AFGL 4029: a cluster of massive young stars
Résumé
The molecular cloud IC 1848A, located at the border of the extended H ii region S 199, harbors the bright in-frared source AFGL 4029. A young star cluster is observed in this direction. We present an optical and near infrared study of this cluster, which contains at least thirty B stars. The visual extinction affecting the stars attains 30 mag, and shows large variations on very small scales. The most massive star, possibly a B1V, ionizes the ultracompact H ii region G138.300+1.558. The youngest object of the cluster, AFGL 4029-IRS 1-identical to the radio source G138.295+1.555-is a massive pre-main-sequence object illuminating a reflection nebula. AFGL 4029-IRS 1 is luminous (∼ 10 4 L) and highly reddened (A V = 25-30 mag); displaying many of the spectral characteristics of pre-main-sequence objects (including bright and broad emission lines and the presence of Fe ii emission), it is very similar to the most luminous Herbig Ae/Be stars. AFGL 4029-IRS 1 shows evidence of mass ejection: it emits an ionized stellar wind with terminal velocities of about 400 km s −1 and a mass loss rate of about 7 10 −6 M yr −1 ; it is associated with a CO outflow and a high velocity optical jet; a bright unresolved H 2 clump is observed in its vicinity. The whole complex is a very efficient star forming region, as about 10% of the mass of the parental molecular cloud has been used to form B stars.
Domaines
Astrophysique [astro-ph]
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