Sequential Star Formation in a Cometary Globule (Brc37) of Ic1396

Abstract

We have carried out near-IR/optical observations to examine star formation toward a bright-rimmed cometary globule (BRC37) facing the exciting star(s) of an H ii region (IC1396) containing an IRAS source, which is considered to be an intermediate-mass protostar. With slitless spectroscopy we detected ten Hα emission stars around the globule, six of which are near the tip of the globule and are aligned along the direction to the exciting stars. There is evidence that this alignment was originally toward an O9.5 star, but has evolved to align toward a younger O6 star when that formed. Near-IR and optical photometry suggests that four of these six stars are low-mass young stellar objects (YSOs) with masses of ∼0.4 M . Their estimated ages of ∼1 Myr indicate that they were formed at the tip in advance of the formation of the IRAS source. Therefore, it is likely that sequential star formation has been taking place along the direction from the exciting stars toward the IRAS source, due to the UV impact of the exciting star(s). Interestingly, one faint, Hα emission star, which is the closest to the exciting star(s), seems to be a young brown dwarf that was formed by the UV impact in advance of the formation of other YSOs at the tip.

Triggered Star Formation in a Bright-Rimmed Cloud (Brc 5) of Ic 1805

“…Emission line stars as T Tauri candidates have already been reported around BRC 5 (Ogura et al 2002;Ikeda et al 2008). All the Hα emission stars that were identified both in this and previous works are marked in Figures 1 and 2, using the ID numbers of Ikeda et al (2008) and new numbers (14-19) of stars newly detected from this work, using the wider field of view of WFGS2. Two stars (2 and 10) were excluded due to the ambiguous detection of Hα emission in our inspection of this and previous data.…”

“…The properties of these emission stars are shown in Table 1. We noted the misidentification of stars 5 and 8 in Ikeda et al (2008) and made corrections to their coordinates in Table 1.…”

“…A dashed square shows the region of the near-infrared observation. Hα emission stars are marked with circles and Arabic numerals; 1-13 were identified in Ikeda et al (2008) and Ogura et al (2002), and 14-19 are identified in this work. An arrow shows the direction of the incoming UV illumination (P.A.…”

“…Sugitani et al (1991) cataloged 44 BRCs for the northern hemisphere and 45 BRCs are done for the southern hemisphere by Sugitani & Ogura (1994). Young stellar objects (YSOs) are associated with most of these BRCs; Hα emission stars like T Tauri stars are found around BRCs (e.g., Ogura et al 2002;Ikeda et al 2008), and dense cores are detected by millimeter-wave observations (e.g., Fukuda et al 2002;Urquhart et al 2007Urquhart et al , 2009). The average number of Hα emission stars, which are low-and intermediate-mass young stars, is about 16 stars per BRC.…”

“…Morgan et al (2008) showed a positive correlation between the UV field and the luminosity of YSOs for BRCs with tightly curved rims and cometary rims. Younger sources are found away from the ionizing OB stars in some BRCs (e.g., Sugitani et al 1995;Matsuyanagi et al 2006;Getman et al 2007;Urquhart et al 2007;Ikeda et al 2008), which suggests that star formation proceeds from the outside of the cloud to the inside.…”