COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3043


                                   Konkoly Observatory
                                   Budapest
                                   3 July 1987

                                   HU ISSN 0374-0676



  PHOTOMETRY DURING THE END-PHASE OF A SPOT CYCLE IN II Peg*

II Peg is one of the most active RS CVn binaries with strong
chromospheric and transition region emission lines. Its radio
and X - ray emissions are comparable to the other active RS CVn
members. The optical light curve shows variations in amplitude,
shape, phase and mean light level due to the reorientation or
appearence of spot groups. Recent observations by Byrne (1986)
showed that the light curve had a larger amplitude than any of
the previous photometry. He interpreted the behaviour as due
to the occurence of a large single spot group and the brightness 
at the maximum corresponded to the light level of the 
unspotted surface. In an analysis of the then available photometry
of II Peg, Mohin, Raveendran and Mekkaden (1986) found that
between the interval JD 2444175 and JD 2444595, the light curves 
had two minima and they concluded that this phenomenon
could be due to the presence of two active regions located at
different latitudes. But observations in July-November
1981 showed only one minimum (Rodono et al., 1986). Photometry
of II Peg in August-September 1984 by Arevalo, Lazaro and
Fuensalida (1985) indicated that the light curve had two minima. 
Thus the location, area and the number of spot groups change
rapidly in this system.
        Stromgren uvby photometry of II Peg was carried out
at European Southern Observatory, La Silla, during 11 nights
in October 1986 using the ESO 50 cm telescope and a single

*Based on observations collected at European Southern Observatory, 
La Silla, Chile

beam photometer with ice cooled EMI 6256 tube. All observations
were made differentially with respect to the comparison star
HD 223094. Sufficient numbers of standard stars were observed
for the conversion of the instrumental magnitudes to the standard 
system. The standard error for an individual observation
in y is 0.015 mag. The Julian days of observation are converted
to photometric phases using the ephemerides of Rucinsky (1977).

       JD = 2443033.10 + 6.724183dE


                         [FIGURE 1]


Figure 1 is a plot of the y band light curve of II Peg. It is
known that Stromgren y is nearly the same as Johnson V and so a
comparative study of the present work with the photometry 
available in the literature is possible. The y magnitudes at
light maximum and mean light level are converted to Johnson V
values using the relation V = y + 0.075(b-y) - 0.003 (Olsen, 1983)
and found to be 7.29 and 7.49 mag. respectively.
        The shape of the light curve and the maximum brightness
of II Peg are similar to the observations of Byrne (1986)
made one month earlier, but the amplitude is 0.40 mag.; less than
in the previous month. Also the minimum of the light curve
seems to be advanced by 0.10P. Though the current maximum is
the brightest except for the observations of Chugainov (1976)
in 1974, it is rather not possible to attribute this value to
the unspotted light level since the very active nature of II Peg
causes sudden changes in the light curve and continuous 
observations over a few cycles are necessary to estimate the maximum
brightness.
       If we assume that the two spot groups observed till
early 1985 merged to form the current single spot group, then
what we observe in II Peg at present is the end-phase of a spot
cycle. A decade of photometry of II Peg shows that the system
is one of the most spot active binaries exhibiting single or
multiple spot groups at different latitudes and changes occur
within a short time scale. Simultaneous photometric and 
spectroscopic observations over a few consecutive cycles are needed
to infer the activity in this system.



                     M.V. MEKKADEN 1,2
                     1 Sternwarte Bonn
                      Auf dem Hugel 71
                      5300 Bonn, F.R.Germany
                     2 Indian Institute of Astrophysics
                      Bangalore, India


References:
Arevalo, M.J., Lazaro, C. and Fuensalida, J.J.: 1985, 
       I.B.V.S. No. 2840.
Byrne, P.B.: 1986, I.B.V.S. No. 2951.
Chugainov, P.F.: 1976, Izv.Krymsk.Astrofiz. Obs., 54, 89. [BIBCODE 1976IzKry..54...89C ]
Mohin, S., Raveendran, A.V. and Mekkaden, M.V.: 1986, I.A.U.
       Symp. 118, 309. [BIBCODE 1986IAUS..118..309M ]
Olsen, E.H.: 1983, Astron.Astrophys.Supl., 54,55. [BIBCODE 1983A&AS...54...55O ]
Rodono, M., et al.: 1986, Astron.Astrophys., 165, 135. [BIBCODE 1986A&A...165..135R ]
Rucinsky, S.M.: 1977, P.A.S.P., 89, 280. [BIBCODE 1977PASP...89..280R ]