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Unformatted text preview: rom the two empirical relations we can derive T M . 6 and the liFetime oF a main-sequenxce star, t life M L M-3 T-4 . 8 . The main-sequence cut-o temperatures oF the two clusters shoudl indicate their age. t A t B T B T A 4 . 8 2 . 1 Cluster A should thereFore be a bit more than twice as old as cluster B. Problem 3: Cepheids This Cepheid has an absolute brightness M B =-3 . 58 . The distance is therefore D = (10 pc) 10 . 2 ( m B-M B ) = (10 pc) 10 4 . 82 650 , 000 pc 2 . 1 10 6 light-years The observed radiation was therefore emitted two million years ago, or in other words, the star is now two million years older than it was at the time of emission. The lifetime of a Cepheid in this phase is shorter than that, and thus we would not Fnd it....
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