Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........14s&link_type=abstract
Ph.D. Thesis Cornell Univ., Ithaca, NY.
Astronomy and Astrophysics
Astronomy
Astronomical Models, Clouds, Cosmic Dust, Infrared Astronomy, Interstellar Matter, Radio Astronomy, Carbon Monoxide, Color, Infrared Astronomy Satellite, Line Spectra, Microwave Spectra, Spatial Resolution, Visual Observation
Scientific paper
We present comprehensive radio, infrared, and optical observations of a diffuse interstellar cloud, and calculate the expected emission from interstellar grains. The cloud is unique in being relatively tenuous and very sharply defined both spatially and in velocity, and provides an almost ideal laboratory for study of the diffuse interstellar medium. We have mapped with high resolution the atomic gas in the cloud via the 21 cm line. The maximum H I column density is 4 x 1020 H-atom cm-2. Our sensitive search for carbon monoxide emission yielded an upper limit on the integrated CO intensity of 0.036 K km s-1, suggesting that little or no molecular material is present in the cloud. We present data on the cloud in the 12, 25, 60, and 100 micron bands from the Infrared Astronomical Satellite. The Inu(100)/NH ratio is 0.52 plus or minus 0.05 x 10-14 Jy sr-1 sq cm, comparable to previous surveys of lower spatial resolution. The Inu(60)/Inu(100) ratio is 0.32 plus or minus 0.03, about 50 percent larger than average values. The grain distribution in the cloud may have been modified by shocks. We have performed deep optical imaging in the B, V, R, and I bands, and have detected emission from the cloud at the level of 27-28 magnitudes per square arcsecond. The optical colors of the cloud show a slight excess in the R and I bands over predictions of a simple scattering model. This excess is not as large as that found in other investigations and may indicate that the particles responsible for excess red emission are severely dehydrogenated. We calculate the infrared emission from a grain model including stochastically heated small particles. To match the flux distribution of the cloud, 20 percent or more of the grain mass must consist of 5 A grains. We also compute photoelectric gas heating from these models and find that it is comparable with other estimates of heating and cooling. A very recent observational upper limit on (CII) emission from the cloud falls in the middle of the heating estimates.
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