A Ground-Based Search for Thermal Emission from the Exoplanet TrES-1

TL;DR

This study demonstrates a ground-based method to detect thermal emission from exoplanets during secondary eclipses, achieving sensitivity close to theoretical predictions, and discusses limitations and future improvements.

Contribution

The paper presents a novel ground-based observational technique to measure exoplanet thermal emission during secondary eclipses with high sensitivity.

Findings

Achieved 0.15% detection sensitivity in eclipse depth

Sensitivity approaches the predicted 0.05-0.1% planetary emission

Identified key factors limiting measurement precision

Abstract

Eclipsing planetary systems give us an important window on extrasolar planet atmospheres. By measuring the depth of the secondary eclipse, when the planet moves behind the star, we can estimate the strength of the thermal emission from the day side of the planet. Attaining a ground-based detection of one of these eclipses has proven to be a significant challenge, as time-dependent variations in instrument throughput and atmospheric seeing and absorption overwhelm the small signal of the eclipse at infrared wavelengths. We gathered a series of simultaneous L grism spectra of the transiting planet system TrES-1 and a nearby comparison star of comparable brightness, allowing us to correct for these effects in principle. Combining the data from two eclipses, we demonstrate a detection sensitivity of 0.15% in the eclipse depth relative to the stellar flux. This approaches the sensitivity required to detect the planetary emission, which theoretical models predict should lie between 0.05-0.1% of the stellar flux in our 2.9-4.3 micron bandpass. We explore the factors that ultimately limit the precision of this technique, and discuss potential avenues for future improvements.