A SPECTRAL ATLAS OF THE HERBIG AE STAR AB AURIGAE - THE VISIBLE DOMAIN FROM 391 TO 874 NM

The visible spectrum of the pre-main-sequence Herbig Ae star AB Aur (A 0Ve), recorded by the MUSICOS echelle spectrograph, was used to elabor ate a high resolution (R = 38000) spectral atlas, with line identifica tion, in the wavelength range 391-874 nm. The numerous spectral featur es were individually measured and their identification was carried out with the help of a synthetic spectrum and a laboratory wavelength lis t for relevant atomic species. For 120 spectral features present in th e spectrum, we identified contributions from about 215 lines. The pres ence of 19 ions from 15 different elements is firmly established. From the analysis of several well-defined photospheric lines, we determine d for AB Aur a vsini value of 80 +/- 5 kms-1. From a detailed comparis on of the photospheric lines with the synthetic spectra calculated wit h classical photospheric models of Kurucz (1979), we deduced an effect ive temperature T(eff) = 10220(+150/-100) K and a surface gravity log (g) = 4.10 +/- 0.06. Upper limits were derived for the veiling of phot ospheric lines reaching from 3.5% at 4500 angstrom to 16% at 6100 angs trom. If AB Aur possesses an accretion disk with an optically thin inn er region, as conjectured by Hillenbrand et al. (1992), then the absen ce of veiling implies an accretion rate lower than 7.5 10(-8) M. yr-1. The spectral lines in the spectrum of AB Aur can be classified in 6 c ategories: photospheric lines identical to those of a synthetic spectr um calculated with a classical photospheric model; lines with filled-i n cores; asymmetric absorption lines; emission lines; lines which are deeper than predicted; P Cygni profiles for the first lines of the H I Balmer series. All these different features are consistent with a mod el including a photosphere with T(eff) = 10000 K and log (g) = 4, an e xtended chromosphere with a temperature reaching 17000 K, and a stella r wind. The regions of formation of a set of typical lines of this spe ctrum were compared with each other, by computing absorption coefficie nts at line center, using an existing atmospheric model for AB Aur.