The Monitor project: the search for transits in the open cluster NGC 2362

TL;DR

This study conducted a systematic search for transiting planets in the young open cluster NGC 2362, setting upper limits on hot Jupiter occurrence rates in very young stars and demonstrating the survey's potential for broader application.

Contribution

First systematic transit search in a ~5 Myr open cluster, providing constraints on hot Jupiter frequency in very young stars and assessing the Monitor Project's capabilities.

Findings

Identified 6 candidate light curves compatible with planetary transits.

Placed 99% confidence upper limits of 0.22 and 0.70 on hot Jupiter fractions for different orbital periods.

Demonstrated the Monitor Project's potential to constrain planetary occurrence in young clusters.

Abstract

We present the results of a systematic search for transiting planets in a ~5 Myr open cluster, NGC 2362. We observed ~1200 candidate cluster members, of which ~475 are believed to be genuine cluster members, for a total of ~100 hours. We identify 15 light curves with reductions in flux that pass all our detection criteria, and 6 of the candidates have occultation depths compatible with a planetary companion. The variability in these six light curves would require very large planets to reproduce the observed transit depth. If we assume that none of our candidates are in fact planets then we can place upper limits on the fraction of stars with hot Jupiters (HJs) in NGC 2362. We obtain 99% confidence upper limits of 0.22 and 0.70 on the fraction of stars with HJs (f_p) for 1-3 and 3-10 day orbits, respectively, assuming all HJs have a planetary radius of 1.5R_Jup. These upper limits represent observational constraints on the number of stars with HJs at an age <~10 Myr, when the vast majority of stars are thought to have lost their protoplanetary discs. Finally, we extend our results to the entire Monitor Project, a survey searching young, open clusters for planetary transits, and find that the survey as currently designed should be capable of placing upper limits on f_p near the observed values of f_p in the solar neighbourhood.