Diagnosing Triggered Star Formation in the Galactic HII region Sh 2-142

Abstract

Stars are formed by gravitational collapse, spontaneously or, in some cases under the constructive influence of nearby massive stars, out of molecular cloud cores. Here we present an observational diagnosis of such triggered formation processes in the prominent H II region Sh 2-142, which is associated with the young star cluster NGC 7380, and with some bright-rimmed clouds as the signpost of photoionization of molecular cloud surfaces. Using near- (2MASS) and mid-infrared (WISE) colors, we identified candidate young stars at different evolutionary stages, including embedded infrared sources having spectral energy distributions indicative of active accretion. We have also used data from our optical observations to be used in SEDs, and from Gaia EDR3 to study the kinematics of young objects. With this young stellar sample, together with the latest CO line emission data (spectral resolution ∼0.16 km s−1 , sensitivity ∼0.5 K), a positional and aging sequence relative to the neighboring cloud complex, and to the bright-rimmed clouds, is inferred. The propagating stellar birth may be responsible, at least partially, for the formation of the cluster a few million years ago, and for the ongoing activity now witnessed in the cloud complex.