The First Six Outbursting Cool DA White Dwarf Pulsators

TL;DR

This paper reports the discovery and analysis of six cool pulsating DA white dwarfs exhibiting irregular outbursts, characterized by flux increases, pulsation spectrum complexity, and their position near the DAV instability strip's cool edge.

Contribution

It introduces two new outbursting DAVs, expanding the known sample to six, and details their common observational features and pulsation behaviors.

Findings

Outbursts increase flux by up to 15% and last hours.

Outbursts recur irregularly on days timescales.

Outbursting DAVs are near the cool edge of the instability strip.

Abstract

Extensive observations from the Kepler spacecraft have recently revealed a new outburst phenomenon operating in cool pulsating DA (hydrogen atmosphere) white dwarfs (DAVs). With the introduction of two new outbursting DAVs from K2 Fields 7 (EPIC 229228364) and 8 (EPIC 220453225) in these proceedings, we presently know of six total members of this class of object. We present the observational commonalities of the outbursting DAVs: (1) outbursts that increase the mean stellar flux by up to 15%, last many hours, and recur irregularly on timescales of days; (2) effective temperatures that locate them near the cool edge of the DAV instability strip; and (3) rich pulsation spectra with modes that are observed to wander in amplitude/frequency.