Mu Cephei

Coordinates: Sky map 21h 43m 30.46s, +58° 46′ 48.2″
Source: Wikipedia, the free encyclopedia.
Not to be confused with MY Cephei.
μ Cephei
Location of μ Cep (circled)
Observation data
J2000.0
Constellation Cepheus
Right ascension 21h 43m 30.4609s[1]
Declination +58° 46′ 48.166″[1]
Apparent magnitude (V) +4.08[2] (3.43 - 5.1[3])
Characteristics
Evolutionary stage Red supergiant or hypergiant[4]
Spectral type M2-Ia[5] (M2e Ia[6]) (M2 Ia+)[7]
U−B color index +2.42[2]
B−V color index +2.35[2]
Variable type SRc[3]
Distance
3,060 ly
(940+140
−40[11] pc)
Absolute magnitude (MV)–7.63[12]
Details
Myr
HIP 107259, SAO
33693
Database references
SIMBADdata

Mu Cephei (

spectrum
of this star has served as a spectral standard by which other stars are classified.

Mu Cephei is more than 100,000 times brighter than the Sun, with an

largest known stars with a radius around or over 1,000 times that of the sun (R☉), and were it placed in the Sun's position it would engulf the orbit of Mars and Jupiter
.

History

1785 portrait of William Herschel
Zooming to the μ Cep (Garnet star) in the constellation Cepheus.

The deep red color of Mu Cephei was noted by William Herschel, who described it as "a very fine deep garnet colour, such as the periodical star ο Ceti".[17] It is thus commonly known as Herschel's "Garnet Star".[18] Mu Cephei was called Garnet sidus by Giuseppe Piazzi in his catalogue.[19][20] An alternative name, Erakis, used in Antonín Bečvář's star catalogue, is probably due to confusion with Mu Draconis, which was previously called al-Rāqis [arˈraːqis] in Arabic.[21]

In 1848, English astronomer John Russell Hind discovered that Mu Cephei was variable. This variability was quickly confirmed by German astronomer Friedrich Wilhelm Argelander. Almost continual records of the star's variability have been maintained since 1881.[22]

The angular diameter of μ Cephei has been measured

mas across.[23]
μ Cephei was used as one of the original "dagger stars", those with well-defined spectra that could be used for the classification of other stars, for MK spectral classifications. In 1943 it was the standard star for M2  Ia, updated in 1980 to be the standard star for the new type M2- Ia.[5][24]

Distance

Mu Cephei (circled) as can be seen in binoculars. The bright star on the right is Alpha Cephei (Alderamin).
H-alpha
and OIII wavelengths (north is towards top left)

The distance to Mu Cephei is not very well known. The

parsecs. However, this value is close to the margin of error. A determination of the distance based upon a size comparison with Betelgeuse gives an estimate of 390±140 parsecs.[25]

Calculation of the distance from the measured angular diameter, surface brightness, and calculated luminosity leads to 641 pc. Averaging the distances of nearby luminous stars with similar reddening and reliable

Gaia Data Release 2 parallaxes gives a distance of 940 pc.[11]

Surroundings

Mu Cephei is surrounded by a shell extending out to a distance at least equal to 0.33 times the star's radius with a temperature of 2,055±25 K. This outer shell appears to contain molecular gases such as CO, H2O, and SiO.[25] Infrared observations suggest the presence of a wide ring of dust and water with an inner radius about twice that of the star itself, extending to about four times the radius of the star.[26][27]

The star is surrounded by a spherical shell of ejected material that extends outward to an angular distance of

6″ with an expansion velocity of 10 km s−1. This indicates an age of about 2,000–3,000 years for the shell. Closer to the star, this material shows a pronounced asymmetry, which may be shaped as a torus
.

Variability

A visual band light curve for Mu Cephei, adapted from Brelstaff et al. (1997)[22]

Mu Cephei is a

semiregular variable of type SRc. Its apparent brightness varies erratically between magnitude 3.4 and 5.1. Many different periods have been reported, but they are consistently near 860 days or 4,400 days.[28]

Properties

stars, including Mu Cephei.
1. Mercury < Mars < Venus < Earth
2. Earth < Neptune < Uranus < Saturn < Jupiter
3. Jupiter < Wolf 359 < Sun < Sirius
4. Sirius < Pollux < Arcturus < Aldebaran
5. Aldebaran < Rigel < Antares < Betelgeuse
6. Betelgeuse < Mu Cephei < VV Cephei A < VY Canis Majoris
.
Mu Cephei compared to the Sun. The orbits of Jupiter, Mars, Earth, Venus, and Mercury are visible in full-size.

A very luminous red supergiant, Mu Cephei is among the largest stars visible to the naked eye, and one of the

hypergiant.[4]

The

light years gives it a radius of 1,650 R☉.[29]

The radius has been estimated to be 830 R☉ in 2010 based on the star's effective temperature of 3660 K and the 111,200 L☉ luminosity estimate.[30]

A 2019 paper measurement based on the 641+148
−144 pc distance gives the star a lower luminosity below 140,000 L☉ and a correspondingly lower radius of 972±228 R☉, and as well as a lower temperature of 3,551±136 K. These parameters are all consistent with those estimated for Betelgeuse.[14]

The initial mass of Mu Cephei has been estimated from its position relative to theoretical stellar evolutionary tracks to be between 15 M☉ and 25 M☉.[14][15] The star currently has a mass loss rate of (4.9±1.0)×10−7 M☉ per year.[14]

Supernova

Mu Cephei is nearing death. It has begun to

Wolf-Rayet stars before their cores collapse, and Mu Cephei appears to be massive enough for this to happen. A post-red supergiant will produce a type IIn or type II-b supernova, while a Wolf Rayet star will produce a type Ib or Ic supernova.[31]

Components

There are several faint stars within two arc-minutes of Mu Cephei, and listed in multiple star catalogues.

NAME Right ascension Declination Apparent magnitude (V) Database references
μ Cep B (CCDM J21435+5847B) 21h 43m 27.8s +58° 46′ 45″ 12.3
μ Cep C (CCDM J21435+5847C) 21h 43m 25.6s +58° 47′ 08″ 12.7 Simbad

See also

References

  1. ^
    Bibcode:1997A&A...323L..49P
    .
  2. ^
    Bibcode:1978A&AS...34....1N
    .
  3. ^
    Bibcode:2009yCat....102025S
    .
  4. ^
    S2CID 119281306
    .
  5. ^
    S2CID 123149047
    .
  6. S2CID 122700080
    .
  7. ^
    ISSN 0004-6280
    .
  8. S2CID 17804304
    .
  9. ^
    doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR
    .
  10. ^ Hipparcos, the New Reduction (van Leeuwen, 2007)
  11. ^
    S2CID 210714093
    .
  12. ^
    S2CID 15109583
    .
  13. ^
    S2CID 118629873
    .
  14. ^
    S2CID 119423161
    .
  15. ^
    S2CID 17789027
    .
  16. ^
    S2CID 204924849
    .
  17. Philosophical Transactions
    : 257.
  18. Allen, R. H. (1899). Star Names: Their Lore and Meaning. G. E. Stechert. p. 158
    . editions:CmkItwtawcMC.
  19. ^ Piazzi, G., ed. (1803). Præcipuarum Stellarum Inerrantium Positiones Mediæ Ineunte Seculo XIX: ex Observationibus Habitis in Specula Panormitana ab anno 1792 ad annum 1802. Panormi.
  20. ^ Piazzi, G., ed. (1814). Praecipuarum Stellarum Inerrantium Positiones Mediae Ineunte Saeculo XIX: ex Observationibus Habitis in Specula Panormitana ab anno 1792 ad annum 1813. Panormi. p. 159.
  21. ^ Laffitte, R. (2005). Héritages arabes: Des noms arabes pour les étoiles (2éme revue et corrigée ed.). Paris: Librairie Orientaliste Paul Geunthner / Les Cahiers de l'Orient. p. 156, note 267.
  22. ^
    Bibcode:1997JBAA..107..135B
    .
  23. S2CID 67789347
    .
  24. Bibcode:1993AAS...183.1710G
  25. ^
    S2CID 13980310
    .
  26. S2CID 14881959
    .
  27. doi:10.1086/309185
    .
  28. S2CID 5203133
    .
  29. ^ "Jim Kaler-Garnet star".
  30. S2CID 16131273
    .
  31. S2CID 38736311
    .

External links


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