Survey of interstellar C I: Insights on carbon abundances, UV grain albedos, and pressures in the interstellar medium

Journal Article · Sun Jul 01 00:00:00 EDT 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/157163· OSTI ID:6097440

Jenkins, E B; Shaya, E J

Interstellar absorption lines of C I have been analyzed for 33 stars with 0.05 < or = E (B - V) < or = 0.50 observed by the Copernicus satellite. For about half of the stars C I was detected in one or two of the states of fine-structure excitation, and for many other cases upper limits for the excited populations could be derived. The degrees of excitation revealed that much of the interstellar gas containing C I exists at pressures p/k<10/sup 4/ cm/sup -3/ K but that a small fraction of the material is at p/k> or approx. = 10/sup 5/ cm/sup -3/ K.The C I column densities scale with those of hydrogen (atomic plus molecular) to approximately the 2.5 power but with considerable scatter in the relationship. A much tighter correspondence was found between C I and Na I or K I, but the trends are steeper than linear, an effect we attribute to the greater shielding of carbon-ionizing photons by dust in the thicker clouds. We conclude that the attenuation of radiation below 1100 A is more rapid than that at longer wavelengths by more than the ratio of extinctions. A simple interpretation of this phenomenon is that grain albedos decrease from about 0.5 at 5 ..mu..m/sup -1/< or approx. =lambda/sup -1/< or approx. =7 ..mu..m/sup -1/ to less than about 0.2 for the range 9 ..mu..m/sup -1/<11 ..mu..m/sup -1/. The abundance of C relative to that of Na or K is very close to the solar ratio. Depletions of carbon with respect to the total amount of hydrogen appear to range from none at all to a factor of 10, but a sensitivity to assumptions about some of the physical conditions within clouds may lead to errors in this result.

• Research Organization: Princeton University Observatory
• OSTI ID: 6097440
• Journal Information: Astrophys. J.; (United States), Vol. 231:1
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON
COSMOCHEMISTRY
INTERSTELLAR SPACE
CHEMICAL COMPOSITION
ABSORPTION SPECTRA
ABUNDANCE
ALBEDO
ATTENUATION
COSMIC GASES
FINE STRUCTURE
INTERSTELLAR GRAINS
IONIZATION
SPECTRAL DENSITY
STARS
ULTRAVIOLET SPECTRA
CHEMISTRY
ELEMENTS
FLUIDS
FUNCTIONS
GASES
NONMETALS
PARTICLES
SPACE
SPECTRA
SPECTRAL FUNCTIONS
640105* - Astrophysics &amp; Cosmology- Galaxies