Θ_Aquarii
Theta Aquarii
Star in the constellation Aquarius
Theta Aquarii (θ Aquarii, abbreviated Theta Aqr, θ Aqr), officially named Ancha /ˈæŋkə/[7] (distinguish Ankaa, with the same pronunciation), is a star in the equatorial constellation of Aquarius. Visible to the naked eye at apparent magnitude 4.175,[2] it is located at a distance of around 187 light-years (57 parsecs) from the Sun.[1] Since it is near the ecliptic it can be occulted by the Moon, or very rarely by planets.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 16m 50.03635s[1] |
| Declination | –07° 46′ 59.8480″[1] |
| Apparent magnitude (V) | 4.175[2] |
| Characteristics | |
| Spectral type | G8 III–IV[3] |
| U−B color index | +0.818[2] |
| B−V color index | +0.983[2] |
| Astrometry | |
| Radial velocity (Rv) | –13.77 ± 0.17[4] km/s |
| Proper motion (μ) | RA: +118.80[1] mas/yr Dec.: –22.18[1] mas/yr |
| Parallax (π) | 17.40 ± 0.23 mas[1] |
| Distance | 187 ± 2 ly (57.5 ± 0.8 pc) |
| Absolute magnitude (MV) | +0.23[3] |
| Details | |
| Mass | 2.39[5] to 2.78[3] M☉ |
| Radius | 12[4] R☉ |
| Luminosity | 72[4] to 83[3] L☉ |
| Surface gravity (log g) | 2.8[4] cgs |
| Temperature | 4,864[4] K |
| Metallicity [Fe/H] | +0.01[4] to +0.09[3] dex |
| Rotational velocity (v sin i) | 1.6[4] km/s |
| Age | 437[3] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
θ Aquarii (Latinised to Theta Aquarii) is the star's Bayer designation.
It bore the traditional name Ancha; Medieval Latin for "the haunch". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[8] to catalogue and standardize proper names for stars. The WGSN approved the name Ancha for this star on 12 September 2016, and it is now so included in the List of IAU-approved Star Names.[7]
In Chinese, 泣 (Qì), meaning Weeping, refers to an asterism consisting of Theta Aquarii and Rho Aquarii.[9] Consequently, the Chinese name for Theta Aquarii itself is 泣二 (Qì èr, English: the Second Star of Weeping).[10] Possibly, the name Lei, meaning "tears (weeping)" in Chinese, derives from the Chinese name for this star.[11]
Ancha belongs to the spectral class G8 with a luminosity class of III–IV suggesting that, at an age of 437[3] million years, this star is part way between the subgiant and giant stages of its evolution. Estimates of the star's mass range from 2.39[5] to 2.78[3] times the Sun's mass, with a radius of about 12[4] times that of the Sun. It is radiating from 72[4] to 83[3] times as much luminosity as the Sun from its enlarged outer envelope at an effective temperature of 4,864 K.[4] At this heat, the star glows with the yellow hue of a G-type star.[12]
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
- Gutierrez-Moreno, Adelina; et al. (1966). "A System of photometric standards". Publications of the Department of Astronomy University of Chile. 1. Publicaciones Universidad de Chile, Department de Astronomy: 1–17. Bibcode:1966PDAUC...1....1G.
- Takeda, Yoichi; et al. (August 2008), "Stellar Parameters and Elemental Abundances of Late-G Giants", Publications of the Astronomical Society of Japan, 60 (4): 781–802, arXiv:0805.2434, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781, S2CID 16258166.
- Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
- Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P.
- "* tet Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-06-30.
- "Naming Stars". IAU.org. Retrieved 16 December 2017.
- IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
- (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-08-11 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
- Richard Hinckley Allen. "Star Names — Their Lore and Meaning". www.constellationsofwords.com.
- "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2013-12-03, retrieved 2012-01-16.