MT Pegasi

MT Pegasi (HD 217813) is a single,[10] yellow-hued star in the northern constellation of Pegasus. With an apparent visual magnitude of 6.616,[2] it is a dim star that is at or below the nominal limit for visibility with the naked eye. Based upon an annual parallax shift of 41.12 mas[1] as measured from Earth's orbit, it is located 79.31 light years away. This star is a member of the Ursa Major Moving Group, a collection of stars that originated in the same open cluster and now share a common motion through space.[11]

MT Pegasi
Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension  23h 03m 04.97743s[1]
Declination +20° 55′ 06.8628″[1]
Apparent magnitude (V) 6.616[2]
Characteristics
Spectral type G1 V[3]
U−B color index +0.115[2]
B−V color index +0.633[4]
Variable type BY Dra[5]
Astrometry
Radial velocity (Rv)+2.084±0.005[6] km/s
Proper motion (μ) RA: −117.509[1] mas/yr
Dec.: −28.387[1] mas/yr
Parallax (π)41.1236 ± 0.0450[1] mas
Distance79.31 ± 0.09 ly
(24.32 ± 0.03 pc)
Absolute magnitude (MV)4.65±0.03[2]
Details[7]
Mass1.066+0.020
−0.030 M☉
Radius1.01+0.04
−0.02 R☉
Luminosity1.07+0.12
−0.10 L☉
Surface gravity (log g)4.47+0.02
−0.04 cgs
Temperature5,885±44 K
Metallicity [Fe/H]−0.03±0.03[4] dex
Rotation5.82±1.47[8]
Rotational velocity (v sin i)3.2±0.05 km/s
Age1.20+2.16
−1.20 Gyr
Other designations
MT Peg, BD+20° 5264, HD 217813, HIP 113829, SAO 90973[9]
Database references
SIMBADdata

This is a G-type main-sequence star with a stellar classification of G1 V.[3] Harlan and Taylor (1970) had assigned it a class of G5 V,[12] but this gives a poor match to the color index.[13] HD 217813 was found to be variable in 1995 and hence it was given the variable star designation MT Pegasi (MT Peg). It displays brightness variations with a period of several days, which is caused by star spots that are modulated by the star's rotation period.[13] MT Peg is classified as a BY Draconis variable.[5]

MT Peg is considered a young solar analog, which means it is a solar-type star representative of how a young, more active Sun may have appeared when it was less than 1.5 billion years old.[8] The estimated age based upon the chromospheric activity level is 397 years, per Gray et al. (2015).[8] Marsden et al. (2014) gave a larger age estimate of 1.2 billion years, but with a margin of error that overlaps the younger value.[7] Age estimates of the Ursa Major group are around 300 million years old.[11]

The star has 1.07 times the mass of the Sun and 1.01 times the Sun's radius.[7] It is spinning with a projected rotational velocity of 3.2 km/s,[7] giving it a rotation period of 5.8 days.[8] The elemental composition of the stellar atmosphere is similar to the Sun. MT Peg is radiating 1.07 times the Sun's luminosity from its photosphere at an effective temperature of 5,885 K.[7]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Koen, C.; Kilkenny, D.; van Wyk, F.; Marang, F. (2010), "UBV(RI)C JHK observations of Hipparcos-selected nearby stars", Monthly Notices of the Royal Astronomical Society, 403 (4): 1949–1968, Bibcode:2010MNRAS.403.1949K, doi:10.1111/j.1365-2966.2009.16182.x.
  3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
  4. Rich, Evan A.; et al. (December 2017), "The fundamental stellar parameters of FGK stars in the SEEDS survey", Monthly Notices of the Royal Astronomical Society, 472 (2): 1736–1752, arXiv:1708.02541, Bibcode:2017MNRAS.472.1736R, doi:10.1093/mnras/stx2051.
  5. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars: Version GCVS 5.1", Astronomy Reports, 61 (1): 80–88, Bibcode:2017ARep...61...80S.
  6. Soubiran, C.; et al. (April 2013), "The catalogue of radial velocity standard stars for Gaia. I. Pre-launch release", Astronomy & Astrophysics, 552: 11, arXiv:1302.1905, Bibcode:2013A&A...552A..64S, doi:10.1051/0004-6361/201220927, A64.
  7. Marsden, S. C.; et al. (November 2014), "A BCool magnetic snapshot survey of solar-type stars", Monthly Notices of the Royal Astronomical Society, 444 (4): 3517–3536, arXiv:1311.3374, Bibcode:2014MNRAS.444.3517M, doi:10.1093/mnras/stu1663.
  8. Gray, R. O.; et al. (December 2015), "The Young Solar Analogs Project. I. Spectroscopic and Photometric Methods and Multi-year Timescale Spectroscopic Results", The Astronomical Journal, 150 (6): 19, arXiv:1511.00279, Bibcode:2015AJ....150..203G, doi:10.1088/0004-6256/150/6/203, 203.
  9. "HD 217813". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-08-15.
  10. Fuhrmann, K.; et al. (2017), "Multiplicity among Solar-type Stars", The Astrophysical Journal, 836: 139, Bibcode:2017ApJ...836..139F, doi:10.3847/1538-4357/836/1/139.
  11. Ammler, M.; Guenther, E. W.; König, B.; Neuhäuser, R. (March 2005), "High-resolution spectroscopy of the UMa group", in Favata, F.; Hussain, G. A. J.; Battrick, B. (eds.), Proceedings of the 13th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, held 5-9 July, 2004 in Hamburg, Germany, European Space Agency, p. 391, Bibcode:2005ESASP.560..391A
  12. Harlan, E. A.; Taylor, D. C. (March 1970), "MK classifications for F-and G-type stars. II", Astronomical Journal, 75: 165–166, Bibcode:1970AJ.....75..165H, doi:10.1086/110956.
  13. Depasquale, J. M.; et al. (August 2000), "MT Pegasi (= HD 217813) - A Young Sun with Starspots", Information Bulletin on Variable Stars, 4933: 1, Bibcode:2000IBVS.4933....1D.
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