55 Cancri: Stellar Astrophysical Parameters, a Planet in the Habitable Zone, and Implications for the Radius of a Transiting Super-Earth

Creators: von Braun, Kaspar; Boyajian, Tabetha S.; ten Brummelaar, Theo A.; Kane, Stephen R.; van Belle, Gerard T.; Ciardi, David R.; Raymond, Sean N.; Lόpez-Morales, Mercedes; McAlister, Harold A.; Schaefer, Gail; Ridgway, Stephen T.; Sturmann, Laszlo; Sturmann, Judit; White, Russel; Turner, Nils H.; Farrington, Chris; Goldfinger, P. J.

Abstract

The bright star 55 Cancri is known to host five planets, including a transiting super-Earth. The study presented here yields directly determined values for 55 Cnc's stellar astrophysical parameters based on improved interferometry: R = 0.943 ± 0.010 R_☉, T EFF = 5196 ± 24 K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 ± 2.5 Gyr, implying a stellar mass of 0.905 ± 0.015 M_☉. Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32 AU) shows that planet f, with period ~260 days and M sin i = 0.155 M_(Jupiter), spends the majority of the duration of its elliptical orbit in the circumstellar HZ. Though planet f is too massive to harbor liquid water on any planetary surface, we elaborate on the potential of alternative low-mass objects in planet f's vicinity: a large moon and a low-mass planet on a dynamically stable orbit within the HZ. Finally, our direct value for 55 Cancri's stellar radius allows for a model-independent calculation of the physical diameter of the transiting super-Earth 55 Cnc e (~2.05 ± 0.15 R_⊕), which, depending on the planetary mass assumed, implies a bulk density of 0.76 ρ_⊕ or 1.07 ρ_⊕.

Additional Information

© 2011 American Astronomical Society. Received 2011 June 1; accepted 2011 July 22; published 2011 September 26. The authors thank B.-O. Demory and J. N. Winn for many open conversations and exchange of extremely useful information about the planetary radius of 55 Cnc e during the reparation of this manuscript, E. K. Baines for discussions about interferometric data quality, and D. Spiegel for very helpful suggestions on the issues interferometric visibilities and planet habitability. We would further like to extend our gratitude to the anonymous referee for careful reading of the manuscript and the insightful comments that improved the quality of this publication. T.S.B. acknowledges support provided by NASA through Hubble Fellowship grant #HST-HF-51252.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. S.T.R. acknowledges partial support from NASA grant NNH09AK731. The CHARA Array is funded by the National Science Foundation through NSF grants AST-0606958 and AST-0908253 and by Georgia State University through the College of Arts and Sciences, the W. M. Keck Foundation, the Packard Foundation, and the NASA Exoplanet Science Institute. This research made use of the SIMBAD literature database, operated at CDS, Strasbourg, France, and of NASA's Astrophysics Data System. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research made use of the NASA/IPAC/NExScI Star and Exoplanet Database, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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