The Nature of the Stingray Nebula from Radio Observations
  We have analysed the full suite of Australia Telescope Compact Array data for
the Stingray planetary nebula. Data were taken in the 4- to 23-GHz range of
radio frequencies between 1991 and 2016. The radio flux density of the nebula
generally declined during that period, but between 2013 and 2016 it shows signs
of halting that decline. We produced the first spatially resolved radio images
of the Stingray nebula from data taken in 2005. A ring structure, which appears
to be associated with the ring seen in HST images, was visible. In addition, we
found a narrow extension to the radio emission towards the eastern and western
edges of the nebula. We derived the emission measure of the nebula - this
decreased between 1992 and 2011, suggesting that the nebula is undergoing
recombination. The radio spectral index is broadly consistent with a free-free
emission mechanism, however a single data point hints that a steeper spectral
index has possibly emerged since 2013, which could indicate the presence of
synchrotron emission. If a non-thermal component component has emerged, such as
one associated with a region that is launching a jet or outflow, we predict
that it would intensify in the years to come.
