Unbound Tails and Compressed Heads: A JCMT Study of the SFO 38 Cloud

Abstract

SFO 38, located in the Cepheus molecular cloud within the northern part of the HII region IC 1396, is shaped by intense ultraviolet radiation from the nearby O6.5V-type star HD 206267 and represents a classic example of a bright-rimmed cloud (BRC) undergoing radiatively driven implosion (RDI). While previous studies have examined the southern globule using CS and 13CO (1-0), we present a refined analysis using high-resolution JCMT-HARP observations in the 12CO, 13CO, and C18O (J = 3-2) lines, deriving key physical parameters along with virial mass and turbulence properties of the southern head. We also perform the first detailed investigation of the northeastern and northwestern tails, determining their morphological dimensions and internal conditions, including excitation temperature, column density, mass, and volume density. Spectral and stability analyses reveal that the tail regions are gravitationally unbound and dynamically expanding, explaining the lack of active star formation. Our results further shed light on the evolutionary fate of these structures, assessing whether they may accumulate sufficient material to become future sites of star formation or remain quiescent. Overall, this work highlights the dual role of RDI in this BRC: while it triggers star formation in the dense head, it simultaneously disperses and dynamically reshapes the extended tails.