Observations of Heavy-Element Recombination Lines in the Rho Ophiuchi Dark Cloud at 13 CM Wavelength,
OWENS VALLEY RADIO OBSERVATORY PASADENA CALIF
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High-sensitivity observations at the carbon 140 alpha and 141 alpha recombination line frequencies in the direction of the Rho Ophiuchi dust cloud show the presence of recombination lines of carbon and sulfur, but not of other heavy elements. These results require that the elements Si, Fe and Mg are depleted by factors greater than 15, 10 and 2 respectively, most likely into interstellar grains, whereas sulphur is undepleted and that only approximately 16 of the carbon is present in the gas phase in the cloud. From the observed size of the CII region, theta is approximately equal to 3.2 arcmin, together with the observed carbon depletion, the authors infer that the density in the carbon-line-emitting region is nH approximately equal to 25000cc, and that the size of the SII region is significantly larger than that of CII region. The agreement between the widths of the recombination lines which arise in a small region of the cloud and those of the more widely distributed molecular species suggests that the lines in this cloud are broadened by microturbulence on a scale much 0.1 parsecs.