Outbursts in two new cool pulsating DA white dwarfs

TL;DR

This paper reports the discovery of two new outbursting pulsating white dwarfs observed by K2, expanding the known sample and showing that outbursts occur only in the coolest DAVs near the red edge of the instability strip.

Contribution

It identifies two new outbursting white dwarfs and establishes their occurrence is limited to the coolest DAVs near the red edge of the instability strip.

Findings

Outbursts cause up to 15% flux increase.

Outbursts recur every 2.4 to 5 days.

Only the coolest DAVs exhibit outbursts.

Abstract

The unprecedented extent of coverage provided by Kepler observations recently revealed outbursts in two hydrogen-atmosphere pulsating white dwarfs (DAVs) that cause hours-long increases in the overall mean flux of up to 14%. We have identified two new outbursting pulsating white dwarfs in K2, bringing the total number of known outbursting white dwarfs to four. EPIC 211629697, with T_eff = 10,780 +/- 140 K and log(g) = 7.94 +/- 0.08, shows outbursts recurring on average every 5.0 d, increasing the overall flux by up to 15%. EPIC 229227292, with T_eff = 11,190 +/- 170 K and log(g) = 8.02 +/- 0.05, has outbursts that recur roughly every 2.4 d with amplitudes up to 9%. We establish that only the coolest pulsating white dwarfs within a small temperature range near the cool, red edge of the DAV instability strip exhibit these outbursts.