  Photometric lightcurves were also obtained for 14 of them during the Spitzer
observations to provide the context of the observations and reliable estimates
of their absolute magnitudes. The extracted mid-IR spectra were analyzed using
a modified standard thermal model (STM) and a thermophysical model (TPM) that
takes into account the shape and geometry of the large primary at the time of
the Spitzer observation. We derived a reliable estimate of the size, albedo,
and beaming factor for each of these asteroids, representing three main
taxonomic groups: C, S, and X. For large (volume-equivalent system diameter Deq
$\lt$ 130 km) binary asteroids, the TPM analysis indicates a low thermal
inertia ($\Gamma$ < $\sim$100 J s-1/2K-1m-2) and their emissivity spectra
display strong mineral features, implying that they are covered with a thick
layer of thermally insulating regolith. The smaller (surface-equivalent system
diameter Deff $\lt$17 km) asteroids also show some emission lines of minerals,
but they are significantly weaker, consistent with regoliths with coarser
grains, than those of the large binary asteroids. The average bulk densities of
these multiple asteroids vary from 0.7-1.7 g/cm3 (P-, C- type) to $\sim$2 g/cm3
(S-type). The highest density is estimated for the M-type (22) Kalliope (3.2
$\pm$ 0.9 g/cm3). The spectral energy distributions (SED) and emissivity
spectra, made available as a supplement document, could help to constrain the
surface compositions of these asteroids.
