Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21812912s&link_type=abstract
American Astronomical Society, AAS Meeting #218, #129.12; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
Using the Expanded Very Large Array and the Green Bank Telescope, we have observed the ammonia maser in NGC 7538 for the first time since its discovery in 1984. We present the first interferometric observations of the maser, demonstrating the nonthermal nature of the emission and providing a precise location for the maser in the star-forming complex. We also detect several new maser components that have appeared in the last 25 years. This maser is the nonmetastable (J,K) = (9,6) transition of ammonia at 18.5 GHz.
We present a single epoch of observation with the EVLA in September 2010 and two epochs with the GBT in December 2010 and January 2011, with the following results: (1) We find several new emission peaks near -56 km/s in addition to the known emission near -60 km/s. All of the emission features have flux densities of approximately 1 Jy. (2) In GBT observing epochs separated by six weeks we do not find any of the maser features to vary in intensity. (3) In both the GBT and EVLA data, we resolve spectrally the emission feature near -60 km/s into two peaks and the emission features near -56 km/s into at least four peaks, all with widths of approximately 0.5 km/s. (4) At the three-arcsecond angular resolution of the EVLA observations, we find all of the maser features to be spatially coincident with each other on the sky and to lie at the location of the compact HII region IRS1. (5) The maser features are angularly unresolved in the EVLA images, indicating a lower limit of 500 K brightness temperatures. Given equivalent thermal line widths of 100 K, these brightness temperatures indicate nonthermal emission.
This work is supported by the Thomas Penrose Bennett Prize Fund and the Lovejoy Science Fund of St. Paul's School.
Hoffman Ian M.
Seojin Kim Stella
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