The OGLE Collection of Variable Stars. Anomalous Cepheids in the
  Magellanic Clouds
  We present a collection of 250 anomalous Cepheids (ACs) discovered in the
OGLE-IV fields toward the Large (LMC) and Small Magellanic Cloud (SMC). The LMC
sample is an extension of the OGLE-III Catalog of ACs published in 2008, while
the SMC sample contains the first known bona fide ACs in this galaxy. The total
sample is composed of 141 ACs in the LMC and 109 ACs in the SMC. All these
stars pulsate in single modes: fundamental (174 objects) or first overtone (76
objects). Additionally, we report the discovery of four ACs located in the
foreground of the Magellanic Clouds. These are the first fundamental-mode ACs
known in the Galactic field.
  We demonstrate that the coefficients phi_21 and phi_31 determined by the
Fourier light curve decomposition are useful discriminators between classical
Cepheids and ACs, at least in the LMC and in the field of the Milky Way. In the
SMC, the light curve shapes and mean magnitudes of short-period classical
Cepheids make them similar to ACs, which is a source of difficulties in the
discrimination of both classes of pulsators. The presence of unidentified ACs
in the catalogs of classical Cepheids may be partly responsible for the
observed non-linearity of the period-luminosity relation observed for
short-period Cepheids in the SMC. We compare spatial distributions of ACs,
classical Cepheids and RR Lyr stars. We show that the distribution of ACs
resembles that of old stars (RR Lyr variables), although in the LMC there are
visible structures typical for young population (classical Cepheids): the bar
and spiral arms. This may suggest that ACs are a mixture of relatively young
stars and mergers of very old stars.
