Retired A Stars and Their Companions. VI. A Pair of Interacting Exoplanet Pairs Around the Subgiants 24 Sextanis and HD 200964
Abstract
We report radial velocity (RV) measurements of the G-type subgiants 24 Sextanis (= HD 90043) and HD 200964. Both are massive, evolved stars that exhibit periodic variations due to the presence of a pair of Jovian planets. Photometric monitoring with the T12 0.80 m APT at Fairborn Observatory demonstrates both stars to be constant in brightness to <=0.002 mag, thus strengthening the planetary interpretation of the RV variations. Based on our dynamical analysis of the RV time series, 24 Sex b, c have orbital periods of 452.8 days and 883.0 days, corresponding to semimajor axes 1.333 AU and 2.08 AU, and minimum masses 1.99 M Jup and 0.86 M Jup, assuming a stellar mass M sstarf= 1.54 M ⊙. HD 200964 b, c have orbital periods of 613.8 days and 825.0 days, corresponding to semimajor axes 1.601 AU and 1.95 AU, and minimum masses 1.99 M Jup and 0.90 M Jup, assuming M sstarf= 1.44 M ⊙. We also carry out dynamical simulations to properly account for gravitational interactions between the planets. Most, if not all, of the dynamically stable solutions include crossing orbits, suggesting that each system is locked in a mean-motion resonance that prevents close encounters and provides long-term stability. The planets in the 24 Sex system likely have a period ratio near 2:1, while the HD 200964 system is even more tightly packed with a period ratio close to 4:3. However, we caution that further RV observations and more detailed dynamical modeling will be required to provide definitive and unique orbital solutions for both cases, and to determine whether the two systems are truly resonant.
Based on observations obtained at the Lick Observatory, which is operated by the University of California, and W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology.- Publication:
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The Astronomical Journal
- Pub Date:
- January 2011
- DOI:
- 10.1088/0004-6256/141/1/16
- arXiv:
- arXiv:1007.4552
- Bibcode:
- 2011AJ....141...16J
- Keywords:
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- planets and satellites: detection;
- planets and satellites: formation;
- planets and satellites: fundamental parameters;
- planets and satellites: individual: HD200964 b HD200964 c 24 Sex b 24 Sex c;
- stars: individual: 24 Sex HD200964;
- techniques: radial velocities;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- AJ accepted