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The aim of the present study is to test whether the cold accretion of gasthrough a "cosmic filament" Macci\`o et al. 2006 is a possible formationscenario for the polar disk galaxy NGC 4650A. If polar disks form from coldaccretion of gas, the abundances of the HII regions may be similar to those ofvery late-type spiral galaxies, regardless of the presence of a bright centralstellar spheroid, with total luminosity of few 10^9 Lsun. We use deep long slitspectra obtained with the FORS2 spectrograph at the VLT in the optical andnear-infrared wavelength ranges for the brightest HII regions in the disk polardisk of NGC 4650A. The strongest emission lines ([OII] Hbeta, [OIII], Halpha)were used to derived oxygen abundances, metallicities and the global starformation rates for the disk. The deep spectra available allowed us to measurethe Oxygen abundances (12 + log (O/H)) using the "Empirical method" based onintensities of the strongest emission lines, and the "Direct method", based onthe determination of the electron temperature from the detection of weakauroral lines, as the [OIII] at 4363 Angstrom. The Oxygen abundance measuredfor the polar disk is then compared with those measured for different galaxytypes of similar total luminosities, and then compared against the predictionsof different polar ring formation scenarios. The average metallicity values forthe polar disk in NGC 4650A is Z=0.2 Zsun, and it is lower that the valuesmeasured for ordinary spirals of similar luminosity. Moreover the gradient ofthe metallicity is flat along the polar disk major axis, which implies none ornegligible metal enrichment from the stars in the older central spheroid. Thelow metallicity value in the polar disk NGC 4650A and the flat metallicitygradient are both consistent with a later infall of metal-poor gas, as expectedin the cold accretion processes.

Chemical abundances in the polar disk of NGC4650A: implications for cold accretion scenario