# The peculiar chemistry of the inner ejecta of Eta Carina

## TL;DR

This study uses ALMA observations to analyze the inner ejecta of Eta Carina, revealing an asymmetric structure with peculiar chemistry and evidence of ejecta from a historic eruption, distinct from the Great Eruption's composition.

## Contribution

It provides the first detailed chemical and kinematic analysis of Eta Carina's inner ejecta, highlighting its unique composition and relation to past eruptions.

## Key findings

- Discovery of an asymmetric extended structure northwest of Eta Carina.
- Ejecta likely originated from the 1890s eruption, propagating within the stellar wind cavity.
- The ejecta shows a lack of CO and nitrogen-bearing molecules, unlike the Great Eruption ejecta.

## Abstract

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$^{-1}$.