Pi1 Orionis

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π1 Orionis
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The location of Pi1 Orionis (π1) in the constellation of Orion (shown as a red circle with a red center).
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Orion
Right ascension 04h 54m 53.72877s[1]
Declination +10° 09′ 02.9952″[1]
Apparent magnitude (V) 4.74[2]
Spectral type A3 Va[3]
U−B color index +0.09[2]
B−V color index +0.08[2]
Proper motion (μ) RA: +41.49[1] mas/yr
Dec.: −128.73[1] mas/yr
Parallax (π) 28.04 ± 0.25[1] mas
Distance 116 ± 1 ly
(35.7 ± 0.3 pc)
Absolute magnitude (MV) 1.76±0.08[4]
Mass 1.97±0.07[4] M
Radius 1.67[5] R
Luminosity 16.6[5] L
Surface gravity (log g) 4.15[3] cgs
Temperature 8,611[3] K
Metallicity [Fe/H] −1.24[3] dex
Rotational velocity (v sin i) 120[6] km/s
Age 100[5] Myr
Other designations
π1 Ori, 7 Orionis, BD+09° 683, HD 31295, HIP 22845, HR 1570, SAO 94201.[7]
Database references

Pi1 Orionis1 Ori, π1 Orionis) is a star in the equatorial constellation of Orion. It is faintly visible to the naked eye with an apparent visual magnitude of 4.74.[2] Based upon an annual parallax shift of 28.04 mas,[1] it is located about 116 light years from the Sun.

This is an A-type main sequence star with a stellar classification of A3 Va.[3] It is a Lambda Boötis star,[8] which means the spectrum shows lower than expected abundances for heavier elements.[9] Pi1 Orionis is a relatively young star, just 100 million years old,[5] and is spinning fairly rapidly with a projected rotational velocity of 120 km/s.[6] It has nearly double[4] the mass of the sun and 167% of the Sun's radius. The star radiates 16.6[5] times the solar luminosity from its outer atmosphere at an effective temperature of 8,611 K.[3]

An infrared excess indicates there is a debris disk with a temperature of 80 K orbiting 49 AU from the star. The dust has a combined mass 2.2% that of the Earth.[5]


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b c d e f 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, Bibcode:2006AJ....132..161G, arXiv:astro-ph/0603770Freely accessible, doi:10.1086/504637. 
  4. ^ a b c Gerbaldi, M.; et al. (June 1999), "Search for reference A0 dwarf stars: Masses and luminosities revisited with HIPPARCOS parallaxes", Astronomy and Astrophysics Supplement, 137: 273–292, Bibcode:1999A&AS..137..273G, doi:10.1051/aas:1999248. 
  5. ^ a b c d e f Rhee, Joseph H.; et al. (May 2007), "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs", The Astrophysical Journal, 660 (2): 1556–1571, Bibcode:2007ApJ...660.1556R, arXiv:astro-ph/0609555Freely accessible, doi:10.1086/509912. 
  6. ^ a b Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, Bibcode:2007A&A...463..671R, arXiv:astro-ph/0610785Freely accessible, doi:10.1051/0004-6361:20065224. 
  7. ^ "* pi.01 Ori". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-11-15. 
  8. ^ Gray, R. O.; Corbally, C. J. (August 1993), "A search for Lambda Bootis stars in OB associations", Astronomical Journal, 106 (2): 632–636, Bibcode:1993AJ....106..632G, doi:10.1086/116668. 
  9. ^ Kamp, I.; et al. (April 2008), "λ Bootis stars: Current status and new insights from Spitzer", Contributions of the Astronomical Observatory Skalnaté Pleso, 38 (2): 147–156, Bibcode:2008CoSka..38..147K.