Starspots, spin-orbit misalignment, and active latitudes in the HAT-P-11 exoplanetary system

TL;DR

This study analyzes Kepler data of HAT-P-11 to understand starspot activity, stellar obliquity, and active latitudes, revealing two possible configurations consistent with observed transit anomalies.

Contribution

It provides the first detailed analysis linking starspot crossings with stellar obliquity and active latitudes in the HAT-P-11 system, suggesting potential activity cycle variations.

Findings

Identified preferred phases of spot-crossing anomalies indicating active latitudes.

Derived two possible stellar obliquity and active latitude solutions.

Proposed that active latitudes may shift over time similar to solar cycles.

Abstract

We present the analysis of 4 months of Kepler photometry of the K4V star HAT-P-11, including 26 transits of its "super-Neptune" planet. The transit data exhibit numerous anomalies that we interpret as passages of the planet over dark starspots. These spot-crossing anomalies preferentially occur at two specific phases of the transit. These phases can be understood as the intersection points between the transit chord and the active latitudes of the host star, where starspots are most abundant. Based on the measured characteristics of spot-crossing anomalies, and previous observations of the Rossiter-McLaughlin effect, we find two solutions for the stellar obliquity (psi) and active latitude (l): either psi = 106 and l = 19.7, or psi = 97 and l = 67 (all in degrees). If the active latitude changes with time in analogy with the "butterfly diagram" of the Sun's activity cycle, future observations should reveal changes in the preferred phases of spot-crossing anomalies.