Sequential and Spontaneous Star Formation Around the Mid-Infrared Halo HII Region KR 140

TL;DR

This study investigates the distribution and origins of young stellar objects around the KR 140 HII region, revealing that spontaneous star formation dominates over sequential processes driven by the HII region's expansion.

Contribution

It provides new insights into star formation mechanisms, showing that spontaneous processes are significant in the molecular cloud surrounding KR 140, contrary to previous assumptions.

Findings

YSOs are concentrated along dense filamentary structures.

Some clumps are sites of recent star formation.

Massive starless clumps may trigger future star formation.

Abstract

We use 2MASS and MSX infrared observations, along with new molecular line (CO) observations, to examine the distribution of young stellar objects (YSOs) in the molecular cloud surrounding the halo HII region KR 140 in order to determine if the ongoing star-formation activity in this region is dominated by sequential star formation within the photodissociation region (PDR) surrounding the HII region. We find that KR 140 has an extensive population of YSOs that have spontaneously formed due to processes not related to the expansion of the HII region. Much of the YSO population in the molecular cloud is concentrated along a dense filamentary molecular structure, traced by C18O, that has not been erased by the formation of the exciting O star. Some of the previously observed submillimetre clumps surrounding the HII region are shown to be sites of recent intermediate and low-mass star formation while other massive starless clumps clearly associated with the PDR may be the next sites of sequential star formation.