Mass vs. period of X-ray selected h Per members detected (black) and undetected (gray) in X-rays. Filled and open symbols indicate single and binary stars, respectively. Red lines separate the loci corresponding to supersaturation and saturation, assuming centrifugal stripping (dash-dotted line) or polar updraft (dashed line) theories. The blue dashed line marks the expected separation between non-saturation and saturation.