RR Lyrae in the LMC: Insights Into the Oosterhoff Phenomenon
  Although more than eight decades have passed since P. Th. Oosterhoff drew
attention to differences in the properties of RR Lyrae variables in globular
clusters, the origin and significance of the Oosterhoff groups remain unclear.
Nonetheless, the accumulation of extensive new observations of RR Lyrae stars
in globular clusters of the Milky Way and Local Group galaxies allows a fresh
look at the phenomenon. Insights come not only from surveys of variables within
the original Oosterhoff groups I and II but also from recent observations of
the Oosterhoff-intermediate systems found especially in smaller Local Group
galaxies. We will compare properties of RR Lyrae in several systems to
investigate what they reveal about system-to-system differences of transition
temperature between fundamental-mode and first overtone pulsators and of
horizontal branch luminosity. Both transition temperature and horizontal branch
luminosity have at various times been credited as playing roles in the creation
of the Oosterhoff dichotomy.
