The luminosities of type II Cepheids and RR Lyrae variables
  Recent work on the luminosities of type II Cepheids (CephIIs) and RR Lyrae
variables is reviewed.In the near infrared (JHKs) the CephIIs in globular
clusters show a narrow, linear, period-luminosity relation over their whole
period range (about 1 to 100 days). The CephIIs in the general field of the LMC
follow this relation for periods shorter than about 20 days. At longer period
(the region of the RV Tau stars), the LMC field stars have a significant
scatter and in the mean are more luminous than the PL relation. The OGLEIII
optical data for the LMC field variables show similar trends. Infrared colours
of stars in the RV Tau period range show marked mean differences between three
groupings; the Galactic field, the LMC field, and globular clusters. In the
case of the Galactic field, at least, this may be strongly influenced by
selection effects. In the period range about 4 to 20 days (the W Vir range)
there are stars lying above the PL relation which may be recognized by their
light curves and are all likely to be binaries. The bright Galactic variable,
kappa Pav probably belongs to this group. There is evidence that CephIIs in the
general field (LMC and Galaxy) have a wider range of masses than those in
globular clusters. At present the CephII PL zero-point depends on the pulsation
parallaxes of two stars. Zero-points of RR Lyrae M(V)-[Fe/H] and Ks-log P
relations can be obtained from trigonometrical, statistical and pulsation
parallaxes. These zero-points are compared with those for CephIIs and with the
classical Cepheid scale using variables of these three types in the LMC. Within
the uncertainties (about 0.1mag) the various scales are in agreement.
