V381 Cephei
Triple star system in the constellation Cepheus
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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. It is faintly visible to the naked eye under good observing conditions.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| V381 Cephei A | |
| Right ascension | 21h 19m 15.6852s[1] |
| Declination | +58° 37′ 24.624″[1] |
| Apparent magnitude (V) | 5.51 - 5.71[2] |
| V381 Cephei B | |
| Right ascension | 21h 19m 16.1020s[3] |
| Declination | +58° 37′ 27.844″[3] |
| Apparent magnitude (V) | 9.23[4] |
| Characteristics | |
| Spectral type | M1epIb + B[5] |
| U−B color index | 0.00[6] |
| B−V color index | +1.34[6] |
| Variable type | Lc[2] |
| Astrometry | |
| A | |
| Radial velocity (Rv) | −14.10[7] km/s |
| Proper motion (μ) | RA: −1.893[1] mas/yr Dec.: −4.751[1] mas/yr |
| Parallax (π) | 0.5546±0.1793 mas[1] |
| Distance | approx. 6,000 ly (approx. 1,800 pc) |
| Absolute magnitude (MV) | −5.2[8] |
| B | |
| Proper motion (μ) | RA: −2.490±0.025[3] mas/yr Dec.: −3.704±0.031[3] mas/yr |
| Parallax (π) | 1.1735±0.0171 mas[3] |
| Distance | 2,780 ± 40 ly (850 ± 10 pc) |
| Details | |
| Aa | |
| Mass | 7.2[9] - 16[10] M☉ |
| Radius | 977[11] R☉ |
| Luminosity | 178,000[11] L☉ |
| Temperature | 3,745±170[12][11] K |
| Ab | |
| Mass | 13[10] M☉ |
| B | |
| Mass | 7.1[13] M☉ |
| Radius | 3.4[3] R☉ |
| Luminosity | 1,487[3] L☉ |
| Surface gravity (log g) | 4.18[3] cgs |
| Temperature | 19,965[3] K |
| Metallicity [Fe/H] | −0.30[13] dex |
| Rotational velocity (v sin i) | 42.8[14] km/s |
| Age | 49.1[9] Myr |
| Other designations | |
| V381 Cephei, HR 8164, HIP 105259, BD+58°2249, ADS 14864, 2MASS J21191567+5837246, WDS J21193+5837 | |
| A: HD 203338 | |
| B: HD 203339 | |
| Database references | |
| A | |
| B | |
The star was discovered to be a variable star in 1991, by Elaine M. Halbedel.[15] It was given its variable star designation, V381 Cephei, in 1995.[16]
System
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.[10]
HD 203338 is itself a spectroscopic binary with components Aa and Ab orbiting every 280 years.[10] 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.[17]
Properties
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.[17]
Component B, HD 203339, is a B3 main sequence star with a mass around 11 M☉.[10]