Eta Ceti

η Ceti

Location of η Ceti (circled)
Observation data J2000.0
Constellation	Cetus
Right ascension	01h 08m 35.39148s[1]
Declination	−10° 10′ 56.1570″[1]
Apparent magnitude (V)	+3.446[2]
Characteristics
Evolutionary stage	red clump[3]
Spectral type	K2−IIIb[4]
U−B color index	+1.194[2]
B−V color index	+1.161[2]
Distance		123.9 ± 0.7 ly (38.0 ± 0.2 pc)
Absolute magnitude (MV)	+0.68[6]
Details
Gyr
HIP 5364, HR 334, SAO 147632, 2MASS J01083539-1010560[9]
Database references
SIMBAD	data

Eta Ceti (η Cet, η Ceti) is a

This is a giant star that has been chosen a standard for the stellar classification of K2−IIIb. It has exhausted the hydrogen at its core and evolved away from the main sequence of stars like the Sun. (The classification is sometimes listed as K1.5 IIICN1Fe0.5, indicating a strong CN star^[10] with higher-than-normal abundance of cyanogen and iron relative to other stars of its class.)^[11] It is a red clump star that is generating energy through the nuclear fusion of helium at its core.^[3]

Eta Ceti may have slightly more mass than the Sun and its outer envelope has expanded to 15 times the Sun's radius.

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 (أول النعامات – awwil al naʽāmāt), which was translated into Latin as Prima Struthionum, meaning the first ostrich.^[13] This star, along with θ Cet (Thanih al Naamat), τ Cet (Thalath Al Naamat), ζ Cet (Baten Kaitos) and υ Cet, were Al Naʽāmāt (النعامات), the Hen Ostriches.^[14]

In

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.^[17]

Eta Ceti b has a minimum mass of 2.55 M_J and an orbital period of 403.5 days (about 1.1 years), while Eta Ceti c has a minimum mass of 3.32 M_J and an orbital period of 751.9 days (2.06 years). 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.^[18]

References