|Authors||Thomas Preibisch(1), Anthony G.A. Brown(2), Terry Bridges(3), Eike Guenther(4), Hans Zinnecker(5)|
|Affiliation||(1) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany |
(2) Sterrewacht Leiden, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands
(3) Anglo-Australian Observatory, P.O. Box 296, Epping NSW 1710, Australia
(4) Thüringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany
(5) Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
|Accepted by||The Astronomical Journal|
In the second part of this paper, we also consider the population of 114 high-mass members identified in detailed Hipparcos studies. We construct a combined HR diagram for the 364 high- and low-mass members and find that the whole stellar population is very well characterized by a very narrow age distribution around 5 Myr. We estimate individual masses for all members and construct an empirical mass function covering the mass range from 0.1 Mo up to 20 Mo. A power-law fit to the mass function gives a slope of alpha ~ -2.6 above ~2 Mo and a much flatter slope (alpha ~ -0.9) below ~0.6 Mo. The initial mass function of Upper Sco is not identical, but within the errors consistent with recent determinations of the field initial mass function. There is certainly no deficit of low-mass stars in the Upper Sco OB association, but rather a small excess of low-mass stars. Our results on the stellar age distribution confirm earlier indications that the star formation process in Upper Sco was triggered, and support previous conjectures that the triggering event was a supernova shock-wave originating from the nearby Upper Centaurus Lupus association.