COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3302

                                        Konkoly Observatory
                                        Budapest
                                        9 March 1989

                                        HU ISSN 0374 - 0676


   PHOTOELECTRIC OBSERVATIONS OF AP LEONIS AND ITS PERIOD CHANGES


AP Leo is a W UMa-type binary system (Mauder, 1967; Cristescu, 1979). The
system was observed photoelectrically in B and V bands with the 60 cm reflector
and the single channel photometer at the Xinglong station of Beijing
Observatory during the 1983-1985 and the 1988 seasons.

The stars BD +6d2400 and BD +5d2437 were used as comparison and check star,
respectively. The observations covered a number of orbital cycles. A total of
9 primary and 7 secondary minimum times were obtained. They are given in Table
I.

From Table I, together with the other 112 minima collected from the literature
(since 1899), the average period of AP Leo is found to be 0.4303572d. Figure 1
is the O-C diagram of the epochs of minimum light based on the average
ephemeris:

Min.I= JD hel. 2439536.542 + 0.4303572d*E         (1)
       m.e.            +-2         +-5

Table I. New light minima for AP Leo

JD hel.  (V.)   m.e.     JD hel. (B.)  m.e.   min.
2440000+
    5441.0544  0.0008    5441.0533   0.0007    I
    5444.0668  0.0003    5444.0668   0.0003    I
    5470.0991  0.0005    5470.1006   0.0005    II
    5756.2888  0.0001    5756.2899   0.0001    II
    5787.0595  0.0010    5787.0599   0.0011    I
    5787.2734  0.0009    5787.2735   0.0001    II
    6092.1801  0.0004    6092.1786   0.0003    I
    6139.0901  0.0017    6139.0870   0.0005    I
    6139.3034  0.0002    6139.3041   0.0003    II
    6143.1766  0.0005    6143.1778   0.0004    II
    6146.1883  0.0008    6146.1883   0.0006    II
    6153.2895  0.0003    6153.2891   0.0003    I
    7236.0636  0.0003    7236.0642   0.0002    I
    7236.2760  0.0010    7236.2766   0.0006    II
    7266.1869  0.0004    7266.1861   0.0006    I
    7267.0478  0.0003    7267.0479   0.0004    I


                               [FIGURE 1]

                Figure 1. O-C diagram of minimum times

                               [FIGURE 2]

                Figure 2. V,B light curves of AP Leo


Our analysis indicates that the period of AP Leo appears to exhibit sinusoidal
changes. A new ephemeris of minimum times is derived as follows:

Min.I=J.D.hel. 2439536.535+0.4303570d*E+0.025*
          m.e.         +-4       +-1      +-2

       *sin(2pi*0.000064(0.43035570*E-300.00))              (2)
                     +-2                 +-2

The period indicated by the sinusoidal term is about 43 years. It is suggested
that there could be a third body in the system which may be responsible for
such long term changes in the period of AP Leo.  The ephemeris for the
prediction of forthcoming minima can be derived from the observations in Table
I, as follows:

Min.I=J.D.hel. 2447236.0621 + 0.4303546d*E                    (3)
          m.e.          +-3         +-1

Using the ephemeris (3), the observations in 1988 were combined into B and V
normal light curves as shown in Figure 2.

The photometric solution of the light curves together with a more detailed
analysis of the period changes will be published in a forthcoming paper.


ZHANG JI-TONG, ZHANG RONG-XIAN
ZHAI DI-SHENG, LI QI-SHENG
JIN TIE-LIN
Beijing Observatory
Academia Sinica
Beijing, China

References:

Cristescu, C. 1979, Inf. Bull. Var. Stars, No. 1688.
Mauder, H. 1967, Veroff. Remeis-Sternw. Bamberg, 7, Nr. 61, 1.