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Alpha Ceti (α Ceti, abbreviated Alpha Cet, α Cet), officially named Menkar /ˈmɛŋkɑːr/,[8][9] is the second-brightest star in the constellation of Cetus. It is a cool luminous red giant about 250 light years away.

α Ceti
Cetus constellation map.svg
Red circle.svg
Location of α Ceti (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cetus
Right ascension  03h 02m 16.77307s[1]
Declination +04° 05′ 23.0596″[1]
Apparent magnitude (V) 2.53[2]
Characteristics
Spectral type M1.5 IIIa[3]
U−B color index +1.93[2]
B−V color index +1.64[2]
Variable type None[4]
Astrometry
Radial velocity (Rv)–26.08 ± 0.02[5] km/s
Proper motion (μ) RA: -10.41 ± 0.51[1] mas/yr
Dec.: -76.85 ± 0.36[1] mas/yr
Parallax (π)13.09 ± 0.44[1] mas
Distance249 ± 8 ly
(76 ± 3 pc)
Absolute magnitude (MV)–3.2 ± 0.3[3]
Details
Mass2.3 ± 0.2[6] M
Radius89 ± 5[6] R
Luminosity1455 ± 328[6] L
Surface gravity (log g)0.9 ± 0.1[6] cgs
Temperature3,795 ± 70[6] K
Metallicity [Fe/H]0.00 ± 0.30[6] dex
Rotational velocity (v sin i)6.9[7] km/s
Other designations
Menkar, Menkab, Mekab, Monkar, Al Minhar, 92 Ceti, HR 911, BD+03° 419, HD 18884, SAO 110920, FK5 107, HIP 14135.
Database references
SIMBADdata

Contents

NomenclatureEdit

Alpha Ceti is the star's Bayer designation. It has the traditional names Menkar or Menkab, the former deriving from the Arabic word منخر manħar "nostril" (of Cetus). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[10] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[11] included a table of the first two batches of names approved by the WGSN; which included Menkar for this star.

This star, along with γ Cet (Kaffaljidhma), δ Cet, λ Cet (also Menkar), μ Cet, ξ1 Cet and ξ2 Cet were Al Kaff al Jidhmah, "the Part of a Hand".[12]

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 α Ceti itself is 天囷一 (Tiān Qūn yī, English: the First Star of Circular Celestial Granary.)[13]

StructureEdit

Despite having the Bayer designation α Ceti, at visual magnitude 2.54 this star is actually not the brightest star in the constellation Cetus. That honor goes instead to Beta Ceti at magnitude 2.04. Menkar is a red giant with a stellar classification of M1.5 IIIa. It has more than twice the mass of the Sun and, as a giant star has expanded to about 89 times the Sun's radius. The large area of the photosphere means that it is emitting about 1,455 times as much energy as the Sun, even though the effective temperature is only 3,795 K (compared to 5,778 K on the Sun). The relatively low temperature gives Menkar the red hue of an M-type star.[14]

Menkar has evolved from the main sequence after exhausting the hydrogen at its core. It has also exhausted its core helium, becoming an asymptotic giant branch star,[15] and will probably become a highly unstable star like Mira before finally shedding its outer layers and forming a planetary nebula, leaving a relatively large white dwarf remnant.[16] It has been observed to vary in brightness, but only with an amplitude of about one hundredth of a magnitude.[17]

NamesakesEdit

See alsoEdit

ReferencesEdit

  1. ^ a b c d e van Leeuwen, F. (November 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. ^ a b c Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  3. ^ a b Tsuji, T. (October 2008), "Cool luminous stars: the hybrid nature of their infrared spectra", Astronomy and Astrophysics, 489 (3): 1271–1289, arXiv:0807.4387, Bibcode:2008A&A...489.1271T, doi:10.1051/0004-6361:200809869
  4. ^ Wittkowski, M.; et al. (November 2007). "Polychromatic Interferometry of Mira Variables". In Kerschbaum, F.; Charbonnel, C.; Wing, R. F. (eds.). Why Galaxies Care About AGB Stars: Their Importance as Actors and Probes, proceedings of the conference held 7-11 August 2006 at University Campus, Vienna, Austria. Why Galaxies Care About Agb Stars: Their Importance as Actors and Probes. ASP Conference Series. 378. p. 262. Bibcode:2007ASPC..378..262W.
  5. ^ Famaey, B.; et al. (January 2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics. 430 (1): 165–186. arXiv:astro-ph/0409579. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272.
  6. ^ a b c d e f Wittkowski, M.; et al. (December 2006), "Tests of stellar model atmospheres by optical interferometry. IV. VINCI interferometry and UVES spectroscopy of Menkar", Astronomy and Astrophysics, 460 (3): 855–864, arXiv:astro-ph/0610150, Bibcode:2006A&A...460..855W, doi:10.1051/0004-6361:20066032
  7. ^ Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
  8. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  9. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  10. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  11. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  12. ^ Star Name - R.H. Allen p.160
  13. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 11 日
  14. ^ "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
  15. ^ Eggen, Olin J. (1992). "Asymptotic giant branch stars near the sun". The Astronomical Journal. 104: 275. doi:10.1086/116239.
  16. ^ Kaler, James B., "MENKAR (Alpha Ceti)", Stars, University of Illinois, retrieved 2011-12-24
  17. ^ Koen, Chris; Eyer, Laurent (2002). "New periodic variables from the Hipparcos epoch photometry". Monthly Notices of the Royal Astronomical Society. 331 (1): 45. Bibcode:2002MNRAS.331...45K.

External linksEdit