I Spy Transits and Pulsations: Empirical Variability in White Dwarfs Using Gaia and the Zwicky Transient Facility

Abstract

We present a novel method to detect variable astrophysical objects and transient phenomena using anomalous excess scatter in repeated measurements from public catalogs of Gaia DR2 and Zwicky Transient Facility (ZTF) DR3 photometry. We first provide a generalized, all-sky proxy for variability using only Gaia DR2 photometry, calibrated to white dwarf stars. To ensure more robust candidate detection, we further employ a method combining Gaia with ZTF photometry and alerts. To demonstrate its efficacy, we apply this latter technique to a sample of roughly 12,100 white dwarfs within 200 pc centered on the ZZ Ceti instability strip, where hydrogen-atmosphere white dwarfs are known to pulsate. By inspecting the top 1% of the samples ranked by these methods, we demonstrate that both the Gaia-only and ZTF-informed techniques are highly effective at identifying known and new variable white dwarfs, which we verify using follow-up, high-speed photometry. We confirm variability in all 33 out of 33 (100%) observed white dwarfs within our top 1% highest-ranked candidates, both inside and outside the ZZ Ceti instability strip. In addition to dozens of new pulsating white dwarfs, we also identify five white dwarfs highly likely to show transiting planetary debris; if confirmed, these systems would more than triple the number of white dwarfs known to host transiting debris.

A catalogue of white dwarfs in Gaia EDR3

“…Though the two metrics are based on different data sets, if they are both capable of identifying genuine variable Gaia sources, there should be a significant overlap in the samples of variable candidates selected using them. We find that about half of the top 1 per cent variable white dwarf candidates within 200 pc selected by Guidry et al (2021) also have EXCESS FLUX ERROR >4. Additionally all eight new ZZ Ceti that Guidry et al (2021) identified using their Gaia variability index have EXCESS FLUX ERROR >4.6.…”

“…We find that about half of the top 1 per cent variable white dwarf candidates within 200 pc selected by Guidry et al (2021) also have EXCESS FLUX ERROR >4. Additionally all eight new ZZ Ceti that Guidry et al (2021) identified using their Gaia variability index have EXCESS FLUX ERROR >4.6.…”

“…However, only a relative small fraction of objects with this level of variability (amplitude 1-30 per cent; Mukadam et al 2013) can be reliably identified using this metric. Guidry et al (2021) carried out a similar exploration of white dwarf variability in Gaia DR2 by calculating a variability index with a similar scope to our EXCESS FLUX ERROR. Though the two metrics are based on different data sets, if they are both capable of identifying genuine variable Gaia sources, there should be a significant overlap in the samples of variable candidates selected using them.…”

Velocity-imaging the rapidly precessing planetary disc around the white dwarf HE 1349–2305 using Doppler tomography

“…The observational evidence of planetary systems around white dwarfs is abundant (Zuckerman & Becklin 1987;Graham et al 1990;Aannestad et al 1993;Vanderburg et al 2015;Gänsicke et al 2019;Manser et al 2019;Vanderbosch et al 2020;Vanderburg et al 2020;Guidry et al 2021;Vanderbosch et al 2021). To date, the majority of detections of planetary material at white dwarfs have come from identifying pollutant metals in their atmospheres -the result of ac-white dwarf ( 1 R ).…”

Spectral analysis of cool white dwarfs accreting from planetary systems: from the UV to the optical

“…Additional observational evidence comes from the presence of gas discs within the circumstellar dust discs (Gänsicke et al 2006;Farihi et al 2012;Melis et al 2012;Gentile Fusillo et al 2021), which may be related to the presence of intact solid planetesimals embedded within some of the dusty debris discs (Manser et al 2019). The fundamental hypothesis of planetesimals reaching the tidal disruption radius (Jura 2003) has unambiguously been corroborated by the detection of two systems exhibiting deep and rapidly evolving photometric transits caused by disintegrating planetary bodies (Vanderburg et al 2015;Vanderbosch et al 2019;Guidry et al 2021;Vanderbosch et al 2021). More recently this body of evidence has come to include bona fide planets orbiting close to the white dwarf -in one case detection of an evaporating giant planet (Gänsicke et al 2019) and another from photometric transits of a planet crossing the line-of-sight of the white dwarf (Vanderburg et al 2020).…”