Pi Hydrae
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 | |
| Evolutionary stage | horizontal branch[3] |
| Spectral type | K1 III–IV[4] or K2-III Fe-0.5[5] |
| U−B color index | +1.040[6] |
| B−V color index | +1.120[6] |
| 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[7] |
| Details[8] | |
| 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[9] km/s |
| Age | 6.29±3.05 Gyr |
| Other designations | |
| π Hya, Pi Hya, 49 Hydrae, CPD−26°5170, FK5 519, HD 123123, HIP 68895, HR 5287, SAO 182244[10] | |
| Database references | |
| SIMBAD | data |
The spectrum of this star shows it to have a stellar classification of K1 III-IV,[4] 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 61 times the Sun's luminosity from its outer envelope with an effective temperature of 4,565 K,[8] giving it the orange hue of a K-type star.[11]
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.[12]
In Chinese astronomy, π Hydrae forms with γ Hydrae the asterism Ping (平), representing a judge.[13] The Chinese name for π Hydrae itself is Ping èr (平二), the second star of Ping.[14] R. H. Allen's 1899 book Star Names instead claimed the Chinese name Ping Sing, translated as "a Tranquil Star", for ι Hydrae (Ukdah).[15]