COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3607 Konkoly Observatory Budapest 20 May 1991 HU ISSN 0374 - 0676 PERIOD CHANGES IN HD79889 HD79889 was first reported as a variable star by Oja(1987), who estimated a period of 0.0958697d with a V amplitude of 0.4m, and regarded it as a member of high amplitude delta Scuti star class. We carried out observations by 60cm reflector of Xinglong station in Beijing observatory in the V-band of standard Johnson UBV system from the year 1988 to 1989, and obtained 13 times of maximum. A light-curve was constructed in Fig. 1 for November 13, 1988. We adopted the same comparison stars used by Oja, C1=HD79763, C2=HD80079 whose spectral types are A0 which is close to the A3 reported in the same catalogue for HD79889 (Rodriguez et al., 1990). For the purpose to study periodic long-term variations, we collected other materials about HD79889 and had altogether 32 points of times of maximum. Table 1 is the data on it, the figures with asterisk were taken from the references. Columns 2-5 represent heliocentric epoch of maximum, cycle number, residuals with linear equation and parabola respectively. Column 6 is the weight for each data. Using a linear formula, maximum light occurs at the heliocentric epoch T max= = 2446506.00785 + 0.09586943E Fig. 2 shows how the O-Cs vary with cycle number E. A further fitting with the least squares method gives: T max= = T_0 + P_0E + 0.5 beta E^s T_0 = 2446506.00774 +- 0.00014 P_0 = 0.095869547 +- 5.8 x 10^-8 Beta = -2.1 x 10^-11 +- 5 x 10^-12 Table 1. Times of light maximum on HD79889 No. T_0(I) E(I) L(O-C) Q(O-C) W 1* 46498.3379 -80.0 -.0004 -.0003 .5 2* 46506.0074 0.0 -.0005 -.0003 1.0 3* 46507.3501 14.0 .0001 .0002 .5 4* 46507.4459 15.0 .0000 .0001 .5 5* 46508.4049 25.0 .0003 .0004 .5 6* 46509.4587 36.0 .0005 -.0003 .5 7* 46510.4175 46.0 -.0003 -.0002 .5 8* 46524.4152 192.0 .0004 .0005 .5 9* 46950.4595 4636.0 .0010 .0008 .5 10* 46951.4174 4646.0 .0002 -.0000 .5 11* 47115.6420 6359.0 .0004 .0002 1.0 12* 47118.6131 6390.0 -.0004 -.0006 1.0 13* 47118.7102 6391.0 .0008 .0006 1.0 14* 47121.6813 6422.0 -.0000 -.0002 1.0 15* 47219.5637 7443.0 -.0003 -.0005 1.0 16 47265.1025 7918.0 .0005 .0003 1.0 17 47486.3692 10226.0 .0006 .0006 1.0 18 47488.2852 10246.0 -.0008 -.0008 1.0 19 47488.3811 10247.0 -.0008 -.0008 .8 20 47489.2450 10256.0 .0003 .0003 .8 21 47489.3412 10257.0 .0006 .0006 1.0 22 47493.1755 10297.0 .0001 .0001 1.0 23 47493.2703 10298.0 -.0009 -.0009 1.0 24 47542.2705 10809.0 -.0000 .0000 1.0 25 47544.2730 10830.0 -.0008 -.0007 .5 26 47544.3695 10831.0 -.0002 -.0001 1.0 27* 47551.4645 10905.0 .0005 .0006 1.0 28* 47551.5599 10906.0 .0000 .0001 1.0 29* 47553.5729 10927.0 -.0002 -.0001 1.0 30* 47553.6692 10928.0 .0002 .0003 1.0 31 47627.0088 11693.0 -.0003 -.0001 .8 32 47634.0080 11766.0 .0004 .0006 .5 [FIGURE 1] Fig. 1 Light curve relative to com. star on Nov. 13 1988 [FIGURE 2] Fig. 2 The O-C diagram It indicates that the long period variation accords with the parabola, namely, the rate of period change is negative, and the pulsation period is decreasing. Considering the short span of time, the fit error is quite big, but the tendency of period change is remarkable. The star deserves further study. Many observations need to be done so that more accurate values will be obtained. LIU YANYING, JIANG SHIYANG Beijing Astronomical Observatory Chinese Academy Of Sciences CAO MING Shaanxi Astronomical Observatory Chinese Academy Of Sciences REFERENCES : Oja, T. A. Ap., 184 (1987), 215. [BIBCODE 1987A&A...184..215O ] Rodriguez, E. et al, Rev. Mexicana Astron. Astrof., 20 (1990), 37. [BIBCODE 1990RMxAA..20...37R ]