3 Aquarii

3 Aquarii (abbreviated 3 Aqr) is a variable star in the equatorial constellation of Aquarius. 3 Aquarii is the Flamsteed designation; it also bears the Bayer designation k Aquarii and the variable star designation EN Aquarii. With a mean apparent visual magnitude of 4.429,[2] it is visible to the naked eye in dark skies. It has an annual parallax shift of 5.57 milliarcseconds with a 5% margin of error,[1] which translates to a physical distance of around 590 light-years (180 parsecs) from Earth.

This article is about k Aquarii. It is not to be confused with κ Aquarii.
3 Aquarii
Location of 3 Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 20h 47m 44.23898s[1]
Declination –05° 01′ 39.7220″[1]
Apparent magnitude (V) 4.429[2]
Characteristics
Spectral type M3 III[3]
U−B color index +1.914[2]
B−V color index +1.651[2]
Variable type Lb[4]
Astrometry
Radial velocity (Rv)–22.0[5] km/s
Proper motion (μ) RA: +1.68[1] mas/yr
Dec.: –40.06[1] mas/yr
Parallax (π)5.57 ± 0.28[1] mas
Distance590 ± 30 ly
(180 ± 9 pc)
Absolute magnitude (MV)−1.83[6]
Details
Radius108[7] R☉
Temperature3,933[8] K
Other designations
EN Aqr, BD–05°5378, FK5 1543, HD 198026, HIP 102624, HR 7951, SAO 144814.[9]
Database references
SIMBADdata

With a stellar classification of M3 III,[3] this is a red giant star that has exhausted the hydrogen at its core and evolved away from the main sequence of stars like the Sun. It is classified as a slow irregular variable, type Lb,[4] and the luminosity of this star varies over time, following multiple periods of variability.[10] The measured angular diameter of this star, after correction for limb darkening, is 5.60 ± 0.70 mas.[11] At the estimated distance of 3 Aquarii,[1] this yields a physical size of about 108 times the radius of the Sun.[7] The effective temperature of the outer atmosphere is 3,933 K,[8] giving this star the cool reddish hue of an M-type star.

Pulsation periods[10]
Period
(days)		 Amplitude
(Magnitude)
20.20.020
24.90.038
27.20.027
35.00.021
36.90.024
143.90.022
197.20.027

References
  1. 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.
  2. Gutierrez-Moreno, Adelina; et al. (1966). "A System of photometric standards". Publ. Dept. Astron. Univ. Chile. Publicaciones Universidad de Chile, Department de Astronomy. 1: 1–17. Bibcode:1966PDAUC...1....1G.
  3. Morgan, W. W.; et al. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11: 29. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.
  4. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  5. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W.
  6. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644. Vizier catalog entry
  7. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1.. The radius (R*) is given by:
  8. Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247, S2CID 118362423.
  9. "* k Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-16.
  10. 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.
  11. Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
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