  Galaxy-galaxy interactions rearrange the baryons in galaxies and trigger
substantial star formation; the aggregate effects of these interactions on the
evolutionary histories of galaxies in the Universe are poorly understood. We
combine B and R-band photometry and optical spectroscopy to estimate the
strengths and timescales of bursts of triggered star formation in the centers
of 190 galaxies in pairs and compact groups. Based on an analysis of the
measured colors and EW(H-alpha), we characterize the pre-existing and triggered
populations separately. The best-fitting burst scenarios assume stronger
reddening corrections for line emission than for the continuum and continuous
star formation lasting for \gtrsim a hundred Myr. The most realistic scenarios
require an initial mass function that is deficient in the highest-mass stars.
The color of the pre-existing stellar population is the most significant source
of uncertainty. Triggered star formation contributes substantially (probably >=
50%) to the R-band flux in the central regions of several galaxies; tidal tails
do not necessarily accompany this star formation. Many of the galaxies in our
sample have bluer centers than outskirts, suggesting that pre- or non-merger
interactions may lead to evolution along the Hubble sequence. These objects
would appear blue and compact at higher redshifts; the older, redder outskirts
of the disks would be difficult to detect. Our data indicate that galaxies with
larger separations on the sky contain weaker, and probably older, bursts of
star formation on average. However, confirmation of these trends requires
further constraints on the colors of the older stellar populations and on the
reddening for individual galaxies.
