2 Preselection of suitable candidates

Since B stars are frequently fast rotators and/or show emission in their Balmer lines (Be stars, cf. Jaschek et al. 1981), a great effort was made to select the small number of stars which are suitable for an abundance fine analysis: non-Be and with projected rotational velocities $v \sin i$ below 100km s^-1.

Preselection of slow rotators in NGC 2004 was made from spectra obtained with the Siding Springs Observatory (SSO) 2.3 m telescope using the Double-beam Spectrograph. Aperture plates were fabricated to obtain medium resolution (0.3 Å/pixel) spectra ( $4100~{\rm\AA}<\lambda<5100~{\rm\AA}$) for 34 MS B stars.

To determine $v\, \sin i$ we have used a $\chi^{2}$ minimization technique which locates an optimal match between the observed spectrum and rotationally broadened synthetic spectra interpolated from a grid of models which spans $4000\,{\rm K}\,\le T_{\rm eff}\le 50\,000$K and $5.0\ge \log g \ge 0.0$ (Gonzáles Delgado & Leitherer 1999). More details can be found in Keller et al. (2002). Principle limitations on this technique are given by the S/N and resolution obtainable with the instrument used.

As can be seen from Table 1, our preselection was very successful: four of the six targets (nearly 70%) rotate at a rate low enough to analyse their metal content spectroscopically.