2 Material

We observed fourteen bright Ae and A-type shell stars (Table 1) at the Observatoire de Haute Provence (OHP) with the 152 cm telescope, in April 1996,with the Aurelie spectrograph (see Gillet et al. 1994) with a Thomson 7832 double bar detector, with 2048 photodiodes $(750 \times 13 \;\mu )$.The grating had 300 grooves /mm, blazed at 6000 A. The original dispersion is 33 A/mm, with a resolution of 1.3 A. Calibrations were made with a tungsten lamp for the flat field,and in wavelength by means of a thorium - argon hollow cathode for the blue and the red and thorium-neon for the near infrared.

  

Table 1: Observational data

Numbers given in this table are the dates in April 1996.
(11= April 11, 1996).

  

Table 2: Classifications of the MK standards observed

Our intention was to observe these stars in three wavelength regions: in the blue $(\lambda4000{-}4800)$, the H alpha(=H3) region $(\lambda6200{-} 7000)$ and the Paschen region $(\lambda8100{-}8900)$, but due to cloudy nights this coverage could not be achieved for all stars. The stars were not observed simultaneously in the different ranges, but in view of the slowness of the changes, time differences of at most five days are probably unimportant. Several MK standards were observed for each region (see Table 2). We did not observe standards for the Paschen region, because these have already been published in Andrillat et al. (1995).

We have measured the equivalent widths with the computer program IHAP of ESO. The precision of the equivalent widths is of the order of $\pm 10\%$ for medium and strong lines and somewhat less for the weaker lines. The equivalent widths are given in Tables 3 and 4 for the red and infrared regions respectively. No values were measured in the blue region, due to the large number of metallic lines which produce many blends. The lines $\lambda\lambda$ 6347(Si II M.2), 6371(Si II M.2), 6456(Fe II M.74), 6496(Ba II M.2) and 6516(Fe II M.40) are absent in A0 V (except 6516) appear in A2 and strenghten with advancing type toward late A. No difference in the behavior of these lines seem to exist between the class III and V stars in this spectral range.

  

Table 3: Equivalent width of absorption lines in the H a region

$^\ast$ A sharp absorption core exists, superimposed upon the broad absorption line.
Equivalent widths given in A.
p means visible, but not measured.

  

Table 4: Equivalent width of absorption lines measured in the Paschen region

Note * blend with Ca II.
OI is blended with P 18.
Equivalent widths given in A.