Nu Cephei
Star in the constellation Cepheus
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Nu Cephei is a blue-hued variable star in the northern constellation Cepheus. Its name is a Bayer designation that is Latinized from ν Cephei, and abbreviated Nu Cep or ν Cep. This is a pulsating α Cygni variable star that ranges in apparent visual magnitude from 4.25 to 4.35.[2] This is bright enough to make it visible to the naked eye as a fourth-magnitude star. Distance estimates place it at about 3,500 light-years from Earth. It is drifting closer to the Sun with a line of sight velocity component of −26 km/s.[6]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 21h 45m 26.925s[1] |
| Declination | +61° 07′ 14.900″[1] |
| Apparent magnitude (V) | 4.25 to 4.35[2] |
| Characteristics | |
| Evolutionary stage | Blue supergiant[3] |
| Spectral type | A2Iab[4] |
| Apparent magnitude (U) | 4.94[5] |
| Apparent magnitude (B) | 4.81[5] |
| Apparent magnitude (J) | 3.14[5] |
| Apparent magnitude (K) | 2.85[5] |
| U−B color index | +0.119[4] |
| B−V color index | +0.518[4] |
| Variable type | Alpha Cygni[2] |
| Astrometry | |
| Radial velocity (Rv) | −25.90[6] km/s |
| Proper motion (μ) | RA: −3.545 mas/yr[1] Dec.: −2.025 mas/yr[1] |
| Parallax (π) | 0.9321±0.0865 mas[1] |
| Distance | 3,500 ± 300 ly (1,070 ± 100 pc) |
| Absolute magnitude (MV) | −6.82[7] |
| Details | |
| Mass | 15.4[8] M☉ |
| Radius | 137[8] R☉ |
| Luminosity | 102,000[8] L☉ |
| Surface gravity (log g) | 1.35[4] cgs |
| Temperature | 8,800[4] K |
| Rotational velocity (v sin i) | 15[4] km/s |
| Age | 8[3] Myr |
| Other designations | |
| ν Cep, 10 Cephei, BD+60°2288, FK5 1572, HD 207260, HIP 107418, HR 8334, SAO 19624[9] | |
| Database references | |
| SIMBAD | data |
ν Cephei is a member of the Cepheus OB2 stellar association,[3] which includes stars such as μ Cephei and VV Cephei.[10]
Properties
The stellar classification of this star is A2Iab,[4] matching an evolved blue supergiant. It began life as an approximately 20 M☉[8][3] main sequence star around eight million years ago. Nu Cephei has exhausted its core hydrogen and expanded and cooled into a supergiant. Elemental abundance analyses indicate that it has not yet spent time as a red supergiant, which would have brought about convection of fusion products to the surface in a dredge-up.[3]
ν Cephei is currently about 15 times as massive as the sun, 137 times as large, and 100,000 times as luminous.[8] Its large size and luminosity cause it to be somewhat unstable and produce irregular pulsations. This is a common feature of class A and B supergiants, which are grouped as α Cygni variable stars. Variability was first reported by Helmut Abt in 1957.[12] The brightness changes by at most a tenth of a magnitude.[2] A variety of values for the variability period have been published, including 5 to 10 days,[13] 7.6 days[14][12] and 90 days.[15]