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

Abstract

We report on a radial-velocity search for short-period planets in the Pleiades open cluster. We observed 30 Pleiades member stars at the Okayama Astrophysical Observatory with the High Dispersion Echelle Spectrograph. To evaluate and mitigate the effects of stellar activity on radial-velocity (RV) measurements, we computed four activity indicators (full width at half maximum, V-span, W-span, and S-H alpha). Among our sample, no short-period planet candidates were detected. Stellar intrinsic RV jitter was estimated to be 52 m s(-1), 128 m s(-1), and 173 m s(-1) for stars with v sin i of 10 km s(-1), 15 km s(-1), and 20 km s(-1), respectively. We determined the planet occurrence rate from our survey and set the upper limit to 11.4% for planets with masses 1-13 M-JUP and period 1-10 d. 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 in the range 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 planets with an orbital period of 3 d and masses of 1-5, 5-13, and 13-80 M-JUP, respectively.