2011ApJ...740...49V

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 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 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_⊕.