EPIC 212803289: a subGiant With a Warm Jupiter and Possibly a Brown Dwarf

EPIC 212803289: a subgiant hosting a transiting warm Jupiter in an eccentric orbit and a long-period companion

Authors:

Smith et al

Abstract:

We report the discovery from K2 of a transiting planet in an 18.25-d, eccentric (0.19± 0.04) orbit around EPIC 212803289, an 11th magnitude subgiant in Virgo. We confirm the planetary nature of the companion with radial velocities, and determine that the star is a metal-rich ([Fe/H] = 0.20±0.05) subgiant, with mass 1.60+0.14−0.10 M⊙ and radius 3.1±0.1 R⊙. The planet has a mass of 0.97±0.09 MJup and a radius 1.29±0.05 RJup. A measured systemic radial acceleration of −2.12±0.04 ms−1d−1 offers compelling evidence for the existence of a third body in the system, perhaps a brown dwarf orbiting with a period of several hundred days.

KELT-11b/HD 93396b: a Highly Inflated hot Saturn Orbiting a subGiant Host Star

KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396

Authors:

Pepper et al

Abstract:

We report the discovery of a transiting exoplanet, KELT-11b, orbiting the bright (V=8.0) subgiant HD 93396. A global analysis of the system shows that the host star is an evolved subgiant star with Teff=5370±51 K, M∗=1.438+0.061−0.052M⊙, R∗=2.72+0.21−0.17R⊙, log g∗=3.727+0.040−0.046, and [Fe/H]=0.180±0.075. The planet is a low-mass gas giant in a P=4.736529±0.00006 day orbit, with MP=0.195±0.018MJ, RP=1.37+0.15−0.12RJ, ρP=0.093+0.028−0.024 g cm−3, surface gravity log gP=2.407+0.080−0.086, and equilibrium temperature Teq=1712+51−46 K. KELT-11 is the brightest known transiting exoplanet host in the southern hemisphere by more than a magnitude, and is the 6th brightest transit host to date. The planet is one of the most inflated planets known, with an exceptionally large atmospheric scale height (2763 km), and an associated size of the expected atmospheric transmission signal of 5.6%. These attributes make the KELT-11 system a valuable target for follow-up and atmospheric characterization, and it promises to become one of the benchmark systems for the study of inflated exoplanets.

K2-39b: a hot Jupiter Around a Subgiant Host Star

The K2-ESPRINT Project V: a short-period giant planet orbiting a subgiant star

Authors:

Van Eylen et al

Abstract:

We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood, but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 is an evolved star with a spectroscopically derived stellar radius and mass of 3.88+0.48−0.42 R⊙ and 1.53+0.13−0.12 M⊙, respectively, and a very close-in transiting planet, with a/R⋆=3.4. Radial velocity (RV) follow-up using the HARPS, FIES and PFS instruments leads to a planetary mass of 50.3+9.7−9.4 M⊕. In combination with a radius measurement of 8.3±1.1 R⊕, this results in a mean planetary density of 0.50+0.29−0.17 g~cm−3. We furthermore discover a long-term RV trend, which may be caused by a long-period planet or stellar companion. Because K2-39b has a short orbital period, its existence makes it seem unlikely that tidal destruction is wholly responsible for the differences in planet populations around subgiant and main-sequence stars. Future monitoring of the transits of this system may enable the detection of period decay and constrain the tidal dissipation rates of subgiant stars.