Shallow Ultraviolet Transits of WD 1145+017

Abstract

WD 1145+017 is a unique white dwarf system that has a heavily polluted atmosphere, an infrared excess from a dust disk, numerous broad absorption lines from circumstellar gas, and changing transit features, likely from fragments of an actively disintegrating asteroid. Here, we present results from a large photometric and spectroscopic campaign with Hubble, Keck , VLT, Spitzer, and many other smaller telescopes from 2015 to 2018. Somewhat surprisingly, but consistent with previous observations in the u' band, the UV transit depths are always shallower than those in the optical. We develop a model that can quantitatively explain the observed "bluing" and the main findings are: I. the transiting objects, circumstellar gas, and white dwarf are all aligned along our line of sight; II. the transiting object is blocking a larger fraction of the circumstellar gas than of the white dwarf itself. Because most circumstellar lines are concentrated in the UV, the UV flux appears to be less blocked compared to the optical during a transit, leading to a shallower UV transit. This scenario is further supported by the strong anti-correlation between optical transit depth and circumstellar line strength. We have yet to detect any wavelength-dependent transits caused by the transiting material around WD 1145+017.

16 pages, 11 figures, 6 tables, ApJ, in press

References in corpus (12)

• The frequency of planetary debris around young white dwarfs
• A gaseous metal disk around a white dwarf
• Numerical Simulations of Collisional Cascades at the Roche Limits of White Dwarf Stars
• Explaining the variability of WD 1145+017 with simulations of asteroid tidal disruption
• The Drop during Less than 300 days of a Dusty White Dwarf's Infrared Luminosity
• WD 1145+017 Photometric Observations During 8 Months of High Activity
• Numerical Simulations of Gaseous Disks Generated from Collisional Cascades at the Roche Limits of White Dwarf Stars
• Most white dwarfs with detectable dust discs show infrared variability
• Evidence for eccentric, precessing gaseous debris in the circumstellar absorption towards WD 1145+017
• WD 1145+017: Optical Activity During 2016-2017 and Limits on the X-Ray Flux
• No Timing Variations Observed in Third Transit of Snow-Line Exoplanet Kepler-421b
• Kepler Transit Depths Contaminated by a Phantom Star

Cited by in corpus (8)

• The frequency of gaseous debris discs around white dwarfs
• Relentless and Complex Transits from a Planetesimal Debris Disk
• The dust never settles: collisional production of gas and dust in evolved planetary systems
• Modeling of the Variable Circumstellar Absorption Features of WD 1145+017
• The lifetimes of planetary debris discs around white dwarfs
• WD 1145+017: Alternative models of the atmosphere, dust clouds, and gas rings
• Revisiting the Chemical Composition of WD 1145+017: Impact of Circumstellar Disks Contamination on Photospheric Abundances
• Planetesimals drifting through dusty and gaseous white dwarf debris discs: Types I, II and III-like migration