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Pi Arietis

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Pi Arietis

Pi Arietis
Diagram showing star positions and boundaries of the Aries constellation and its surroundings

Location of π Arietis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aries
Right ascension 02h 49m 17.55924s[1]
Declination +17° 27′ 51.5168″[1]
Apparent magnitude (V) 5.21[2]
Spectral type B6 V + A0 V + F8 V[3]
U−B color index –0.47[2]
B−V color index –0.06[2]
Radial velocity (Rv) +8.8[4] km/s
Proper motion (μ) RA: +2.60[1] mas/yr
Dec.: –14.10[1] mas/yr
Parallax (π) 4.18 ± 0.69[1] mas
Distance approx. 800 ly
(approx. 240 pc)
Rotational velocity (v sin i) 70[5] km/s
Other designations
42 Arietis, BD+16 355, HD 17543, HIP 13165, HR 836, SAO 93127.[6]

Pi Arietis (π Ari, π Arietis) is the Bayer designation for a multiple star system in the northern constellation of Aries. Based upon parallax measurements made during the Hipparcos mission, this system is approximately 800 light-years (250 parsecs) distant from Earth and has an apparent visual magnitude of 5.21. This is bright enough to be faintly seen with the naked eye.

The primary member of this system is a massive, B-type main sequence star with a stellar classification of B6 V. It is a close spectroscopic binary with an orbital period of 3.854 days, an eccentricity of 0.04, and a combined visual magnitude of 5.30. At an angular separation of 3.28 arcseconds is a magnitude 8.46 A-type main sequence star with a classification of A0 Vp. Finally, a fourth member of the system is a magnitude 11.0 F-type main sequence star with a classification of F8V at an angular separation of 25.2 arcseconds from the primary.[3]


This star, along with δ Ari, ε Ari, ζ Ari, and ρ3 Ari, were Al Bīrūnī's Al Buṭain (ألبطين), the dual of Al Baṭn, the Belly.[7] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Buṭain were the title for five stars : δ Ari as Botein, π Ari as Al Buṭain I, ρ3 Ari as Al Buṭain II, ε Ari as Al Buṭain III dan ζ Ari as Al Buṭain IV.[8]

In Chinese, 左更 (Zuǒ Gēng), meaning Official in Charge of the Forest, refers to an asterism consisting of π Arietis, ν Arietis, μ Arietis, ο Arietis and σ Arietis.[9] Consequently, π Arietis itself is known as 左更五 (Zuǒ Gēng wu, English: the Fifth Star of Official in Charge of the Forest.)[10]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction",  
  2. ^ a b c Crawford, D. L.; Barnes, J. V.; Golson, J. C. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal 76: 1058,  
  3. ^ a b Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems",  
  4. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington,  
  5. ^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365,  
  6. ^ "42 Ari -- Star", SIMBAD Astronomical Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-08-07. 
  7. ^  
  8. ^ Rhoads, Jack W. (November 15, 1971), "Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars" (PDF), Jet Propulsion Laboratory, California Institute of Technology. 
  9. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  10. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 21 日

External links

  • Aladin previewer
  • Aladin sky atlas
  • HR 836
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