COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1583 Konkoly Observatory Budapest 1979 April 9 PHOTOMETRY OF THE RECURRENT NOVA WZ SAGITTAE AT OUTBURST The recurrent nova WZ Sge was observed during 8 nights from 3 to 23 December 1978 (UT). The observations were made at the Ostrowik station of the Warsaw University Observatory. The 60-cm reflector was used with a conventional single-channel photometer housing an EMI 9781 photomultiplier. The variable was monitored through the B filter, with a few observations obtained through the V. BD +17d4225, with magnitudes V = 8.755m and B-V = +0.160m according to Krzeminski and Smak (1971), served as the comparison star. The accuracy of our observations was fairly good although influenced somewhat by the low altitude of WZ Sge above the horizon. All eight of our light curve are characterized by the absence of narrow minima, so they are radically different from the preoutburst curves, for example, those of Krzeminski and Smak (1971). Only in the light curve of 3 December are the minima clearly seen, but the times of these minima are earlier by 13 minutes than predicted by the preoutburst ephemeris (Robinson et al. 1978). Up to 14 December our observations and those of Heiser and Henry (1979) show two maxima in the light curves: a higher one (primary) and a lower one (secondary) separated by a half period. Gradually with time the secondary became more clearly defined. On 13 December the two maxima were nearly equal in height. Later on the primary maxima disappeared and only the secondary could be seen, as a big hump. We derived times of maxima from our light curves and the light curves of Heiser and Henry (1979) and used these times along with the times published by Targan (1979b) to study the period of WZ Sge. All these times (O) are listed in Table 1 along with cycle numbers (E) and residuals (O-C) computed from the preoutburst ephemeris JD(hel.)= 2437547.72845+0.0566878455d E (1) Table 1 --------------------------------------------------------------- Date Obs.Maxima Cycle Residuals Cycle Residuals Observer (UT) (O) (E) (O-C) (E') (O-C') Dec. JD(hel.) (Days). (Days) 1978 2443800+ 111000+ --------------------------------------------------------------- 3 S 46.266 108 0.065 - - B,U 3 P 46.293 109 0.034 - - B,U 6 P 48.503 148 0.034 - - H,H 6 P 49.242 161 0.036 - - B,U 6 S 49.268 161 0.062 - - B,U 6 P 49.298 162 0.036 - - B,U 7 P 50.261 179 0.035 - - B,U 8 P 51.220 196 0.030 - - B,U 8 S 51.244 196 0.054 - - B,U 8 P 51.277 197 0.030 - - B,U 10 P 52.526 219 0.032 - - H,H 12 P 55.496 271 0.054 - - H,H 13 S 55.528 271 0.086 - - H,H 14 S 57.4767 305 0.1076 0 -0.0008 T 15 S 57.537 306 0.111 1 +0.002 H,H 15 S 58.4496 322 0.1168 17 -0.0005 T 19* S 62.236 388 0.162 83 +0.010 B,U 19 S 62.4575 392 0.1566 87 +0.0024 T 21 S 64.171 422 0.170 117 0.000 B,U 21 S 64.228 423 0.170 118 -0.001 B,U 21 S 64.285 424 0.170 119 -0.001 B,U 22 S 65.201 440 0.179 135 0.000 B,U 23 S 65.541 446 0.179 141 -0.003 H,H 26 S 69.495 515 0.221 210 +0.002 H,H ------------------------------------------------------------ P - Primary maximum; S - Secondary maximum; H,H - Heiser and Henry, 1979; T - Targan, 1979b; B,U - Bohusz and Udalski * - Lower weight; time of this maximum has not been used in deriving the period. of Robinson et al. (1978). The O-C residuals are plotted versus E in Figure 1. The times of primary maxima are shown as filled circles, those of secondary as open circles. The cross denotes the maximum of Patterson quoted by Targan (1979b). Looking at Figure 1 one should note that until about 9 December (E=111200) the period can be regarded as constant and equal to its preoutburst value. It is possible that between 6 and 8 December the period was shorter by 0.3% though this effect nay be spurious. The period increased sharply by 1% on or about 10 December (E= 111215). Thus we confirm the period increase noted first by Targan (1979a). Observations from 14 to 26 December indicate that the period remained fairly constant after the increase. The ephemeris giving the best fit to these later times of maximum is JD(hel.)= 2443857.4775+0.057213d E' (2) [FIGURE 1] Figure 1: The (O-C) diagram for the maxima of WZ Sge calculated using ephemeris of Robinson et al. (1978). Filled and open circles refer to primary and secondary maxima, respectively The straight line represents elements: JD(hel.)=2443857.4775+0.057213d E'. The cross denotes the epoch of maximum of elements given by Patterson (quoted by Targan, 1979b). The arrow indicates the beginning of outburst. Table 1 gives also cycle number E' and residuals (O-C') computed with the above ephemeris. Our value for this new period is close to but a bit shorter than that of Targan (1979b) or that of Patterson as quoted by Targan (1979b). We suggest that the period increase might be connected with the appearance of the superhump thus implying that WZ Sge is a member of the SU UMa subclass of dwarf novae best exemplified by VW Hya (Haefner, Schoembs, Vogt, 1978). Generally the light curves show an amplitude of about 0.25m in B. The composite light curve for 6, 7, 8 December is plotted in Figure 2. Phases in this figure are computed with the ephemeris JD(hel.)= 2443849.2425 + 0.056515d E" (3) which best satisfies the times of maximum on those three nights. [FIGURE 2] Figure 2: Composite light curve of WZ Sge assembled from nights 6, 7, 8 December 1978. Phase is calculated from the elements: JD(hel.)= 2443849.2425 + 0.056515d E". [FIGURE 3] Figure 3: Composite light curve of WZ Sge assembled from nights 19, 21, 22 December 1978. Phase is calculated from the elements: JD(hel.) - 2443857.4775 + 0.057213d E'. maximum observed on 19 December is denoted by open circles. Figure 3 shows the analogous curve for 19, 21, 22 December. Phases in this figure are computed with the elements in Equation (2) and indicate that the new period is satisfactory. We would like to thank Dr. Whit Ludington for timely passing the information about the nova outburst and Drs. A. Kruszewski, W. Krzeminski, I. Semeniuk for their help in preparing this paper. EWA BOHUSZ ANDRZEJ UDALSKI Warsaw University Observatory Al. Ujazdowskie 4 00-478 Warszawa, Poland References: Haefner, R., Schoembs, R., Vogt, N., 1978, ESO Scientific Preprint, No. 33 Heiser, A.M., and Henry, G.W., 1979, I.B.V.S. No. 1559 Krzeminski, W., and Smak, J., 1971, Acta Astr., 21, 133 [BIBCODE 1971AcA....21..133K ] Robinson, E.L., Nather, R.E., and Patterson, J., 1978, Ap.J. 219, 168 [BIBCODE 1978ApJ...219..168R ] Targan, D., 1979a, IAU Circular, No. 3320 [BIBCODE 1979IAUC.3320....3T ] Targan, D., 1979b, I.B.V.S., No. 1539