Spin-orbit alignments for Three Transiting Hot Jupiters: WASP-103b, WASP-87b, & WASP-66b

TL;DR

This study measures the spin-orbit alignments of three transiting Hot Jupiters using spectroscopic Rossiter-McLaughlin effect observations, finding they are likely on nearly aligned orbits with their host stars.

Contribution

First measurements of spin-orbit angles for WASP-103b, WASP-87b, and WASP-66b using the CYCLOPS2 system, revealing their likely aligned orbital configurations.

Findings

WASP-103b has a nearly aligned orbit with a small projected angle.

WASP-87b and WASP-66b also show near alignment with their host stars.

The systems are consistent with moderate or low spin-orbit misalignments.

Abstract

We have measured the sky-projected spin-orbit alignments for three transiting Hot Jupiters, WASP-103b, WASP-87b, and WASP-66b, using spectroscopic measurements of the Rossiter-McLaughlin effect, with the CYCLOPS2 optical-fiber bundle system feeding the UCLES spectrograph on the Anglo-Australian Telescope. The resulting sky projected spin-orbit angles of $\lambda = 3^{\circ}\pm33^{\circ}$, $\lambda = -8^{\circ}\pm11^{\circ}$, and $\lambda = -4^{\circ}\pm22^{\circ}$ for WASP-103b, WASP-87b, and WASP-66b, respectively, suggest that these three planets are likely on nearly aligned orbits with respect to their host star's spin axis. WASP-103 is a particularly interesting system as its orbital distance is only 20% larger than its host star's Roche radius and the planet likely experiences strong tidal effects. WASP-87 and WASP-66 are hot ($T_{eff}=6450\pm120$ K and $T_{eff}=6600\pm150$ K, respectively) mid-F stars making them similar to the majority of stars hosting planets on high obliquity orbits. Moderate spin-orbit misalignments for WASP-103b and WASP-66b are consistent with our data, but polar and retrograde orbits are not favored for these systems.