On improved Cepheid distance estimators
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In this paper, we derive a physical argument for the existence of Period-luminosity and period-luminosity-colour relations at maximum light. We examine in detail a sample of Cepheids in the Large Magellanic Cloud, and compare the variance of some PL and PLC type distance indicators based on mean and maximum light. We show that a PLC relation based on maximum light leads to a distance estimator with a dispersion about $10 \%$ smaller than its counterpart using mean light. We also show that a PLC type relation constructed using observations at both maximum and mean light has a significantly $( > 50 \%)$ smaller dispersion than a PLC relation using either maximum or mean light alone. A comparable $( > 30 \%)$ reduction in the dispersion of the corresponding distance estimator, however, in this case requires the relation be applied to a large $( n > 30)$ group of equidistant Cepheids in, e.g., a distant galaxy. Recent HST observations of IC4182, M81 and M100 already provide suitable candidate data sets for this relation.
Plain Latex version 3.141, 25 pages including figures and tables. (Requires style file laa.sty) Astronomy and Astrophysics in press
Plain Latex version 3.141, 25 pages including figures and tables. (Requires style file laa.sty) Astronomy and Astrophysics in press