Lambda Aquarii

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Lambda Aquarii
Aquarius constellation map.svg
Red circle.svg
Location of λ Aquarii (circled)
Observation data
Epoch J2000       Equinox J2000
Constellation Aquarius
Right ascension 22h 52m 36.87404s [1]
Declination −07° 34′ 46.5489″ [1]
Apparent magnitude  (V)3.722 [2] (3.57 to 3.80) [3]
Characteristics
Evolutionary stage AGB [4]
Spectral type M2.5 IIIa Fe–1 [5]
U−B color index +1.721 [2]
B−V color index +1.641 [2]
Variable type Lb [3]
Astrometry
Radial velocity (Rv)−10.46±0.53 [6] km/s
Proper motion (μ)RA: +14.964 mas/yr [1]
Dec.: +32.742 mas/yr [1]
Parallax (π)8.9360±0.2356  mas [1]
Distance 365 ± 10  ly
(112 ± 3  pc)
Absolute magnitude  (MV)−1.5 [7]
Details
Mass 2.96±0.5 [8]   M☉
Radius 100.17+2.67
−2.81 [9]   R☉
Luminosity 1,716 [10]   L☉
Temperature 3,702 [10]   K
Metallicity [Fe/H]−2.25 [7]   dex
Other designations
λ Aqr, 73 Aquarii, BD−08°968, FK5 864, HD 216386, HIP 112961, HR 8698, SAO 146362 [11]
Database references
SIMBAD data

Lambda Aquarii is a variable star in the equatorial constellation of Aquarius. The apparent visual magnitude of this star ranges from 3.57 down to 3.80, [3] which is bright enough to be visible with the naked eye. The star is eclipsed by the sun from about 1-4 March; [12] thus the star can be viewed the whole night, crossing the sky, in early September, in the current epoch. Lambda Aquarii is located at a distance of 365 light-years (112  pc ) from the Sun based on parallax, [1] but is drifting closer with a radial velocity of −10.5 km/s. [6]

Contents

This star lies just 0.39 degrees south of the ecliptic [13] and so is subject to lunar and planetary occultations. [14] [15] [16] On 16 April 2014, it was occulted by Venus as viewed from Australia, New Zealand and the West Pacific. [17]

Naming

The name Lambda Aquarii is Latinized from the Bayer designation λ Aquarii, and abbreviated Lambda Aqr or λ Aqr.

This star has been called Hydor [18] ( /ˈhaɪdɔːr/ ) from the ancient Greek Ὕδωρ "water", a name given by Proclus, according to Richard Hinckley Allen. Another Greek name for the star is Ekkhysis, from εκχυσις "outpouring". [19] These names originally referred to a constellation of faint stars in the region of Aquarius and Cetus; they were associated with this star by Bayer's Uranometria (1603) and Allen's Star Names (1899). [20] However, the IAU Working Group on Star Names decided to officially adopt the name Hydor for 2 Ceti, since there are other cultural names for λ Aquarii. [21]

In Indian astronomy, this is the main star of the nakshatra Satabhisa or Shatabhisha (spelled Catabhisaj by Allen), meaning "a hundred physicians". [19] [22] Some sources instead attribute this name to γ Aquarii (Sadachbia), which is likely a reading or writing error. [22] λ Aquarii also has the Tibetan name Mondru. [20]

In Chinese, 壘壁陣 (Lěi Bì Zhèn), meaning Line of Ramparts , refers to an asterism consisting of λ Aquarii, κ Capricorni, ε Capricorni, γ Capricorni, δ Capricorni, ι Aquarii, σ Aquarii, φ Aquarii, 27 Piscium, 29 Piscium, 33 Piscium and 30 Piscium. [23] Consequently, λ Aquarii itself is 壘壁陣七 (Lěi Bì Zhèn qī, English: the Seventh Star of Line of Ramparts). [24]

Properties

A visual band light curve for Lambda Aquarii, plotted from data published by Tabur et al. (2009). The inset plot shows the same data folded with a period of 24.5 days, after a linear trend had been removed. LambdaAqrLightCurve.png
A visual band light curve for Lambda Aquarii, plotted from data published by Tabur et al. (2009). The inset plot shows the same data folded with a period of 24.5 days, after a linear trend had been removed.

The stellar classification of Lambda Aquarii is M2.5 IIIa Fe–1, [5] indicating this is an aging red giant star with an underabundance of iron showing in its spectrum. This star is on the asymptotic giant branch and is generating energy through the nuclear fusion of hydrogen and helium along concentric shells surrounding an inert core of carbon and oxygen. [4] With 3.6 [26] times the mass of the Sun, it has expanded to 100 [9] times the Sun's radius.

Lambda Aquarii has a magnetic field with an effective strength measured at 220±60  Gauss . [27] It is classified as slow irregular variable and pulsation periods of 24.5, 32.0, and 49.5 days have been identified. [25] On average, it is radiating nearly 1,600 times the luminosity of the Sun from the photosphere at an effective temperature of 3,702 K. [10]

References

  1. 1 2 3 4 5 6 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv: 2208.00211 . Bibcode:2023A&A...674A...1G. doi: 10.1051/0004-6361/202243940 . S2CID   244398875. Gaia DR3 record for this source at VizieR.
  2. 1 2 3 Gutierrez-Moreno, Adelina; et al. (1966). "A System of photometric standards". Publ. Dept. Astron. Univ. Chile. 1. Publicaciones Universidad de Chile, Department de Astronomy: 1–17. Bibcode:1966PDAUC...1....1G.
  3. 1 2 3 Samus, N. N.; Kazarovets, E. V.; et al. (2017). "General Catalogue of Variable Stars" . Astronomy Reports. 61 (1) (5.1 ed.): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID   125853869 . Retrieved 2019-11-23.
  4. 1 2 Lebzelter, T.; Hron, J. (January 2008). "BRITE stars on the AGB". Communications in Asteroseismology. 152: 178–181. Bibcode:2008CoAst.152..178L. doi: 10.1553/cia152s178 .
  5. 1 2 Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv: 0806.2878 . Bibcode:2008MNRAS.389..869E. doi: 10.1111/j.1365-2966.2008.13596.x . S2CID   14878976.
  6. 1 2 Famaey, B.; et al. (May 2009). "Spectroscopic binaries among Hipparcos M giants. I. Data, orbits, and intrinsic variations". Astronomy and Astrophysics. 498 (2): 627–640. arXiv: 0901.0934 . Bibcode:2009A&A...498..627F. doi:10.1051/0004-6361/200810698. S2CID   18739721.
  7. 1 2 Dupree, A. K.; et al. (October 2007). "Hubble Space Telescope Observations of Chromospheres in Metal-Deficient Field Giants". The Astronomical Journal. 134 (4): 1348–1359. arXiv: 0709.1709 . Bibcode:2007AJ....134.1348D. doi:10.1086/520925. S2CID   14481140.
  8. ↑ Halabi, Ghina M.; Eid, Mounib El (2015). "Exploring masses and CNO surface abundances of red giant stars". Monthly Notices of the Royal Astronomical Society. 451 (3): 2957. arXiv: 1507.01517 . Bibcode:2015MNRAS.451.2957H. doi: 10.1093/mnras/stv1141 . S2CID   118707332.
  9. 1 2 Baines, Ellyn K.; et al. (November 2021). "Angular Diameters and Fundamental Parameters of Forty-Four Stars from the Navy Precision Optical Interferometer". The Astronomical Journal. 162 (5): 198. arXiv: 2211.09030 . Bibcode:2021AJ....162..198B. doi: 10.3847/1538-3881/ac2431 . ISSN   0004-6256.
  10. 1 2 3 McDonald, I.; et al. (October 2017). "Fundamental parameters and infrared excesses of Tycho-Gaia stars". Monthly Notices of the Royal Astronomical Society. 471: 770–791. arXiv: 1706.02208 . doi: 10.1093/mnras/stx1433 . ISSN   0035-8711. Lambda Aquarii's database entry at VizieR.
  11. ↑ "* lam Aqr". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2012-07-01.
  12. ↑ Ford, Dominic. "In-The-Sky.org Planetarium" . Retrieved 2021-06-07.
  13. ↑ John Pratt's stars re-publication by Dr J.P. Pratt (Doctor of Astronomy, University of Arizona) of sidereal coordinate data. Note: possibly a non-book published source.
  14. ↑ Schmidtke, P. C.; Africano, J. L. (January 2011). "KPNO Lunar Occultation Summary. III". The Astronomical Journal. 141 (1): 7. Bibcode:2011AJ....141...10S. doi:10.1088/0004-6256/141/1/10. S2CID   120313180. 10.
  15. ↑ Nather, R. Edward; et al. (June 1970). "The Angular Diameter of Lambda Aquarii". Astrophysical Journal. 160: L181. Bibcode:1970ApJ...160L.181N. doi:10.1086/180555.
  16. ↑ Dyachenko, V.; et al. (August 2018). "Lunar occultation observations at the SAO RAS 6-m telescope". Monthly Notices of the Royal Astronomical Society. 478 (4): 5683–5688. Bibcode:2018MNRAS.478.5683D. doi: 10.1093/mnras/sty1427 .
  17. ↑ Meeus, Jan (2002). "Mutual occultations of planets". More Mathematical Astronomy Morsels (PDF). pp. 174–185. ISBN   0943396743. Archived from the original (PDF) on 2025-04-05. Retrieved 2025-02-21.
  18. ↑ Kaler, James B. "Hydor". STARS. Retrieved 2017-08-17.
  19. 1 2 Allen, Richard Hinckey. "Star Names: Their Lore and Meaning" . Retrieved 2017-08-17.
  20. 1 2 "Hydor". All Skies Encyclopaedia. IAU Working Group on Star Names . Retrieved 26 August 2025.
  21. ↑ "IAU Catalog of Star Names" . Retrieved 26 August 2025.
  22. 1 2 "Satabhisa". All Skies Encyclopaedia. IAU Working Group on Star Names . Retrieved 26 August 2025.
  23. ↑ (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.
  24. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日 Archived 2011-05-21 at the Wayback Machine
  25. 1 2 Tabur, V.; et al. (December 2009). "Long-term photometry and periods for 261 nearby pulsating M giants". Monthly Notices of the Royal Astronomical Society . 400 (4): 1945–1961. arXiv: 0908.3228 . Bibcode:2009MNRAS.400.1945T. doi: 10.1111/j.1365-2966.2009.15588.x . S2CID   15358380.
  26. ↑ Tsuji, Takashi (May 2007). Kupka, F.; et al. (eds.). "Convection in Astrophysics, Proceedings of IAU Symposium #239 held 21-25 August, 2006 in Prague, Czech Republic". Proceedings of the International Astronomical Union. 2: 307–310. arXiv: astro-ph/0610180 . Bibcode:2007IAUS..239..307T. doi:10.1017/S1743921307000622. S2CID   119362842. Isotopic abundances of Carbon and Oxygen in Oxygen-rich giant stars.
  27. ↑ Rustem, Abdurepqet; et al. (September 2023). "A Catalog and Statistical Analysis for Magnetic Stars". Research in Astronomy and Astrophysics. 23 (9). id. 095024. arXiv: 2307.12315 . Bibcode:2023RAA....23i5024R. doi:10.1088/1674-4527/ace9b0.
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