Rotation/saturation/dynamos -- Oral Presentation
Rotational modulation of X-ray emission in Orion Nebula young
stars
Ettore Flaccomio, INAF - Osservatorio Astronomico di Palermo
G. Micela (INAF), S. Sciortino (INAF), E. D. Feigelson (Penn State University), W. Herbst (Wesleyan University), F. Favata(ESA), F.R. Harnden Jr. (SAO, NASA) S. D. Vrtilek(SAO) Harnden Jr. (SAO, NASA) S. D. Vrtilek(SAO)
I will present results of a search for rotational modulation
of X-ray light-curves in a sample of young Orion Nebula Cluster stars.
The study, aiming at understanding the spatial distribution of X-ray
emitting plasma on pre-main sequence stars, is part of the Chandra Orion
Ultradeep Project (COUP) and was 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. I will focus on a subsample of 233 X-ray-bright stars
with known rotational periods. 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$_{bol} \sim 10^{-3}$) showing that
saturation is not due to the filling of the stellar surface with X-ray
emitting regions.