Accession Number : ADA018646

Title :   Observations of Heavy-Element Recombination Lines in the Rho Ophiuchi Dark Cloud at 13 CM Wavelength,


Personal Author(s) : Knapp,G. R. ; Kuiper,T. B. H. ; Brown,Robert L.

Report Date : 1975

Pagination or Media Count : 19

Abstract : 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 1/6 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 n(H) approximately equal to 25000/cc, 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.

Descriptors :   *Radiofrequency spectroscopy, *Interstellar matter, Dust clouds, Line spectra, Gas ionization, Physical properties, Nebulae, Hydrogen, Carbon, Sulfur, Iron, Magnesium, Silicon, Wavelengths, Emission spectra, Extraterrestrial radio waves

Subject Categories : Astrophysics

Distribution Statement : APPROVED FOR PUBLIC RELEASE