COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1539 Konkoly Observatory Budapest 1979 January 30 PHOTOMETRY OF WZ SAGITTAE DURING ITS 1978 OUTBURST Photoelectric photometry of the recurrent nova and eclipsing binary WZ Sagittae reveals that a 0.8 minute, or 1% change in its photometric period took place during its recent outburst. Whereas the premaximum period given by Robinson et al. (1978) is 81.63 minutes, outburst observations since December 10, 1978 are more consistent with an 82.42 minute period. Observations were made on seven evenings between December 10 and December 23, 1978, using the 36 cm Schmidt-Cassegrain telescope of Brown University. The photometer employs an RCA 1P21 tube (uncooled) and the standard U,B,V filters. All measurements were made through the V filter. BD+17d4224 [V=8.76 (Krzeminski and Kraft, 1964)] was the comparison star. The slowly changing features of the light curves are sometimes masked by sudden fluctuations in brightness. These fluctuations are partly intrinsic to WZ Sge and partly related to the poor photometric conditions at. Sagitta's low altitude. The most distinct minima observed during this period are listed in column one of Table 1. Table 1 -------------------------------------------------------------------------------- O E C O-C C' O-C' Obs.Minima Eclipse Calc.Minima Residuals Revised Revised (JD_Hel2443800.0+) Number (JD_Hel2443800.0+) (Days) Calc.Min. Residuals (JD_Hel2443800.0+) (Days) -------------------------------------------------------------------------------- 57.4621 111307 57.4825 -0.0203 57.46298 -0.0009 58.4382 111324 57.4462 -0.0080 58.4360 0.0022 62.4397 111394 62.4143 0.0254 62.4423 -0.0026 66.4499 111464 66.3825 0.0674 66.4487 0.0012 -------------------------------------------------------------------------------- The predicted times of minima, T (column three), were calculated using the premaximum elements: T=JD_Hel 2437547.72845+0.0566878455d E (Robinson et al. 1978). +-3 +-7 [FIGURE 1] [FIGURE 2] The residuals are plotted in Figure 1. The revised elements that give the best fit for our data are T=JD_Hel 2443857.46298+ 0.057234d E. The values in the fifth column and the residuals in the sixth column of Table 1 are based upon these revised elements. Observers at the University of Texas McDonald Observatory found it easier to discern the maxima during the outburst, and their observations conform to the elements: T_max= JD_Hel2443852.552+ 0.057250d E (Patterson 1979). Table 2 shows that their elements do predict this author's observations of maxima within observational error. The maxima were. obtained by selecting what appeared to be well defined primary maxima, and neglecting occasional isolated high readings as well as a secondary hump separated from the primary by half the orbital period, which was occasionally observed. Table 2 ------------------------------------------------ O C O-C Observed Maxima Calculated Maxima (Days) (JD_Hel2443860.0+) (JD_Hel2443800.0+) ------------------------------------------------ 57.4767 57.4755 0.0012 58.4496 58.4488 0.0008 62.4575 62.4563 0.0012 ------------------------------------------------ A magnitude versus phase diagram combining the observations of JD 2443857 and JD 2443862 shows the general form of the 0.3m amplitude variation in V, while providing further evidence that the assumed new period is correct. (See Figure 2). The phase was computed by using the revised ephemeris. Allowance was made for gradual variation in brightness as the nova faded. It should be noted that observations by E. Bogusz and A. Udalski of the Warsaw University Observatory indicate that WZ retained its normal periodicity through December 8-9 (Kruszewski and Krzeminski, 1979). Apparently the period change occurred somewhere between December 8-9 and December 10, when the new period was first observed. In conclusion, observations from December 10, 1978 indicate that the photometric period of WZ Sagittae has increased by 0.8 minutes. Observations of WZ Sge upon its reappearance from behind the sun would be of importance in understanding the nature of such changes in period. The author thanks all of those who assisted in the observations, and gratefully acknowledges valuable discussions with Richard Bates, Joseph Patterson, and Adam Schultz. DAVID TARGAN Ladd Observatory Department of Physics Brown University, Providence, R.I. 02912, U.S.A. References: Kruszewski, A., and Krzeminski, W., IAU Circular 3318, Jan. 3, 1979 [BIBCODE 1979IAUC.3318....3K ] Krzeminski, W., and Kraft, R.P., 1964, Ap.J. 140, 921 [BIBCODE 1964ApJ...140..921K ] Patterson, J., 1979 Private communication Robinson, E.L., Nather, R.E., and Patterson, J., 1978, Ap.J. 219, 168 [BIBCODE 1978ApJ...219..168R ]