Pulsational Mapping of Calcium Across the Surface of a White Dwarf

Thompson, Susan E.; Montgomery, M. H.; Hippel, Ted von; Nitta, A.; Dalessio, J.; Provencal, J. L.; Strickland, W.; Holtzman, Jon A.; Mukadam, Anjum S.; Sullivan, D. J.; Nagel, T.; Kozieł-Wierzbowska, D.; Kundera, T.; Zoła, S.; Winiarski, M.; Dróżdż, M.; Kuligowska, Elżbieta; Ogłoza, W.; Bognár, Zs.; Handler, G.; Kanaan, A.; T., Ribeira,; Rosen, Rachel A.; Reichart, D.; Haislip, J. B.; Barlow, B. N.; Dunlap, B. H.; Ivarsen, K.; Lacluyzé, A.; Mullally, Fergal

doi:10.1088/0004-637x/714/1/296

Cited by 13 publications

(11 citation statements)

References 40 publications

(75 reference statements)

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“…By studying the pulsation light curve of G29-38, Montgomery (2005) derived the rotation axis (pulsation axis) θ to be 65 • (see Fig. 7 for a cartoon illustration), which is comparable to 55 • derived from comparing the amplitudes of the harmonics (Thompson et al 2010). The white dwarf rotation axis might not be aligned with the axis i of the opaque disk, which is derived to be 30 •1 .…”

Section: External Perturbationmentioning

confidence: 72%

Infrared Variability of Two Dusty White Dwarfs

Rogers

et al. 2018

ApJ

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The most heavily polluted white dwarfs often show excess infrared radiation from circumstellar dust disks, which are modeled as a result of tidal disruption of extrasolar minor planets. Interaction of dust, gas, and disintegrating objects can all contribute to the dynamical evolution of these dust disks. Here, we report on two infrared variable dusty white dwarfs, SDSS J1228+1040 and G29-38. For SDSS J1228+1040, compared to the first measurements in 2007, the IRAC [3.6] and [4.5] fluxes decreased by 20% by 2014 to a level also seen in the recent 2018 observations. For G29-38, the infrared flux of the 10 µm silicate emission feature became 10% stronger between 2004 and 2007, We explore several scenarios that could account for these changes, including tidal disruption events, perturbation from a companion, and runaway accretion. No satisfactory causes are found for the flux drop in SDSS J1228+1040 due to the limited time coverage. Continuous tidal disruption of small planetesimals could increase the mass of small grains and concurrently change the strength of the 10 µm feature of G29-38. Dust disks around white dwarfs are actively evolving and we speculate that there could be different mechanisms responsible for the temporal changes of these disks.

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Section: External Perturbationmentioning

confidence: 72%

Infrared Variability of Two Dusty White Dwarfs

Rogers

et al. 2018

ApJ

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“…A similar process operates in the intermediate polar class of cataclysmic variable to produce a truncated gaseous accretion disk around the WD (see review of this class in Warner 2003). Based on observations of the Ca II lines during pulsations of the archetype dusty WD G29-38, Thompson et al (2010) have suggested that the Ca is being accreted onto the poles of the WD, rather than equatorially, suggesting that the WD is magnetic. Brinkworth et al (2007) (see the Appendix in that paper) calculated the critical surface charge on a dust grain, Q crit , such that the motion of the dust would be influenced by the WD magnetic field.…”

Section: Discussionmentioning

confidence: 99%

THE WIRED SURVEY. IV. NEW DUST DISKS FROM THE McCOOK & SION WHITE DWARF CATALOG

Hoard¹,

Debes²,

Wachter³

et al. 2013

ApJ

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We have compiled photometric data from the Wide-field Infrared Survey Explorer All Sky Survey and other archival sources for the more than 2200 objects in the original McCook & Sion Catalog of Spectroscopically Identified White Dwarfs. We applied color-selection criteria to identify 28 targets whose infrared spectral energy distributions depart from the expectation for the white dwarf photosphere alone. Seven of these are previously known white dwarfs with circumstellar dust disks, five are known central stars of planetary nebulae, and six were excluded for being known binaries or having possible contamination of their infrared photometry. We fit white dwarf models to the spectral energy distributions of the remaining ten targets, and find seven new candidates with infrared excess suggesting the presence of a circumstellar dust disk. We compare the model dust disk properties for these new candidates with a comprehensive compilation of previously published parameters for known white dwarfs with dust disks. It is possible that the current census of white dwarfs with dust disks that produce an excess detectable at K-band and shorter wavelengths is close to complete for the entire sample of known WDs to the detection limits of existing near-IR all-sky surveys. The white dwarf dust disk candidates now being found using longer wavelength infrared data are drawn from a previously underrepresented region of parameter space, in which the dust disks are overall cooler, narrower in radial extent, and/or contain fewer emitting grains.

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“…There has been some discussions about whether the accretion from the debris disk occurs as a continuous or a discontinuous process and whether the accreted material follows a particular geometry. In the case of G 29-38, Thompson et al (2010) find a hint that the accretion geometry could be time dependent, pointing to a discontinuous accretion producing spots of heavy elements on the white dwarf surface (see also Montgomery et al 2008) and to the influence of a potential magnetic field on the accretion process. However, the time variability of the heavy element abundances, Ca in the case of G 29-38, which would be the signature of such a discontinuous accretion, was not confirmed (Debes & López-Morales 2008).…”

Section: Numerical Computationsmentioning

confidence: 93%

Importance of fingering convection for accreting white dwarfs in the framework of full evolutionary calculations: the case of the hydrogen-rich white dwarfs GD 133 and G 29-38

Wachlin

Vauclair

et al. 2017

A&A

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Context. A large fraction of white dwarf stars show photospheric chemical composition polluted by heavy elements accreted from a debris disk. Such debris disks result from the tidal disruption of rocky planetesimals which had survived to whole stellar evolution from the main sequence to the final white dwarf stage. Determining the accretion rate of this material is an important step towards estimating the mass of the planetesimals and towards understanding the ultimate fate of the planetary systems. Aims. The accretion of heavy material with a mean molecular weight, µ, higher than the mean molecular weight of the white dwarf outer layers, induces a double-diffusive instability producing the fingering convection and an extra-mixing. As a result, the accreted material is diluted deep into the star. We explore the effect of this extra-mixing on the abundance evolution of Mg, O, Ca, Fe and Si in the cases of the two well studied polluted DAZ white dwarfs: GD 133 and G 29-38. Methods. We performed numerical simulations of the accretion of material having a chemical composition similar to the bulk Earth composition. We assumed a continuous and uniform accretion and considered a range of accretion rates from 10 4 g/s to 10 10 g/s. Two cases are simulated, one using the standard mixing length theory (MLT) and one including the double-diffusive instability (fingering convection). Results. The double-diffusive instability develops on a very short time scale. The surface abundance rapidly reaches a stationary value while the depth of the zone mixed by the fingering convection increases. In the case of GD 133, the accretion rate needed to reproduce the observed abundances exceeds by more than 2 orders of magnitude the rate estimated by neglecting the fingering convection. In the case of G 29-38 the needed accretion rate is increased by approximately 1.7 dex. Conclusions. Our numerical simulations of the accretion of heavy elements on the hydrogen-rich white dwarf GD 133 and G 29-38 show that fingering convection is an efficient mechanism to mix the accreted material deeply. We find that when fingering convection is taken into account, accretion rates higher by 1.7 to 2 dex than those inferred from the standard MLT are needed in order to reproduce the abundances observed in G 29-38 and GD 133.

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Pulsational Mapping of Calcium Across the Surface of a White Dwarf

Cited by 13 publications

References 40 publications

Infrared Variability of Two Dusty White Dwarfs

Infrared Variability of Two Dusty White Dwarfs

THE WIRED SURVEY. IV. NEW DUST DISKS FROM THE McCOOK & SION WHITE DWARF CATALOG

Importance of fingering convection for accreting white dwarfs in the framework of full evolutionary calculations: the case of the hydrogen-rich white dwarfs GD 133 and G 29-38

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