Structure and Evolution of Pre-Main Sequence Stars

TL;DR

This paper discusses the structure and evolution of pre-main sequence stars, emphasizing the importance of high-resolution X-ray spectroscopy to understand their magnetic activity, physical conditions, and impact on stellar and disk evolution.

Contribution

It highlights the need for highly resolved X-ray spectroscopy with greater efficiency to study PMS stars' physical conditions and magnetic activity evolution.

Findings

X-ray emission in PMS stars is complex and non-isothermal.

Current high-resolution spectrometers lack the effective area for large sample analysis.

Enhanced spectroscopy will enable detailed understanding of PMS star evolution.

Abstract

Low-mass pre-main sequence (PMS) stars are strong and variable X-ray emitters, as has been well established by EINSTEIN and ROSAT observatories. It was originally believed that this emission was of thermal nature and primarily originated from coronal activity (magnetically confined loops, in analogy with Solar activity) on contracting young stars. Broadband spectral analysis showed that the emission was not isothermal and that elemental abundances were non-Solar. The resolving power of the Chandra and XMM X-ray gratings spectrometers have provided the first, tantalizing details concerning the physical conditions such as temperatures, densities, and abundances that characterize the X-ray emitting regions of young star. These existing high resolution spectrometers, however, simply do not have the effective area to measure diagnostic lines for a large number of PMS stars over required to answer global questions such as: how does magnetic activity in PMS stars differ from that of main sequence stars, how do they evolve, what determines the population structure and activity in stellar clusters, and how does the activity influence the evolution of protostellar disks. Highly resolved (R>3000) X-ray spectroscopy at orders of magnitude greater efficiency than currently available will provide major advances in answering these questions. This requires the ability to resolve the key diagnostic emission lines with a precision of better than 100 km/s.