Beta Ceti - Deneb Kaitos, Diphda

Though the Beta star of Cetus, the Whale, Deneb Kaitos is - at magnitude 2.04 - the brightest in the constellation. Beta Ceti is easy to find, standing out in an otherwise lonely area south of the Great Square of Pegasus, northeast of Fomalhaut.

Beta Ceti's Arabic name means simply the "whale's tail," and is taken from a longer phrase that describes the star's position a bit more precisely in the southern branch of the tail. A less common name for the star is "Diphda," from the Arabic "ad-dafda' at-tani", meaning the "first frog," where Fomalhaut is the "second frog."

Properties

Like many other naked eye stars, Deneb Kaitos is a dying class K0 III giant, but warmer than most. Falling near the border of classes G and K, it has a temperature of 4800 K. Its distance of only 96 light years accounts for its relative brightness. Its computed luminosity is 145 times the Sun's, accounting for infrared radiation. Combined with the temperature, that luminosity gives it a radius 17 times solar - large, but not that large as giant stars go. Its mass is estimated to be about three times the Sun's.

Deneb Kaitos presents an enigma. It still has characteristics of its sunlike main-sequence phase, when it was fusing hydrogen into helium, and appeared something like Vega or Altair. Beta Ceti is one of the brightest X-ray stars in the solar neighborhood; its high-energy radiation comes from a corona (rather like the Sun's) which is magnetically heated to a few million K. Such magnetism is expected to be related to rotation, yet the star rotates rather slowly.

This high X-ray activity suggests that Deneb Kaitos has only recently begun to expire, and would therefore have a contracting helium core. Its detailed chemical composition, however, suggests that it has been around long enough to begin fusing its internal helium to carbon. Deneb Kaitos shows us that even the nearby stars are not all that well understood.

In 1923, Camille Flammarion reported that Beta Ceti had suddenly flared up to double its brightness, but this was later discounted by the astronomers of Mount Wilson Observatory. It is now believed that the Parisian astronomer may have confused it with its near neighbor, ο Ceti (Mira), which is a true variable star.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]