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Star in the constellation Cygnus From Wikipedia, the free encyclopedia
55 Cygni (55 Cyg) is a blue supergiant star in the constellation Cygnus. It is thought to be a member of the Cygnus OB7 stellar association at about 2,700 light years.
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Cygnus |
Right ascension | 20h 48m 56.29119s[1] |
Declination | +46° 06′ 50.8824″[1] |
Apparent magnitude (V) | 4.86[2] (4.81 - 4.87[3]) |
Characteristics | |
Spectral type | B2.5Ia[4] - B4Ia[5] |
U−B color index | −0.45[2] |
B−V color index | +0.42[2] |
Variable type | L[3] or α Cyg[6] |
Astrometry | |
Radial velocity (Rv) | −7.2[7] km/s |
Proper motion (μ) | RA: −2.65[1] mas/yr Dec.: −2.84[1] mas/yr |
Parallax (π) | 1.40 ± 0.17 mas[1] |
Distance | 830[8] pc |
Absolute magnitude (MV) | −6.93[8] - −7.26[9] |
Details[6] | |
Mass | 23[9] M☉ |
Radius | 54 - 65 R☉ |
Luminosity | 324,000 - 478,000 L☉ |
Surface gravity (log g) | 2.35 - 2.50 cgs |
Temperature | 18,600 - 19,000 K |
Rotational velocity (v sin i) | 61[9] km/s |
Other designations | |
Database references | |
SIMBAD | data |
Its apparent magnitude is 4.86, but this is slightly variable and the star is also called V1661 Cyg. When first analysed, it was classified as an irregular supergiant variable,[11] but subsequent studies have treated it as an Alpha Cygni variable. It shows pulsations with multiple periods from a few hours to 22 days, and both p- and g-modes.[6] Apart from p- and g-modes, strange mode and associated instabilities have also been found in models of this star.[12] The spectrum also shows variation, leading to different classifications being given for the star.[13]
The exact properties of 55 Cygni are not known precisely and are also variable. It is a hot luminous supergiant several hundred thousand times as luminous as the sun. This star was originally a standard for the B3 Ia spectral type.[14]
The type of pulsations that 55 Cyg exhibits suggest that it was previously a red supergiant that has shed its outer layers. The most massive red supergiants are expected to pass through a blue supergiant phase before becoming a Wolf-Rayet star and eventually exploding as a type Ib or Ic supernova.[6]
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