Long-Term Evolution in Transit Duration of Extrasolar Planets from Magnetic Activity in their Parent Stars

TL;DR

This paper discusses how magnetic activity in stars can cause long-term variations in the transit duration of orbiting exoplanets, affecting measurements and offering a new way to study stellar radius changes.

Contribution

It introduces the potential impact of stellar magnetic activity on transit duration variations and suggests using transit measurements to monitor stellar radius changes over time.

Findings

Transit duration can vary by a fraction of a second per year due to stellar activity.

Magnetic activity effects are more pronounced in late-type stars like M-dwarfs.

Transit timing analysis should account for stellar radius variations caused by magnetic activity.

Abstract

Existing upper limits on variations in the photospheric radius of the Sun during the solar magnetic activity cycle are at a fractional amplitude of 2x10^{-4}. At that level, the transit duration of a close-in planet around a Sun-like star could change by a fraction of a second per year. This magnitude of variation is larger than that caused by other studied effects (owing to proper motion or general-relativistic effects), and should be included in the analysis of constraints on multi-planet systems from transit timing. A temporal correlation between the transit duration and spectroscopic measures of stellar activity can be used to separate the stellar radius change from other effects. The magnetic activity effect could be significantly larger for late-type stars, such as M-dwarfs, which are more variable than the Sun. In general, precision transit measurements provide a new tool for measuring long-term variations of stellar radii.