A light curve for II Pegasi, plotted from Hipparcos data[1]
Observation data Epoch J2000 Equinox J2000
Constellation
Pegasus
Right ascension
23h 55m 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 constellation of Pegasus 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]
^Cite error: The named reference HipDataAccess was invoked but never defined (see the help page).
^ abcdeVan Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
^ abCite error: The named reference Osten2007 was invoked but never defined (see the help page).
^ abSamus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
^ abcdefghijklCite error: The named reference Berdyugina1997 was invoked but never defined (see the help page).
^Karataș, Yüksel; Bilir, Selçuk; Eker, Zeki; Demircan, Osman; Liebert, James; Hawley, Suzanne L.; Fraser, Oliver J.; Covey, Kevin R.; Lowrance, Patrick; Kirkpatrick, J. Davy; Burgasser, Adam J. (2004). "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution". Monthly Notices of the Royal Astronomical Society. 349 (3): 1069–1092. arXiv:astro-ph/0404219. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x. S2CID 15290475.
^Cite error: The named reference Covino2000 was invoked but never defined (see the help page).
^Wanjek, Christopher (6 November 2006). "Monster Stellar Flare Seen by NASA Scientists Dwarfs All Others". National Aeronautics and Space Administration. Archived from the original on 10 June 2015. Retrieved 31 March 2014.
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