###
Seven Long-Period Planet Candidates

Using archival data from NASA’s Kepler space telescope, Wang et al. (2015) present the validation of seven long-period planet candidates that have planet confidence over 99.7 percent. These long-period planet candidates include 3 single-transit planets (KIC-3558849c, KIC-5951458b, and KIC-8540376d), 3 planets with double transits (KIC-8540376c, KIC-9663113c, and KIC-10525077b), and 1 planet with 4 transits (KIC-5437945c). All seven long-period planet candidates orbit stars hotter than the Sun in orbits with periods ranging from ~100 to over ~1000 days.

KIC-3558849c was observed to transit its host star once. Based on its transit duration and the properties of its host star, the planet’s orbital period is estimated to be between 1311 to 1708 days and the radius of the planet is between 6.0 to 7.9 Rᴇ, where Rᴇ denotes the Earth’s radius. The host star of KIC-3558849c has 0.87 to 1.09 times the mass and 0.90 to 1.11 times the radius of the Sun, and the star’s surface temperature is ~6175 K. KIC-3558849c is validated with a planet confidence of 99.7 percent. This planetary system has another planet candidate identified as KIC-3558849b. Its orbital period is 160.85 days and it measures ~2.35 Rᴇ.

KIC-5951458b is a long-period planet that was observed to transit its host star once in what was probably a grazing transit. As a result, its properties are only weakly constrained. Nevertheless, the planet is validated with a planet confidence of 99.8 percent. The orbital period of KIC-5951458b is estimated to be between 1168 to 13722 days and its radius can assume a wide range of values centred on ~6.6 Rᴇ. The host star of KIC-5951458b has 0.77 to 1.19 times the mass and 0.70 to 2.34 times the radius of the Sun, and the star’s surface temperature is ~6260 K.

KIC-8540376d (one observed transit) and KIC-8540376c (two observed transits) belong to the same planetary system which also consists of a third planet candidate whose orbital period is 10.7 days and whose radius is ~1.0 Rᴇ. KIC-8540376d is estimated to have an orbital period of between 74 to 114 days and its radius is ~2.4 Rᴇ. KIC-8540376c orbits its host star interior to KIC-8540376d. The orbital period of KIC-8540376c is 31.8 days and its radius is ~4.1 Rᴇ. Both KIC-8540376d and KIC-8540376c are validated with planet confidence levels of 99.9 percent. The host star of this planetary system has 0.84 to 1.23 times the mass and 0.70 to 1.82 times the radius of the Sun, and the star’s surface temperature is ~6475 K.

KIC-9663113c was observed to transit its host star twice. The orbital period of this planet is 572.4 days and the radius of the planet is between 3.9 to 5.2 Rᴇ. KIC-9663113c is probably a Neptune-like planet whose estimated equilibrium temperature is ~232 K, and the planet is validated with a planet confidence of 99.9 percent. The host star of KIC-9663113c has 0.85 to 1.10 times the mass and 0.91 to 1.15 times the radius of the Sun, and the star’s surface temperature is ~6065 K. This planetary system also hosts a second planet identified as KIC-9663113b. Its orbital period is 20.74 days and its radius is ~3.3 Rᴇ. The estimated equilibrium temperature on KIC-9663113b is ~702 K.

KIC-10525077b was observed to transit its host star on two occasions. However, there is a data gap between the two transits and this makes it impossible to tell whether the planet’s orbital period is 854.08 days or half the value at 427.04 days. KIC-9663113b is estimated to be ~5.5 Rᴇ in radius and it is validated with a planet confidence of 99.8 percent. The host star of KIC-10525077b has 0.89 to 1.13 times the mass and 0.91 to 1.11 times the radius of the Sun, and the star’s surface temperature is ~6090 K. This planetary system also hosts another planet candidate whose orbital period is 11.01 days and whose radius is ~1.36 Rᴇ.

KIC-5437945c was observed to transit its host star 4 times. Its orbital period is 440.8 days and its radius is ~6.4 Rᴇ. At that distance from its host star, the planet’s equilibrium temperature is ~308 K. KIC-5437945c is validated with a planet confidence of 99.9 percent. The host star of KIC-5437945c has 0.90 to 1.24 times the mass and 0.95 to 1.53 times the radius of the Sun, and the star’s surface temperature is ~6340 K. This planetary system also has another planet candidate identified as KIC-5437945b. Its orbital period is 220.13 days and its radius is ~6.1 Rᴇ. The equilibrium temperature on KIC-5437945b is ~389 K.

Reference:
Wang et al. (2015), “Planet Hunters. VIII. Characterization of 41 Long-Period Exoplanet Candidates from Kepler Archival Data”, arXiv:1512.02559 [astro-ph.EP]