COMMISSIONS 27 AND 42 OF THE IAU
               INFORMATION BULLETIN ON VARIABLE STARS
                            Number 4077

                                                  Konkoly Observatory
                                                  Budapest
                                                  31 August 1994

                                                  HU ISSN 0374 - 0676


              PERIOD CHANGE OF DELTA Sct STAR HD 79889


  HD 79889 was first reported as a variable star by Oja (1986). Some astronomers calculated 
its period: 0.0958697d (Oja, 1987), 0.095869448d (Rodriguez et al., 1990), 0.095869483d
(Wunder et al., 1992). Liu et al. (1991) studied its period variation and obtained a negative 
rate of period change (-2.1x10^-11 dc^-2). However Tang et al. (1992) observed this
star and obtained a positive rate of period change (1.1x10^-11 dc^-2).
  In order to study its period change we observed this star with the 60 cm telescope at
Xinglong Station of Beijing Astronomical Observatory from 30 January to 12 February
1993 and from 16 February to 4 March 1994. The Johnson V filter was used. HD 80079
was used as comparison. 16 times of maximum light obtained by us are listed in Table 1,
where T_max is the time of maximum light in HJD, E is cycle number, W is weight. The
light curves for two nights are plotted in Figure 1.

        Table 1. Times of maximum light of HD 79889 (1993-1994)
             No.   T_max            E     W
             1   2449018.0768     -2.0   1.0
             2   2449018.1726     -1.0   1.0
             3   2449018.2685      0.0   1.0
             4   2449018.3644      1.0   1.0
             5   2449019.0352      8.0   1.0
             6   2449021.0500     29.0   1.0
             7   2449022.0079     39.0   1.0
             8   2449030.0605    123.0   1.0
             9   2449031.0192    133.0   1.0
            10   2449400.0215   3982.0   1.0
            11   2449400.1173   3983.0   1.0
            12   2449401.0753   3993.0   1.0
            13   2449401.1713   3994.0   1.0
            14   2449413.0593   4118.0   1.0
            15   2449413.1553   4119.0   1.0
            16   2449416.1272   4150.0   1.0

  Besides our 16 times of maximum light we collected all data of HD 79889 obtained by
other astronomers (Oja, 1987; Rodriguez et al., 1990; Liu et al., 1991; Wunder et al.,
1992; Tang et al., 1992). We acquired altogether 60 times of maximum light. On the base
of 60 times of maximum light we calculated the improved elements of HD 79889 by the
method of least squares:

             T_max=HJD2449018.2684+0.09586954d x E              (1)


                             [FIGURE 1]

          Figure 1. Light curve relative to comparison star.

                             [FIGURE 2]

      Figure 2. The (O-C)_L diagram of HD 79889 and its fit curve.


  In order to study the variations of period we used the above formula and calculated
all times of maximum light. Then the residuals between observations and calculations
(O-C)_L were obtained. The (O-C)_L were fitted with a parabola as shown in Figure 2.
The parabola means variation of the period. So we obtained the equation by the method
of least squares:
        T_max=HJD2449018.2684+0.09586963d x E + 0.5 x G x E^2   (2)

G is the rate of period change. Its value is 8.8x10^-12(dc^-2). Since the rate of period
change is positive, it means that the pulsation period is increasing. This result agrees
with that obtained by Tang et al. (1992).


                          LIU ZONGLI
                          JIANG SHIYANG
                          Beijing Astronomical Observatory
                          Chinese Academy of Sciences
                          100080, Beijing, China



References:

Liu, Y. Y., Jiang, S. Y., Cao, M., 1991, Inf. Bull. Var. Stars, No. 3607
Oja, T. 1986, Astron. & Astrophys. Suppl. Ser., 65, 405 [BIBCODE 1986A&AS...65..405O ]
Oja, T., 1987, A&A, 184, 215 [BIBCODE 1987A&A...184..215O ]
Rodriguez, E., Lopez de Coca, P. et al., 1990, Rev. Mexicana Astron. Astrof., 20, 37 [BIBCODE 1990RMxAA..20...37R ]
Tang, Q. Q., Yang, D. W., Jiang, S. Y., 1992, Inf. Bull. Var. Stars, No. 3771
Wunder, E., Wieck, M., Garzarolli, M., 1992, Inf. Bull. Var. Stars, No. 3791