COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                    NUMBER 596

                                Konkoly Observatory
                                Budapest
                                1971 December 2



THE ECLIPSING BINARY AB CASSIOPEIAE AS A DELTA SCUTI STAR


    The eclipsing binary AB Cas has been observed in
several nights from 1967 to 1971 with the 40-cm refractor
of the Teramo Observatory; an E.M.I. 9502 photomultiplier
coupled with a Schott GG14 filter assured a response very
close to the V magnitude system.
      The light curve derived by these observations is
shown in Fig. 1; the phases have been computed according to
the elements

    Hel. Minimum = J.D. 2439771.580 + 1.3668755d

and the magnitude differences are referred to an anonymous
star whose V magnitude resulted 10.50m.
    A 0.10m deep secondary minimum is detectable, but
the most interesting feature is the presence of brightness
fluctuations of amplitude 0.05m and period 1h 24m; the
incommensurability with the eclipsing period causes the
cancelling out of these fluctuations in the most part of
the composite light curve, but they are clearly apparent in
the phase interval 0.08p - 0.20p where almost all the 
observations belong to the same night. Some single-night runs
are reported on a larger scale against the phase of the
binary period (in minor panel of Fig. 1 and in Fig. 2).
     The average period derived from several cycles 
observed in 1970 and 1971 results to be 0.058d but the single
cycles show deviations reaching 0.007d. The brightness
fluctuations seem to be enhanced during the secondary

                    [FIGURE 1]
                    [FIGURE 2]

minima and disappear near the central phase of the primary
minima: a behaviour to be expected in the case of an 
intrinsic variability of the warmer star which is almost
totally eclipsed. The photometric patterns and the spectrum
and luminosity of the primary component - an A3 star of
absolute visual magnitude +2.2m - allow to classify the
star as a Delta Scuti variable.
      AB Cas is a detached system consisting in an A3 and
an early K main sequence stars; the mass of the A3 star has
been evaluated in 2 solar masses (Gaposhkin, 1940): a
typical value for a Delta Scuti variable. Furthermore, the
star fits well the period-luminosity relation found for
this class of variables (Kam-Ching Leung, 1970).
      A detailed study of AB Cas will be published 
elsewhere.



                       P. TEMPESTI
                Osservatorio Astronomico di Teramo
                         Italy



References:

S. Gaposhkin, 1940, Harvard Reprint No. 201
Kam-Ching Leung, 1970. Astron. J. 75. 643. [BIBCODE 1970AJ.....75..643L ]