COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3141 Konkoly Observatory Budapest 1 February 1988 HU ISSN 0374-0676 ON THE PERIOD CHANGE OF THE RR LYRAE-TYPE VARIABLE XZ CYGNI Based upon 2500 photographic, photovisual and visual observations obtained by the author between 1957 - 1985, as well as upon published data by other authors, an analysis was made of the behaviour of the mean fundamental pulsation period of XZ Cygni (Bezdenezhnyi 1977, 1986). Table I shows the moments of 46 mean maxima derived, the corresponding (O-C)-residuals and the numbers of the main cycle E calculated by means of Klepikova's (1970) linear elements: Max. hel. = J.D. 2436933.981 + 0.466579d E. Table I Max.hel O-C E notes Max.hel. O-C E notes J.D. J.D. 2400000+ 2400000+ 36084.336 -0.006 - 1821 pg 45906.225 -0.537 +19231 pg 36435.217 +0.017 - 1069 pg 46281.385 -0.507 +20035 pg 37074.422 +0.004 + 301 pg 44412.441 -0.802 +18030 pg 37512.536 +0.005 + 1240 pg 45209.502 -0.657 +17738 pg 37896.533 -0.006 + 2063 pg 45608.474 -0.611 +18593 pg 38354.243 -0.001 + 3044 pg 45916.483 -0.544 +19253 pg 38983.187 -0.010 + 4392 pg 46303.290 -0.531 +20082 pg 39377.418 -0.040 + 5237 pg 36448.269 -0.008 - 1041 pv 39721.299 -0.032 + 5974 pg 36809.416 +0.012 - 267 pv 40230.267 -0.099 + 7065 pg 37174.269 -0.002 + 515 pv 40986.458 -0.233 + 8686 pg 37521.410 +0.003 + 1259 pv 41642.349 -0.351 +10092 pg 37904.475 +0.008 + 2080 pv 41545.280 -0.368 + 9884 pg 38253.480 +0.014 + 2828 pv 42292.140 -0.501 +11485 pg 38645.411 +0.010 + 3668 pv 42626.588 -0.590 +12202 pg 38990.168 -0.026 + 4407 pv 42981.525 -0.720 +12963 pg 39373.244 -0.011 + 5228 pv 43357.487: -0.821 +13769 pg 39785.202 -0.045 + 6111 pv 43732.535 -0.902 +14573 pg 40465.384 -0.133 + 7569 pv 44081.555 -0.883 +15321 pg 40814.336 -0.183 + 8317 pv 44467.495: -0.804 +16148 pg 41176.325 -0.262 + 9093 pv 44814.253 -0.714 +16891 pg 41649.323 -0.372 +10107 pv 45187.586 -0.644 +17691 pg 41565.368 -0.347 + 9927 v 45561.369 -0.591 +18492 pg 41906.355 -0.419 +10658 v Using the observations spanning from 1905 to 1954 published by Klepikova (1959), our mean maxima, and the material obtained by other authors (see Bezdenezhnyi, 1986), the system of nine linear elements was determined by a least squares solution. All the elements of XZ Cygni are discussed and compared with those published elsewhere. Table II No. Interval J.D. Mo P References 1 2417000-24800 2417201.243 0.4665861 Martin and Plummer (1914) +/-9 +/-2 Bezdenezhnyi (1986) 2 24800-34600 25031.492 0.4665818 Payne-Gaposchkin (1947) +/-2 +/-1 Bezdenezhnyi (1986) 3 34600-38700 36933.981 0.466579 Klepikova (1970) 4 38700-39800 38983.184 0.466560 Bezdenezhnyi (1986) +/-16 +/-4 5 39800-40750 40465.383 0.466516 Bezdenezhnyi (1986) +/-11 +/-2 6 40750-42300 40445.805 0.4664831* Bezdenezhnyi (1977) +/-3 7 42300-43900 43628.486 0.466442 Taylor (1978-79) and +/-45 +/-3 Bezdenezhnyi (1986) 8 43900-45200 45209.507 0.466679 Bezdenezhnyi (1986) +/-6 9 45200-46300 45209.511 0.466637 Bezdenezhnyi (1986) +/-7 * the period P = 0.466480 is of good fit as well (Bezdenezhnyi, 1986) +/- 4 [FIGURE 1] Figure 1 O-C diagram for XZ Cyg In Figure 1 (O-C)-values are shown versus E for 80 years. V.P. BEZDENEZHNYI Odessa Observatory, USSR. References: Bezdenezhnyi, V.P. 1977, The Variable Stars, Suppl. 3, 14, 125. [BIBCODE 1977PZP.....3..125B ] Bezdenezhnyi, V.P. 1986, in: "The Problems of Astronomy", V.2 Ukrain. Res. Inst. Sci. Techn. Inform. (UkrNIINTI) No 430, p.127-148. Klepikova, L.A. 1959, The Variable Stars, 12, 164. [BIBCODE 1958PZ.....12..164K ] Klepikova, L.A. 1970, S.A.C. 42. Martin, C. and Plummer, H.C. 1914, M.N. 74, 225. [BIBCODE 1914MNRAS..74..225M ] Payne-Gaposchkin, C. 1947, H.A. 118, No 19. [BIBCODE 1952AnHar.118..147P ] Taylor, P.O. 1978-79, J.A.A.V.S.O. 7, No 2, 82. [BIBCODE 1978JAVSO...7...82T ]