M. Catelan, ON THE OOSTERHOFF-ARP-SANDAGE PERIOD-SHIFT EFFECT AND ITS EVOLUTIONARY INTERPRETATION, Astronomy and astrophysics, 285(2), 1994, pp. 469-472
Synthetic models of the horizontal branch are employed to show that th
e present theoretical predictions for the slope of the mean ab-type RR
Lyrae period shift-metallicity relation, DELTA[log P(ab)] - [Fe/H], a
re incompatible with the recent observational results by Sandage (1993
, AJ 106, 687), unless hysteresis is highly effective in the determina
tion of RR Lyrae types. The new instability strip topology by Bono & S
telling-werf (1992, MSAIt 63, 357) further strengthens this conclusion
. However, the recent results of Catelan (1994, AJ, submitted) recomme
nd caution before regarding hysteresis as the final explanation for ex
isting problems involving RR Lyrae stars in Galactic globular clusters
.