A radiation driven implosion model for the enhanced luminosity of protostars near HII regions

¹ Theoretical Institute for Advanced Research in Astrophysics, Dept. of Physics, National Tsing Hua University, 101, Sec. 2, Kuang-Fu Rd., Hsin-Chu, 30013, Taiwan e-mail: motoyama@tiara.sinica.edu.tw
² Nobeyama Radio Observatory, Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305, Japan
³ Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan

Received: 29 December 2006
Accepted: 7 February 2007

Abstract

Context.Molecular clouds near regions tend to harbor more luminous protostars.

Aims.We investigate whether a radiation-driven implosion mechanism enhances the luminosity of protostars near regions of high ionizing fluxes.

Methods.We performed numerical simulations to model collapse of cores exposed to UV radiation from O stars. We investigated the dependence of mass loss rates on the initial density profiles of cores and variation of UV fluxes. We derived simple analytic estimates of accretion rates and final masses of protostars.

Results.The radiation-driven implosion mechanism can increase accretion rates of protostars by 1–2 orders of magnitude. On the other hand, mass loss due to photo-evaporation is not high enough to have a significant impact on the luminosity. The increase in accretion rate results in luminosity 1–2 orders of magnitude higher than those of protostars that form without external triggering.

Conclusions.Radiation-driven implosion can help explain the observed higher luminosity of protostars in molecular clouds near regions.