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标题：Planar infall of CH3OH gas around Cepheus A HW2
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作者：A. Sanna ; A. Sanna ; L. Moscadelli 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2017
卷号：603
页码：1-9
DOI：10.1051/0004-6361/201730773
语种：English
出版社：EDP Sciences
摘要：Aims. In order to test the nature of an (accretion) disk in the vicinity of Cepheus A HW2, we measured the three-dimensional velocity field of the CH3OH maser spots, which are projected within 1000 au of the HW2 object, with an accuracy on the order of 0.1 km s-1. Methods. We made use of the European VLBI Network (EVN) to image the 6.7 GHz CH3OH maser emission toward Cepheus A HW2 with 4.5 milliarcsec resolution (3 au). We observed at three epochs spaced by one year between 2013 and 2015. During the last epoch, in mid-March 2015, we benefited from the newly deployed Sardinia Radio Telescope. Results. We show that the CH3OH velocity vectors lie on a preferential plane for the gas motion with only small deviations of 12° ± 9° away from the plane. This plane is oriented at a position angle of 134° east of north, and inclined by 26° with the line of sight, closely matching the orientation of the previously reported disk-like structure. Knowing the orientation of the equatorial plane, we can reconstruct a face-on view of the CH3OH gas kinematics onto the plane. CH3OH maser emission is detected within a radius of 900 au from HW2, and down to a radius of about 300 au, the latter coincident with the extent of the dust emission at 0.9 mm. The velocity field is dominated by an infall component of about 2 km s-1 down to a radius of 300 au, where a rotational component of 4 km s-1 becomes dominant. We discuss the nature of this velocity field and the implications for the enclosed mass. Conclusions. These findings directly support the interpretation that the high-density gas and dust emission that surrounds Cepheus A HW2 traces an accretion disk.
关键词：enISM: kinematics and dynamicsmasersstars: formationstars: individual: Cepheus A HW2