Modeling of the hydrogen maser disk in MWC 349

Details Modeling of the hydrogen maser disk in MWC 349 Modeling of the hydrogen maser disk in MWC 349

Apr 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...424..976p&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 424, no. 2, p. 976-982

Astronomy and Astrophysics

Astronomy

30

Approximation, Astronomical Models, Hydrogen Masers, Hydrogen Recombinations, Radio Astronomy, Radio Spectra, Stellar Envelopes, Doppler Effect, Electron Density Profiles, Electron Energy, Opacity, Optical Thickness, Ring Structures, Size Determination, Stellar Mass

Scientific paper

Maser amplification in a Keplerian circumstellar disk seen edge on-the idea put forward by Gordon (1992), Martin-Pintado, & Serabyn (1992), and Thum, Martin-Pintado, & Bachiller (1992) to explain the millimeter hydrogen recombination lines in MWC 349-is further justified and developed here. The double-peaked (vs. possible triple-peaked) form of the observed spectra is explained by the reduced emission from the inner portion of the disk, the portion responsible for the central ('zero velocity') component of a triple-peaked spectrum. Radial gradient of electron density and/or free-free absorption within the disk are identified as the probable causes of this central 'hole' in the disk and of its opacity. We calculate a set of synthetic maser spectra radiated by a homogeneous Keplerian ring seen edge-on and compare them to the H30-alpha observations of Thum et al., averaged over about 1000 days. We used a simple graphical procedure to solve an inverse problem and deduced the probable values of some basic disk and maser parameters. We find that the maser is essentially unsaturated, and that the most probable values of electron temperature. Doppler width of the microturbulence, and electron density, all averaged along the amplification path are, correspondingly, Te less than or equal to 11,000 K, Vmicro less than or equal to 14 km/s, ne approx. = (3 +/- 2) x 107/cu cm. The model shows that radiation at every frequency within the spectrum arises in a monochromatic 'hot spot.' The maximum optical depth within the 'hot spot' producing radiation at the spectral peak maximum is taumax approx. = 6 +/- 1; the effective width of the masing ring is approx. = 0.4-0.7 times its outer diameter; the size of the 'hot spot' responsible for the radiation at the spectral peak frequency is approx. = 0.2-0.3 times the distance between the two 'hot spots' corresponding to two peaks. An important derivation of our model is the dynamical mass of the central star, M* approx. = 26 solar masses (D/1.2 kpc), D being the distance to the star. Prospects for improving the model are discussed.

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