COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1997 Konkoly Observatory Budapest 1981 July 28 HU ISSN 0374-0676 AR AURIGAE - TRIPLE SYSTEM? The binary AR Aur is well known as a detached system. Since the discovery of its variability by Pedersen and Steensgard in 1931 it has been observed by several observers photoelectrically. Between 1935 and 1939 the period was 4.13467d according to Huffer. and Eggen (1947). There are two other estimations referred to this period, 4.134581d by Nassau (1937) and 4.1346607d by Woodward (1943). O'Connell (1979) analysed all the visual, photographic and photoelectric observations made up to 1978 and claimed that the period of this binary had undoubtedly changed. He derived the value 4.134686d for the period between 1963 and 1970. Besides, he concluded that the period became decreasing in about 1974. [FIGURE 1] AR Aur is one of the objects we have studied from the point of view of their Ap characteristics. Between 1979 and 1981 we managed to observe two primary and one secondary minima photoelectrically, The observations were made by the photoelectric photometer attached to the cassegrain focus of the 0.6 m telescope at the Skalnate Pleso Observatory. Our results together with all the photoelectric minima given by O'Connell (1979) are listed in Table I. Because of their large scatter we have omitted the visual and the photographic minima. Figure 1 shows the O-C diagram constructed according to the ephemeris JD/MinI/ = 2 427 887.7217 + 4.1346662 x /E + 2543/ /1/ The period in this formula is the average one that we obtained taking into account only the first and the last primary minima from Table I. It is obvious in Figure 1 that a continual change of the period has taken place in the system. The part since 1964 up to now can be fitted well by a parabola that results in the following ephemeris JD/MinI/ = 2 438 402.1832 + 4.134695 x E - 2.2 x 10^-8 x E^2 /2/ +-.0007 +-.000002 +-.2 [FIGURE 2] The O-C residual after this parabola fitting are shown in Figure 2. The mean period derived for our three minima is 4.134652d +-.000006. All the observations obtained so far have displayed at first an increase of the period until about 1964 followed by a decrease till 1981. As this system is detached, such cyclic changes of the period can be induced by a third body in the system. Unfortunately, a lack of observations between 1935 and 1964 does not allow us to decide whether the residual in Figure 1 should be best fitted by a double or a single wave. At any rate, a duration of one cycle is shorter then about fifty years, therefore the third body can not be the star HR 1732, that was said to be in a physical connection with AR Aur (Hoffleit, 1964). Table I JD E Date O- C O- C Observer 2 400 000.+ /1/ /2/ 27 887.7217 -2543 1935.23 .0000 Huffer and Eggen 27 889.7892 -2542.5 1935.24 +.0002 " 38 404.2504 0.5 1964.03 +.0052 .0002 O'Connell 38 435.2603 8 1964.11 +.0051 .0005 " 39 098.8783 168.5 1965.93 +.0092 .0004 Johansen 39 154.6964 182 1966.08 +.0093 .0006 " 39 940.2880 372 1968.23 +.0143 .0012 O'Connell 40 246.2538 446 1969.07 +.0148 .0009 " 40 248.3215 446.5 1969.08 +.0152 .0012 " 40 498.4683 507 1969.76 +.0147 .0002 Gulmen 40 930.5414 611.5 1970.94 +.0151 .0002 Battistini et al. 41 941.464 856 1973.71 +.0119 .0023 Schellerman et al. 44 153.5008 1391 1979.77 +.0022 .0013 This paper 44 612.4465 1502 1981.02 .0000 +.0002 " 44 614.5150 1502.5 1981.03 +.0012 +.0014 " J. ZVERKO, D. CHOCHOL, K. JUZA, J. ZIZNOVSKY Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatranska Lomnica, Czechoslovakia References: Hoffleit, D.: 1964, Cat. of Bright Stars, Yale Univ. Obs., New Haven, Connecticut. [BIBCODE 1964cbs..book.....H ] Huffer, C.M., Eggen, O.J.: 1947, Astrophys. J. 106, p. 106. [BIBCODE 1947ApJ...106..106H ] O'Connell, D.J.K.: 1979, Ricerche Astron. 8, p. 563. [BIBCODE 1979RA......8..563O ] Pedersen, Steensgard: 1931, Beob. Zirk. 13, p. 70. Woodward, E.J.: 1943, Harv. Bull. 917, p 7.