Astronomy:56 Pegasi
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| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Pegasus |
| Right ascension | 23h 07m 06.74189s[1] |
| Declination | 25° 28′ 05.7739″[1] |
| Apparent magnitude (V) | 4.74[2] |
| Characteristics | |
| Evolutionary stage | red giant branch[3][1] |
| Spectral type | K0.5II:Ba1CN-2CH-0.5[4] |
| U−B color index | +1.14[2] |
| B−V color index | +1.32[2] |
| Astrometry | |
| Radial velocity (Rv) | −27.55[5] km/s |
| Proper motion (μ) | RA: −2.747[1] mas/yr Dec.: −31.682[1] mas/yr |
| Parallax (π) | 5.1778 ± 0.1118[1] mas |
| Distance | 630 ± 10 ly (193 ± 4 pc) |
| Absolute magnitude (MV) | −1.32[6] |
| Orbit[7] | |
| Primary | 56 Peg A |
| Companion | 56 Peg B |
| Period (P) | 111.15±0.03 d |
| Semi-major axis (a) | 0.79+0.10 −0.08 astronomical unit|AU |
| Eccentricity (e) | 0.072+0.048 −0.045 |
| Inclination (i) | 90+42 −41° |
| Longitude of the node (Ω) | 90+60 −42° |
| Periastron epoch (T) | 2455289+15 −85 HJD |
| Argument of periastron (ω) (secondary) | 55+270 −37° |
| Semi-amplitude (K1) (primary) | 1.47±0.04[8] km/s |
| Orbit[7] | |
| Primary | 56 Peg A |
| Companion | 56 Peg C |
| Period (P) | 15,200+2,600 −1,600 d |
| Semi-major axis (a) | 22.1+3.6 −2.8 astronomical unit|AU |
| Eccentricity (e) | 0.39+0.13 −0.12 |
| Inclination (i) | 157+4 −5° |
| Longitude of the node (Ω) | 153+14 −17° |
| Periastron epoch (T) | 2469014±2800 HJD |
| Argument of periastron (ω) (secondary) | 73+21 −24° |
| Details | |
| 56 Peg A | |
| Mass | 4.3±1.1[7] M☉ |
| Radius | 41[9] R☉ |
| Luminosity | 680[10] L☉ |
| Surface gravity (log g) | 1.41[11] cgs |
| Temperature | 4,185±85[9] K |
| Metallicity [Fe/H] | −0.38[11] dex |
| Rotational velocity (v sin i) | 4.4[12] km/s |
| Age | 100±100[13] Myr |
| 56 Peg B | |
| Mass | 0.13+0.06 −0.03[7] M☉ |
| 56 Peg C | |
| Mass | 0.85+0.25 −0.18[7] M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
56 Pegasi is a triple star[7] system in the northern constellation of Pegasus. It is visible to the naked eye with a combined apparent visual magnitude of 4.74.[2] The system is approximately 630 light years away from the Sun based on parallax,[15] but is drifting closer with a radial velocity of −28 km/s.[5] It is listed as a member of the Wolf 630 moving group.[16]
Characteristics
The variable radial velocity of this star was announced in 1911 by W. W. Campbell.[8] The inner system, made up by the primary and secondary components, is a single-lined spectroscopic binary in an nearly circular orbit with a period of 111.15 days. The average separation between components is 0.79 astronomical units.[7]
The primary component is a peculiar bright giant with a stellar classification of K0.5 II: Ba1 CN-2 CH-0.5.[4] This notation indicates it is a K-type giant with some uncertainty about the classification, along with an overabundance of barium and underabundances of the CN and CH radicals. It is an active star,[6] roughly 100 million years old[13], with 4.3 times the Sun's mass.[7] The star has expanded to 41 times the radius of the Sun[9] and is radiating 680 times the Sun's luminosity[10] from its enlarged photosphere at an effective temperature of 4,185 K.[9]
The secondary has a mass 0.13 times the mass of the Sun.[7]
The tertiary component is a white dwarf with 0.85 times the mass of the Sun. This companion lost mass when it was an AGB star, causing s-process elements, produced by nucleosynthesis, to be transferred to the primary star, resulting in its current unusual abundances. This star has an orbital period of 41.6 years, a moderate eccentricity, and an average separation of 22 AU.[7]
The system displays an excess of ultraviolet radiation that must be coming from the secondary. Simon et al. (1982) classified this object as a subdwarf O star.[17] Alternatively, it may be a white dwarf companion with an accretion disk.[18][8] Several puzzling features in the evolutionary history of this pair may be explained if the primary is a fast rotator being seen nearly pole-on. The star may have been spun up during a mass transfer episode with the secondary.[6]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 2.3 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues 2237. Bibcode: 2002yCat.2237....0D.
- ↑ Escorza, A.; Siess, L.; Van Winckel, H.; Jorissen, A. (2020). "Binary evolution along the red giant branch with BINSTAR: The barium star perspective". Astronomy and Astrophysics 639: A24. doi:10.1051/0004-6361/202037487. Bibcode: 2020A&A...639A..24E.
- ↑ 4.0 4.1 Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series 71: 245. doi:10.1086/191373. Bibcode: 1989ApJS...71..245K.
- ↑ 5.0 5.1 Famaey, B. et al. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data". Astronomy & Astrophysics 430: 165–186. doi:10.1051/0004-6361:20041272. Bibcode: 2005A&A...430..165F.
- ↑ 6.0 6.1 6.2 Frankowski, A.; Jorissen, A. (February 2006). "The puzzling case of 56 Pegasi: a fast rotator seen nearly pole-on". The Observatory 126: 25–37. Bibcode: 2006Obs...126...25F.
- ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 Escorza, A.; De Rosa, R. J. (March 2023). "Barium and related stars, and their white-dwarf companions: III. The masses of the white dwarfs". Astronomy & Astrophysics 671: A97. doi:10.1051/0004-6361/202244782. ISSN 0004-6361. Bibcode: 2023A&A...671A..97E.
- ↑ 8.0 8.1 8.2 Griffin, R. F. (2006). "Spectroscopic binary orbits from photoelectric radial velocities - Paper 186: 56 Pegasi". The Observatory 126: 1. Bibcode: 2006Obs...126....1G.
- ↑ 9.0 9.1 9.2 9.3 Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal 158 (1): 20. doi:10.3847/1538-3881/ab1cbd. Bibcode: 2019AJ....158...20M.
- ↑ 10.0 10.1 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A. Vizier catalog entry
- ↑ 11.0 11.1 Cardiel, Nicolás; Zamorano, Jaime; Bará, Salvador; Sánchez De Miguel, Alejandro; Cabello, Cristina; Gallego, Jesús; García, Lucía; González, Rafael et al. (2021). "Synthetic RGB photometry of bright stars: Definition of the standard photometric system and UCM library of spectrophotometric spectra". Monthly Notices of the Royal Astronomical Society 504 (3): 3730. doi:10.1093/mnras/stab997. Bibcode: 2021MNRAS.504.3730C.
- ↑ De Medeiros, J. R.; Mayor, M. (1999). "A catalog of rotational and radial velocities for evolved stars". Astronomy and Astrophysics Supplement Series 139 (3): 433. doi:10.1051/aas:1999401. Bibcode: 1999A&AS..139..433D. Vizier catalog entry
- ↑ 13.0 13.1 Tetzlaff, N. et al. (2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society 410 (1): 190–200. doi:10.1111/j.1365-2966.2010.17434.x. Bibcode: 2011MNRAS.410..190T. Vizier catalog entry
- ↑ "56 Peg". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=56+Peg.
- ↑ Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. Vizier catalog entry
- ↑ McDonald, A. R. E.; Hearnshaw, J. B. (August 1983). "The Wolf 630 moving group of stars". Monthly Notices of the Royal Astronomical Society 204 (3): 841–852. doi:10.1093/mnras/204.3.841. Bibcode: 1983MNRAS.204..841M.
- ↑ Simon, T. et al. (1982). "On the reality of a boundary in the H-R diagram between late-type stars with and without high temperature outer atmospheres". Astrophysical Journal 257: 225. doi:10.1086/159981. Bibcode: 1982ApJ...257..225S.
- ↑ Schindler, M. et al. (December 1982). "Ultraviolet and X-ray detection of the 56 Pegasi system /K0 IIp + WD/ - Evidence for accretion of a cool stellar wind onto a white dwarf". Astrophysical Journal, Part 1 263: 269–276. doi:10.1086/160501. Bibcode: 1982ApJ...263..269S.
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