A New Timescale for Period Change in the Pulsating DA White Dwarf WD 0111+0018

TL;DR

This paper reports the fastest observed period change in a pulsating white dwarf, suggesting an additional evolutionary timescale beyond cooling, and confirms the nonlinear nature of combination frequencies.

Contribution

It provides the first measurement of an extremely rapid period change in a pulsating white dwarf, revealing new insights into stellar evolution processes.

Findings

Observed period change exceeds cooling predictions by over two orders of magnitude.

Nonlinear combination frequencies share the evolutionary characteristics of their parent modes.

The results imply an additional timescale influences pulsation period evolution.

Abstract

We report the most rapid rate of period change measured to date for a pulsating DA (hydrogen atmosphere) white dwarf (WD), observed in the 292.9 s mode of WD 0111+0018. The observed period change, faster than 10^{-12} s/s, exceeds by more than two orders of magnitude the expected rate from cooling alone for this class of slow and simply evolving pulsating WDs. This result indicates the presence of an additional timescale for period evolution in these pulsating objects. We also measure the rates of period change of nonlinear combination frequencies and show that they share the evolutionary characteristics of their parent modes, confirming that these combination frequencies are not independent modes but rather artifacts of some nonlinear distortion in the outer layers of the star.