ON THE DIFFICULTY OF DETERMINING THE COLOR-TERM IN THE CEPHEID PLC RELATION
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1993
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Abstract
We present here a new tentative to determine the color-term of the Cepheid period - luminosity - color relation, using a large sample of 100 galactic Cepheids, whose distances are known from the visual surface brightness method (approximately 10% accuracy). The derived coefficient seems lower (between 0 and 1) than both its observed value in the Magellanic Clouds (about 2.1) and the semi-theoretical value of about 3.4. Systematic effects due to metallicity are investigated, and discarded as a possible explanation of the discrepancy. Statistical effects are reviewed, and a formalism useful to other topics is presented. Statistical corrections remove only part of the discrepancy we find. We therefore still recommend not to use the PLC relation to determine extragalactic distances, but to prefer a simple PL relation, as long as the question of the PLC color-term is not clearly resolved.
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CEPHEIDS