Radio and Infrared Emission from a [WC]-Type Planetary Nebula in the LMC

Abstract

Radio continuum emission has been detected from a planetary nebula in the Large Magellanic Cloud: this is the first radio continuum detection for any planetary nebula outside our galaxy. The radio flux density is a factor of two lower than predicted from the \hbeta\ flux. This could be due either to a two-component morphology or to a stellar contribution to the \hbeta\ emission. We have modeled the optical and infrared spectrum using the photo-ionisation code Cloudy: a very good fit is obtained if we assume the nebula is carbon rich. The derived diameter implies an evolutionary age of the nebula of $<1000\yr$, similar to what is derived from the IRAS colours alone. The central star, which is of [WC] type, has a much higher stellar temperature than Galactic [WC] stars showing similar circumstellar IRAS colours. An explanation could be that the expansion velocity of the nebula is lower than those of its galactic counterparts. This radio detection indicates that accurate nebular luminosities could be determined from their radio emission for many LMC planetary nebulae.