Anomalous Cepheids (ACs) are metal-deficient, core-helium-burning pulsating stars with masses in the range 1.2-2.2 M_S. Until recently, all known ACs were pure single-mode pulsators. The first candidate for an AC pulsating in more than one radial mode - OGLE-GAL-ACEP-091 - was recently identified in the Milky Way based on the photometric database of the Optical Gravitational Lensing Experiment (OGLE) survey. We analyze this object showing that it is actually a triple-mode pulsator. Its position in the Petersen diagram, the light-curve morphology quantified by Fourier coefficients, and absolute magnitudes derived from the Gaia parallax are consistent with the assumption that OGLE-GAL-ACEP-091 is an AC. Our grid of linear pulsation models indicates that OGLE-GAL-ACEP-091 is a 1.8 M_S star with a metallicity of about [Fe/H] = -0.5 dex.
@article{arxiv.2009.06642,
title = {OGLE-GAL-ACEP-091 -- The First Known Multi-Mode Anomalous Cepheid},
author = {I. Soszyński and R. Smolec and A. Udalski and M. K. Szymański and P. Pietrukowicz and D. M. Skowron and J. Skowron and P. Mróz and R. Poleski and S. Kozłowski and P. Iwanek and M. Wrona and M. Gromadzki and K. Ulaczyk and K. Rybicki},
journal= {arXiv preprint arXiv:2009.06642},
year = {2020}
}
Comments
7 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters