Infrared Variability of Two Dusty White Dwarfs

Xu, Siyi; Su, K. Y. L.; Rogers, Laura K.; Bonsor, Amy; Olofsson, J.; Veras, Dimitri; Lieshout, R. Van; Dufour, Patrick; Green, Elizabeth M.; Schlawin, Everett; Farihi, Jay; Wilson, T. G.; Wilson, D. J.; Gänsicke, B. T.

doi:10.3847/1538-4357/aadcfe

Cited by 47 publications

(43 citation statements)

References 77 publications

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“…The Spitzer images for WD J0347+1624 and WD J2100 +2122 show that the targets are clear of nearby contaminating sources, and large-aperture photometry of the IRAC Ch 1 and Ch 2 images does not resolve the discrepancy between the AllWISE and Spitzer photometry. Recently, infrared variability of dusty debris disks around white dwarfs has been detected on timescales of months and years (Farihi et al 2018b;Xu et al 2018;Swan et al 2019b;Wang et al 2019). Intrinsic variability remains a plausible explanation for these two targets and presents some issues for our attempts to fit or describe the infrared excess, as the spectral energy distributions presented in Figure 3 include survey data with epochs spanning several years.…”

Section: Establishing the Infrared Excessmentioning

confidence: 99%

Five New Post-main-sequence Debris Disks with Gaseous Emission

Dennihy

Lai

et al. 2020

ApJ

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Observations of debris disks, the products of the collisional evolution of rocky planetesimals, can be used to trace planetary activity across a wide range of stellar types. The most common end points of stellar evolution are no exception, as debris disks have been observed around several dozen white dwarf stars. But instead of planetary formation, post-main-sequence debris disks are a signpost of planetary destruction, resulting in compact debris disks from the tidal disruption of remnant planetesimals. In this work, we present the discovery of five new debris disks around white dwarf stars with gaseous debris in emission. All five systems exhibit excess infrared radiation from dusty debris, emission lines from gaseous debris, and atmospheric absorption features indicating ongoing accretion of metal-rich debris. In four of the systems, we detect multiple metal species in emission, some of which occur at strengths and transitions previously unseen in debris disks around white dwarf stars. Our first year of spectroscopic follow-up hints at strong variability in the emission lines that can be studied in the future, expanding the range of phenomena these post-main-sequence debris disks exhibit.

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Section: Establishing the Infrared Excessmentioning

confidence: 99%

Five New Post-main-sequence Debris Disks with Gaseous Emission

Dennihy

Lai

et al. 2020

ApJ

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“…The origin of these gaseous components is uncertain, but current mechanisms include: runaway sublimation of dust at the inner edge of the debris disc due to angular momentum conservation (Rafikov 2011;Metzger et al 2012), a collisional cascade of rocky bodies being ground down into dust and gas (Kenyon & Bromley 2017a,b), collisions produced via a tidal stream of planetary debris impacting on a pre-existing disc (Jura 2008;Malamud et al 2021), and a disc-embedded planetesimal that survived the tidal disruption process, inducing the production of gas through collisions or sublimation (Manser et al 2019;Trevascus et al 2021). Recent observations show that variability of the infrared excess from debris discs is common (Xu & Jura 2014;Xu et al 2018;Swan et al 2019;Wang et al 2019), and it has been proposed that the observed variations are due to the production and destruction of dust via planetesimal collisions which could also produce observable gaseous material (Farihi et al 2018;Swan et al 2021). This is further corroborated by the discovery that debris discs with a gaseous component in emission appear to show the largest amounts of infrared variability (Swan et al 2020), indicating they are the most dynamically active white dwarf debris discs.…”

Section: Introductionmentioning

confidence: 99%

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

Manser

Dennihy

Gänsicke

et al. 2021

Monthly Notices of the Royal Astronomical Society

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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.

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“…There are a handful of objects in the literature with previous detections of a change in their dusty emission, as discussed in Section 3.3. For WD J0959−0200, Xu & Jura (2014) found a drop in K band flux from 57 µJy to 46 µJy which is equivalent to a peak-to-peak drop of 18.5%, and Xu et al (2018b) found a K band peak-to-peak drop of 13% for WD 1226+110. We note the difficulty in comparing the peak-to-peak variability quoted for these objects with the median variability quoted in this work.…”

Section: Expected Variabilitymentioning

confidence: 98%

Near-infrared variability in dusty white dwarfs: tracing the accretion of planetary material

Rogers

Bonsor

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The inwards scattering of planetesimals towards white dwarfs is expected to be a stochastic process with variability on human time-scales. The planetesimals tidally disrupt at the Roche radius, producing dusty debris detectable as excess infrared emission. When sufficiently close to the white dwarf, this debris sublimates and accretes on to the white dwarf and pollutes its atmosphere. Studying this infrared emission around polluted white dwarfs can reveal how this planetary material arrives in their atmospheres. We report a near-infrared monitoring campaign of 34 white dwarfs with infrared excesses with the aim to search for variability in the dust emission. Time series photometry of these white dwarfs from the United Kingdom Infrared Telescope (Wide Field Camera) in the J, H and K bands were obtained over baselines of up to three years. We find no statistically significant variation in the dust emission in all three near-infrared bands. Specifically, we can rule out variability at ∼ 1.3% for the 13 white dwarfs brighter than 16th mag in K band, and at ∼ 10% for the 32 white dwarfs brighter than 18th mag over time-scales of three years. Although to date two white dwarfs, SDSS J095904.69−020047.6 and WD 1226+110, have shown K band variability, in our sample we see no evidence of new K band variability at these levels. One interpretation is that the tidal disruption events which lead to large variabilities are rare, occur on short time-scales, and after a few years the white dwarfs return to being stable in the near-infrared.

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Infrared Variability of Two Dusty White Dwarfs

Cited by 47 publications

References 77 publications

Five New Post-main-sequence Debris Disks with Gaseous Emission

Five New Post-main-sequence Debris Disks with Gaseous Emission

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

Near-infrared variability in dusty white dwarfs: tracing the accretion of planetary material

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