# Submillimeter Array Imaging of the Maser Emission from the $$H30\alpha$$ Radio Recombination Line in MWC 349A

 Title: Submillimeter Array Imaging of the Maser Emission from the $$H30\alpha$$ Radio Recombination Line in MWC 349A Author: Weintroub, Jonathan; Moran, James M.; Wilner, David J.; Young, Ken Harbour; Rao, Ramprasad; Shinnaga, Hiroko Note: Order does not necessarily reflect citation order of authors. Citation: Weintroub, Jonathan, James M. Moran, David J. Wilner, Ken Harbour Young, Ramprasad Rao, and Hiroko Shinnaga. 2008. “Submillimeter Array Imaging of the Maser Emission from the $$H30\alpha$$ Radio Recombination Line in MWC 349A.” Astrophysical Journal 677 (2) (April 20): 1140-1150. doi:10.1086/529132. Full Text & Related Files: moran-submillimeter-array.pdf (528.6Kb; PDF) Abstract: We used the Submillimeter Array to map the angular distribution of the H30α recombination line (231.9 GHz) in the circumstellar region of the peculiar star MWC 349A. The resolution was 1.2'', but because of high signal-to-noise ratio we measured the positions of all maser components to accuracies better than 0.01'', at a velocity resolution of $$1 km s^{−1}$$. The two strongest maser components (called high-velocity components) at velocities near –14 and $$32 km s^{−1}$$ are separated by 0.048'' ± 0.001'' (60 AU) along a position angle of 102° ± 1°. The distribution of maser emission at velocities between and beyond these two strongest components were also provided. The continuum emission lies at the center of the maser distribution to within 10 mas. The masers appear to trace a nearly edge-on rotating disk structure, reminiscent of the water masers in Keplerian rotation in the nuclear accretion disk of the galaxy NGC 4258. However, the maser components in MWC 349A do not follow a simple Keplerian kinematic prescription with v ~ $$r^{−1/2}$$, but have a larger power-law index. We explore the possibility that the high-velocity masers trace spiral density or shock waves. We also emphasize caution in the interpretation of relative centroid maser positions where the maser is not clearly resolved in position or velocity, and we present simulations that illustrate the range of applicability of the centroiding method. Published Version: doi:10.1086/529132 Other Sources: http://arxiv.org/abs/0801.0608 Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:11595848 Downloads of this work: