Physical Properties
The Tau Ceti system is believed to have only one stellar component. A dim optical companion has been observed, which is possibly gravitationally bound, but it is more than 10 arcseconds distant from the primary. No astrometric or radial velocity perturbations have been deduced, suggesting a star that does not have a large companion in a close orbit, such as a "hot Jupiter". Any potential gas giants around Tau Ceti are likely to be located more at Jupiter-like distances.
Most of what is known about the physical properties of Tau Ceti has been determined through spectroscopic measurements. By comparing the spectrum to computed models of stellar evolution, the age, mass, radius and luminosity of Tau Ceti can be estimated. However, using an astronomical interferometer, measurements of the radius of the star can be made directly to an accuracy of 0.5%. It deploys a long baseline to measure angles much smaller than can be resolved with a conventional telescope. Through this means, the radius of Tau Ceti has been measured as 79.3 ± 0.4% of the solar radius. This is about the size that is expected for a star with somewhat lower mass than the Sun.
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