Stratification of phosphorus in the atmosphere of the chemically peculiar B-type star HR 1512 |
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| Authors: | L S Lyubimkov D B Poklad T M Rachkovskaya |
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| Institution: | (1) Scientific Research Institute Crimean Astrophysical Observatory, Crimea, Ukraine |
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| Abstract: | A number of empirical relationships are shown to indicate an increase in the abundance of phosphorus logε(P) with height in the atmosphere of HR 1512. These include: (a) a correlation of logε(P) with the observed equivalent width Wobs of PII lines; (b) a correlation of logε(P) with the wavelength of the lines; (c) a systematic divergence in the values of logε(P) for lines with different excitation potentials El; in particular, lines with lower El correspond on the average to higher abundances logε(P); and, (d) a distinct dependence of logε(P) on the average geometrical height of formation, Hf. In addition, assuming that logε(P) is constant in the star's atmosphere leads to a systematic discrepancy between the theoretical equivalent widths Wth and the observed values Wobs. By a trial and error method we have found a distribution of the phosphorus abundance logε(P) with height H such that the systematic difference between Wth and Wobs vanishes. It turned out, however, that a simpler, step distribution of logε(P) yields equally good agreement between Wth and Wobs. Although the solution is nonunique, both distributions have some features in common, specifically: (1) a sharp rise in logε(P) occurs in the same range of heights H corresponding to optical thicknesses τ
5000 ≈ 10−2–10−3, i.e., stratification of phosphorus takes place in rather high layers of the atmosphere of HR 1512, and (2) the upper bound,
logε
up(P) = 8.9, is the same in both cases, so that in the region of the rise, logε(P) increases by 3.4 dex. A comparison with available data for HgMn, Am, and Ap type stars shows that similar sharp changes in
the abundances logε of several elements occur in other CP stars, at the same optical depths or in even higher layers of their atmospheres.
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Translated from Astrofizika, Vol. 51, No. 2, pp. 239–253 (May 2008). |
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| Keywords: | stars chemical peculiar abundances stratification |
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