Astrophys. J., 660, 704-711 (2007/May-1)
A simultaneous optical and X-ray variability study of the Orion nebula cluster. II. A common origin in magnetic activity.
STASSUN K.G., VAN DEN BERG M. and FEIGELSON E.
Abstract (from CDS):
We present a statistical analysis of simultaneous optical and X-ray light curves, spanning 600 ks, for 814 pre-main-sequence (PMS) stars in the Orion Nebula Cluster. The aim of this study is to establish the relationship, if any, between the sites of optical and X-ray variability and thereby to elucidate the origins of X-ray production in PMS stars. In a previous paper, we showed that optical and X-ray variability in PMS stars are very rarely time-correlated. Here, using time-averaged variability indicators to examine the joint occurrences of optical and X-ray variability, we confirm that the two forms of variability are not directly causally related. However, a strong and highly statistically significant correlation is found between optical variability and X-ray luminosity. As this correlation is found to be independent of accretion activity, we argue that X-ray production in PMS stars must instead be intimately connected with the presence and strength of optically variable, magnetically active surface regions (i.e., spots) on these stars. Moreover, because X-ray variability and optical variability are rarely time-correlated, we conclude that the sites of X-ray production are not exclusively cospatial with these regions. We argue that solar-analog coronae, heated by topologically complex fields, can explain these findings.
Galaxy: Open Clusters and Associations: Individual: Name: Orion Nebula Cluster - Stars: Flare - Stars: Magnetic Fields - Stars: Pre-Main-Sequence - Stars: Spots - X-Rays: Stars
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<Available at CDS (J/ApJ/660/704): table1.dat>
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