J. B. Whiteoak

Synthesis images of 6.7-GHz methanol masers

We have produced images of a number of galactic methanol sources in the 6.7 GHz (51−60A+) transition, and compared them with earlier maps of the 12.2-GHz (20 - 3-1 E) methanol masers. We find that, in several cases, the 6.7-GHz and 12.2-GHz maser positions are coincident to within 20 milliarcsec, placing a tight constraint on pumping mechanisms. We also confirm the 12.2-GHz result that the methanol masers tend to be located along lines, perhaps indicating jets, shock fronts, or edge-on protoplanetary discs.

Ammonia Observations of NGC 6334 I(N)

Coincident with the far-infrared source NGC 6334 I(N) and water maser source E is a massive dense cloud which has the most intense ammonia (1, 1) emission of any known interstellar cloud. We have mapped the (3, 3) emission and find the cloud is extended 0.8 pc in the direction parallel to the Galactic plane, and 0.5 pc perpendicular to it. It has a velocity gradient of 1 km/s.pc perpendicular to the Galactic plane. The gas kinetic temperature is about 30 K and the density is greater than 10(exp 6)/cc. The mass of the cloud is about 3000 solar mass, 3 times greater than previously estimated. The para-ammonia column density is 6 - 8 x 10(exp 15)/sq cm. An ammonia abundance of 0.5 - 1.5 x 10(exp -8) is inferred, where the larger number assumes an early time ortho/para ratio. This suggests either a cloud age of less than approximately 10(exp 6) yr, or substantial depletion of ammonia.

Refrigeration of the 18.3 GHz C_3H_2 Transition in Dark Clouds G1.6-0.25

We have observed 1 10 -1 01 (18.3 GHz) transition of ortho-cyclopropenylidene, C 3 H 2 , at 24 positions in the unusual dense cloud G1.6-0.025. Except for one position, the transition is refrigerated, a phenomenon which has not been seen in this transition before and was not predicted to occur. In general, the absorption correlates with the absorption seen in the 2 0 -3 −1 (12.2 GHz) transition of methanol, but there are significant differences. We suspect that collisional excitation at relatively high kinetic temperature (50 K) enhanced by photon trapping is responsible for the refrigeration

Detection of the 2(0) to 3(-1) transition of C-13H3OH at 14.8 GHz

Observations of the 2(0) to 3(-1) E-type transition of C-13H3OH at 14.78 GHz have been made toward the continuum sources Sgr A, Sgr B2, and W33. For the cases of Sgr B2 and one position in Sgr A, a C-12/C-13 abundance ratio of 40 is obtained which is much higher than the values (20-25) found for other molecules. For W33, the value 50 obtained (50) is lower than that derived from H2CO observations, but is comparable to that noted from CO observations.

Detection of the 20 → 3-1 Transition of 13CH3OH

The 20 → 3-1 E-type transition of 13CH3OH at 14.78 GHz has been detected towards four continuum sources: Sgr B2, two positions in Sgr A (the peaks of the ’+ 20 km/s’ and the ’40 km/s’ clouds), and W33. The NASA Deep Space Network 70-m antenna near Canberra, Australia, which has a 66 arcsec beam at this frequency, was used. A comparison of the 13C and 12C profiles for Sgr B2 indicates a rest frequency of 14,782.27 ±.03 MHz, 0.12 MHz above the laboratory value of Haque et al. (1974). For the Galactic Centre sources, the 12C/13C abundance ratios derived using the simplest assumptions lie in the range 30–40, higher than the 20–25 range derived from H2CO observations. For W33 the apparent value of ~50 is lower than the value of ~100 derived by Henkel et al. (1983) from H2CO.