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Abstract: Low-mass pre-main sequence PMS stars are strong and variable X-rayemitters, as has been well established by EINSTEIN and ROSAT observatories. Itwas originally believed that this emission was of thermal nature and primarilyoriginated from coronal activity magnetically confined loops, in analogy withSolar activity on contracting young stars. Broadband spectral analysis showedthat the emission was not isothermal and that elemental abundances werenon-Solar. The resolving power of the Chandra and XMM X-ray gratingsspectrometers have provided the first, tantalizing details concerning thephysical conditions such as temperatures, densities, and abundances thatcharacterize the X-ray emitting regions of young star. These existing highresolution spectrometers, however, simply do not have the effective area tomeasure diagnostic lines for a large number of PMS stars over required toanswer global questions such as: how does magnetic activity in PMS stars differfrom that of main sequence stars, how do they evolve, what determines thepopulation structure and activity in stellar clusters, and how does theactivity influence the evolution of protostellar disks. Highly resolvedR>3000 X-ray spectroscopy at orders of magnitude greater efficiency thancurrently available will provide major advances in answering these questions.This requires the ability to resolve the key diagnostic emission lines with aprecision of better than 100 km-s.

Author: Norbert S. Schulz, Glenn Allen, Mark W. Bautz, Claude C. Canizares, John Davis, Dan Dewey, David P. Huenemoerder, Ralf Heilmann,


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