NGC-7538 IRS-1 - SUBARCSECOND RESOLUTION RECOMBINATION LINE AND (NH3)-N-15 MASER OBSERVATIONS

The (NH3)-N-15 (J, K) = maser emission associated with NGC 7538 IRS 1 has been imaged with 0".2 resolution. The masers are distributed in a 0".2 region coincident with the 1.3 cm wavelength continuum core of the NGC 7538 IRS 1 H II region. The strongest (NH3)-N-15 masers are found concentrated in two regions separated by approximately 0".2. These masers may be amplifying the strong double-lobe radio continuum core of the IRS 1 H II region. The velocities of the (NH3)-N-15 masers range from -62 to -53 km s-1 and show a systematic velocity gradient from SW (-62 km s-1) to NE (-52 to -54 km s-1). The orientation of this gradient is similar to that found by Scoville et al. (1986) for the (CO)-C-13 emission toward IRS 1. The orientation of this several hydrogen recombination line transitions are reported. These observations show that the velocity of the IRS 2 H II region is similar to that of the ambient molecular cloud, almost-equal-to -65 km s-1. However, unlike IRS 2, the IRS 1 H II region is significantly redshifted with respect to the molecular cloud. The velocity of the IRS 1 H II region, as determined from H 76-alpha data, is almost-equal-to -22 km s-1. We interpret this as implying that the ionized gas is champagne flowing off the foreground molecular cloud.