A Model of the Pulsating Extremely Low-Mass White Dwarf Precursor WASP 0247-25B

TL;DR

This paper models the evolution and pulsation of the low-mass white dwarf precursor WASP 0247-25B, successfully matching observed properties and predicting excited pulsation modes, thus testing evolutionary theories of such pulsators.

Contribution

It provides the first detailed evolutionary and pulsation model for WASP 0247-25B, incorporating rotational mixing and predicting observable pulsation modes consistent with measurements.

Findings

Models closely reproduce observed properties.

Predicted pulsation modes are excited and match observed periods.

Identified three possible seismic solutions based on mode assumptions.

Abstract

We present an analysis of the evolutionary and pulsation properties of the extremely low-mass white dwarf precursor (B) component of the double-lined eclipsing system WASP 0247-25. Given that the fundamental parameters of that star have been obtained previously at a unique level of precision, WASP 0247-25B represents the ideal case for testing evolutionary models of this newly-found category of pulsators. Taking into account the known constraints on the mass, orbital period, effective temperature, surface gravity, and atmospheric composition, we present a model that is compatible with these constraints and show pulsation modes that have periods very close to the observed values. Importantly, these modes are predicted excited. Although the overall consistency remains perfectible, the observable properties of WASP 0247-25B are closely reproduced. A key ingredient of our binary evolutionary models is represented by rotational mixing as the main competitor against gravitational settling. Depending on assumptions made about the values of the degree index l for the observed pulsation modes, we found three possible seismic solutions. We discuss two tests, rotational splitting and multicolor photometry, that should readily identify the modes and discriminate between these solutions. However, this will require improved temporal resolution and higher S/N observations than currently available.