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Published online by Cambridge University Press: 12 April 2016
Our photometry revealed that the old nova V603 Aql has four different coherent periods, including a period present in X-rays and so it is quite unique among all novae. Thus we classify V603 Aql as an intermediate polar (IP) system. Some time ago Hefner and Metz (1985) found that the period of the sinusoidal light variations of V603 Aql is 3.5 hour and thus it is longer by about 5 percent than the spectroscopic orbital period of 3.3 hour. Our observations covering over 30 hours and spanning 30 days confirm their result. However, we discovered also another coherent oscilation with a small amplitude of 0.02 mag and period of 61 min (Udalski and Schwarzenberg-Czerny, 1989). Our analysis of the X-ray observations by Drechsel et al. (1983) revealed 25 percent modulation with the same period and thus confirmed our discovery (Fig. 1). Additionaly we found in our light curves evidence of the 2.5 day beat period of the 3.3 and 3.5 hour periods.