Magnetic field measurements around massive young stellar objects with the EVN.

Abstract

Although there has been significant progresses in the last years, the formation process of high-mass stars (M>8 M_sun is still unclear. This is mainly due to the fast evolution and large distances of the massive young stellar objects (YSOs) that make difficult to observe, with fine details, a sufficient number of massive YSOs at each evolutionary stages. However, in the last 10 years some pieces of information regarding the gas motion and the magnetic field close to the YSOs have been gathered by observing and analyzing the maser emission of mainly water and methanol molecules. In particular, we have performed full polarization observations of 6.7 GHz methanol masers and/or 22 GHz water maser with the European VLBI Network (EVN) towards a large number of sources in order to provide measurements of magnetic fields orientation and strength at milliarcsecond resolution around massive protostars. These measurements can be made at this high angular resolution only by observing and analyzing the polarized emission of masers. From the linearly and circularly polarized emissions we can determine the orientation and the strength of the magnetic field, respectively. Here, we present the updated statistics of the possible alignment between the magnetic field and the bipolar outflows ejected from the massive protostars. In addition, and for the first time, we will provide lower limits of the magnetic field strength measured from the Zeeman-splitting of the methanol maser by using the very recently determined Lande g-factors for the methanol maser transitions. Furthermore, the up-to-date results of the monitoring project of the 22 GHz water masers detected towards the massive star-forming region W75N(B) will be also presented.