Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008ap.....51..197l&link_type=abstract
Astrophysics, Volume 51, Issue 2, pp.197-208
Astronomy and Astrophysics
Astrophysics
Stars, Chemical Peculiar, Abundances, Stratification
Scientific paper
A number of empirical relationships are shown to indicate an increase in the abundance of phosphorus logɛ(P) with height in the atmosphere of HR 1512. These include: (a) a correlation of logɛ(P) with the observed equivalent width Wobs of PII lines; (b) a correlation of logɛ(P) with the wavelength of the lines; (c) a systematic divergence in the values of logɛ(P) for lines with different excitation potentials El; in particular, lines with lower El correspond on the average to higher abundances logɛ(P); and, (d) a distinct dependence of logɛ(P) on the average geometrical height of formation, Hf. In addition, assuming that logɛ(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 logɛ(P) with height H such that the systematic difference between Wth and Wobs vanishes. It turned out, however, that a simpler, step distribution of logɛ(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 logɛ(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, logɛ up(P) = 8.9, is the same in both cases, so that in the region of the rise, logɛ(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 logɛ of several elements occur in other CP stars, at the same optical depths or in even higher layers of their atmospheres.
Lyubimkov Leonid S.
Poklad Dmitry B.
Rachkovskaya Tamara M.
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