Remnant Molecular Clouds in the Ori OB 1 Association

Katsuo Ogura
Koji Sugitani

Kokugakuin University, Higashi, Shibuya-ku, Tokyo 150, Japan
ogura@kokugakuin.ac.jp
Institute for Natural Sciences, Nagoya-City University, Mizuho-ku, Nagoya 467, Japan
sugitani@nsc.nagoya-cu.ac.jp

Abstract:

We suggest and give some evidence that as an HII region expands and the O star(s) evolve(s) into B giant(s) remains of the molecular clouds first appear as bright-rimmed clouds, then as cometary globules and finally as small clouds which are visible by the reflected light from the B giants. We propose to call the last one ''reflection clouds'' and all three categories collectively ''remnant clouds''. A list is presented of about 80 objects of these remnant clouds in the Ori OB 1 association. In the Belt region there is a beautiful spatial sequence from bright-rimmed clouds through cometary globules to reflection clouds. We suspect that retarded star formation in remnant clouds can explain the presence of so-called dispersed T Tau stars in the peripheries of OB associations.

Keywords:

ISM: molecular clouds - ISM:globules - HII regions - OB associations
stars: formation

© Copyright Astronomical Society of Australia 1997