Time resolved spectroscopy of dust and gas from extrasolar planetesimals orbiting WD 1145+017

TL;DR

This study uses time-resolved spectroscopy to analyze dust and gas around WD 1145+017, revealing color differences and spectral line changes during transits, which suggest gas absorption is blocked by disintegrating asteroids.

Contribution

First high-quality time-resolved spectroscopic observations of WD 1145+017 showing color and spectral line variations during transits, confirming gas blocking by disintegrating planetesimals.

Findings

Transits are deeper in the red spectral arm.

Spectral lines are shallower during transits.

Gas absorption decreases during transits, indicating gas is between the white dwarf and transiting objects.

Abstract

Multiple long and variable transits caused by dust from possibly disintegrating asteroids were detected in light curves of WD 1145+017. We present time-resolved spectroscopic observations of this target with QUCAM CCDs mounted in the Intermediate dispersion Spectrograph and Imaging System at the 4.2-m William Herschel Telescope in two different spectral arms: the blue arm covering 3800-4025 {\AA} and the red arm covering 7000-7430 {\AA}. When comparing individual transits in both arms, our observations show with 20 {\sigma} significance an evident colour difference between the in- and out-of-transit data of the order of 0.05-0.1 mag, where transits are deeper in the red arm. We also show with > 6 {\sigma} significance that spectral lines in the blue arm are shallower during transits than out-of-transit. For the circumstellar lines it also appears that during transits the reduction in absorption is larger on the red side of the spectral profiles. Our results confirm previous findings showing the u'-band excess and a decrease in line absorption during transits. Both can be explained by an opaque body blocking a fraction of the gas disc causing the absorption, implying that the absorbing gas is between the white dwarf and the transiting objects. Our results also demonstrate the capability of EMCCDs to perform high-quality time resolved spectroscopy of relatively faint targets.