  AB Dor, Speedy Mic and Rst137B are in their early post-T Tauri evolutionary
phase (<100Myr), at the age of fastest rotation in the life of late-type stars.
They straddle the coronal saturation-supersaturation boundary first defined by
young stars in open clusters. High resolution Chandra X-ray spectra have been
analysed to study their coronal properties as a function of coronal activity
parameters Rossby number, $L_X/L_{bol}$ and a coronal temperature index. Plasma
emission measure distributions as a function of temperature show broad peaks at
T~10e7K. Differences between stars suggest that as supersaturation is reached
the DEM slope below the temperature of peak DEM becomes shallower, while the
DEM drop-off above this temperature becomes more pronounced. A larger sample
comprising our three targets and 22 active stars studied in the recent
literature reveals a general increase of plasma at T>10e7 toward the
saturated-supersaturated boundary but a decline beyond this among
supersaturated stars. All three of the stars studied in detail here show lower
coronal abundances of the low FIP elements Mg, Si and Fe, relative to the high
FIP elements S, O and Ne, as compared to the solar mixture. The coronal Fe
abundances of the stellar sample are inversely correlated with Lx/Lbol,
declining slowly with rising Lx/Lbol, but with a much more sharp decline at
Lx/Lbol>3x10e-4. For dwarfs the Fe abundance is also well-correlated with
Rossby number. The coronal O/Fe ratios for dwarfs show a clear increase with
decreasing Rossby number, apparently reaching saturation at [O/Fe]=0.5 at the
coronal supersaturation boundary. Similar increases in O/Fe with increasing
coronal temperature and $L_X/L_{bol}$ are seen.
