In an extended photometric campaign of RR Lyrae variables of the globular
cluster M3, an aberrant light-curve, non-Blazhko RRab star, V123, was detected.
Based on its brightness, colors and radial velocity curve, V123 is a bona fide
member of M3. The light curve of V123 exhibits neither a bump preceding light
minimum, nor a hump on the rising branch, and has a longer than normal rise
time, with a convex shape. Similar shape characterizes the mean light curves of
some large-modulation-amplitude Blazhko stars, but none of the regular RRab
variables with similar pulsation periods. This peculiar object thus mimics
Blazhko variables without showing any evidence of periodic amplitude and/or
phase modulation. We cannot find any fully convincing answer to the peculiar
behavior of V123, however, the phenomenon raises again the possibility that
rotation and aspect angle might play a role in the explanation of the Blazhko
phenomenon, and some source of inhomogeneity acts (magnetic field, chemical
inhomogeneity) that deforms the radial pulsation of Blazhko stars during the
modulation.Comment: 5 pages, 5 figures; accepted for publication in ApJ Letter
