Refining the Stellar Parameters of Ceti: a Pole-on Solar Analog

To accurately characterize the planets a star may be hosting, stellar parameters must first be well determined. tau Ceti is a nearby solar analog and often a target for exoplanet searches. Uncertainties in the observed rotational velocities have made constraining tau Ceti's inclination difficult. For planet candidates from radial velocity (RV) observations, this leads to substantial uncertainties in the planetary masses, as only the minimum mass (m sin i) can be constrained with RV. In this paper, we used new long-baseline optical interferometric data from the CHARA Array with the MIRC-X beam combiner and extreme precision spectroscopic data from the Lowell Discovery Telescope with EXPRES to improve constraints on the stellar parameters of tau Ceti. Additional archival data were obtained from a Tennessee State University Automatic Photometric Telescope and the Mount Wilson Observatory HK project. These new and archival data sets led to improved stellar parameter determinations, including a limb-darkened angular diameter of 2.019 +/- 0.012 mas and rotation period of 46 +/- 4 days. By combining parameters from our data sets, we obtained an estimate for the stellar inclination of 7 degrees +/- 7 degrees. This nearly pole-on orientation has implications for the previously reported exoplanets. An analysis of the system dynamics suggests that the planetary architecture described by Feng et al. may not retain long-term stability for low orbital inclinations. Additionally, the inclination of tau Ceti reveals a misalignment between the inclinations of the stellar rotation axis and the previously measured debris disk rotation axis (i(disk) = 35 degrees +/- 10 degrees).