Pi Hydrae

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Pi Hydrae, Latinized from π Hydrae, is a star in the constellation Hydra with an apparent visual magnitude of 3.3, making it visible to the naked eye. Parallax measurements put this star at a distance of about 101 ly from the Earth. The spectrum of this star shows it to have a stellar classification of K1 III-IV, 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. Pi Hydrae is radiating 61 times the Sun's luminosity from its outer envelope with an effective temperature of 4,565 K, giving it the orange hue of a K-type star. 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.

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