Velocity-imaging the rapidly precessing planetary disc around the white dwarf HE 1349–2305 using Doppler tomography

Abstract

The presence of planetary material in white dwarf atmospheres, thought to be accreted from a dusty debris disc produced via the tidal disruption of a planetesimal, is common. Approximately five per cent of these discs host a co-orbital gaseous component detectable via emission from atomic transitions – usually the 8600 Å Ca ii triplet. These emission profiles can be highly variable in both morphology and strength. Furthermore, the morphological variations in a few systems have been shown to be periodic, likely produced by an apsidally precessing asymmetric disc. Of the known gaseous debris discs, that around HE 1349–2305 has the most rapidly evolving emission line morphology, and we present updated spectroscopy of the Ca ii triplet of this system. The additional observations show that the emission line morphologies vary periodically and consistently, and we constrain the period to two aliases of 459 ± 3 d and 502 ± 3 d. We produce images of the Ca ii triplet emission from the disc in velocity space using Doppler tomography – only the second such imaging of a white dwarf debris disc. We suggest that the asymmetric nature of these velocity images is generated by gas moving on eccentric orbits with radially-dependent excitation conditions via photo-ionisation from the white dwarf. We also obtained short-cadence (≃ 4 min) spectroscopy to search for variability on the time-scale of the disc’s orbital period (≃ hours) due to the presence of a planetesimal, and rule out variability at a level of ≃ 1.4 per cent.

On the Rigidly Precessing, Eccentric Gas Disk Orbiting the White Dwarf SDSS J1228+1040

“…J1228 is likely not unusual. First, many white dwarfs with gaseous disks show variable emissions, indicating eccentric, precessing disks (Gänsicke et al 2008;Melis et al 2010;Wilson et al 2014;Cauley et al 2018;Manser et al 2021). Similar dynamics as we reveal here for J1228 may be in play in all of these disks.…”

“…Interestingly, some of them exhibit asymmetric lines that are most easily interpreted as the signature of an eccentric disk. Moreover, these disks also appear to be time variable (e.g., Wilson et al 2014Wilson et al , 2015Dennihy et al 2018;Manser et al 2021). For instance, J1228, the best monitored system (Manser et al 2016(Manser et al , 2019, shows gradual variations of its line profile over a timescale of decades.…”

Planetary Systems Around White Dwarfs

“…One manifestation of the activity is through flux changes due to some physical process in the dust Farihi et al 2018b;Xu et al 2018;Wang et al 2019;Rogers et al 2020;Swan et al 2020;Wilson, Hermes & Gänsicke 2020). Another manifestation is through the secular (long-term) precession of gas, as well as its variability (Wilson et al 2014;Manser et al 2016aManser et al ,b, 2019Manser et al , 2021Redfield et al 2017;Cauley et al 2018;Dennihy et al 2018Dennihy et al , 2020Fortin-Archambault, Dufour & Xu Both dust and gas can also represent windows into composition, although planetary chemistry is primarily obtained from photospheric debris measurements (subsection 2.4). Pre-JWST, the only dusty disc close enough and bright enough to Earth for which chemical constraints can be modelled in detail orbits G 29-38 (Reach et al 2005(Reach et al , 2009; broader chemical dust models can still be fit around other white dwarfs (Xu et al 2018).…”

A DZ white dwarf with a 30 MG magnetic field

“…A vast array of evidence now supports accretion of exoplanetesimals from an accompanying planetary system as the source of this metal pollution. Many metal-rich white dwarfs are observed with infra-red excesses resulting from circumstellar debris disks (Zuckerman & Becklin 1987;Jura 2003;Rocchetto et al 2015;Swan et al 2019a), with a sub-population of those also exhibiting gaseous emission from the sublimated part of the disk (Gänsicke et al 2006(Gänsicke et al , 2007Dennihy et al 2016;Manser et al 2020Manser et al , 2021. In a few cases, when the disk is viewed edge-on, irregular transits are observed demonstrating the tidal disruption of exoplanetesimals close to the white dwarf Roche radius (Vanderburg et al 2015;Vanderbosch et al 2020Vanderbosch et al , 2021Guidry et al 2021;Farihi et al 2022).…”