COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3770 Konkoly Observatory Budapest 14 September 1992 HU ISSN 0374 - 0676 NEW PHOTOELECTRIC PHOTOMETRY AND NEW TIMES OF LIGHT MAXIMUM OF AD CMi AD CMi is a very important Delta Scuti type variable due to its 0.30 magnitude amplitude and stable light curve. Recently Jiang (1987) and Rodriguez et al. (1988) published numerous careful observations and suggested a rather different rate of increasing period variation. To check how its period varies with time, we observed it again from February to April, 1992 at Xinglong station of Beijing Astronomical Observatory by using the 60 cm reflector and its single channel photoelectric photometer in V-band. The comparison star was BD+1d1938 for Feb. 3, and BD+1d1939 for other dates. From these observations we derived 6 times of light maximum. Figure 1 only presents three of these light curves. [FIGURE 1] Fig. 1 Light curve relative to comparison star Table 1 Times of maximum and new O-C Residuals of AD CMi for linear and quadratic fits No. T_max E (O-C)_L (O-C)_Q W 1 36601.8228 0.0 0.0017 0.0004 1.0 2 36602.8068 8.0 0.0017 0.0004 1.0 3 36602.9296 9.0 0.0017 0.0004 1.0 4 36604.8971 25.0 0.0016 0.0003 1.0 5 36627.7700 211.0 6.0012 0.0000 1.0 6 36628.7538 219.0 0.0012 0.0000 1.0 7 36629.7373 227.0 0.0009 -0.0003 1.0 8 36629.8602 228.0 0.0009 -0.0004 1.0 9 36931.7620 2683.0 0.0003 -0.0005 1.0 10 36932.7470 2891.0 0.0015 0.0007 1.0 11 38934.8364 2708.0 0.0003 -0.0004 1.0 12 36969.7620 2992.0 0.0012 0.0005 1.0 13 41010.6985 35852.0 -0.0040 -0.0011 0.5 14 42429.4582 47389.0 -0.0010 0.0021 0.1 15 43182.4290 53512.0 -0.0030 -0.0001 2.0 16 43536.3488 56390.0 -0.0038 -0.0010 2.0 17 43536.4714 56391.0 -0.0042 -0.0014 2.0 18 44645.0877 65406.0 -0.0029 -0.0007 2.0 19 45766.3713 74524.0 -0.0007 0.0005 1.0 20 45768.3377 74540.0 -0.0019 -0.0007 1.0 21 45768.4606 74541.0 -0.0020 -0.0008 1.0 22 45771.4134 74585.0 -0.0006 0.0006 1.0 23 45772.3961 74573.0 -0.0017 -0.0005 1.0 24 45772.5187 74574.0 -0.0020 -0.0009 1.0 25 46417.3991 79818.0 0.0001 0.0006 0.5 26 46418.2596 79825.0 -0.0002 0.0003 2.0 27 46418.3825 79826.0 -0.0003 0.0002 2.0 28 46419.2434 79833.0 -0.0002 0.0003 2.0 29 46419.3663 79834.0 -0.0002 0.0002 2.0 30 46443.1010 80027.0 0.0004 0.0008 1.0 31 46443.2243 80028.0 0.0007 0.0011 2.0 32 46443.3470 80029.0 0.0004 0.0008 2.0 33 46444.0850 80035.0 0.0006 0.0010 1.0 34 46444.2082 80038.0 0.0008 0.0012 2.0 35 46144.3312 80037.0 0.0008 0.0012 2.0 36 48653.2017 97999.0 0.0035 0.0005 1.0 37 48656.1511 98023.0 0.0016 -0.0015 2.0 38 48656.2762 98024.0 0.0037 0.0006 2.0 39 48713.0884 98486.0 0.0017 -0.0015 1.0 40 48714.0724 98494.0 0.0019 -0.0013 1.0 41 48717.0242 98518.0 0.0023 -0.0009 1.0 In Table 1 we listed all the time of light maximum from the literature and our recent observations. A least squares linear solution of the ephemeris leads to the following formula: T_max = HJD2436601.8211 + 0.122974490d E. +/- 4 +/- 6 [FIGURE 2] Fig. 2 The O-C diagram Figure 2 shows how the (O-C)_L varies with cycle number E and also a parabolic curve of the least squares quadratic solution as follows: T_max = HJD2436601.8224 + 0.12297429d E + 2.19 x 10^-12 E^2. +/- 2 +/- 1 +/- 11 Evidently, the quadratic fit is much better, so the period is clearly increasing with a rate of (1.3 +/- 0.07) x 10^-8 days/year. On account of so small sigma (only about 5% of the variation rate), our result is considerably reliable. But the very reliable observations in 1985 and 1986 could not be fitted by the curve well. We do not know why it is so. Therefore more observations are urgently needed to make clear the real situation about the period variation. * YANG DAWEI Physics Department Hebei Teachers University 050016, Shijiazhuang, Hebei People's Republic of China * TANG QUINGQUAN Physics Department Sichuan Teachers College 637002, Nanchong, Sichuan People's Republic of China JIANG SHIYANG Beijing Astronomical Observatory 100080, Chinese Academy of Sciences Beijing, People's Republic of China (The project is supported by Natural Science Foundation of China) References: Jiang, S.: 1987, Acta Astronomica Sinica, 28, 57. [BIBCODE 1987AcASn..28...57J ] Rodriguez, E., Rolland, A. & Lopez de Coca, P.: 1988, Rev. Mexicana Astron. Astrof., 16, 7. [BIBCODE 1988RMxAA..16....7R ] * Visiting Astronomer in Beijing Astronomical Observatory