Eta Carinae: a stable star behind a dynamic circumstellar environment

DAMINELI, A; FERNANDEZ LAJUS E; ET AL.

Bariloche

Conferencia; Massive Stars and Supernovae; 2018

Analysis of the light curve of eta Carinae (eta Car) over the last half century reveals a rich set of variabilities with different time scales. These variations can be quantified only after separating the light from the central object (eta core) from the nebular ejecta. We used CCD images from the La Plata Observatory, cross-calibrated with coeval ACS/HRC images, to distinguish the light variations of the central object from those changes in the nebula. We confirm previous suggestions that the central source is brightening more quickly than the nebula, and show that this is due to the continuous dissipation of dust in our line-of-sight. The dust dissipation started in the 1990´s, and corresponds to a decrease in V-band extinction of Av=0.7 mag per binary orbital period. If this dissipation continues at its present rate, eta Car will once again be a 3rd magnitude star by 2027. This current brightening is similar to the brightening jump that occurred between 1941-45, which was accompanied by the appearance of high excitation lines. After correcting for the long-term brightening, the stellar light curve displays a large amplitude (Δmag=0.6) quasi-periodic oscilllation (P~ 5.5 yr) which we suggest is due to a ?light house" effect produced by the wind-wind collision cavity as it sweeps around the primary with the orbital motion of the companion star. The same mechanism produces a sharp periodic brightening near periastron passage of ΔV = 0.35 mag. The long and deep UV minimum is due to the temporary recombination of Fe++ in the primary star when the secondary moves behind the primary. We identify two apparently non-periodic Δmag