The most recent eruption of Eta Carina: discovery of chemically peculiar and asymmetric ejecta

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 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, associated with the Weigelt blobs, is only traced in HCO$^+$ and not detected in the other lines; and (2) an absorption component toward 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 lack of nitrogen-bearing molecules. We explore possible explanations for this situation, that clearly differentiates this region from the ejecta of the Great Eruption, rich in CNO-processed matter. In addition, we find that morphology and kinematics of this structure are consistent with a one-sided mass ejection. Its dynamical age is lower than 90 years, which places the structure in relation to the 1941 Eta Car brightening.