Lambda Aquarii

Lambda Aquarii
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]
Distance365 ± 10 ly
(112 ± 3 pc)
Absolute magnitude (MV)−1.5[7]
Details
Mass2.96±0.5[8] M☉
Radius100.17+2.67
−2.81[9] R☉
Luminosity1,716[10] L☉
Temperature3,702[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
SIMBADdata

Lambda Aquarii, informally known as Hydor (/ˈhaɪdɔːr/),[12][13] is a variable star in the equatorial constellation of Aquarius. The name is Latinized from the Bayer designation λ Aquarii. 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. It lies just 0.39 degrees south of the ecliptic[14] and so is subject to lunar occultations.[15][16] The star is eclipsed by the sun from about 1-4 March;[17] 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]

A visual band light curve for Lambda Aquarii, plotted from data published by Tabur et al. (2009).[18] 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[19] times the mass of the Sun, it has expanded to 100[9] times the Sun's radius. It is classified as slow irregular variable and pulsation periods of 24.5, 32.0, and 49.5 days have been identified.[18] 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]

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  2. ^ a b c Cite error: The named reference sps1966 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference Samus2017 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference cia152_178 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference mnras389_2_869 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference aaa498_2_627 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference aj134_4_1348 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference halabi was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference baines2021 was invoked but never defined (see the help page).
  10. ^ a b c Cite error: The named reference tycho-gaia was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Kaler was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Allen was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Pratt was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Schmidtke_Africano_2011 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Nather_et_al_1970 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference in-the-sky was invoked but never defined (see the help page).
  18. ^ a b Cite error: The named reference mnras400_4_1945 was invoked but never defined (see the help page).
  19. ^ Cite error: The named reference tsuji2007 was invoked but never defined (see the help page).