CAOSP abstracts, Volume: 27, No.: 3, year: 1998

Abstract: I have carried out spectrum synthesis of R = 120,000 spectra of several A and B stars having v sin i less than about 6 km/s. The following conclusions emerge: (1) As T(e) descends from 12,000 to 8,000 K, microturbulent velocity deduced from abundance analysis rises steadily from 0 to about 5 km/s. (2) Stars with microturbulent velocity greater or equal to 1 km/s show direct evidence in their line profiles of the presence of macroscopic gas motions in the form of line asymmetry (bisector curvature) which grows with increasing microturbulent velocity.(3) Above T(e) approx. 9,000 K, both weak and strong spectral lines can be modelled with reasonable accuracy by conventional LTE spectrum synthesis with a single assumed model atmosphere, abundance table, v sin i, and an appropriate (constant) value of microturbulent velocity. (4) In contrast, at T(e) approx. 8,000 K the weak spectral lines are much narrower than the strong lines. If the synthesis model is constrained in v sin i and microturbulent velocity by the weak lines, no satisfactory model can be found for the strong spectral lines. Consequently, chemical abundances for such stars based only on strong lines may be significantly in error.

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