X-ray sources and their optical counterparts. II

The binary star system of Hercules X-1, an x-ray source, and its optical counterpart HZ Hercules, a 14th-magnitude variable, is described. Discussion focuses on the irregular behavior (nonperiodic optical flickerings) of HZ Hercules apparently resulting from heating of the primary star by the x-ray companion. X rays from an external source are suggested as a new probe with which to study the structure and physical processes in the atmosphere of a more or less normal star. (U.S.)