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Rotating and infalling motion around the high-mass young stellar object Cepheus A-HW2 observed with the methanol maser at 6.7 GHz

Citation

Sugiyama, K and Fujisawa, K and Doi, A and Honma, M and Kobayashi, H and Murata, Y and Motogi, K and Niinuma, K and Ogawa, H and Wajima, K and Sawada-Satoh, S and Ellingsen, SP, Rotating and infalling motion around the high-mass young stellar object Cepheus A-HW2 observed with the methanol maser at 6.7 GHz, Astronomy and Astrophysics, 562 Article A82. ISSN 1432-0746 (2014) [Refereed Article]


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Copyright Statement

Copyright 2014 EDP Sciences

DOI: doi:10.1051/0004-6361/201321278

Abstract

Context: Proper motion observations of masers can provide information on dynamic motions on scales of a few milliarcseconds per year (mas yr-1) at radii of 1001000 au scales from central young stellar objects (YSOs).

Aims: The 6.7 GHz methanol masers are one of the best probes for investigations of the dynamics of high-mass YSOs, and in particular for tracing the rotating disk. We have measured the internal proper motions of the 6.7 GHz methanol masers associated with Cepheus A (Cep A) HW2 using Very Long Baseline Interferometery (VLBI) observations.

Methods: We conducted three epochs of VLBI monitoring observations of the 6.7 GHz methanol masers in Cep A-HW2 with the Japanese VLBI Network (JVN) over the period 20062008. In 2006, we were able to use phase-referencing to measure the absolute coordinates of the maser emission with an accuracy of a few milliarcseconds. We compared the maser distribution with other molecular line observations that trace the rotating disk.

Results: We measured the internal proper motions for 29 methanol maser spots, of which 19 were identified at all three epochs and the remaining ten at only two epochs. The magnitude of proper motions ranged from 0.2 to 7.4 km s-1, with an average of 3.1 km s-1. Although there are large uncertainties in the observed internal proper motions of the methanol maser spots in Cep A, they are well fitted by a disk that includes both rotation and infall velocity components. The derived rotation and infall velocities at the disk radius of 680 au are 0.50.7 and 1.80.7 km s-1, respectively.

Conclusions: Assuming that the modeled disk motion accurately represents the accretion disk around the Cep A-HW2 high-mass YSO, we estimated the mass infall rate to be 3נ10-4n8Myr-1 (n8 is the gas volume density in units of 108cm-3). The combination of the estimated mass infall rate and the magnitude of the fitted infall velocity suggests that Cep A-HW2 is at an evolutionary phase of active gas accretion from the disk onto the central high-mass YSO. The infall momentum rate is estimated to be 5נ10-4n8Myr-1kms-1, which is larger than the estimated stellar radiation pressure of the HW2 object, supporting the hypothesis that this object is in an active gas accretion phase.

Item Details

Item Type:Refereed Article
Keywords:stars: formation, ISM: individual objects: Cepheus A, masers, instrumentation: high angular resolution
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Galactic Astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Ellingsen, SP (Professor Simon Ellingsen)
ID Code:90106
Year Published:2014
Deposited By:Mathematics and Physics
Deposited On:2014-03-27
Last Modified:2015-04-24
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