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

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5. Elemental abundances

With [FORMULA], [FORMULA] and [FORMULA] values determined, one can then derive elemental abundances. Note that no detailed abundance analysis has previously been performed for any star of our sample.

As a first step, we used WIDTH9 to derive the elemental abundances for the sharp-lined stars. These abundances were then used as input for a detailed spectral synthesis. It should be noted that use of the WIDTH9 code was restricted by the necessity of taking into account only unblended or slightly blended lines, the number of which is small even in the spectra of the blue stragglers. Abundances for the main sequence stars with rotationally broadened spectral lines can be found only by means of the SYNSPEC code, which allows one to find an optimal fit of the synthetic spectrum to the observed one. This procedure was performed separately for each order. Generally, the fit was quite satisfactory for all lines of a given element for a single value of the abundance. This indicates that the oscillator strengths of the calculated lines are rather accurate and that there are no significant errors in the continuum placement. Therefore, we will not discuss line-to-line abundance scattering here, but will restrict ourselves to a discussion of systematical errors caused by a poor choice of the atmospheric parameters and NLTE effects (see next section).

In Figs. 8-11 we give some examples of the synthetic spectra convolved with the instrumental and rotational profiles, plotted together with the observed ones. For rapidly rotating stars, we also show the deconvolved synthetic spectra with the aim of demonstrating to what extent the original spectrum is altered due to rapid rotation. Note that for blends only approximate wavelengths are given.

[FIGURE] Fig. 8a - c. Fragments of observed (circles) and synthetic ([FORMULA]) spectra for HD 162586 ([FORMULA] = 12650 K, [FORMULA] = 4.05, [FORMULA] = 30 km s-1).

[FIGURE] Fig. 9a - c. Fragments of observed and synthetic spectra for HD 170054 ([FORMULA] = 14800 K, [FORMULA] = 4.30, [FORMULA] = 20 km s-1).

[FIGURE] Fig. 10a and b. Fragments of observed and synthetic ([FORMULA] - convolved, [FORMULA] [FORMULA] = 0 km s-1) spectra for HD 170011 ([FORMULA] = 8700 K, [FORMULA] = 3.70, [FORMULA] = 130 km s-1)

[FIGURE] Fig. 11a and b. Fragments of observed and synthetic spectra for HD 170095 ([FORMULA] = 9200 K, [FORMULA] = 3.90, [FORMULA] = 190 km s-1).

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© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000
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