  There are a number of observational hints from astrophysics which point to
the existence of stellar energy losses beyond the ones accounted for by
neutrino emission. These excessive energy losses may be explained by the
existence of a new sub-keV mass pseudoscalar Nambu--Goldstone boson with tiny
couplings to photons, electrons, and nucleons. An attractive possibility is to
identify this particle with the axion -- the hypothetical pseudo
Nambu--Goldstone boson predicted by the Peccei--Quinn solution to the strong CP
problem. We explore this possibility in terms of a DFSZ-type axion and of a
KSVZ-type axion/majoron, respectively. Both models allow a good global fit to
the data, prefering an axion mass around 10 meV. We show that future axion
experiments -- the fifth force experiment ARIADNE and the helioscope IAXO --
can attack the preferred mass range from the lower and higher end,
respectively. An axion in this mass range can also be the main constituent of
dark matter.
