Gravitational Influence from Planets on the Measured Rates of Period Change of Pulsating White Dwarfs

TL;DR

This paper investigates how unseen planets orbiting white dwarfs can cause apparent changes in pulsation periods, potentially confounding measurements used to study stellar cooling and fundamental physics.

Contribution

It quantifies the impact of planetary reflex motion on period change measurements, highlighting an extrinsic error source often overlooked in white dwarf pulsation studies.

Findings

Median reflex motion error is comparable to expected cooling signals.

Close-in planets can induce period change errors up to 10^{-11} ss^{-1}.

Planetary effects can significantly bias interpretations of stellar evolution.

Abstract

The measured rates of period change, $\dot{P}$, in the signals of pulsating white dwarf stars are often interpreted as direct detections of structural changes from secular cooling. Due to the intrinsic nature of this quantity, $\dot{P}$ analysis has been used to probe fundamental physics, such as constraining the mass of hypothetical axion particles. However, most white dwarfs are expected to host planets that could induce an external source of period change, caused by the light travel time variations from reflex motion about the system barycenter. Assuming a plausible distribution of planets that could orbit white dwarf stars, we quantify the amount of reflex motion expected from undiscovered planets as an important source of extrinsic error in $\dot{P}$ analyses. While the median error from reflex motion is $\sim10^{-15}$ ss$^{-1}$ (similar to the secular $\dot{P}$ rates expected for cool DAV pulsators), individual close-in planets could cause $\dot{P}$ errors as large as $10^{-11}$ ss$^{-1}$