Measurements were carried out on the CO J = 3-2 emission line at 345 GHz from a number of translucent and high-latitude molecular clouds, as well as on the J = 2-1 and J = 1-0 lines of both the (C... Show moreMeasurements were carried out on the CO J = 3-2 emission line at 345 GHz from a number of translucent and high-latitude molecular clouds, as well as on the J = 2-1 and J = 1-0 lines of both the (C-12)O and (C-13)O. It is shown that the physical conditions in the high-latitude clouds are very similar to those in the translucent clouds. The densities derived from measured (C-12)O 1-0/3-2 ratios were often found to be higher than those based on the C2 excitation, while densities derived from measured 3-2/(C-13)O 1-0 ratios were similar to those based on C2. Show less
High resolution solar spectra obtained from the ATMOS Fourier Transform Spectrometer (Spacelab 3 flight on April 29-May 6, 1985) have made it possible to identify and measure a large number of... Show moreHigh resolution solar spectra obtained from the ATMOS Fourier Transform Spectrometer (Spacelab 3 flight on April 29-May 6, 1985) have made it possible to identify and measure a large number of lines of the vibration-rotation fundamental bands of the X2 Pi state of CH. From about 100 lines of the 1-0, 2-1, and 3-2 bands and adopting theoretical transition probabilities, a solar carbon abundance of 8.60 + or - 0.05 is derived. This value is compared with new results inferred from other carbon abundance indicators. The final recommended solar abundance of carbon is 8.60 + or - 0.05. Show less
Interstellar absorption-line spectroscopy of NGC 2264 is reported which shows that the CO molecule has a column density of 5 x 10 to the 18th/sq cm and a rotational excitation temperature of 28 K.... Show moreInterstellar absorption-line spectroscopy of NGC 2264 is reported which shows that the CO molecule has a column density of 5 x 10 to the 18th/sq cm and a rotational excitation temperature of 28 K. A direct upper limit on the H2 column density implies that at least 6 percent of a solar carbon abundance is in the form of CO. The upper limit on the H3(+) abundance implies that the cosmic-ray ionization rate is of the order of 10 to the -16th/s or less. The H3(+) upper limit, together with a previous radio detection of H2D(+) emission, implies either an enormous overabundance of the deuterated molecule or else that most of the radio emission comes from clouds not located directly between use and the infrared source. Observations of the sources AFGL 2591 and NGC 2024 IRS2 indicate that upper limits on H3(+) imply cosmic ray ionization rates of less than 3 and 60 x 10 to the -17th/s, respectively. Show less
Recent high-resolution observations of interstellar absorption lines of CH and CN toward Zeta Oph obtained by Crane et al. (1986), and Palazzi et al. (1988), exhibit line widths that suggest... Show moreRecent high-resolution observations of interstellar absorption lines of CH and CN toward Zeta Oph obtained by Crane et al. (1986), and Palazzi et al. (1988), exhibit line widths that suggest thermal line broadening at high temperature, T about 1200 K. Observations of CO line emission at 2.6 mm toward Zeta Oph (Langer et al.,1987) indicate that the molecular gas resides in four distinct velocity components that span less than 3 km/s in Doppler velocity. Simulated CH and CN absorption line profiles are compared for high-temperature (T = 1200 K) thermal broadening and for a combination of low-temperature (T = 50 K) thermal plus turbulent broadening. It is shown that the two broadening models reproduce existing observations comparably well and are virtually indistinguishable at a lambda/Delta-lambda ratio of about 100,000. The observed differences in the CH and CN line widths may reflect slightly different distributions of those molecules along the line of sight. The simulations use very recent, improved laboratory spectroscopic data on CH (Bernath). Some related consequences of such unresolved velocity structure on the ultraviolet absorption lines of CO are examined. Indirect diagnostics of temperature in the Zeta Oph cloud favor low-temperature thermal plus turbulent broadening, and the implied rate of dissipation of turbulence is in harmony with estimates of the global input of mechanical energy into to interstellar medium. Show less
Interstellar absorption lines of CH and CH(+) have been detected toward the star HD 210121, which is located behind a previously unknown high-latitude cloud. The CH observations and the measured... Show moreInterstellar absorption lines of CH and CH(+) have been detected toward the star HD 210121, which is located behind a previously unknown high-latitude cloud. The CH observations and the measured extinction toward the star provide independent measures of the H2 column density along the line of sight, which are compared with that deduced from CO mm observations. The inferred CH(+) column density is comparatively small, suggesting that shocks do not play a dominant role in the chemistry in the cloud. Show less
The effects of the presence of a substantial component of large molecules on the chemistry of diffuse molecular clouds are explored, and detailed models of the zeta Persei and zeta Ophiuchi clouds... Show moreThe effects of the presence of a substantial component of large molecules on the chemistry of diffuse molecular clouds are explored, and detailed models of the zeta Persei and zeta Ophiuchi clouds are constructed. The major consequence is a reduction in the abundances of singly charged atomic species. The long-standing discrepancy between cloud densities inferred from rotational and fine-structure level populations and from the ionization balance can be resolved by postulating a fractional abundance of large molecules of 1 x 10 to the -7th for zeta Persei and 6 x 10 to the -7th for zeta Ophiuchi. If the large molecules are polycyclic aromatic hydrocarbons (PAH) containing about 50 carbon atoms, they contain 1 percent of the carbon in zeta Persei and 7 percent in zeta Ophiuchi. Other consequences of the possible presence of PAH molecules are discussed. Show less
The limitations of steady state models of interstellar clouds are explored by means of comparison with observational data corresponding to clouds in front of Zeta Per, Zeta Oph, Chi Oph, and... Show moreThe limitations of steady state models of interstellar clouds are explored by means of comparison with observational data corresponding to clouds in front of Zeta Per, Zeta Oph, Chi Oph, and Omicron Per. The improved cloud models were constructed to reproduce the observed H and H2(J) column densities for several lines of sight. The main difference from previous models is the treatment of self-shielding in the H2 lines. Other improvements over previous models are discussed as well. Show less
Observations of C2 in the (3,O) band around 7720 A toward Zeta Ophiuchi are presented and used to provide additional support for the suggestion of a low temperature in the center of the principal... Show moreObservations of C2 in the (3,O) band around 7720 A toward Zeta Ophiuchi are presented and used to provide additional support for the suggestion of a low temperature in the center of the principal cloud toward that star. Twelve absorption features belonging to the P, Q, and R branches and originating from levels up to J-double prime = 10 can be identified. Measured equivalent widths and the column densities obtained from them by assuming a linear relationship are presented. The column densities in the various rotational levels generally agree well with those found from observations of C2 in the (2,0) Phillips band around 8750 A. The observed C2 rotational distribution implies a low kinetic temperature of roughly 30 K and a relatively low but uncertain density of roughly 200/cm in the center of the cloud. Show less
Grevesse, N.; Sauval, A.J.; Dishoeck, E.F. van 1984
High resolution solar spectra have permitted the measurement with great accuracy of equivalent widths of vibration-rotation lines of OH in the X2Pi state near 3-micron wavelength. Using recent... Show moreHigh resolution solar spectra have permitted the measurement with great accuracy of equivalent widths of vibration-rotation lines of OH in the X2Pi state near 3-micron wavelength. Using recent theoretical results for the transition probabilities, a solar oxygen abundance of (8.93 + or - 0.02) is derived which is in perfect agreement with the abundance deduced from the OH pure rotation lines. The solar abundance of oxygen is therefore A(O) = 8.92 + or - 0.035, as inferred from the analysis of 43 vibration-rotation lines and 81 pure rotation lines of the OH molecule. It is confirmed that the dipole moment function of Werner, Rosmus and Reinsch (1983) together with the Holweger-Mueller (1974) solar atmosphere model are to be preferred in the analysis of the data. Show less
