The Variable Stars and Blue Horizontal Branch of the Metal-rich Globular Cluster NGC 6441

We present time-series VI photometry of the metal-rich ([Fe/H] = -0.53)globular cluster NGC 6441. Our color-magnitude diagram shows that the extendedblue horizontal branch seen in Hubble Space Telescope data exists in theoutermost reaches of the cluster. The red clump slopes nearly parallel to thereddening vector. A component of this slope is due to differential reddening,but part is intrinsic. The blue horizontal branch stars are more centrallyconcentrated than the red clump stars. We have discovered about 50 new variablestars near NGC 6441, among them eight or more RR Lyrae stars which are veryprobably cluster members. Comprehensive period searches over the range 0.2-1.0days yielded unusually long periods (0.5-0.9 days) for the fundamentalpulsators compared with field RR Lyrae of the same metallicity. Three similarlong-period RR Lyrae are known in other metal-rich globulars. With over tenexamples in hand, it seems that a distinct sub-class of RR Lyrae is emerging.The observed properties of the horizontal branch stars are in reasonableagreement with recent models which invoke deep mixing to enhance theatmospheric helium abundance, while they conflict with models which assume highinitial helium abundance. The light curves of the c-type RR Lyrae seem to haveunusually long rise times and sharp minima. Reproducing these light curves instellar pulsation models may provide another means of constraining the physicalvariables responsible for the anomalous blue horizontal branch extension andsloped red clump observed in NGC 6441.Comment: 30 pages plus 6 EPS and 6 JPEG figures; uses AAS TeX. Accepted by the Astronomical Journal. Minor changes include computing He abundance, modifications to Figs 1 and 8, and expansion on idea that blue HB stars may be produced in binarie