COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2205

                                  Konkoly Observatory
                                  Budapest
                                  1982 October 6

                                  HU ISSN 0374-0676


         SPECTROSCOPIC INVESTIGATION OF VZ Cnc


VZ Cnc is an RRs star according to the GCVS (Kukarkin et al.
1969). One of its main features is the clearly marked Blazhko
effect. Fitch (1955) obtained the period of the Blazhko effect
(PB = 0.716d, P0 = 0.178d). The light variation period P0 has 
remained constant for 70000 epochs (Firmanyuk, 1980). Photoelectric
observations of VZ Cnc were carried out for two nights in March
1980 with the aid of the Crimean Astrophysical Observatory's
64 cm reflector. Comparison of the author's observations with
those of Todoran (1976) and Mochan  (1980) shows   that P0
continues to be constant and the observations satisfy the linear
elements:
Max hel JD = 2433631.8655+ 0.17836367d.E          (Todoran, 1976)
The Psi phases of the Blazhko effect are also calculated in accordance 
with linear elements:
Max hel JD = 2433631.8605+ 0.716292d .E (Todoran, 1976).
The spectroscopic material was obtained in February and March
1980 with the aid of a diffraction-grating spectrograph in
Nasmith focus of the 122 cm reflector of the Crimean Astrophysical
Observatory. 39 spectrograms with linear dispersion of 37 angstrom/mm
were obtained. These spectrograms were processed by the generally
accepted methods and divided into two groups in accordance with
the Psi phases of the Blazhko effect (maximum and minimum).
The estimates of Teff and log g_eff for various phases of light
variation and Blazhko effect were made as a result of the 
comparison of observational Hgamma profiles, and theoretically calculated
by the Kurucz method (1979). The observed profiles are in better
agreement with Kurucz's (1979) ones than the calculations of
Searle and Oke (1962). To eliminate the effects of the splitting
of the lines we gave more weight to the longer wavelength wing,
although the profile of the line was always symmetrical within



the errors of measurements.
  The results are presented in Figure 1. The changes of effective


                         [FIGURE 1]


temperature with the light variation phase differ for the different
Blazhko effect phases studied. The amplitude of Teff variation
for Psi = 0.453 - 0.730 is greater than for Psi = 0.730 - 0.920.
Also the moments of maxima for these curves are displaced. The
Teff variation curve for the maximum of the Blazhko effect
(Psi = 0.453 - 0.730) is more asymmetric and in the phases phi=
0.750 - 0.920 we observe a sharp increase in Teff, whereas the
curve for Psi = 0.730 - 0.920 shows smooth variation with light
variation phase.
  The accuracy of the determination of log g_eff does not permit
us to discover the differences connected with the Blazhko effect,
nor to trace the g_eff variation with phase with any degree of
confidence. Our average value of < log g_eff > = 2.7 is greater
than that obtained by Danziger and Oke (1967), but it does not
fall into the region of g_eff, accepted for the RRs and delta Sct
stars (Jones, 1973).
  We defined the electron concentration in the atmosphere of
VZ Cnc by the methods of Inglis-Teller and Unsold. The calculations 
were made utilizing the methods and corrections expounded



by Kopylov (1961, 1966). The average electron concentrations are
log ne(nm) = 13.22 and log ne (Hgamma, Hdelta) = 15.17. These quantities
correspond to the electron concentrations in the atmospheres of
the normal stars A8 III - F2 III. The electron concentrations
ne(nm) calculated for each phase showed no clear dependence on
period. Consequently, it would seem that the conditions in the
atmospheric layers, responsible for the formation of nm are
relatively stable. According to log ne(nm) - Sp plots (Kopylov,
1961) VZ Cnc is a star of luminosity class III.
  The variation in the strength of hydrogen lines with phase of
light variation is common for stars of this type. The amplitude
of variation is 25 - 40% and decreases with increase in line
number.





          G.A. GARBUSOV

          Odessa Astronomical Observatory
          Odessa, U.S.S.R.





References:

Danziger I.J., Oke J.B., 1967, Astrophys. J., 147, 151 [BIBCODE 1967ApJ...147..151D ]
Firmanyuk B.N., 1980, dissertation, Odessa
Fitch W.S., 1955, Astrophys. J., 121, 690 [BIBCODE 1955ApJ...121..690F ]
Jones D.H.P., 1973,Astrophys. J. Suppl. Ser., 25, 487 [BIBCODE 1973ApJS...25..487J ]
Kopylov I.M., 1961, Izv. Krym. Astrofiz, Obs., 26, 232
Kopylov I.M., 1966, Izv. Krym. Astrofiz. Obs., 35, 11
Kukarkin, B.V. et al., 1969, General Catalogue of Variable Stars, Moscow [BIBCODE 1969gcvs.book.....K ]
Kurucz R.L., 1979, Astrophys. J. Suppl. Ser., 40, No. 1 [BIBCODE 1979ApJS...40....1K ]
Mochan A.I., 1980, (unpublished)
Searle L., Oke J.B., 1962, Astrophys. J., 135, 790 [BIBCODE 1962ApJ...135..790S ]
Todoran I., 1976, I.B.V.S. No. 1141