The chemical diversity of exo-terrestrial planetary debris around white dwarfs

By B. Gänsicke, D. Koester, J. Farihi, J. Girven, S. Parsons, E. Breedt. 2012

238 citations recorded by the source corpus.

We present Hubble Space Telescope (HST) ultraviolet spectroscopy of the white dwarfs PG 0843+516, PG 1015+161, SDSS 1228+1040, and GALEX 1931+0117, which accrete circumstellar planetary debris formed from the destruction of asteroids. Combined with optical data, a minimum of five and a maximum of 11 different metals are detected in their photospheres. With metal sinking time-scales of only a few days, these stars are in accretion/diffusion equilibrium, and the photospheric abundances closely reflect those of the circumstellar material. We find C/Si ratios that are consistent with that of the bulk Earth, corroborating the rocky nature of the debris. Their C/O values are also very similar to those of bulk Earth, implying that the planetary debris is dominated by Mg and Fe silicates. The abundances found for the debris at the four white dwarfs show substantial diversity, comparable at least to that seen across different meteorite classes in the Solar system. PG 0843+516 exhibits significant overabundances of Fe and Ni, as well as of S and Cr, which suggests the accretion of material that has undergone melting, and possibly differentiation. PG 1015+161 stands out by having the lowest Si abundance relative to all other detected elements. The Al/Ca ratio determined for the planetary debris around different white dwarfs is remarkably similar. This is analogous to the nearly constant abundance ratio of these two refractory lithophile elements found among most bodies in the Solar system. Based on the detection of all major elements of the circumstellar debris, we calculate accretion rates of ≃1.7 × 108 to ≃1.5 × 109 g s−1. Finally, we detect additional circumstellar absorption in the Si IV 1394, 1403 A doublet in PG 0843+516 and SDSS 1228+1040, reminiscent to similar high-ionization lines seen in the HST spectra of white dwarfs in cataclysmic variables. We suspect that these lines originate in hot gas close to the white dwarf, well within the sublimation radius.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/14159667fa28ea60341b42faf1328b2b9fd5999d

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In Astronomy and Astrophysics

1. J. Farihi
2. A. Mustill
3. Amy Bonsor
4. B. Gänsicke
5. D. Veras
6. D. Koester
7. S. O. Kepler
8. M. C. Wyatt

In Instrumentation

1. J. Farihi
2. A. Mustill
3. Amy Bonsor
4. M. C. Wyatt
5. L. Althaus
6. B. Gänsicke
7. D. Koester
8. A. Córsico

Citations in the corpus

• FORETELLINGS OF RAGNARÖK: WORLD-ENGULFING ASYMPTOTIC GIANTS AND THE INHERITANCE OF WHITE DWARFS (2012, background): “…metal-polluted atmospheres or with circumstellar discs strongly suggests that planets, feeding asteroidal or cometary material to locations close to the star, exist around these degenerate stellar remnants (Zuckerman et al. 2003; Gänsicke et al. 2006; Farihi et al. 2009; Gänsicke et al. 2012).”
• Circumstellar Debris and Pollution at White Dwarf Stars (2016, background): “These findings from infrared spectroscopy of debris in situ are consistent with, and almost certainly mirrored by, the carbonpoor compositions established via several metal-enriched white dwarfs (Jura et al., 2012; Gänsicke et al., 2012; Farihi et al., 2013b).”
• Pulsating white dwarfs: new insights (2019, background): “…including our Sun, will evolve into WDs, and nowadays observational evidence convincingly demonstrates that numerous WDs foster remnants of planetary systems — even planetary matter, shedding light on the chemical composition of extra-solar planets (Gänsicke et al., 2012; Hollands et al., 2018).”
• Simulations of two-planet systems through all phases of stellar evolution: implications for the instability boundary and white dwarf pollution (2013, background): “Observations confidently detect pollution at cooling ages from a few tens of Myr (e.g. Gänsicke et al. 2012) to several Gyr (Koester et al. 2011), but cannot detect pollution at earlier times when the WD is too hot to rule out a primordial origin for metals7 nor at later times when the WDs are too…”
• The frequency of planetary debris around young white dwarfs (2014, background): “7 in Gänsicke et al. (2012), it is clear tht WD 1015+161 has overall a much lower Si abundance compared to the other stars.”