Distinguishing Axion Models with IAXO
  Helioscopes, such as the proposed International Axion Observatory (IAXO),
have significant discovery potential for axions and axion-like particles. In
this note, we argue that beyond discovery they can resolve details of the
model. In particular, in the region suggested by stellar cooling anomalies,
there is a good chance to measure the mass of the particle and separately its
couplings to electrons and photons. This can give crucial information on the
nature of the underlying model. To achieve this, energy resolved detectors and
a setup with low energy threshold are needed.
