Abstract
ABSTRACT White dwarfs that exhibit transit signatures of planetary debris and accreted planetary material provide exceptional opportunities to probe the material composition and dynamical structure of planetary systems. Although previous theoretical work investigating the role of minor body disruption around white dwarfs has focused on spherical bodies, Solar system asteroids can be more accurately modelled as triaxial ellipsoids. Here, we present an analytical framework to identify the type of disruption (tidal fragmentation, total sublimation, or direct impact) experienced by triaxial asteroids approaching white dwarfs on extremely eccentric (e ∼ 1) orbits. This framework is then used to identify the outcomes for simplified Main belt analogues of 100 bodies across five different white dwarf temperatures. We also present an empirical relationship between cooling age and effective temperature for both DA and DB white dwarfs to identify the age of the white dwarfs considered here. We find that using a purely spherical shape model can underestimate the physical size and radial distance at which an asteroid is subjected to complete sublimation, and these differences increase with greater elongation of the body. Contrastingly, fragmentation always occurs in the largest semi-axis of a body and so can be modelled by a sphere of that radius. Both fragmentation and sublimation are greatly affected by the body’s material composition, and hence by the composition of their progenitor asteroid belts. The white dwarf temperature, and hence cooling age, can affect the expected debris distribution: higher temperatures sublimate large elongated asteroids, and cooler temperatures accommodate more direct impacts.
Highlights
White dwarfs provide a unique opportunity to investigate the composition of exoplanetary bodies
This paper aims to expand on the work presented in Brown et al (2017), which investigates the destruction of quasi-spherical bodies approaching a white dwarf on a parabolic trajectory
Increasing observations of minor bodies being disrupted around white dwarfs provide motivation for increasing our understanding of the processes which lead to these bodies being destroyed
Summary
White dwarfs provide a unique opportunity to investigate the composition of exoplanetary bodies. The shorter period is roughly twice that of the debris orbiting WD 1145+017 and much less than that around ZTF J0139+5245 These transits show much shallower depths of 10 per cent and exhibit variability across the entire phase of the orbit, which suggests this object is in a different stage of disruption compared to the two previously discovered objects. These three minor bodies actively disrupting in different orbital configurations raise questions about the circumstances that lead to planestesimal disruption around white dwarfs, and the object around ZTF J0139+5245 showcases the importance of adopting aspherical asteroid models.
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