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Summer students 2012: EVN observations of maser polarization in the masssive star-forming region IRAS22272+6358A

Submitter: Luis Henry Quiroga-Nunez
Description: My summer project was developed at JIVE, where I reduced and analyzed data from 6.7 GHz methanol maser observations, which were made last October by using seven antennas of the European VLBI Network (EVN). The observations were pointed towards the massive (14.2 solar masses) protostar IRAS22272+6358A, which is located in the dark cloud L1205 that is in the Local Spur Arm at a distance of about 0.8 kpc. The data reduction was done by using AIPS. We measured the linearly and circularly polarized emissions of the methanol masers located around IRAS22272+6358A . The aim of my project was to calculate the orientation and strength of the magnetic field around the massive protostar.

We detected twenty-three methanol masers, which are aligned with the outflow, with a peak flux density between 0.1 and 4.8 Jy/beam (rms=3mJy/beam). In three masers we were able to detect linearly polarized emission, with a linear polarization fraction between 0.7% and 1.2% with a weighted linear polarization angle of about 75 degrees. Unfortunately, we did not detect circular polarization in any maser feature (<4 sigma),consequently we were not able to estimate the strength of the magnetic field. Using a Full Radiative Transfer Method, we measured the Emerging Brightness Temperature and the Intrinsic Thermal Linewidth for each maser that showed linear polarization. Finally with these values, we were able to find that the magnetic field is perpendicular to the linear polarization vectors allowing us to determine the orientation of the magnetic field in three dimensions. IRAS22272+6358A is part of a larger project which is focused on measuring the magnetic field in several massive star-forming regions,with the objective of improving (based on observations) the future simulations.

I would like to thank all the people at JIVE and ASTRON who made this summer an enriching experience. Special thanks to my supervisors: Dr. Gabriele and Dr. Huib from JIVE, and special thanks also to Dr. Alicia from ASTRON.

Image. Left: CO emission integrated in different velocity intervals, (-19.5, -13.5) km/s for the low velocity blue-shifted emission (blue contours) and (-8.5, -2.5) km/s for the red-shifted emission (red contours), overlaid on the 2.7mm continuum emission (greyscale). The orientation of the outflow is P.A.~140 degrees. More information: Beltran et al. 2006, A&A,457, 865.

Right: Distribution of 6.7 GHz methanol masers detected around IRAS22272+6358A. The maser LSR radial velocity is indicated by color. A 0.6 Jy/beam symbol is plotted for illustration. The linear polarization vectors, scaled logarithmically according to linear polarization fraction, are over plotted. The dashed line shows the fit for the maser distribution. The thick line is the projection on the plane of the sky of the magnetic field. The green arrows indicate the direction of the bipolar CO outflow in accordance with Beltran et al. (2006).
Copyright: Luis Henry Quiroga-Nunez , Beltran et al. 2006, A&A,457, 865.
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