Dust within globular clusters: A large bubble in NGC 6624?

FORTE, J. C.; CELLONE, S. A.; MÉNDEZ, M.; VEGA, E. I.

ASTROPHYSICAL JOURNAL

The American Astronomical Society

Año: 1992 vol. 388 p. 383 - 391

0004-637X

An analysis of dark patches, based on multicolor CCD frames, and polarimetry of stars in the field of the globular cluster NGC 6624 are presented. The apparent extinctions in a number of dark patches reveal a nongray behavior with wavelength. The fitting of a given extinction law indicates minimum intrinsic visual extinctions ranging from 0.20 to 0.30 mag. These results are consistent with photometric measurements made in annular segments and with differential reddening effects in the C-M diagram, suggesting the existence of a large-scale dust feature associated with the cluster. The overall appearance of the distribution of the dark-arcsec patches is reminiscent of a bubble-like geometry not centered at the cluster nucleus and with a 50-arcsec radius. The apparent center of this structure is located at some 9 arcsec from the position of the X-ray burster 1820 - 30.