COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2417

                                        Konkoly Observatory
                                        Budapest
                                        18 October 1983

                                        HU ISSN 0374-0676


         SPECTROSCOPIC INVESTIGATION OF SZ Lyn AND SS Psc



  The discrepancy between the hydrogen and ionized calcium spectral classes
is a characteristic feature of RR Lyrae stars. This discrepancy is determined
by the parameter DeltaS (Preston, 1959), measured in tenths of a spectral class.
DeltaS changes with the phase of light variation, reaching the highest values in
pre-maximum phases. One can note one more discrepancy for the stars in question,
viz. the difference between the ionized calcium and metal spectral
classes.

  Parallel photoelectric (Garbuzov, 1980a, 1980b) and spectroscopic observations
of SZ Lyn and SS Psc were performed to investigate in detail the changes
of hydrogen spectral classes: Sp(H), ionized calcium spectral classes: Sp(KCa II)
and spectral classes determined from the other metals: Sp(ml) (mainly Fe I,
Ca I and Ti II, all 13 criteria) with the phase of light variation. Spectroscopic
observations were carried out from October 1979 to January 1980 with
the diffraction-grating spectrograph of the 122 cm reflector of the Crimean
Astrophysical Observatory of the Academy of Sciences of the USSR. The linear
dispersion of the spectrograph is 125 A/mm. The exposure time was 0.14p for
SZ Lyn and 0.1p for SS Psc. Spectra were exposed on Kodak 103aO emulsion. For
SS Psc the plates were baked for 52 hours at t = 63dC in rarefied air. The
criteria for the quantitative spectral classification were taken from Fenina
(1975). The systems of equivalent widths of both investigations coincide with
each other.
  SZ Lyn. The pulsation period of SZ Lyn is 0.12d, its light varies in the
limits of 9.12m to 9.62m in V. The deviations of O-C residuals with the period
of 1146d can be explained by the binary nature of the star. The results of
the classification are given in Figure 1. Phases of light variation are
calculated with respect to linear elements (Barnes and Moffett, 1975):

       Max hel JD = 2438124.3977 + 0.12053481d*E.

The hydrogen spectral class (Sp H) shows smooth variation with the phase of
light variation. The ionized calcium spectral class (Sp KCa II) at the phases
of 0.0p - 0.6p nearly coincides with Sp H; at the phases of 0.6p - 0.9p it appears
earlier. The intensity of KCaII at these phases abruptly weakens by twice the
original value. The maximum of the calcium curve precedes the maximum of the
hydrogen curve.


                          [FIGURE 1]


The metal spectral class practically coincides with the spectral class
determined from hydrogen absorption lines, only for the phases 0.85 - 0.20
it is a little later. The amplitude of the change of metal line intensity
(except K CaII) is small.
   SS Psc. The period of pulsation of this star is 0.28d, its light changes
from 10.76m to 11.18m in B. Initially SS Psc was classified as an RRc star. The
change of spectral classes with the phase of light variation is, on the whole,
similar to that in the spectrum of SZ Lyn. This fact and the value of
Delta(B-V)/DeltaV = 0.39 put SS Psc together with SZ Lyn and VZ Cnc. These stars are
characterized by the normal metal content, and the coincidence of hydrogen
and metal spectral classes qualitatively show it.
 The greatest discrepancy between the hydrogen and the ionized calcium
spectral classes is in the premaximum phases. The shock wave effects may
affect the intensity of hydrogen and ionized calcium spectral lines. Thus,
in the spectrum of SZ Lyn we observe the faint splitting and the emission in
the core of hydrogen line H_alpha at these phases (Garbuzov, Zaikova, 1983). 
This phenomenon can be interpreted as a results of moving out of the shock wave
through the stellar atmosphere. The emission is poor and it cannon change
the intensity of hydrogen spectral lines essentially. The ionization potential
of Ca II is rather low, 11.8 eV. Calcium is completely ionized in the atmospheres
of hot stars. The K Ca II line is very weak in the spectra of A0 stars
(its equivalent width is about 0.3 A) whereas in F0 stars the equivalent width
of this line is about 3 A. Analysis of the change in the K Ca II equivalent
width of SZ Lyn shows the presence of a powerful mechanism in the stellar
atmosphere, not connected with the change in B-V and V, that produces the
variability of this line. A strong change in the equivalent width of the
K Ca II line at nearly constant B-V, observed at some light variation phases
of SZ Lyn, is caused by the action of this mechanism. It may also be due to
the ionization of the upper atmosphere induced by the moving of the shock
wave and by the ultraviolet radiation from behind the front of the shock
wave. Another mechanism is possible, which is also connected with the movement
of the shock wave. As a result  of the shock wave movement the absorption lines
are shifted into the short wavelength region, it will be there that the
photons of continuum, moving out from deep layers of the stellar atmosphere,
will be absorbed (irradiation effect). So there will be the additional surge
of the energy to the gas and then its heating. Thus the rise of DeltaS at pre-
maximum phases may be the shock wave effect.



                              G.A. GARBUZOV
                         Odessa Astronomical Observatory
                         Odessa, U.S.S.R.


References:

Barnes T.G., Moffett T.J., 1975, Astron. J., 80, 48 [BIBCODE 1975AJ.....80...48B ]
Fenina Z.N., 1975, Peremennye Zvezdy, 20, No. 1, 103 [BIBCODE 1975PZ.....20..103F ]
Garbuzov G.A., 1980a, Astr.Tsirk., No. 1138, 7 [BIBCODE 1980ATsir1138....7G ]
Garbuzov G.A., 1980b, I.B.V.S. No. 1854
Garbuzov G.A., Zaikova L.P., 1983, unpublished
Preston G.W., 1959, Astrophys. J., 130, No. 2, 507 [BIBCODE 1959ApJ...130..507P ]