Pseudoscalar conversion and X-rays from stars

We consider limits on photon couplings of the form gΦFF̃ to a massless pseudoscalar Φ. Such pseudoscalars can be produced in stellar interiors and then reconverted into photons in the presence of the galactic magnetic field. If the coupling g is large, all stars, especially giants and supergiants, would be copious producers of X-rays. Measurements by the HEAO 1 satellite on α-Ori indicate the coupling g is constrained to be g < 2.5×10−11 GeV−1, a factor of four better than previous limits.