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

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 3800-4025Å and the red arm covering 7000-7430Å. When comparing individual transits in both arms, our observations show with 20 σ 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 σ 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.

Shallow Ultraviolet Transits of WD 1145+017

“…This effect is most prominent when there is a deep transit. Previous spectroscopic studies were around the time when the circumstellar line was mostly red-shifted and only a reduction of line strength in the red-shifted component has been reported (Redfield et al 2017;Izquierdo et al 2018;Karjalainen et al 2019) and, this study reports the same characteristics apply to the blue-shifted component.…”

“…They are broad (line widths ∼ 300 km s −1 ), asymmetric, and arise mostly from transitions with lower energy levels <3 eV above ground. The circumstellar lines display short-term variabilitya reduction of absorption flux coinciding with the transit feature (Redfield et al 2017;Izquierdo et al 2018;Karjalainen et al 2019), as well as long-term variability -they have evolved from being strongly red-shifted to blue-shifted in a couple of years (Cauley et al 2018). The long-term variability can be explained by preces- sion of an eccentric ring, either under general relativity or by an external perturber.…”

Circularization of tidal debris around white dwarfs: implications for gas production and dust variability

“…Only one WD (SDSS 1228+1040) stands out in having both emission and absorption (Gänsicke et al 2012). To contrast, WD 1145+017 has a similarly highly inclined (i.e edge-on) disc and has been heavily monitored (see Cauley et al (2018); Rappaport et al (2018); Izquierdo et al (2018); Karjalainen et al (2019); Xu et al (2019); Fortin-Archambault et al (2020) and numerous older references therein), yet it does not appear to have emitting gas. The situation is similar with SDSS J1043+0855 (Manser et al 2016b;Melis & Dufour 2017).…”

Detections and constraints on white dwarf variability from time-series GALEX observations

“…Observations of debris disks and IR excesses (e.g., Barber et al 2012;Rocchetto et al 2015), as well as abundances consistent with bulk Earth accreted material (e.g., Gänsicke et al 2012), provide strong evidence of rocky debris around WDs. Yet direct evidence of transiting planetesimals/asteroids has only been found in WD 1145+017 (Vanderburg et al 2015;Gänsicke et al 2016;Izquierdo et al 2018;Karjalainen et al 2019). This source has multiple orbiting bodies with trails of debris, resulting Recovery Rate (%) Figure 6.…”