Context :

Aims : We derive the age and metallicity of circumnuclear star formation regions ( CNSFRs ) located in the spiral galaxies NGC 6951 and NGC 1097 , and investigate the cause of the very low equivalent widths of emission lines found for these regions .

Methods : We used optical two-dimensional spectroscopic data obtained with Gemini GMOS-IFUs and a grid of photoionization models to derive the the metallicities and ages of CNSFRs .

Results : We find star formation rates in the range 0.002-0.14 M _ { \odot } \ > yr ^ { -1 } and oxygen abundance of 12+log ( O/H ) \approx 8.8 dex , similar to those of most metal-rich nebulae located in the inner region of galactic disks .

Conclusions : We conclude that the very low emission-line equivalent widths observed in CNSFRs are caused by the “ contamination ” of the continuum by ( 1 ) contribution of the underlying bulge continuum combined with ( 2 ) contribution from previous episodes of star formation at the CNSFRs .