Astron. Astrophys. 339, 759-772 (1998)

The ultracompact H II region G45.45+0.06

A pearl necklace in the sky ^{* **}

M. Feldt ¹, B. Stecklum ², Th. Henning ¹, T.L. Hayward ³, Th. Lehmann ¹ and R. Klein <sup>1

1</sup> Astrophysikalisches Institut und Universitäts-Sternwarte, Schillergäßchen 2-3, D-07745 Jena, Germany
² Thüringer Landessternwarte, Sternwarte 5, D-07778 Tautenburg, Germany
³ Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853, USA

Received 13 March 1998 / Accepted 2 September 1998

Abstract

We present new imaging data on the ultracompact H II region G45.45+0.06 at near- and mid-infrared wavelengths. High-resolution data were taken in the H and bands using ESO's adaptive optics system ADONIS. The resulting images with a generic resolution of 0:004 for the first time allow the resolution of the object into several single point-like sources. Additionally, we present images obtained in the mid-infrared at 3.5, 10, and 12 µm. A Br image was obtained to serve as a measure for the extinction towards this region. We derive the physical properties of the point sources and show that some of them are young, massive stars. By combining our data with earlier VLA maps, we measure the extinction towards the region and discuss the history of the object. Finally, we conclude that G45.45+0.06 is a young OB cluster similar to the KL/BN Region in Orion and that sequential star formation is the reason for its present morphology.

Key words: methods: observational H ii regions stars: formation stars: early-type

* Based on observations collected at the European Southern Observatory, La Silla, Chile. Prop. ID:55.C-0647
** Based on observations collected at the DSAZ astronomical centre on Calar Alto, Spain

Send offprint requests to: M. Feldt (e-mail: mfeldt@astro.uni-jena.de)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
  • 2.1. Adaptive optics imaging
  • 2.2. MIR imaging
  • 2.3. Narrow band imaging
  • 2.4. The astrometric reference frame
  • 2.5. Photometry
  • 2.6. A word on image filtering
• 3. Results
• 4. Discussion
  • 4.1. The extinction towards G45
  • 4.2. Point sources
    • 4.2.1. Sources inside the VLA map
    • 4.2.2. Other point sources
    • 4.2.3. A young cluster?
  • 4.3. The nebula
  • 4.4. The role of dust in UCH II s
  • 4.5. The nature and history of G45
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998
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