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Description
We present 237 new spectroscopically confirmed pre-main-sequence K- and M-type stars in the young Upper Scorpius subgroup of the Sco-Cen association, the nearest region of recent massive star formation. Using the Wide-Field Spectrograph at the Australian National University 2.3 m telescope at Siding Spring, we observed 397 kinematically and photometrically selected candidate members of Upper Scorpius, and identified new members by the presence of lithium absorption. The HR-diagram of the new members shows a spread of ages, ranging from ~3 to 20Myr, which broadly agrees with the current age estimates of ~5-10Myr. We find a significant range of Li 6708 equivalent widths among the members, and a minor dependence of HR-diagram position on the measured equivalent width of the Li 6708{AA} line, with members that appear younger having more lithium. This could indicate the presence of either populations of different age, or a spread of ages in Upper Scorpius. We also use Wide-Field Infrared Survey Explorer data to infer circumstellar disc presence in 25 of the members on the basis of infrared excesses, including two candidate transition discs. We find that 11.2+/-3.4% the M0-M2 spectral type (0.4-0.8M_{sun}_) Upper Sco stars display an excess that indicates the presence of a gaseous disc.
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