COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 3238 Konkoly Observatory Budapest 16 September 1988 HU ISSN 0374 - 0676 FAST CHANGES IN THE SHAPE OF THE LIGHT CURVE OF THE OLD NOVA V603 Aql V603 Aql (Nova 1918) is a relatively little studied object despite being the brightest old nova. In particular it was only in 1985 that it was found that its photometric and spectroscopic periods differ by several percent (Hafner and Metz 1985). In this short communique we report preliminary results of 9 white light photometric runs obtained in July/August 1988 and spanning 29 days altogether (Table 1). With the double beam photometers we observed simultaneously V603 Aql and the comparison star BD +0d4026. On all occasions 20 seconds integration times were used. In order to remove effects of atmospheric extinction we divided variable star counts by comparison star counts. In Figure 1 samples of our results are presented. In particular we would like to draw attention to substantial changes in the shape and amplitude of light curves obtained on consecutive nights. On the one hand presence of such changes interferes with the study of the photometric period, to the extent of it being indetectable on some occasions (Slovak 1981). Thus one of our motivations to reobserve this star was to confirm Hafner and Metz findings. On the other hand presence of the changes and difference of the two periods point to some mechanism of light variation independent of orbital motion. Were the mechanism related in one or other way to accretion, modulation of the light curve by changes in the accretion rate would arise in a natural way. Apart from the periodic variations some light curves exhibit violent flickering. Any effects of the instrumental origin are less than 0.01 mag in amplitude as may be appreciated by looking on the uncorrected for extinction comparison star light curve obtained simultaneously and presented also in Figure 1. The observations were obtained with the twin 60-cm telescopes of High Pedagogical School (WSP) in Cracow and Warsaw University Observatories located respectively at Mt. Suhora 70 km south of Cracow and at Ostrowik near Warsaw. At Mt. Suhora we used a double beam photometer donated by the European Southern Observatory to Warsaw Observatory following the initiative and through the action of Prof. Edward H. Geyer. [FIGURE 1] Table 1. Journal of the Observations. No. Date Run Start Duration Telescope (J.D.hel.-2447300) (day) 1 1988-07-23 66.381 0.139 Mt. Suhora 2 1988-07-25 68.372 0.155 Ostrowik 3 1988-07-26 69.358 0.171 Ostrowik 4 1988-08-14 88.339 0.161 Ostrowik 5 1988-08-17 91.318 0.019 Mt. Suhora 6 1988-08-18 92.315 0.173 Mt. Suhora 7 1988-08-19 93.310 0.104 Mt. Suhora 8 1988-08-20 94.311 0.154 Mt. Suhora 9 1988-08-21 95.324 0.147 Mt. Suhora The Ostrowik double beam photometer and the data acquisition systems for both telescopes were developed in Warsaw University Observatory (Szymanski and Udalski 1988). Observations at Mt. Suhora were possible thanks to the invitation to collaboration by the Director of the new observatory, Prof. Jerzy M. Kreiner. Support from grant CPBP 164 is gratefully acknowledged. A. UDALSKI M. SZYMANSKI A. SCHWARZENBERG-CZERNY, Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland. References: Hafner, R., and Metz, K., 1985, Astron. Astropys., 145, 311. [BIBCODE 1985A&A...145..311H ] Slovak, M.H., 1981, Ap. J., 248, 1059. [BIBCODE 1981ApJ...248.1059S ] Szymanski, M., and Udalski, A., 1988, in preparation. [BIBCODE 1989AcA....39....1S ]