COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3349

                                           Konkoly Observatory
                                           Budapest
                                           7 July 1989

                                           HU ISSN 0374 - 0676


      MINIMA AND THE PERIOD OF THE ECLIPSING BINARY DF HYDRAE


Minima of the eclipsing binary star DF Hya were published by Whitney (1959), by
Koch et al. (1962) and by Hoffmann (1983), respectively.  Whitney (1959)
derived the elements:

Min.= JD hel.2431138.231+0.3305990d E.

Hoffmann (1983) revised the period of this system and he suggested that the
period of DF Hya be 0.3302005 days.

In 1985 photoelectric observations of DF Hya were carried out in B and V with
the integrating photometer at the 100 cm telescope of Yunnan Observatory. The
minima of DF Hya were determined from our observations by the quadratic fit
method.


                               [FIGURE 1]

                   Fig. 1   o-c residuals of DF Hya


The list below contains seven minima obtained by Whitney (1959), one minimum
given by Koch et al. (1962), two minima determined by Hoffmann (1983) and four
minima derived from our observations. The columns contain: heliocentric time
of minimum, phase of minimum, (o-c)I, (o-c)II and references.

Min.JD hel.   phase       (o-c)I     (o-c)II    References
2400000+
30677.048     I           -0.098     +0.020   Whitney (1959)
31204.677     I           -0.105     +0.008   Whitney (1959)
31497.927     I           -0.096     +0.015   Whitney (1959)
31937.615     I           -0.105     +0.002   Whitney (1959)
32675.856     I           -0.092     +0.010   Whitney (1959)
33382.658     I           -0.110     -0.015   Whitney (1959)
34847.708     II          -0.110     -0.026   Koch et al.(1962)
35242.608     I           -0.110     -0.030   Whitney (1959)
45021.3400    II          -0.0007    +0.0002  Hoffmann (1983)
45021.5060    I            0         +0.0009  Hoffmann (1983)
46115.1385    I           +0.0110    +0.0030  present paper
46115.3043    II          +0.0115    +0.0035  present paper
46117.1235    I           +0.0124    +0.0044  present paper
46117.2886    II          +0.0122    +0.0042  present paper

The values of (o-c)I were obtained by the following elements:

Min.=JD hel.2445021.5060+0.3305990d E.

The values of (o-c)II were obtained according to the revised elements:

Min.=JD hel.2445021.5051+0.33060169d E.

The accumulated effect of the o-c illustrated in figure 1 shows that the period
of DF Hya was increasing in the years 1959 - 1985 and that the plot of o-c
residuals can be well approximated with a parabola. Visual and photographic
minima were assigned a weight of one while photoelectric minima were assigned
a weight of five. Using the weighted least-squares method, a new ephemeris was
derived as follows:

Min.=JD hel.2445021.5009+0.33060443d E + 7.5d * 10^-11 E^2.


YUNLIN ZHANG, QINGYAO LIU   Yunnan Observatory
YULAN YANG, BI WANG, and    Academia Sinica
ZHOUSHENG ZHANG             Kunming, P.O. Box 110
                            People's Republic of China

References:

Hoffmann, M., 1983, Inf. Bull. Var. Stars, No. 2344.
Koch, J. C. and Koch, R. H., 1962, Astro. J. 67, 462. [BIBCODE 1962AJ.....67..462K ]
Whitney, B. S. 1959, Astro. J., 64, 258. [BIBCODE 1959AJ.....64..258W ]