In the sample of hot Neptunes, there are 73 (roughly one-third of the sample) that are known to have additional transiting objects. The hot Neptune sample contains the 222 KOI with periods between 0.8 and 6.3 d and sizes between 0.126 and 0.6 R Jup (see Fig. 2). Comparison with Nearby Populations Warm Jupiters. However, such planets would typically have larger sizes and smaller orbital period variations-and would therefore likely be seen in the transit search described above unless there is a nearly universal tendency for large mutual inclination. Larger masses, two to three orders of magnitude larger, are allowed planets far from resonance. Thus, for these systems, where the timing uncertainty is between 0.1 and 15 min, the maximum allowed companion mass in or near a resonant orbit is between the masses of Mars and a few times the Earth. There is a noticeable lack of planet candidates from multiple transiting systems for large planets on short orbital periods-where the hot Jupiter planets are defined.įor those systems not showing TTVs, rather than giving specific calculations for the maximum allowed companion mass in each, we point out that numerical simulations show that an Earth-mass planet on a circular orbit near the 2∶1 MMR can easily induce a TTV signal with approximately 1-min amplitude on a Jupiter-mass planet with a 4-d orbit, and that in this regime the TTV signal scales linearly with the mass of the perturbing planet. orbital period for KOI given in B11 that are analyzed here, with the boundaries of the hot Jupiter and comparison samples shown. Fig. 2 is a scatter plot of candidate size vs. Also, KOI-928.01, a known triple star system involving an eclipsing binary ( 31), is excluded from the hot Neptune sample, which leaves 222 hot Neptune systems and 31 warm Jupiter systems. In each of these samples, there is one system that we ignore because they are missing several quarters of data. These cuts yield 224 hot Neptunes and 32 warm Jupiters. The warm Jupiters satisfy the same size criteria as the hot Jupiters, but have periods between 6.3 and 15.8 d. For the hot Neptunes, we select all KOI with sizes between 0.126 and 0.6 R Jup and periods between 0.8 and 6.3 d. In addition to the sample of hot Jupiters, we consider two neighboring samples of KOI, specifically hot Neptunes and warm Jupiters. Thus, although some theories are fading into disfavor, the fundamental mechanism that produces the hot Jupiter population remains unexplained. Still other arguments point out the importance of including interactions with distant planets ( 29, 30). 10), and the lack of near-resonant companions is at odds with nominal predictions of disk migration. Yet, no evidence suggests that hot Jupiters preferentially have companions capable of driving their orbits inward through Kozai cycles and tidal friction (contrary to predictions in ref. Hot Jupiters are, however, known to have distant stellar or planetary companions ( 27, 28). Nevertheless, strong limits on resonant or near-resonant companions, with mass constraints smaller than the mass of the Earth near the 2∶1 and 3∶2 MMRs, exist from TTV studies ( 24, 25), and nothing has turned up in searches for additional transiting companions to hot Jupiters ( 26). Stability considerations may restrict orbits that are much closer than the 3∶2 MMR. Few companion planets are found in hot Jupiter systems-none in nearby orbits ( 23).
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