  Rotation properties (spin-axis direction and rotation period) and coarse
shape models of asteroids can be reconstructed from their disk-integrated
brightness when measured from various viewing geometries. These physical
properties are essential for creating a global picture of structure and
dynamical evolution of the main belt. The number of shape and spin models can
be increased not only when new data are available, but also by combining
independent data sets and inverting them together. Our aim was to derive new
asteroid models by processing readily available photometry. We used asteroid
photometry compiled in the Lowell Observatory photometry database with
photometry from the Gaia Data Release 2. Both data sources are available for
about 5400 asteroids. In the framework of the Asteroids@home distributed
computing project, we applied the light curve inversion method to each asteroid
to find its convex shape model and spin state that fits the observed
photometry. Due to the limited number of Gaia DR2 data points and poor
photometric accuracy of Lowell data, we were able to derive unique models for
only ~1100 asteroids. Nevertheless, 762 of these are new models that
significantly enlarge the current database of about 1600 asteroid models. Our
results demonstrate the importance of a combined approach to inversion of
asteroid photometry. While our models in general agree with those obtained by
separate inversion of Lowell and Gaia data, the combined inversion is more
robust, model parameters are more constrained, and unique models can be
reconstructed in many cases when individual data sets alone are not sufficient.

Earth and Planetary Astrophysics