Star formation in the S233 region

TL;DR

This study investigates the potential for triggered star formation at the edge of the HII region S233, using spectral analysis and imaging to identify signs of ongoing star formation processes.

Contribution

The paper provides observational evidence supporting the collapse of a pre-existing clump as the mechanism for star formation in S233, challenging the collect-and-collapse model.

Findings

Spectral classification of the ionizing star as B0.5 V.

Detection of a red-shifted gas clump with infrared source.

Indications of star formation triggered by clump collapse.

Abstract

The main objective of this paper is to study the possibility of triggered star formation on the border of the HII region S233, which is formed by a B-star. Using high-resolution spectra we determine the spectral class of the ionizing star as B0.5 V and the radial velocity of the star to be -17.5(1.4) km/s. This value is consistent with the velocity of gas in a wide field across the S233 region, suggesting that the ionizing star was formed from a parent cloud belonging to the S233 region. By studying spatial-kinematic structure of the molecular cloud in the S233 region, we detected an isolated clump of gas producing CO emission red-shifted relative to the parent cloud. In the UKIDSS and WISE images, the clump of gas coincides with the infrared source containing a compact object and bright-rimmed structure. The bright-rimmed structure is perpendicular to the direction of the ionizing star. The compact source coincides in position with IRAS source 05351+3549. All these features indicate a possibility of triggering formation of a next-generation star in the S233 region. Within the framework of a theoretical one-dimensional model we conclude that the "collect-and-collapse" process is not likely to take place in the S233 region. The presence of the bright-rimmed structure and the compact infrared source suggest that the "collapse of the pre-existing clump" process is taking place.