COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 1483 Konkoly Observatory Budapest 1978 October 6 THE PERIOD VARIABILITY OF THE CLOSE BINARY W SERPENTIS The ephemeris for W Ser (HD 166126: F5e Ib) can be improved beyond the representation by Wood and Forbes (1973). The published timings of minimum light available to the present authors are those derived from visual estimates by Zinner (1912, 1922), Banachiewicz (1928a, b), Lause (1930), Bauer (1945), Zacharov (1954) and Tsesevich (1955); photographic estimates by Gaposchkin (1937) and Filin (1948); visual observations by McLaughlin (1961); and photoelectric measures by Fresa (1957, 1962), Lynds (1957), Hall (1967), Walraven (1969) and Kruszewski (1972). In addition, E. F. G. observed two times (in the b-bandpass) with a photoelectric photometer equipped with an RCA 4509 multiplier at Biruni Observatory, Pahlavi University, Shiraz, Iran: 2443363.23 and 2443646.675. The photographic estimates by O'Connell (1937) were not available to the present authors. Fifty four timings of minimum light were accumulated and were assigned weights of 1, 2, and 3 according to the measurements being estimates, visual observations, or photoelectric observations, respectively. Residuals were first computed from the ephemeris: Pr. Min. = 2426625.241 + 14.15782 E, (1) and these residuals were then subjected tc least squares polynomial fitting. A quadratic fit is definitely inferior to a cubic one and the latter is shown among the residuals in the figure. The improved ephemeris becomes: Pr. Min. = 2426625.493 + 14.15486E +(3.140x10E-6)*E*E+(1.432*10E-9)*E*E*E. (2) If the cubic term is ignored, the period change may be evaluated: DeltaP = 0.54 sec/cycle, DeltaP/P = 4.44 x 10E-7 This period change is comparable to the recent ones for beta Lyr (Herczeg 1973) and RX Cas (Kreiner 1978). [FIGURE 1] The O-C diagram from equation (1) for W Ser. Small circles refer to visual or photographic estimates, triangles refer to visual observations, and squares refer to photoelectric measures. The curve represents equation (2). It may be noted that the present phases of the (O-C)-diagrams for W Ser and RX Cas appear to be similar to each other. In another communication, Plavec and Koch (1978) remark upon the similarity of the satellite UV spectra of these two systems. It will be interesting to see if their respective period changes can be correlated in any way with the richness of the emission spectra and, by inference, with the vigor of the presumed mass transfer. Plavec and Koch also note that the emission spectrum of SX Cas is stronger than that for RX Cas and W Ser, and from Whitney's (1978) period study it is possible to infer that SX Cas is at a phase in its period variation different from that of the two other systems. An approximation to a linear ephemeris after E = + 715 (from (1) and (2)) may be suggested: Pr. Min. = 2436748.10 + 14.16540E'. (3) R. H. KOCH E. F. GUINAN Department of Astronomy Department of Astronomy University of Pennsylvania Villanova University Philadelphia, PA 19104 Villanova, PA 19085 and Biruni Observatory Pahlavi University Shiraz, Iran References: Banachiewicz, T. 1928a, S.A.C. 6, 66 Banachiewicz, T. 1928b, S.A.C. 6, 69 Bauer, C.A. 1945, Ap.J. 101, 208 [BIBCODE 1945ApJ...101..208B ] Fresa, A. 1957, A.J. 62, 362 [BIBCODE 1957AJ.....62..362F ] Fresa, A. 1962, M.S.A.I. 33, 151 [BIBCODE 1962MmSAI..33..151F ] Filin, A.Ya., 1948, Perem. Zvezdy 7, 90 Gaposchkin, S. 1937, H.A. 105, 511 Hall, R.C. 1967, A.J. 72, 778 [BIBCODE 1967AJ.....72..778H ] Herczeg, T.J. 1973, I.B.V.S. No. 820 Kreiner, J.M. 1978, I.B.V.S. No. 1403 Kruszewski, A. 1972, A.A. 22, 405 [BIBCODE 1972AcA....22..405K ] Lause, F. 1930, A.A.c 1, 98 Lynds, C.R. 1957, Ap.J. 126, 81 [BIBCODE 1957ApJ...126...81L ] McLaughlin, D.B. 1961, A.J. 66, 351 [BIBCODE 1961AJ.....66..351M ] O'Connell, D.J.K. 1937, Ann. Bosscha Lembang 8, 22 Plavec, M. and Koch, R.H. 1978, I.B.V.S. No. 1482 Tsesevich, V.P. 1955, Odessa Izv. 4, 6 Walraven., J.H. 1969, I.B.So.Hem. 15, 40 Whitney, B.S. 1978, I.B.V.S. No. 1430 Wood, D.B. and Forbes, J.E. 1963, A.J. 68, 257 [BIBCODE 1963AJ.....68..257W ] Zacharov, G.P. 1954, Perem. Zvezdy 10, 48 Zinner, E. 1912, A.N. 190, 377 [BIBCODE 1912AN....190..377Z ] Zinner, E. 1922, A.A.A.N. 4 (3), C1