White dwarf planetary systems Alexander Mustill Lund Observatory - PowerPoint PPT Presentation

White dwarf planetary systems Alexander Mustill Lund Observatory Collaborators: Amy Bonsor, Melvyn B. Davies, Jay Farihi, Boris Gänsicke, Raúl Maldonado, Chris Manser, Dimitri Veras, Eva Villaver, Mark Wyatt, …

White dwarfs tell us what extra-Solar planets and asteroids are made of Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarfs tell us what extra-Solar planets and asteroids are made of • ~50% of WDs show metal lines in their spectra Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarfs tell us what extra-Solar planets and asteroids are made of • ~50% of WDs show metal lines in their spectra • Metals should sink on short timescales: accretion is ongoing or recent Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarfs tell us what extra-Solar planets and asteroids are made of • ~50% of WDs show metal lines in their spectra • Metals should sink on short timescales: accretion is ongoing or recent • Leading candidate: pulverised asteroids/planets scattered close to the WD Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarfs tell us what extra-Solar planets and asteroids are made of • ~50% of WDs show metal lines in their spectra • Metals should sink on short timescales: accretion is ongoing or recent • Leading candidate: pulverised asteroids/planets scattered close to the WD • Composition gives us insight into planetary and asteroidal compositions beyond the Solar System (review: Jura & Young 2014) Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarf planetary systems: discs and close-in planetesimals Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarf planetary systems: discs and close-in planetesimals Spectroscopic signatures of accreted metals (~45% • flux of WDs, Wilson et al. 2019) and possible planet (Gänsicke et al. 2019) λ Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarf planetary systems: discs and close-in planetesimals Spectroscopic signatures of accreted metals (~45% • flux of WDs, Wilson et al. 2019) and possible planet (Gänsicke et al. 2019) λ Dust discs detected through IR excesses (~1.5% of • flux WDs, Wilson et al. 2019) λ Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarf planetary systems: discs and close-in planetesimals Spectroscopic signatures of accreted metals (~45% • flux of WDs, Wilson et al. 2019) and possible planet (Gänsicke et al. 2019) λ Dust discs detected through IR excesses (~1.5% of • flux WDs, Wilson et al. 2019) λ Gas discs detected through Keplerian emission • flux features (~0.1% of WDs, Gänsicke et al. 2007, Manser et al. 2020) λ Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarf planetary systems: discs and close-in planetesimals Spectroscopic signatures of accreted metals (~45% • flux of WDs, Wilson et al. 2019) and possible planet (Gänsicke et al. 2019) λ Dust discs detected through IR excesses (~1.5% of • flux WDs, Wilson et al. 2019) λ Gas discs detected through Keplerian emission • flux features (~0.1% of WDs, Gänsicke et al. 2007, Manser et al. 2020) λ Transits of disintegrating asteroids (2 known, • flux Vanderburg et al. 2015, Vanderbosch et al. 2019) time Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

White dwarf planetary systems: discs and close-in planetesimals Spectroscopic signatures of accreted metals (~45% • flux of WDs, Wilson et al. 2019) and possible planet (Gänsicke et al. 2019) λ Dust discs detected through IR excesses (~1.5% of • flux WDs, Wilson et al. 2019) λ Gas discs detected through Keplerian emission • flux features (~0.1% of WDs, Gänsicke et al. 2007, Manser et al. 2020) λ Transits of disintegrating asteroids (2 known, • flux Vanderburg et al. 2015, Vanderbosch et al. 2019) time line strength and shape Spectral signatures of non-transiting asteroids • (1 known, Manser,…, Mustill et al. 2019) time Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

Unifying idea: Material is driven towards the WD on highly-eccentric orbits by large bodies in the outer system. It undergoes orbital circularisation, pulverisation and vaporisation, forms a close-in disc, and ultimately accretes onto the WD. Reviews: Farihi 2016 (observations), Veras 2016 (theory) Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

How and why does material get close to the white dwarf? AGB star loses mass (50% for 1M ⊙ ) and increases in radius (1au for 1M ⊙ ) Stellar radius Mustill & Villaver 2012 Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

How and why does material get close to the white dwarf? AGB star loses mass (50% for 1M ⊙ ) and increases in radius (1au for 1M ⊙ ) Planets escaped Stellar mass loss causes orbit expansion to conserve L = [ GM ★ a (1 - e 2 )] 1/2 Stellar radius Mustill & Villaver 2012 Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

How and why does material get close to the white dwarf? AGB star loses mass (50% for 1M ⊙ ) and increases in radius (1au for 1M ⊙ ) Planets escaped Stellar mass loss causes orbit expansion to conserve L = [ GM ★ a (1 - e 2 )] 1/2 Planets engulfed Stellar radius expansion strengthens tides Stellar radius Mustill & Villaver 2012 Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

exoplanets.org | 3/28/2017 3.0 10 3 ♃ 2.5 Planet Mass [Earth Mass] Mass of Star [Solar Mass] ♄ 100 Present-day Solar radius 2.0 ♆ ⛢ 10 1.5 ⊕ ♀ 1 1.0 ♂ ☿ 0.5 0.1 0.0 0.01 -3 0.01 0.1 1 10 100 10 Semi-Major Axis [Astronomical Units (AU)]

exoplanets.org | 3/28/2017 3.0 10 3 ♃ 2.5 Planet Mass [Earth Mass] Mass of Star [Solar Mass] ♄ 100 Present-day Solar radius 2.0 ♆ ⛢ 10 1.5 Engulfed by giant star Survive engulfment ⊕ ♀ 1 1.0 ♂ ☿ 0.5 0.1 Mustill & Villaver 2012 survival limit 0.0 0.01 -3 0.01 0.1 1 10 100 10 Semi-Major Axis [Astronomical Units (AU)]

WDs observed typically descend from single stars slightly more massive than Sun Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

WDs observed typically descend from single stars slightly more massive than Sun Few in number Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

WDs observed typically descend from single stars slightly more massive than Sun Have not Few in number evolved Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

WDs observed typically descend from single stars slightly more massive than Sun Have not Few in number evolved Koester et al 2014 Typical exoplanet surveys Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

Asteroid delivery by destabilised planetary systems Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

Asteroid delivery by destabilised planetary systems • Loss of stellar mass also increase the planet:star mass ratio. This ratio sets the timescale and strength of planet–planet and planet– asteroid interactions Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

Asteroid delivery by destabilised planetary systems • Loss of stellar mass also increase the planet:star mass ratio. This ratio sets the timescale and strength of planet–planet and planet– asteroid interactions • E.g., the Hill spheres of planets expand: r H = a ( M pl /3 M ★ ) 1/3 Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

Asteroid delivery by destabilised planetary systems • Loss of stellar mass also increase the planet:star mass ratio. This ratio sets the timescale and strength of planet–planet and planet– asteroid interactions • E.g., the Hill spheres of planets expand: r H = a ( M pl /3 M ★ ) 1/3 • This destabilises formerly stable systems (Debes & Sigurdsson 2002, Mustill et al., 2014, 2018) Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

Asteroid delivery by destabilised planetary systems • Loss of stellar mass also increase the planet:star mass ratio. This ratio sets the timescale and strength of planet–planet and planet– asteroid interactions • E.g., the Hill spheres of planets expand: r H = a ( M pl /3 M ★ ) 1/3 • This destabilises formerly stable systems (Debes & Sigurdsson 2002, Mustill et al., 2014, 2018) Mustill et al 2014 Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11

Asteroid delivery by destabilised planetary systems Frewen & Hansen (2014) showed that an eccentric, low-mass (super-Earth or Neptune) planet is an efficient deliverer of material, but did not look at the origin of the eccentricity Alexander Mustill (Lund University) — Compact Objects For All — 2020-02-11