The Bok globule BHR 160: Structure and star formation

Abstract

Context. BHR 160 is a virtually unstudied cometary globule within the Sco OB4 association in Scorpius at a distance of 1600 pc. It is part of a system of cometary clouds which face the luminous O star HD 155806. BHR 160 is special because it has an intense bright rim. Aims. We attempt to derive physical parameters for BHR 160 and to understand its structure and the origin of its peculiar bright rim. Methods. BHR 160 was mapped in the 12CO, 13CO and C18O (2−1) and (1−0) and CS (3−2) and (2−1) lines. These data, augmented with stellar photometry derived from the ESO VVV survey, were used to derive the mass and distribution of molecular material in BHR 160 and its surroundings. Archival mid-infrared data from the WISE satellite was used to find IR excess stars in the globule and its neighbourhood. Results. An elongated 10 by 00 .6 core lies adjacent to the globule bright rim. 12CO emission covers the whole globule, but the 13CO, C 18O and CS emission is more concentrated to the core. The 12CO line profiles indicate the presence of outflowing material near the core, but the spatial resolution of the mm data is not sufficient for a detailed spatial analysis. The BHR 160 mass estimated from the C 18O mapping is 100 ± 50 M (d/1.6 kpc)2 where d is the distance to the globule. Approximately 70% of the mass lies in the dense core. The total mass of molecular gas in the direction of BHR 160 is 210±80 (d/1.6 kpc)2 M when estimated from the more extended VVV near-infrared photometry. We argue that the bright rim of BHR 160 is produced by a close-by early B-type star, HD 319648, that was likely recently born in the globule. This star is likely to have triggered the formation of a source, IRS 1, that is embedded within the core of the globule and detected only in Ks and by WISE and IRA