The discoveries of WASP-91b, WASP-105b and WASP-107b: Two warm Jupiters and a planet in the transition region between ice giants and gas giants

Abstract

We report the discoveries of three transiting exoplanets. WASP-91b is a warm Jupiter (1.34 M Jup , 1.03 R Jup ) in a 2.8-day orbit around a metal-rich K3 star. WASP-105b is a warm Jupiter (1.8 M Jup , 0.96 R Jup ) in a 7.9-day orbit around a metal-rich K2 star. WASP-107b is a warm super-Neptune/sub-Saturn (0.12 M Jup , 0.94 R Jup ) in a 5.7-day orbit around a solar-metallicity K6 star. Considering that giant planets seem to be more common around stars of higher metallicity and stars of higher mass, it is notable that the hosts are all metalrich, late-type stars. With orbital separations that place both WASP-105b and WASP-107b in the weak-tide regime, measurements of the alignment between the planets' orbital axes and their stars' spin axes may help us to understand the inward migration of shortperiod, giant planets. The mass of WASP-107b (2.2 M Nep , 0.40 M Sat ) places it in the transition region between the ice giants and gas giants of the Solar System. Its radius of 0.94 R Jup suggests that it is a low-mass gas giant with a H/He-dominated composition. The planet thus sets a lower limit of 2.2 M Nep on the planetary mass above which large gaseous envelopes can be accreted and retained by proto-planets on their way to becoming gas giants. We may discover whether WASP-107b more closely resembles an ice giant or a gas giant by measuring its atmospheric metallicity via transmission spectroscopy, for which WASP-107b is a very good target.

Confirmation of WASP-107b’s Extended Helium Atmosphere with Keck II/NIRSPEC

“…Since WASP-107b is a slow rotator (v sin i = 2.5 ± 0.8 km s −1 , Anderson et al 2017), the predicted amplitude of the Rossiter-McLaughlin effect is expected to be small (Dai & Winn 2017). Indeed, using equation 5 of Dai & Winn (2017), with the R P /R * we calculate from our He light curve in section 4, we find that the expected signal amplitude is 133 m s −1 .…”

“…WASP-107b, detected by Anderson et al (2017), is a warm sub-Saturn with a mass of 0.119 M J , radius of 0.924 R J , and equilibrium temperature of 736 K (Močnik et al 2017). Because of its deep transit (2.09 %, Močnik et al 2017) and large atmospheric scale height (855 km, derived from Močnik et al 2017), it is an excellent target for atmospheric studies.…”

Helium in the eroding atmosphere of an exoplanet

“…WASP-107b is one of the lowest density planets known, with a radius similar to that of Jupiter (0.94±0.02R J ) and a much lower mass (0.12±0.01M J ) 3 . It orbits an active K6 dwarf every 5.7 days at a distance of 0.055±0.001 astronomical units.…”

“…Here we present the first detection of helium on an exoplanet, at a confidence level of 4.5σ . We measured the near-infrared transmission spectrum of the warm gas giant WASP-107b 3…”

Three hot-Jupiters on the upper edge of the mass–radius distribution: WASP-177, WASP-181, and WASP-183

“…These translate to transit depth variations of just under 300 ppm for WASP-177 and WASP-181 and ∼ 300 ppm for WASP-183. If we account for the K-band flux and scale in the same way as Anderson et al (2017), we get atmospheric signals of; 70, 41 and 60. In reality, we can expect this metric to be an over estimate of detectability for WASP-177 b and WASP-183 b as the grazing nature of their transits reduces the impact of the atmospheric signal further.…”