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 5,297 K, giving it the characteristic orange hue of a K-type star. As a typical K-type dwarf, 54 Piscium is smaller and fainter than the Sun, at 85% of the
Sun's mass and half of the
luminosity. The
angular diameter has been directly determined by
interferometry using the
CHARA array, yielding a true radius 85% of the
Sun's radius. The rotational period of 54 Piscium is about 40.2 days. The age of the star is about 6.4 billion years, based on
chromospheric activity and
isochronal analysis. Another study suggest a higher age of ten billion years. 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, whereas Cenarro et al. (2007) published a value of –0.15 dex. 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. 54 Piscium B and the planet
54 Piscium b. In 2006, a direct image of 54 Piscium showed that there was a
brown dwarf companion to 54 Piscium A. 54 Piscium B is thought to be a "methane brown dwarf" of the
spectral type "T7.5V". The mass of this object is about 50 times the
mass of Jupiter, lower than the
limit for hydrogen burning of about . Despite its large mass, 54 Piscium B is smaller than Jupiter with just 80% its radius. Similar to
Gliese 570 D, this brown dwarf is thought to have a surface temperature of about . When 54 Piscium B was directly imaged by
NASA's
Spitzer Space Telescope, it was shown that the brown dwarf had a
projected separation of around 476
astronomical units from the primary star. 54 Piscium B was the first brown dwarf to be detected around a star with an already known
extrasolar planet (based on
radial velocity surveys). == Planetary system ==