 HN Peg B (circled) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Pegasus |
| Right ascension | 21 44 31.330 |
| Declination | +14° 46′ 18.98″ |
| Apparent magnitude (V) | 5.92 - 5.95 |
| Characteristics | |
| Spectral type | G0 V CH-0.5 |
| U−B color index | +0.031 |
| B−V color index | +0.588 |
| Variable type | BY Dra |
| Astrometry | |
| Radial velocity (Rv) | −16.68±0.09 km/s |
| Proper motion (μ) | RA: +231.108 mas/yr Dec.: −113.200 mas/yr |
| Parallax (π) | 55.148 ± 0.0348 mas |
| Distance | 59.14 ± 0.04 ly (18.13 ± 0.01 pc) |
| Absolute magnitude (MV) | 4.70 |
| Details | |
| HN Peg A | |
| Mass | 1.085±0.091 M☉ |
| Radius | 1.002±0.018 R☉ |
| Luminosity (bolometric) | 1.090 L☉ |
| Surface gravity (log g) | 4.45 cgs |
| Temperature | 5,961 K |
| Metallicity | −0.06 dex |
| Rotation | 4.84 d |
| Rotational velocity (v sin i) | 12.81 km/s |
| Age | 237±33 Myr |
| HN Peg B | |
| Radius | 0.101 R☉ |
| Surface gravity (log g) | 4.81 cgs |
| Temperature | 1,115 K |
| Other designations | |
| HN Peg, BD+14°4668, FK5 3737, GJ 836.7, HD 206860, HIP 107350, HR 8314, SAO 107364 | |
| 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, 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, but it is drifting closer with a radial velocity of −16.7 km/s.
This is a G-type main sequence star with a stellar classification of G0 V CH-0.5 and an estimated age of just 237 million years. It has slightly more mass and a slightly larger radius than the Sun, but a somewhat lower metallicity. It is spinning relatively quickly, with an estimated rotation period of 4.84 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. Its apparent magnitude varies between a maximum of 5.92 and a minimum of 5.95 over a period of 24.9 days. 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.
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, 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. 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. 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.
This star displays an emission of infrared excess that suggests there is a circumstellar disk of debris in orbit. HN Pegasi is most likely a thin disk population star. It is a member of the nearby Hercules-Lyra association of stars that share a common motion through space.
References
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- 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.
- ^ 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.
- "V* HN Peg -- Variable of BY Dra type", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2015-12-07.
- "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 7 September 2024.
- 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.
- 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.
- 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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