Year 1 of the ZTF high-cadence Galactic plane survey: strategy, goals, and early results on new single-mode hot subdwarf B-star pulsatos

We present the goals, strategy, and first results of the high-cadence Galactic plane survey using the Zwicky Transient Facility (ZTF). The goal of the survey is to unveil the Galactic population of short-period variable stars, including short-period binaries, and stellar pulsators with periods less than a few hours. Between 2018 June and 2019 January, we observed 64 ZTF fields resulting in 2990deg(2) of high stellar density in the ZTF-r band along the Galactic plane. Each field was observed continuously for 1.5 to 6h with a cadence of 40sec. Most fields have between 200 and 400 observations obtained over 2-3 continuous nights. As part of this survey, we extract a total of approximate to 230million individual objects with at least 80 epochs obtained during the high-cadence Galactic plane survey reaching an average depth of ZTF-r approximate to 20.5mag. For four selected fields with 2-10million individual objects per field, we calculate different variability statistics and find that approximate to 1-2 per cent of the objects are astrophysically variable over the observed period. We present a progress report on recent discoveries, including a new class of compact pulsators, the first members of a new class of Roche lobe filling hot subdwarf binaries as well as new ultracompact double white dwarfs and flaring stars. Finally, we present a sample of 12 new single-mode hot subdwarf B-star pulsators with pulsation amplitudes between ZTF-r = 20-76mmag and pulsation periods between P = 5.8-16min with a strong cluster of systems with periods approximate to 6min. All of the data have now been released in either ZTF Data Release 3 or Data Release 4.

Automated summary

The high-cadence Galactic plane survey conducted using ZTF aims to uncover the population of short-period variable stars in the Galaxy. Initial results show the discovery of various new stellar features and phenomena, with approximately 230 million objects observed and data released for further study.