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56 Pegasi

56 Pegasi
Location of 56 Pegasi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension 23h 07m 06.74364s[1]
Declination 25° 28′ 05.788″[1]
Apparent magnitude (V) 4.74[2]
Characteristics
Spectral type K0.5II:Ba1CN-2CH-0.5[3] + sdO[4][5]
U−B color index +1.14[2]
B−V color index +1.32[2]
Astrometry
Radial velocity (Rv)−27.55[6] km/s
Proper motion (μ) RA: −4.288[1] mas/yr
Dec.: −32.639[1] mas/yr
Parallax (π)6.1131 ± 0.4108 mas[1]
Distance530 ± 40 ly
(160 ± 10 pc)
Absolute magnitude (MV)−1.32[7]
Orbit[5]
Period (P)111.140±0.14 d
Eccentricity (e)0
Periastron epoch (T)51738.8±0.5 MJD
Semi-amplitude (K1)
(primary)		1.47±0.04 km/s
Details
56 Peg A
Mass5.4[8] M☉
Radius41[9] R☉
Luminosity18.2 - 18.9[9] L☉
Surface gravity (log g)0.50[10] cgs
Temperature4,185±85[9] K
Metallicity [Fe/H]−0.21[11] dex
Rotational velocity (v sin i)4.4[12] km/s
Age100±100[8] Myr
Other designations
56 Peg, NSV 14429, BD+24°4716, FK5 3848, GC 32201, HD 218356, HIP 114155, HR 8796, SAO 91019, 2MASS J23070675+2528055[13]
Database references
SIMBADdata

56 Pegasi is a binary star 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 590 light years away from the Sun based on parallax,[14] but is drifting closer with a radial velocity of −28 km/s.[6] It is listed as a member of the Wolf 630 moving group.[15]

The variable radial velocity of this star was announced in 1911 by W. W. Campbell. It is a single-lined spectroscopic binary in an assumed circular orbit with a period of 111.1 days. The a sin i value for this system is 0.01511 ± 0.00040 AU (2.26 ± 0.06 Gm), where a is the semimajor axis and i is the (unknown) orbital inclination. This value provides a lower bound on the true semimajor axis, which in this case is their actual separation.[5]

The primary component is a peculiar bright giant with a stellar classification of K0.5 II: Ba1 CN-2 CH-0.5.[3] 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,[16] roughly 100 million years old, with 5.4 times the Sun's mass.[8] The star has expanded to 40[17] times the radius of the Sun and is radiating 680[11] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,416 K.[18]

The system displays an excess of ultraviolet radiation that must be coming from the secondary companion. Simon et al. (1982) classified this object as a subdwarf O star.[4] Alternatively, it may be a white dwarf companion with an accretion disk.[19][5] 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.[16]

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  8. ^ a b c Cite error: The named reference Tetzlaff2011 was invoked but never defined (see the help page).
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  11. ^ a b Cite error: The named reference XHIP was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference deMedeiros1999 was invoked but never defined (see the help page).
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  14. ^ Cite error: The named reference hipparcos was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Bubar2010 was invoked but never defined (see the help page).
  16. ^ a b Cite error: The named reference Frankowski2006 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference vanBelle2009 was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference Perez2011 was invoked but never defined (see the help page).
  19. ^ Cite error: The named reference Schindler1982 was invoked but never defined (see the help page).

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