2 Observational data

The spectra were obtained with the ECHELEC spectrograph, mounted at the Coudé focus of the ESO 1.52m telescope at La Silla. They were collected from June 1989 to January 1995 in the framework of an ESO Key Programme aimed at the determination of fundamental parameters of early-type stars observed by HIPPARCOS (Gerbaldi & Mayor 1989), nearer than 100 pc. In total, 871 spectra were collected for 525 stars whose spectral types range from B8 to F2 (Fig. 1). Most of these stars belong to the main sequence (half of the sample are in luminosity class V, and a fifth is classified IV or IV-V). These stars are all brighter than the V magnitude 8.

It is worth noticing that the spectra which are the subject of the present paper were also studied by Grenier et al. (1999) to derive radial velocities, and that the 71 A0 dwarf stars observed were investigated by Gerbaldi et al. (1999). Basically, this sample includes objects with no radial velocity or only for one epoch. Some stars with no determination were added from the Bright Star Catalogue (Hoffleit & Jaschek 1982). The observational programme is more detailed by Grenier et al. (1999).

Figure 1: Distribution of the spectral type for the 525 programme stars.

Figure 2: Normalized spectrum of Sirius, covering the 4210-4500 Å range, around H$\gamma$. The 15 selected lines (listed in Table 2) are indicated.

The observations were made in the spectral range 4210-4500Å (Fig. 2). The linear dispersion is about 3.1Å ${\rm mm}^{-1}$, the slit width of $320\,\mu$m corresponds to $1\hbox{$.\!\!^{\prime\prime}$ }52$ on the sky, and the power of resolution is about 28000.

The complete reduction of the spectra using MIDAS package, from CCD frame to linear spectrum, is detailed by Burnage & Gerbaldi (1990, 1992).