An iterative filter to reconstruct planetary transit signals in the presence of stellar variability

TL;DR

This paper introduces a post-detection filtering algorithm that effectively reduces stellar variability effects in transit signals, leading to more accurate planetary parameter estimates without compromising the transit signal.

Contribution

The paper presents a novel iterative filter that improves parameter estimation accuracy in transit light curves by preserving the transit signal while removing stellar variability.

Findings

Median 40% reduction in relative error of planet parameters.

Significantly better performance on active stars.

Preserves orbital period signal for potential reflected light detection.

Abstract

The detrending algorithms which are widely used to reduce the impact of stellar variability on space-based transit surveys are ill-suited for estimating the parameters of confirmed planets, as they unavoidably alter the transit signal. We present a post-detection detrending algorithm, which filters out signal on other timescales than the period of the transit while preserving the transit signal. We compare the performance of this new filter to a well-established pre-detection detrending algorithm, by applying both to a set of 20 simulated light curves containing planetary transits, stellar variability, and instrumental noise as expected for the CoRoT space mission, and performing analytic fits to the transits. Compared to the pre-detection benchmark, the new post-detection filter systematically yields significantly reduced errors (median reduction in relative error over our sample of about 40%) on the planet-to-star radius ratio, system scale and impact parameter. This is particularly important for active stars, where errors induced by variability can otherwise dominate the final error budget on the planet parameters. Aside from improving planet parameter estimates, the new filter preserves all signal at the orbital period of the planet, and thus could also be used to search for light reflected by the planet.