Drifting asteroid fragments around WD 1145+017

Abstract

We have obtained extensive photometric observations of the polluted white dwarf WD 1145+017 which has been reported to be transited by at least one, and perhaps several, large asteroids with dust emission. Observation sessions on 37 nights spanning 2015 November to 2016 January with small to modest size telescopes have detected 237 significant dips in flux. Periodograms reveal a significant periodicity of 4.5004 hours consistent with the dominant ("A") period detected with K2. The folded light curve shows an hour-long depression in flux with a mean depth of nearly 10%. This depression is, in turn, comprised of a series of shorter and sometimes deeper dips which would be unresolvable with K2. We also find numerous dips in flux at other orbital phases. Nearly all of the dips associated with this activity appear to drift systematically in phase with respect to the "A" period by about 2.5 minutes per day with a dispersion of ∼0.5 min/d, corresponding to a mean drift period of 4.4928 hours. We are able to track ∼15 discrete drifting features. The "B"-"F" periods found with K2 are not detected, but we would not necessarily have expected to see them. We explain the drifting motion as due to smaller fragmented bodies that break off from the asteroid and go into a slightly smaller orbit. In this interpretation, we can use the drift rate to determine the mass of the asteroid, which we find to be ≈ 10 23 grams, or about 1/10th the mass of Ceres.

Remnant planetary systems around bright white dwarfs

“…Subsequent passes further degrade the debris and it eventually embodies a disc geometry. Vanderburg et al (2015) have recently identified the first disintegrating asteroid around the dusty WD 1145+017 (see also Gänsicke et al 2016;Rappaport et al 2016), providing support to this interpretation. The signature of a disc orbiting a WD is excess emission in the infrared due to the reprocessed light from this dust.…”

Evidence for Eccentric, Precessing Gaseous Debris in the Circumstellar Absorption toward WD 1145 + 017

“…Subsequent photometric monitoring has revealed significant evolution of the transit depths and morphologies Rappaport et al 2016;Croll et al 2017). Xu et al (2016) presented high-resolution spectra of WD 1145+017 that showed circumstellar gas lines were present in several metal species with depths ≈10%-30% below the continuum.…”

The fate of exomoons in white dwarf planetary systems

“…For example, for multiple Ceres-mass and lower co-orbital bodies with orbital periods of just about 4.5 h, the resulting orbital period deviations due to their mutual perturbations are of the order of seconds (Gurri et al 2017;Veras, Marsh & Gänsicke 2016b). This deviation is observationally relevant for the WD 1145+017 system Gary et al 2016;Rappaport et al 2016), but only because these orbits are so compact. Mutual perturbations amongst moons are primarily important during the formation of the moons themselves and their subsequent evolution around their parent planet; in our Solar system, there exist several relevant examples (e.g.…”

“…A recent success is WD 1145+017 (Vanderburg et al 2015), a white dwarf which is both polluted and bears a debris disc, and which has recently been shown to also host disintegrating planetesimals. Hourly changes in the shape and depth of the transit light curves of the white dwarf WD 1145+017 have invigorated the post-main-sequence planetary community, motivating a large-scale observational effort Croll et al 2016;Gänsicke et al 2016;Gary et al 2016;Rappaport et al 2016;Redfield et al 2016;Xu et al 2016) and dedicated attempts to explain these observations (Gurri, Veras & Gänsicke 2017;Veras et al 2016c). The parallel understanding of the state-of-the-art dynamical and theoretical aspects of post-mainsequence planetary science is summarized in Veras (2016a).…”