COMMISSION 27 AND 42 OF THE IAU
                   INFORMATION BULLETIN ON VARIABLE STARS
                               Number 3818

                                                         Konkoly Observatory
                                                         Budapest
                                                         9 December 1992

                                                         HU ISSN 0374 - 0676


                  UBV LIGHT CURVE OF RT And FOR 1991


   The continuation of a long term project of photometry of the short period RS
CVn system RT And is reported here.
   Photometric observations for this star have been made previously by several
authors listed by Dapergolas et al. (1988,1991).
   The star was observed photometrically for a total of 5 nights with the 1.2m
Kryonerion telescope from 10 Sep. 1991 to 16 Sep. 1991 using a single-channel
photon counting photometer described by Dapergolas and Korakitis (1987). The
photometer employs a high gain 9789QB phototube and UBV conventional filters.
Its output is fed directly to a microcomputer enabling rapid data access.
   The data reduction method is the standard one. Comparison and check stars
are BD +52d3384 and BD +52d3377 respectively and the accuracy of the
observations presented here is +-0.015 mag for V, B and +-0.025 for U.
   Table I lists the dates of observations and the corresponding phases
covered.
   The derived light curves for U, B, V colours are illustrated in Figures 1,
2, 3.

                Table I

        Date                 Phase

        10 September 1991   .77-.30
        11 September 1991   .35-.89
        12 September 1991   .92-.48
        14 September 1991   .14-.67
        16 September 1991   .49-.83


   In Table II the times of minima and the O-C values are listed for the V, B,
and U bands respectively. Times of minima are calculated using the method
described by Kwee and van Woerden (1956) whereas the O-C values were determined
from the linear ephemeris

             T=2441141.88902+0.628929513d x E

given by Kholopov (1982).
   From Figures 1, 2 and 3, it can be seen that the light curves show asymmetry
in the secondary minima that gets larger in short wavelengths.
   The variability in the levels of maxima noticed previously by Mancuso et al.
(1979), Dapergolas et al. (1988, 1991) is also present here (see Figure 4),
where the light curves for the years 1989, 1990 and 1991 in V are superimposed.


                              [FIGURE 1]
                              [FIGURE 2]
                              [FIGURE 3]
                              [FIGURE 4]



                   V colour            B colour                    U colour
Date        Type   Heliocen.   O-C     Heliocen,   O-C     Heliocen.   O-C
                        J.D.   phase        J.D.   phase        J.D.   phase
                    2440000+            2440000+            2440000+

10 Sep.91   I      8510.4262   0.998   8510.4262   0.998   8510.4257   0.998
                    +-0.0001            +-0.0001            +-0.0002
11 Sep.91   II     8511.3688   0.497   8511.3696   0.498   8511.3688   0.497
                    +-0.0003            +-0.0004            +-0.0007
12 Sep.91   I      8512.3124   0.998   8512.3126   0.998   8512.3123   0.997
                    +-0.0001            +-0.0001            +-0.0001
14 Sep.91   II     8514.5131   0.497   8514.5137   0.498   8514.5143   0.499
                    +-0.0004            +-0.0004            +-0.0005


  This variability is probably due to the photospheric activity of the system
as it is assumed by Dapergolas et al. (1988, 1991), Zeilik et al. (1989) and
Gordon et al. (1990). This activity derived from the distortion in the light
curve outside the eclipse is probably due to the presence of dark spots on the
surface of the active star.


                                    A. DAPERGOLAS
                                    and E. KONTIZAS
                                    National Observatory of Athens
                                    Astronomical Institute
                                    P.O. Box 20048
                                    GR Athens 118-10, Greece

                                    M. KONTIZAS
                                    Section of Astrophysics, Astronomy
                                    and Mechanics
                                    Department of Physics
                                    University of Athens
                                    Panepistimiopolis, GR-157 83
                                    Zografos, Athens, Greece



References:

Dapergolas, A. and Korakitis, R.: 1987, Publ. Nat. Obs. of Athens, Ser. II, N28.
Dapergolas, A., Kontizas, E. and Kontizas, M.: 1988, Inf. Bull. Var. Stars, No. 3267.
Dapergolas, A., Kontizas, E. and Kontizas, M.: 1991, Inf. Bull. Var. Stars, No. 3661.
Gordon, S., Hall, M., Ledlow, M., Mann, E. and Zeilik, M.: 1990, Inf. Bull. Var. Stars, No. 3469
Kholopov, P.N.: 1982, "General Catalogue of Variable Stars", IVth edition,
     vol. I, p. 103.
Kwee, K.K. and van Woerden, H.: 1956, Bull. Astr. Inst. Netherlands, 12, 327. [BIBCODE 1956BAN....12..327K ]
Mancuso, S., Milano, L. and Russo, G.: 1979, Astron. Astrophys. Suppl. Ser.,
     36, 415. [BIBCODE 1979A&AS...36..415M ]
Zeilik, M., Beckert, D., Cox, J., Dolby, M., Ledlow, M., Newberry, M. and
     Rhodes, M.: 1989, Inf. Bull. Var. Stars, No. 3301.