Follow - up Observations of the Neptune Mass Transiting Extrasolar Planet Hat - P - 11 b

We have confirmed the existence of the transiting super Neptune extrasolar planet HAT-P-11b. On May 1, 2009 UT the transit of Hat-P-11b was detected at the University of Arizona’s 1.55m Kuiper Telescope with 1.7 millimag rms accuracy. We find a central transit time of Tc = 2454952.92534± 0.00060 BJD; this transit occurred 80 ± 73 seconds sooner than previous measurements (71 orbits in the past) would have predicted. Hence, our transit timing rules out large deviations from the ephemeris of Bakos et al. (2009). We measure a slightly larger planetary radius of Rp = 0.452 ± 0.020RJ (5.07 ± 0.22R⊕) compared to Bakos and co-workers’ value of 0.422 ± 0.014RJ (4.73 ± 0.16R⊕). Our values confirm that Hat-P-11b is very similar to GJ 436b (the only other known transiting super Neptune) in radius and other bulk properties. Subject headings: planetary systems, stars: individual: Hat-P-11