Epsilon Pegasi

From the Science Archives, the open-project database of science information
Jump to navigation Jump to search

ε Pegasi
Pegasus constellation map.svg
Red circle.svg
Location of ε Peg (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
Distance690 ± 20 ly
(211 ± 8 pc)
Absolute magnitude (MV)–4.142[6]
Details
Mass11.7 ± 0.8[7] M
Radius185[8] R
Diameter185[8] D
Luminosity3895[9] L
Luminosity (bolometric)12,250[9] L
Surface gravity (log g)1.01[6] cgs
Temperature4,379[6] K
Metallicity [Fe/H]–0.04[6] dex
Rotational velocity (v sin i)8[10] km/s
Age20.0 ± 4.5[7] Myr
Other designations
Enif, Enf, Enir, Al Anf, Os Pegasi, Fom,[citation needed] 8 Peg, BD+09° 4891, FK5 815, HD 206778, HIP 107315, HR 8308, SAO 127029.[11]
Database references
SIMBADdata

Enif (Epsilon Pegasi). Though given only the fifth letter of the Greek alphabet by Bayer, Enif, at mid second magnitude (2.39), is still the brightest star in the constellation Pegasus. It just beats out Markab (Alpha) and Scheat (Beta), both in the Great Square, which received Alpha through Delta, showing the Square's importance. Enif is the brightest by cheating a bit, as it is rather roundly trounced by Alpheratz, Delta Pegasi. Modern constellation boundaries, however, place Alpheratz formally in Andromeda, where it is better known as Alpha Andromedae, leaving the field clear for Enif to triumph. The name, from Arabic, means "the nose," referring to the muzzle of Perseus' winged horse, with which he rescued Andromeda. Physically, Enif is a coolish, orange class K (K2) supergiant with a temperature of 4460 [degrees] Kelvin. From its distance of 670 light years, we calculate a total luminosity 6700 times that of the Sun, as befits a supergiant. Also befitting its great status is its diameter, which from direct measures of angular diameter and its luminosity and temperature is 150 times that of the Sun, large enough to take the star halfway to the orbit of the planet Venus. If Enif were our star, it would appear 40° across in our sky, about the angular extent of the entire constellation of Pegasus itself. As a supergiant, Enif is both dying and massive. It seems to have a mass around 10 times that of the Sun and is now either fusing its helium into carbon and oxygen or is about to start. Like Betelgeuse, it might either explode as a supernova or turn into a heavy, rare neon-oxygen white dwarf that has shrunk to less than the size of Earth. Even with all these great qualities, however, Enif still seems like an ordinary (if such there be) supergiant. Two characteristics set it apart. It seems to be part of a family of three very similar supergiants, the other two the Alpha and Beta stars of nearby Aquarius, Sadalmelik and Sadalsuud. The triplets, all at roughly the same luminosity and distance (Sadalmelik at 760 light years, Sadalsuud at 610) may have been born together in the same extended group, and over the past 15 or so million years of their existence have drifted well over 100 light years apart. Most intriguing, however, is Enif's possible erratic and violent behavior. In 1972, an observer in Florida saw Enif as bright as Altair in Aquila, five times brighter than normal, whereupon it faded. For over 10 minutes it appeared to pop some kind of enormous flare, one vastly brighter than the small ones that occur frequently on the Sun. Such events are rare -- only two dozen or so are known -- and not well documented, nor is there any theory for them. We apparently do not understand supergiants -- or any other kind of star for that matter -- quite as well as we think we do.

- Written by Jim Kaler (Original source)

References[edit]

  1. 1.0 1.1 1.2 1.3 1.4 1.5 Cite error: Invalid <ref> tag; no text was provided for refs named aaa474_2_653
  2. Cite error: Invalid <ref> tag; no text was provided for refs named araa11_29
  3. 3.0 3.1 Cite error: Invalid <ref> tag; no text was provided for refs named saaoc8_59
  4. Cite error: Invalid <ref> tag; no text was provided for refs named gcvs
  5. Cite error: Invalid <ref> tag; no text was provided for refs named aaa430_165
  6. 6.0 6.1 6.2 6.3 Cite error: Invalid <ref> tag; no text was provided for refs named aaa480_1_91
  7. 7.0 7.1 Cite error: Invalid <ref> tag; no text was provided for refs named mnras410_1_190
  8. Cite error: Invalid <ref> tag; no text was provided for refs named lang2006
  9. 9.0 9.1 Cite error: Invalid <ref> tag; no text was provided for refs named mnras226_563
  10. Cite error: Invalid <ref> tag; no text was provided for refs named coapa239_1
  11. Cite error: Invalid <ref> tag; no text was provided for refs named SIMBAD


Add your comment
The Science Archives welcomes all comments. If you do not want to be anonymous, register or log in. It is free.


As a reminder, article comments are only for discussions on how to improve the article. Please direct other comments to a user's talk page. Please be formal and do not use excessive uppercase. Please be advised you may receive an automatic block if you break the article comments policy. For information regarding what is acceptable/not acceptable in article comments, please message Icons-flag-ru.png Joey (talk), Natalia (talk), Icons-flag-fr.png ynoss (talk), or Icons-flag-ca.png Daniel (older account/talk).