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Centro de Astrofísica da Universidade do Porto

A ring-shaped embedded young stellar (proto) Cluster

M. S. N. Kumar, D. K. Ojha, C. J. Davis

Abstract
We present subarcsecond (FWHM~0.5") J, H, K, and L' images of a young stellar cluster associated with a candidate massive protostar IRAS 22134+5834. The observations reveal a centrally symmetric, flattened cluster enclosing a central dark region. The central dark region is possibly a cavity within the flattened cluster. It is surrounded by a ring composed of five bright stars and the candidate massive protostar IRAS 22134+5834. We construct JHKL' color-color and HK color-magnitude diagrams to identify the young stellar objects and estimate their spectral types. All the bright stars in the ring are found to have intrinsic infrared excess emission and are likely to be early- to late-B type stars. We estimate an average foreground extinction to the cluster of Av~5 mag and individual extinctions to the bright stars in the range Av~20-40 mag, indicating possible cocoons surrounding each massive star. This ring of bright stars is devoid of any H II region. It is surrounded by an embedded cluster, making this an example of a (proto)cluster that is in one of the dynamically least relaxed states. These observations are consistent with the recent nonaxisymmetric calculations of Li & Nakamura, who present a star formation scenario in which a magnetically subcritical cloud fragments into multiple magnetically supercritical cores, leading to the formation of small stellar groups.

The Astrophysical Journal
Volume 598, Page 1107
December 2003

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