75 Ceti

75 Ceti
Observation data; Epoch J2000.0 Equinox J2000.0
Constellation	Cetus
Right ascension	02h 32m 09.42241s
Declination	−01° 02′ 05.6166″
Apparent magnitude (V)	+5.36
Characteristics
Spectral type	K1 III
B−V color index	+1.004±0.002
Astrometry
Radial velocity (Rv)	−6.34±0.13 km/s
Proper motion (μ)	RA: −23.268 mas/yr ; Dec.: −30.987 mas/yr
Parallax (π)	12.1717 ± 0.0962 mas
Distance	268 ± 2 ly ; (82.2 ± 0.6 pc)
Absolute magnitude (MV)	0.808
Details
Mass	1.85±0.05 M☉
Radius	10.38+0.15; −0.26 R☉
Luminosity	56.1±0.6 L☉
Surface gravity (log g)	2.67±0.04 cgs
Temperature	4,846+163; −128 K
Metallicity [Fe/H]	0.00±0.06 dex
Age	1.41±0.01 Gyr
Other designations
	75 Cet, BD–01°353, GC 3043, HD 15779, HIP 11791, HR 739, SAO 129959
Database references
SIMBAD	data
Exoplanet Archive	data

75 Ceti is a single^[9] star in the equatorial constellation of Cetus with at least two planets.^[6] It is visible to the naked eye as a dim, orange-hued star with an apparent visual magnitude of +5.36.^[2] The star is located 268 light-years (82 parsecs) distant from the Sun, based on parallax, but is drifting closer with a radial velocity of −6 km/s.^[1]

In Chinese, 天囷 (Tiān Qūn), meaning Circular Celestial Granary, refers to an asterism consisting of α Ceti, κ¹ Ceti, λ Ceti, μ Ceti, ξ¹ Ceti, ξ² Ceti, ν Ceti, γ Ceti, δ Ceti, 75 Ceti, 70 Ceti, 63 Ceti and 66 Ceti. Consequently, 75 Ceti itself is known as the Tenth Star of Circular Celestial Granary.^[10]

This is an aging giant star with a stellar classification of K1 III,^[3] having exhausted the supply of hydrogen at its core and expanded to 10.6^[7] times the Sun's radius, or 0.05 AU. It is a red clump giant,^[5] which indicates it is on the horizontal branch and is generating energy through helium fusion at the core. The star is 1.4^[5] billion years old with 1.9^[5] times the Sun's mass. It is radiating 56^[7] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,846 K.^[7]

Planetary system

A planetary companion was discovered by Doppler measurements at the Okayama Astrophysical Observatory, and announced in 2012. The planet's discoverers consider the planet, designated 75 Ceti b, to be "typical" of gas giants.^[11] Note that (like many recorded planets) b takes in much more insolation than does Jupiter and, indeed, Earth.^[12]

There may be additional periodic factors in the data, corresponding to m sin i of around 0.4 M_J and 1 M_J, at distances of ~0.9 AU and ~4 AU, where i is the orbital inclination and m is the planet's actual mass.^[11] In 2023, the presence of a second, Jupiter-mass planet orbiting at 4 AU (75 Ceti c) was confirmed, which is more irradiated than Earth as well. The shorter period signal corresponding to a possible planet at 0.9 AU was found to be an alias of the true period of planet c.^[6]

The 75 Ceti planetary system^[6]
Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	≥2.479+0.074 −0.090 $M$ _J	1.912+0.002 −0.003	696.62+1.33 −1.69	0.093+0.026 −0.042	—	—
c	≥0.912+0.088 −0.143 $M$ _J	3.929+0.058 −0.052	2051.62+45.98 −40.47	0.023+0.191 −0.003	—	—