Identification of the X-Ray Pulsar in Hercules: a New Optical Pulsar

A series of photographic, photoelectric, and spectroscopic observations beginning 1972 June 1 has led to the optical identification of Her X-l (2U 1705 + 34), a pulsed X-ray source in an eclipsing binary system, with the thirteenth magnitude blue variable star HZ Herculis. The detection of optical pulses at the frequency of the X-ray pulsar on three nights makes the identification conclusive and establishes HZ Her as the second known optical pulsar. The strength of the optical pulses may be correlated with the orbital phase but is not obviously related to the high or low intensity states of the X-ray source.