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Title:
A Simultaneous Optical and X-Ray Variability Study of the Orion Nebula Cluster. I. Incidence of Time-correlated X-Ray/Optical Variations
Authors:
Stassun, Keivan G.; van den Berg, M.; Feigelson, Eric; Flaccomio, Ettore
Affiliation:
AA(Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235; .), AB(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.), AC(Department of Astronomy and Astrophysics, Penn State University, University Park, PA 16802.), AD(INAF-Osservatorio Astronomico di Palermo Giuseppe S. Vaiana, Piazza del Parlamento 1, 91034 Palermo, Italy.)
Publication:
The Astrophysical Journal, Volume 649, Issue 2, pp. 914-926. (ApJ Homepage)
Publication Date:
10/2006
Origin:
UCP
ApJ Keywords:
Galaxy: Open Clusters and Associations: Individual: Name: Orion Nebula Cluster, Stars: Flare, Stars: Magnetic Fields, Stars: Pre-Main-Sequence, Stars: Spots, X-Rays: Stars
DOI:
10.1086/506422
Bibliographic Code:
2006ApJ...649..914S

Abstract

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.

This study is part of the Chandra Orion Ultradeep Project (COUP).

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