The peculiar chemistry of the inner ejecta of Eta Carina

We investigated continuum and molecular line emission of four species (CO, HCN, H$^{13}$CN, and HCO$^+$) at 0.8 mm in the inner arcsec around Eta Car, using ALMA archival observations at a resolution better than 0.2 arcsec. We report the discovery of two key features: (1) an extended continuum structure asymmetrically located with respect to the star and clearly independent from the point source. This structure is only traced in HCO$^+$ and not detected in the other lines; and (2) an absorption component near the continuum point source, only traced by HCN and H$^{13}$CN in their vibrational-ground and vibrationally-excited states. This absorbing gas is attributed to a hot bullet of N-enriched material expelled at a projected velocity of 40 km s$^{-1}$. In the extended structure we measure unusual abundances due to the non-detection of neither CO nor nitrogen-bearing molecules. We explore possible explanations for this situation, that clearly differentiates this region from the ejecta of the Great Eruption, rich in HCN and H$^{13}$CN. In addition, we analyse the kinematics of this structure, concluding that the HCO$^+$ gas is the molecular counterpart of the shock cone produced by the wind-wind collisions of Eta Car and its companion.