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Observation data Epoch J2000 Equinox J2000 | |
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Constellation | Pegasus |
Right ascension | 23h55m 04.05313s[2] |
Declination | +28° 38′ 01.2422″[2] |
Apparent magnitude (V) | 7.4[3] (7.18–7.78[4]) |
Characteristics | |
II Pegasi A | |
Evolutionary stage | subgiant[5] |
Spectral type | K2 IV[5] |
Variable type | RS CVn[4] |
II Pegasi B | |
Evolutionary stage | main sequence[5] |
Spectral type | M0-M3 V[5] |
Astrometry | |
II Pegasi A | |
Radial velocity (Rv) | −20.50[6] km/s |
Proper motion (μ) | RA: 576.22[2] mas/yr Dec.: 34.69[2] mas/yr |
Parallax (π) | 25.06 ± 0.51 mas[2] |
Distance | 130 ± 3 ly (39.9 ± 0.8 pc) |
Absolute magnitude (MV) | 3.8[5] |
Details | |
II Pegasi A | |
Mass | 0.8[5] M☉ |
Radius | 3.4[5] R☉ |
Luminosity | 1.06 L☉ |
Surface gravity (log g) | 3.2[5] cgs |
Temperature | 4,600[5] K |
II Pegasi B | |
Mass | 0.4[5] M☉ |
Luminosity | 0.53 L☉ |
Other designations | |
II Peg, GJ 4375, HD 224085, BD+27°4642, HIP 117915, LHS 4044, SAO 91578 | |
Database references | |
SIMBAD | data |
II Pegasi is a binary star system in the constellationofPegasus with an apparent magnitude of 7.4 and a distance of 130 light-years. It is a very active RS Canum Venaticorum variable (RS CVn), a close binary system with active starspots.
The primary (II Pegasi A) is a cool subgiant, an orange K-type star. It has begun to evolve off the main sequence and expand.[5] Starspots cover about 40% of its surface. The star produces intense flares observable at all wavelengths.[7]
Its smaller companion (II Pegasi B) is too close to have been observed directly. It is a red dwarf, an M-type main-sequence star. The stars are tidally locked in a very close orbit with a period of 6.7 days and a separation of a few stellar radii.[5]
X-ray flares from II Pegasi A were observed with the Ariel 5 satellite in the 1970s and with later X-ray observatories. In December 2005, a superflare was detected by the Swift Gamma-Ray Burst Mission.[3] It was the largest stellar flare ever seen and was a hundred million times more energetic than the Sun's typical solar flare.[8]
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