COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2790

                                        Konkoly Observatory
                                        Budapest
                                        13 September 1985

                                        HU ISSN 0374 - 0676


            SPECTROPHOTOMETRIC INVESTIGATION OF
             MAGNETIC VARIABLE STAR AF (73) Dra.


  The investigations of AF Dra carried out by Preston (1967a), Babcock (1958),
Preston (1967b) show variability in the magnetic field amplitude, in the
radial velocity and in the intensity of absorption lines of some chemical
elements. Moreover the lines of Ti, Mn, Y, Ba, and Eu compared with iron and
chromium show considerable variations correlating with the magnetic field
intensity. Herein there are no estimations of abundance parameters lg (N/H)
for separate chemical elements. Spectral characteristics of AF Dra A3IVp does
not give sufficient information on the peculiarities of its atmosphere. Probably
in this case first the metal abundances in the stellar atmosphere should be
determined as it had been suggested by Foy (1979) and only then the spectral
type and luminosity class should be ascertained.

  In the present work two spectrograms of AF Dra obtained in SAO, Academy of
Sciences of the USSR, with the 6 m telescope have been studied. The spectra
have been exposed in near phases (phi=0.3) but the results of the investigation
are given for each spectrogram separately. Some differences in the parameters
obtained may be due not only to the errors of determination but also to their
rapid variability. The spectrograms are obtained with the dispersion 9 angstrom/mm
in the wavelength interval from 3800 to 4900 angstrom. The parameters of excitation
temperature Theta(ex), electron pressure lg Pe, abundances of a number of chemical
elements (lg N/H) have been determined by the "curve of growth" method using
the most perfect system of oscillator strength developed in Oxford and the solar
data obtained at the Main Astronomical Observatory of the Ukrainian Academy of
Sciences. After the analogous scope of material is collected enough for other
phases of the magnetic field variation, it may be possible to unambiguously
estimate the chemical composition of the atmosphere of AF Dra and determine
principal regularities of its spectral peculiarities.
  It should be noted that in the spectrograms studied the lines of elements
lighter than titanium are practically absent. The strong line of ionized
magnesium Mg 4481.1 is an exception. The line of ionized calcium Ca II is




                                 Table I

J.D.(hel)=2444817.4990d   J.D.(hel)=2444817.5024d   Sun

Theta(ex) =0.819             Theta(ex) =0.793

lgPe=0.40                    lgPe =0.28
                     
lg (N/H)             lg (N/H)             lg (N/H)
Mg 7.89(1)           7.79(1)              7.49(Kurucz, 1979)
Ti 4.70(17)          4.80(16)             4.88(Kostik, 1983)
Cr 6.13(28)          6.33(15)             5.69(Kostik, 1983)
Mn 5.74(8)           5.34(5)              5.15(Kurucz, 1979)
Fe 6.68(58)          6.92(48)             7.44(Blackwell, 1980)
Co 5.37[7)           5.52(7)              4.98(Gurtovenko, 1983)
Sr 1.85(2)           1.74(2)              2.77(Kurucz, 1979)
Y 2.80(3)            2.21(3)              1.57(Kurucz, 1979)
Zr -                 1.88(4)              2.37(Kurucz, 1979)
Eu 2.23(2)           2.40(2)              0.51(Biemont, 1982)

weakened abnormally (Wlambda=0.3 Angstrom) as compared with stationary stars of A3 spectral
type (Wlambda=1.5-2.0 Angstrom). The lines of neutral and ionized nickel, are absent too.
  Table I gives the Julian dates of observations J.D. with corresponding
parameters of excitation temperature Theta(exc), electron pressure lg Pe determined
from ionization equation and the parameter of abundance lg(N/H) for those
elements, the lines of which are surely identified in the spectrograms. The number
of lines is given in brackets. The solar data are given for comparison with the
source of information.
  On the basis of results obtained one can suppose the following. Absence
of lines of some elements in the spectra studied does not mean that the
given element is absent in the stellar atmosphere. Its lines can appear in
other phases. The overabundance and significant difference in the yttrium
and europeum abundance in separate spectra may be due to enhanced ionization
of these atoms influenced by the magnetic field. The parameters of iron and
chromium are only of real quantitative significance because of the greatest
stability of their atoms.





                      Z.N. FENINA
                      The Main Astronomical Observatory
                      of the Ukrainian Academy of Sciences
                      Goloseevo, Kiev, 252127, USSR


References :

Babcock, H.W., 1958, Astrophys.J.Suppl., 3, 141 [BIBCODE 1958ApJS....3..141B ]
Biemont, E., Karner, C., Meyer, G., Trager, F, Putlitz, G., 1982, Astron.Astrophys.
       107, 1, 166. [BIBCODE 1982A&A...107..166B ]
Blackwell, D.E., Shallis, M.J., 1979, Mon.Not.Roy. astr. S. 186, 3, 673. [BIBCODE 1979MNRAS.186..673B ]
Gurtovenko, E.A., Kostik, R.I., Orlova, T.V., 1983, Astronom.J., 60, 4, 758. [BIBCODE 1983AZh....60..758G ]
Foy, R., 1979, Astron and Astrophys, 78, 1, 25. [BIBCODE 1979A&A....78...25F ]
Kostik, R.I., Orlova, T.V., 1983, Astrometria and Astrophys., 49, 39. [BIBCODE 1983AAfz...49...39K ]
Kurucz, R.L., 1979, Astrophys.J.Suppl.Ser., 40, 1, 340.p.p. [BIBCODE 1979ApJS...40....1K ]
Preston, G.W., 1967a, Astronomical.J. 72, 9, 1088. [BIBCODE 1967AJ.....72.1084W ]
Preston, G.W., 1967b, Astrophys.J., 150, 3, 871. [BIBCODE 1967ApJ...150..871P ]