Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 461, Issue 1, Pages 794-815Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stw1300
Keywords
circumstellar matter; stars: pre-main-sequence; open clusters and associations: individual: Scorpius-Centaurus, Sco OB2, Upper Scorpius; Upper Centaurus-Lupus, Lower Centaurus-Crux
Categories
Funding
- School of Arts and Sciences at the University of Rochester
- NSF [AST-1008908, AST-1313029]
- NASA Nexus for Exoplanet System Science programme (NExSS)
- Robert Martin Ayers Sciences Fund
- National Aeronautics and Space Administration
- National Science Foundation
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1313029] Funding Source: National Science Foundation
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We present results of a spectroscopic survey for new K-and M-type members of Scorpius-Centaurus (Sco-Cen), the nearest OB Association (similar to 100-200 pc). Using an X-ray, proper motion and colour-magnitude selected sample, we obtained spectra for 361 stars, for which we report spectral classifications and Li and H alpha equivalent widths. We identified 156 new members of Sco-Cen, and recovered 51 previously published members. We have combined these with previously known members to form a sample of 493 solar-mass (similar to 0.7-1.3 M-circle dot) members of Sco-Cen. We investigated the star formation history of this sample, and re-assessed the ages of the massive main-sequence turn-off and the G-type members in all three subgroups. We performed a census for circumstellar discs in our sample using WISE infrared data and find a protoplanetary disc fraction for K-type stars of 4.4(-0.9)(+1.6) per cent for Upper Centaurus-Lupus and Lower Centaurus-Crux at similar to 16 Myr and 9.0(-2.2)(+4.0) per cent for Upper Scorpius at similar to 10 Myr. These data are consistent with a protoplanetary disc e-folding time-scale of similar to 4-5 Myr for similar to 1 M-circle dot stars, twice that previously quoted, but consistent with the Bell et al. revised age scale of young clusters. Finally, we construct an age map of Scorpius-Centaurus which clearly reveals substructure consisting of concentrations of younger and older stars. We find evidence for strong age gradients within all three subgroups. None of the subgroups are consistent with being simple, coeval populations which formed in single bursts, but likely represents a multitude of smaller star formation episodes of hundreds to tens of stars each.
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