Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal

Kaiser, Bastian; Clemens, J. C.; Blouin, Simon; Dufour, Patrick; Hegedus, R. J.; Reding, Joshua S.; Bédard, Antoine

doi:10.1126/science.abd1714

Cited by 39 publications

(35 citation statements)

References 69 publications

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“…This has led to the characterisation of many different types of planetary compositions (Swan et al 2019), for example, lithospheric material rich in Ca and Al (Zuckerman et al 2011), core-like material rich in Fe and Ni (Gänsicke et al 2012;Wilson et al 2015;Hollands et al 2018), and in one instance (Xu et al 2017) cometary material rich in volatile elements such as N and S. Some rocky material has also been established as enriched in water-ice due to the over abundance of oxygen (Farihi et al 2013;Raddi et al 2015), and more generally from the presence of trace hydrogen in heliumdominated atmospheres (Gentile Fusillo et al 2017;Hoskin et al 2020;Izquierdo et al 2021). Most recently, atmospheres enriched in the alkali metals, Li and K, have been identified in a handful of cool white consistent with either accretion of primordial Li-enhancement (Kaiser et al 2020) or continental-crust like material (Hollands et al 2021). Additionally, Be has been detected at two systems as a signature of spallation by high energy particles (Klein et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Spectral analysis of cool white dwarfs accreting from planetary systems: from the ultraviolet to the optical

Hollands

Tremblay

Gänsicke

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The accretion of planetary debris into the atmospheres of white dwarfs leads to the presence of metal lines in their spectra. Cool metal-rich white dwarfs, which left the main-sequence many Gyr ago, allow the study of the remnants of the oldest planetary systems. Despite their low effective temperatures (Teff), a non-neglible amount of their flux is emitted in the near ultraviolet (NUV), where many overlapping metal lines can potentially be detected. We have observed three metal-rich cool white dwarfs with the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST), and compare the results determined from the NUV data with those previously derived from the analysis of optical spectroscopy. For two of the white dwarfs, SDSS J1038−0036 and SDSS J1535+1247, we find reasonable agreement with our previous analysis and the new combined fit of optical and NUV data. For the third object, SDSS J0956+5912, including the STIS data leads to a ten percent lower Teff, though we do not identify a convincing explanation for this discrepancy. The unusual abundances found for SDSS J0956+5912 suggest that the accreted parent-body was composed largely of water ice and magnesium silicates, and with a mass of up to ≃ 2 × 1025 g. Furthermore SDSS J0956+5912 shows likely traces of atomic carbon in the NUV. While molecular carbon is not observed in the optical, we demonstrate that the large quantity of metals accreted by SDSS J0956+5912 can suppress the C2 molecular bands, indicating that planetary accretion can convert DQ stars into DZs (and not DQZs/DZQs).

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Section: Introductionmentioning

confidence: 99%

Spectral analysis of cool white dwarfs accreting from planetary systems: from the ultraviolet to the optical

Hollands

Tremblay

Gänsicke

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…For example, Kaiser et al (2021) and Hollands et al (2021) discovered five cool (T eff < 5000 K) white dwarfs with trace Li in their atmospheres. This rare polluting element is extremely difficult to detect in hotter white dwarfs and could be the signpost of accretion of the crust of a planetary object (Hollands et al 2021).…”

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confidence: 99%

A catalogue of white dwarfs in Gaia EDR3

Fusillo

Tremblay

Cukanovaite

et al. 2021

Monthly Notices of the Royal Astronomical Society

154

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We present a catalogue of white dwarf candidates selected from Gaia early data release three (EDR3). We applied several selection criteria in absolute magnitude, colour, and Gaia quality flags to remove objects with unreliable measurements while preserving most stars compatible with the white dwarf locus in the Hertzsprung-Russell diagram. We then used a sample of over 30 000 spectroscopically confirmed white dwarfs and contaminants from the Sloan Digital Sky Survey (SDSS) to map the distribution of these objects in the Gaia absolute magnitude-colour space. Finally, we adopt the same method presented in our previous work on Gaia DR2 to calculate a probability of being a white dwarf (PWD) for ≃ 1.3 million sources which passed our quality selection. The PWD values can be used to select a sample of ≃ 359 000 high-confidence white dwarf candidates. We calculated stellar parameters (effective temperature, surface gravity, and mass) for all these stars by fitting Gaia astrometry and photometry with synthetic pure-H, pure-He and mixed H-He atmospheric models. We estimate an upper limit of 93 per cent for the overall completeness of our catalogue for white dwarfs with G ≤ 20 mag and effective temperature (Teff) >7000 K, at high Galactic latitudes (|b| > 20○). Alongside the main catalogue we include a reduced-proper-motion extension containing ≃ 10 200 white dwarf candidates with unreliable parallax measurements which could, however be identified on the basis of their proper motion. We also performed a cross-match of our catalogues with SDSS DR16 spectroscopy and provide spectral classification based on visual inspection for all resulting matches.

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“…Casey et al 2016). Recently, several works show pollution of Be and Li in white dwarfs, likely due to accretion of icy exomoons that formed around giant exoplanets or of other rocky bodies in exoplanetary systems (Klein et al 2021;Doyle et al 2021;Kaiser et al 2021). Other works, as Jorissen et al (2020), found that the binary frequency appears normal among the Lirich giants, excluding a causal relationship between Li enrichment and binarity.…”

Section: Lithium-rich Giant Starsmentioning

confidence: 99%

The Gaia-ESO survey: Mixing processes in low-mass stars traced by lithium abundance in cluster and field stars

Magrini

Lagarde²,

Charbonnel³

et al. 2021

A&A

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Aims. We aim to constrain the mixing processes in low-mass stars by investigating the behaviour of the Li surface abundance after the main sequence. We take advantage of the data from the sixth internal data release of Gaia-ESO, IDR6, and from the Gaia Early Data Release 3, EDR3s. Methods. We selected a sample of main-sequence, sub-giant, and giant stars in which the Li abundance is measured by the Gaia-ESO survey. These stars belong to 57 open clusters with ages from 130 Myr to about 7 Gyr and to Milky Way fields, covering a range in [Fe/H] between ∼ − 1.0 and ∼ + 0.5 dex, with few stars between ∼ − 1.0 and ∼ − 2.5 dex. We studied the behaviour of the Li abundances as a function of stellar parameters. We inferred the masses of giant stars in clusters from the main-sequence turn-off masses, and for field stars through comparison with stellar evolution models using a maximum likelihood technique. We compared the observed Li behaviour in field giant stars and in giant stars belonging to individual clusters with the predictions of a set of classical models and of models with mixing induced by rotation and thermohaline instability. Results. The comparison with stellar evolution models confirms that classical models cannot reproduce the observed lithium abundances in the metallicity and mass regimes covered by the data. The models that include the effects of both rotation-induced mixing and thermohaline instability account for the Li abundance trends observed in our sample in all metallicity and mass ranges. The differences between the results of the classical models and of the rotation models largely differ (up to 2 dex), making lithium the best element with which to constrain stellar mixing processes in low-mass stars. We discuss the nature of a sample of Li-rich stars. Conclusions. We demonstrate that the evolution of the surface abundance of Li in giant stars is a powerful tool for constraining theoretical stellar evolution models, allowing us to distinguish the effect of different mixing processes. For stars with well-determined masses, we find a better agreement of observed surface abundances and models with rotation-induced and thermohaline mixing. Rotation effects dominate during the main sequence and the first phases of the post-main-sequence evolution, and the thermohaline induced mixing after the bump in the luminosity function.

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Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal

Cited by 39 publications

References 69 publications

Spectral analysis of cool white dwarfs accreting from planetary systems: from the ultraviolet to the optical

Spectral analysis of cool white dwarfs accreting from planetary systems: from the ultraviolet to the optical

A catalogue of white dwarfs in Gaia EDR3

The Gaia-ESO survey: Mixing processes in low-mass stars traced by lithium abundance in cluster and field stars

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