2011PASP..123..127S

The theory of slow convective cycles in the envelopes of RR Lyrae stars showing the Blazhko effect predicts an anticorrelation between the pulsation period and radius for hot members of the group, contrary to what might be expected from the (period, mean density) relation. This negative correlation has actually been observed by Jurcsik et al. for the hot stars MW Lyr, DM Cyg, and (in part) CZ Lac, the only stars so far measured accurately for radius variations over a Blazhko cycle. Significantly cooler members of the group would be expected to show a normal, positive correlation between pulsation period and radius.