COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 2976 Konkoly Observatory Budapest 16 January 1987 HU ISSN 0374 - 0676 ON THE PERIOD OF QQ VULPECULAE: NEW MINIMA FROM OLD PLATES QQ Vul is an AM Her-type system with the longest known period. However, the value of this period was not known so precisely, as it is needed to accurate phase determination. In this paper we present the previous results of the re-examination of the observations from Moscow (Andronov and Yavorskij 1983) and Sonneberg (Fuhrmann, 1984 ) plate collections. The modified version of the program published by Andronov (1985) was adopted for the period search and light curve approximation using the cubic spline functions. The values of P=0d.1545207+-3*10^-7 (M) and P=0d.1545204d+-3*10^-7 (S) were derived for all Moscow (M) and Sonneberg (S) observations. No peaks were seen at the periodograms near the positions of the previously published periods. The derived moments of "normal" minima are the moments of time, nearest to the mean time of the observations in a fixed season, which have the corresponding phase. The accuracy of the moments of minima was usually 0.001-0.002d, but never larger than 0.005d. All the available moments of minima are presented in Table I, together with 19 minima published by Andronov e.a. (1986 a, b) and 3 minima derived from the photoelectric light curves published by Nousek e.a. (1984) and Mukai e.a. (1986). The following linear elements were obtained using the least-square method : Min. HJD = 2440000.0628 + 0d.154520356*E (A) +- 8 +- 22 The residuals from this ephemeris are shown in Fig.1. Assuming the cyclic variation of them, one may obtain the best fit formula: Min.HJD = 2440000.0633+0d.154520351*E+0d.00618*cos(2pi(E-E_0)/P_E) (C) +- 7 +- 18 +- 96 where E_0=4125+-692, P_E=27712+-945. The phase of the periodic variations may also be written as 2pi(t-t_0)/Pt, where t_0=2440637+-107, and P_t=4282+-146. As in other polars, the cyclic changes of (O-A) might be interpreted by the "swinging dipole" model (Andronov, 1982, 1986; Campbell, 1984). The amplitude of the changes of the orientation of the magnetic axis of the white dwarf, is 14+-2 deg, that is nearly the same as the value of 17 deg observed in AM Herculis (Andronov, 1982). But the cycle duration is four times longer as compared with 1100d in AM Herculis. These "swingings" may cause the changes of the photometric and spectral characteristics of QQ Vul observed by Mukai et al. (1986). [FIGURE 1] It must be pointed out that we observe the cyclic but not periodic changes in (O-A) and in other characteristics. Not only the cycle, but the amplitude is variable as well. So the equation (C) corresponds only to the mean value of the cycle length. One of the possible explanations might be connected with the long term changes of the characteristics of the secondary's atmosphere (Wenzel and Fuhrmann 1983). The large dispersion of O-C of 0.006 = 0.04p, as one may see from photographic and photoelectric observations, is also characteristic for polars, because of the heterogeneities of the accretion flow which lead to the rapid changes in the accretion column's structure. However, this phenomenon has to be investigated using statistical methods in future works. It might be noted that in the third "long-period" polar H 0538+608 recently discovered by Remillard e.a.(1986), the shapes of the polarization and photometric curves underwent changes, which are much more pronounced compared with other polars. The possible explanation might be that the white dwarf in this object is still synchronizing, but not synchronized (eg. Andronov, 1986), so the "waltz" stage is not become yet to a "swing" stage. Table I T D-R D-C E 27779.677 0.0101 0.0039 -79086 S* 27979.477 0.0153 0.0093 -77793 S* 28190.244 0.0165 0.0114 -76429 S* 28345.842 0.0125 0.0083 -75422 S 29294.724 -0.0149 -0.0113 -69281 S* 29647.189 -0.0108 -0.0052 -67000 S 29823.508 0.0004 0.0065 -65859 S* 29990.529 -0.0151 -0.0089 -64778 S 30221.689 -0.0175 -0.0119 -63282 S* 30389.042 -0.0101 -0.0052 -62199 S 30523.021 -0.0002 0.0038 -61332 S* 30730.382 -0.0055 -0.0031 -59990 S 30937.593 -0.0063 -0.0057 -58649 S* 31103.241 -0.0041 -0.0050 -57577 S 31310.310 0.0076 0.0049 -56237 S 35342.516 0.0051 0.0046 -30142 S* 35990.261 0.0008 -0.0045 -25950 S 36814.777 -0.0038 -0.0085 -20614 S* 36907.946 -0.0106 -0.0143 -20011 S 37583.358 -0.0070 -0.0056 -15640 S 37791.343 -0.0064 -0.0033 -14294 S 37904.757 -0.0104 -0.0064 -13560 S* 38061.448 -0.0030 0.0020 -12546 M 38177.490 -0.0058 -0.0003 -11795 S 38264.640 -0.0052 0.0006 -11231 S* 38533.824 0.0043 0.0105 - 9489 M 38629.295 -0.0183 -0.0122 - 8871 S* 38825.389 -0.0106 0.0051 - 7602 S* 38836.682 0.0024 0.0078 - 7529 M 38946.693 -0.0051 -0.0002 - 6817 M 38982.386 -0.0063 -0.0016 - 6586 S* 39159.312 -0.0061 -0.0026 - 5441 M* 39168.131 0.0053 0.0087 - 5384 S 39341.491 -0.0066 -0.0046 - 4262 M* 39584.715 0.0024 0.0022 - 2688 M 39726.413 0.0052 0.0038 - 1771 M* 39853.275 0.0060 0.0035 - 950 M 40081.352 0.0110 0.0068 526 M* 40239.882 0.0031 -0.0020 1552 M 40466.252 0.0008 -0.0052 3017 M* 40660.947 0.0002 -0.0060 4277 M 40797.387 -0.0013 -0.0073 5160 M* 41119.563 -0.0002 -0.0049 7245 M 41492.732 0.0021 0.0002 9660 M 41578.495 0.0063 0.0052 10215 M* 41752.947 0.0048 0.0053 11344 M 41879.810 0.0066 0.0082 12165 M 42241.536 0.0005 0.0049 14506 M 42453.696 0.0041 0.0093 15879 M 42978.905 -0.0016 0.0043 19278 M 42984.007 0.0012 0.0071 19311 M 43034.673 -0.0155 -0.0097 19639 M 43217.173 -0.0040 0.0010 20820 M 43372.473 0.0031 0.0070 21825 M 43572.107 -0.0032 -0.0008 23117 M 43746.717 -0.0012 -0.0003 24247 M 44101.345 0.0026 0.0003 26542 M* 44222.803 0.0076 0.0044 27328 M 44457.830 0.0091 0.0043 28849 M 44656.538 0.0040 -0.0018 30135 M 44798.384 0.0003 -0.0058 31053 M 45231.818 0.0047 -0.0009 33858 N 45232.740 -0.0004 -0.0060 33864 N 45460.509 0.0056 0.0012 35338 S 45485.542 0.0063 0.0021 35500 S 45501.615 0.0092 0.0051 35604 S 45530.502 0.0009 -0.0030 35791 Ab 45530.652 -0.0037 -0.0075 35792 Ab 45562.490 0.0031 -0.0005 35998 Ab 45562.650 0.0086 0.0050 35999 Ab 45563.570 0.0015 -0.0021 36005 Ab 45908.619 0.0066 0.0058 38238 Mu 45961.305 0.0011 0.0009 38579 Ab 45963.315 0.0024 0.0021 38592 Ab 45969.345 0.0061 0.0059 38631 Ab 46006.275 0.0057 0.0058 38870 Ab 46296.455 -0.0035 -0.0008 40748 Ab 46324.270 -0.0022 0.0007 40928 Ab 46328.295 0.0053 0.0082 40954 Ab 46328.445 0.0008 0.0037 40955 Ab 46489.454 -0.0004 0.0037 41997 Ab 46621.418 0.0032 0.0031 42851 Aa 46626.352 -0.0075 -0.0025 42883 Aa 46638.241 -0.0165 -0.0115 42960 Aa 46639.328 -0.0112 -0.0061 42967 Aa 46653.399 -0.0015 0.0036 43058 Aa 46655.399 -0.0103 -0.0052 43071 Aa Remarks: S,M - Mean minima from Sonneberg and Moscow Plates; * - observations from two or three subsequent seasons were used N - minima from Nousek e.a. (1984) Mu - Mukai e.a. (1986) Aab - Andronov (1986ab) Because of its longest known period, QQ Vulpeculae is in some sense the intermediate object between "classical" and "intermediate" polars. So further simultaneous multicolour observations might clarify the details of the structure and evolution of magnetic close binaries. I.L. ANDRONOV Friedrich-Schiller Universitat Jena Sektion Physik, Universitats-Sternwarte, GDR On leave from Odessa State University Faculty of Physics, Department of Astronomy, USSR B. FUHRMANN Zentralinstitut für Astrophysik der Akademie der Wissenschaften der DDR Sternwarte Sonneberg GDR References: Andronov, I.L., 1982, Preprint VINITI No. 5981-82 Dep., 23pp. 1985, Preprint UkrNIINTI No. 134 Uk-85 Dep. 38 pp. 1986, in: "Eruptive Phenomena in Stars", ed. L. Szabados, Commun. Konkoly Obs. Hung. Acad. Sci. No. 86, 371. [BIBCODE 1986CoKon..86..371A ] [CoKon No. 86] Andronov, I.L., Kudashkina, L.S., Poplavskaya N.V., Kimeridze G.N., 1986a, Bull. Abastum. Astrofiz. 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