55 Cancri: Stellar astrophysical parameters, a planet in the habitable zone, and implications for the radius of a transiting super-earth

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 55Cnc's stellar astrophysical parameters based on improved interferometry: R = 0.943 ± 0.010 R ∞, T EFF = 5196 ± 24K. We use isochrone fitting to determine 55Cnc's age to be 10.2 ± 2.5Gyr, implying a stellar mass of 0.905 ± 0.015 M ∞. Our analysis of the location and extent of the system's habitable zone (HZ; 0.67-1.32AU) shows that planet f, with period 260days and Msin 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 55Cnc 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⊕. © 2011. The American Astronomical Society. All rights reserved.