Classification of Upper Sco stars from spectroscopy

This sample includes many of the faintest spectroscopically confirmed members (K=16-17mag), which should have masses down to ~0.007-0.01M_{sun}_ for the range of ages in Upper Sco (7-14Myr). Using my updated membership catalog for Upper Sco, I have estimated the initial mass function (IMF) for a field in the center of the association that encompasses ~80% of the known members.

I have derived IMFs in the same manner for previous membership samples in three other star-forming populations, consisting of IC 348, Taurus, and Chameleon I. When using logarithmic mass bins, the substellar IMFs for Upper Sco and the other young regions are roughly flat down to the completeness limits of ~0.01M_{sun}_. These IMFs are broadly similar to mass functions recently measured for the solar neighborhood. Finally, I have used W1-W2 colors to search for excess emission from circumstellar disks among the late-type objects in my new census of Upper Sco.