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HN Pegasi

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HN Pegasi

HN Peg B (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pegasus
Right ascension 21h 44m 31.330s[1]
Declination +14° 46′ 18.98″[1]
Apparent magnitude (V) 5.92 - 5.95[2]
Characteristics
Spectral type G0 V CH-0.5[3]
U−B color index +0.031[4]
B−V color index +0.588[4]
Variable type BY Dra[5]
Astrometry
Radial velocity (Rv)−16.68±0.09[6] km/s
Proper motion (μ) RA: +231.108 mas/yr[1]
Dec.: −113.200 mas/yr[1]
Parallax (π)55.148 ± 0.0348 mas[1]
Distance59.14 ± 0.04 ly
(18.13 ± 0.01 pc)
Absolute magnitude (MV)4.70[7]
Details
HN Peg A
Mass1.085±0.091[5] M☉
Radius1.002±0.018[5] R☉
Luminosity (bolometric)1.090[7] L☉
Surface gravity (log g)4.45[8] cgs
Temperature5,961[8] K
Metallicity [Fe/H]−0.06[8] dex
Rotation4.84 d[9]
Rotational velocity (v sin i)12.81[10] km/s
Age237±33[5] Myr
HN Peg B
Radius0.101[11] R☉
Surface gravity (log g)4.81[11] cgs
Temperature1,115[11] K
Other designations
HN Peg, BD+14°4668, FK5 3737, GJ 836.7, HD 206860, HIP 107350, HR 8314, SAO 107364[12]
Database references
SIMBADHN Peg A
HN Peg B

HN Pegasi is the variable star designation for a young, Sun-like star in the northern constellation of Pegasus. It has an apparent visual magnitude of 5.9,[4] which, according to the Bortle scale, indicates that it is visible to the naked eye from suburban skies. Parallax measurements put the star at a distance of around 59 light years from the Sun,[1] but it is drifting closer with a radial velocity of −16.7 km/s.[6]

A light curve for HN Pegasi, plotted from TESS data.[13] The 4.84 day rotation period is marked in red.

This is a G-type main sequence star with a stellar classification of G0 V CH-0.5[3] and an estimated age of just 237 million years. It has slightly more mass and a slightly larger radius than the Sun,[5] but a somewhat lower metallicity.[8] It is spinning relatively quickly, with an estimated rotation period of 4.84[9] days.

The surface magnetic field of the star has a complex and variable geometry. It is a BY Draconis variable star with an active chromosphere, which means there is a rotational modulation of its luminosity due to star spots. Much like the Sun, the star spot activity undergoes a periodic cycle of maxima and minima lasting roughly 5.5±0.3 yr.[5] Its apparent magnitude varies between a maximum of 5.92 and a minimum of 5.95 over a period of 24.9 days.[2] However, the rotation period is on average 4.84 days. The star shows an anti-solar pattern of rotation, with the rotation rate steadily increasing during each cycle before dropping back to the initial value upon the start of a new cycle.[9]

In 2007, the discovery of a brown dwarf companion was announced. HN Peg B was spotted using the Spitzer Space Telescope at an angular separation of 43.2 arc sec, showing a methane absorption characteristic of T-type dwarfs. The separation corresponds to a projected physical distance of 795 AU,[14] which is uncommonly wide for such brown dwarf companions. The estimated mass of the object is 28 MJ. Based upon its spectrum, HN Peg B has relatively thin cloud decks.[11] HN Peg B was observed with Hubble WFC3 and found to be variable in the 1.1-1.7 μm range. It varied with an amplitude of 1.206 ±0.025% and a rotation period of 15.4 ±0.5 hours. The water absorption band at 1.4 μm had a reduced amplitude. The condensation particles causing the variation have a particle size larger than 1 μm.[15] It also showed variability in a Spitzer light curve, with an amplitude of 1.1 ±0.5% at 4.5 μm and 0.77 ±0.15% at 3.6 μm.[16]

This star displays an emission of infrared excess that suggests there is a circumstellar disk of debris in orbit.[7] HN Pegasi is most likely a thin disk population star.[8] It is a member of the nearby Hercules-Lyra association of stars that share a common motion through space.[5]

References

[edit]
  1. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009), "General Catalogue of Variable Stars (Samus+ 2007-2013)", VizieR On-line Data Catalog: B/GCVS, vol. 1, Bibcode:2009yCat....102025S.
  3. ^ a b 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, S2CID 119476992.
  4. ^ a b c Blanco, C.; et al. (1979), "Photoelectric observations of stars with variable H and K emission components. III", Astronomy and Astrophysics Supplement Series, 36: 297–306, Bibcode:1979A&AS...36..297B.
  5. ^ a b c d e f g Boro Saikia, S.; et al. (January 2015), "Variable magnetic field geometry of the young sun HN Pegasi (HD 206860)", Astronomy & Astrophysics, 573: 16, arXiv:1410.8307, Bibcode:2015A&A...573A..17B, doi:10.1051/0004-6361/201424096, S2CID 53316047, A17.
  6. ^ a b Nidever, David L.; et al. (August 2002), "Radial Velocities for 889 Late-Type Stars", The Astrophysical Journal Supplement Series, 141 (2): 503–522, arXiv:astro-ph/0112477, Bibcode:2002ApJS..141..503N, doi:10.1086/340570, S2CID 51814894.
  7. ^ a b c Ertel, S.; et al. (May 2012), "A peculiar class of debris disks from Herschel/DUNES. A steep fall off in the far infrared", Astronomy & Astrophysics, 541: 14, arXiv:1203.6784, Bibcode:2012A&A...541A.148E, doi:10.1051/0004-6361/201118077, S2CID 5457432, A148.
  8. ^ a b c d e Ramírez, I.; et al. (February 2013), "Oxygen abundances in nearby FGK stars and the galactic chemical evolution of the local disk and halo", The Astrophysical Journal, 764 (1): 78, arXiv:1301.1582, Bibcode:2013ApJ...764...78R, doi:10.1088/0004-637X/764/1/78, S2CID 118751608.
  9. ^ a b c Messina, S.; Guinan, E. F. (October 2003), "Magnetic activity of six young solar analogues II. Surface Differential Rotation from long-term photometry", Astronomy and Astrophysics, 409 (3): 1017–1030, Bibcode:2003A&A...409.1017M, doi:10.1051/0004-6361:20031161.
  10. ^ Martínez-Arnáiz, R.; et al. (September 2010), "Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter", Astronomy and Astrophysics, 520: A79, arXiv:1002.4391, Bibcode:2010A&A...520A..79M, doi:10.1051/0004-6361/200913725, S2CID 43455849.
  11. ^ a b c d Leggett, S. K.; et al. (August 2008), "HN Peg B: A Test of Models of the L to T Dwarf Transition", The Astrophysical Journal, 682 (2): 1256–1263, arXiv:0804.1386, Bibcode:2008ApJ...682.1256L, doi:10.1086/589146, S2CID 15701830.
  12. ^ "V* HN Peg -- Variable of BY Dra type", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2015-12-07.
  13. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 7 September 2024.
  14. ^ Luhman, K. L.; et al. (January 2007), "Discovery of Two T Dwarf Companions with the Spitzer Space Telescope", The Astrophysical Journal, 654 (1): 570–579, arXiv:astro-ph/0609464, Bibcode:2007ApJ...654..570L, doi:10.1086/509073, S2CID 11576708.
  15. ^ Zhou, Yifan; Apai, Dániel; Metchev, Stanimir; Lew, Ben W. P.; Schneider, Glenn; Marley, Mark S.; Karalidi, Theodora; Manjavacas, Elena; Bedin, Luigi R.; Cowan, Nicolas B.; Miles-Páez, Paulo A.; Lowrance, Patrick J.; Radigan, Jacqueline; Burgasser, Adam J. (2018-03-01). "Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B". The Astronomical Journal. 155 (3): 132. arXiv:1801.09757. Bibcode:2018AJ....155..132Z. doi:10.3847/1538-3881/aaabbd. ISSN 0004-6256.
  16. ^ Metchev, Stanimir A.; Heinze, Aren; Apai, Dániel; Flateau, Davin; Radigan, Jacqueline; Burgasser, Adam; Marley, Mark S.; Artigau, Étienne; Plavchan, Peter; Goldman, Bertrand (2015-02-01). "Weather on Other Worlds. II. Survey Results: Spots are Ubiquitous on L and T Dwarfs". The Astrophysical Journal. 799 (2): 154. arXiv:1411.3051. Bibcode:2015ApJ...799..154M. doi:10.1088/0004-637X/799/2/154. ISSN 0004-637X.
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