Pi Hydrae
Location of π Hydra (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 14h 06m 22.29749s[1]
Declination –26° 40′ 56.5024″[1]
Apparent magnitude (V) 3.25[2]
Characteristics
Spectral type K1 III–IV[3] or K2-III Fe-0.5[4]
U−B color index +1.040[5]
B−V color index +1.120[5]
Astrometry
Radial velocity (Rv)+26.7[2] km/s
Proper motion (μ) RA: +43.70[1] mas/yr
Dec.: −141.18[1] mas/yr
Parallax (π)32.30 ± 0.16 mas[1]
Distance101.0 ± 0.5 ly
(31.0 ± 0.2 pc)
Absolute magnitude (MV)0.79[6]
Details
Mass1.76[6] to 2.45[7] M☉
Radius12–13[8] R☉
Surface gravity (log g)2.65[9] cgs
Temperature4,670[9] K
Metallicity [Fe/H]0.04[10] dex
Rotational velocity (v sin i)2.25[9] km/s
Other designations
Markeb, π Hya, Pi Hya, 49 Hydrae, CPD26 5170, FK5 519, HD 123123, HIP 68895, HR 5287, SAO 182244[11]
Database references
SIMBADdata

Pi Hydrae, Latinized from π Hydrae, is a star in the constellation Hydra with an apparent visual magnitude of 3.3,[2] making it visible to the naked eye. Parallax measurements put this star at a distance of about 101 light-years (31 parsecs) from the Earth.

The spectrum of this star shows it to have a stellar classification of K1 III-IV,[3] with the luminosity class of 'III-IV' suggesting it is in an evolutionary transition stage somewhere between a subgiant and a giant star. It has a low projected rotational velocity of 2.25 km s−1.[9] Pi Hydrae is radiating energy from its outer envelope with an effective temperature of 4,670 K,[9] giving it the orange hue of a K-type star.[12]

Pi Hydrae is a type of giant known as a cyanogen-weak star, which means that its spectrum displays weak absorption lines of CN− relative to the metallicity. (The last is a term astronomers use when describing the abundance of elements other than hydrogen and helium.) Otherwise, it appears to be a normal star of its evolutionary class, having undergone first dredge-up of nuclear fusion by-products onto its surface layers.[10] The measured angular diameter of this star, after correction for limb darkening, is 3.76 ± 0.04 mas.[13] At its estimated distance, this yields a physical size of about 12–13 times the radius of the Sun.[8] It has an estimated mass of 2.45 times the mass of the Sun.[7]

References

  1. 1 2 3 4 5 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. 1 2 3 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
  3. 1 2 Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992
  4. ↑ Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  5. 1 2 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 (3): 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667
  6. 1 2 Hekker, S.; et al. (August 2006), "Precise radial velocities of giant stars. I. Stable stars", Astronomy and Astrophysics, 454 (3): 943–949, arXiv:astro-ph/0604502, Bibcode:2006A&A...454..943H, doi:10.1051/0004-6361:20064946, S2CID 119529768
  7. 1 2 Edvardsson, B. (January 1988), "Spectroscopic surface gravities and chemical compositions for 8 nearby single sub-giants", Astronomy and Astrophysics, 190 (1–2): 148–166, Bibcode:1988A&A...190..148E
  8. 1 2 Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
  9. 1 2 3 4 5 Hekker, S.; Meléndez, J. (December 2007), "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters", Astronomy and Astrophysics, 475 (3): 1003–1009, arXiv:0709.1145, Bibcode:2007A&A...475.1003H, doi:10.1051/0004-6361:20078233, S2CID 10436552
  10. 1 2 Luck, R. Earle (February 1991), "Chemical abundances for cyanogen-weak giants", Astrophysical Journal Supplement Series, 75: 579–610, Bibcode:1991ApJS...75..579L, doi:10.1086/191542
  11. ↑ "49 Hya -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-16
  12. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16
  13. ↑ Richichi, A.; Percheron, I.; Khristoforova, M. (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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