COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2046 Konkoly Observatory Budapest 1981 November 27 HU ISSN 0374-0676 PERIOD CHANGES OF AC And The method of the envelopes was successfully used for the investigation of the multiperiodic variable star AC And (Guman, 1982). Since 1926 a dozen of observation sequences are available which make possible to find the period variations of this unique star. The results are collected in Table I. For each series of observations, from the envelopes we obtained virtual maximum moments (Om) for a mean Julian Date, J.D.mean, for each of the three periods. From these Om dates the following linear elements have been calculated by the method of least squares for the three periods: J.D. 2424708.058 + 0.71121566d * E_0.7 J.D. 2424708.143 + 0.52512765d * E_0.5 J.D. 2424708.110 + 0.42105993d * E_0.4 The Om-C residuals from these linear elements are presented in the columns headed (Om-C). According to the deviations from the linear elements the periods vary. Namely, the 0.711d period has been first increasing, and after J.D. 2433400 decreasing, the other two periods have been continuously increasing (supposing continuous variation). These variations are fitted in with the following cubic and parabolic elements, respectively: TABLE I. 0.711d Period 0.525d Period 0.421d Period JDmean Om E (Om-C) [Om-C] Om E (Om-C) [Om-C] Om E (Om-C) [Om-C] Typ Reference ------------------------------------------------------------------------------------------------------------------------------------ 2424833 .296d 176 +.064d +.008d .189d 238 +.066d -.010d .206d 297 +.042d +.009d pg. Guthnick,Prager(1927) 2425596 .376 1249 +.010 -.011 .166 1691 +.032 -.003 .557 2110 +.011 -.009 vis. Lause (1937) 2426693 .749 2792 -.023 -.008 .155 3780 +.030 +.020 .402 4715 -.005 -.011 vis. Lause (1932) 2426955 .475 3160 -.024 -.003 .159 4274 -.005 -.009 .330 5337 +.024 +.021 vis. Florja (1937) 2426968 .279 3178 -.022 -.001 .285 4304 -.007 -.011 .381 5368 +.022 +.019 vis. Lause (1933) 2428392 .122 5180 -.033 +.009 .403 7016 -.036 -.013 .362 8750 -.022 -.009 pg. Lurje (1950) 2428485 .286 5311 -.038 +.005 .366 7193 -.020 +.004 .398 8971 -.040 -.027 vis. Lause (1937) 2433183 .589 11957 -.024 -.020 .640 16140 -.063 -.005 .588 20129 -.037 -.003 pg. Guman (1982) 2435383 .446 15010 +.041 +.010 .414 20329 -.049 -.001 .197 25353 -.045 -.017 pe. Guman (1982) 2436811 .524 17032 +.041 -.007 .235 23067 -.027 +.005 .139 28768 -.023 -.003 pe. Notni (1963) 2437000 .055 17283 +.057 +.008 .318 23408 -.013 +.017 .133 29193 +.021 +.039 pe. Fitch,Szeidl(1976)* 2442702 .465 25301 -.060 -.001 .791 34267 +.099 -.007 .157 42735 +.051 -.009 pe. Jakate (1978) ------------------------------------------------------------------------------------------------------------------------------------ Mean error +-.044d+-.010d +-.050d+-.012d +-.035d+-.020d * The Om dates calculated from the five noncoupled elements. [FIGURE 1] [+1.119d*10^-5(E_0.7 - 12266)+1.020d*10^-10(E_0.7 - 12266)^2 - - 0.046d*10^-13(E_0.7 - 12266)^3] [-0.058d + 4.760d*10^-10(E_0.5 - 15705)^2] [-0.034d + 1.769d*10^-10(E_0.4 - 19720)^2] The Om-C residuals computed with the formulae extended with the above presented elements of higher order are listed in the columns headed [Om-C]. These results are also represented in Figure 1. In the upper part we have plotted the Om-C residuals from the linear elements and the cubic and parabolic fittings, respectively. The changes of the periods, derived from the higher fittings, are plotted in the lower part of the figure. The variations of the periods, particularly the variation of the 0.711d period, are very exciting. If this last variation has not been secular, but periodic, the period can be estimated as roughly 44 years. Therefore the photoelectric observation of this star is very desirable. I. GUMAN Debrecen, Ibolya u. 6. 4027 Hungary References: Fitch, W.S., Szeidl, B.: 1976, Astrophys. J. 203, 616. [BIBCODE 1976ApJ...203..616F ] Florja, N.T.: 1937, Astron. Zhurn. 14, 11. Guman, I.: 1982, Budapest, Mitt. No. 78. (to be published) [BIBCODE 1982CoKon..78....1G ] Guthnick, P., Prager, R.: 1927, Kl. Veroff. Berlin-B. 4, 17. Jakate, S.M.: 1978, Astrophys. J. 224, 603. [BIBCODE 1978ApJ...224..603J ] Lause, F.: 1932, Astr. Nachr. 245, 329. Lause, F.: 1933, Astr. Nachr. 249, 377. [BIBCODE 1933AN....249..377L ] Lause, F.: 1937, Astr. Nachr. 264, 143. [BIBCODE 1937AN....264..143L ] Lurje, M.: 1950, Perem. Zvezdy 7, 182. Notni, P.: 1963, Astr. Nachr. 287, 65. [BIBCODE 1963AN....287...65N ]