Deciphering the Pulsations of G 29-38 with Optical Time Series Spectroscopy

TL;DR

This study uses optical time series spectroscopy from VLT to analyze pulsations in white dwarf G 29-38, identifying pulsation modes and their spherical degrees to improve stellar interior models.

Contribution

It introduces new measurements of pulsation modes and their spherical degrees, including four newly identified modes, enhancing asteroseismic understanding of G 29-38.

Findings

Confirmed several spherical degree ($1$) identifications.

Added four new mode degree identifications, including $2$ and possibly $4$.

Total of eleven modes with known spherical degrees.

Abstract

We present optical time series spectroscopy of the pulsating white dwarf star G29-38 taken at the Very Large Telescope (VLT). By measuring the variations in brightness, Doppler shift, and line shape of each spectrum, we explore the physics of pulsation and measure the spherical degree ($\ell$) of each stellar pulsation mode. We measure the physical motion of the g-modes correlated with the brightness variations for three of the eight pulsation modes in this data set. The varying line shape reveals the spherical degree of the pulsations, an important quantity for properly modeling the interior of the star with asteroseismology. Performing fits to the H$\beta$, H$\gamma$, and H$\delta$ lines, we quantify the changing shape of the line and compare them to models and previous time series spectroscopy of G~29-38. These VLT data confirm several $\ell$ identifications and add four new values, including an additional $\ell$=2 and a possible $\ell$=4. In total from both sets of spectroscopy of G29-38, eleven modes now have known spherical degrees.