Epsilon Pegasi

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Epsilon Pegasi
Diagram showing star positions and boundaries of the Pegasus constellation and its surroundings
Cercle rouge 100%.svg

Location of ε Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension 21h 44m 11.15614s[1]
Declination +09° 52′ 30.0311″[1]
Apparent magnitude (V) 2.399[1]
Characteristics
Spectral type K2 Ib[2]
U−B color index +1.722[3]
B−V color index +1.527[3]
Variable type LC[4]
Astrometry
Radial velocity (Rv) 3.39 ± 0.06[5] km/s
Proper motion (μ) RA: +26.92[1] mas/yr
Dec.: +0.4[1] mas/yr
Parallax (π) 4.73 ± 0.17[1] mas
Distance 690 ± 20 ly
(211 ± 8 pc)
Absolute magnitude (MV) –4.142[6]
Details
Mass 11.7 ± 0.8[7] M☉
Radius 185[8] R☉
Luminosity 3895[9] L☉
Luminosity (bolometric) 12,250[9] L☉
Surface gravity (log g) 1.01[6] cgs
Temperature 4,379[6] K
Metallicity [Fe/H] –0.04[6] dex
Rotational velocity (v sin i) 8[10] km/s
Age 20.0 ± 4.5[7] Myr
Other designations
Enif, Enf, Enir, Al Anf, Os Pegasi, Fom, 8 Peg, BD+09 4891, FK5 815, HD 206778, HIP 107315, HR 8308, SAO 127029.[11]
Database references
SIMBAD data

Epsilon Pegasi (ε Peg, ε Pegasi) is the brightest star in the northern constellation of Pegasus. It has the traditional name Enif (EE-nif). The name Enif is derived from the Arabic word for nose, due to its position as the muzzle of Pegasus. With an apparent visual magnitude of 2.4,[3] 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,[12][13] yielding a value of around 690 light-years (210 parsecs).[1]

Other traditional names for the star include Fom al Feras, Latinised to Os Equi.[14] In Chinese, 危宿 (Wēi Sù), meaning Rooftop (asterism), refers to an asterism consisting of ε Pegasi, α Aquarii and θ Peg.[15] Consequently, ε Pegasi itself is known as 危宿三 (Wēi Sù sān, English: the Third Star of Rooftop.)[16]

Properties

This is an evolved star that has entered the supergiant stage, as indicated by the stellar classification of K2 Ib.[2] It is estimated to be 12[7] times the Sun's mass. The measured angular diameter of this star, after correction for limb darkening, is 8.17 ± 0.09 mas.[17] At the estimated distance of this star, this yields an enormous physical size of about 185 times the radius of the Sun.[8] From this expanded envelope, it is radiating roughly 12,250[9] times the luminosity of the Sun at an effective temperature of 4,337 K.[6] This temperature is cooler than the Sun, giving it the orange-hued glow of a K-type star.[18]

Enif probably only has a few million years left to go, although it is unknown whether it will explode in a supernova or die off as a rare neon-oxygen white dwarf, due to its mass straddling the dividing line between stars destined to explode or not. Enif has been observed to brighten radically upon a few occasions, giving rise to the theory that it (and possibly other supergiants) erupt in massive flares that dwarf those of our own Sun.[19] It is a type LC slow irregular variable star that varies from +0.7 to +3.5 in magnitude.[4] 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.[9] It has a relatively high peculiar velocity of 21.6 km s−1.[7]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 3.2 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ 4.0 4.1 Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ 7.0 7.1 7.2 7.3 Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 Lua error in package.lua at line 80: module 'strict' not found.. The radius (R*) is given by:
    \begin{align} 2\cdot R_* & = \frac{(10^{-3}\cdot 211\cdot 8.17)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 370.8\cdot R_{\bigodot} \end{align}
  9. ↑ 9.0 9.1 9.2 9.3 Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  16. ↑ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.

Coordinates: Sky map 21h 44m 11.158s, +09° 52′ 30.04″

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