High-resolution Near-infrared Observations of a Small Cluster Associated with a Bright-rimmed Cloud in W5

Abstract

We have carried out near-infrared (IR) observations to examine star formation toward the bright-rimmed cloud SFO 12, of which the main exciting star is O7V star in W5-W. We found a small young stellar object (YSO) cluster of six members embedded in the head of SFO 12 facing its exciting star, aligned along the UV radiation incident direction from the exciting star. We carried out high-resolution near-IR observations with the Subaru adaptive optics (AO) system and revealed that three of the cluster members appear to have circumstellar envelopes, one shows an arm-like structure in its envelope. Our near-IR and L ′ -band photometry and Spitzer IRAC data suggest that formation of two members at the tip side occurred in advance of other members toward the central part, under our adopted assumptions. Our near-IR data and previous 2 studies imply that more YSOs are distributed in the region just outside the cloud head on the side of the main exciting star, but there is little sign of star formation toward the opposite side. We infer that star formation has been sequentially occurring from the exciting star side to the central part. We examined archival data of far-infrared and CO (J = 3-2) which reveals that, unlike in the optical image, SFO 12 has a headtail structure which is along the UV incident direction. This suggests that SFO 12 is affected by strong UV from the main exciting star. We discuss the formation of this head-tail structure and star formation there by comparing with a radiation-driven implosion (RDI) model.

H II regions and high-mass starless clump candidates

“…H ii regions could trigger star formation with several mechanisms, mainly depending on the density and configuration of the surrounding medium (see Sect. 5 in Deharveng et al 2010), such as the collect and collapse (C&C) mechanism in IR dust bubbles (Zavagno et al 2010;Samal et al 2014;Duronea et al 2017) or the radiation-driven implosion (RDI) mechanism in pillars or bright rimmed clouds (Bertoldi 1989;Imai et al 2017;Marshall & Kerton 2019).…”

ATOMS: ALMA three-millimeter observations of massive star-forming regions – XIII. Ongoing triggered star formation within clump-fed scenario found in the massive (∼1500 M⨀) clump

“…This sequential star formation is thought to be a relic of shock propagation. The shock driv en by o v er-pressure IBL propagates into the clump's interior and then triggers clumps/cores to collapse and sequentially form stars (Sugitani, Tamura & Ogura 1995 ;Fukuda, Hanawa & Sugitani 2002 ;Ikeda et al 2008 ;Chauhan et al 2009 ;Getman et al 2009 ;Choudhury, Mookerjea & Bhatt 2010 ;Fukuda et al 2013 ;Panwar et al 2014 ;Imai et al 2017 ). Following the shock speed estimation formula and methods in Urquhart et al ( 2007 ),…”

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -XIII. Ongoing triggered star formation within clump-fed scenario found in the massive ($\sim1500$ $\rm M_\odot$) clump

“…This sequential star formation is thought to be a relic of shock propagation. The shock driven by over-pressure IBL propagates into the clump's interior and then triggers clumps/cores to collapse and sequentially form stars (Sugitani et al 1995;Fukuda et al 2002;Ikeda et al 2008;Getman et al 2009;Chauhan et al 2009;Choudhury et al 2010;Fukuda et al 2013;Panwar et al 2014;Imai et al 2017). Following the shock speed estimation formula and methods in Urquhart et al (2007):…”