Copernicus observations of C I: pressures and carbon abundances in diffuse interstellar clouds

Journal Article · Fri Jul 01 00:00:00 EDT 1983 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/161100· OSTI ID:5471333

Jenkins, E B; Jura, M; Loewenstein, M

Using the Copernicus satellite, we observed ultraviolet absorption lines of interstellar neutral carbon atoms toward 27 stars. In addition to deriving column densities of C I (both in its ground state and the two excited fine-structure levels), we used our equivalent widths to revise the f-values of some of the C I transitions measured by other investigators. We also observed H/sub 2/ from the J = 4 level so that we could compare the rotational excitation of H/sub 2/ with the fine-structure excitation of C I. From the amount of fine-structure excitation of C I in each case, we have derived information on the thermal gas pressures within the diffuse clouds. Most clouds have p/k between 10/sup 3/ cm/sup -3/ K and 10/sup 4/ cm/sup -3/ K, but we found that at least 6% of the C I-bearing material is at p/k>10/sup 4/ cm/sup -3/ K, and one-third of the gas has upper limits for pressure below 10/sup 3/ cm/sup -3/ K, assuming temperatures are not appreciably below 20 K. An analysis of radial velocities for the absorption lines showed no distinctive trends for the kinematics of high- or low-pressure gas components. From the apparent lack of acceleration of high-pressure clouds, we conclude that it is unlikely that streaming intercloud material is causing significant ram pressurization. We have compared our results with the predictions for pressure fluctuations caused by supernova explosions in the theory of McKee and Ostriker.

• Research Organization: Princeton University Observatory
• OSTI ID: 5471333
• Journal Information: Astrophys. J.; (United States), Vol. 270:1
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC GASES
GEOCHEMISTRY
ABSORPTION SPECTRA
ABUNDANCE
CARBON
CARBON IONS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
FINE STRUCTURE
HYDROGEN
INTERSTELLAR GRAINS
LINE WIDTHS
MOLECULES
RADIAL VELOCITY
ULTRAVIOLET SPECTRA
CHARGED PARTICLES
CHEMISTRY
ELEMENTS
FLUIDS
GASES
IONS
NONMETALS
PARTICLES
SPECTRA
VELOCITY
640105* - Astrophysics & Cosmology- Galaxies