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Star in the constellation Hydra From Wikipedia, the free encyclopedia
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.
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 | |
Mass | 1.76[6] to 2.45[7] M☉ |
Radius | 12–13[8] R☉ |
Surface gravity (log g) | 2.65[9] cgs |
Temperature | 4,670[9] K |
Metallicity [Fe/H] | 0.04[10] dex |
Rotational velocity (v sin i) | 2.25[9] km/s |
Other designations | |
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.[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]