  In this paper we discuss four early F-type variable stars whose periods are
an order of magnitude slower than known pulsators of comparable luminosity.
They cannot be stars undergoing simple radial pulsations. For one or more of
these stars we can discount the possibility that the variability is due to
rotational modulation of star spots, interactions with (or tidal distortions
by) a close companion, or obscuration by a rotating lumpy ring of dust orbiting
the star. They are certainly not eclipsing binaries. The only possibility left
seems to be non-radial pulsations, though this explanation involves
difficulties of its own. If they are indeed pulsating stars exhibiting non-
radial gravity modes, they would be the first stars on the cool side of the
Cepheid instability strip in the Hertzsprung-Russell Diagram to be so
identified.
