COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2268

                                    Konkoly Observatory
                                    Budapest
                                    1983 January 13

                                    HU ISSN 0374-0676


     ON THE VARIABILITY OF THE 5200 angstrom STRUCTURE FOR alpha2 CVn


 The magnetic star alpha2 CVn has been investigated at Torun Observatory in
order to look for the variability of the broad absorption structure at about
5200 angstrom. The observations were made in May-July 1982 by means of the Canadian
Copernicus Spectrograph on the 90 cm Schmidt-Cassegrain telescope. The 
spectrograph has an image-slicer of 3 arcsec aperture, giving the reciprocal
dispersion of about 160 angstrom/mm. The spectra were taken on Kodak IIa-F preflashed
plates.

 The standard stars alpha Lyr, alpha Aql and gamma UMa were observed along with alpha2CVn to
remove the influence of emulsion sensitivity, instrument transmission 
characteristics and atmospheric extinction.
 For resulting spectra of alpha2 CVn the continua have been drawn as straight
lines between 4900 and 6200 angstrom, according to Mihalas' (1966) model of A star.
The equivalent widths of the range 4900-5400 angstrom have been computed. Their
phase dependence is shown in Figure 1. The phases are computed according to
the ephemeris found by Farnsworth (1932).


                             [FIGURE 1]

 Figure 1: Phase variation of equivalent width of the 4900-5400 A region in
           the spectrum of alpha2 CVn. Standard deviations are indicated. The
           solid line is a best fitted double-wave obtained by least 
           squares method.


                     

 The Pearson's approximation quality parameter chi^2 is 2.74 in this case.
Because of the small number of observational points we checked the reliability
of our results trying to approximate the sets of casual points located at the
same phases and with the same errors like in the case of observations, by the
double-wave. This procedure has been applied to 100 various sets. The mean
chi^2 for them is of an order of magnitude greater than for the observations.
 As can be seen the variability of the 5200 angstrom structure is clear. The maxima
of the double-wave are in good agreement with those obtained by Burbidge and
Burbidge (1955) and Cohen et al. (1969) for equivalent widths of individual
elements. The maximum at phi = 0.05 corresponds to group A elements (rare
earths, Ti, Mn) and that at phi = 0.55 to group B (Fe, Cr).
 Further observations are still running and a detailed discussion will be
published elsewhere.




          J. GERTNER, M. MUCIEK, M. MIKOLAJEWSKI
          Institute of Astronomy
          Nicolaus Copernicus University
          ul. Chopina 12/18 87-100 Torun,
          Poland




References:

Burbidge, G.R. and Burbidge E.M., 1955, ApJ. Suppl. 1, 431 [BIBCODE 1955ApJS....1..431B ]
Cohen, J.G., Deutsch A.J. and Greenstein J.L., 1969, ApJ 156, 629 [BIBCODE 1969ApJ...156..629C ]
Farnsworth, G., 1932, ApJ 75, 364 [BIBCODE 1932ApJ....75..364F ]
Mihalas, D., 1966, ApJ Suppl. 13, No. 114 [BIBCODE 1966ApJS...13....1M ]