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

1. Introduction

Fifty years ago, Bok & Reilly (1947) drew attention to two classes of small dark clouds, the large and the small globules. The large globules, or Bok globules as they are known today, are now well studied at optical, infrared and mm-wavelengths. Such studies have borne out Bok's conjecture that the large globules can be intimately related to the process of star formation (e.g. Bok 1977, Reipurth 1983, Keene 1983, Yun & Clemens 1990).

The small globules, on the other hand have been largely overlooked. Bok noted the fact that small globules are found always in association with HII regions and luminous OB stars. Indeed, wide field CCD images of HII regions almost invariably show the presence of these tiny globules.

The Rosette Nebula is a large, relatively nearby HII region, which is particularly abundant in small globules. Herbig (1974) discussed these globules, and suggested that they are pinched-off blobs from elephant trunks, produced as an HII region expands into surrounding molecular clouds.

A remarkable and beautiful set of small globules was discovered by Thackeray (1950) in the large southern HII region IC 2944. Fig. 1 shows IC 2944 from a red ESO Schmidt plate and the location of Thackeray's small globules.

Fig. 1. The HII region IC 2944 as seen on a red ESO Schmidt plate. The small globules discovered by A.D. Thackeray are in the middle of the figure. Seven H emission line stars, ESO H  301-307, are marked as 1-7. The image is approximately 53 x 46 arcmin. North is up and east is left

In this note, we present detailed CCD images of these globules, and, based on the images and an objective prism H emission star survey, conclude that star formation has not taken place in the globules.

© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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