η Carinae: The 1998 brightening and the smearing-out effect

Abstract

A comparison of broad-band photometry of the Homunculus (ground-based data) and of broad-band and narrow-band photometry of the central region (HST-based) from 1997 to 2003 reveals that, apart from the brightening in 1998, the Homunculus as well as the central star varied in a very similar way. This excludes smearing-out effects as an explanation for the difference between the brightening of the central region and that of the Homunculus during 1998. A plausible reason for the homologous light behaviour is enhanced extinction decrease in the line-of-sight to the central region during a global brightening occurring after the 1998.0 spectroscopic event. From 1998 to 2004 there is indeed a brightness excess of ∼0.3m between the Homunculus and the extrapolated secular brightening. We also illustrate that ground-based aperture photometry of the Homunculus is a reliable diagnostic tool for studying the variability of the central star.