Astron. Astrophys. 327, 1185-1193 (1997)

Thackeray's globules in IC 2944 ^*

Bo Reipurth ¹, Patrice Corporon; ^{2 1}, Michael Olberg ³ and Guillermo Tenorio-Tagle; <sup>5 4

1</sup> European Southern Observatory, Casilla 19001, Santiago 19, Chile
² Laboratoire d'Astrophysique - Observatoire de Grenoble, BP 53X F-38041 Grenoble Cédex 9, France
³ Onsala Space Observatory, S-439 92 Onsala, Sweden
⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3, UK
⁵ Royal Greenwich Observatory, Madingley Road, Cambridge CB3 OEZ, UK

Received 10 January 1997 / Accepted 5 May 1997

Abstract

We have studied the complex of small globules discovered by A.D. Thackeray in the southern HII region IC 2944. They are located precisely on the line-of-sight to the luminous OB stars in the region, and thus appear as shadows against the bright HII region. Thanks to this geometry, exceptionally fine details can be discerned on CCD images, which show that the globules are generally sharp-edged and highly structured, and that the complex contains a multitude of fragments in all sizes down to the resolution element of about one arcsec (1800 AU). CO millimeter observations reveal that the largest globule consists of two kinematically separate entities, with masses of about 11 and 4 M . Very large velocity differences exist between the various globules, suggesting that the globules comprise a highly dynamic system perhaps one million years old. We believe that the globules are the remnants of an elephant-trunk observed from behind, originating as a Rayleigh-Taylor instability in an expanding neutral shell powered by the hot HII region. The globule complex is now in an advanced stage of disintegration. We have found no evidence for star formation in any of the globules.

Key words: stars: formation stars: pre-main sequence ISM: individual objects: IC 2944 ISM: clouds radio lines: ISM

* Based on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: B. Reipurth

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Contents

• 1. Introduction
• 2. Observations
• 3. The globules and the HII region
• 4. Masses and kinematics of the globules
• 5. A search for young stars
• 6. Comparison with globules in NGC 6611
• 7. The detectability of globules in HII regions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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