A Dark Spot on a Massive White Dwarf

Kilic, Mukremin; Gianninas, A.; Bell, Keaton J.; Curd, Brandon; Brown, Warren R.; Hermes, J. J.; Dufour, Patrick; Wisniewski, John P.; Winget, D. E.; Winget, K. I.

doi:10.1088/2041-8205/814/2/l31

Cited by 35 publications

(28 citation statements)

References 33 publications

(50 reference statements)

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“…Low level (few percent) photometric variations have been detected in non-pulsating white dwarfs and attributed to surface inhomogeneities that rotate in and out of view (Brinkworth et al 2004;Kilic et al 2015;Maoz et al 2015;Hermes et al 2017b). By combining Kepler photometry with Hubble Space Telescope (HST) ultraviolet (UV) spectroscopy for seven white dwarfs, Hallakoun et al (2018) tested the hypothesis that low level variations in the photometry could be attributed to an accretion hot spot or inhomogeneous distribution of metals across the white dwarf surface.…”

Section: Discussionmentioning

confidence: 99%

Horizontal spreading of planetary debris accreted by white dwarfs

Cunningham

Tremblay

Bauer

et al. 2021

Monthly Notices of the Royal Astronomical Society

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White dwarfs with metal-polluted atmospheres have been studied widely in the context of the accretion of rocky debris from evolved planetary systems. One open question is the geometry of accretion and how material arrives and mixes in the white dwarf surface layers. Using the 3D radiation-hydrodynamics code CO5BOLD, we present the first transport coefficients in degenerate star atmospheres which describe the advection-diffusion of a passive scalar across the surface-plane. We couple newly derived horizontal diffusion coefficients with previously published vertical diffusion coefficients to provide theoretical constraints on surface spreading of metals in white dwarfs. Our grid of 3D simulations probes the vast majority of the parameter space of convective white dwarfs, with pure-hydrogen atmospheres in the effective temperature range 6000–18 000 K and pure-helium atmospheres in the range 12 000–34 000 K. Our results suggest that warm hydrogen-rich atmospheres (DA; ≳ 13 000 K) and helium-rich atmospheres (DB, DBA; ≳ 30 000 K) are unable to efficiently spread the accreted metals across their surface, regardless of the time dependence of accretion. This result may be at odds with the current non-detection of surface abundance variations at white dwarfs with debris discs. For cooler hydrogen- and helium-rich atmospheres, we predict a largely homogeneous distribution of metals across the surface within a vertical diffusion timescale. This is typically less than 0.1 per cent of disc lifetime estimates, a quantity which is revisited in this paper using the overshoot results. These results have relevance for studies of the bulk composition of evolved planetary systems and models of accretion disc physics.

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Section: Discussionmentioning

confidence: 99%

Horizontal spreading of planetary debris accreted by white dwarfs

Cunningham

Tremblay

Bauer

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…While methods exist to measure WD rotations (e.g., Koester et al 1998, Kilic et al 2015, these observations are challenging. Further, it is difficult to use WD rotations to infer information about their progenitor's rotational histories (Kawaler 2015, Hermes et al 2017).…”

Section: Synthetic Initial-final Mass Relationmentioning

confidence: 99%

A Novel Approach to Constrain Rotational Mixing and Convective-core Overshoot in Stars Using the Initial–Final Mass Relation

Cummings

Kalirai

Choi

et al. 2019

ApJL

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The semi-empirical initial-final mass relation (IFMR) connects spectroscopically analyzed white dwarfs in star clusters to the initial masses of the stars that formed them. Most current stellar evolution models, however, predict that stars will evolve to white dwarfs ∼0.1 M less massive than that found in the IFMR. We first look at how varying theoretical mass-loss rates, third dredgeup efficiencies, and convective-core overshoot may help explain the differences between models and observations. These parameters play an important role at the lowest masses (M initial < 3 M ). At higher masses, only convective-core overshoot meaningfully affects white dwarf mass, but alone it likely cannot explain the observed white dwarf masses nor why the IFMR scatter is larger than observational errors predict. These higher masses, however, are also where rotational mixing in main sequence stars begins to create more massive cores, and hence more massive white dwarfs. This rotational mixing also extends a star's lifetime, making faster rotating progenitors appear like less massive stars in their semi-empirical age analysis. Applying the observed range of young B-dwarf rotations to the MIST or SYCLIST rotational models demonstrates a marked improvement in reproducing both the observed IFMR data and its scatter. The incorporation of both rotation and efficient convectivecore overshoot significantly improves the match with observations. This work shows that the IFMR provides a valuable observational constraint on how rotation and convective-core overshoot affect the core evolution of a star.

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“…Moreover, surface abundance spots in white dwarfs may be connected with the accretion of debris material. All these processes can lead to the photometric variability, which was detected in evolved compact stars (e.g., Dupuis et al, 2000;Kilic et al, 2015).…”

Section: Motivation: Main-sequence Chemically Peculiar Starsmentioning

confidence: 99%

Light variability of white dwarfs and subdwarfs due to surface abundance spots

Krticka,

Prvak,

Krtickova

et al. 2021

Preprint

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Classical main-sequence chemically peculiar stars show light variability that originates in surface abundance spots. In the spots, the flux redistribution due to line (bound-bound) and bound-free transitions is modulated by stellar rotation and leads to light variability. White dwarfs and hot subdwarfs may also have surface abundance spots either owing to the elemental diffusion or as a result of accretion of debris. We model the light variability of typical white dwarfs and hot subdwarfs that results from putative surface abundance spots. We show that the spots with radiatively supported iron overabundance may cause observable light variability of hot white dwarfs and subdwarfs. Accretion of debris material may lead to detectable light variability in warm white dwarfs. We apply our model to the helium star HD 144941 and conclude that the spot model is able to explain most of observed light variations of this star.

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A Dark Spot on a Massive White Dwarf

Cited by 35 publications

References 33 publications

Horizontal spreading of planetary debris accreted by white dwarfs

Horizontal spreading of planetary debris accreted by white dwarfs

A Novel Approach to Constrain Rotational Mixing and Convective-core Overshoot in Stars Using the Initial–Final Mass Relation

Light variability of white dwarfs and subdwarfs due to surface abundance spots

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