Triggered Star Formation in Galaxy Pairs at z = 0.08 − 0.38 (Short title: "Triggered Star Formation")

We measure the strength, frequency, and timescale of tidally triggered star formation at redshift z = 0.08 − 0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9,825 Smithsonian Hectospec Lensing Survey (SHELS) galaxies with R 1/5) pair galaxies with MR < −20.8 in the redshift range z = 0.08 − 0.31. The size and completeness of the spectroscopic survey allows us to focus on regions of low local density. The spectrophotometric calibration enables the use of the the 4000 u break (Dn4000), the Hspecific star formation rate (SSFRH�), and population models to characterize the galaxies. We show that Dn4000 is a useful population classification tool; it closely tracks the identification of emission line galaxies. The sample of major pair galaxies in regions of low local density with low Dn4000 demonstrates the expected anti-correlation between pair-wise projected separation and a set of star formation indicators explored in previous studies. We measure the frequency of triggered star formation by comparing the SSFRHin the volume-limited sample in regions of low local density: 32� 7% of the major pair galaxies have SSFRHat least double the median rate of the unpaired field galaxies. Comparison of stellar population models for pair and for unpaired field galaxies implies a timescale for triggered star formation of � 300 − 400 Myr.