Xi1 Ceti

Xi¹ Ceti , Latinized from ξ¹ Ceti, is a binary star^[10] system located in the equatorial constellation of Cetus. It is visible to the naked eye with a combined apparent visual magnitude of +4.36.^[2] The distance to this system is approximately 340 light years based on parallax measurements, and it is drifting closer to the Sun with a radial velocity of −4 km/s.^[2] The proximity of the star to the ecliptic means it is subject to lunar occultations.^[11]

For other stars with this Bayer designation, see ξ Ceti.

Xi¹ Ceti

Location of ξ1 Ceti (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cetus
Right ascension	02h 12m 59.99769s[1]
Declination	+08° 50′ 48.2023″[1]
Apparent magnitude (V)	+4.36[2] [combined]
Characteristics
Spectral type	G7III Ba0.4 Fe-1[3] + DA4[4]
B−V color index	0.878±0.024[2]
Astrometry
Radial velocity (Rv)	−3.93±0.09[2] km/s
Proper motion (μ)	RA: −24.498[1] mas/yr Dec.: −5.952[1] mas/yr
Parallax (π)	9.5451±0.3275 mas[1]
Distance	340 ± 10 ly (105 ± 4 pc)
Absolute magnitude (MV)	–0.99[5]
Orbit[6]
Period (P)	1,642.1±1.3
Semi-major axis (a)	≥ 0.896 ± 0.020 AU (134 ± 3 Gm)
Eccentricity (e)	0 (fixed)
Periastron epoch (T)	34,985±5 MJD
Semi-amplitude (K1) (primary)	5.91±0.14 km/s
Details
A
Mass	3.80[5] M☉
Radius	18.2+1.0 −2.4[1] R☉
Luminosity	209.9±8.2[1] L☉
Surface gravity (log g)	2.60[1] cgs
Temperature	5,184±50[5] K
Metallicity [Fe/H]	−0.01[5] dex
Age	100[7] Myr
B
Mass	0.8[5] M☉
Surface gravity (log g)	8.4[8] cgs
Other designations
ξ1 Cet, ksi01 Cet, 65 Ceti, NSV 749, BD+08°345, HD 13611, HIP 10324, HR 649, SAO 110408, WDS 02130+0851, WD 02130+0851[9]
Database references
SIMBAD	data
Exoplanet Archive	data

The spectroscopic binary nature of Xi¹ Ceti was discovered in 1901 by William Wallace Campbell using the Mills spectrograph at the Lick Observatory.^[12][6] The pair have a circular orbit with a period of 4.5 years and a separation of 3.8 AU.^[5] It is a suspected eclipsing binary with an amplitude of 0.03 in magnitude, which would suggest the orbital plane has a high inclination.^[13]

The primary, designated component A, is a mild barium^[14] giant star with a stellar classification of G7III Ba0.4 Fe-1.^[3] Morgan and Keenan in 1973 had classified it as a bright giant star with an anomalous underabundance of the CN molecule.^[15] Evidence has been found for an overabundance of s-process elements,^[5] although this is disputed.^[7] The star has 3.8^[5] times the mass and 18^[1] times the radius of the Sun. The companion, component B, is a small white dwarf companion with 80% of the mass of the Sun and a class of DA4.^[4] It was detected in 1985 by its ultraviolet emission.^[8]

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, the Chinese name for Xi¹ Ceti itself is "the Fifth Star of Circular Celestial Granary", Tiān Qūn Wu.^[16]