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] |
| U−B color index | +1.040[4] |
| B−V color index | +1.120[4] |
| 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 |
| Distance | 101.0 ± 0.5 ly (31.0 ± 0.2 pc) |
| Absolute magnitude (MV) | 0.79[5] |
| Details | |
| Mass | 1.76[5] to 2.45[6] M☉ |
| Radius | 12–13[7] R☉ |
| Surface gravity (log g) | 2.65[8] cgs |
| Temperature | 4,670[8] K |
| Metallicity [Fe/H] | 0.04[9] dex |
| Rotational velocity (v sin i) | 2.25[8] km/s |
| Other designations | |
Pi Hydrae (π Hya, 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.[8] Pi Hydrae is radiating energy from its outer envelope with an effective temperature of 4,670 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.[9] The measured angular diameter of this star, after correction for limb darkening, is 3.76 ± 0.04 mas.[12] At its estimated distance, this yields a physical size of about 12–13 times the radius of the Sun.[7] It has an estimated mass of 2.45 times the mass of the Sun.[6]
References
- ↑ 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, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ↑ 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 (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W
- ↑ 3.0 3.1 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, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637
- ↑ 4.0 4.1 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: 667–679, Bibcode:1975MNRAS.172..667J
- ↑ 5.0 5.1 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
- ↑ 6.0 6.1 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
- ↑ 7.0 7.1 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:
- ↑ 8.0 8.1 8.2 8.3 8.4 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
- ↑ 9.0 9.1 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
- ↑ "49 Hya -- Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-16
- ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
- ↑ Richichi; 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
External links
- Kaler, James B., "PI HYA (Pi Hydrae)", Stars (University of Illinois), retrieved 2012-01-16
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