COMMISSION 27 OF THE I. A. U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                              Number 2500

                                                   Konkoly Observatory
                                                   Budapest
                                                   28 March 1984

                                                   HU ISSN 0374-0676



             PHOTOELECTRIC OBSERVATIONS OF CY AQUARII


 The SX Phe-type star CY Aqr (V_max = 10.4m) has attracted considerable 
attention in the past because of its very short period.
We obtained some 543 observations during October/November, 1983
in the V- and B-band (standard Corning filters) using a single
channel photometer attached to the 60 cm RC telescope of the
L. Figl-Observatory (University of Vienna). The comparison star
was a star denoted "a" by Zissell (1968). This star is about 11'
to the north-east of CY Aqr and similar in color; therefore no
correction for differential extinction was necessary. Zissell
found the intensity of this star to be constant. Because of the
short period only either B- or V-filter was used for a single
run. No transformation to the UBV system was made. The cycle
repetition time of the observations was 2 minutes, combining 15
second integrations for sky, CY Aqr and comparison star; time
accuracy of the measurements was kept below 1 second.
 We were able to derive 12 times of maximum covering 41 days
671 cycles). Table I shows the time of the light maximum. No 
dependence of time of maximum on colors could be detected. O - C
values are calculated with respect to three different ephemerides;
O-C_1 refers to the ephemeris derived only from our own observations 
using a linear least square solution:

       Max.hel. = 2445641.2942d + 0.06103822d.E.
                     +-0.00009 +- 0.00000044

O - C_2 uses the ephemeris given by Mahdy and Szeidl (1980) for
observations after 1952; O - C_3 are based on new light elements
using a quadratic term given by Rolland et al. (1984) :
Max.hel. = JH 2440892.6370d + 0.061038318d. E - 4.58, 10^-13, E^2
 Although sometimes variations in amplitude and shape of the
light curve have been reported in the past, we could not find
any significant change within the observing period. The mean


      JD hel         O- C_1       O- C_2       E_2        O- C_3    Color
     2445000+

     621.3351      + 0.0004d     - 0.0011d    185341    + 0.0013d     V
     629.3301      - 0.0006      - 0.0021     185472    + 0.0003      V
     631.2843      + 0.0004      - 0.0002     185504    + 0.0013      V
     631.3453      + 0.0003      - 0.0011     185505    + 0.0012      V
     635.3122      - 0.0002      - 0.0017     185570    + 0.0007      B
     635.3732      - 0.0003      - 0.0028     185571    + 0.0006      B
     641.2940      - 0.0002      - 0.0017     185668    + 0.0007      B
     641.3550      - 0.0002      - 0.0017     185669    + 0.0007      B
     645.2621      + 0.0004      - 0.0009     185733    + 0.0013      B
     645.3225      - 0.0002      - 0.0017     185734    + 0.0007      B
     661.2532      - 0.0005      - 0.0020     185995    + 0.0004      V
     662.2920      + 0.0007      - 0.0009     186012    + 0.0016      V


                            [FIGURE 1]



amplitudes in blue and visual light are 0.87m and 0.73m respectively. 
Figure 1 shows the mean light curves in blue and visual
light and also for their differences (Delta).





                A. PURGATHOFER +

                A. SCHNELL

                Institute for Astronomy
                University of Vienna
                Turkenschanzstrasse 17
                A-1180 Vienna, Austria





References:

Mahdy, H.A., Szeidl, B.: 1980, Mitt.Sternw.Ungar.Akad.Wiss. Nr. 74
						[BIBCODE 1980CoKon..74....1M ]
Rolland, H., Pena, J.H., Lopez de Coca, P., Peniche, R.: 1984, preprint
Zissell, R.: 1968, Astron.J. 73, 696 [BIBCODE 1968AJ.....73..696Z ]