Improved atmospheric characterisation of Gliese 1214 b through stellar activity corrections

Transmission spectroscopy is a primary method used to study the atmospheres of planets outside our solar system as they pass in front of their host stars. However, star spots and other surface features on a host star can mimic or hide the signal of a planet's atmosphere, causing errors in data gathered by telescopes like the James Webb Space Telescope. A new method has been developed to accurately measure and remove this stellar interference.

To test this, researchers monitored the Red dwarf star Gliese 1214 while the James Webb Space Telescope observed its orbiting planet, Gliese 1214 b. They employed two different analytical techniques: a physical modeling system called StarSim, which maps the star's surface activity, and a machine learning tool named UnSPOTTER, which uses neural networks to predict and subtract noise.

Both methods confirmed that the observations of Gliese 1214 took place during a quiet period with minimal stellar activity. Using the UnSPOTTER tool, researchers were able to constrain contamination levels to approximately 15 parts per million. This work highlights that coordinating ground-based monitoring with space telescope observations is vital for accurate planetary data.

Key findings
- Two distinct analytical frameworks were used to identify and remove stellar interference from planetary observations.
- Observations of Gliese 1214 were confirmed to have occurred at a favorable rotation phase with low surface activity.
- UnSPOTTER provides high-precision corrections constrained to roughly 15 parts per million.
- Coordinated monitoring is essential to prevent stellar activity from biasing atmospheric studies of exoplanets.

Scientific study

Correcting stellar contamination in transmission spectroscopy with contemporaneous monitoring: Application to GJ 1214 b (external link)