A Prograde, Low-Inclination Orbit for the Very Hot Jupiter WASP-3b

TL;DR

This study measures the orbital alignment of exoplanet WASP-3b, finding it has a prograde, low-inclination orbit, and reports an unusual redshift possibly caused by stellar activity or observational artifacts.

Contribution

First spectroscopic measurement of the Rossiter-McLaughlin effect for WASP-3b revealing a low orbital inclination and orbital alignment.

Findings

WASP-3b has a sky-projected orbital axis aligned within a few degrees of the stellar equator.

Detected an anomalous redshift possibly due to stellar activity or observational effects.

Confirmed the planet's prograde, low-inclination orbit.

Abstract

We present new spectroscopic and photometric observations of the transiting exoplanetary system WASP-3. Spectra obtained during two separate transits exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the sky-projected angle between the planetary orbital axis and the stellar rotation axis, lambda = 3.3^{+2.5}_{-4.4} degrees. This alignment between the axes suggests that WASP-3b has a low orbital inclination relative to the equatorial plane of its parent star. During our first night of spectroscopic measurements, we observed an unexpected redshift briefly exceeding the expected sum of the orbital and RM velocities by 140 m/s. This anomaly could represent the occultation of material erupting from the stellar photosphere, although it is more likely to be an artifact caused by moonlight scattered into the spectrograph.