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We present an analysis of the red giant component of the recurrent nova V3890Sgr, using data obtained before and after its 2019 eruption. Its effectivetemperature is $T_{\rm eff}=3050\pm$200 K for $\log{g}=0.7$, although there aremodest changes in $T_{\rm eff}$. There is an overabundance of both carbon($0.20\pm0.05$~dex) and sodium ($1.0\pm0.3$~dex) relative to their solarvalues, possibly the result of ejecta from the 1990 nova eruption beingentrained into the red giant photosphere. We find $^{12}$C/$^{13}$C $=25\pm2$,a value similar to that found in red giants in other recurrent novae. Theinterpretation of the quiescent spectrum in the 5--38$\,mu$m region requiresthe presence of photospheric SiO absorption and cool ($\sim400$~K) dust in thered giant environment. The spectrum in the region of the Na{\sc i} D lines iscomplex, and includes at least six interstellar components, together withlikely evidence for interaction between ejecta from the 2019 eruption andmaterial accumulated in the plane of the binary. Three recurrent novae withgiant secondaries have been shown to have environments with different dustcontent, but photospheres with similar $^{12}$C/$^{13}$C ratios. The SiOfundamental bands most likely have a photospheric origin in the all threestars.

The recurrent nova V3890~Sgr: a near-infrared and optical study of the red giant component and its environment