Dust models compatible with Planck intensity and polarization data in
  translucent lines of sight
  The dust properties inferred from the analysis of Planck observations in
total and polarized emission challenge current dust models. We propose new dust
models compatible with polarized and unpolarized data in extinction and
emission for translucent lines of sight ($0.5 < A_V < 2.5$). We amended the
DustEM tool to model polarized extinction and emission. We fit the spectral
dependence of the mean extinction, polarized extinction, SED and polarized SED
with PAHs, astrosilicates and amorphous carbon (a-C). The astrosilicate
population is aligned along the magnetic field lines, while the a-C population
may be aligned or not. With their current optical properties, oblate
astrosilicate grains are not emissive enough to reproduce the emission to
extinction polarization ratio $P_{353}/p_V$ derived with Planck data. Models
using prolate astrosilicate grains with an elongation $a/b=3$ and an inclusion
of 20% of porosity succeed. The spectral dependence of the polarized SED is
steeper in our models than in the data. Models perform slightly better when a-C
grains are aligned. A small (6%) volume inclusion of a-C in the astrosilicate
matrix removes the need for porosity and perfect grain alignment, and improves
the fit to the polarized SED. Dust models based on astrosilicates can be
reconciled with Planck data by adapting the shape of grains and adding
inclusions of porosity or a-C in the astrosilicate matrix.
