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The study of the chemical abundances of HII regions in polar ring galaxiesand their implications for the evolutionary scenario of these systems has beena step forward both in tracing the formation history of the galaxy and givinghints on the mechanisms at work during the building of disk by cold accretionprocess. It's now important to establish whether such results are typical forthe class of polar disk galaxies as whole. The present work aims at checkingthe cold accretion of gas through a "cosmic filament" as a possible scenariofor the formation of the polar structures in UGC7576 and UGC9796. If these formby cold accretion, we expect the HII regions abundances and metallicities to belower than those of same-luminosity spiral disks, with values of the order of Z~ 1/10 Zsun, as predicted by cosmological simulations. We have used deeplong-slit spectra, obtained with DOLORES@TNG in the optical wavelengths, of thebrightest HII regions associated with the polar structures to derive theirchemical abundances and star formation rate. We used the "Empirical methods",based on the intensities of easily observable lines, to derive the oxygenabundance 12+log(O/H) of both galaxies. Such values are compared with thosetypical for different morphological galaxy types of comparable luminosity. Theaverage metallicity values for UGC7576 and UGC9796 are Z = 0.4 Zsun and Z = 0.1Zsun respectively. Both values are lower than those measured for ordinaryspirals of similar luminosity and UGC7576 presents no metallicity gradientalong the polar structure. These data, toghether with other observed features,available for the two PRGs in previous works, are compared with the predictionsof simulations of tidal accretion, cold accretion and merging, to disentanglebetween these scenarios.

Chemical abundances of the PRGs UGC7576 and UGC9796. I. Testing the formation scenario