Astronomy:Gamma Piscium

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Short description: G-type giant star in the constellation Pisces
γ Piscium
Location of γ Piscium (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Pisces
Right ascension  23h 17m 09.937s[1]
Declination +03° 16′ 56.25″[1]
Apparent magnitude (V) 3.699[2]
Characteristics
Evolutionary stage Horizontal branch[3]
Spectral type G8 III[4]
U−B color index +0.572 [2]
B−V color index +0.924[2]
Astrometry
Radial velocity (Rv)−13.6[5] km/s
Proper motion (μ) RA: 759.268[1] mas/yr
Dec.: 17.568[1] mas/yr
Parallax (π)24.1958 ± 0.2967[6] mas
Distance135 ± 2 ly
(41.3 ± 0.5 pc)
Absolute magnitude (MV)0.68±0.08[7]
Details
Mass0.97±0.12[3] M☉
Radius11.28±0.10[4] R☉
Luminosity62.7±3.3[4] L☉
Surface gravity (log g)2.43 ± 0.06[7] cgs
Temperature4833±62[4] K
Metallicity [Fe/H]−0.51[7] dex
Age~12[3] Gyr
Other designations
Yunyu, Gamma Psc, γ Piscium, γ Psc, 6 Piscium, BD+02°4648, FK5 878, GC 32415, HD 219615, HIP 114971, HR 8852, SAO 128085, PPM 173938, 2MASS J23170996+0316563[8]
Database references
SIMBADdata
Exoplanet ArchivePsc data

Gamma Piscium, also named Yunyu,[9] is a star approximately 135 light-years away from Earth in the equatorial-northern zodiac constellation of Pisces. It is a yellow star with a spectral type of G8 III, meaning it has a surface temperature of 4,833 K and is a giant star. It is slightly cooler than the Sun, yet it is 11[4] solar radii in size and shines with the light of 63 Suns.[4] The star is a member of the red clump, which means it is undergoing core helium fusion.[10] At an apparent magnitude of 3.7,[2] it is the second brightest star in the constellation Pisces, between Eta and Alpha.

Naming

Gamma Piscium (Latinized from γ Piscium) is the star's Bayer designation.

In Chinese astronomy, 霹靂 (Pī Lì), meaning Thunderbolt, refers to an asterism consisting of γ Piscium, β Piscium, θ Piscium, ι Piscium and ω Piscium. Consequently, the Chinese name for γ Piscium itself is 霹靂二 (Pī Lì èr, English: the Second Star of Thunderbolt.)[11] However, many of the Chinese constellations have changed over time, and γ Piscium was originally part of Yún Yǔ (Cloud and Rain, 雲雨). The IAU Working Group on Star Names approved the name Yunyu for this star on 17 September 2026; the name Pili was assigned to ω Piscium.[9]

Properties

Gamma Piscium moves across the sky at three-quarters of an arcsecond per year, which at 135 light years corresponds to 153 kilometers per second. This suggests it is a visitor from another part of the Milky Way Galaxy; in astronomical terms, it will quickly leave the vicinity of the Sun. Its metallicity is only one-fourth that of the Sun, and visitors from outside the thin disk that composes the Milky Way tend to be metal-poor. Gamma Piscium is part of the asterism known as the "circlet of Pisces."[12]

Planetary system

In 2021, a gas giant planet was detected by the radial velocity method.[13]

The Gamma Piscium planetary system[13]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b >1.34+0.02−0.31 MJ 1.32+0.05−0.08 555.1+6.0−2.5 0.204+0.114−0.141 — —

References

  1. ↑ 1.0 1.1 1.2 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 2.3 Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars 8: 59, Bibcode: 1984SAAOC...8...59C 
  3. ↑ 3.0 3.1 3.2 Fuhrmann, Klaus; Chini, Rolf (January 2022), "On the Brightest Horizontal Branch Population II Star γ Piscium", Research Notes of the AAS 6 (1): 14, doi:10.3847/2515-5172/ac4a78, 14, Bibcode: 2022RNAAS...6...14F. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Baines, Ellyn K. et al. (2018). "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer". The Astronomical Journal 155 (1): 30. doi:10.3847/1538-3881/aa9d8b. Bibcode: 2018AJ....155...30B. 
  5. ↑ Wielen, R. et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode: 1999VeARI..35....1W 
  6. ↑ Van Leeuwen, Floor (2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V.  Vizier catalog entry
  7. ↑ 7.0 7.1 7.2 da Silva, L. et al. (November 2006), "Basic physical parameters of a selected sample of evolved stars", Astronomy and Astrophysics 458 (2): 609–623, doi:10.1051/0004-6361:20065105, Bibcode: 2006A&A...458..609D 
  8. ↑ "* gam Psc". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+gam+Psc. 
  9. ↑ 9.0 9.1 "IAU Catalog of Star Names". https://exopla.net/star-names/modern-iau-star-names/. 
  10. ↑ Liu, Y. J. et al. (December 2007), "The abundances of nearby red clump giants", Monthly Notices of the Royal Astronomical Society 382 (2): 553–566, doi:10.1111/j.1365-2966.2007.11852.x, Bibcode: 2007MNRAS.382..553L. 
  11. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 8 日
  12. ↑ "SPACE.com -- SpaceWatch -- Pisces Rising". http://www.space.com/spacewatch/spacewatch_001113.html. 
  13. ↑ 13.0 13.1 Teng, Huan-Yu; Sato, Bun'ei; Takarada, Takuya; Omiya, Masashi; Harakawa, Hiroki; Izumiura, Hideyuki; Kambe, Eiji; Takeda, Yoichi et al. (2022), "Regular radial velocity variations in nine G- and K-type giant stars: Eight planets and one planet candidate", Publications of the Astronomical Society of Japan 74: 92–127, doi:10.1093/pasj/psab112 



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