Eta Ceti


Eta Ceti is a star in the equatorial constellation of Cetus. It has the traditional name Deneb Algenubi or Algenudi. The apparent visual magnitude of this star is +3.4, making it the fourth-brightest star in this otherwise relatively faint constellation. The distance to this star can be measured directly using the parallax technique, yielding a value of.
This is a giant star with a stellar classification of K1 III, having exhausted the hydrogen at its core and evolved away from the main sequence of stars like the Sun. It is a red clump star that is generating energy through the nuclear fusion of helium at its core.
Eta Ceti may have slightly more mass than the Sun and its outer envelope has expanded to 15 times the Sun's radius. It is radiating 74 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 4,356 K. This heat gives the star the orange-hued glow of a K-type star.

In culture

The name Deneb Algenubi was from Arabic ذنب القيطس الجنوبي - al-dhanab al-qayṭas al-janūbī, meaning the southern tail of the sea monster. In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Naamat, which was translated into Latin as Prima Struthionum, meaning the first ostrich. This star, along with θ Cet, τ Cet, ζ Cet and υ Cet, were Al Naʽāmāt, the Hen Ostriches.
In Chinese, 天倉, meaning Square Celestial Granary, refers to an asterism consisting of η Ceti, ι Ceti, θ Ceti, ζ Ceti, τ Ceti and 57 Ceti. Consequently, the Chinese name for η Ceti itself is 天倉二

Planetary system

In 2014, two exoplanets around the star were discovered using the radial velocity method. Planets discovered by radial velocity have poorly known masses because if the orbit of the planets were inclined away from the line of sight, a much larger mass would have to compensate for the angle.
Eta Ceti b has a minimum mass of and an orbital period of 403.5 days, while Eta Ceti c has a minimum mass of and an orbital period of 751.9 days. Assuming the orbits of the two are coplanar, then the two planets must be locked in a 2:1 orbital resonance, otherwise the system would become dynamically unstable. Although the inclinations from the line of sight are unknown, the value is constrained to be 70° or less: if any higher, the higher masses would render the system dynamically unstable, with no stable solutions.