Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.3017l&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #30.17; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astronomy
1
Scientific paper
We used the ARO 12-m radio telescope at Kitt Peak, AZ, to search for new millimeter-wavelength, high-rotational-excitation methanol masers at 146.6 and 156.8 GHz in nine galactic sources: DR21, DR21N, DR21(OH), NGC7538M, NGC7538S, NGC7538W, NGC7538(IRS9), W75N, and W75N(OFF). Some of these sources were recently discovered by one of us (P.P.) as new sources of the 44 GHz methanol maser line. The 146.6 GHz line was detected in all the sources except W75N(OFF). The 156.8 GHz line was detected in DR21, DR21(OH), NGC 7538(IRS9), and W75N. The total radial velocity interval of detectable spectral features is typically less than 5 km s-1. The low-intensity broad spectral ``pedestal’ (due to thermal radiation from the surrounding cloud or the overlapping of narrow masing components) is seen in both lines. Strong narrow components were seen only in the 146.6 GHz line. For the four sources where both lines were detected, the 147/157 peak intensity ratio varies in broad limits, from approximately 1 to more than 15. Available statistical equilibrium calculations of methanol level populations allow one to suppose that the 147/157 ratio may be a steep function of the gas density and/or temperature in the masing condensations. If this hypothesis is correct, the 147/157 line ratio may become a sensitive probe of physical conditions in Class I methanol masers, along with the 44/36 GHz ratio first proposed as a diagnostic tool by one of us (P.P.). More statistical equilibrium calculations are needed to make this potential probe a quantitative one. This project was supported by the NSF/REU grant AST-0354056 and the Nantucket Maria Mitchell Association.
Lemonias Jenna J.
Pratap Preethi
Strelnitski Vladimir
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