Iota Hydrae
Star in the constellation Hydra
From Wikipedia, the free encyclopedia
Iota Hydrae, formally named Ukdah /ˈʌkdə/,[10] is a star in the constellation of Hydra, about 8° to the north-northwest of Alphard (Alpha Hydrae)[11] and just to the south of the celestial equator.[12] Visible to the naked eye, it is a suspected variable star with an apparent visual magnitude that ranges between 3.87 and 3.91.[4] Based upon an annual parallax shift of 12.39 mas measured during the Hipparcos mission,[1] it is located around 263 light-years distant.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 39m 51.36145s[1] |
| Declination | −01° 08′ 34.1135″[1] |
| Apparent magnitude (V) | 3.91[2] |
| Characteristics | |
| Evolutionary stage | probable red giant branch[a] |
| Spectral type | K2.5 III[2] |
| B−V color index | 1.32 |
| Variable type | Suspected[4] |
| Astrometry | |
| Radial velocity (Rv) | +24.19±0.36[5] km/s |
| Proper motion (μ) | RA: +46.96[1] mas/yr Dec.: −62.39[1] mas/yr |
| Parallax (π) | 12.39±0.14 mas[1] |
| Distance | 263 ± 3 ly (80.7 ± 0.9 pc) |
| Absolute magnitude (MV) | −0.63[6] |
| Details | |
| Mass | 1.92[2] M☉ |
| Radius | 30±0.04[7] R☉ |
| Luminosity | 241±7[8] L☉ |
| Surface gravity (log g) | 1.78±0.04[8] cgs |
| Temperature | 4,238±22[8] K |
| Metallicity [Fe/H] | −0.06±0.05[8] dex |
| Rotational velocity (v sin i) | 4.5[5] km/s |
| Age | 2.47[2] Gyr |
| Other designations | |
| Ukdah, ι Hya, 35 Hya, BD−00°2231, FK5 1250, HD 83618, HIP 47431, HR 3845, SAO 137035[9] | |
| Database references | |
| SIMBAD | data |
Nomenclature
ι Hydrae (Latinised to Iota Hydrae, abbreviated ι Hya, Iota Hya) is the star's Bayer designation.
This star along with Tau1 Hydrae, Tau2 Hydrae and 33 Hydrae (A Hydrae), were Ptolemy's Καμπή (Kampē); but Kazwini knew them as عقدة ʽuqdah (or ʽuḳdah) "knot".[13] According to a 1971 NASA memorandum,[14] Ukdah was the name of an asterism of four stars: Tau1 Hydrae as Uḳdah I, Tau2 Hydrae as Uḳdah II, 33 Hydrae as Uḳdah III and Iota Hydrae as Uḳdah IV. In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN approved the name Ukdah for Iota Hydrae on 1 June 2018 and it is now so included in the List of IAU-approved Star Names.[10]
In Chinese, 星宿 (Xīng Sù), meaning Star (asterism), refers to an asterism consisting of ι Hydrae, Alphard, τ1 Hydrae, τ2 Hydrae, 26 Hydrae, 27 Hydrae, HD 82477 and HD 82428.[16] Consequently, ι Hydrae is known as 星宿四 (Xīng Sù sì, English: the Fourth Star of Star).[17] R. H. Allen's 1899 book Star Names claimed the Chinese name Ping Sing, translated as "a Tranquil Star", for ι Hydrae,[13] but this name belongs instead to an asterism of γ Hydrae and π Hydrae.[18]
Properties
This is an evolved K-type giant star with a stellar classification of K2.5 III.[2] It is a Barium star, which means that, for a giant star, it displays unusually strong absorption lines of singly-ionized barium and strontium.[19] Iota Hydrae has nearly twice the mass of the Sun[2] and has expanded to 30 times the Sun's radius.[7] It is around 2.5 billion years old[2] and is spinning with a leisurely projected rotational velocity of 4.5 km/s.[5] It may be a member of the Wolf 630 moving group of stars that share a common trajectory through space.[20]
Notes
- 36% chance of being on the horizontal branch[3]