COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2117

                                Konkoly Observatory
                                Budapest
                                1982 March 25

                                HU ISSN 0374-0676




 PHOTOMETRIC OBSERVATIONS OF THE ECLIPSING VARIABLE ZZ Cyg



  ZZ Cyg is an eclipsing binary of EA type (F7:V + K5 IV:,
10.61 - 11.69 V, P = 0.6286148d), well enough investigated as an
Algol star. This system is of special interest nevertheless
because there is information on possible Delta Scuti type physical 
variability of the hotter component: light amplitude is
about 0.05m with a period about 0.1 day (Hall, Cannon, 1974). If so, then the
hotter component of the ZZ Cyg system is the first known pulsating Delta
Scuti star which lies well outside the instability strip adopted
now: M_v = + 4.16, T_e = 5920d K, these parameters are from the
paper of Brancewicz and Dworak (1980). The place of the hotter
component of ZZ Cyg on the HR diagram is shown in Figure 1:
the star is situated to the right from the Delta Scuti 
instability strip.

                         [FIGURE 1]

  Mass and radius values from the same paper allow us to 
calculate the pulsation constant Q equal to about 0.08 and the
rotation velocity V_rot = 97 km/sec (assuming the synchronism
between rotation and revolution in this system) for the hotter
component of ZZ Cyg. The large rotation velocity is not surprising 
for Delta Scuti stars, but Q = 0.08 is too large and this
is the reason for doubts at least in the correctness of the period
value.
  For the direct examination of the hypothesis of the hotter
component being a pulsating star we observed ZZ Cyg photoelectrically. 
Naturally, we are interested in the behaviour of
ZZ Cyg outside the principal minimum. This star was observed at
the High Altitude Station of Sternberg Astronomical Institute,
near Alma-Ata. The 48-cm reflector with one-channel pulse counting 
photometer was used for seven nights during July-September,
1981. A diaphragm of 29" was used and consequently ZZ Cyg was
observed together with the visual component (rho = 8.5"). Mean
accuracy of our photometry was 0.01 magnitude. During the whole
observing season 450 light measurements were obtained in the
BV system. BD + 46d2930 was used as a comparison star.
All light measurements made during different nights were in good
accordance. This indicates the absence of any pulsational light
variability of the F7-component of ZZ Cyg; at least, this
concerns to short periodic light variability of Delta Scuti type.

                         [FIGURE 2]

  The mean light curve of ZZ Cyg based on our observations is
shown in Figure 2, light elements are from the Third Supplement
to GCVS. This light curve shows rather strong effect of 
ellipticity of the components.
  We observed min I during the night 4/5 July, 1981:
JD Hel = 2444790.3971, O-C = +0.0120 days, the depth of min I
is 1.13 in B and 1.02 in V.







M.S. FROLOV                   A.V. MIRONOV
E.N. PASTUKHOVA               Sternberg Astronomical Institute
Astronomical Council of the   USSR
USSR Academy of Sciences





References:
Brancewicz, H.K., Dworak, T.Z.: 1980 Acta Astron. 30, 501. [BIBCODE 1980AcA....30..501B ]
Hall, D.S., Cannon, R.O.: 1974, Acta Astron. 24, 79. [BIBCODE 1974AcA....24...79H ]