Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21113801f&link_type=abstract
American Astronomical Society, AAS Meeting #211, #138.01; Bulletin of the American Astronomical Society, Vol. 39, p.983
Astronomy and Astrophysics
Astronomy
Scientific paper
In a comprehensive survey of observations from the high resolution spectrographs onboard the Hubble Space Telescope, the Goddard High-Resolution Spectrograph (GHRS) and the Space Telescope Imaging Spectrograph (STIS), we have detected interstellar CII absorption for the 1334.5 Angstrom ground-state transition and the 1335.7 Angstrom (doublet) collisionally populated excited-state transition for sightlines toward stars within 100 parsecs. We derive column densities of CII in each of the states and use methods implemented by Wood & Linsky (1996) to measure the electron volume densities along the lines of sight. Electron volume densities in the Local Interstellar Medium (LISM) are particularly difficult to ascertain, but are essential for understanding the ionization structure of the LISM and density variations which impact the morphology of the heliosphere. To combat systematic error due to the saturation of the CII resonance line, we also use SII measurements as a proxy to determine column densities. Our sample consists of 13 stars, a significant improvement in the number of measurements that allows us to search for variations in density for the first time. Our mean volume densities are n_e=0.10 +0.12 or -0.05 cm^-3 and, based on SII as a proxy, n_e(CII_SII)=0.13 +0.14 or -0.07 cm^-3. We identify sightlines with interstellar clouds and, when available, investigate the cloud's self-shielding of ionizing sources.
Falcon Ross
Redfield Seth
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