Monday, August 8, 2016

EPIC 211391664b is a Warm Neptune-Sized Planet

Barragán et al. (2016) present the detection of EPIC 211391664b, a transiting Neptune-sized planet in a 10.14 day orbit around an F-type star that is located ~1400 light years away. From transit and radial velocity observations, EPIC 211391664b has ~4.3 times the radius and 32.2 ± 8.1 times the mass of Earth. For comparison, Neptune has 3.9 times the radius and 17.1 times the mass of Earth. Although only slightly larger in size than Neptune, EPIC 211391664b has almost twice the mass of Neptune. EPIC 211391664b joins a relatively small group of Neptune-sized planets whose mass and radius are known to better than 3σ. The equilibrium temperature on EPIC 211391664b is estimated to be ~1100 K. In about 3 billion years from now, EPIC 211391664b is expected to be engulfed as its host star evolves into a red giant.

Barragán et al. (2016), “EPIC 211391664b: A 32-Mᴇ Neptune-sized planet in a 10-day orbit transiting an F8 star”, arXiv:1608.01165 [astro-ph.EP]

Sunday, August 7, 2016

A Year on KELT-16b is Less than 24 Hours

Oberst et al. (2016) present the discovery of KELT-16b, a highly irradiated, ultra-short period hot-Jupiter transiting a relatively bright F-type main sequence star. Transit and radial velocity observations indicate that KELT-16b has ~1.415 times the radius and ~2.75 times the mass of Jupiter, giving it a mean density of roughly 1.2 times the density of water. KELT-16b circles its host star every 23 hours 15 minutes. This planet joins WASP-18b, WASP-19b, WASP-43b, WASP-103b and HATS-18b as the only transiting hot-Jupiters with orbital periods under a day. The host star of KELT-16b has ~ 1.211 times the mass and ~ 1.360 times the radius of the Sun, and its effective temperature is 6236 ± 54 K.

Due to its ultra-short orbit, KELT-16b is highly irradiated by its host star, and its estimated equilibrium temperature is ~2453 K. The large day-to-night temperature difference on KELT-16b may be extreme enough for gaseous titanium oxide (TiO) and vanadium oxide (VO) to condense and rain out at the planet’s day-night terminator. At present, KELT-16b orbits only ~1.7 Roche radii from its host star. The Roche radius is basically the distance from its host star whereby KELT-16b is expected to become tidally disrupted. Tidal evolution models predict that KELT-16b could be tidally shredded by its host star in as little as half a million years.

Oberst et al. (2016), “KELT-16b: A highly irradiated, ultra-short period hot Jupiter nearing tidal disruption”, arXiv:1608.00618 [astro-ph.EP]

Tuesday, August 2, 2016

Occurrence Rate of Long Period Planets

Figure 1: Artist's impression of an exoplanet.

Kepler is a planet-hunting telescope that searches for planets that transit their host stars. It is most sensitive to planets with short orbital periods. Nevertheless, Foreman-Mackey et al. (2016) performed a fully automated search for long period planets with only one or two transits in the archival Kepler light curves. The search was done for ~40,000 Sun-like stars and it led to the detection of 16 long period planet candidates. These planet candidates have orbital periods between 2 to over 50 years. Based on this finding, the occurrence rate of planets with orbital periods in the range 2 to 25 years and radii in the range 0.1 to 1 times the radius of Jupiter is estimated to be 2.00 ± 0.72 planets per Sun-like star.

Figure 2: The catalogue of long period transiting planet candidates (green points with error bars) compared to the Kepler planet candidates (blue points) and confirmed planets, and the Solar System planets (orange squares). The vertical solid line shows the absolute maximum period accessible to transit searches that require at least three transits in the Kepler data. Foreman-Mackey et al. (2016)

Foreman-Mackey et al. (2016), "The population of long-period transiting exoplanets", arXiv:1607.08237 [astro-ph.EP]

Monday, August 1, 2016

WASP-127b is a Heavily Inflated Super-Neptune

WASP-127b is a heavily inflated super-Neptune with 0.18 times the mass and 1.35 times the radius of Jupiter. This means the density of WASP-127b is only ~7 percent the density of Jupiter, making it one of the least dense planets known. In fact, the surface gravity on WASP-127b is over 4 times weaker than on Earth. WASP-127b is in a 4.178 day orbit around a G5 main sequence star that has 1.31 ± 0.05 times the mass and 1.33 ± 0.03 times the radius of the Sun. The heavily inflated nature of WASP-127b gives the planet a very extended atmosphere with a remarkably large scale height estimated to be 2500 ± 400 km. Such a “puffy” atmosphere makes WASP-127b an ideal target for transmission spectroscopy. Being so close to its host star, the temperature on WASP-127b is estimated to be ~1400 K.

Lam et al. (2016), “From Dense Hot Jupiter to Low Density Neptune: The Discovery of WASP-127b, WASP-136b and WASP-138b”, arXiv:1607.07859 [astro-ph.EP]