XSHOOTER spectroscopy of the enigmatic planetary nebula Lin49 in the
  Small Magellanic Cloud
  We performed a detailed spectroscopic analysis of the fullerene
C60-containing planetary nebula (PN) Lin49 in the Small Magellanic Cloud using
XSHOOTER at the ESO VLT and the Spitzer/IRS instruments. We derived nebular
abundances for nine elements. We used TLUSTY to derive photospheric parameters
for the central star. Lin49 is C-rich and metal-deficient PN (Z~0.0006). The
nebular abundances are in good agreement with Asymptotic Giant Branch
nucleosynthesis models for stars with initial mass 1.25 Msun and metallicity Z
= 0.001. Using the TLUSTY synthetic spectrum of the central star to define the
heating and ionising source, we constructed the photoionisation model with
CLOUDY that matches the observed spectral energy distribution (SED) and the
line fluxes in the UV to far-IR wavelength ranges simultaneously. We could not
fit the ~1-5 um SED using a model with 0.005-0.1 um-sized graphite grains and a
constant hydrogen density shell owing to the prominent near-IR excess, while at
other wavelengths the model fits the observed values reasonably well. We argue
that the near-IR excess might indicate either (1) the presence of very small
particles in the form of small carbon clusters, small graphite sheets, or
fullerene precursors, or (2) the presence of a high-density structure
surrounding the central star. We found that SMC C60 PNe show a near-IR excess
component to lesser or greater degree. This suggests that these C60 PNe might
maintain a structure nearby their central star.
