Scorpius-Centaurus Association
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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 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 blue stars in the constellations Scorpius, Lupus (constellation), 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. 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)[2], and the total stellar population in each of the three subgroups is probably of the order 1000-2000[3].
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[4], and the group is mostly like 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[5], 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 [6].
[edit] References
- ^ 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: 354-399.
- ^ Preibisch, T., et al.. "Exploring the Full Stellar Population of the Upper Scorpius OB Association". Astronomical Journal 124: 404-416.
- ^ Mamajek, E.E., Meyer, M.R., & Liebert, J. (2002). "Post-T Tauri Stars in the Nearest OB Association". Astronomical Journal 124: 1670-1694.
- ^ Madsen, S., et al. (2002). "Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations". Astronomy & Astrophysics 381: 446-463.
- ^ de Geus, E.J. (1992). "Interaction of Stars and Interstellar Matter in Scorpio Centaurus". Astronomy & Astrophysics 262: 258-270.
- ^ Fields, B.D., Hochmuth, K.A., & Ellis, J. (2005). "Deep-Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis". Astrophys. J. 621: 902-907.
