2. Summary of observational data
The variable absorption lines of Na I, Ca II, K I, Fe II, Mg II and other ions have been observed many times in the spectra of HAeBe stars (see, e.g., Finkenzeller & Mundt 1984; Catala et al. 1986a; Tjin A Djie et al. 1989 and for a recent review Catala 1994). Because of their variability, the lines can be considered as the circumstellar ones that originate in the layers located far from the stellar surface.
The lines are not very deep () and are saturated practically in all cases. The strengths of the sodium and calcium absorption lines are approximately equal (Catala et al. 1986a) and their equivalent width usually does not exceed 0.6 - 0.8 Å. However, the equivalent width of the Ca II H and K lines in the spectrum of HR 5999 reaches 2 - 3 Å (Tjin A Djie et al. 1989). These lines may be partially attributed to the stellar photosphere (Catala et al. 1986b).
The possibility to measure the line width (FWHM) is tightly connected with the spectral resolution used. For the narrow components of the Na I D and Ca II K lines, Catala et al. (1986a) found FWHM 10 - 20 km s-1. Sometimes separated blueshifted or (and) redshifted components with the radial velocities up to 100 - 200 km s-1 are observed. The timescale of the absorption feature variations is about some hours or days and is often determined by the time resolution of observations.
Spectra of a few HAeBe stars have been obtained in deep minima: WW Vul by Timoshenko & Filip'ev (1983), SV Cep by Timoshenko (1985), HR 5999 by Tjin A Djie et al. (1989), and UX Ori by Grinin et al. (1994). Using the observations with a low spectral resolution Timoshenko & Filip'ev (1983) have detected the variations of W (Ca II) in the range 1.5 - 3 Å for WW Vul. The authors described the quantitative behaviour of the line profiles as follows: when the star became brighter, the line became deeper and broader. The observations of HR 5999 by Tjin A Djie et al. (1989) appear to support this conclusion. Two spectra of UX Ori in a deep light minimum published by Grinin et al. (1994) show that the Na I D lines have weak inverse P Cyg profiles.
At present, it is difficult to find a definite relation between the behaviour of the absorption lines and the brightness variations. This was demonstrated by the figures in the papers of Grinin et al. (1994, 1996) and de Winter (1996). These figures show that the variations of profiles of the sodium lines are unrelated to the brightness variations. On the other hand, the detailed investigation of HR 5999 made by Tjin A Djie et al. (1989) shows that the equivalent width of the Na I D2 line decreases from 0.8 Å to 0.2 Å when the star brightness changes from 6:m9 to 7:m2. The radial velocity of the line does not correlate with the brightness variations.
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998