Wide-Field Survey of Emission-line Stars in IC 1396

TL;DR

This extensive survey of emission-line stars in IC 1396 identified 639 H-alpha emitters, revealing their spatial distribution, ages, and masses, and suggesting a prolonged, possibly triggered, star formation process in the region.

Contribution

The paper provides the first large-scale, detailed analysis of emission-line stars in IC 1396, including their spatial distribution, ages, and implications for star formation history.

Findings

Most PMS candidates are younger than 3 Myr.

Stars in the east region are generally older, with few formed in the last 1 Myr.

Star formation may have been continuous for 10 Myr, possibly triggered by the exciting star.

Abstract

We have made an extensive survey of emission-line stars in the IC 1396 HII region to investigate the low-mass population of pre-main sequence (PMS) stars. A total of 639 H-alpha emission-line stars were detected in an area of 4.2 deg^2 and their i'-photometry was measured. Their spatial distribution exhibits several aggregates near the elephant trunk globule (Rim A) and bright-rimmed clouds at the edge of the HII region (Rim B and SFO 37, 38, 39, 41), and near HD 206267, which is the main exciting star of the HII region. Based on the extinction estimated from the near-infrared (NIR) color-color diagram, we have selected pre-main sequence star candidates associated with IC 1396. The age and mass were derived from the extinction corrected color-magnitude diagram and theoretical pre-main sequence tracks. Most of our PMS candidates have ages of < 3 Myr and masses of 0.2-0.6 Mo. Although it appears that only a few stars were formed in the last 1 Myr in the east region of the exciting star, the age difference among subregions in our surveyed area is not clear from the statistical test. Our results may suggest that massive stars were born after the continuous formation of low-mass stars for 10 Myr. The birth of the exciting star could be the late stage of slow but contiguous star formation in the natal molecular cloud. It may have triggered to form many low-mass stars at the dense inhomogeneity in and around the HII region by a radiation-driven implosion.