OGLE-GAL-ACEP-091 -- The First Known Multi-Mode Anomalous Cepheid

TL;DR

This paper reports the discovery and analysis of the first known multi-mode Anomalous Cepheid, a star pulsating in three radial modes, providing new insights into the properties and behavior of such stars.

Contribution

It is the first to identify a triple-mode Anomalous Cepheid and characterizes its pulsation modes, mass, and metallicity using observational data and pulsation models.

Findings

OGLE-GAL-ACEP-091 is a triple-mode pulsator.

Its properties are consistent with being a 1.8 M_S star with [Fe/H] ≈ -0.5.

The star's position and light curve support its classification as an Anomalous Cepheid.

Abstract

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.