Eta Aquarii, Latinized from η Aquarii, is the Bayer designation for a star in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of 4.04.[2] The distance to this star, as determined by parallax measurements, is about 168 light-years (52 parsecs).[1] It is drifting closer to the Sun with a radial velocity of –8 km/s.[2] Eta Aquarii is near the radiant of a meteor shower named after it.
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 35m 21.38126s[1] |
| Declination | –00° 07′ 02.9888″[1] |
| Apparent magnitude (V) | 4.04[2] |
| Characteristics | |
| Spectral type | B9IV-Vn[3] or B8/9V[4] |
| U−B color index | –0.28[5] |
| B−V color index | –0.10[5] |
| Astrometry | |
| Radial velocity (Rv) | –8.0[2] km/s |
| Proper motion (μ) | RA: +89.74[1] mas/yr Dec.: –56.10[1] mas/yr |
| Parallax (π) | 19.43 ± 0.25 mas[1] |
| Distance | 168 ± 2 ly (51.5 ± 0.7 pc) |
| Absolute magnitude (MV) | 0.31±0.15[6] |
| Details[6] | |
| Mass | 2.96±0.04 M☉ |
| Radius | 2.77±0.30 R☉ |
| Luminosity | 102.8 L☉ |
| Surface gravity (log g) | 4.02±0.04 cgs |
| Temperature | 11,042±301 K |
| Rotational velocity (v sin i) | 271±32 km/s |
| Age | 65[7] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The stellar classification of Eta Aquarii is B9IV-Vn,[3] which may indicate that it is beginning to evolve away from the main sequence into a subgiant as the supply of hydrogen at its core becomes exhausted. It is 65[7] million years old and is spinning rapidly with a high projected rotational velocity of 271 km/s.[6] This rotation is causing an equatorial bulge, giving the star an oblate figure with a 24% larger radius at the equator than at the poles.[9] The Doppler effect from the rapid rotation is causing the absorption lines in the star's spectrum to blur, as indicated by the 'n' suffix in the star's classification. Eta Aquarii has an estimated 2.96 times the mass of the Sun and 2.8 times the Sun's radius. The star is radiating 103 times the luminosity of the Sun from its photosphere at an effective temperature of 11,042 K.[6]
Naming
editThis star, along with γ Aqr (Sadachbia), π Aqr (Seat) and ζ Aqr (Sadaltager / Achr al Achbiya), were al Aḣbiyah (الأخبية), the Tent.[10][11]
In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of η Aquarii, γ Aquarii, ζ Aquarii, π Aquarii.[12] Consequently, the Chinese name for η Aquarii itself is 墳墓三 (Fén Mù sān, English: the Third Star of Tomb.)[13]
References
edit- ^ a b c d e f 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.
- ^ a b c d Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, 35 (35), Astronomisches Rechen-Institut Heidelberg: 1, Bibcode:1999VeARI..35....1W.
- ^ a b Cowley, A. (November 1972), "Spectral classification of the bright B8 stars", Astronomical Journal, 77: 750–755, Bibcode:1972AJ.....77..750C, doi:10.1086/111348.
- ^ Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
- ^ a b Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
- ^ a b c d Cochetti, Y. R.; et al. (February 2020), "Be and Bn stars: Balmer discontinuity and stellar-class relationship", Astronomy & Astrophysics, 634: 29, arXiv:1912.12994, Bibcode:2020A&A...634A..18C, doi:10.1051/0004-6361/201936444, S2CID 209516349, A18.
- ^ a b David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
- ^ "eta Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-06-30.
- ^ van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
- ^ Davis, George R (1944). "The pronunciations, derivations, and meanings of a selected list of star names". Popular Astronomy. 52: 8. Bibcode:1944PA.....52....8D.
- ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 52. ISBN 0-486-21079-0. Retrieved 2010-12-12.
- ^ (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) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日 Archived 2011-05-22 at the Wayback Machine