COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3316

                                         Konkoly Observatory
                                         Budapest
                                         5 April 1989

                                         HU ISSN 0374 - 0676


            ON THE MISCLASSIFICATION OF CK Aquarii *


CK Aqr is classified in the General Catalogue of Variable Stars (1985) (here
after GCVS) as a delta Sct star varying from 12.9 to 13.8p. The elements given
in the GCVS were obtained by Tsesevich (1964, 1969):

               Min=HJD 2437547.319+0.12406245d*E

The variability of this star was originally discovered by Shapley and Hugues
(1935) who gave the same range of variation and period than in the GCVS but
with the indication "cluster type" variable.

In the frame of our study of faint delta Sct stars, CK Aqr has been measured in
the Johnson photometric system on 1984 October 21, 22 and 27 with the 1 meter
telescope of Pic du Midi Observatory (France) by J.F. Le Borgne and A. Figer
and on 1987 July 2 and 3 with the 1 meter telescope of European Southern
Observatory (La Silla, Chile) by E. Poretti. 57 measurements through Johnson
U, B and V filters were obtained at Pic du Midi and 176 measurements through
Johnson B and V filters at ESO. The resulting light curves are characteristic
of a W UMa type eclipsing binary and not of a delta Sct star. The V magnitude
varies from 12.86 to 13.47. There is a slight B-V variation from 0.70 to 0.78.
Only a mean value of U-B can be obtained from Pic du Midi measurements: 0.08
+-0.18.

The analysis of the light curves of the 5 nights allows to calculate the period
without ambiguity, especially from the light minimum times given in the table
below even if the large gap between the two series of observations does not
allow to link Pic du Midi and ESO minima.

List of V and B light minimum times of CK Aqr

Date          Observatory   V minimum (HJD)
21 OCT 1984   Pic du Midi    2445995.368
22 OCT 1984       "          2445996.356
27 OCT 1984       "          2446001.318
02 JUL 1987      ESO         2446979.935:
03 JUL 1987       "          2446980.788
03 JUL 1987       "          2446980.929

The period obtained is 0.2833+-0.0002 day. The period given by Tsesevich is an
alias of half the value of the true period. The two folded light curves are
given in the figure. The V light curve is characterized by minima and maxima
at different magnitude: V maxima at 12.86 and 12.95, minima at 13.38 and
13.47. Such a light curve is known to characterize binary systems with
circumstellar matter. Note also that at the minima the light curve is not
perfectly regular and that is why the minima of the B-V curve do not coincide
with the V minima but occur during the ascending branches. Moreover, the
eclipses may be total. The mean value of B-V, not corrected for interstellar
reddening, is in good agreement with Eggen's (1967) period-colour relation.
The colours of CK Aqr are compatible with the colours of unreddened G5-G8
stars.


                              [FIGURE 1]




J.F. Le BORGNE^1,3, E. PORETTI^2,3, A. FIGER^3

1 Observatoires Midi-Pyrenees
  14 avenue Edouard Belin
  31400 Toulouse, France

2 Osservatorio Astronomico di Brera
  Via E. Bianchi, 46
  22055 Merate (CO), Italy

3 GEOS
  12 rue Bezout
  75014 Paris, France


References:

Eggen, O.J.: 1967, Mem. R. Astr. Soc. 70, 111 [BIBCODE 1967MmRAS..70..111E ]
Shapley, H., Hugues, E.M.: 1935, Annals of Harvard College Observatory 90, 169
Tsessevich, V.P.: 1964, Astronomical Circular, Kazan, 295, 3 [BIBCODE 1964ATsir.295....3T ]
Tsessevich, V.P.: 1969, "RR Lyrae Stars", Israel Program for Scientific
   Translations, Jerusalem. [BIBCODE 1969rls..book.....T ]

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