Young stellar population of bright-rimmed clouds BRC 5, BRC 7 and BRC 39

Neelam Panwar,M. R. Samal,A. K. Pandey,J. Jose,D. K. Ojha,K. Ogura,B. C. Bhatt,W. P. Chen

doi:10.1093/mnras/stu1244

Abstract

Bright-rimmed clouds (BRCs), illuminated and shaped by nearby OB stars, are potential sites of recent/ongoing star formation. Here we present an optical and infrared photometric study of three BRCs: BRC 5, BRC 7 and BRC 39 to obtain a census of the young stellar population, thereby inferring the star formation scenario, in these regions. In each BRC, the Class I sources are found to be located mostly near the bright rim or inside the cloud, whereas the Class II sources are preferentially outside, with younger sources closer to the rim. This provides strong support to sequential star formation triggered by radiation-driven implosion due to the ultraviolet radiation. Moreover, each BRC contains a small group of young stars being revealed at its head, as the next-generation stars. In particular, the young stars at the heads of BRC 5 and BRC 7 are found to be intermediate-/high-mass stars, which, under proper conditions, may themselves trigger further star birth, thereby propagating star formation out to long distances.

Highlights

The immense stellar winds and UV radiation from massive stars present in a star-forming region have dramatic impact on the immediate vicinity
The optical colour-magnitude diagram (CMD) can be used to diagnose the evolutionary status for young stellar objects (YSOs) not deeply embedded in the cloud
On the basis of optical and IR observations to characterise the young stellar aggregates of Bright-rimmed clouds (BRCs) 5, BRC 7, and BRC 39, we confirm the significant role played by massive stars on the star formation activity in neighboring clouds

Summary

Introduction

The immense stellar winds and UV radiation from massive stars present in a star-forming region have dramatic impact on the immediate vicinity. Elmegreen & Lada (1977) proposed that the expanding ionisation front plays a constructive role in inciting a sequence of star formation activities in the neighbourhood. In the ‘collect and collapse’ scenario, the material accumulated by the expanding ionisation front and shock front of the Hii region becomes gravitationally unstable, so it fragments and collapses to form stars (Elmegreen & Lada 1977). In the RDI scenario, a pre-existing dense clump is exposed to the ionising radiation from a massive star or stars, and the photoionisation induced shock compresses the head part of the clump to collapse, which leads to formation of stars (e.g., Bertoldi 1989, Lefloch & Lazareff 1995). The aligned elongated distribution of young stellar objects (YSOs) in a small molecular cloud is considered as an observational signature of the RDI process (Ogura et al 2002, Lee et al 2005)

Results

Discussion

Conclusion