II Pegasi
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.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Pegasus |
| Right ascension | 23h 55m 04.05313s[1] |
| Declination | +28° 38′ 01.2422″[1] |
| Apparent magnitude (V) | 7.4[2] (7.18 - 7.78[3]) |
| Characteristics | |
| II Pegasi A | |
| Evolutionary stage | subgiant[4] |
| Spectral type | K2 IV[4] |
| Variable type | RS CVn[3] |
| II Pegasi B | |
| Evolutionary stage | main sequence[4] |
| Spectral type | M0-M3 V[4] |
| Astrometry | |
| II Pegasi A | |
| Radial velocity (Rv) | -20.50[5] km/s |
| Proper motion (μ) | RA: 576.22[1] mas/yr Dec.: 34.69[1] mas/yr |
| Parallax (π) | 25.06 ± 0.51[1] mas |
| Distance | 130 ± 3 ly (39.9 ± 0.8 pc) |
| Absolute magnitude (MV) | 3.8[4] |
| Details | |
| II Pegasi A | |
| Mass | 0.8[4] M☉ |
| Radius | 3.4[4] R☉ |
| Luminosity | 1.06 L☉ |
| Surface gravity (log g) | 3.2[4] cgs |
| Temperature | 4600[4] K |
| II Pegasi B | |
| Mass | 0.4[4] M☉ |
| Luminosity | 0.53 L☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
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.[4] Starspots cover about 40% of its surface. The star produces intense flares observable at all wavelengths.[6]
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.[4]
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.[2] It was the largest stellar flare ever seen and was a hundred million times more energetic than The Sun's typical solar flare.[7]
References
- 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.
- 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.
- 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.
- 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.
- Karataş, Y.; Bilir, S.; Eker, Z.; Demircan, O. (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. arXiv:astro-ph/0404219. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x. S2CID 15290475.
- 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.
- Wanjek, Christopher (6 November 2006). "Monster Stellar Flare Seen by NASA Scientists Dwarfs All Others". National Aeronautics and Space Administration. Retrieved 31 March 2014.