Beat Cepheids as Probes of Stellar and Galactic Metallicity

The mere location of a Beat Cepheid model in a Period Ratio vs. Perioddiagram (Petersen diagram) puts very tight constraints on its metallicity Z.The Beat Cepheid Peterson diagrams are revisited with linear nonadiabaticturbulent convective models, and their accuracy as a probe for stellarmetallicity is evaluated. They are shown to be largely independent of thehelium content Y, and they are also only weakly dependent on themass-luminosity relation that is used in their construction. However, they arefound to show sensitivity to the relative abundances of the elements that arelumped into the metallicity parameter Z. Rotation is estimated to have but asmall effect on the 'pulsation metallicities'. A composite Petersen diagram ispresented that allows one to read off upper and lower limits on the metallicityZ from the measured period P0 and period ratio P1/P0.Comment: 9 pages, 12 color figures (black and white version available from 1st author's website). With minor revisions. to appear in Ap