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

We report a study of the stellar content of the Near-infrared cluster [DBS2003],157 embedded in the extended H,{\sc 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,{\sc V}, $3.35\pm 0.61$,kpc) and IRS,339 (O9,{\sc V}, $3.24\pm 0.56$,kpc). Adopting the average distance of $3.29\pm 0.58$,kpc and comparing the Lyman continuum luminosity of these stars with that required to account for the radio continuum flux of the H,{\sc 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 MIR data from the 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 ultra-compact H,{\sc ii} region, has been identified. The analysis of its spectral energy distribution between 2 and $100\mu$m revealed that this source shows a spectral index $\alpha =3.6$ between 2 and $25\mu$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 $L=7.7\times {10}^3{L}_{\text{sun}}$ and $M = 10,M_{\sun}$, respectively, which corresponds to a B0–B1,{\sc V} ZAMS star.