Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...415l..59c&link_type=abstract
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 415, no. 1, p. L59-L62.
Astronomy and Astrophysics
Astrophysics
28
Atomic Energy Levels, Electron States, Line Spectra, Silicon, Transition Probabilities, Radiative Lifetime, Ultraviolet Spectra
Scientific paper
Intensity ratios of lines of the spin-changing 'intersystem' multiplet of S II (4P yields 2P0) at 234 nm have been used to determine electron densities and temperatures in a variety of astrophysical environments. However, the accuracy of these diagnostic calculations have been limited by uncertainties associated with the available atomic data. We report the first laboratory measurement, using an ion-trapping technique, of the radiative lifetimes of the three metastable levels of the 3s3p2 4P term of Si II. Our results are 104 +/- 16, 406 +/- 33, and 811 +/- 77 micro-s for lifetimes of the J = 1/2, 5/2, and 3/2 levels, respectively. A-values were derived from our lifetimes by use of measured branching fractions. Our A-values, which differ from calculated values by 30 percent or more, should give better agreement between modeled and observed Si II line ratios.
Bergeson S. D.
Calamai Anthony G.
Smith Peter L.
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