Marco C Lam

From data collection to photometric fitting and analysis of white dwarfs, to generating a white dwarf luminosity function requires numerous astrophysical, mathematical, and computational domain knowledge. The steep learning curve makes it difficult to enter the field, and often individuals have to reinvent the wheel to perform identical data reduction and analysis tasks. We have gathered a wide range of publicly available white dwarf cooling models and synthetic photometry to provide a toolkit that allows (i) visualization of various models, (ii) photometric fitting of a white dwarf with or without distance and reddening, and (iii) the computing of white dwarf luminosity functions with a choice of initial mass function, main-sequence evolution model, star-formation history, initial–final mass relation, and white dwarf cooling model. We have recomputed and compared the effective temperature of the white dwarfs from the Gaia EDR3 white dwarf catalogue. The two independent works show excellent agreement in the temperature solutions.

Blue large amplitude pulsators (BLAPs) are hot, subluminous stars undergoing rapid variability with periods of under 60 min. 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 time-scales 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 GBP − GRP 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 one of them as a BLAP, and tentatively assign an additional eight of them as BLAPs for future population studies.