A revised orbital ephemeris for HAT-P-9b

► Two transits of HAT-P-9b were shown to be 24 minutes earlier than the expected transit time. ► We have revised the orbital ephemeris of HAT-P-9b to 3.922814 +/- 0.000002 days. ► We find no evidence for additional planets via the TTV technique. We present here three transit observations of HAT-P-9b taken on 14 February 2010 and 05 April 2010 UT from the University of Arizona’s 1.55 m Kuiper telescope on Mt. Bigelow. Our two light curves were obtained in the Arizona-I filter for all our observations, and underwent the same reduction process. Both transits occurred approximately 24 min earlier than expected from the ephemeris of Shporer et al. (2009). However, due to the large time span between our observed transits and those of Shporer et al. (2009), a 6.5 s shift downwards in orbital period from the value of Shporer et al. (2009) is sufficient to explain all available transit data. We find a new period of 3.922814 ± 0.000002 days for HAT-P-9b, an order of magnitude more precise than previous measurements, with no evidence for significant nonlinearities in the transit period.