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Astron. Astrophys. 356, 517-528 (2000)

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3. Method of the analysis

To derive elemental abundances we employed both the spectral synthesis technique and equivalent width analysis (the latter only for stars with sharp lines). The spectral synthesis was performed using the SYNSPEC code developed and described by Hubeny, Lanz & Jeffery (1994), while the equivalent width analysis was based on the well-known Kurucz WIDTH9 code. While performing the spectral synthesis for the hot stars of our sample, special attention was paid to the accurate calculation of the [FORMULA] line profiles using updated Stark broadening parameters (for details see Hubeny, Lanz & Jeffery 1994).

Absolute abundance determinations depend dramatically upon the oscillator strengths selected for the analysis. For stars with intermediate temperatures, one can employ oscillator strengths based on solar spectroscopic data and the solar chemical composition (Grevesse, Noels & Sauval 1996), because the great majority of the prominent lines in their spectra are also present in the solar spectrum. We obtained so-called "solar" oscillator strengths by fitting the synthetic and observed solar spectrum (Kurucz et al., 1984), using the synthetic spectrum with the solar atmosphere model from the Kurucz (1992) grid and a microturbulence velocity [FORMULA] = 1 km s- 1 (see Paper I for details).

For the hottest stars of our sample, a great number of the lines belong to ionized carbon, magnesium, silicon, and sulphur. These lines are not visible in the solar spectrum and we have to rely on other sources for the oscillator strengths. In the present study we used an updated compilation provided by the Vienna Atomic Line Database (VALD). For the investigation of the main sequence stars, a larger number of lines has been used. However, we note that most of the [FORMULA], [FORMULA] and [FORMULA] lines which are visible in the spectra of our hot stars also dominate the spectra of the program main sequence stars. The list of used oscillator strengths is available from the authors.

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© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000