AFGL-4029 - A CLUSTER OF MASSIVE YOUNG STARS

The molecular cloud IC 1848A, located at the border of the extended H II region S 199, harbors the bright infrared 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, po ssibly 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 ra dio source G138.295+1.555 - is a massive pre-main-sequence object illu minating a reflection nebula. AFGL 4029-IRS 1 is luminous (similar to 10(4) L.) and highly reddened (A(V) = 25-30 mag); displaying many of t he spectral characteristics of pre-main-sequence objects (including br ight 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 w ith 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 hig h velocity optical jet; a bright unresolved H-2 clump is observed in i ts vicinity. The whole complex is a very efficient star forming region , as about 10% of the mass of the parental molecular cloud has been us ed to form B stars.