2014 Special Seminar:
We have mapped the optical linear polarisation towards some nearby starless and prestellar cores namely L1521E, L1544, L1517, L1498 and in five cores harboring Very Low Luminosity Objects (VeLLOs) which are IRAM 04191+1522, L1521F, L328, L673-7 and L1014.
We use these measurements to determine the plane-of-sky magnetic field orientation in the cores. The field is measured from the polarization of background starlight seen through the cloud. These magnetic field studies are basically done to understand the role of magnetic field in cloud formation and subsequent star formation.
Since the optical polarimetric technique helps in tracing the magnetic field in the low density parts of the clouds hence we also combine our data with the archival near-infrared and submillimeter polarization measurements to see the magnetic field geometry in the high density regions i.e. the inner parts of the cores.
The polarisation observations of stars projected on cores with VeLLOs namely IRAM 04191, L328, L673-7 and L1014 were obtained in R-band and those of L1521F were obtained in the V-band. The angular offsets between the envelope magnetic field direction (inferred from optical polarisation measurements) and the outflow position angles from the VeLLOs in IRAM 04191, L1521F, L328, L673-7 and L1014 are found to be 84, 53, 24, 08 and 1522, respectively. The mean value of the offsets for all the five clouds is 37 If we exclude IRAM 04191, the mean value reduces to become 25.
In IRAM 04191, the offset between the projected envelope and the inner magnetic field (inferred from the submillimeter data obtained using SCUBA-POL) is found to be 68. The inner magnetic field, however, is found to be nearly aligned with the projected position angles of the minor axis, the rotation axis of the cloud and the outflow from the IRAM 04191-IRS. We discuss a possible explanation for the nearly perpendicular orientation between the envelope and core scale magnetic fields in IRAM04191.
The angular offset between the envelope magnetic field direction and the minor axis of IRAM 04191, L1521F, L673-7 and L1014 are 82, 60, 47 and 55, respectively. The mean value of the offsets between the envelope magnetic field and the minor axis position angles for the four cores is found to be 60. The results obtained from our study on the limited sample of five cores with VeLLOs show that the outflows in three of them tend to nearly align with the envelope magnetic field.