The pulsating DA white dwarf star EC 14012-1446: results from four epochs of time-resolved photometry

TL;DR

This study analyzes over 200 hours of photometry of the pulsating white dwarf EC 14012-1446 across four epochs, revealing 19 independent frequencies, amplitude and frequency variations, and insights into its rotation, despite challenges in mode identification.

Contribution

First detailed multi-epoch photometric analysis of EC 14012-1446 revealing its pulsation modes, amplitude variations, and rotation period, highlighting complexities in mode interpretation.

Findings

Detected 19 independent pulsation frequencies.

Inferred a rotation period of approximately 0.61 days.

Observed amplitude and frequency variability in modes.

Abstract

The pulsating DA white dwarfs are the coolest degenerate stars that undergo self-driven oscillations. Understanding their interior structure will help to understand the previous evolution of the star. To this end, we report the analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA white dwarf star EC 14012-1446 acquired during four observing epochs in three different years, including a coordinated three-site campaign. A total of 19 independent frequencies in the star's light variations together with 148 combination signals up to fifth order could be detected. We are unable to obtain the period spacing of the normal modes and therefore a mass estimate of the star, but we infer a fairly short rotation period of 0.61 +/- 0.03 d, assuming the rotationally split modes are l=1. The pulsation modes of the star undergo amplitude and frequency variations, in the sense that modes with higher radial overtone show more pronounced variability and that amplitude changes are always accompanied by frequency variations. Most of the second-order combination frequencies detected have amplitudes that are a function of their parent mode amplitudes, but we found a few cases of possible resonantly excited modes. We point out the complications in the analysis and interpretation of data sets of pulsating white dwarfs that are affected by combination frequencies of the form f_A+f_B-f_C intruding into the frequency range of the independent modes.