  We use the spectra of Pleiades and field stars from LAMOST DR2 archive to
study how spottedness and activity vary as a function of mass at young ages. We
obtained standard TiO band strength by measuring TiO bands near 7050 $\AA$ from
LAMOST spectra (R$\approx$1800) for large sample of field GKM dwarfs with solar
metallicity. Analysis show that active dwarfs, including late G- and early
K-type, have extra TiO absorption compare to inactive counterparts, indicating
the presence of cool spots on their surface. Active late K- and M-dwarfs show
deeper TiO2 and shallower TiO4 compare to inactive stars at a given TiO5, which
could be partly explained through cool spots. We estimated cool spot fractional
coverage for 304 Pleiades candidates by modelling their TiO2 (&TiO5) band
strength with respect to standard value. Results show that surface of large
fraction of K- and M-type members have very large spot coverage ($\sim$50%). We
analysed a correlation between spot coverage, rotation and the amplitude of
light variation, and found spot coverage on slow rotators ($R_{o}$ > 0.1)
increases with decreasing Rossby Number $R_{o}$. Interestingly, we detected a
saturation-like feature for spot coverage in fast rotators with a saturation
level of 40%-50%. In addition, spot distribution in hotter fast rotators show
more symmetrical compare to slow rotators. More interestingly, we detected
large spot coverage in many M type members with no or little light variation.
In bigger picture, these results provide important constraints for stellar
dynamo on these cool active stars.

Solar and Stellar Astrophysics