HN Pegasi

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HN Pegasi
HN Pegasi B.jpg
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]
Distance 59.14 ± 0.04  ly
(18.13 ± 0.01  pc)
Absolute magnitude  (MV)4.70 [7]
Details
HN Peg A
Mass 1.085±0.091 [5]   M☉
Radius 1.002±0.018 [5]   R☉
Luminosity (bolometric)1.090 [7]   L☉
Surface gravity (log g)4.45 [8]   cgs
Temperature 5,961 [8]   K
Metallicity [Fe/H]−0.06 [8]   dex
Rotation 4.84  d [9]
Rotational velocity (v sin i)12.81 [10]  km/s
Age 237±33 [5]   Myr
HN Peg B
Radius 0.101 [11]   R☉
Surface gravity (log g)4.81 [11]   cgs
Temperature 1,115 [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
SIMBAD HN 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. The 4.84 day rotation period is marked in red. HNPegLightCurve.png
A light curve for HN Pegasi, plotted from TESS data. 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]

Related Research Articles

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Pi<sup>2</sup> Pegasi Single star in the constellation Pegasus

π2 Pegasi, Latinized as Pi2 Pegasi, is a single star in the northern constellation Pegasus. It is yellow-white in hue and visible to the naked eye as a faint point of light with an apparent visual magnitude of +4.28. The distance to this object is approximately 263 light years based on parallax, and it is drifting further away with a radial velocity of +5 km/s. This star is an outlying member of the Ursa Major Moving Group.

<span class="mw-page-title-main">56 Pegasi</span> Star in the constellation Pegasus

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. The system is approximately 590 light years away from the Sun based on parallax, but is drifting closer with a radial velocity of −28 km/s. It is listed as a member of the Wolf 630 moving group.

σ Pegasi, Latinised as Sigma Pegasi, is a binary star system in the northern constellation of Pegasus. With a combined apparent visual magnitude of 5.16, it is faintly visible to the naked eye. Based upon an annual parallax shift of 36.66 mas as seen from Earth, the system is located 89 light years distant from the Sun. It has a relatively high proper motion, advancing across the celestial sphere at the rate of 0.524 arcseconds per year.

10 Canum Venaticorum is an ordinary star in the northern constellation of Canes Venatici. It has an apparent visual magnitude of 5.95, which, according to the Bortle scale, can be faintly seen with the naked eye from suburban locations. Based upon an annual parallax shift of 0.057 arcseconds, this system is 57.26 light-years from Sun. It is drifting further away with a radial velocity of +80 km/s.

HD 219623 is a solitary star in the northern circumpolar constellation of Cassiopeia. HD 219623 is its Henry Draper Catalogue designation. It has an apparent visual magnitude of 5.59, which lies in the brightness range that is visible to the naked eye. According to the Bortle scale, it can be observed from dark suburban skies. Parallax measurements place it at an estimated distance of around 67.2 light years. It has a relatively high proper motion, advancing 262 mas per year across the celestial sphere.

<span class="mw-page-title-main">DY Pegasi</span> Star in the constellation Pegasus

DY Pegasi, abbreviated DY Peg, is a binary star system in the northern constellation of Pegasus. It is a well-studied SX Phoenicis variable star with a brightness that ranges from an apparent visual magnitude of 9.95 down to 10.62 with a period of 1.75 hours. This system is much too faint to be seen with the naked eye, but can be viewed with large binoculars or a telescope. Based on its high space motion and low abundances of heavier elements, it is a population II star system.

<span class="mw-page-title-main">LO Pegasi</span> Star in the constellation Pegasus

LO Pegasi is a single star in the northern constellation of Pegasus that has been the subject of numerous scientific studies. LO Pegasi, abbreviated LO Peg, is the variable star designation. It is too faint to be viewed with the naked eye, having an apparent visual magnitude that ranges from 9.04 down to 9.27. Based on parallax measurements, LO Peg is located at a distance of 79 light years from the Sun. It is a member of the young AB Doradus moving group, and is drifting closer with a radial velocity of −23 km/s.

References

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  5. 1 2 3 4 5 6 7 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. 1 2 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. 1 2 3 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. 1 2 3 4 5 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. 1 2 3 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. 1 2 3 4 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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