Triggered star formation in Orion cometary clouds? I. The case of L1616

We present new 1.2 mm continuum maps and near- and mid-infrared images of the cometary cloud L1616 located to the west of the Orion OB associations and apparently shaped by the winds and radiation coming from the massive, hot stars in the OB association. The new data reveal evidence for ongoing star formation in the cloud in addition to the known cluster of somewhat more evolved stars illuminating the NGC 1788 reflection nebula in the head of the cometary cloud. The 1.2 mm survey reveals a tight group of dust continuum sources, the brightest of which is seen to drive a powerful near-infrared H2 jet, apparently a very young protostar of Class 0 type. The location of the newly discovered protostar with respect to the older cluster and the direction towards the OB association suggests an age sequence due to a wave of star formation driven through the cloud and triggered by the impact of the nearby OB association: the older generation of stars is located on the side of the cloud directly facing the OB association, whereas a new generation of star formation takes place deeper within the cloud.