X-ray emission and variability of young, nearby stars

Abstract

X-ray emission has played a major role in the recent identification of several groups of young, nearby stars. The ROSAT All-Sky Survey (RASS) is due to its spatial completeness an important tool for discovering stellar associations and investigating their X-ray properties. However, it has comparatively low sensitivity and poor temporal coverage, and is therefore of limited use for variability studies. The situation is greatly improved by the new generation of X-ray observatories, e.g. for coronal X-ray sources XMM has about an order of magnitude higher sensitivity than the RASS and provides much longer exposure times allowing continuous monitoring for more than 40 h. We demonstrate the capabilities of both the RASS by comparing X-ray luminosity functions (XLF) of different young stellar associations, and XMM by discussing one young very nearby star in detail, GJ 182.