| Metallicity in the galactic center: The Arches cluster (2004) | |||||||||||||||
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| Metallicity the Galactic Center The Arches cluster Francisco Najarro Donald Figer John Hillier Rolf Kudritzki najarro damir iem csic arXiv astro Jul ABSTRACT present quantitative spectral analysis five very massive stars the Arches cluster located near the Galactic center determine stellar parameters stellar wind properties and most importantly metallicity content The analysis uses new technique presented here for the first time and uses line blanketed NLTE wind atmosphere models fit high resolution near infrared spectra late type nitrogen rich Wolf Rayet stars and OfI stars the cluster relies the fact that massive stars reach maximum nitrogen abundance that related initial metallicity when they are the WNL phase determine the present day nitrogen abundance the WNL stars the Arches cluster mass fraction and constrain the stellar metallicity the cluster solar This result invariant assumptions about the mass luminosity relationship the mass loss rates and rotation speeds addition from this analysis find the age the Arches cluster Myr assuming coeval formation Subject headings Galaxy abundances stars abundances stars Wolf Rayet infrared stars Galaxy center Introduction The determination metal abundances function time and Galactic location disk bulge and halo provides crucial information for understanding the formation and Instituto Estructura Materia CSIC Serrano Madrid Spain Space Telescope Science Institute San Martin Drive Baltimore Department Physics and Astronomy University. We present a quantitative spectral analysis of five very massive stars in the Arches cluster, located near the Galactic center, to determine stellar parameters, stellar wind properties and, most importantly, metallicity content. The analysis uses a new technique, presented here for the first time, and uses line-blanketed NLTE wind/atmosphere models fit to high-resolution near-infrared spectra of late-type nitrogen-rich Wolf-Rayet stars and OfI+ stars in the cluster. It relies on the fact that massive stars reach a maximum nitrogen abundance that is related to initial metallicity when they are in the WNL phase. We determine the present-day nitrogen abundance of the WNL stars in the Arches cluster to be 1.6% (mass fraction) and constrain the stellar metallicity in the cluster to be solar. This result is invariant to assumptions about the mass-luminosity relationship, the mass-loss rates, and rotation speeds. In addition, from this analysis, we find the age of the Arches cluster to be 2-2.5 Myr, assuming coeval formation. (Refer to PDF file for exact formulas).. We thank George Meynet and Andre Maeder for useful discussions. F. N. acknowledges grants AYA2003-02785-E and ESP2002-01627. | |||||||||||||||
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