Identifying Blue Large Amplitude Pulsators from Gaia DR2 & ZTF DR3
  Blue Large Amplitude Pulsators (BLAPs) are hot, subluminous stars undergoing
rapid variability with periods of under 60 mins. They have been linked with the
early stages of pre-white dwarfs and hot subdwarfs. They are a rare class of
variable star due to their evolutionary history within interacting binary
systems and the short timescales relative to their lifetime in which they are
pulsationally unstable. All currently known BLAPs are relatively faint (15-19
mag) and are located in the Galactic plane. These stars have intrinsically blue
colours but the large interstellar extinction in the Galactic plane prevents
them from swift identification using colour-based selection criteria. In this
paper, we correct the Gaia $G$-band apparent magnitude and
$G_{\mathrm{BP}}-G_{\mathrm{RP}}$ colours of 89.6 million sources brighter than
19 mag in the Galactic plane with good quality photometry combined with
supplementary all-sky data totalling 162.3 million sources. Selecting sources
with colours consistent with the known population of BLAPs and performing a
cross-match with the Zwicky Transient Facility (ZTF) DR3, we identify 98 short
period candidate variables. Manual inspection of the period-folded light curves
reveals 22 candidate BLAPs. Of these targets, 6 are consistent with the
observed periods and light curves of the known BLAPs, 10 are within the
theoretical period range of BLAPs and 6 are candidate high-gravity BLAPs. We
present follow-up spectra of 21 of these candidate sources and propose to
classify 1 of them as a BLAP, and tentatively assign an additional 8 of them as
BLAPs for future population studies.
