Submillimetre variability of Eta Carinae: Cool dust within the outer ejecta

Abstract

Previous submillimetre (submm) observations detected 0.7 M. of cool dust emission around the luminous blue variable (LBV) star η Carinae. These observations were hindered by the low declination of η Carinae and contamination from free-free emission originating from the stellar wind. Here, we present deep submm observations with LABOCA at 870 μm, taken shortly after a maximum in the 5.5-year 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 ionized emission features suggests the 870 μm is dominated by emission from the ionized wind and not thermal emission from dust. We estimate 0.4 ±0.1 M. of dust surrounding η 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 η Carinae has ejected >40 M. of gas within this time-scale. © 2009 RAS.