HCO-C-13, AND (HCN)-C-12 APERTURE SYNTHESIS OBSERVATIONS OF THE CIRCUMNUCLEAR MOLECULAR RING IN THE GALACTIC-CENTER(, (HCN))

We observed Sgr A West in the J = 1 --> 0 transition lines of (HCN)-C- 13 and HCO+ with a spatial resolution of 12'' by 6'' and spectral reso lution of 4 km s-1 in 1988 and 1990 with the three-element millimeter interferometer at the Hat Creek Radio Observatory. We also remapped th e data of the (HCN)-C-12 J = 1 --> 0 spectral line data from Gusten et al. (1987) to match the scale and resolution of our (HCN)-C-13 and HC O+ maps. We find that the clumps in the ring have optical depths in (H CN)-C-12 J = 1 --> 0 in the range from 2 to 10 and that the HCO+ emiss ion is distributed similarly to the HCN emission, but that the abundan ce ratio [HCO+]/[HCN] appears to be 5 to 15 times lower than that meas ured in interstellar, quiescent molecular clouds. Model calculations o f the excitation of HCN and comparison with the HCN J = 3 --> 2 intens ities, reported by Jackson et al. (1992), suggest that the [HCN]/[H-2] abundance ratio is unusually large. We also find that the diameters o f the HCN emission regions in the clumps have diameters almost-equal-t o 0.05 to 0.12 pc with molecular gas densities in the range from 0.4 t o 5 x 10(6) cm-3. The most consistent model of the clumps, assuming T( gas) almost-equal-to 250 K, has tau(HCN J = 1 --> 0) almost-equal-to 4 and n(H-2) 2 x 10(6) cm-3 within regions of diameter d(clumps) almost -equal-to 0.1 pc, and molecular abundances [HCN]/[H-2] almost-equal-to 8 X 10(-8) and [HCO+]/[H-2] almost-equal-to 10(-9).