2006ApJ...649..914S -
Astrophys. J., 649, 914-926 (2006/October-1)
A simultaneous optical and X-ray variability study of the Orion Nebula Cluster. I. Incidence of time-correlated X-ray/optical variations.
STASSUN K.G., VAN DEN BERG M., FEIGELSON E. and FLACCOMIO E.
Abstract (from CDS):
We present a database of BVRI time-series photometry of the Orion Nebula Cluster obtained with two ground-based telescopes at different longitudes to provide simultaneous coverage with the 13 day Chandra observation of the cluster. The resulting database of simultaneous optical and X-ray light curves for some 800 pre-main-sequence (PMS) stars represents, by a factor of hundreds, the largest synoptic, multi-wavelength-regime, time-series study of young stars to date. This database will permit detailed analyses of the relationship between optical and X-ray variability among a statistically significant ensemble of PMS stars, with the goal of elucidating the origins of PMS X-ray production. In this first paper, we present the optical observations, describe the combined X-ray/optical database, and perform an analysis of time-correlated variability in the optical and X-ray light curves. We identify 40 stars (representing 5% of our study sample) with possible time-correlated optical and X-ray variability. Examples of both positive and negative time correlations are found, possibly representing X-ray flares and persistent coronal features associated with both cool and hot surface spots (i.e., magnetically active regions and accretion shocks). We also find two possible examples of ``white-light'' flares coincident with X-ray flares; these may correspond to the impulsive heating phase in solar-analog flares. However, although interesting, these represent unusual cases. More generally, we find very little evidence to suggest a direct causal link between the sources of optical and X-ray variability in PMS stars. The conclusion that accretion is a primary driver of X-ray production in PMS stars is not supported by our findings.
Abstract Copyright:
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Journal keyword(s):
Galaxy: Open Clusters and Associations: Individual: Name: Orion Nebula Cluster - Stars: Flare - Stars: Magnetic Fields - Stars: Pre-Main-Sequence - Stars: Spots - X-Rays: Stars
Simbad objects:
53
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