  Mass loss rates for the tenuous, hot winds of cool stars are extremely
difficult to measure, yet they are a crucial ingredient in the stars'
rotational evolution. We present a new method for measuring these mass loss
rates in young, rapidly-rotating stars. These stars are known to support
systems of "slingshot prominences" fed by hot wind material flowing up from the
stellar surface into the summits of closed magnetic loop structures. The
material gathers and cools near the co-rotation radius until its density
becomes large enough that it is visible as a transient absorption feature in
the hydrogen Balmer lines and strong resonance lines such as Ca II H \&\ K.
Here we present the key insight that the sonic point usually lies well below
the condensation region. The flow at the wind base is therefore unaffected by
the presence of an overlying prominence, so we can use the observed masses and
recurrence times of the condensations to estimate the mass flux in the wind.
These measurements extend the relationship between mass loss rate per unit
surface area and X-ray flux to span 5 orders of magnitude. They demonstrate no
evidence of the suspected weakening of stellar mass loss rates at high X-ray
flux levels.
