C14 Automatic Imaging Telescope Photometry of GJ1214

TL;DR

This study provides photometric monitoring of GJ1214 to contextualize upcoming JWST observations, revealing stellar brightness variations and suggesting a rotation period likely over 50 days, which impacts atmospheric studies of GJ1214b.

Contribution

The paper offers the first detailed photometric context for GJ1214 during JWST observations, highlighting stellar activity and its implications for exoplanet atmospheric analysis.

Findings

GJ1214 entered a high brightness phase in 2021-2022.

JWST observations occurred during a low activity epoch.

Star's rotation period is likely over 50 days.

Abstract

GJ1214b is the highest signal-to-noise sub-Neptune for atmospheric studies. Although most previous transmission spectroscopy measurements have revealed a frustratingly featureless spectrum, JWST observations are expected to give new insights to this benchmark planet. We have performed photometric monitoring of GJ1214 (the host star) to provide context for these observations. We find that GJ1214 entered a period of relatively high brightness during 2021 and 2022. This implies that the JWST MIRI/LRS phase curve observation of GJ1214b in July 2022 was obtained during an epoch of low activity for the spot-dominated host star. Like previous works, we are unable to definitively identify the star's rotation period. Nevertheless, we confirm that it is likely >50 days.