Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aj....133..622w&link_type=abstract
The Astronomical Journal, Volume 133, Issue 2, pp. 622-630.
Astronomy and Astrophysics
Astronomy
2
Dust, Extinction, Ism: Globules, Ism: Individual: Dc 314.8-5.1, Stars: Distances, Stars: Formation, Stars: Individual: Hd 130079
Scientific paper
The southern dark globule DC 314.8-5.1 contains a reflection nebula illuminated by a normal B9 V star, HD 130079. This serendipitous association provides the opportunity to evaluate the distance to the globule with greater accuracy than would otherwise be possible, subject to accurate accounting for the effects of interstellar extinction and reddening. It is shown that the dust in the line of sight has optical properties characterized by elevated values of the ratio of extinction to reddening (RV=AV/EB-V) and the wavelength of maximum polarization (λmax), signifying growth that most probably results from grain-grain coagulation within the globule. Taking this into account yields a distance of 342+/-50 pc, significantly lower than previous estimates that assume the standard diffuse interstellar medium average extinction law. Comparison of this result with the loci of other major sources of extinction along the line of sight suggests that the globule is isolated; it appears to not be physically associated with the adjacent Circinus molecular cloud and star formation complex G317.0-4.0. Estimates are made of the mean number density (nH>~9×103 cm-3) and mass (30-100 Msolar) of DC 314.8-5.1. A stellar census of the region using the Two Micron All Sky Survey suggests that it is not a site of vigorous star formation, although two (out of 387) sources are identified that appear to be good candidates for young stellar object status on the basis of their near-infrared colors. A deep mid-infrared survey will be needed to determine whether DC 314.8-5.1 is, indeed, starless (with respect to indigenous birth) or a site of sedentary low-mass star formation. The globule may also prove to be a valuable laboratory for future study of the interaction of dense molecular gas and dust in a quiescent core with the relatively soft UV radiation field emanating from the embedded B9 V star.
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