Cepheids: A New Class of X-Ray Variable: Part I: l Car

Recent Cepheid X-ray observations have found the surprising result of increased emission at maximum radius, a pulsation phase when the photosphere is quiescent. Recent interferometric observations of Cepheids have found circumstellar envelopes (also surprising) which may be related and raise questions of possible mass-loss and increased infrared flux as sources of scatter in the physics behind the Cepheid Leavitt (P-L) relation. The X-ray variation is a new diagnostic to understand the physics Cepheid upper atmospheres. This program requests an observation of the cool long period Cepheid l Car at the phase of maximum radius to investigate the dependence of the X-ray flux on convection.