Eswaraiah (NTHU, Taiwan), Shih-Ping Lai (NTHU, Taiwan), and collaborators
Isolated dark globules are the potential sites for the formation of low mass stars. It has been shown that turbulence appears to be sub- or trans-Alfvénic in dark globules, whose role in preventing gravitational collapse is limited. Therefore, magnetic fields (B-fields) are proposed to play a crucial role in controlling the stability and contraction of these clouds. Based on the optical polarization observations towards a dark globule LDN1225 (located in Cepheus OB3 cloud complex at a distance of 730 pc) we mapped the B-field orientation in the low-density parts of the cloud. Using the dispersions in polarization angles, gas velocity (using CO data from PMO), and number density, we have estimated the B-field strength, using Chandrasekhar-Fermi method, to be 56±13μG. B-field pressure is found to dominate over the turbulent pressure. Moreover, the structure-function analysis suggest that large-scale ordered B-fields dominate over the turbulent component in the LDN 1225. Furthermore, the mass-to-flux ratio is found to be less than the critical value suggesting LDN1225 is subcritical. These results imply that cloud support, especially in the regions where optical polarimetry and 12CO mapping are applicable, is mainly rendered by the B-fields.