White dwarf planets

Mustill, Alexander J.; Villaver, E.; Veras, Dimitri; Bonsor, Amy; Wyatt, M. C.

doi:10.1051/epjconf/20134706008

Cited by 9 publications

(10 citation statements)

References 21 publications

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“…However, to estimate the WD accretion rate we also need to account for the reaction of the planetary system to the mass loss that occurs during post-MS evolution. Research shows that stellar evolution can change the stability of some orbits in the system due to the large amount of mass lost during the asymptotic giant branch and to a lesser extent the red giant branch (Mustill et al 2013;Veras et al 2013). From a purely gravitational standpoint, the ECZ dependence on the planet-to-star mass ratio (Equation 3) indicates that the ECZ will widen, due to the decrease in stellar mass.…”

Section: Stellar Evolutionmentioning

confidence: 99%

Eccentric planets and stellar evolution as a cause of polluted white dwarfs

Frewen

Hansen

2014

Monthly Notices of the Royal Astronomical Society

178

188

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A significant fraction of white dwarfs are observed to be polluted with metals despite high surface gravities and short settling times. The current theoretical model for this pollution is accretion of rocky bodies, which are delivered to the white dwarf through perturbations by orbiting planets. Using N-body simulations, we examine the possibility of a single planet as the source of pollution. We determine the stability of test particles on circular orbits in systems with a single planet located at 4 au for a range of masses and eccentricities, comparing the fractions that are ejected and accreted by the star. In particular, we compare the instabilities that develop before and after the star loses mass to form a white dwarf, a process which causes the semi-major axes of orbiting bodies to expand adiabatically. We determine that a planet must be eccentric (e > 0.02) to deliver significant (> 0.5 per cent) amounts of material to the central body, and that the amount increases with the planetary eccentricity. This result is robust with respect to the initial eccentricities of the scattered particles in the case of planetary eccentricity above ∼ 0.4 and the case of randomly-distributed particle longitude of pericentre. We also find that the efficiency of the pollution is enhanced as planetary mass is reduced. We demonstrate that a 0.03 M Jup planet with substantial eccentricity (e > 0.4) can account for the observed levels of pollution for initial disc masses of order 1 M ⊕ . Such discs are well within the range estimated for initial planetesimals discs and well below that estimated for our own solar system within the context of the Nice model. However, their long term survival to the white dwarf stage is uncertain as estimates for the collisional evolution of planetesimal discs suggest they should be ground down below the required levels on Gyr timescales. Thus, planetary scattering by eccentric, sub-Jovian planets can explain the observed levels of pollution in white dwarfs, but only if current estimates of the collisional erosion of planetesimal discs are in error.

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Section: Stellar Evolutionmentioning

confidence: 99%

Eccentric planets and stellar evolution as a cause of polluted white dwarfs

Frewen

Hansen

2014

Monthly Notices of the Royal Astronomical Society

178

188

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“…A number of scenarii of planetary systems evolution through the giant and asymptotic giant branches have demonstrated that massive planets may survive these phases of the star evolution and be able to perturb the planetesimal orbits to large eccentricity (e.g. Debes & Sigurdsson 2002;Debes et al 2012;Mustill et al 2013;Veras et al 2013Veras et al , 2014bVeras et al ,a, 2015bVeras 2016;Veras et al 2016;Frewen & Hansen 2014).…”

Section: Introductionmentioning

confidence: 99%

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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“…The present survey does not probe for planets initially in closer orbits (<2 to 3 A.U. ), which during the RG/AGB phase might have merged with the star due to dynamical friction and tidal interactions (Mustill et al 2013;Veras et al 2014).…”

Section: Discussionmentioning

confidence: 68%

Search for giant planets around seven white dwarfs in the Hyades cluster with the Hubble Space Telescope

Brandner

Zinnecker

Kopytova

2020

Monthly Notices of the Royal Astronomical Society

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Only a small number of exoplanets has been identified in stellar cluster environments. We initiated a high angular resolution direct imaging search using the Hubble Space Telescope (HST) and its NICMOS instrument for self-luminous giant planets in orbit around seven white dwarfs in the 625 Myr old nearby (≈45 pc) Hyades cluster. The observations were obtained with NIC1 in the F110W and F160W filters, and encompass two HST roll angles to facilitate angular differential imaging. The difference images were searched for companion candidates, and radially averaged contrast curves were computed. Though we achieve the lowest mass detection limits yet for angular separations ≥0.5″, no planetary mass companion to any of the seven white dwarfs, whose initial main sequence masses were >2.8 M⊙, was found. Comparison with evolutionary models yields detection limits of ≈5 to 7 Jupiter masses according to one model, and between 9 and ≈12 MJup according to another model, at physical separations corresponding to initial semimajor axis of ≥5 to 8 A.U. (i.e., before the mass loss events associated with the red and asymptotic giant branch phase of the host star). The study provides further evidence that initially dense cluster environments, which included O- and B-type stars, might not be highly conducive to the formation of massive circumstellar disks, and their transformation into giant planets (with m≥6 MJupiter and a≥6 A.U.). This is in agreement with radial velocity surveys for exoplanets around G- and K-type giants, which did not find any planets around stars more massive than ≈3 M⊙.

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White dwarf planets

Cited by 9 publications

References 21 publications

Eccentric planets and stellar evolution as a cause of polluted white dwarfs

Eccentric planets and stellar evolution as a cause of polluted white dwarfs

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

Search for giant planets around seven white dwarfs in the Hyades cluster with the Hubble Space Telescope

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