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Mu2 Scorpii

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For other star systems with a similar Bayer designation, see Mu Scorpii.
μ2 Scorpii
(Pipirima)
Location of μ2 Scorpii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 16h 52m 20.14532s[1]
Declination −38° 01′ 03.1258″[1]
Apparent magnitude (V) +3.56[2]
Characteristics
Evolutionary stage subgiant[3]
Spectral type B2 IV[4]
U−B color index −0.878[2]
B−V color index −0.219[2]
Astrometry
Radial velocity (Rv)+1.4[5] km/s
Proper motion (μ) RA: −11.09[1] mas/yr
Dec.: −23.32[1] mas/yr
Parallax (π)6.88±0.12 mas[1]
Distance474 ± 8 ly
(145 ± 3 pc)
Absolute magnitude (MV)−2.25[6]
Details[3]
Mass9.1±0.3 M☉
Radius5.6±0.2 R☉
Luminosity2,385[7] L☉
Surface gravity (log g)3.8±0.2 cgs
Temperature21,700±900 K
Rotational velocity (v sin i)58[8] km/s
Age20±4 Myr
Other designations
Pipirima, μ2 Sco, CD−37°11037, HD 151985, HIP 82545, HR 6252, SAO 208116[9]
Database references
SIMBADdata
Exoplanet Archivedata

Mu2 Scorpii, also named Pipirima /pɪˈpɪrɪmə/,[10] is a star in the zodiac constellation of Scorpius. It has an apparent visual magnitude of +3.56,[2] which is bright enough to be seen with the naked eye. Its distance from the Sun is about 474 light-years, as determined by parallax measurements.[1] It is a member of the Upper Centaurus–Lupus subgroup of the Scorpius–Centaurus association.[11] A super-Jupiter or brown dwarf is known to orbit it, and another is suspected.[3]

Nomenclature

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μ2 Scorpii (Latinised to Mu2 Scorpii, abbreviated μ2 Sco, Mu2 Sco) is the star's Bayer designation.

A traditional Polynesian story is told of a brother and sister who flee their parents into the sky and become stars. In one account, the children become Shaula and Lesath in the tip of the tail of Scorpius,[12] and in another they become Mu2 and Mu1 Scorpii.[13][14] In the Tahitian version of this story, the brother and sister are named Pipiri and Rehua, and their parents call them Pipiri ma while chasing them into the sky: ma "with, and" is used after names to mean "et al."[12][15] (In a similar version of the story told in the Cook Islands, they become Omega1 and Omega2 Scorpii).[12]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN approved the name Pipirima for this star on 5 September 2017 (along with Xamidimura for its partner) and it is now so included in the List of IAU-approved Star Names.[10]

In Chinese astronomy, Mu2 Scorpii is identified as the second added star of the Tail asterism (Chinese: 尾宿增二; pinyin: Wěi Xiù zēng èr).[18] It was historically called Shengong (Chinese: 神宮; pinyin: Shéngōng),[19] a name which was later applied to the star cluster NGC 6231, and has been adopted by the IAU Working Group on Star Names for the star HD 153072.[20]

Properties

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Mu2 Scorpii is a blue-white B-type subgiant star with a stellar classification of B2 IV.[4] It has an estimated diameter of 5.6 solar radii and a mass of 9.1 times the Sun's mass,[3] and shines with 2,385 times the Sun's luminosity.[7] The large mass of this star makes it a supernova progenitor. The outer atmosphere has an effective temperature of 21,700 K. It is some 20 million years old[3] and is spinning with a projected rotational velocity of 58 km/s.[8]

Planetary system

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Two sub-stellar objects slightly above the deuterium burning limit were found in 2022 by direct imaging around Mu2 Scorpii. The outer one, designated μ2 Scorpii b, is definitely an orbiting planet or brown dwarf, and the inner one is a planetary candidate.[3]

The Mu2 Scorpii planetary system[3]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(years) 		Eccentricity Inclination Radius
c (unconfirmed) 18.5±1.5 MJ 18.9+11.7
−5.0 		— 0.61+0.19
−0.32 		62.8+9.9
−16.6° 		—
b 14.4±0.8 MJ 242.4+114.5
−52.1 		— 0.56+0.27
−0.26 		96.6+21.5
−20.5° 		—

References

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  1. ^ a b c d e f 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. ^ a b c d Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement, 15: 459, Bibcode:1968ApJS...15..459G, doi:10.1086/190168.
  3. ^ a b c d e f g Squicciarini, V.; Gratton, R.; Janson, M.; Mamajek, E. E.; Chauvin, G.; Delorme, P.; Langlois, M.; Vigan, A.; Ringqvist, S. C.; Meeus, G.; Reffert, S.; Kenworthy, M.; Meyer, M. R.; Bonnefoy, M.; Bonavita, M.; Mesa, D.; Samland, M.; Desidera, S.; d'Orazi, V.; Engler, N.; Alecian, E.; Miglio, A.; Henning, T.; Quanz, S. P.; Mayer, L.; Flasseur, O.; Marleau, G.-D. (May 2022), "A scaled-up planetary system around a supernova progenitor", Astronomy & Astrophysics, 664: A9, arXiv:2205.02279, Bibcode:2022A&A...664A...9S, doi:10.1051/0004-6361/202243675, S2CID 248524983
  4. ^ a b Hiltner, W. A.; et al. (July 1969), "MK Spectral Types for Bright Southern OB Stars", The Astrophysical Journal, 157: 313, Bibcode:1969ApJ...157..313H, doi:10.1086/150069.
  5. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), "The Revision of the General Catalogue of Radial Velocities", Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E.
  6. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  7. ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
  8. ^ a b Uesugi, Akira; Fukuda, Ichiro (1970), "Catalogue of rotational velocities of the stars", Contributions from the Institute of Astrophysics and Kwasan Observatory, University of Kyoto, Bibcode:1970crvs.book.....U.
  9. ^ "mu.02 Sco", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2016-09-20.
  10. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  11. ^ Bobylev, V. V.; Bajkova, A. T. (September 2007), "Kinematics of the Scorpius–Centaurus OB association", Astronomy Letters, 33 (9): 571–583, arXiv:0708.0943, Bibcode:2007AstL...33..571B, doi:10.1134/S1063773707090010, S2CID 15785349.
  12. ^ a b c Johannes Carl Andersen (1931) Myths and Legends of the Polynesians. 1995 Dover reprint, p.400ff.
  13. ^ Allen, Richard Hinckley (1899), "Scorpio", Star-Names and Their Meanings (1963 Dover reprint ed.), New York: G.E. Stechert, 1899, retrieved 2016-09-22.
  14. ^ "IAU Catalog of Star Names". Retrieved 7 October 2025.
  15. ^ Herbert John Davies, A Tahitian and English dictionary, with introductory remarks on the Polynesian language, and a short grammar of the Tahitian dialect. London Missionary Society, 1851.
  16. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  17. ^ Yi, Shitong (April 1981). 中西对照恒星图表 [Atlas Comparing Chinese and Western Star Maps and Catalogues] (in Chinese). 科学出版社.
  18. ^ Stellarium, citing Yi Shitong, 1981[17]
  19. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 10 日 Archived 2011-05-22 at the Wayback Machine
  20. ^ "Shengong (神宫)". All Skies Encyclopaedia. IAU Working Group on Star Names. Retrieved 7 October 2025.
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