WASP-20b and WASP-28b: a hot Saturn and a hot Jupiter in near-aligned orbits around solar-type stars
Anderson et al
We report the discovery of the planets WASP-20b and WASP-28b along with measurements of their sky-projected orbital obliquities. WASP-20b is an inflated, Saturn-mass planet (0.31 MJup; 1.46 RJup) in a 4.9-day, near-aligned (λ=8.1±3.6∘) orbit around CD-24 102 (V=10.7; F9). WASP-28b is an inflated, Jupiter-mass planet (0.91 MJup; 1.21 RJup) in a 3.4-day, near-aligned (λ=8±18∘) orbit around a V=12, F8 star. As intermediate-mass planets in short orbits around aged, cool stars (7+2−1 Gyr for WASP-20 and 5+3−2 Gyr for WASP-28; both with Teff < 6250 K), their orbital alignment is consistent with the hypothesis that close-in giant planets are scattered into eccentric orbits with random alignments, which are then circularised and aligned with their stars' spins via tidal dissipation.