Is There a Difference in Luminosity between Field and Cluster RR Lyrae   Variables?
  Recent Hipparcos results have lent support to the idea that RR Lyrae variables in the halo field and in globular clusters differ in luminosity by ~0.2mag. In this Letter, we study the pulsation properties of RR Lyraes in clusters with distances determined via main-sequence fitting to Hipparcos parallaxes for field subdwarfs, and compare them with the properties of field variables also analyzed with Hipparcos. We show that the period-temperature distributions for field and cluster variables are essentially indistinguishable, thus suggesting that there is no significant difference in luminosity between them. 
M. Catelan (NASA/GSFC)