Hydrogen Masers. II. MWC 349A
1996; IOP Publishing; Volume: 470; Linguagem: Inglês
10.1086/177937
ISSN1538-4357
AutoresV. Strelnitski, H. A. Smith, V. O. Ponomarev,
Tópico(s)Astrophysics and Star Formation Studies
Resumoview Abstract Citations (25) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrogen Masers. II. MWC 349A Strelnitski, Vladimir S. ; Smith, Howard A. ; Ponomarev, Victor O. Abstract The conditions of masing and lasing in the hydrogen recombination lines (HRLs) in the disk and outflow of MWC 349A are studied. Comparison of the observed integrated fluxes of virtually all the α-lines measured in this source from H2α through H92α with a simple model of spontaneous emission shows that observable HRL masing is limited to the interval of the principal quantum numbers n ≈ 10-40. We use our analytical and numerical results for the conditions of optimum masing and the morphological parameters of the photoevaporated circumstellar disk modeled by Hollenbach and coworkers to obtain analytical approximations and quantitative estimates for the expected unsaturated maser gain and the degree of saturation in HRL masers in the disk of MWC 349A. It is shown that the unsaturated gains of the infrared HRL lasers should be very high, but in fact all of these lasers are strongly saturated. Because of saturation, their relative intensity with respect to the spontaneous emission should drop steeply toward smaller n's, which explains why optical and near-infrared HRL lasers are not seen in MWC 349A. This result is quite general and makes the prognosis for observable high-frequency HRL lasers in other sources pessimistic as well. An exception might arise because of special geometry, if lasing were confined to a very small solid angle. We show that weak masing from the outflow of MWC 349A is only possible in low-n α-lines (n ≲ 20-30), and then only if the outflow begins much closer to the central star than the Hollenbach model predicts (≈3 x 1015 cm). We therefore conclude that maser emission from the disk, rather than from the outflow, is responsible for the observed weak amplification of the "pedestal" spectral components in the α-lines with n ≲ 40. The fluxes in the lower frequency α-lines are well explained by spontaneous emission from the outflow, with proper corrections for free-free absorption. We review the current state and prospects of observations of masing and lasing hydrogen β-lines in MWC 349A. We argue in favor of "close in n," rather than "close in frequency" α/β pairs for intensity analysis, when maser amplification is present. Publication: The Astrophysical Journal Pub Date: October 1996 DOI: 10.1086/177937 arXiv: arXiv:astro-ph/9511119 Bibcode: 1996ApJ...470.1134S Keywords: STARS: INDIVIDUAL ALPHANUMERIC: MWC 349; STARS: MASS LOSS; MASERS; RADIO LINES: STARS; Astrophysics E-Print: 21 pages (plain TeX), 3 encapsulated PostScript figures (tared and compressed) full text sources arXiv | ADS | data products SIMBAD (2) Related Materials (1) Part 1: 1996ApJ...470.1118S
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