Other
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21340919i&link_type=abstract
American Astronomical Society, AAS Meeting #213, #409.19; Bulletin of the American Astronomical Society, Vol. 41, p.210
Other
Scientific paper
Most of the emission lines observed with high or moderate resolution in MWC349A show a double-peaked structure. Although the double-peaked profiles of masing mm hydrogen recombination lines and the quasi-thermal near-IR lines have been explained by their formation in an edge-on Keplerian circumstellar disk (Hamann & Simon 1986; Gordon 1992), the double-peaked profiles of optical lines (Hα and HeI λ5876) were ascribed to the absorption central reversal (Hartmann et al. 1980). We obtained an Hα spectrum of MWC349A with the Kitt Peak 0.9-m Coudé Feed Telescope, with a resolution of 0.25Å per pixel. The double-peaked profile of the line and its equivalent width have not changed noticeably since the 1979 observations of Hartmann et al. Our numerical modeling shows that, in principle, the observed characteristics of the line can be explained by its formation in a differentially rotating disk, but, if it is the same Keplerian disk that gives rise to the masing hydrogen recombination lines, the Hα line should be formed in a very narrow (ΔR/R 0.01) ring and relatively far (a few A.U.) from the central star. The radiative transfer in the disk can hardly account for the observed broad wings of the double-peaked Hα profile; the electron scattering mechanism (Hartmann et al.) seems necessary to explain the wings. High resolution spectroscopy of other optical and IR lines will help discriminate between the two alternatives (disk vs. self-absorption) and shed more light on the structure and kinematics of the complex envelope of this unique object. This project was supported by the NSF/REU grant AST-0354056 and the Nantucket Maria Mitchell Association.
Ilsedore Cleeves Lauren
Joyce Richard R.
Strelnitski Vladimir
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