  Sub-Chandrasekhar mass carbon-oxygen white dwarfs (CO WDs) with a surface
helium (He) shell have been proposed as progenitors of Type Ia supernovae (SNe
Ia). If true, the resulting thermonuclear explosions should be able to account
for at least some of the range of SNe Ia observables. To study this, we conduct
a parameter study based on 3D simulations of double detonations in CO WDs with
a He shell, assuming different core and shell masses. An admixture of C to the
shell and solar metallicity are included in the models. The hydrodynamic
simulations are carried out using the AREPO code. This allows us to follow the
He shell detonation with high numerical resolution, and improves the
reliability of predicted nucleosynthetic shell detonation yields. The addition
of C to the shell leads to a lower production of 56Ni while including solar
metallicity increases the production of IMEs. The production of higher mass
elements is further shifted to stable isotopes at solar metallicity. Moreover,
we find different core detonation ignition mechanisms depending on the core and
shell mass configuration. This has an influence on the ejecta structure. We
present the bolometric light curves predicted from our explosion simulations
using the radiative transfer code ARTIS, and make comparisons with SNe Ia data.
The bolometric light curves of our models show a range of brightnesses, able to
account for sub-luminous to normal SNe Ia. We show the model bolometric
width-luminosity relation compared to data for a range of viewing angles. We
find that, on average, our brighter models lie within the observed data. The
ejecta asymmetries produce a wide distribution of observables, which might
account for outliers in the data. However, the models overestimate the extent
of this compared to data. We also find the bolometric decline rate over 40 days
appears systematically faster than data. (abridged)
