Quantitative spectroscopy of O-stars in the Magellanic clouds. I. Theyoung open cluster NGC 346 in the SMC.
Abstract
High-resolution Cassegrain echelle spectra of four of the brightest stars in the young open cluster NGC 346 in the SMC, obtained with the ESO 3.6 m telescope, are analyzed quantitatively using improved non-LTE model atmospheres and line formation calculations. Atmospheric parameters (T_eff_ log(g), He abundance) are determined, which together with the SMC distance modulus yield luminosities and masses. A comparison with evolutionary tracks shows that the observed stellar parameters are consistent with a cluster age of 2.6 +/- 0.5 10^6^ years, for the program stars zero-age main sequence masses of 110, 90, 60 and 45 solar masses are found. The analysis therefore confirms that very massive stars of about one hundred solar masses exist also in the SMC. The effects of wind blanketing on the emergent ionizing flux and the photospheric structure are investigated by detailed calculations of multiline radiation-driven stellar winds. Two values of metallicity, corresponding to the Galaxy and the SMC, are considered. While for galactic metallicity wind blanketing effects prove to be observable, they are found to be negligible for the SMC. The ionization of the giant H II region N 66 in which the cluster stars are embedded is discussed. By comparison with the observed radio fluxes it is found that the four stars studied provide already half of the Lyman continuum photons needed to ionize the full complex. It is likely that the other half is provided by the remaining cluster population.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 1989
- Bibcode:
- 1989A&A...226..235K
- Keywords:
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- Astronomical Spectroscopy;
- Magellanic Clouds;
- O Stars;
- Open Clusters;
- Abundance;
- Cassegrain Optics;
- Charge Coupled Devices;
- Stellar Evolution;
- Stellar Luminosity;
- Stellar Temperature;
- Astrophysics