A Second Look at the Metal Line Variability of G29-38

TL;DR

This study investigates the variability of metal lines in the white dwarf G29-38, finding no significant short-term or long-term changes in spectral line equivalent widths, thus questioning previous reports of variability.

Contribution

The paper provides high-resolution spectroscopic data that challenge earlier claims of rapid metal line variability in G29-38, offering more precise measurements over multiple timescales.

Findings

No evidence of Ca II K line variability over six days.

Equivalent width scatter consistent with measurement errors (~7%).

No significant long-term variability over ten years.

Abstract

The pulsating white dwarf G29-38 possesses a dust disk and metal lines attributed to the accretion of its disk material. \citet{vonhipg29} have reported variability in the equivalent width of G29-38's CaII K line on the timescale of days. We use high resolution optical spectroscopy of G29-38's CaII K line to test this observation. Over six days spanning in June 2007 and October 2007 we see no evidence for variability in the equivalent width of the Ca II K line. We also sample the variability of the Ca II K line over integrated timescales of $\sim$100-500 seconds, where errors from incomplete coverage of pulsation modes are predicted to be $\sim$8-15%. We find that the scatter of the equivalent widths over this time period is consistent with measurement errors at the 7% level, slightly weaker than predicted but within the uncertainties of predictions. Weaker Ca and Mg lines observed show no significant variability on yearly timescales over ten years based on our data and other high resolution spectra. We conclude that further study is warranted to verify if the accretion onto G29-38 is variable.