R.B. Loren

Cyanoacetylene as a density probe of molecular clouds

Total gas volume densities have been estimated for a sample of 19 molecular clouds from observations of HC/sub 3/N. These density estimates are based on observations of only the J = 5--4 and j = 9--8 transitions for 10 clouds. Better estimates were possible for the nine clouds in which three or more transitions were detected. Isothermal, homogeneous-density models could be fitted to the multi-line data for four clouds; only one cloud (Sgr B2) required a two-component model. The data are consistent with the more elaborate density-gradient models published for the S140 and L1529 coulds.

Detection of interstellar CO/sup +/ toward OMC-1

We report the detection of CO/sup +/ toward OMC-1. The identification is based on the detection of only one line, the N = 2-1, J = 5/2--3/2 transition at 236.063 GHz. The CO/sup +/ column density we derive in OMC-1 is approx.2 x 10/sup 12/ cm/sup -2/, implying an abundance of CO/sup +/ one to three orders of magnitude greater than that predicted by models of ion-molecule chemistry in molecular clouds. The CO/sup +/ emission may originate from the same region in OMC-1 which produces the carbon recombination lines.

High-temperature cyanide in Orion molecular cloud 1

The K = 0 through K = 6 lines of the J = 13--12 and J = 12--11 rotational transitions of methyl cyanide (CH/sub 3/CN) at 239 GHz and 221 GHz have been observed toward OMC-1. The relative strengths of the ..delta..K = 0 transitions have been used to obtain the excitation temperatures of the CH/sub 3/CN emitting region. The easily excited K = 0 to K = 2 transitions yield T/sub EX/ roughly-equal80--120 K, while the higher excitation K = 4 to K = 6 transitions yield much greater temperatures: T/sub EX/ roughly-equal270 K. At least two regions of distinct T/sub EX/ and also distinct V/sub LSR/ and velocity dispersion are present. The low temperature region is characterized by a small CH/sub 3/CN line width (..delta..Vroughly-equal5 km s/sup -1/) and a V/sub LSR/ roughly-equal9 km s/sup -1/. The hot region has larger velocity dispersion (..delta..Vroughly-equal8 km s/sup -1/) and V/sub LSR/ roughly-equal6 km s/sup -1/.

Calibration of millimeter-wavelength spectral lines−effect of harmonic mixer response

The cooled Schottky-diode receivers used to observe millimeter-wavelength spectral lines exhibit harmonic response, that is, response in sidebands associated with harmonics of the local oscillator frequency. Ignoring this response leads to a systematic error if the line intensities are calibrated by observing braod-band noise sources. The inferred line intensities are all lower than the true values. Experimental data confirm the relevance of the effect for astronomical observations. Although the error is not large, careful observers should be aware of it for projects that require exceptionally well-calibrated data. 8 references.

High resolution J = 2--1 and J = 1--0 carbon monoxide self-reversed line profiles toward molecular clouds

High resolution spectra of the J = 2--1 and J = 1--0 transitions of /sup 12/Co and /sup 13/Co have been obtained toward eight molecular clouds which have self-reversed /sup 12/CO line profiles. Accurate comparison of these two transitions is used to infer some of the physical conditions in the cloud cores and the absorbing envelopes.

Temperature gradients across the Rho Oph B1/B2 molecular core: The effects of heating by low luminosity stars on cloud cores

The nearby (160 pc) p Ophiuchi molecular cloud complex offers a laboratory for studying the effects of molecular core heating by young stars. We mapped the cold dense cores Rho Oph B1/B2 and L1689N in both DCO+(J=I -0) and H13CO+(J=1-0). Since the enhancement of DCO + relative to H13CO + varies strongly with temperature, the smM1 scale heating of the gas by the young stars in the area can be measured.

C2H and HC3N in Interstellar Clouds

A survey for the molecules C 2 H and HC 3 N in a variety of interstellar clouds has been completed. Both molecules are very widespread, in cold dark clouds as well as in hot clouds. C 2 H emission has been mapped in L1534. In cold clouds the fractional abundance X(C 2 H) is found to be 2-6×10 −9 . The ratio of abundances X(C 2 H)/X(HC 3 N) falls in the range 6-10, consistent with some gas-phase reaction schemes for these molecules.

C 2 H and HC 3 N in Interstellar Clouds

A survey for the molecules C 2 H and HC 3 N in a variety of interstellar clouds has been completed. Both molecules are very widespread, in cold dark clouds as well as in hot clouds. C 2 H emission has been mapped in L1534. In cold clouds the fractional abundance X(C 2 H) is found to be 2-6×10 −9 . The ratio of abundances X(C 2 H)/X(HC 3 N) falls in the range 6-10, consistent with some gas-phase reaction schemes for these molecules.