A Collage of Small Planets from the Lick–Carnegie Exoplanet Survey: Exploring the Super-Earth and Sub-Neptune Mass Regime*

Abstract

Analysis of new precision radial velocity (RV) measurements from the Lick Automated Planet Finder (APF) and Keck HIRES have yielded the discovery of three new exoplanet candidates orbiting two nearby K dwarfs not previously reported to have companions (HD 190007 and HD 216520. We also report new velocities from both the APF and the Planet Finder Spectrograph (PFS) for the previously reported planet host stars GJ 686 and HD 180617 and update the corresponding exoplanet orbital models. Of the newly discovered planets, HD 190007 b has a period of 11.72 days, an RV semiamplitude of K = 5.64±0.55 m s −1 , a minimum mass of 16.46±1.66 M ⊕ , and orbits the slightly metalrich, active K4 dwarf star HD 190007 (d = 12.7 pc). HD 216520 b has an orbital period of 35.45 days, an RV semi-amplitude of K = 2.28±0.20 m s −1 , and a minimum mass of 10.26±0.99 M ⊕ , while HD 216520 c has an orbital period of P = 154.43 days, an RV semi-amplitude of K = 1.29±0.22 m s −1 , and a minimum mass of 9.44 ± 1.63 M ⊕. Both of these planets orbit the slightly metal-poor, inactive K0 dwarf star HD 216520 (d = 19.6 pc). We find that our updated best fit models for HD 180617 b and GJ 686 b are in good agreement with the previously published results. For HD 180617 b we obtain an orbital period of 105.91 days, an RV semi-amplitude of K = 2.696±0.224 m s −1 , and a minimum mass of 12.214±1.05 M ⊕. For GJ 686 b we find the orbital period to be 15.53 days, the RV semi-amplitude to be K = 3.004±0.180 m s −1 , and the minimum mass to be 6.624±0.432 M ⊕. Using an injection-recovery exercise, we find that HD 190007 b and HD 216520 b are unlikely to have

Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions*

“…To search for evidence of these long-term magnetic cycles, in addition to shorter-term rotational periods, in our RV data sets we first derive an S-index value from each RV spectrum. For the HIRES APF and PFS data sets, these S-index values are generated automatically as part of the data reduction pipelines, and further details can be found in Butler et al (2017) and Burt et al (2021). We determine errors for each instrument's S-index values taking into account photon noise.…”

A review of planetary systems around HD 99492, HD 147379, and HD 190007 with HARPS-N

“…It is slightly metal-rich, with an age that remains uncertain. However, Burt et al (2021) suggest that the star is at least 1 Gyr old, based on data from the Kepler mission.…”

Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions

“…our RV data sets we first derive an S-index value from each RV spectrum. For the HIRES APF and PFS data sets, these S-index values are generated automatically as part of the data reduction pipelines and further details can be found in Butler et al (2017) and Burt et al (2021). We determine errors for each instrument's S-index values taking into account photon noise.…”