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Triple star system in the constellation Cepheus From Wikipedia, the free encyclopedia
V381 Cephei (HR 8164) is a triple star system in the northern constellation of Cepheus. Its apparent magnitude is slightly variable between 5.5 and 5.7.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 21h 19m 15.682s[1] |
| Declination | +58° 37′ 24.550″[1] |
| Apparent magnitude (V) | 5.51 - 5.71[2] |
| Characteristics | |
| Spectral type | M1epIb + B[3] |
| U−B color index | 0.00[4] |
| B−V color index | +1.34[4] |
| Variable type | Lc[2] |
| Astrometry | |
| Radial velocity (Rv) | −14.10[5] km/s |
| Proper motion (μ) | RA: −1.435[6] mas/yr Dec.: −5.427[6] mas/yr |
| Parallax (π) | 1.59 ± 0.23 mas[6] |
| Distance | approx. 2,100 ly (approx. 630 pc) |
| Absolute magnitude (MV) | −5.2[7] |
| Details | |
| Aa | |
| Mass | 7.2[8] - 16[9] M☉ |
| Radius | 977[10] R☉ |
| Luminosity | 178,000[10] L☉ |
| Temperature | 3,745±170[1][10] K |
| Ab | |
| Mass | 13[9] M☉ |
| B | |
| Mass | 7.1[11] M☉ |
| Radius | 3.4[12] R☉ |
| Luminosity | 1,487[12] L☉ |
| Surface gravity (log g) | 4.18[12] cgs |
| Temperature | 19,965[12] K |
| Metallicity [Fe/H] | −0.30[11] dex |
| Rotational velocity (v sin i) | 42.8[13] km/s |
| Age | 49.1[8] Myr |
| Other designations | |
| A: HD 203338 | |
| B: HD 203339 | |
| Database references | |
| A | |
| B | |
V381 Cephei is a visual double star with components A and B separated by 4.6". The primary is HD 203338 and the secondary is the magnitude 9.2 HD 203339.[9]
HD 203338 is itself a spectroscopic binary with components Aa and Ab orbiting every 280 years.[9] It forms a VV Cephei-type binary system with a hot companion which is accreting mass from the primary. The long period means that it exhibits fewer peculiarities than other VV Cephei binaries.[14]
Component Aa is a red supergiant and its close companion is a B2 main sequence star. The supergiant is a pulsating variable with a small amplitude and poorly defined period. It is generally given spectral class qualifiers indicating peculiarities and emission, which may be associated with the disc around the hot secondary.[14]
Component B, HD 203339, is a B3 main sequence star with a mass around 11 M☉.[9]
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