The young stellar cluster [DBS2003] 157 associated with the H ii region GAL 331.31−00.34

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

Publisher： Oxford University Press

ISSN： 0035-8711

Source： Monthly Notices of the Royal Astronomical Society, Vol.423, Iss.3, 2012-07, pp. : 2425-2435

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Abstract

ABSTRACTWe 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.

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