# Testing the white dwarf mass-radius relationship with eclipsing binaries

## TL;DR

This study provides high-precision, model-independent measurements of white dwarf masses and radii in eclipsing binaries, confirming theoretical models and revealing differences based on core composition and surface hydrogen layers.

## Contribution

It offers the most precise white dwarf mass-radius measurements to date and compares these with theoretical models, highlighting core composition effects and hydrogen envelope consistency.

## Key findings

- Measured radii agree with theoretical predictions across masses and temperatures.
- White dwarfs below 0.48M$_\odot$ match helium core models, larger than C/O models.
- Most white dwarfs have thick hydrogen envelopes, unaffected by common envelope evolution.

## Abstract

We present high precision, model independent, mass and radius measurements for 16 white dwarfs in detached eclipsing binaries and combine these with previously published data to test the theoretical white dwarf mass-radius relationship. We reach a mean precision of 2.4 per cent in mass and 2.7 per cent in radius, with our best measurements reaching a precision of 0.3 per cent in mass and 0.5 per cent in radius. We find excellent agreement between the measured and predicted radii across a wide range of masses and temperatures. We also find the radii of all white dwarfs with masses less than 0.48M$_\odot$ to be fully consistent with helium core models, but they are on average 9 per cent larger than those of carbon-oxygen core models. In contrast, white dwarfs with masses larger than 0.52M$_\odot$ all have radii consistent with carbon-oxygen core models. Moreover, we find that all but one of the white dwarfs in our sample have radii consistent with possessing thick surface hydrogen envelopes ($10^{-5} \ge M_\mathrm{H}/M_\mathrm{WD} \ge 10^{-4}$), implying that the surface hydrogen layers of these white dwarfs are not obviously affected by common envelope evolution.