  | |
| Observation data EpochJ2000.0 EquinoxJ2000.0 | |
|---|---|
| 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−Bcolor index | +0.82[2] |
| B−Vcolor 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[6] | |
| Mass | 3.09±0.1 M☉ |
| Radius | 17.61±0.19 R☉ |
| Luminosity | 174.2±9.3 L☉ |
| Surface gravity (log g) | 2.48[7] cgs |
| Temperature | 4,996±30 K |
| Metallicity[Fe/H] | –0.21[8] dex |
| Rotational velocity (v sin i) | 2.5[8] km/s |
| Age | 370±40 Myr |
| Other designations | |
| 16 Hydrae,BD+06 2060,FK5 334,HD 76294,HIP 43813,HR 3547,SAO 117264[9] | |
| Database references | |
| SIMBAD | data |
Zeta Hydrae (ζ Hya, ζ Hydrae) is a solitarystar in theequatorialconstellation ofHydra. This is a generally faint constellation, so, at anapparent visual magnitude of +3.10,[2] this is thethird-brightest member afterAlphard andGamma Hydrae.
The distance to this star has been measured using theparallax technique, yielding a value of roughly 167light-years (51parsecs).[1] At this distance, thevisual magnitude of the star is diminished by 0.03 as a result ofextinction 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 theGaia spacecraft which computes a parallax of 20.7182 ± 0.3925 mas and, if correct, a distance of 157 ± 3 light years.[11]
With astellar classification of G9 II-III,[3] this is anevolvedgiant star that is radiating 174 times theluminosity of the Sun from itsouter envelope at aneffective temperature of around 5,000 K.[6] At this heat, the star glows with the yellow hue of aG-type star.[12] The radius of this star, measured usinginterferometry, is 17.6 times the Sun's radius. It has an estimated 3.1 times the mass of the Sun and is around370 million years old.[6]
This star, along withδ Hya (Lisan al Sudja),ε Hya,η Hya,ρ Hya andσ Hya (Minchir), were Ulug Beg'sMin al Azʽal, "Belonging to the Uninhabited Spot".[13] According to the catalogue of stars in theTechnical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars,Min al Azʽal orMinazal were the title for five stars:δ Hya asMinazal I,η Hya asMinazal II,ε Hya asMinazal III,ρ Hya asMinazal IV and ζ Hya asMinazal V (excludeσ Hya).[14]
InChinese,柳宿 (Liǔ Sù), meaningWillow, refers to anasterism consisting of ζ Hydrae,δ Hydra,σ Hydrae,η Hydrae,ρ Hydrae,ε Hydrae,ω Hydrae andθ Hydrae[15] Consequently, ζ Hydrae itself is known as柳宿六 (Liǔ Sù liù, English:the Sixth Star of Willow).[16]
The people ofGroote Eylandt calledUnwala, "The Crab", for the star cluster including this star,δ Hya (Lisan al Sudja),ε Hya (Ashlesha),η Hya,ρ Hya andσ Hya (Minchir).[17]
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