Observations of Classical Cepheids

Calibration of the Period-Luminosity relation for Classical Cepheids is still far from settled: the debate continues as to whether there is a unique relation from galaxy to galaxy and what the precise form is in any one system. In the Milky Way we suffer from poor sample size; in the Magellanic Clouds it is still a matter of low accuracy in the observations. Work is in progress at several observatories to alleviate both of these problems through studying not only galactic Cepheids but also those in the LMC, SMC, M33 and NGC 300. Arellano & Percy (CTI0/DD0) have begun a photoelectric monitoring of the apparently brightest F & G supergiants in the Milky Way. The aim is to detect near-by very-low-amplitude Cepheids which are binaries or are intrinsically low amplitude variables. This should provide a better qualitative hold on the sense of the amplitude dependence on effective temperature, as well as the true fequency of the cepheid phenomenon.