  As the nearest known AGB star (d=64pc) and one of the brightest (mK-2), L2
Pup is a particularly interesting benchmark object to monitor the final stages
of stellar evolution. We report new lucky imaging observations of this star
with the VLT/NACO adaptive optics system in twelve narrow band filters covering
the 1.0-4.0 microns wavelength range. These diffraction limited images reveal
an extended circumstellar dust lane in front of the star, that exhibits a high
opacity in the J band and becomes translucent in the H and K bands. In the L
band, extended thermal emission from the dust is detected. We reproduce these
observations using Monte-Carlo radiative transfer modeling of a dust disk with
the RADMC-3D code. We also present new interferometric observations with the
VLTI/VINCI and MIDI instruments. We measure in the K band an upper limit to the
limb-darkened angular diameter of theta_LD = 17.9 +/- 1.6 mas, converting to a
maximum linear radius of R = 123 +/- 14 Rsun. Considering the geometry of the
extended K band emission in the NACO images, this upper limit is probably close
to the actual angular diameter of the star. The position of L2 Pup in the
Herzsprung-Russell diagram indicates that this star has a mass around 2 Msun
and is probably experiencing an early stage of the asymptotic giant branch. We
do not detect any stellar companion of L2 Pup in our adaptive optics and
interferometric observations, and we attribute its apparent astrometric wobble
in the Hipparcos data to variable lighting effects on its circumstellar
material. We however do not exclude the presence of a binary companion, as the
large loop structure extending to more than 10 AU to the North-East of the disk
in our L band images may be the result of interaction between the stellar wind
of L2 Pup and a hidden secondary object. The geometric configuration that we
propose, with a large dust disk seen almost edge-on, appears particularly
favorable to test and develop our understanding of the formation of bipolar
nebulae.
