Non-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1

TL;DR

This study uses a self-contamination technique on Spitzer data to investigate stellar activity effects on TRAPPIST-1's transits, finding no significant contamination but acknowledging possible undetected small-scale activity.

Contribution

It applies a novel self-contamination method to TRAPPIST-1 transits, providing constraints on stellar activity influence on transit measurements.

Findings

No significant evidence of stellar contamination detected.

Small-scale magnetic activity could still be present undetected.

Transit depths are not significantly affected by stellar spots.

Abstract

We apply the transit light curve self-contamination technique of Morris et al. (2018) to search for the effect of stellar activity on the transits of the ultracool dwarf TRAPPIST-1 with 2018 Spitzer photometry. The self-contamination method fits the transit light curves of planets orbiting spotted stars, allowing the host star to be a source of contaminating positive or negative flux which influences the transit depths but not the ingress/egress durations. We find that none of the planets show statistically significant evidence for self-contamination by bright or dark regions of the stellar photosphere. However, we show that small-scale magnetic activity, analogous in size to the smallest sunspots, could still be lurking in the transit photometry undetected.