Precise Atmospheric Parameters for the Shortest Period Binary White Dwarfs: Gravitational Waves, Metals, and Pulsations

TL;DR

This paper provides precise atmospheric parameters, chemical abundances, and binary system details for 61 low mass white dwarfs, exploring their pulsations, gravitational wave emissions, and the effects of shell flashes, advancing understanding of their evolution.

Contribution

It introduces new spectroscopic measurements, including metal abundances, and compares stellar radii with models, offering insights into white dwarf evolution and gravitational wave predictions.

Findings

Good agreement between spectroscopic and model-independent radii for most white dwarfs.

Metal and helium abundances vary with temperature and mass, suggesting shell flashes influence composition.

Calculated gravitational wave strains indicate some systems are detectable by eLISA.

Abstract

We present a detailed spectroscopic analysis of 61 low mass white dwarfs and provide precise atmospheric parameters, masses, and updated binary system parameters based on our new model atmosphere grids and the most recent evolutionary model calculations. For the first time, we measure systematic abundances of He, Ca and Mg for metal-rich extremely low mass white dwarfs and examine the distribution of these abundances as a function of effective temperature and mass. Based on our preliminary results, we discuss the possibility that shell flashes may be responsible for the presence of the observed He and metals. We compare stellar radii derived from our spectroscopic analysis to model-independent measurements and find good agreement except for those white dwarfs with Teff < 10,000 K. We also calculate the expected gravitational wave strain for each system and discuss their significance to the eLISA space-borne gravitational wave observatory. Finally, we provide an update on the instability strip of extremely low mass white dwarf pulsators.