Data recently returned for d Cep from the Chandra X-ray Observatory, combined with previous X-ray measures secured with the XMM-Newton X-ray satellite, have shown that d Cep has X-ray variations occurring in accord with the supergiant star's 5.4 day pulsation period. X-rays are observed at all phases of the star’s pulsations, but sharply rise by ~400% near the times when the star swells to its maximum diameter of about 45 times that of the Sun.
Read full story here