Starspots on WASP-85

TL;DR

This study detects starspots on WASP-85A using K2 data, revealing the star's rotation, star-planet alignment, and absence of additional planets, with implications for understanding stellar activity and exoplanet systems.

Contribution

First detection of starspots on WASP-85A with analysis of star-planet alignment and stellar rotation period from K2 data.

Findings

Starspots detected on WASP-85A

Planet's orbit is aligned with star’s rotational axis

No evidence of additional planets in the system

Abstract

By analysing K2 short-cadence observations we detect starspots on WASP-85A, the host star of the hot Jupiter WASP-85Ab. The detection of recurring starspot occultation events indicates that the planet's orbit is aligned with the star's rotational axis ($\lambda<14^{\circ}$) and suggests a stellar rotational period of $15.1 \pm 0.6$ d. The K2 lightcurve reveals a rotational modulation with a period of $13.6 \pm 1.6$ d, consistent with the period determined from starspots. There are no significant transit-timing variations and thus no evidence of any additional planet in the system. Given the pronounced rotational modulation we are only able to place an upper limit of 100 parts per million for any phase-curve modulations and the secondary eclipse.