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

TL;DR

This study refines the stellar and planetary parameters of 55 Cancri, identifies its habitable zone, and discusses the potential habitability of its planets and moons, including a model-independent size estimate of the transiting super-Earth.

Contribution

It provides improved stellar parameters, habitable zone analysis, and a direct measurement of the super-Earth's size, offering new insights into the system's potential habitability.

Findings

55 Cancri's stellar radius is 0.943 R_sun.

The habitable zone extends from 0.67 to 1.32 AU.

The transiting super-Earth has a diameter of approximately 2.05 Earth radii.

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: $R=0.943 \pm 0.010 R_{\odot}$, $T_{\rm EFF} = 5196 \pm 24$ K. We use isochrone fitting to determine 55 Cnc's age to be 10.2 $\pm$ 2.5 Gyr, implying a stellar mass of $0.905 \pm 0.015 M_{\odot}$. Our analysis of the location and extent of the system's habitable zone (0.67--1.32 AU) shows that planet f, with period $\sim$ 260 days and $M \sin i = 0.155 M_{Jupiter}$, spends the majority of the duration of its elliptical orbit in the circumstellar habitable zone. 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 habitable zone. 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 ($\sim 2.05 \pm 0.15 R_{\earth}$), which, depending on the planetary mass assumed, implies a bulk density of 0.76 $\rho_{\earth}$ or 1.07 $\rho_{\earth}$.