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 an asymmetric extended structure northwest of the star,
independent from the continuum point source. The structure is only traced by
continuum and HCO$^+$, and not detected in the other lines. Kinematics of this
structure reveal that the HCO$^+$ gas likely arises from ejecta expelled in the
1890s eruption. The ejecta is propagating outward within the cavity produced by
the current wind-wind interaction of Eta Car A and its companion. Chemical
analysis of the ejecta reveals an apparent lack of CO and nitrogen-bearing
species. We explore possible explanations for this peculiar chemistry, that
differentiates this structure from the ejecta of the Great Eruption, rich in
HCN and H$^{13}$CN. We also report 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$^{-1}$.
