Star formation in the Vela molecular clouds

Abstract

We present the latest results from a sensitive (K ∼ 18 mag) near-infrared (JHK) imaging survey of IRAS selected young stellar objects associated with the Vela molecular ridge. These enlarge the sample of 12 fields, previously studied, adding 10 sites of recent star formation. The spectral energy distributions derived from near-infrared and 1.3-mm photometry allowed to identify at least 5 Class I sources. Their bolometric luminosities indicate that they are protostellar objects of intermediate mass (∼2-10 M� ). Herbig Ae/Be stars and compact UCHII regions could account for the far infrared emission towards some of the remaining fields. The most luminous IRAS sources have also been found associated with young embedded star clusters. The physical properties of the clusters have been determined and used to improve on the statistical relationships already suggested by our previous work. They have sizes of >0.1 pc and volume densities of 10 3 -10 4 stars pc −3 . Where identified, the Class I sources tend to lie near the centre of the clusters and it is confirmed that the most massive ones are associated with the richest clusters. The less luminous Class I sources (∼10 2 L� ) are found either isolated or within small groups of young stellar objects. It is proposed to use the relationship between the bolometric luminosity of the IRAS sources and the total number of cluster members as a test of the initial mass function at the highest masses.