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We present deep 3500$-$10000 $\AA$ spectra of H II regions and planetarynebulae (PNe) in the starburst irregular galaxy NGC 4449, acquired with theMulti Object Double Spectrograph at the Large Binocular Telescope. Using the"direct" method, we derived the abundance of He, N, O, Ne, Ar, and S in six HII regions and in four PNe in NGC 4449. This is the first case of PNe studiedin a starburst irregular outside the Local Group. Our H II region and PN sampleextends over a galacto-centric distance range of $\approx$2 kpc and spans$\approx$0.2 dex in oxygen abundance, with average values of $12+\log(O/H)=8.37\pm 0.05$ and $8.3 \pm 0.1$ for H II regions and PNe, respectively. PNe and HII regions exhibit similar oxygen abundances in the galacto-centric distancerange of overlap, while PNe appear more than $\sim$1 dex enhanced in nitrogenwith respect to H II regions. The latter result is the natural consequence of Nbeing mostly synthesized in intermediate-mass stars and brought to the stellarsurface during dredge-up episodes. On the other hand, the similarity in Oabundance between H II regions and PNe suggests that NGC 4449' s interstellarmedium has been poorly enriched in $\alpha$ elements since the progenitors ofthe PNe were formed. Finally, our data reveal the presence of a negative oxygengradient for both H II regions and PNe, whilst nitrogen does not exhibit anysignificant radial trend. We ascribe the (unexpected) nitrogen behaviour as dueto local N enrichment by the conspicuous Wolf-Rayet population in NGC 4449.

PNe and H II regions in the starburst irregular galaxy NGC 4449 from LBT MODS data