http://arxiv.org/abs/1807.11305
Understanding the properties of dust produced during the asymptotic giant branch phase of stellar evolution is important for understanding the evolution of stars and galaxies. Recent observations of the carbon AGB star R Scl have shown an excess emission from the detached shell around the star at submillimetre wavelengths, indicating that the dust in the shell may have so far unknown properties. We aim to constrain the properties of the dust observed in the submillimetre in the detached shells around the three carbon AGB stars U Ant, DR Ser, and V644 Sco, and to investigate possible submm-excesses also in these sources. We observed the carbon AGB stars U Ant, DR Ser, and V644 Sco at 870 micron using LABOCA on APEX. Combined with observations from the optical to far-infrared, we produced dust radiative transfer models of the spectral energy distributions (SEDs) with contributions from the stars, present-day mass-loss and detached shells. We tested the effect of different total dust masses and grain sizes on the SED, and attempted to consistently reproduce the SEDs from the optical to the submm. We derive dust masses in the shells of a few 10e-5 Msun, assuming spherical, solid grains. The best-fit grain radii are comparatively large, and indicate the presence of grains between 0.1 micron-2 micron. In all cases we detect an excess at 870 micron that cannot be reproduced by simply changing the grain size. We investigate the possibility of the presence of a population of cold grains, a broken emissivity law at far-infrared wavelengths, and the presence of spinning nanoparticles. However, based on the current observational data, it is not possible to draw any firm conclusions. But submm-excess has been observed in four detached-shell sources, and implies that the detached shells contain dust with currently unknown properties.
M. Maercker, T. Silva, E. Beck, et. al.
Tue, 31 Jul 18
66/69
Comments: Accepted by A&A
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