Multiperiodic pulsations of the unique DAQ white dwarf J0551+4135: insights into a merger remnant

TL;DR

This study investigates the pulsation properties of the unique DAQ white dwarf J0551+4135, revealing its oscillation modes, estimating its mass and age, and providing new evolutionary models, with implications for understanding merger remnants.

Contribution

The paper presents the first detailed time-series photometry and modeling of J0551+4135, a white dwarf with a merger origin, including new evolutionary models for spectroscopic analysis.

Findings

Detected ten significant pulsation peaks with frequencies 987-1180 μHz.

Estimated mass of approximately 1.13 solar masses and age around 1.7 Gyr for a CO core.

Identified non-radial gravity-mode oscillations indicating complex internal structure.

Abstract

2MASS J05513444+4135297 (herafter J0551+4135) is the only pulsating DAQ white dwarf known with a carbon and hydrogen atmosphere. Its unusual atmospheric composition and kinematics indicate a white dwarf merger origin. We present time-series photometry of J0551+4135 obtained using the Apache Point Observatory 3.5m, Gemini North 8m, and Gran Telescopio Canarias 10m telescopes. J0551+4135 exhibits variations in pulsation amplitude and frequency over time. We detect ten significant recurring peaks across different subsets of observations, with frequencies ranging from 987 to 1180~$\mu$Hz, consistent with non-radial gravity ($g$)-mode oscillations. We present new evolutionary models suitable for spectroscopic characterization of DAQ white dwarfs, and derive a mass of $1.13 \pm 0.01\,M_\odot$ and a cooling age of $1.7 \pm 0.1$ Gyr for a CO core, and $1.12 \pm 0.01\,M_\odot$ and $1.6 \pm 0.1$\,Gyr for an ONe-core white dwarf, respectively. However, detailed asteroseismology of this unique pulsator has to wait until fully-consistent DAQ evolutionary models are available. Further observations, including multi-site campaigns to reduce daily aliasing and to improve the signal-to-noise ratio would be helpful for identification of additional modes and constraining the internal structure of this unique pulsator.