Pi Hydrae

Pi Hydrae, Latinized from π Hydrae, is a star in the constellation Hydra with an apparent visual magnitude of 3.3,^[2] making it visible to the naked eye. Parallax measurements put this star at a distance of about 101 light-years (31 parsecs) from the Earth.

Pi Hydrae

Location of π Hydra (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Hydra
Right ascension	14h 06m 22.29749s[1]
Declination	–26° 40′ 56.5024″[1]
Apparent magnitude (V)	3.25[2]
Characteristics
Spectral type	K1 III–IV[3] or K2-III Fe-0.5[4]
U−B color index	+1.040[5]
B−V color index	+1.120[5]
Astrometry
Radial velocity (Rv)	+26.7[2] km/s
Proper motion (μ)	RA: +43.70[1] mas/yr Dec.: −141.18[1] mas/yr
Parallax (π)	32.30±0.16 mas[1]
Distance	101.0 ± 0.5 ly (31.0 ± 0.2 pc)
Absolute magnitude (MV)	0.79[6]
Details[7]
Mass	1.40±0.21 M☉
Radius	12.49±0.49 R☉
Luminosity	60.8±2.6 L☉
Surface gravity (log g)	2.40±0.11 cgs
Temperature	4,565±75 K
Metallicity [Fe/H]	−0.16±0.10 dex
Rotational velocity (v sin i)	2.25[8] km/s
Age	6.29±3.05 Gyr
Other designations
Markeb, π Hya, Pi Hya, 49 Hydrae, CPD26 5170, FK5 519, HD 123123, HIP 68895, HR 5287, SAO 182244[9]
Database references
SIMBAD	data

The spectrum of this star shows it to have a stellar classification of K1 III-IV,^[3] with the luminosity class of 'III-IV' suggesting it is in an evolutionary transition stage somewhere between a subgiant and a giant star. It has a low projected rotational velocity of 2.25 km s⁻¹.^[8] Pi Hydrae is radiating 61 times the Sun's luminosity from its outer envelope with an effective temperature of 4,565 K,^[7] giving it the orange hue of a K-type star.^[10]

Pi Hydrae is a type of giant known as a cyanogen-weak star, which means that its spectrum displays weak absorption lines of CN⁻ relative to the metallicity. (The last is a term astronomers use when describing the abundance of elements other than hydrogen and helium.) Otherwise, it appears to be a normal star of its evolutionary class, having undergone first dredge-up of nuclear fusion by-products onto its surface layers.^[11]