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Red giant star in the constellation Cetus From Wikipedia, the free encyclopedia
Alpha Ceti (α Ceti, abbreviated Alpha Cet, α Cet), officially named Menkar /ˈmɛŋkɑːr/,[9][10] is the second-brightest star in the constellation of Cetus. It is a cool luminous red giant estimated to be about 250 light years away based on parallax.
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 | |
Evolutionary stage | AGB[3] |
Spectral type | M1.5 IIIa[4] |
U−B color index | +1.93[2] |
B−V color index | +1.64[2] |
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 mas[1] |
Distance | 249 ± 8 ly (76 ± 3 pc) |
Absolute bolometric magnitude (Mbol) | −3.2±0.3[4] |
Details | |
Mass | 2.3±0.2;[6] 1.465–1.933[7] M☉ |
Radius | 100.2±3.4[7] R☉ |
Luminosity | 1,764±342[7] L☉ |
Surface gravity (log g) | 0.66±0.07[7] cgs |
Temperature | 3,738±170[7] K |
Metallicity [Fe/H] | −0.24±0.09[7] dex |
Rotational velocity (v sin i) | 6.9[8] km/s |
Other designations | |
Database references | |
SIMBAD | data |
Alpha Ceti is the star's Bayer designation. It has the traditional name Menkar, deriving from the Arabic word منخر manħar "nostril" (of Cetus). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[11] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[12] 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".[13]
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.)[14]
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.[4] It has more than twice the mass of the Sun[6] and, as a giant star, has expanded to about 100 times the Sun's radius.[7] The large area of the photosphere means that it is emitting about 1,765 times as much energy as the Sun, even though the effective temperature is only 3,738 K (compared to 5,778 K on the Sun).[7] The relatively low temperature gives Menkar the red hue of an M-type star.[17]
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,[3] 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.[18] It has been observed to periodically vary in brightness, but only with an amplitude of about one hundredth of a magnitude.[16]
Menkar (AK-123) was a United States Navy Crater class cargo ship named after the star.
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