II Pegasi

II Pegasi

A light curve for II Pegasi, plotted from Hipparcos data
Observation data
Epoch J2000      Equinox ICRS
Constellation Pegasus
Right ascension 23h 55m 04.05313s
Declination +28° 38′ 01.2422″
Apparent magnitude (V) 7.18–7.78
Characteristics
II Pegasi A
Evolutionary stage subgiant
Spectral type K2 IV
Variable type RS CVn
II Pegasi B
Evolutionary stage main sequence
Spectral type M0-M3 V
Astrometry
II Pegasi A
Radial velocity (Rv)−20.50 km/s
Proper motion (μ) RA: 576.22 mas/yr
Dec.: 34.69 mas/yr
Parallax (π)25.06±0.51 mas
Distance130 ± 3 ly
(39.9 ± 0.8 pc)
Absolute magnitude (MV)3.8
Details
II Pegasi A
Mass0.8 M☉
Radius3.4 R☉
Luminosity1.06 L☉
Surface gravity (log g)3.2 cgs
Temperature4,600 K
II Pegasi B
Mass0.4 M☉
Luminosity0.53 L☉
Other designations
II Peg, GJ 4375, HD 224085, BD+27°4642, HIP 117915, LHS 4044, SAO 91578
Database references
SIMBADdata

II Pegasi is a binary star system in the constellation Pegasus with an apparent magnitude of between 7.2 and 7.8 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. Starspots cover about 40% of its surface. The star produces intense flares observable at all wavelengths.

Its smaller companion (II Pegasi B) is too close to be 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.

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. It was the largest stellar flare ever seen and was a hundred million times more energetic than the Sun's typical solar flare.

References

  1. ↑ "Hipparcos Tools Interactive Data Access". Hipparcos. ESA. Retrieved 8 December 2021.
  2. 1 2 3 4 5 Van 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.
  3. 1 2 Samus, 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.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 Berdyugina, Svetlana V.; Jankov, S.; Ilyin, I.; Tuominen, I.; Fekel, F. C. (1998). "The active RS Canum Venaticorum binary II Pegasi. I. Stellar and orbital parameters". Astronomy and Astrophysics. 334: 863–872. Bibcode:1998A&A...334..863B.
  5. ↑ 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.
  6. ↑ Covino, S.; Tagliaferri, G.; Pallavicini, R.; Mewe, R.; Poretti, E. (2000). "The active binary star II Pegasi with it BeppoSAX". Astronomy and Astrophysics. 355 (2): 681–687. arXiv:astro-ph/9911352. Bibcode:2000A&A...355..681C.
  7. ↑ Osten, Rachel A.; Drake, Stephen; Tueller, Jack; Cummings, Jay; Perri, Matteo; Moretti, Alberto; Covino, Stefano (2007). "Nonthermal Hard X-Ray Emission and Iron Ka Emission from a Superflare on II Pegasi". The Astrophysical Journal. 654 (2): 1052–1067. arXiv:astro-ph/0609205. Bibcode:2007ApJ...654.1052O. doi:10.1086/509252. S2CID 16118115.
  8. ↑ 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.