COMMISSIONS 27 AND 42 OF THE IAU
              INFORMATION BULLETIN ON VARIABLE STARS
                            Number 4035

                                                 Konkoly Observatory
                                                 Budapest
                                                 30 May 1994

                                                 HU ISSN 0374 - 0676


           RAPID SPECTRAL VARIATIONS OF THE Be STAR gamma Cas


 Spectroscopic observations of the Be star gamma Cas were carried out on November 5 and 6,
1992. The purpose was to study the relations between the Be phenomena in the gaseous
circumstellar disk and the activity of the central star. The spectroscopic observations
were made with the French ISIS spectograph fibre-feeded from the 2.16m telescope at
Xinglong station of Beijing Observatory (Felenbok and Guerin,1988). The detector is a
Thomson red sensitive CCD with 576x384 pixels. By using a 600 grooves mm^-1 grating
in second order we get a reciprocal dispersion of 2.7 A/mm in the Halpha region. Total
of 13 profiles were obtained. The data were reduced using the MIDAS image processing
software on a Sun 4 station computer of Beijing observatory. The spectral scans for the
Halpha and HeI6678 region of gamma Cas are shown in Figures 1 and 2, respectively. The Halpha
emission displayed a triangular profile skewed to the red. From Tables 1 and 2 we see
that the Halpha emission seems to show rapid fluctuations in equivalent width on a timescales
of about 45 minutes, and the spectral scans of the HeI6678 region have lower signal-to-
noise ratio due to greater zenith distance and shorter exposure time. Nevertheless, rapid
variations of HeI6678 in equivalent with can also be seen. In addition, from Figure 3 it
is clear that there is a systematic trend of red shift in the Halpha profiles.
 We suggest that the rapid variations of the HeI6678 may be attributed primarily to
photospheric activity, while the changes in Halpha may indicate that some material in the
envelope was falling back onto the central star at the time of our observations.


Table 1. The results of the measurement of Halpha for gamma Cas

No.   observing    exposure         Equivalent   V/R
      date        time (min.)       width (A)
1     5 Nov.1992      20            -17.280      1.121
2     5 Nov.1992      15            -17.502      1.167
3     5 Nov.1992      20            -17.621      1.164
4     6 Nov.1992      20            -17.810      1.139
5     6 Nov.1992      20            -16.710      1.157
6     6 Nov.1992      25            -16.614      1.176
7     6 Nov.1992      25            -17.104      1.152


                            [FIGURE 1]

        Figure 1. Spectral scans of gamma Cas in Halpha region

                            [FIGURE 2]

     Figure 2. Spectral scans of gamma Cas in HeI lambda 6678 region

                            [FIGURE 3]

        Figure 3. The red shifts of Halpha profile of gamma Cas 

                   
Table 2. The results of the EW measurement of HeI6678 for gamma Cas

No.   observing    exposure         Equivalent
      date         time (min.)      width (A)
1     6 Nov.1992      20            -0.170
2     6 Nov.1992      20            -0.212
3     6 Nov.1992      20            -0.405
4     6 Nov.1992      20            -0.996
5     9 Nov.1992      20            -0.255
6     9 Nov.1992      20            -0.169


                        Xiao-zhen GUO
                        Jun-jie WANG
                        Shi-yang JIANG
                        Beijing Astronomical Observatory
                        Chinese Academy of Sciences
                        Beijing 100080, China



Reference:
Felenbok, P., Guerin, J., 1988, in Proc. IAU Symposium No. 132, p. 31 [BIBCODE 1988IAUS..132...31F ]