Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...482l.105s&link_type=abstract
Astrophysical Journal Letters v.482, p.L105
Astronomy and Astrophysics
Astronomy
96
Ism: Dust, Extinction, Ism: Abundances, Ultraviolet: Ism
Scientific paper
We have obtained spectra of the interstellar intersystem C II] lambda 2325 line toward the star tau Canis Majoris. The absorption spectra were obtained with the echelle mode (3.5 km s-1 resolution) of the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope and have a co-added signal-to-noise ratio of approximately 850. The C II] line has a measured equivalent width W lambda = 0.21 +/- 0.07 mA, which corresponds to a column density of 7.6 +/- 2.5 x 1016 cm-2. Of the six interstellar lines of sight that have reliably measured (>2 sigma ) carbon abundances, the tau CMa sight line has the lowest fractional H2 abundance, f(H2), by over 3 orders of magnitude. Although this suggests that the physical conditions in the interstellar gas toward tau CMa are different from the other sight lines, the measured gas-phase C/H ratio is the same: 106 C/H = 135 +/- 46 for tau CMa versus 106 C/H = 140 +/- 20 for the others (Cardelli et al.). The constant interstellar gas-phase C/H over a wide range of f(H2) suggests that even under very different conditions, no carbon is being exchanged between the gas and dust phases of the interstellar medium. It also supports, and extends to a larger distance, the suggestion by Cardelli et al. that the intrinsic (gas-phase plus dust-phase) interstellar C/H ratio in the vicinity of the Sun is constant and below the solar C/H value.
Cardelli Jason A.
Guerin Kenneth P.
Meyer David M.
Sofia Ulysses John
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