Optical polarimetry: tracing magnetic fields in Bok globules

G. Maheswar*and Archana Soam
Aryabhatta Research Institute of Observational Sciences, Nainital 263129, India

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The relative role played by the magnetic field and the turbulence in cloud formation and evolution and in di erent stages of star formation is a matter of serious study. By using linear polarization measurements in optical wavelengths of stars that are located behind the clouds, one can map the plane-of-sky component of magnetic field. Here we present the preliminary results of the linear polarimetry of background stars projected on three clouds, namely, IRAM 04191+1522 (R band), L1521F (V band) and L1014 (R band). These clouds, previously classified as starless, are found to harbour very low luminosity objects (VeLLOs, L ≤ 0.1Lʘ) detected during observations with Spitzer Space telescope (SST). A protostar located on the stellar/substellar boundary (M = 0.08Mʘ) would have an accretion luminosity of L ~ 1.6Lʘ, assuming a spherical mass accretion predicted by the standard model onto a protostellar object of typical radius R ~ 3Rʘ. VeLLOs, with luminosities more than an order of magnitude lower than this, are dicult to understand in the context of standard model of star formation.

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Keywords : ISM: magnetic fields – polarization – star: formation