magnitudes for selected areas

B.E. Penprase ¹, J.D. Rhodes ² and E.L. Harris  <sup>*  1

1</sup> Pomona College Department of Physics and Astronomy, 610 N. College Avenue, Claremont CA, USA (penprase@shanti.pomona.edu)
² Princeton University, Department of Physics, Princeton, N.J., USA (jrhodes@pupgg.princeton.edu)

Received 8 September 1997 / Accepted 17 July 2000

Abstract

To investigate the distance and linear dimensions of the Draco Molecular Cloud (MBM 41) we have obtained new CCD photometry for a selection of stars in 20 selected areas toward the cores of the cloud. The selected areas were chosen to coincide with the brightest IRAS emitting portions of the cloud, and also with dense ¹²CO emission from the cloud. For each area we have obtained V and B photometry, and a subset of the fields has also been observed through a narrow-band H filter and in the U band.

We present V and B magnitudes for the 362 stars which have high-quality observations in both bands. In addition we have derived star counts in the V band using a larger sample of 465 stars, which is complete to a limiting magnitude of V=19.0. The star counts were compared to a galactic model from Bahcall & Soneira (1980). Using the galactic model of star counts, slightly modified to include the effects of a cloud of arbirary distance and extinction, we find a best fit to our data with values of A_V = 2.5 and 800 d 1300 pc for the Draco molecular cloud. We also report results of photometric spectral classification using the index , which was found to correlate well with for our photometric standard stars. The modelled colors of the stellar sample were compared with the catalog values, and the observed colors best matched a cloud distance of d = pc, with A_V = 2.5 and R_V = 1.5. Our photometry detects reddening and extinction from the densest portions of the Draco cloud, and it seems likely that the cloud is within the range of distances 800 d 1300 pc, which corresponds to a height = 640 pc above the galactic plane, and linear dimensions as large as 40 pc for the cloud.

Key words: ISM: clouds ISM: dust, extinction ISM: general ISM: structure Galaxy: halo techniques: photometric

* Funded by a Hirsch Grant to B.E. Penprase

Send offprint requests to: B.E. Penprase

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Contents

• 1. Introduction
• 2. Observations
• 3. Results
  • 3.1. Photometric catalog of V and for stars toward the Draco cloud
  • 3.2. Photometric determination of the Draco cloud distance
  • 3.3. The index and photometric spectral classification
  • 3.4. Derivation of cloud extinction and distance from star count models
  • 3.5. Theoretical colors for stars and effects of distance, A_V and R_V
• 4. Conclusions
• Acknowledgements
• Appendices
  • Appendix A.
  • Appendix B.
• References

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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