  We put upper limits of secondary burst of star formation in elliptical
galaxies of the Gonzalez's (1993) sample, most of which locates in small
groups, based on the colour dispersion around the U-V versus central velocity
dispersion relation, and the equivalent width of Hbeta absorption. There are
significant number of Hbeta strong galaxies which have EW(Hbeta)>2A, however
they do not always have bluer colours in U-V. To be consistent with small
colour dispersion of U-V, the mass fraction of secondary burst to the total
mass should be less than only 10% at the maximum within recent 2Gyr. This
result suggests that even if recent galaxy merging produce some ellipticals, it
should not have been accompanied by an intensive star burst, and hence it could
not involve large gas-rich systems. A capture of dwarf galaxy is more likely to
explain dynamical disturbances observed in some elliptical galaxies.
  The above analysis based on the U-V is not compatible with the one based on
the line indices, which requires that more than 10% of mass is present in a
2Gyr old star burst to cover the full range of the observed Hbeta (de Jong &
Davies 1997). The discrepancy might be partly explained by the internal
extinction localized at the region where young stars form. However, considering
that the Hbeta index might have great uncertainties both in models and in
observational data, we basically rely on U-V analysis.
