# Astronomy:Zeta Equulei

Observation data Epoch J2000      Equinox J2000 Constellation The location of ζ Equulei (circled) Equuleus 21h 04m 34.65147s[1] +5° 30′ 10.3032″[1] 5.593[2] K5 III[3] +1.934[2] +1.651[2] Radial velocity (Rv) –15.26 ± 0.2[4] km/s Proper motion (μ) RA: +13.15[1] mas/yr Dec.: +0.66[1] mas/yr Parallax (π) 4.24 ± 0.42[1] mas Distance 770 ± 80 ly (240 ± 20 pc) Absolute magnitude (MV) –1.02[5] Radius 63[6] R☉ Luminosity 949[7] L☉ Temperature 3,893[8] K Rotational velocity (v sin i) 4.6[7] km/s ζ Equ, 3 Equ, BD+04° 4606, HD 200644, HIP 104031, HR 8066, SAO 126518.[9] SIMBAD data

ζ Equulei (Latinised to Zeta Equulei, abbreviated to ζ Equ or Zeta Equ) is a single[3] star located in the small northern constellation of Equuleus. It is faintly visible to the naked eye at an apparent visual magnitude of 5.6.[2] Based upon an annual parallax shift of 4.24 mas,[1] Zeta Equulei is roughly 770 light-years (240 parsecs) distant from Earth, give or take an 80 light-year margin of error. At that distance, the apparent brightness of the star is diminished by 0.15 in visual magnitude because of extinction from interstellar gas and dust.[4]

## Properties

Zeta Equulei is an evolved giant star with a stellar classification of K5 III.[3] The measured angular diameter of this star, after correction for limb darkening, is 2.44 ± 0.03 mas.[10] At the estimated distance of Delta Ophiuchi,[1] this yields a physical size of about 63 times the radius of the Sun.[6] It is radiating an estimated 949[7] times the luminosity of the Sun from this expanded outer envelope at an effective temperature of 3,893 K.[8] At this heat, it shines with the orange-hued glow of a K-type star.[11]

## References

1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode2007A&A...474..653V.
2. Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars 8: 59, Bibcode1984SAAOC...8...59C.
3. 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, doi:10.1111/j.1365-2966.2008.13596.x, Bibcode2008MNRAS.389..869E.
4. Famaey, B. et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics 430 (1): 165–186, doi:10.1051/0004-6361:20041272, Bibcode2005A&A...430..165F.
5. Ryon, Jenna; Shetrone, Matthew D.; Smith, Graeme H. (August 2009), "Comparing the Ca ii H and K Emission Lines in Red Giant Stars", Publications of the Astronomical Society of the Pacific 121 (882): 842–856, doi:10.1086/605456, Bibcode2009PASP..121..842R.
6. 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:
\displaystyle{ \begin{align} 2\cdot R_* & = \frac{(240\cdot 2.44\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 126\cdot R_{\bigodot} \end{align} }
7. Henry, Gregory W. et al. (September 2000), "Photometric Variability in a Sample of 187 G and K Giants", The Astrophysical Journal Supplement Series 130 (1): 201–225, doi:10.1086/317346, Bibcode2000ApJS..130..201H.
8. Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics 515: A111, doi:10.1051/0004-6361/201014247, Bibcode2010A&A...515A.111S.
9. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, doi:10.1051/0004-6361:20042039, Bibcode2005A&A...431..773R
10. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-07-21.