Zeta Hydrae (ζ Hya, ζ Hydrae) is a solitary star in the equatorial constellation of Hydra. This is a generally faint constellation, so, at an apparent visual magnitude of +3.10,[2] this is the third-brightest member after Alphard and Gamma Hydrae.
Observation data Epoch J2000.0 Equinox J2000.0 | |
---|---|
Constellation | Hydra |
Right ascension | 08h 55m 23.62614s[1] |
Declination | +05° 56′ 44.0354″[1] |
Apparent magnitude (V) | 3.10[2] |
Characteristics | |
Spectral type | G9 II-III[3] |
U−B color index | +0.82[2] |
B−V color index | +1.00[2] |
Astrometry | |
Radial velocity (Rv) | +22.8[4] km/s |
Proper motion (μ) | RA: –100.06[1] mas/yr Dec.: +15.46[1] mas/yr |
Parallax (π) | 19.51 ± 0.18 mas[1] |
Distance | 167 ± 2 ly (51.3 ± 0.5 pc) |
Absolute magnitude (MV) | –0.24[5] |
Details | |
Mass | 4.2[6] M☉ |
Radius | 17.9[7] R☉ |
Luminosity | 132[7] L☉ |
Surface gravity (log g) | 2.48[7] cgs |
Temperature | 4,925[6] K |
Metallicity [Fe/H] | –0.21[8] dex |
Rotational velocity (v sin i) | 2.5[8] km/s |
Age | 400[5] Myr |
Other designations | |
Database references | |
SIMBAD | data |
The distance to this star has been measured using the parallax technique, yielding a value of roughly 167 light-years (51 parsecs).[1] At this distance, the visual magnitude of the star is diminished by 0.03 as a result of extinction from intervening gas and dust.[5] Delta Hydrae is about 12.9 light-years (4.0 parsecs) from Zeta Hydrae and may be a largely co-moving object.[10] The star has one of the lower-error margin readings among those of the Gaia spacecraft which computes a parallax of 20.7182 ± 0.3925 mas and, if correct, a distance of 157 ± 3 light years.[11]
With a stellar classification of G9 II-III,[3] this is an evolved giant star that is radiating 132[7] times the luminosity of the Sun from its outer envelope at an effective temperature of 4,925 K.[6] At this heat, the star glows with the yellow hue of a G-type star.[12] The radius of this star, as measured using interferometry, is about 18 times the Sun's radius.[7] It has an estimated 4.2 times the mass of the Sun[6] and is around 400 million years old.[5]
This star, along with δ Hya (Lisan al Sudja), ε Hya, η Hya, ρ Hya and σ Hya (Minchir), were Ulug Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".[13] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Min al Azʽal or Minazal were the title for five stars:δ Hya as Minazal I, η Hya as Minazal II, ε Hya as Minazal III, ρ Hya as Minazal IV and ζ Hya as Minazal V (exclude σ Hya).[14]
In Chinese, 柳宿 (Liǔ Sù), meaning Willow, refers to an asterism consisting of ζ Hydrae, δ Hydra, σ Hydrae, η Hydrae, ρ Hydrae, ε Hydrae, ω Hydrae and θ Hydrae[15] Consequently, ζ Hydrae itself is known as 柳宿六 (Liǔ Sù liù, English: the Sixth Star of Willow).[16]
The people of Groote Eylandt called Unwala, "The Crab", for the star cluster including this star, δ Hya (Lisan al Sudja), ε Hya, η Hya, ρ Hya and σ Hya (Minchir).[17]