Epsilon Pegasi
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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,<ref name=saaoc8_59/> 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,<ref name=aaa323_L49/><ref name=GSM/> yielding a value of around Template:Convert.<ref name=aaa474_2_653/>
NomenclatureEdit
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)<ref name="WGSN">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> included a table of the first two batches of names approved by the WGSN; which included Enif for this star.<ref name="IAU-CSN">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Other traditional names for the star include Fom al Feras, Latinised to Os Equi.<ref>Template:Cite journal</ref> In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning Rooftop (asterism), refers to an asterism consisting of Epsilon Pegasi, Alpha Aquarii and Theta Pegasi.<ref>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.</ref> Consequently, the Chinese name for Epsilon Pegasi itself is {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, Template:Langx.)<ref>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.</ref>
Physical characteristicsEdit
Epsilon Pegasi is a red supergiant star, as indicated by the stellar classification of K2 Ib.<ref name=araa11_29/> It is estimated to be between 11 and 12 times the Sun's mass<ref name=Neuhäuser2022/> and has an enormous size of 183 times the radius of the Sun.<ref name=Baines2025/> From this expanded envelope, it is radiating roughly 8,500 times the luminosity of the Sun<ref name=tycho-gaia/> at an effective temperature of Template:Val.<ref name=Baines2025/> This temperature is cooler than the Sun, giving it the orange-hued glow of a K-type star.<ref name=csiro/>
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.<ref name=vsx/><ref name=kaler/> It has also been observed as faint as magnitude 3.5.<ref name=vsx/>
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.<ref name=mnras226_563/> It has a relatively high peculiar velocity of Template:Val.<ref name=mnras410_1_190/>
EvolutionEdit
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.<ref name=stock>Template:Cite journal</ref> 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,<ref name=kaler/> otherwise it may be able to produce a supernova,<ref>Template:Cite journal</ref> albeit an electron capture supernova.<ref>Template:Cite journal</ref>
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.<ref name=Neuhäuser2022/>
Pulfrich effectEdit
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.<ref name=handbook/>