Theta Pegasi

Theta Pegasi
Location of θ Pegasi (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pegasus
Right ascension 22h 10m 11.98528s[1]
Declination +06° 11′ 52.3078″[1]
Apparent magnitude (V) +3.52[2]
Characteristics
Evolutionary stage main sequence[3]
Spectral type A2V[4] + M4-5.5[5]
B−V color index 0.086±0.002[2]
Astrometry
Radial velocity (Rv)−7.9±2.4[2] km/s
Proper motion (μ) RA: +282.18[1] mas/yr
Dec.: +30.46[1] mas/yr
Parallax (π)35.34 ± 0.85 mas[1]
Distance92 ± 2 ly
(28.3 ± 0.7 pc)
Absolute magnitude (MV)1.24[2]
Orbit[5]
Semi-major axis (a)6.55+3.0
−0.48
au
Eccentricity (e)0.54+0.28
−0.15
Inclination (i)66.7+8.5
−14
°
Details
θ Peg A
Mass2.09 ± 0.16[6] M
Radius2.6225±0.0829[5] R
Luminosity23.7012±1.1418[4] L
Surface gravity (log g)3.95[6] cgs
Temperature7872±82[4] K
Metallicity [Fe/H]−0.38[4] dex
Rotational velocity (v sin i)136[6] km/s
Age448[6] Myr
θ Peg B
Mass0.280+0.18
−0.059
[5] M
Surface gravity (log g)5.5[5] cgs
Temperature3200[5] K
Other designations
Biham, θ Peg, 26 Peg, FK5 834, HD 210418, HIP 109427, HR 8450, SAO 127340[7]
Database references
SIMBADdata

θ Pegasi, Latinized as Theta Pegasi, is a single[8] star in the equatorial constellation of Pegasus, lying about 7.5 degrees southwest of Enif.[9] It has the traditional name Biham /ˈb.æm/,[10][11] and the Flamsteed designation 26 Pegasi. This object is visible to the naked eye as a white-hued point of light with an apparent visual magnitude of +3.52.[2] The system is located 92 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −8 km/s.[2]

This object an A-type main-sequence star with a stellar classification of A2V.[4] It is 448[6] million years old with a high rate of spin, showing a projected rotational velocity of 136 km/s.[6] This star has 2.09[5] times the mass of the Sun and 2.6[12] times the Sun's radius. It is radiating 25 times the luminosity of the Sun from its outer envelope at an effective temperature of 7,951 K.[12] The star appears to display a slight infrared excess.[13]

θ Pegasi was suspected of being a binary star due to an acceleration detected by Hipparcos. In 2021, a low-mass companion star was discovered, associated with θ Pegasi.[5] It is a red dwarf with a spectral type of M4 to M5.5, and a luminosity of 0.5% that of the Sun.[5] The orbit around the primary is estimated to be moderately eccentric, at 0.54, and has a semimajor axis of 6.55 au.[5]

  1. ^ a b c d e Cite error: The named reference van Leeuwen2007 was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference zorec2012 was invoked but never defined (see the help page).
  4. ^ a b c d e Cite error: The named reference apj771_1_40 was invoked but never defined (see the help page).
  5. ^ a b c d e f g h i j Steiger, Sarah; et al. (2021). "SCExAO/MEC and CHARIS Discovery of a Low-mass, 6 au Separation Companion to HIP 109427 Using Stochastic Speckle Discrimination and High-contrast Spectroscopy". The Astronomical Journal. 162 (2): 44. arXiv:2103.06898. Bibcode:2021AJ....162...44S. doi:10.3847/1538-3881/ac02cc. S2CID 244399987.
  6. ^ a b c d e f Cite error: The named reference David2015 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference DeRosa2014 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Mollise2012 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Kunitzsch was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference IAU-CSN was invoked but never defined (see the help page).
  12. ^ a b Cite error: The named reference apj746_1_101 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Nuñez2017 was invoked but never defined (see the help page).

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