A correlation between host star activity and planet mass for close-in extrasolar planets?

TL;DR

This paper investigates the reported correlation between close-in exoplanet mass and host star X-ray luminosity, revealing it is due to selection biases rather than true star-planet interactions.

Contribution

The study demonstrates that the previously observed correlation is caused by observational biases and not by physical star-planet interactions.

Findings

The correlation is due to flux limits and detection biases.

No correlation is found in a complete, unbiased sample.

Star-planet interaction effects are not supported by the data.

Abstract

The activity levels of stars are influenced by several stellar properties, such as stellar rotation, spectral type and the presence of stellar companions. In analogy to binaries, planetary companions are also thought to be able to cause higher activity levels in their host stars, although at lower levels. Especially in X-rays, such influences are hard to detect because coronae of cool stars exhibit a considerable amount of intrinsic variability. Recently, a correlation between the mass of close-in exoplanets and their host star's X-ray luminosity has been detected, based on archival X-ray data from the ROSAT All-Sky Survey. This finding has been interpreted as evidence for Star-Planet Interactions. We show in our analysis that this correlation is caused by selection effects due to the flux limit of the X-ray data used and due to the intrinsic planet detectability of the radial velocity method, and thus does not trace possible planet-induced effects. We also show that the correlation is not present in a corresponding complete sample derived from combined XMM-Newton and ROSAT data.