Chandra
Orion Ultradeep Project
X-ray rotation
As our Sun rotates every ~27 days, its sunspots and coronal structures are alternately visible and eclipsed causing a period modulation in the solar radiation at many wavelengths. In pre-main sequence Orion stars, which are far more magnetically active than the Sun today, this rotational modulation of visible light due to huge starspots has been seen in several hundred stars. But it had rarely been seen in the X-ray band, mainly because past observations were short compared to the typical 2-10 day rotation periods of young stars.
The COUP lightcurve
here exhibits, in addition to two obvious flares, a sine-shaped variation
in the underlying X-ray emission with the same 8.5 day period seen for the
visible light starspots.
Here is the same lightcurve, after the flares are removed, shown folded with the 8.5 day period.
We find 16 cases, or 7% of the examined stars, like this where X-ray periods are equal to the optical periods, indicating that the stellar surface has a single optically-faint and X-ray-bright active region. In 7 cases, we find X-ray periods equal to half of the optical periods, suggesting two bright hemispheres in the X-ray corona. In all these cases, the X-ray emitting magnetic fields must be smaller than the star itself.
COUP scientists have prepared some additional informative Web pages on X-ray rotation of the Sun and stars here.
The full paper on COUP X-ray rotation is:
Rotational modulation of X-ray emission in Orion Nebula young stars
E. Flaccomio, G. Micela, S. Sciortino1, E. D. Feigelson, W. Herbst, F. Favata, F.R. Harnden Jr., S. D. Vrtilek
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X-ray rotation
As our Sun rotates every ~27 days, its sunspots and coronal structures are alternately visible and eclipsed causing a period modulation in the solar radiation at many wavelengths. In pre-main sequence Orion stars, which are far more magnetically active than the Sun today, this rotational modulation of visible light due to huge starspots has been seen in several hundred stars. But it had rarely been seen in the X-ray band, mainly because past observations were short compared to the typical 2-10 day rotation periods of young stars.
Here is the same lightcurve, after the flares are removed, shown folded with the 8.5 day period.
We find 16 cases, or 7% of the examined stars, like this where X-ray periods are equal to the optical periods, indicating that the stellar surface has a single optically-faint and X-ray-bright active region. In 7 cases, we find X-ray periods equal to half of the optical periods, suggesting two bright hemispheres in the X-ray corona. In all these cases, the X-ray emitting magnetic fields must be smaller than the star itself.
COUP scientists have prepared some additional informative Web pages on X-ray rotation of the Sun and stars here.
The full paper on COUP X-ray rotation is:
Rotational modulation of X-ray emission in Orion Nebula young stars
E. Flaccomio, G. Micela, S. Sciortino1, E. D. Feigelson, W. Herbst, F. Favata, F.R. Harnden Jr., S. D. Vrtilek
Back to the COUP home page