COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
			  Number 3066



					        Konkoly Observatory
					        Budapest
					        12 August 1987
	
					        HU ISSN 0374-0676


       OPTICAL BEHAVIOUR OF AT CANCRI IN THE SEASON 1986/87

  In linking to the sequence of comparison stars given in the IBVS No. 2363
this cataclysmic star was measured on 72 blue-sensitive plates (ORWO-ZU21 +
GG13 + BG12) from 18 nights obtained with the 50/70/172 cm Schmidt camera of
Sonneberg Observatory covering the time interval between 27 November 1986 and
27 April 1987, The observations are listed in Table I.

                      Table I
J D. hel      mB      J.D. hel      mB      J.D. hel       mB
244....               244...                244....

6762.575      12m72   6827.559      15m84   6876.414      13m35
6762.593      12.76   6827.580      15.45   6877.341      13.02
6763.536      12.49   6827.601      15.49   6877.359      12.82
6763.556      12.50   6828.388      15.29   6877.378      12.95
6763.575      12.41   6828.407      15.81   6877.398      12.77
6763.594      12.45   6828.428      16.19   6877.418      12.86
6764.522      12.56   6828.452      15.77   6877.437      12.80
6764.541      12.39   6828.471      16.14   6881.384      13.04
6764.561      12.52   6828.574      15.96   6881.404      13.53
6764.581      12.59   6850.376      15.87   6881.429      12.92
6769.536      12.67   6850.395      15.68   6881.450      13.06
6769.555      12.66   6850.413      15.48   6884.349      15.33
6769.574      12.60   6850.436      15.70   6884.385      15.26
6799.597      12.37   6850.456      15.70   6885.353      15.88
6799.615      12.19   6850.496      16.06   6885.372      16.44::
6799.632      12.27   6850.515      16.12   6885.391      16.31
6826.547      15.88   6851.401      15.43   6885.410      15.82
6826.567      15.87   6851.419      15.67   6885.430      15.91
6826.587      15.93   6851.438      16.28   6909.363      15.92
6826.609      15.77   6851.458      16.22   6909.383      15.50
6827.448      15.74   6851.479      15.54   6909.405      15.71
6827.471      15.81   6851.503      15.54   6910.383      16.02
6827.490      16.01   6876.379      13.48   6910.401      16.08
6827.509      15.82   6876.397      13.37   6913.385      16.35


                             [FIGURE 1]



  The long-term light curve of AT Cnc, which results from the mean brightness
values of each night and which is given in Figure 1 shows variations between
mB = 16.35m and mB = 12.28m. A remarkable decrease of brightness was observed
with Delta mB = 2.93 within 3.962d between 26 March and 30 March.
  Reducing all observations to one common epoch by means of the improved
orbital elements given the IBVS No. 2918 the orbital light changes and the
displaced minimum phase in the high state to phase ~ 0.5 can be confirmed.
  In opposition to other series of observations from former years, which
are reduced in the IBVS No. 2918 concerning the present observations of the
low state (14.5m < mB < 16.4m) no positive statements about the behaviour of the
orbital light changes can be made. The results mentioned are given in Figures
2 and 3, where the magnitudes mB from the high and the low state of brightness 
are plotted against the phases.


                            [FIGURE 2]
                            [FIGURE 3]




      W. GOTZ
Akademie der Wissenschaften
der DDR, Zentralinstitut für
Astrophysik, Sternwarte Sonneberg