98 Aquarii

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98 Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg

Location of 98 Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 23h 22m 58.22606s[1]
Declination –20° 06′ 02.0963″[1]
Apparent magnitude (V) +3.97[2]
Spectral type K0 III[3]
U−B color index +0.948[2]
B−V color index +1.089[2]
Radial velocity (Rv) –6.5[4] km/s
Proper motion (μ) RA: –121.28[1] mas/yr
Dec.: –97.59[1] mas/yr
Parallax (π) 19.96 ± 0.23[1] mas
Distance 163 ± 2 ly
(50.1 ± 0.6 pc)
Mass 2.1[5] M
Radius 14[6] R
Surface gravity (log g) 2.4[5] cgs
Temperature 4,630[5] K
Metallicity [Fe/H] –0.30[5] dex
Other designations
b1 Aquarii, BD–20 6587, FK5 1612, HD 220321, HIP 115438, HR 8892, SAO 191858.[7]

98 Aquarii is the Flamsteed designation for a star in the equatorial constellation Aquarius. The Bayer designation for this star is b1 Aquarii. It is visible to the naked eye with an apparent visual magnitude of +3.97.[2] The distance to this star, 163 light-years (50 parsecs), is known from parallax measurements made with the Hipparcos spacecraft.[1]

With over double the mass of the Sun,[5] this is an evolved giant star that has a stellar classification of K0 III.[3] The measured angular diameter of this star is 2.54 ± 0.13 mas.[8] At the estimated distance of 98 Aquarii,[1] this yields a physical size of about 14 times the radius of the Sun.[6] The expanded outer envelope has an effective temperature of 4,630 K,[5] giving it the orange glow of a K-type star.[9]


  1. ^ a b c d e f g 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. 
  2. ^ a b c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society 172: 667–679, Bibcode:1975MNRAS.172..667J. 
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H. 
  4. ^ Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W. 
  5. ^ a b c d e f Melo, C. H. F. et al. (August 2005), "On the nature of lithium-rich giant stars. Constraints from beryllium abundances", Astronomy and Astrophysics 439 (1): 227–235, arXiv:astro-ph/0504133, Bibcode:2005A&A...439..227M, doi:10.1051/0004-6361:20041805. 
  6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1. . The radius (R*) is given by:
    \begin{align} 2\cdot R_*
 & = \frac{(50.1\cdot 2.54\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\
 & \approx 27.4\cdot R_{\bigodot}
  7. ^ "98 Aqr -- Star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2006-11-05. 
  8. ^ Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039. 
  9. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16.