Epsilon Pegasi

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Template:Short description

ε Pegasi
Template:Location mark
Location of ε Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 2.37 - 2.45[2]
Characteristics
Evolutionary stage Red supergiant
Spectral type K2 Ib-II[3]
U−B Template:Engvar +1.722[4]
B−V Template:Engvar +1.527[4]
Variable type LC[2]
Astrometry
Radial velocity (Rv)Template:Val[5] km/s
Proper motion (μ) RA: +26.92[1] mas/yr
Dec.: +0.4[1] mas/yr
Parallax (π)4.73±0.17 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)−4.142[6]
Details
Mass11–12[7] Template:Solar mass
RadiusTemplate:Val[8] Template:Solar radius
LuminosityTemplate:Val[9] Template:Solar luminosity
Luminosity (visual, LV)3,895[10] Template:Solar luminosity
Surface gravity (log g)1.01[6] cgs
TemperatureTemplate:Val[8] K
Metallicity [Fe/H]−0.04[6] dex
Rotational velocity (v sin i)8[11] km/s
AgeTemplate:Val[12] Myr
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Enif, 8 Pegasi, BD+09°4891, FK5 815, HD 206778, HIP 107315, HR 8308, SAO 127029[13]
Database references
SIMBADdata

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Epsilon Pegasi (Latinised from ε Pegasi, abbreviated Epsilon Peg, ε Peg), formally named Enif Template:IPAc-en, is the brightest star in the northern constellation of Pegasus.

With an average apparent visual magnitude of 2.4,[4] this is a second-magnitude star that is readily visible to the naked eye. The distance to this star can be estimated using parallax measurements from the Hipparcos astrometry satellite,[14][15] yielding a value of around Template:Convert.[1]

Nomenclature

ε Pegasi (Latinised to Epsilon Pegasi) is the star's Bayer designation.

It bore the traditional name Enif derived from the Arabic word for 'nose', due to its position as the muzzle of Pegasus. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[17] included a table of the first two batches of names approved by the WGSN; which included Enif for this star.[18]

Other traditional names for the star include Fom al Feras, Latinised to Os Equi.[19] In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Rooftop (asterism), refers to an asterism consisting of Epsilon Pegasi, Alpha Aquarii and Theta Pegasi.[20] Consequently, the Chinese name for Epsilon Pegasi itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx.)[21]

Physical characteristics

Epsilon Pegasi is a red supergiant star, as indicated by the stellar classification of K2 Ib.[22] It is estimated to be between 11 and 12 times the Sun's mass[7] and has an enormous size of 183 times the radius of the Sun.[8] From this expanded envelope, it is radiating roughly 8,500 times the luminosity of the Sun[9] at an effective temperature of Template:Val.[8] This temperature is cooler than the Sun, giving it the orange-hued glow of a K-type star.[23]

Epsilon Pegasi is a slow irregular variable star that usually has a brightness between magnitudes 2.37 and 2.45. However, it was once observed very briefly at magnitude 0.7, giving rise to the theory that it (and possibly other supergiants) erupt in massive flares that dwarf those of the Sun.[24][25] It has also been observed as faint as magnitude 3.5.[24]

The spectrum shows an overabundance of the elements strontium and barium, which may be the result of the s-process of nucleosynthesis in the outer atmosphere of the star.[10] It has a relatively high peculiar velocity of Template:Val.[12]

Evolution

Epsilon Pegasi has exhausted its core hydrogen and expanded away from the main sequence. It is almost certainly on the horizontal branch fusing helium in its core.[26] If it loses more mass in the supergiant phase in its evolution, it may shed its outer layers and leave behind an unusual high mass oxygen–neon white dwarf near the Chandrasekhar limit,[25] otherwise it may be able to produce a supernova,[27] albeit an electron capture supernova.[28]

Based on its position on the color-magnitude diagram, Enif may have evolved from a whitish-yellow color to its current red color in the last 2,000 years, though there is currently no historical record supporting this.[7]

Pulfrich effect

Epsilon Pegasi is a fine example to observe the Pulfrich effect. This optical phenomenon is described on page 1372 of Burnham's Celestial Handbook. According to John Herschel: The apparent pendulum-like oscillation of a small star in the same vertical as the large one, when the telescope is swung from side to side.[29]

See also

References

Template:Reflist

Template:Sky Template:Stars of Pegasus Template:Portal bar

  1. ↑ a b c d e f Cite error: Invalid <ref> tag; no text was provided for refs named aaa474_2_653
  2. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named gcvs
  3. ↑ Script error: No such module "Citation/CS1".
  4. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named saaoc8_59
  5. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aaa430_165
  6. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named aaa480_1_91
  7. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named Neuhäuser2022
  8. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named Baines2025
  9. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named tycho-gaia
  10. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named mnras226_563
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named coapa239_1
  12. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named mnras410_1_190
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named SIMBAD
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aaa323_L49
  15. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named GSM
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ Script error: No such module "citation/CS1".
  18. ↑ Script error: No such module "citation/CS1".
  19. ↑ Script error: No such module "Citation/CS1".
  20. ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
  21. ↑ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.
  22. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named araa11_29
  23. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named csiro
  24. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named vsx
  25. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named kaler
  26. ↑ Script error: No such module "Citation/CS1".
  27. ↑ Script error: No such module "Citation/CS1".
  28. ↑ Script error: No such module "Citation/CS1".
  29. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named handbook
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