Relentless and Complex Transits from a Planetesimal Debris Disk

TL;DR

This study observes complex, persistent transiting debris around white dwarf WD 1054-226, revealing harmonic structures and stable spectral features, suggesting a circumstellar debris disk with intricate dynamics and composition.

Contribution

It provides detailed high-cadence, multi-wavelength photometry and spectroscopy of transiting debris around a white dwarf, uncovering harmonic patterns and stable metal absorption features.

Findings

Detection of a 25.02-hour orbital period with harmonic transits.

Presence of multiple harmonics and independent periodic features.

Absence of detectable dust emission despite circumstellar debris.

Abstract

This article reports quasi-continuous transiting events towards WD 1054-226 at d=36.2 pc and V=16.0 mag, based on simultaneous, high-cadence, multi-wavelength imaging photometry using ULTRACAM over 18 nights from 2019 to 2020 March. The predominant period is 25.02 h, and corresponds to a circular orbit with blackbody Teq = 323 K, where a planetary surface can nominally support liquid water. The light curves reveal remarkable night-to-night similarity, with changes on longer timescales, and lack any transit-free segments of unocculted starlight. The most pronounced dimming components occur every 23.1 min -- exactly the 65th harmonic of the fundamental period -- with depths of up to several per cent, and no evident color dependence. Myriad additional harmonics are present, as well as at least two transiting features with independent periods. High-resolution optical spectra are consistent with stable, photospheric absorption by multiple, refractory metal species, with no indication of circumstellar gas. Spitzer observations demonstrate a lack of detectable dust emission, suggesting that the otherwise hidden circumstellar disk orbiting WD 1054-226 may be typical of polluted white dwarfs, and only detected via favorable geometry. Future observations are required to constrain the orbital eccentricity, but even if periastron is near the Roche limit, sublimation cannot drive mass loss in refractory parent bodies, and collisional disintegration is necessary for dust production.