Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-07-18
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
15 pages, 4 figures, Accepted for publication in PASJ
Scientific paper
The HII region IC 1848 harbors a lot of intricate elephant trunk-like structures that look morphologically different from usual bright-rimmed clouds (BRCs). Of particular interest is a concentration of thin and long elephant trunk-like structures in the southeastern part of IC 1848E. Some of them have an apparently associated star (or two stars) at their very tip. We conducted $VI_{c}$ photometry of several of these stars. Their positions on the $V/(V-I_{c})$ color-magnitude diagram as well as the physical parameters obtained by SED fittings indicate that they are low-mass pre-main-sequence stars having ages of mostly one Myr or less. This strongly suggests that they formed from elongated, elephant trunk-like clouds. We presume that such elephant trunk-like structures are genetically different from BRCs, on the basis of the differences in morphology, size distributions, and the ages of the associated young stars. We suspect that those clouds have been caused by hydrodynamical instability of the ionization/shock front of the expanding HII region. Similar structures often show up in recent numerical simulations of the evolution of HII regions. We further hypothesize that this mechanism makes a third mode of triggered star formation associated with HII regions, in addition to the two known mechanisms, i.e., collect-and-collapse of the shell accumulated around an expanding HII region and radiation-driven implosion of BRCs originated from pre-existing cloud clumps.
Bhatt Bhuwan Chandra
Chauhan Neelam
Ogura Katsuo
Pandey Anil K.
Samal Manash R.
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