Retired A Stars and Their Companions VI. A Pair of Interacting Exoplanet Pairs Around the Subgiants 24 Sextanis and HD200964
John Asher Johnson, Matthew Payne, Andrew W. Howard, Kelsey I. Clubb,, Eric B. Ford, Brendan P. Bowler, Gregory W. Henry, Debra A. Fischer, Geoffrey, W. Marcy, John M. Brewer, Christian Schwab, Sabine Reffert, Thomas B. Lowe

TL;DR
This study reports the discovery of two pairs of Jovian exoplanets orbiting evolved subgiant stars, with evidence suggesting they are in mean motion resonances, supported by radial velocity data and dynamical simulations.
Contribution
First detailed characterization of two interacting exoplanet pairs around subgiants, including dynamical analysis indicating possible mean motion resonances.
Findings
Both systems host two Jovian planets with specific orbital periods and masses.
Dynamical simulations suggest the planets are likely in mean motion resonances.
Further observations are needed to confirm the resonant configurations.
Abstract
We report radial velocity measurements of the G-type subgiants 24 Sextanis (=HD90043) and HD200964. Both are massive, evolved stars that exhibit periodic variations due to the presence of a pair of Jovian planets. Photometric monitoring with the T12 0.80m APT at Fairborn Observatory demonstrates both stars to be constant in brightness to <= 0.002 mag, thus strengthening the planetary interpretation of the radial velocity variations. 24 Sex b,c have orbital periods of 453.8 days and 883~days, corresponding to semimajor axes 1.333 AU and 2.08 AU, and minimum masses (Msini) 1.99 Mjup and 0.86 Mjup, assuming a stellar mass 1.54 Msun. HD200964 b,c have orbital periods of 613.8 days and 825 days, corresponding to semimajor axes 1.601 AU and 1.95 AU, and minimum masses 1.85 Mjup and 0.90 Mjup, assuming M* = 1.44 Msun. We also carry out dynamical simulations to properly account for…
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