Theta Piscium

Theta Piscium, Latinized from θ Piscium, is a single,^[7] orange-hued star in the zodiac constellation of Pisces, the fish. The annual parallax shift of this star was measured during the Hipparcos mission as 21.96 mas,^[1] which yields a distance estimate of about 149 light years. It is a faint star but visible to the naked eye with an apparent visual magnitude of 4.27.^[2] The star is moving away from the Sun with a radial velocity of +6 km/s.^[2]

Theta Piscium

Location of θ Piscium (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Pisces
Right ascension	23h 27m 58.09529s[1]
Declination	+06° 22′ 44.3720″[1]
Apparent magnitude (V)	4.27[2]
Characteristics
Evolutionary stage	red clump[3]
Spectral type	K1 III[2]
U−B color index	+1.00
B−V color index	+1.062[2]
Astrometry
Radial velocity (Rv)	+6.05±0.19[2] km/s
Proper motion (μ)	RA: −123.83[1] mas/yr Dec.: −43.26[1] mas/yr
Parallax (π)	21.96±0.25 mas[1]
Distance	149 ± 2 ly (45.5 ± 0.5 pc)
Absolute magnitude (MV)	+0.83[2]
Details
Mass	1.58[4] M☉
Radius	11[5] R☉
Luminosity	51.3[5] L☉
Surface gravity (log g)	2.70[3] cgs
Temperature	4,684±23[4] K
Metallicity [Fe/H]	0.06[3] dex
Rotational velocity (v sin i)	3.1[5] km/s
Age	2.45[4] Myr
Other designations
θ Psc, 10 Piscium, BD+05°5173, FK5 1614, GC 32647, HD 220954, HIP 115830, HR 8916, SAO 128196, PPM 174110[6]
Database references
SIMBAD	data

At the estimated age of 2.5 billion years,^[4] this is an aging giant star with a stellar classification of K1 III,^[2] which means it has exhausted the supply of hydrogen at its core. It is a red clump star, indicating it is on the horizontal branch of its evolution and is generating energy through helium fusion at its core.^[3] Theta Piscium has 158%^[4] of the Sun's mass and its outer atmosphere has swollen to about 11^[5] times the girth of the Sun. It is brighter yet cooler than the Sun, radiating 51.3^[5] times the Sun's luminosity from its enlarged photosphere at an effective temperature of about 4,684 K.^[4]

Naming

In Chinese, 霹靂 (Pī Lì), meaning Thunderbolt, refers to an asterism consisting of refers to an asterism consisting of θ Piscium, β Piscium, γ Piscium, ι Piscium and ω Piscium. Consequently, the Chinese name for θ Piscium itself is 霹靂三 (Pī Lì sān, English: the Third Star of Thunderbolt.)^[8]