  A finite axion-nucleon coupling, nearly unavoidable for QCD axions, leads to
the production of axions via the thermal excitation and subsequent
de-excitation of Fe-57 isotopes in the sun. We revise the solar bound on this
flux adopting the up to date emission rate, and investigate the sensitivity of
the proposed International Axion Observatory IAXO and its intermediate stage
BabyIAXO to detect these axions. We compare different realistic experimental
options and discuss the model dependence of the signal. Already BabyIAXO has
sensitivity far beyond previous solar axion searches via the nucleon coupling
and IAXO can improve on this by more than an order of magnitude.
