Multiwavelength Transit Observations of the Candidate Disintegrating Planetesimals Orbiting WD 1145+017

Abstract

We present multiwavelength, ground-based follow-up photometry of the white dwarf WD 1145+017, which has recently been suggested to be orbited by up to six or more short-period, low-mass, disintegrating planetesimals. We detect nine significant dips in flux of between 10% and 30% of the stellar flux in our ∼32 hr of photometry, suggesting that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the asymmetric transits that we observe, we confirm that the transit egress is usually longer than the ingress, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals are unclear, but at least one object, and likely more, have orbital periods of ∼4.5 hr. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high-precision photometry also displays low-amplitude variations, suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. We compare the transit depths in the V-and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions, the radius of single-size particles in the cometary tails streaming behind the planetesimals must be ∼0.15 μm or larger, or ∼0.06 μm or smaller, with 2σ confidence.

High-Speed Photometry of the Disintegrating Planetesimals at Wd1145+017: Evidence for Rapid Dynamical Evolution

“…We were not able to identify a group of transit events with a significantly different period, in particular we were not able to recover the periods longer than ;4.49 hr discussed by Vanderburg et al (2015). The periods from our analysis are similar to those found by Croll et al (2015), and are all slightly, but significantly, shorter than the 4.4988h period derived from the K2 data . The uncertainties in the periods derived for the transit groups a-f are too large to identify them with any of the features from Croll et al (2015).…”

“…It is immediately apparent that the morphology of the transits has dramatically evolved since 2015 April/May, when the observations of Vanderburg et al (2015) and Croll et al (2015) were taken: The light curve is riddled with numerous transit events varying in duration from ;3 to ;12 minutes with depths of ;10% to ;60%. Many of the transit features overlap, such that there are only short segments of the light curve which appear unattenuated by debris.…”

“…Here we report the first high-speed photometry of the transits at WD 1145+017, which show a dramatic evolution of the system in the seven months since the observations of Vanderburg et al (2015) and Croll et al (2015) and suggest a rapid evolution of the planetesimals and their debris.…”

“…Given the detection of multiple periodicities in the K2 light curve, Vanderburg et al (2015) argued for the presence of several, possibly six individual planetesimals. Following up WD 1145+017 with ground-based photometry, Vanderburg et al (2015) and Croll et al (2015) detected several relatively short (;10 minutes) and deep (;40%) transit events that did, however, only occasionally repeat at the same phase during subsequent observations. These optical transits were compatible with the ;4.5 hr period identified in the K2 data.…”

Circumstellar debris and pollution at white dwarf stars

“…The photometric data are fairly compelling, with myriad ground-based follow up observations confirming multiple, broad, complex, and evolving transits with periods of approximately five hours and thus near to the Roche limit (Croll et al, 2015;Gänsicke et al, 2016). Furthermore, WD 1145+017 appears highly polluted with metals and has an infrared excess in WISE, and thus at face value it appears to provide striking confirmation of the asteroid disruption model.…”