THE STAR-FORMATION HISTORY OF NGC-7252

The merger remnant NGC 7252 (= Arp 226) shows blue colours and an AF-type spectrum, indicating a major starburst about a billion years ago. Here we develop a quantitative model for the star formation history of this galaxy, using the merger starburst models developed in a companion paper. Comparison with existing observations shows that in the case of NGC 7252 two fairly massive, more than 10 Gyr old Sc type spirals should have merged, inducing a strong starburst which increased the total stellar mass by 20 to 50% within (1 - 5).10(8) yr. With these parameters we obtain good agreement with the observed UBVR colours of NGC 7252, its luminosity and gas content, and with Schweizer's observed spectrum at a time of 1.3-2 Gyr after the beginning of the burst. Our model predicts NIR colours, gas abundances, and the spectrum of NGC 7252 from 1150 to 10.000 angstrom, which may be tested by future observations. Tighter constraints on the strength and duration of the burst than those from existing observations could be derived from gas abundance ratios. We follow the spectral, photometric, and chemical properties of our best fit NGC 7252 model until it evolves into an elliptical galaxy within the next few Gyr. Comparing the spectral age of greater than or similar to 1.3 Gyr with dynamical age estimates from Borne & Richstone's models for the merger orbit suggests that burstlike star formation must have started greater than or similar to 0.5 Gyr before the first pericenter contact of the two disks. Thus in this case the burst is expected to have started when the progenitor's massive halos merged and ended before core merging was complete. The high burst strength required by our models to fit the observational data implies a star formation efficiency high enough that globular clusters (GCs) may be formed. We predict colours and stellar metallicities for such a secondary GC population to be compared to HST observations.