Beta Ceti

Properties

Diphda has an apparent visual magnitude of 2.02, making it the brightest star in Cetus. It has a stellar classification of K0 III, although some sources list a classification of G9.5 III indicating that it lies along the dividing line separating G-type from K-type stars. The luminosity class 'III' means that it is a giant, a star that has consumed the hydrogen at its core and evolved away from the main sequence. With a mass of 3.5 solar masses, Beta Ceti was a B-type star when it formed on the main sequence. After passing through the red giant stage, it underwent a helium flash event and is now a red clump star generating energy through the thermonuclear fusion of helium at its core. Beta Ceti will remain in this mode for over 100 million years.

The effective temperature of the star's outer envelope is about 4,797 K, giving it the characteristic orange hue of a K-type star. In spite of its cooler temperature, Diphda is much more luminous than the Sun with a luminosity of about 150 times that of the Sun, while its photosphere has swollen to around 18 times the size of the Sun, in contrast with the initial radius of 2.01 R_☉ when still in the main sequence.

This star displays flaring activity that results in random outbursts that increase the luminosity of the star over intervals lasting several days. This is a much longer duration than for comparable solar flare activity on the Sun, which typically last for periods measured in hours. In 2005, a relatively high rate of X-ray emission was detected with the XMM-Newton space observatory. It is emitting about 2,000 times the X-ray luminosity of the Sun, allowing the star to be imaged with the Chandra X-ray Observatory.