Hostname: page-component-586b7cd67f-t7czq Total loading time: 0 Render date: 2024-11-26T22:41:39.974Z Has data issue: false hasContentIssue false

Optical Observations of Nearby Interstellar Gas

Published online by Cambridge University Press:  12 April 2016

P.C. Frisch
Affiliation:
Astronomy and Astrophysics Center, University of Chicago
D.G. York
Affiliation:
Astronomy and Astrophysics Center, University of Chicago

Extract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The yellow D lines from neutral sodium are some of the most useful interstellar absorption features for tracing out low density optically thin interstellar material. Hobbs (1978) compared column densities of Nal as determined from the D lines with HI column densities derived from ultraviolet observations and found values of N(NaI)/N(H)<6.3x10-9 in 18 sight-lines with very low reddening, with the exact value of the ratio apparently a function of temperature. If this ratio limit holds for diffuse clouds in nearby space, we expect that observations of the Nal D2 lines at the 3 mA level can be used to trace out nearby clouds with column densities in the range of ≥2.5x1018 cm-2. Thus sensitive measurements of the Nal D lines are a useful way of observing nearby neutral cloud material. With this in mind, we have chosen high-resolution observations of the yellow sodium lines as a means of locating and mapping nearby low density interstellar clouds.

Type
The LISM at Optical Wavelengths: Spectral Line Studies
Copyright
Copyright © NASA 1984

References

Cleary, M.N., Heiles, C., and Haslam, C.G.T. 1979, Astr. Ap. Sup., 36, 95.Google Scholar
Crutcher, R.M. 1982, Ap. J. 254, 82.CrossRefGoogle Scholar
Frisch, P.C. 1981, Nature, 293, 377.Google Scholar
Herbig, G.H. 1968, Zs. F. Ap., 68, 243.Google Scholar
Hirshfeld, A., and Sinnott, R.W. (ed.) 1982, Sky Catalogue 2000.0 (Cambridge University Press and Sky Publishing Corporation)Google Scholar
Hobbs, L.M. 1978, Ap. J., 222, 491.CrossRefGoogle Scholar
Morton, D.C. 1975, Ap. J., 197, 85.Google Scholar
Tinbergen, J. 1982, Astro. Ap., 105, 53.Google Scholar