A search for variable white dwarfs in large-area time-domain surveys: A pilot study in SDSS Stripe 82

We present a method to reliably select variable white dwarfs from large-area time-domain surveys and apply this method in a pilot study to search for pulsating white dwarfs in the Sloan Digital Sky Survey Stripe 82. From a sample 400 high-confidence white dwarf candidates, we identify 24 which show significant variability in their multi-epoch Stripe 82 data. Using colours, we further selected a sample of pulsating white dwarf (ZZ Ceti) candidates and obtained high-cadence follow-up for six targets. We confirm five of our candidates as cool ZZ Cetis, three of which are new discoveries. Among our 24 candidates we also identify: one eclipsing binary, two magnetic white dwarfs and one pulsating PG1159 star. Finally, we discuss the possible causes for the variability detected in the remaining targets. Even with sparse multi-epoch data over the limited area of Stripe 82, we demonstrate that our selection method can successfully identify various types of variable white dwarfs and efficiently select high-confidence ZZ Ceti candidates.