Epsilon Pegasi
Epsilon Pegasi, formally named Enif, is the brightest star in the northern constellation of Pegasus.
With an average apparent visual magnitude of 2.4, 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, yielding a value of around.
Nomenclature
ε 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 IAU [Working Group on Star Names|Working Group on Star Names] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Enif for this star.
Other traditional names for the star include Fom al Feras, Latinised to Os Equi. In Chinese, 危宿, meaning Rooftop , refers to an asterism consisting of Epsilon Pegasi, Alpha Aquarii and Theta Pegasi. Consequently, the Chinese name for Epsilon Pegasi itself is 危宿三
Physical characteristics
Epsilon Pegasi is a red supergiant star, as indicated by the stellar classification of K2 Ib. It is estimated to be between 11 and 12 times the Sun's mass and has an enormous size of 183 times the radius of the Sun. From this expanded envelope, it is radiating roughly 8,500 times the luminosity of the Sun at an effective temperature of. This temperature is cooler than the Sun, giving it the orange-hued glow of a K-type star.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 erupt in massive flares that dwarf those of the Sun. It has also been observed as faint as magnitude 3.5.
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. It has a relatively high peculiar velocity of.
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. 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, otherwise it may be able to produce a supernova, albeit an electron capture supernova.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.