Journal Article

The young stellar cluster [DBS2003] 157 associated with the H <span class="smallCaps">ii</span> region GAL 331.31−00.34*

M. C. Pinheiro, Z. Abraham, M. V. F. Copetti, R. Ortiz, D. A. Falceta-Gonçalves and A. Roman-Lopes

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 3, pages 2425-2435
Published in print July 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21049.x
The young stellar cluster [DBS2003] 157 associated with the H ii region GAL 331.31−00.34*

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We report a study of the stellar content of the near-infrared (NIR) cluster [DBS2003] 157 embedded in the extended H ii region GAL 331.31−00.34, which is associated with the IRAS source 16085−5138. JHK photometry was carried out in order to identify potential ionizing candidates, and the follow-up NIR spectroscopy allowed the spectral classification of some sources, including two O-type stars. A combination of NIR photometry and spectroscopy data was used to obtain the distance of these two stars, with the method of spectroscopic parallax: IRS 298 (O6 V, 3.35 ± 0.61 kpc) and IRS 339 (O9 V, 3.24 ± 0.56 kpc). Adopting the average distance of 3.29 ± 0.58 kpc and comparing the Lyman continuum luminosity of these stars with that required to account for the radio continuum flux of the H ii region, we conclude that these two stars are the ionizing sources of GAL 331.31−00.34. Young stellar objects (YSOs) were searched by using our NIR photometry and mid-infrared (MIR) data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) survey. The analysis of NIR and MIR colour–colour diagrams resulted in 47 YSO candidates.

The GLIMPSE counterpart of IRAS 16085−5138, which presents IRAS colour indices compatible with an ultracompact H ii region, has been identified. The analysis of its spectral energy distribution between 2 and m revealed that this source shows a spectral index α= 3.6 between 2 and m, which is typical of a YSO immersed in a protostellar envelope. Lower limits to the bolometric luminosity and the mass of the embedded protostar have been estimated as L= 7.7 × 103 L and M= 10 M, respectively, which correspond to a B0–B1 V zero-age main sequence star.

Keywords: stars: early-type; stars: pre-main-sequence; H ii regions; Herbig–Haro objects

Journal Article.  6328 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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