A spectral atlas of the Herbig AE star AB Aurigae.

The visible spectrum of the pre-main-sequence Herbig Ae star AB Aur (A0Ve), recorded by the MUSICOS echelle spectrograph, was used to elaborate a high resolution (R = 38000) spectral atlas, with line identification in the wavelength range 391-874 nm. The numerous spectral features were individually measured and their identification was carried out with the help of a synthetic spectrum and a laboratory wavelength list for relevant atomic species. For 120 spectral features present in the spectrum, we identified contributions from about 215 lines. The presence of 19 ions from 15 different elements is firmly established. From the analysis of several well-defined photospheric lines, we determined for AB Aur a υsini value of 80±5 km s^-1. From a detailed comparison of the photospheric lines with the synthetic spectra calculated with classical photospheric models of Kurucz (1979), we deduced an effective temperature T_eff = 10220⁺¹⁵⁰_-100 K and a surface gravity log (9) = 4.10±0.06. Upper limits were derived for the veiling of photospheric lines reaching from 3.5% at 4500 Å to 16% at 6100 Å. If AB Aur possesses an accretion disk with an optically thin inner region, as conjectured by Hillenbrand et al. (1992), then the absence of veiling implies an accretion rate lower than 7.5 10^-8 M_sun yr^-1. The spectral lines in the spectrum of AB Aur can be classified in 6 categories: photospheric lines identical to those of a synthetic spectrum calculated with a classical photospheric model; lines with filled-in 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 model including a photosphere with T_eff = 10000 K and log (9) = 4, an extended chromosphere with a temperature reaching 17000 K, and a stellar wind. The regions of formation of a set of typical lines of this spectrum were compared with each other, by computing absorption coefficients at line center, using an existing atmospheric model for AB Aur.