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Rotational modulation of X-ray emission in Orion Nebula young stars

E. Flaccomio·G. Micela·S. Sciortino·E. D. Feigelson·W. Herbst·F. Favata·F. R. Harnden Jr.·S. D. Vrtilek
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Abstract

We investigate the spatial distribution of X-ray emitting plasma in a sample of young Orion Nebula Cluster stars by modulation of their X-ray light-curves due to stellar rotation. The study, part of the Chandra Orion Ultradeep Project (COUP), is made possible by the exceptional length of the observation: 10 days of ACIS integration during a time span of 13 days, yielding a total of 1616 detected sources in the 17x17 arcmin field of view. We here focus on a subsample of 233 X-ray-bright stars with known rotational periods. We search for X-ray modulation using the Lomb Normalized Periodogram method. X-ray modulation related to the rotation period is detected in at least 23 stars with periods between 2 and 12 days and relative amplitudes ranging from 20% to 70%. In 16 cases, the X-ray modulation period is similar to the stellar rotation period while in seven cases it is about half that value, possibly due to the presence of X-ray emitting structures at opposite stellar longitudes. These results constitute the largest sample of low mass stars in which X-ray rotational modulation has been observed. The detection of rotational modulation indicates that the X-ray emitting regions are distributed inhomogeneneously in longitude and do not extend to distances significantly larger than the stellar radius. Modulation is observed in stars with saturated activity levels (L_X/L_bol ~ 10^(-3)) showing that saturation is not due to the filling of the stellar surface with X-ray emitting regions.

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E. Flaccomio, G. Micela, S. Sciortino, E. D. Feigelson, W. Herbst, F. Favata, F. R. Harnden Jr., S. D. Vrtilek. 2005-06-08. Rotational modulation of X-ray emission in Orion Nebula young stars. https://doi.org/10.1086/432419

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