Study of 3-D structure of Orion-Monoceros Molecular Cloud complex with high-precision VLBI

点击翻译按钮获取中文摘要

VERA is a newly constructed VLBI array promoted by National Astronomical Observatory of Japan in collaboration with Kagoshima University. VERA aims to measure the annual parallaxes of maser sources associated with star-forming regions and Mira valuables in the Galaxy with an accuracy of 10 micro arcseconds. In this project, we plan to measure the distance and 3-dimensional structure of Orion-Monoceros Molecular Cloud complex, which is the nearest high-mass star-forming region, with VERA.At first, we performed a survey of 20 H2O maser sources in Orion-Moniceros Molecular Cloud complex and confirmed that 4 sources were detectable with VERA. Based on this result, we started multi-epoch VLBI monitoring observations of these 4 H2O maser sources ; Orion KL, HH1, OMC-2, and Mon R2. Using the VERA dual-beam receiving system, we performed phase-referencing VLBI and successfully measured absolute proper motion of H2O maser features with respect to the nearby extragalactic radio sources. We detected the annual parallax of Orion KL, 2.3 milli arcseconds, corresponding to the distance of 430 pc from the Sun. This value is consistent with that reported by Genzel et al. (1980), 480 +/- 80 pc, which is determined from the proper motion and radial velocity of the maser features. For other sources, we have not yet obtained annual parallax because the life time of H2O maser features were typically as short as 4-6 months. Therefore, we continue monitoring observations of these sources with VERA.