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Article: Disentangling 2:1 resonant radial velocity orbits from eccentric ones and a case study for HD 27894
Title  Disentangling 2:1 resonant radial velocity orbits from eccentric ones and a case study for HD 27894 

Authors  
Issue Date  2015 
Citation  Astronomy & Astrophysics, 2015, v. 577, article no. A103 How to Cite? 
Abstract  Context. In radial velocity (RV) observations, a pair of extrasolar planets near a 2:1 orbital resonance can be misinterpreted as a single eccentric planet, if data are sparse and measurement precision insufficient to distinguish between these models. Aims: Using the Exoplanet Orbit Database (EOD), we determine the fraction of alleged singleplanet RV detected systems for which a 2:1 resonant pair of planets is also a viable model and address the question of how the models can be disentangled. Methods: By simulation we quantified the mismatch arising from applying the wrong model. Model alternatives are illustrated using the supposed singleplanet system HD 27894 for which we also study the dynamical stability of near2:1 resonant solutions. Results: Using EOD values of the data scatter around the fitted singleplanet Keplerians, we find that for 74% of the 254 putative singleplanet systems, a 2:1 resonant pair cannot be excluded as a viable model, since the error due to the wrong model is smaller than the scatter. For 187 EOD stars chi2probabilities can be used to reject the Keplerian models with a confidence of 95% for 54% of the stars and with 99.9% for 39% of the stars. For HD 27894 a considerable fit improvement is obtained when adding a lowmass planet near half the orbital period of the known Jovian planet. Dynamical analysis demonstrates that this system is stable when both planets are initially placed on circular orbits. For fully Keplerian orbits a stable system is only obtained if the eccentricity of the inner planet is constrained to < 0.3. Conclusions: A large part of the allegedly RV detected singleplanet systems should be scrutinized in order to determine the fraction of systems containing near2:1 resonant pairs of planets. Knowing the abundance of such systems will allow us to revise the eccentricity distribution for extrasolar planets and provide direct constraints for planetary system formation. 
Persistent Identifier  http://hdl.handle.net/10722/215278 
DC Field  Value  Language 

dc.contributor.author  Kürster, M   
dc.contributor.author  Trifonov, TH   
dc.contributor.author  Reffert, S   
dc.contributor.author  Kostogryz, N   
dc.contributor.author  Rodler, F   
dc.date.accessioned  20150821T13:20:42Z   
dc.date.available  20150821T13:20:42Z   
dc.date.issued  2015   
dc.identifier.citation  Astronomy & Astrophysics, 2015, v. 577, article no. A103   
dc.identifier.uri  http://hdl.handle.net/10722/215278   
dc.description.abstract  Context. In radial velocity (RV) observations, a pair of extrasolar planets near a 2:1 orbital resonance can be misinterpreted as a single eccentric planet, if data are sparse and measurement precision insufficient to distinguish between these models. Aims: Using the Exoplanet Orbit Database (EOD), we determine the fraction of alleged singleplanet RV detected systems for which a 2:1 resonant pair of planets is also a viable model and address the question of how the models can be disentangled. Methods: By simulation we quantified the mismatch arising from applying the wrong model. Model alternatives are illustrated using the supposed singleplanet system HD 27894 for which we also study the dynamical stability of near2:1 resonant solutions. Results: Using EOD values of the data scatter around the fitted singleplanet Keplerians, we find that for 74% of the 254 putative singleplanet systems, a 2:1 resonant pair cannot be excluded as a viable model, since the error due to the wrong model is smaller than the scatter. For 187 EOD stars chi2probabilities can be used to reject the Keplerian models with a confidence of 95% for 54% of the stars and with 99.9% for 39% of the stars. For HD 27894 a considerable fit improvement is obtained when adding a lowmass planet near half the orbital period of the known Jovian planet. Dynamical analysis demonstrates that this system is stable when both planets are initially placed on circular orbits. For fully Keplerian orbits a stable system is only obtained if the eccentricity of the inner planet is constrained to < 0.3. Conclusions: A large part of the allegedly RV detected singleplanet systems should be scrutinized in order to determine the fraction of systems containing near2:1 resonant pairs of planets. Knowing the abundance of such systems will allow us to revise the eccentricity distribution for extrasolar planets and provide direct constraints for planetary system formation.   
dc.language  eng   
dc.relation.ispartof  Astronomy & Astrophysics   
dc.rights  Creative Commons: Attribution 3.0 Hong Kong License   
dc.rights  The original publication is available at [Astronomy & Astrophysics]. Credit: Author, A&A, 2015, v. 577, article no. A103, reproduced with permission, ©ESO   
dc.title  Disentangling 2:1 resonant radial velocity orbits from eccentric ones and a case study for HD 27894   
dc.type  Article   
dc.identifier.email  Trifonov, TH: trifonov@hku.hk   
dc.description.nature  published_or_final_version   
dc.identifier.doi  10.1051/00046361/201525872   
dc.identifier.hkuros  248275   