Zeta Hydri

Zeta Hydri, Latinized from ζ Hydri, is a single,[7] white-hued star in the southern constellation of Hydrus. It is faintly visible to the naked eye with an apparent magnitude of 4.83.[2] This distance to this star can be estimated from its annual parallax shift of 11.47 mas,[1] showing it to be about 284 light years away. It is moving further away from the Sun with a radial velocity of +3.6 km/s.[4]

ζ Hydri
Location of ζ Hydri (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hydrus
Right ascension  02h 45m 32.63435s[1]
Declination −67° 36′ 59.8268″[1]
Apparent magnitude (V) 4.83[2]
Characteristics
Spectral type A2IV[2]
U−B color index +0.09[3]
B−V color index +0.06[3]
Astrometry
Radial velocity (Rv)+3.60[4] km/s
Proper motion (μ) RA: +66.41[1] mas/yr
Dec.: +43.38[1] mas/yr
Parallax (π)11.47 ± 0.17[1] mas
Distance284 ± 4 ly
(87 ± 1 pc)
Absolute magnitude (MV)0.13[2]
Details
Mass2.44[5] M☉
Radius3.9[5] R☉
Luminosity79.55[2] L☉
Surface gravity (log g)3.72[6] cgs
Temperature9,144[6] K
Rotational velocity (v sin i)116[6] km/s
Other designations
ζ Hyi, CPD−68° 169, FK5 2191, GC 3354, HD 17566, HIP 12876, HR 837, SAO 248644
Database references
SIMBADdata

The spectrum of this star matches a stellar classification of A2 IV,[2] suggesting it is a subgiant star that is in the process of evolving away from the main sequence as the supply of hydrogen at its core becomes exhausted. It has a high rate of spin, showing a projected rotational velocity of 116 km/s.[6] This is giving the star a slight oblate shape with an equatorial bulge that is 5% larger than the polar radius.[8] It has 2.4 times the mass of the Sun and nearly four times the Sun's radius.[5] Zeta Hydri is radiating 80[2] times the Sun's luminosity into space from its photosphere at an effective temperature of 9,144 K.[6]

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  2. 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. Vizier catalog entry
  3. Mallama, A. (2014). "Sloan Magnitudes for the Brightest Stars". The Journal of the American Association of Variable Star Observers. 42: 443. Bibcode:2014JAVSO..42..443M.Vizier catalog entry
  4. Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W. LCCN 54001336.
  5. Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry
  6. David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. Vizier catalog entry
  7. 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.
  8. Belle, G. T. (2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review. 20: 51. arXiv:1204.2572. Bibcode:2012A&ARv..20...51V. doi:10.1007/s00159-012-0051-2.
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