Publications
of the
MPIfR Optical & Infrared Interferometry Group

K.R. Briggs, M. Güdel, M. Audard, K. Smith, R. Mewe, and T. Den Boggende

X-ray emission from pre-main sequence stars in the Orion star-forming region

In: Schielikke, R.E. (ed.): Short Contrib. Ann. Sci. Meeting Astron. Ges. Freiburg 2003. Astron. Nachr. 324, Suppl. Issue 3 (2003), p.9
"The Sun and Planetary Systems - Paradigms for the Universe"
Annual Scientific Meeting of the Astronomische Gesellschaft, Sep 15-20, 2003, Freiburg, Germany

Abstract

Pre-main sequence (PMS) stars are powerful sources of X-ray emission, with luminosities which may exceed that of the active Sun by 4 orders of magnitude. Yet, the origin of this emission may still be a hot corona, driven by a magnetic dynamo, as in the Sun. The importance of accretion or of magnetic fields connecting the star and its accretion disk remains undetermined.

The Orion star-forming region is the richest site in the sky for the study of X-ray emission from PMS stars, almost a thousand sources being harboured by the Orion Nebula Cluster alone (Feigelson et al. 2002). X-ray luminosities in this population have not shown the correlation with rotation rate one might expect from dynamo-driven coronae (Feigelson et al. 2003), although this may still be consistent with dynamos operating in a saturated regime (Flaccomio et al. 2003), and there have been indications that stars with accretion disks are less luminous than those without (Flaccomio et al. 2003).

However, not all stars are born in such crowded, harshly-irradiated environments as found around the O-type stars of the Trapezium. We have examined a 30 arcmin diameter field in the Orion star-forming region, 40 arcmin north of the Trapezium, in a 20 ks XMM-Newton observation, containing approx 200 sources (see Fig. 1 in PS-File below). We study the relationships between X-ray luminosity and rotation rate, accretion-disk indicators and stellar mass, and perform temporal and spectral analyses of the X-ray emission in order to investigate its origin and to perform comparisons with the high-density Orion Nebula Cluster.