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