Spectra of some planet eating white dwarfs

[Robin Leadbeater]

Intrigued by Dr Amy Bonsor’s  recent BAA webinar “ Planet Eating White Dwarfs”  I thought I would try hunting some of them down and look for the evidence in the spectra.

https://britastro.org/observations/observation.php?id=20210831_232116_04a034fbfd0ae832

Perhaps the same fate awaits us, the only trace of our existence just a few lines in the spectrum of the white dwarf remnant that was once our Sun…     Always look on the bright side of life !

Robin

[Bill Ward]

I certainly hope there’s more than just a shadow of our bones left ; – )

[Alan Thomas]

And, departing, leave behind us

Footprints on the sands of time

(Longfellow)

[Andy Wilson]

Fantastic spectra Robin!

It is an intriguing method for learning about other planetary systems.

Andy

[Robin Leadbeater]

Another interesting WD. No metals or Hydrogen, just  Helium

[Dr Paul Leyland]

Does the absence of C, O, etc, indicate that the progenitor star was of relatively small mass and so significant He burning hadn’t started before it lost its hydrogen envelope in the red giant phase?

Or does it mean that all the heavy material has sunk into the core and that convection is insignificant?

[Robin Leadbeater]

I don’t know how it relates to the progenitor but as I understand it, naked electron degenerate white dwarfs don’t show any spectral features and there are indeed some WD like that, designated spectral type DC.  The spectral features then come from a thin skin of accreted material, the heavier elements rapidly sinking into the interior to become part of the electron degenerate material so most show just H while others have He or a mix of H/He. You do also find some cool white dwarfs with Carbon in their spectrum, presumably also recently accreted.  

[Robin Leadbeater]

A quick literature search though brought up this reference which talks of WD with initial He atmospheres evolving an H dominated atmosphere through upward diffusion of H.

https://arxiv.org/abs/2008.07469

Anything heavier though I suspect must have been accreted.

[David Boyd]

Or possibly dredged up?

https://arxiv.org/pdf/astro-ph/9803121.pdf

[Robin Leadbeater]

Ah interesting. I see that paper suggested Oxygen might be found as well through the same process. One was  found with just O in the spectrum, though by a suggested different mechanism where the He/H is stripped away.

https://physicsworld.com/a/white-dwarf-with-nearly-pure-oxygen-atmosphere-surprises-astronomers/

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