75 Ceti

75 Ceti is a single[7] star in the equatorial constellation of Cetus with at least one planet.[8] 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 271 light years distant from the Sun, based on parallax, but is drifting closer with a radial velocity of −6 km/s.[1]

75 Ceti
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cetus
Right ascension 02h 32m 09.42277s[1]
Declination −01° 02′ 05.6245″[1]
Apparent magnitude (V) +5.36[2]
Characteristics
Spectral type K1 III[3]
B−V color index +1.004±0.002[2]
Astrometry
Radial velocity (Rv)−6.21±0.13[1] km/s
Proper motion (μ) RA: −23.619[1] mas/yr
Dec.: −30.485[1] mas/yr
Parallax (π)12.0264 ± 0.1044[1] mas
Distance271 ± 2 ly
(83.2 ± 0.7 pc)
Absolute magnitude (MV)0.808[4]
Details
Mass1.85±0.05[5] M☉
Radius10.62+0.68
−0.58[1] R☉
Luminosity56.1±0.6[1] L☉
Surface gravity (log g)2.67±0.04[5] cgs
Temperature4,846+163
−128[1] K
Metallicity [Fe/H]0.00±0.06[5] dex
Age1.41±0.01[5] Gyr
Other designations
75 Cet, BD–01°353, GC 3043, HD 15779, HIP 11791, HR 739, SAO 129959[6]
Database references
SIMBADdata
Exoplanet Archivedata
Extrasolar Planets
Encyclopaedia		data

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.[9]

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[1] 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[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,846 K.[1]

The 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.[8] Note that (like many recorded planets) b takes in much more insolation than does Jupiter and, indeed, Earth.[10]

The 75 Ceti planetary system[8]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b >3 MJ 2.1 691.9±3.6 0.117±0.048 — —

There may be additional periodic factors in the data, corresponding to m sin i of around 0.4 MJ and 1 MJ, at distances of ∼0.9 AU and ∼4 AU, where i is the orbital inclination and m is the planet's actual mass. If these additional companions are confirmed, they are more irradiated than Earth as well.

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  3. Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
  4. Liu, Y. J.; et al. (2007). "The abundances of nearby red clump giants". Monthly Notices of the Royal Astronomical Society. 382 (2): 553–66. Bibcode:2007MNRAS.382..553L. doi:10.1111/j.1365-2966.2007.11852.x.
  5. Gallenne, A.; et al. (August 2018). "Fundamental properties of red-clump stars from long-baseline H-band interferometry". Astronomy & Astrophysics. 616: 12. arXiv:1806.09572. Bibcode:2018A&A...616A..68G. doi:10.1051/0004-6361/201833341. S2CID 119331707. A68.
  6. "75 Cet". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-08-01.
  7. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
  8. Sato, Bun'ei; et al. (2012). "Substellar Companions to Seven Evolved Intermediate-Mass Stars". Publications of the Astronomical Society of Japan. 64 (6). 135. arXiv:1207.3141. Bibcode:2012PASJ...64..135S. doi:10.1093/pasj/64.6.135. S2CID 119197073.
  9. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 11 日
  10. Square root of luminosity means that an Earth like planet would have to be >7 AU from the star.
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