Submillimetre Variability of Eta Carinae: cool dust within the outer ejecta

TL;DR

This study presents new submillimetre observations of Eta Carinae revealing variability in flux and suggesting that the emission is dominated by ionised wind rather than dust, with implications for the star's recent mass loss history.

Contribution

It provides the first evidence of submm variability in Eta Carinae and clarifies the nature of the emission as wind-dominated rather than dust emission.

Findings

Detected submm flux variability at 870um.

Estimated 0.4 solar masses of dust surrounding Eta Carinae.

Constrained recent mass loss to over 40 solar masses within the last thousand years.

Abstract

Previous submillimetre (submm) observations detected 0.7 solar masses of cool dust emission around the Luminous Blue Variable (LBV) star Eta Carinae. These observations were hindered by the low declination of Eta Carinae and contamination from free-free emission orginating from the stellar wind. Here, we present deep submm observations with LABOCA at 870um, taken shortly after a maximum in the 5.5-yr radio cycle. We find a significant difference in the submm flux measured here compared with the previous measurement: the first indication of variability at submm wavelengths. A comparison of the submm structures with ionised emission features suggests the 870um is dominated by emission from the ionised wind and not thermal emission from dust. We estimate 0.4 +/- 0.1 solar masses of dust surrounding Eta Carinae. The spatial distribution of the submm emission limits the mass loss to within the last thousand years, and is associated with mass ejected during the great eruptions and the pre-outburst LBV wind phase; we estimate that Eta Carinae has ejected > 40 solar masses of gas within this timescale.