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

Abstract

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 deg2 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 ≈230 million individual objects with at least 80 epochs obtained during the high-cadence Galactic Plane survey reaching an average depth of ZTF-r ≈ 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 ≈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 ≈6 min. All of the data have now been released in either ZTF Data Release 3 or data release 4.

Identifying Blue Large Amplitude Pulsators from Gaia DR2 & ZTF DR3

“…None of our remaining candidate BLAPs are present on the VSX. Finally, ZGP-HGBLAP-02 has been recently identified as a potential single-mode sdB hot subdwarf pulsator (Kupfer et al 2021). Due to the similarity between our High-g BLAP candidates, it is possible that the other five candidates may also be members of this recently discovered type of pulsator.…”

Birth of the ELMs: a ZTF survey for evolved cataclysmic variables turning into extremely low-mass white dwarfs

“…We investigate the origin of scatter in Appendix C. We conclude that long-term brightness variations due to changes in disk structure dominate for most objects with scatter: when a Fourier model is subtracted from the observed light curves, few-percent brightness variations on month-to-year timescales are evident in about half of the sample. Where available, we also investigate observations from the ZTF high-cadence Galactic plane survey (Kupfer et al 2021). As expected, most objects have significantly less scatter in their phased light curves when only a few hours of continuous observations are considered than when we model the full ∼3 year ZTF baseline.…”

Discovery of periodic variables in the hot subdwarf catalogue through a systematic search in Zwicky Transient Facility data

“…We extracted light curves from ZTF DR6 which contains all the public data obtained between March 2018 -April 2021, and data acquired under private surveys spanning March 2018 -December 2019. The private surveys include observational programs awarded by Caltech and performed by the ZTF collaboration, including a high cadence survey of the Galactic Plane (Kupfer et al 2021).…”