Pi Hydrae

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]
Distance101.0 ± 0.5 ly
(31.0 ± 0.2 pc)
Absolute magnitude (MV)0.79[6]
Details
Mass1.76[6] to 2.45[7] M☉
Radius12–13[8] R☉
Surface gravity (log g)2.65[9] cgs
Temperature4,670[9] K
Metallicity [Fe/H]0.04[10] dex
Rotational velocity (v sin i)2.25[9] km/s
Other designations
Markeb, π Hya, Pi Hya, 49 Hydrae, CPD26 5170, FK5 519, HD 123123, HIP 68895, HR 5287, SAO 182244[11]
Database references
SIMBADdata

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.

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.[9] Pi Hydrae is radiating energy from its outer envelope with an effective temperature of 4,670 K,[9] giving it the orange hue of a K-type star.[12]

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.[10] The measured angular diameter of this star, after correction for limb darkening, is 3.76 ± 0.04 mas.[13] At its estimated distance, this yields a physical size of about 12–13 times the radius of the Sun.[8] It has an estimated mass of 2.45 times the mass of the Sun.[7]

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