The Radio Outburst from Carinae

Abstract. Carinae is in the midst of a radio outburst which has made it one of the brightest stellar radio sources in the sky. This paper reviews our current understanding of this outburst, and discusses how the radio emission may be used to study the mass loss history of Car in very recent history (tens of years). 1. Radio Observations of Carinae Carinae has proven to be as remarkable a radio source as it is in nearly every other wavelength range. This paper reports on observations of Car made since 1992 with the Australia Telescope (ATCA) at frequencies from 1.4 to 9 GHz, which reveal an extraordinary outburst in which the radio emission from hot ionized gas within several arcseconds of the star has increased fourfold in several years. Unfortunately we do not have a long time history of the behaviour of the radio ux from Car from which to judge the signicance of the current outburst. The reason for this is largely technical: until the early 1990s, there have been no telescopes in the southern hemisphere capable of separating the ux of Car from that of the surrounding large and radio{bright Carina Nebula at the higher microwave frequencies required to study the core region around the star. While both the Fleurs (1.4 GHz; Retallack 1983) and Molonglo (0.843 MHz; Jones 1985, Whiteoak 1994) radio synthesis telescopes were able both to separate the Car radio source from the Carina Nebula and to estimate the size of the radio source (e.g., Whiteoak 1994 measured a ux of 1.1 0.1 Jy with a size of 5