Alkali metals in white dwarf atmospheres as tracers of ancient planetary crusts. (arXiv:2101.01225v2 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Hollands_M/0/1/0/all/0/1">Mark A. Hollands</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tremblay_P/0/1/0/all/0/1">Pier-Emmanuel Tremblay</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gansicke_B/0/1/0/all/0/1">Boris T. Gänsicke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koester_D/0/1/0/all/0/1">Detlev Koester</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gentile_Fusillo_N/0/1/0/all/0/1">Nicola P. Gentile-Fusillo</a>
White dwarfs that accrete the debris of tidally disrupted asteroids provide
the opportunity to measure the bulk composition of the building blocks, or
fragments, of exoplanets. This technique has established a diversity in
compositions comparable to what is observed in the solar system, suggesting
that the formation of rocky planets is a generic process. Whereas the relative
abundances of lithophile and siderophile elements within the planetary debris
can be used to investigate whether exoplanets undergo differentiation, the
composition studies carried out so far lack unambiguous tracers of planetary
crusts. Here we report the detection of lithium in the atmospheres of four cool
(<5,000 K) and old (cooling ages 5-10 Gyr) metal-polluted white dwarfs, where
one also displays photospheric potassium. The relative abundances of these two
elements with respect to sodium and calcium strongly suggest that all four
white dwarfs have accreted fragments of planetary crusts. We detect an infrared
excess in one of the systems, indicating that accretion from a circumstellar
debris disk is on-going. The main-sequence progenitor mass of this star was
$4.8pm0.2 M_odot$, demonstrating that rocky, differentiated planets may form
around short-lived B-type stars.
White dwarfs that accrete the debris of tidally disrupted asteroids provide
the opportunity to measure the bulk composition of the building blocks, or
fragments, of exoplanets. This technique has established a diversity in
compositions comparable to what is observed in the solar system, suggesting
that the formation of rocky planets is a generic process. Whereas the relative
abundances of lithophile and siderophile elements within the planetary debris
can be used to investigate whether exoplanets undergo differentiation, the
composition studies carried out so far lack unambiguous tracers of planetary
crusts. Here we report the detection of lithium in the atmospheres of four cool
(<5,000 K) and old (cooling ages 5-10 Gyr) metal-polluted white dwarfs, where
one also displays photospheric potassium. The relative abundances of these two
elements with respect to sodium and calcium strongly suggest that all four
white dwarfs have accreted fragments of planetary crusts. We detect an infrared
excess in one of the systems, indicating that accretion from a circumstellar
debris disk is on-going. The main-sequence progenitor mass of this star was
$4.8pm0.2 M_odot$, demonstrating that rocky, differentiated planets may form
around short-lived B-type stars.
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