2015 Seminar List:
When a massive star forms, it photoionizes the surroundings, forming an HII region. The HII regions commonly display highly irregular structures and a variety of peculiar objects.
These objects are classified according to their appearances as fingers or pillars, speck globules, bright-rimmed clouds (BRCs), cometary globules (CGs) and elephant trunks.
The evolution of the BRCs in HII regions is found to be critically dependent on the magnetic field orientation w.r.t. the direction of the propagation of the ionising flux prior to the onset of expansion of HII region in varous MHD simulations.
This is because the evolution of the BRCs may depend on factors such as the luminosity of the central ionizing source, the strength of the magnetic field and its orientation and the distance of the BRCs from the central ionizing source.
In this study, in order to understand the structural evolution of these globules, we carried out a systematic study of multiple BRCs that are associated with the same HII regions.
For this purpose, we chose two HII regions, Sh 185 and Sh 131. These HII regions were selected because of their structural simplicity and proximity to the sun. The advantage of studying multiple BRCs associated with the same HII region is that one can perform a comparative study of the magnetic field morphologies as various locations of the HII region w.r.t. the direction of the ionising radiation from the central source. We made optical polarization measurements of stars projected on Sh-131 and Sh-185 to map the magnetic fields in these regions.
I will be presenting the effects of magnetic fields on the evolution of these BRCs.