The Flamsteed designation 54 Piscium originated in the star catalogue of the British astronomer John Flamsteed, first published in 1712. It has an apparent magnitude of 5.86, allowing it to be seen with the unaided eye under suitable viewing conditions. The star has a classification of K0V, with the luminosity class V indicating this is a main sequence star that is generating energy at its core through the thermonuclear fusion of hydrogen into helium. The effective temperature of the photosphere is about 5,062 K,[3] giving it the characteristic orange hue of a K-type star.[13]
It has been calculated that the star may have 76 percent[6] of the Sun's mass and 46 percent of the luminosity. The radius has been directly determined by interferometry to be 94 percent that of the Sun's radius using the CHARA array.[3] The rotational period of 54 Piscium is about 40.2 days.[9] The age of the star is about 6.4 billion years, based on chromospheric activity and isochronal analysis.[10] There is some uncertainty in the scientific press concerning the higher ratio of elements heavier than hydrogen compared to those found in the Sun; what astronomers term the metallicity. Santos et al. (2004) report the logarithm of the abundance ratio of iron to hydrogen, [Fe/H], to be 0.12 dex,[14] whereas Cenarro et al. (2007) published a value of –0.15 dex.[8]
Long term observation of this star's magnetic activity levels suggests that it is entering a Maunder minimum period, which means it may undergo an extended period of low starspot numbers. It has a Sun-like activity cycle that has been decreasing in magnitude. As of 2010, the most recent period of peak activity was 1992–1996, which showed a lower level of activity than the previous peak in 1976–1980.[9]
In 2006, a direct image of 54 Piscium showed that there was a brown dwarf companion to 54 Piscium A.[6] 54 Piscium B is thought to be a "methane brown dwarf" of the spectral type "T7.5V". The luminosity of this substellar object suggests that it has a mass of 0.051 that of the Sun (50 times the massofJupiter) and 0.082 times the Sun's radius. Similar to Gliese 570 D, this brown dwarf is thought to have a surface temperature of about 810 K (537 °C).[11]
The star rotates at an inclination of 83+7 −56 degrees relative to Earth.[9]
On January 16, 2003, a team of astronomers (led by Geoff Marcy) announced the discovery of an extrasolar planet (named 54 Piscium b) around 54 Piscium.[15][16] The planet has been estimated to have a mass of only 20 percent that of Jupiter (making the planet around the same size and mass of Saturn).
The planet orbits its sun at a distance of 0.28 astronomical units (which would be within the orbit of Mercury), which takes approximately 62 days to complete. It has been assumed that the planet shares the star's inclination and so has real mass close to its minimum mass;[17] however, several "hot Jupiters" are known to be oblique relative to the stellar axis.[18]
The planet has a high eccentricity of about 0.65. The highly elliptical orbit suggested that the gravity of an unseen object farther away from the star was pulling the planet outward. That cause was verified with the discovery of the brown dwarf within the system.
The orbit of an Earth-like planet would need to be centered within 0.68 AU[19] (around the orbital distance of Venus), which in a Keplerian system means a 240-day orbital period. In a later simulation with the brown dwarf, 54 Piscium b's orbit "sweeps clean" most test particles within 0.5 AU, leaving only asteroids "in low-eccentricity orbits near the known planet's apastron distance, near the 1:2 mean-motion resonance". Also, observation has ruled out Neptune-class or heavier planets with a period of one year or less; which still allows for Earth-sized planets at 0.6 AU or more.[20]
A two planet fit to the radial velocities with two circular planets in a 2:1 orbital resonance is possible[21] however it does not significantly improve the solution, and therefore does not justify the additional complexity.[22]
^ abcJohnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
^Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Carnegie Institute Washington D.C. Publication. Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
^"The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16
^Wittenmyer, Robert A.; Wang, Songhu; Horner, Jonathan; Tinney, C. G.; Butler, R. P.; Jones, H. R. A.; O'Toole, S. J.; Bailey, J.; Carter, B. D.; Salter, G. S.; Wright, D.; Zhou, Ji-Lin (2013), "Forever alone? Testing single eccentric planetary systems for multiple companions", The Astrophysical Journal Supplement Series, 208 (1): 2, arXiv:1307.0894, Bibcode:2013ApJS..208....2W, doi:10.1088/0067-0049/208/1/2, S2CID14109907
00h39m21.8s, +21° 15′ 01.7″
