Scorpius-Centaurus Association

The Scorpius-Centaurus Association (sometimes called Sco-Cen) 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 from380 to 470 light years [cite journal|title=A Hipparcos Census of Nearby OB Associations|author=de Zeeuw, P.T., Hoogerwerf, R., de Bruijne, J.H.J., Brown, A.G.A., & Blaauw, A.|year=1999|journal=Astronomical Journal|volume=117|pages=354–399|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....117..354D&db_key=AST&data_type=HTML&format=&high=451740036526807|doi=10.1086/300682] . 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 blue 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 [cite journal|title=The Nearest OB Association: Scorpius-Centaurus (Sco OB2)|author=Preibisch, T., Mamajek, E.|year=2009|journal=Handbook of Star-Forming Regions|volume=2|pages=0|url=http://adsabs.harvard.edu/abs/2008arXiv0809.0407P|year=2009] . Hundreds of stars have beenidentified 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) [cite journal| title=Exploring the Full Stellar Population of the Upper Scorpius OB Association| author=Preibisch, T., et al.|journal=Astronomical Journal|volume=124|pages=404–416|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....124..404P&db_key=AST&data_type=HTML&format=&high=451740036524099| doi=10.1086/341174| year=2002] ,and the total stellar population in each of the three subgroups is probablyof the order 1000-2000 [cite journal|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....124.1670M&db_key=AST&data_type=HTML&format=&high=451740036525142
author=Mamajek, E.E., Meyer, M.R., & Liebert, J.|year=2002|journal=Astronomical Journal
volume=124|pages=1670–1694|title=Post-T Tauri Stars in the Nearest OB Association|doi=10.1086/341952] .

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 [cite journal| title=Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations|author=Madsen, S., et al.|year=2002 |journal=Astronomy & Astrophysics|volume=381|pages=446–463|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002A%26A...381..446M&db_key=AST&data_type=HTML&format=&high=451740036522959| doi=10.1051/0004-6361:20011458] , and the group is most likely gravitationally unbound. Several supernovae have exploded in Sco-Cenover the past 15 million years, leaving a network of expanding gas superbubbles around the group [cite journal| year=1992| url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1992A%26A...262..258D&db_key=AST&data_type=HTML&format=&high=451740036521723
author=de Geus, E.J.| title=Interaction of Stars and Interstellar Matter in Scorpio Centaurus| journal=Astronomy & Astrophysics|volume=262|pages=258–270] , including the Loop I Bubble. To explain the presence of radioactive ⁶⁰Fe in deep oceanferromanganese crusts, it has been hypothesized that a nearby supernova, possiblya member of Sco-Cen, exploded in the Sun's vicinity roughly 3 million years ago [cite journal| year=2005| url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005ApJ...621..902F&db_key=AST&data_type=HTML&format=&high=451740036519929| author=Fields, B.D., Hochmuth, K.A., & Ellis, J.| title=Deep-Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis| journal=Astrophys. J.| volume=621| pages=902–907| doi=10.1086/427797] .

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