On the central ionizing star of G23.96+0.15 and near-IR spectral classification of O stars
Abstract
Aims: A near-infrared study of the main ionizing star of the ultracompact HII region G23.96+0.15 (IRAS 18317-0757) is presented, along with a re-evaluation of the distance to this source, and a re-assessment of H- and K-band classification diagnostics for O dwarfs
Methods: We have obtained near-IR VLT/ISAAC imaging and spectroscopy of G23.96+0.15, plus archival imaging from UKIRT/UFTI. A spectroscopic analysis was carried out using a non-LTE model atmosphere code.
Results: A quantitative H- and K-band classification scheme for O dwarfs is provided, from which we establish an O7.5V spectral subtype for the central star of G23.96+0.15. We estimate an effective temperature of T_eff∼ 38 kK from a spectral analysis.
Conclusions: A spectroscopic distance of 2.5 kpc is obtained for G23.96+0.15, substantially lower than the kinematic distance of 4.7 kpc, in common with recent studies of other Milky way H ii regions. Such discrepancies would be alleviated if sources are unresolved binaries or clusters.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2008
- DOI:
- 10.1051/0004-6361:200810942
- arXiv:
- arXiv:0810.3520
- Bibcode:
- 2008A&A...492..111C
- Keywords:
-
- ISM: HII regions;
- ISM: dust;
- extinction;
- stars: early-type;
- stars: fundamental parameters;
- Astrophysics
- E-Print:
- 5 pages, 3 figures, accepted for Astronomy &