Astronomy:Pi Hydrae

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Short description: Star in the constellation Hydra
Pi Hydrae
Location of π Hydra (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Hydra
Right ascension  14h 06m 22.29749s[1]
Declination −26° 40′ 56.5024″[1]
Apparent magnitude (V) 3.25[2]
Characteristics
Evolutionary stage horizontal branch[3]
Spectral type K1 III–IV[4] or K2-III Fe-0.5[5]
U−B color index +1.040[6]
B−V color index +1.120[6]
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[1] mas
Distance101.0 ± 0.5 ly
(31.0 ± 0.2 pc)
Absolute magnitude (MV)0.79[7]
Details[8]
Mass1.40±0.21 M☉
Radius12.49±0.49 R☉
Luminosity60.8±2.6 L☉
Surface gravity (log g)2.40±0.11 cgs
Temperature4,565±75 K
Metallicity [Fe/H]−0.16±0.10 dex
Rotational velocity (v sin i)2.25[9] km/s
Age6.29±3.05 Gyr
Other designations
π Hya, Pi Hya, 49 Hydrae, CPD−26°5170, FK5 519, HD 123123, HIP 68895, HR 5287, SAO 182244[10]
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,[4] 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 61 times the Sun's luminosity from its outer envelope with an effective temperature of 4,565 K,[8] giving it the orange hue of a K-type star.[11]

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.[12]

In Chinese astronomy, π Hydrae forms with γ Hydrae the asterism Ping (平), representing a judge.[13] The Chinese name for π Hydrae itself is Ping èr (平二), the second star of Ping.[14] R. H. Allen's 1899 book Star Names instead claimed the Chinese name Ping Sing, translated as "a Tranquil Star", for ι Hydrae (Ukdah).[15]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V 
  2. ↑ 2.0 2.1 2.2 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. ↑ Stock, Stephan; Reffert, Sabine; Quirrenbach, Andreas (2018). "Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search". Astronomy and Astrophysics 616: A33. doi:10.1051/0004-6361/201833111. Bibcode: 2018A&A...616A..33S. 
  4. ↑ 4.0 4.1 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, doi:10.1086/504637, Bibcode: 2006AJ....132..161G 
  5. ↑ Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series 71: 245, doi:10.1086/191373, Bibcode: 1989ApJS...71..245K. 
  6. ↑ 6.0 6.1 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, doi:10.1093/mnras/172.3.667, Bibcode: 1975MNRAS.172..667J 
  7. ↑ Hekker, S. et al. (August 2006), "Precise radial velocities of giant stars. I. Stable stars", Astronomy and Astrophysics 454 (3): 943–949, doi:10.1051/0004-6361:20064946, Bibcode: 2006A&A...454..943H 
  8. ↑ 8.0 8.1 Reffert, Sabine; Bergmann, Christoph; Quirrenbach, Andreas; Trifonov, Trifon; Künstler, Andreas (2015-02-01). "Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity". Astronomy and Astrophysics 574: A116. doi:10.1051/0004-6361/201322360. ISSN 0004-6361. Bibcode: 2015A&A...574A.116R. 
  9. ↑ 9.0 9.1 Hekker, S.; Meléndez, J. (December 2007), "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters", Astronomy and Astrophysics 475 (3): 1003–1009, doi:10.1051/0004-6361:20078233, Bibcode: 2007A&A...475.1003H 
  10. ↑ "49 Hya -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Pi+Hydrae, retrieved 2012-01-16 
  11. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16 
  12. ↑ Luck, R. Earle (February 1991), "Chemical abundances for cyanogen-weak giants", Astrophysical Journal Supplement Series 75: 579–610, doi:10.1086/191542, Bibcode: 1991ApJS...75..579L 
  13. ↑ Ridpath, Ian. "Star Tales – Hydra". http://ianridpath.com/startales/hydra.html. 
  14. ↑ "AEEA 天文教育資訊網" (in zh). http://aeea.nmns.edu.tw/2006/0606/ap060627.html. 
  15. ↑ Allen, R. H. (1899), Star Names: Their Lore and Meaning, p. 249, https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Hydra*.html 



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