9 Ceti

9 Ceti is the Flamsteed designation for a star in the equatorial constellation of Cetus. It has an apparent visual magnitude of 6.39,[2] which is below the limit that can be seen with the naked eye by a typical observer.[9] (According to the Bortle scale, it is possible for some observers to see it from dark rural skies.) Based upon measurements made by the Hipparcos spacecraft, this star is around 68 light years away from the Sun.[1] There is a magnitude 12.57 optical companion at an angular separation of 214 arc seconds along a position angle of 294° (as of 1999),[10] although the pair are not physically associated as they have different proper motions.[11]

9 Ceti
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cetus
Right ascension  00h 22m 51.78847s[1]
Declination −12° 12′ 33.9699″[1]
Apparent magnitude (V) 6.39[2]
Characteristics
Spectral type G3 V[2]
U−B color index +0.09[3]
B−V color index +0.66[3]
Astrometry
Radial velocity (Rv)–2.7[2] km/s
Proper motion (μ) RA: +394.45[1] mas/yr
Dec.: +61.14[1] mas/yr
Parallax (π)47.93 ± 0.53[1] mas
Distance68.0 ± 0.8 ly
(20.9 ± 0.2 pc)
Details
Mass1.09[4] M☉
Radius1.00[5] R☉
Surface gravity (log g)4.47[6] cgs
Temperature5,807 ± 50[6] K
Metallicity [Fe/H]0.178[4] dex
Rotation7.655 d[7]
Rotational velocity (v sin i)7.2 ± 0.5[6] km/s
Age850[4] Myr
Other designations
9 Cet, BE Cet, BD−13° 60, GJ 9012, HD 1835, HIP 1803, HR 88, SAO 147237.[8]
Database references
SIMBADdata
ARICNSdata

This is a solar analog, which is defined as a "Population I dwarf with gross properties not very different from those of the Sun".[12] It is a G-type main sequence star with a stellar classification of G3 V,[2] which means it is generating energy through the fusion of hydrogen into helium at its core. The mass and radius of the star are similar to the Sun,[5] although the abundance of elements other than hydrogen and helium is about 50% greater.[4] It is much younger than the Sun, being an estimated 850 million years of age.[4] The effective temperature of the stellar atmosphere is around 5,807 K,[6] giving it the yellow-hued glow of a G-type star.[13]

In 1980, this was found to be a variable star with a periodicity of 7.655 days, and it was given variable star designation BE Cet. This variation in luminosity was interpreted to be the result of rotational modulation of star spot activity in the photosphere,[7] and hence it is classified as a BY Draconis variable.[14] There is considerable variation in the strength of the surface activity—to the point where it has appeared inactive during some observation runs. The strength of the surface magnetic field was measured to be 450 G.[7] The spectrum of this star includes lines of titanium oxide and calcium hydride, which, for a star of this class, is further evidence of star spot activity. Star spots cover an estimated 3% of the surface.[15]

This star has been examined for evidence of a planetary companion or a debris disk, but as of 2015 none has been found.[11] The age of the star and its motion through space suggest that it is a member of the Hyades stellar kinematic group.[16]

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Torres, C. A. O.; et al. (December 2006). "Search for associations containing young stars (SACY). I. Sample and searching method". Astronomy and Astrophysics. 460 (3): 695–708. arXiv:astro-ph/0609258. Bibcode:2006A&A...460..695T. doi:10.1051/0004-6361:20065602.
  3. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  4. Ramirez, I.; et al. (January 2014), "Chemical signatures of planets: beyond solar-twins", Astronomy & Astrophysics, 561: 16, arXiv:1310.8581, Bibcode:2014A&A...561A...7R, doi:10.1051/0004-6361/201322558, A7.
  5. Takeda, Genya; et al. (February 2007), "Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog", The Astrophysical Journal Supplement Series, 168 (2): 297–318, arXiv:astro-ph/0607235, Bibcode:2007ApJS..168..297T, doi:10.1086/509763.
  6. Pavlenko, Ya. V.; et al. (May 2012), "Effective temperatures, rotational velocities, microturbulent velocities and abundances in the atmospheres of the Sun, HD 1835 and HD 10700", Monthly Notices of the Royal Astronomical Society, 422 (1): 542–552, arXiv:1201.5099, Bibcode:2012MNRAS.422..542P, doi:10.1111/j.1365-2966.2012.20629.x.
  7. Stepien, K.; Geyer, E. (May 1996), "Rotation of solar-like main sequence stars", Astronomy and Astrophysics Supplement, 117: 83–91, Bibcode:1996A&AS..117...83S, doi:10.1051/aas:1996141.
  8. "9 Cet". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2015-12-10.
  9. Weaver, Harold F. (October 1947), "The Visibility of Stars Without Optical Aid", Publications of the Astronomical Society of the Pacific, 59 (350): 232, Bibcode:1947PASP...59..232W, doi:10.1086/125956.
  10. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122: 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920, retrieved 2015-07-22
  11. Rodriguez, David R.; et al. (May 2015), "Stellar multiplicity and debris discs: an unbiased sample", Monthly Notices of the Royal Astronomical Society, 449 (3): 3160–3170, arXiv:1503.01320, Bibcode:2015MNRAS.449.3160R, doi:10.1093/mnras/stv483.
  12. Hall, Jeffrey C.; et al. (July 2009), "The Activity and Variability of the Sun and Sun-Like Stars. II. Contemporaneous Photometry and Spectroscopy of Bright Solar Analogs", The Astronomical Journal, 138 (1): 312–322, Bibcode:2009AJ....138..312H, CiteSeerX 10.1.1.216.9004, doi:10.1088/0004-6256/138/1/312.
  13. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 10, 2012, retrieved 2012-01-16.
  14. Kholopov, P. N.; et al. (March 1985), "The 67th Name-List of Variable Stars", Information Bulletin on Variable Stars, 2681: 1, Bibcode:1985IBVS.2681....1K.
  15. Campbell, B.; Cayrel, R. (August 1, 1984), "Spectroscopic evidence for starspots in the G dwarf HD 1835", Astrophysical Journal Letters, 283: L17–L20, Bibcode:1984ApJ...283L..17C, doi:10.1086/184323.
  16. Nakajima, Tadashi; Morino, Jun-Ichi (January 2012), "Potential Members of Stellar Kinematic Groups within 30 pc of the Sun", The Astronomical Journal, 143 (1): 2, Bibcode:2012AJ....143....2N, doi:10.1088/0004-6256/143/1/2.
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