Evolution of the radio outburst from the supermassive star η Carinae from 1992 to 1996

Abstract

An earlier paper, describing observations at a wavelength of 3 cm with the Australia Telescope Compact Array between 1992 June and 1994 May, showed the supermassive star η Carinae to be in the throes of a major outburst. This paper, based on observations at wavelengths of both 3 and 6 cm, describes the evolution of the outburst since 1994 May. From 1994 May to 1995 December, η Carinae's image continued to expand, and its total flux density to increase. These dramatic changes were caused, we believe, by an outburst of UV luminosity, and consequent ionization of pre-existing circumstellar gas clouds. Since 1995 December, η Carinae's total flux density has fallen. The large-scale structure of the radio image closely resembles Hα optical images of the η Carinae 'Homunculus' nebula. In addition, the central area shows fine-scale structure, principally comprising a secondary source about 1.2 arcsec to the northwest of the star, which we believe to be a dense gas cloud, and a ridge of length 4 arcsec centred on the optical position of the star, which we believe to be an equatorial disc or torus. These structures are seen also in 3-cm (H91α) recombination-line emission. © 1997 RAS.