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HN Pegasi

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]

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 emission characteristic of T-type dwarfs. The separation corresponds to a projected physical distance of 795 AU,[13] 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]

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]

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  2. ^ a b Cite error: The named reference gcvs was invoked but never defined (see the help page).
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  7. ^ a b c Cite error: The named reference aa541_A148 was invoked but never defined (see the help page).
  8. ^ a b c d e Cite error: The named reference apj764_1_78 was invoked but never defined (see the help page).
  9. ^ a b c Cite error: The named reference aa409_1017 was invoked but never defined (see the help page).
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  11. ^ a b c d Cite error: The named reference apj682_2_1256 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference apj654_1_570 was invoked but never defined (see the help page).

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