Follow-up observations of the neptune mass transiting extrasolar planet HAT-P-11b

We have confirmed the existence of the transiting super Neptune extrasolar planet HAT-P-11b. On 2009 May 1 UT, the transit of HAT-P-11b was detected at the University of Arizona's 1.55 m Kuiper telescope with 1.7 millimag rms accuracy. We find a central transit time of T_c = 2454952.92534 ± 0.00060 BJD; this transit occurred 80 ± 73 s sooner than previous measurements (71 orbits in the past) would have predicted. Hence, our transit timing rules out the presence of any large (>200 s) deviations from the ephemeris of Bakos etal. We obtain a slightly more accurate period of P = 4.8878045 ± 0.0000043 days. We measure a slightly larger planetary radius of R_p = 0.452 ± 0.020 R_J (5.07 ± 0.22 R _⊕) compared to Bakos and coworkers' value of 0.422 ± 0.014 R_J (4.73 ± 0.16 R _⊕). 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.