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Retired A stars and their companions. VI. A pair of interacting exoplanet pairs around the subgiants 24 sextanis and HD 200964

Johnson, John Asher and Payne, Matthew and Howard, Andrew W. and Clubb, Kelsey I. and Ford, Eric B. and Bowler, Brendan P. and Henry, Gregory W. and Fischer, Debra A. and Marcy, Geoffrey W. and Brewer, John M. and Schwab, Chirstian and Reffert, Sabine and Lowe, Thomas B. (2011) Retired A stars and their companions. VI. A pair of interacting exoplanet pairs around the subgiants 24 sextanis and HD 200964. Astronomical Journal, 141 (1). Art. No. 16. ISSN 0004-6256.

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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_⋆ =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_⋆ = 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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Johnson, John Asher0000-0001-9808-7172
Payne, Matthew0000-0001-5133-6303
Howard, Andrew W.0000-0001-8638-0320
Ford, Eric B.0000-0001-6545-639X
Bowler, Brendan P.0000-0003-2649-2288
Henry, Gregory W.0000-0003-4155-8513
Fischer, Debra A.0000-0003-2221-0861
Marcy, Geoffrey W.0000-0002-2909-0113
Brewer, John M.0000-0002-9873-1471
Schwab, Chirstian0000-0002-4046-987X
Additional Information:© 2011 The American Astronomical Society. Received 2010 June 7; accepted 2010 October 25; published 2010 December 10. 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. We thank the many observers who contributed to the observations reported here. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff, especially Grant Hill, Scott Dahm, and Hien Tran for their support of HIRES and Greg Wirth for support of remote observing. We are also grateful to the time assignment committees of NASA, NOAO, Caltech, and the University of California for their generous allocations of observing time. M.J.P. thanks Stan Peale for his insightful comments regarding the likely libration states of the systems. A.W.H. gratefully acknowledges support from a Townes Post-doctoral Fellowship at the U. C. Berkeley Space Sciences Laboratory. E.B.F. and M.J.P. were supported by NASA Origins of Solar Systems grant NNX09AB35G. G.W.M. acknowledges NASA grant NNX06AH52G. G.W.H acknowledges support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence program. Finally, the authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible.
Funding AgencyGrant Number
University of CaliforniaUNSPECIFIED
Tennessee State UniversityUNSPECIFIED
State of Tennessee Centers of Excellence programUNSPECIFIED
Subject Keywords: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
Issue or Number:1
Classification Code:PACS: 97.20.Ge; 95.85.Kr; 97.20.Li; 97.82.-j; 97.10.Wn
Record Number:CaltechAUTHORS:20110125-161142942
Persistent URL:
Official Citation:John Asher Johnson et al. 2011 The Astronomical Journal 141 16 doi: 10.1088/0004-6256/141/1/16
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21892
Deposited By: Benjamin Perez
Deposited On:26 Jan 2011 16:49
Last Modified:09 Mar 2020 13:19

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