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33rd Winter School in Theoretical Physics on: Exoplanets (28 December, 2015 – 08 January, 2016) at the Israel Institute of Advanced Studies (IIAS), the Hebrew University of Jerusalem. Magnetic field structure of a large Bok Globule CB34 Himadri Sekhar 1 1 Das , A. Bok globules are small, opaque, and isolated nearby molecular clouds. Their cores usually have a quite simple structure that makes them ideally suited for studies of isolated lowmass star formation (Bok 1947, ApJ, 105, 255). & B. J. 2 Medhi Department of Physics, Assam University, Silchar 788011 (INDIA) 2 ARIES, Manora Peak, Nainital 263129 (INDIA) OPTICAL POLARIZATION BOK GLOBULES 1 Das Optical Optical polarimetric observations of CB34 were performed with the 1.04-metre Sampurnanand telescope of he Aryabhatta Research Institute of observational sciencES (ARIES) near Nainital in India on 11-13 March, 2013 and on 20 Feb, 2014. NIR Barnard 68 Fig: The stellar polarization vectors and position angles are superimposed on a 15×15 arcmin2 R-band DSS image of the field containing CB34. A vector with a polarization of 1% is drawn for reference; the length of all polarization vectors is proportional to it. The ‘×’ symbol represents the globule centre RA = 05h47m01s, DEC=+21d01m11s. SUBMILLIMETER POLARIZATION Ref: Launhardt et al. (2010, ApJS, 188, 139) LARGE BOK GLOBULE CB34 CB34 is rather atypical and more massive than other Bok globules. This globule is situated at a distance of ~1.5 kpc. It has three dense cores and is associated with numerous young stars and that seem to have formed from this cloud (Huard et al. 2000, A&A, 362, 635; Khanzadyan et al. 2002, A&A, 383, 502; Launhardt et al. 2010, ApJS, 188, 139). MAGNETIC FIELD IN BOK GLOBULES Magnetic fields play a major role on the evolution of dark clouds and may control the fragmentation of clouds to form stars (Mouschovias & Morton 1991, ApJ, 371, 296; Li & Nakamura 2004, ApJ, 609, L83). In general, they can influence the contraction timescale, the gas-dust coupling, and the shape of cloud fragments, and they host jets and outflows (McKee & Ostriker 2007, ARA&A, 45, 565). POLARIMETRY Fig: 850 μm polarization vectors are sampled on a 10’’ grid. Contours range from 0.1 Jy beam−1 in steps of 0.05 Jy beam−1 The submm observation of CB34 were made at the James Clerk Maxwell Telescope (JCMT), Mauna Kea, Hawaii, using the Submillimeter Common User Bolometer Array (SCUBA). The submm polarization data presented here is taken from the Matthews et al. (2009, ApJS, 182, 143) legacy data set. Their analysis restricted to only six data points. To increase the number of data points, we have reanalyzed the data set and calculated polarization vector at each pixel and use the criteria I > 0, p/Ep > 2 and Ep < 6%. MAGNETIC FIELD STRENGTH The magnetic field strength (in Gauss) in the plane-of-sky is (Chandrasekhar & Fermi 1953, ApJ, 118, 113): Polarization arises from alignment of interstellar dust grains in the presence of a magnetic field (Davis & Greenstein 1951, ApJ, 114, 206). When the light from the background stars passes through the clouds, extinction and reddening are caused due to absorption and scattering by the dust grains present in the clouds. This phenomenon also introduces linear polarization in the starlight, if the dust grains are aligned and dichroic. Optical polarimetric observations of dark cloud can give information about the magnetic field orientation in the low-density edge regions of clouds Polarimetric observations in the infrared and submillimetre range can map the field orientation in the higher density central regions of the clouds. Thus, the resulting polarization map outlines the geometry of the magnetic field lines projected on to the plane of the sky, which in turn helps us to study the relationship between structure kinematics and the embedded magnetic field during various stages of star formation RESEARCH POSTER PRESENTATION DESIGN © 2015 www.PosterPresentations.com CONCLUSIONS The mean value of polarization (optical) and position angle for the 35 field stars is <popt>= 2.14 % and <θopt>= 143.2o with a standard deviation of σp = 0.84% and σθ = 7.8o respectively. The peripheral magnetic field of the cloud CB34 (optical polarization study) is almost aligned with galactic magnetic field having position angle of 146o. The mean polarization and position angle obtained from sub-mm observations are given by <psub>= 12.5 % and <θsub>= 74.5o. The angular offset between peripheral magnetic field and inner magnetic field is ~ 69o. The mangetic field strength at peripheral region is higher (~ 205μG) as compared to inner magnetic field strength (~ 28μG). The inner magnetic field is also not aligned among themselves due to high turbulence of gas at center of the cloud (~ 0.64 km s-1). ACKNOWLEDGEMENTS Ref: Goodman et al. (1995), ApJ, 448, 748 This work is supported by the Science and Engineering Research Board (SERB), a statutory body under Department of Science and Technology (DST), Government of India, under Fast Track scheme for Young Scientist (SR/FTP/PS-092/2011).