# Evidence from K2 for rapid rotation in the descendant of an intermediate-mass star

## TL;DR

This study reports the discovery of the fastest rotating pulsating white dwarf to date, with detailed measurements linking its high mass to rapid rotation, and explores its possible evolutionary origins.

## Contribution

It provides the first measurement of an extremely rapid rotation rate in a high-mass pulsating white dwarf, suggesting a potential link between mass and rotation speed.

## Key findings

- Fastest rotation rate of 1.13 hours measured in a white dwarf.
- Star's mass is 0.87 solar masses, the highest for pulsating white dwarfs.
- Binary merger scenario deemed unlikely based on pulsation data.

## Abstract

Using patterns in the oscillation frequencies of a white dwarf observed by K2, we have measured the fastest rotation rate, 1.13(02) hr, of any isolated pulsating white dwarf known to date. Balmer-line fits to follow-up spectroscopy from the SOAR telescope show that the star (SDSSJ0837+1856, EPIC 211914185) is a 13,590(340) K, 0.87(03) solar-mass white dwarf. This is the highest mass measured for any pulsating white dwarf with known rotation, suggesting a possible link between high mass and fast rotation. If it is the product of single-star evolution, its progenitor was a roughly 4.0 solar-mass main-sequence B star; we know very little about the angular momentum evolution of such intermediate-mass stars. We explore the possibility that this rapidly rotating white dwarf is the byproduct of a binary merger, which we conclude is unlikely given the pulsation periods observed.