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| - VLT/NACO spectro-imaging from 1.04 to 4.05 μm and VLTI interferometry
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| - An edge-on translucent dust disk around the nearest AGB star, L 2 Puppis
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| - As the nearest known AGB star ( d = 64 pc) and one of the brightest ( mK ≈ −2 ), L 2 Pup is a particularly interesting benchmark object to monitor the final stages of stellar evolution. We report new serendipitous imaging observations of this star with the VLT/NACO adaptive optics system in twelve narrow-band filters covering the 1.0−4.0 μm 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 reproduced 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 measured in the K band an upper limit to the limb-darkened angular diameter of θLD = 17.9 ± 1.6 mas, converting to a maximum linear radius of R = 123 ± 14 R⊙. 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 L 2 Pup in the Hertzsprung-Russell diagram indicates that this star has a mass of about 2 M⊙ and is probably experiencing an early stage of the asymptotic giant branch. We did not detect any stellar companion of L 2 Pup in our adaptive optics and interferometric observations, and we attribute its apparent astrometric wobble in the H ipparcos data to variable lighting effects on its circumstellar material. However, we do not exclude the presence of a binary companion, because the large loop structure extending to more than 10 AU to the northeast of the disk in our L-band images may be the result of interaction between the stellar wind of L 2 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.
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