Scorpius-Centaurus Association

The Scorpius-Centaurus Association (sometimes called Sco-Cen or Sco OB2) is the nearest OB Association to the Sun. This stellar association is composed of three subgroups (Upper Scorpius, Upper Centaurus-Lupus, and Lower Centaurus-Crux), whose mean distances range from 380 to 470 light years[1].

The Sco-Cen subgroups range in age from 5 million years (Upper Scorpius) to roughly 15 million years (Upper Centaurus-Lupus and Lower Centaurus-Crux). Many of the bright stars in the constellations Scorpius, Lupus, Centaurus, and Crux are members of the Sco-Cen association, including Antares (the most massive member of Upper Scorpius), and most of the stars in the Southern Cross[2]. Hundreds of stars have been identified as members of Sco-Cen, with masses ranging from roughly 15 solar masses (Antares) down to below the hydrogen-burning limit (i.e. brown dwarfs)[3], and the total stellar population in each of the three subgroups is probably of the order 1000-2000[4]. The Sco-Cen OB association appears to be the most pronounced part of a large complex of recent (<20 million years) and ongoing star-formation. The complex contains several star-forming molecular clouds in Sco-Cen's immediate vicinity—the Rho Oph, Pipe Nebula, Barnard 68, Chamaeleon, Lupus, Corona Australis, and Coalsack cloud complexes (all at distances of ~120-200 parsecs), and several less populous, young stellar groups on the periphery of Sco-Cen, including the ~3-5 million-year-old epsilon Cha group, ~7 million-year-old eta Chamaeleontis cluster (also called Mamajek 1), ~8 million-year-old TW Hydrae association, ~12 million-year-old Beta Pictoris moving group, and possibly the ~30-50 million-year-old IC 2602 open cluster[2].

The stellar members of the Sco-Cen association have convergent proper motions of approximately 0.02-0.04 arcseconds per year, indicative that the stars have nearly parallel velocity vectors, moving at about 20 km/s with respect to the Sun. The dispersion of the velocities within the subgroups are only of order 1–2 km/s[5], and the group is most likely gravitationally unbound. Several supernovae have exploded in Sco-Cen over the past 15 million years, leaving a network of expanding gas superbubbles around the group[6], including the Loop I Bubble. To explain the presence of radioactive 60Fe in deep ocean ferromanganese crusts, it has been hypothesized that a nearby supernova, possibly a member of Sco-Cen, exploded in the Sun's vicinity roughly 3 million years ago[7].

References

  1. ^ de Zeeuw, P.T., Hoogerwerf, R., de Bruijne, J.H.J., Brown, A.G.A., & Blaauw, A. (1999). "A Hipparcos Census of Nearby OB Associations". Astronomical Journal 117 (1): 354–399. arXiv:astro-ph/9809227. Bibcode 1999AJ....117..354D. doi:10.1086/300682. 
  2. ^ a b Preibisch, T., Mamajek, E. (2009). "The Nearest OB Association: Scorpius-Centaurus (Sco OB2)". Handbook of Star-Forming Regions 2: 0. arXiv:0809.0407. Bibcode 2008hsf2.book..235P. 
  3. ^ Preibisch, T., et al. (2002). "Exploring the Full Stellar Population of the Upper Scorpius OB Association". Astronomical Journal 124 (1): 404–416. Bibcode 2002AJ....124..404P. doi:10.1086/341174. 
  4. ^ Mamajek, E.E., Meyer, M.R., & Liebert, J. (2002). "Post-T Tauri Stars in the Nearest OB Association". Astronomical Journal 124 (3): 1670–1694. arXiv:astro-ph/0205417. Bibcode 2002AJ....124.1670M. doi:10.1086/341952. 
  5. ^ Madsen, S., et al. (2002). "Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations". Astronomy & Astrophysics 381 (2): 446–463. arXiv:astro-ph/0110617. Bibcode 2002A&A...381..446M. doi:10.1051/0004-6361:20011458. 
  6. ^ de Geus, E.J. (1992). "Interaction of Stars and Interstellar Matter in Scorpio Centaurus". Astronomy & Astrophysics 262: 258–270. Bibcode 1992A&A...262..258D. 
  7. ^ Fields, B.D., Hochmuth, K.A., & Ellis, J. (2005). "Deep-Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis". Astrophys. J. 621 (2): 902–907. arXiv:astro-ph/0410525. Bibcode 2005ApJ...621..902F. doi:10.1086/427797.