2009ApJ...695..336H

We present the results of a deep (15 ≲ r ≲ 23), 20 night survey for transiting planets in the intermediate-age open cluster M37 (NGC 2099) using the Megacam wide-field mosaic CCD camera on the 6.5 m MMT. We do not detect any transiting planets among the ∼1450 observed cluster members. We do, however, identify a ∼1R_J candidate planet transiting a ∼0.8 M_☉ Galactic field star with a period of 0.77 days. The source is faint (V = 19.85 mag) and has an expected velocity semiamplitude of K ∼ 220 m/s (M/M_J ). We conduct Monte Carlo transit injection and recovery simulations to calculate the 95% confidence upper limit on the fraction of cluster members and field stars with planets as a function of planetary radius and orbital period. Assuming a uniform logarithmic distribution in the orbital period, we find that <1.1%, <2.7%, and <8.3% of cluster members have 1.0R_J planets within extremely hot Jupiter (EHJ; 0.4 < P < 1.0 day), very hot Jupiter (VHJ; 1.0 < P < 3.0 day), and hot Jupiter (HJ; 3.0 < P < 5.0 day) period ranges, respectively. For 0.5R_Jplanets, the limits are less than 3.2% and less than 21% for EHJ and VHJ period ranges, respectively, while for 0.35R_J planets we can only place an upper limit of less than 25% on the EHJ period range. For a sample of 7814 Galactic field stars, consisting primarily of FGKM dwarfs, we place 95% upper limits of <0.3%, <0.8%, and <2.7% on the fraction of stars with a 1.0R_JEHJ, VHJ, and HJ, respectively, assuming that the candidate planet is not genuine. If the candidate is genuine, the frequency of ∼1.0R_J planets in the EHJ period range is 0.002% < f_EHJ< 0.5% with 95% confidence. We place limits of <1.4%, <8.8%, and <47% for 0.5R_Jplanets, and a limit of <16% on 0.3R_J planets in the EHJ period range. This is the first transit survey to place limits on the fraction of stars with planets as small as Neptune.