Planetary transit observations at the University Observatory Jena: XO-1b and TrES-1

We report on observations of transit events of the transiting planets XO-1b and TrES-1 with a 25 cm telescope of the University Observatory Jena. With the transit timings for XO-1b from all 50 available XO, SuperWASP, Transit Light Curve (TLC)-Project- and Exoplanet Transit Database (ETD)-data, including our own I-band photometry obtained in March 2007, we find that the orbital period is P= (3.941501 +/- 0.000001) d, a slight change by ~3 s compared to the previously published period. We present new ephemeris for this transiting planet. Furthermore, we present new R-band photometry of two transits of TrES-1. With the help of all available transit times from literature this allows us to refine the estimate of the orbital period: P=(3.0300722 +/- 0.0000002) d. Our observations will be useful for future investigations of timing variations caused by additional perturbing planets and/or stellar spots and/or moons.