Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278..549b&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 2, p. 549-560
Astronomy and Astrophysics
Astrophysics
52
Calcium, Interstellar Gas, Molecular Clouds, Ratios, Sodium, Absorption Spectra, High Resolution, Line Of Sight, Space Temperature, Spectral Resolution
Scientific paper
We have measured Na/Ca II column-density ratios in the local interstellar medium (LISM) within 30 pc. Thanks to a very high spectral resolution, these ratios are those of the individual clouds we are able to separate. Na I spectra have been corrected for telluric absorptions with the help of synthetic spectra calculated according to each type of observing conditions, allowing to detect extremely low Na I quantities in the LISM. The warm LISM Na I/Ca II ratio is typically smaller than 0.5 with an average value of 0.22. This strongly confirms the observed tendency for the ratio to decrease below 0.5 in the vicinity of the Sun (Welsh et al. 1991). In the very close gas detected between lII = 240 deg and lII = 50 deg, the Na I/Ca II ratio is 0.15 +/- 0.05. In the local interstellar cloud (LIC) surrounding the Sun, now clearly detected, we have derived an upper limit of 0.2, while there are indications that this limit is very close to the real value. The temperature of the LIC being 7000 K, this makes the ratio very little dependent on the electron density and allows to estimate the calcium depletion found to be deltaCa = -1.6 +/- 0.3. According to the depletion density relationship (Phillips et al. 1984), this is a standard depletion for a approx. 0.1/cu cm density cloud.
Bertin P.
Ferlet Roger
Lallement Rosine
Vidal-Madjar Alfred
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