Planets in Open Clusters Detectable by Kepler

TL;DR

This paper investigates the potential for detecting planets in open clusters with Kepler, using models to estimate detection rates and considering the effects of stellar encounters and metallicity.

Contribution

It provides detailed N-body models showing that planets in open clusters are less affected by stellar encounters and estimates Kepler's potential to detect planets in NGC 6791.

Findings

Kepler could detect 1-20 planets in NGC 6791 if planets are as common as in the field.

Most planets in Kepler-detectable orbits are not significantly perturbed by stellar encounters in open clusters.

Detection depends on planet size distribution and data collection duration.

Abstract

While hundreds of planets have been discovered around field stars, only a few are known in star clusters. To explain the lack of short-period giant planets in globular clusters (GC), such as 47 Tucane and \omega\ Centauri, it has been suggested that their low metallicities may have prevented planet formation. Alternatively, the high rates of close stellar encounters in these clusters may have influenced the formation and subsequent evolution of planetary systems. How common are planets in clusters around normal main-sequence stars? Here we consider whether this question can be addressed using data from the Kepler mission. The Kepler field of view contains 4 low-density (relative to GCs) open clusters where the metallicities are about solar (or even higher) and stellar encounters are much less frequent than in typical GCs. We provide detailed $N$-body models and show that most planets in Kepler-detectable orbits are not significantly perturbed by stellar encounters in these open clusters. We focus on the most massive cluster, NGC 6791, which has super-solar metallicity, and find that if planets formed in this cluster at the same frequency as observed in the field, Kepler could detect 1 -- 20 transiting planets depending on the planet-size distribution and the duration of data collection. Due to the large distance to NGC 6791 Kepler will have to search relatively faint ($K_p<20$) stars for the full extended mission to achieve such a yield.