Two 'b's in the Beehive: The Discovery of the First Hot Jupiters in an Open Cluster

TL;DR

This paper reports the discovery of the first hot Jupiters in an open cluster, Praesepe, using radial velocity measurements, providing insights into planet formation and migration in such environments.

Contribution

It presents the first detection of hot Jupiters in an open cluster and analyzes their implications for planet formation and migration timescales.

Findings

Two hot Jupiters discovered in Praesepe cluster.

Hot Jupiter frequency estimated at approximately 3.8%.

Giant planet migration occurred within 600 million years.

Abstract

We present the discovery of two giant planets orbiting stars in Praesepe (also known as the Beehive Cluster). These are the first known hot Jupiters in an open cluster and the only planets known to orbit Sun-like, main-sequence stars in a cluster. The planets are detected from Doppler shifted radial velocities; line bisector spans and activity indices show no correlation with orbital phase, confirming the variations are caused by planetary companions. Pr0201b orbits a V=10.52 late F dwarf with a period of 4.4264 +/- 0.0070 days and has a minimum mass of 0.540 +/- 0.039 Mjup, and Pr0211b orbits a V=12.06 late G dwarf with a period of 2.1451 +/- 0.0012 days and has a minimum mass of 1.844 +/- 0.064 Mjup. The detection of 2 planets among 53 single members surveyed establishes a lower limit on the hot Jupiter frequency of 3.8 (+5.0)(-2.4) % in this metal-rich open cluster. Given the precisely known age of the cluster, this discovery also demonstrates that, in at least 2 cases, giant planet migration occurred within 600 Myr after formation. As we endeavor to learn more about the frequency and formation history of planets, environments with well-determined properties -- such as open clusters like Praesepe -- may provide essential clues to this end.