The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VIII. Type II Cepheids in the Small Magellanic Cloud

TL;DR

This paper presents the OGLE-III catalog of 43 type II Cepheids in the Small Magellanic Cloud, including new subclasses and binary systems, with detailed photometry and variability analysis over 8-13 years.

Contribution

It provides the first identification of type II Cepheids in the SMC, including peculiar W Vir stars and binary systems, expanding understanding of these variables in a new galaxy.

Findings

First catalog of type II Cepheids in the SMC.

Discovery of peculiar W Vir stars as binaries.

Detection of eclipsing and ellipsoidal variability in some stars.

Abstract

The eighth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains type II Cepheids in the Small Magellanic Cloud (SMC). The sample consists of 43 objects, including 17 BL Her, 17 W Vir and 9 RV Tau stars (first examples ever found in the SMC). Seven stars have been classified as peculiar W Vir stars - a recently identified subclass of type II Cepheids. These stars have distinctive light curves, are brighter and bluer than the ordinary W Vir variables. We confirm that a large fraction of the peculiar W Vir stars are members of binary systems. Three type II Cepheids exhibit eclipsing variations superimposed on the pulsation light curves, and three other objects show long-period ellipsoidal variability. All stars with the indication of binarity display secondary periods which may be interpreted as amplitude and/or phase modulations of the pulsation light curves with periods equal to the orbital periods or half the orbital periods. We do not have any model for these modulations, however this phenomenon rules out a possibility of the optical blends of a pulsating star and a binary system. For each object the multi-epoch V- and I-band photometry collected over 8 or 13 years of observations and finding charts are available to the astronomical community from the OGLE Internet archive.