Radial-velocity search and statistical studies for short-period planets in the Pleiades open cluster

TL;DR

This study conducted a radial-velocity survey of 30 stars in the Pleiades cluster to search for short-period planets, finding no candidates and setting upper limits on planet occurrence rates in young open clusters.

Contribution

First to perform a detailed RV survey for short-period planets in the Pleiades, including activity mitigation, and to statistically constrain planet occurrence rates in young clusters.

Findings

No short-period planets detected in the sample.

Estimated stellar RV jitter ranges from 52 to 173 m/s depending on stellar rotation.

Upper limit of 11.4% for planets 1-13 M_JUP with 1-10 day periods.

Abstract

We report radial-velocity search for short-period planets in the Pleiades open cluster. We observed 30 Pleiades member stars at the Okayama Astrophysical Observatory (OAO) with High Dispersion Echelle Spectrograph (HIDES). To evaluate and mitigate the effects of stellar activity on radial-velocity measurements, we computed four activity indicators (FWHM, $V_{\rm span}$, $W_{\rm span}$ and $S_{\rm H{\alpha}}$). Among our sample, no short-period planet candidates were detected. Stellar intrinsic RV jitter was estimated to be ${\rm 52\ m\,s^{-1}}$, ${\rm 128\ m\,s^{-1}}$ and ${\rm 173\ m\,s^{-1}}$ for stars with $v\sin i$ of ${\rm 10\ km\,s^{-1}}$, ${\rm 15\ km\,s^{-1}}$ and ${\rm 20\ km\,s^{-1}}$, respectively. We determined the planet occurrence rate from our survey and set the upper limit to 11.4\% for the planets with masses 1--13 $M_{\rm JUP}$ and period 1--10 days. To set a more stringent constraint on the planet occurrence rate, we combined the result of our survey with those of other surveys targeting open clusters with ages between 30--300 Myr. As a result, the planet occurrence rate in young open clusters was found to be less than 7.4\%, 2.9\% and 1.9\% for the planets with an orbital period of three days and masses between 1--5, 5--13, and 13--80 $M_{\rm JUP}$, respectively.