White dwarf in the Gliese 86 system

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ajtribick
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White dwarf in the Gliese 86 system

Post #1by ajtribick » 15.06.2005, 16:51

Gl86B: a white dwarf orbits an exoplanet host star

So now we have evidence that planets can survive one of the stars in their system going through the red giant phase...

Michael Kilderry
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Post #2by Michael Kilderry » 16.06.2005, 06:55

I wonder what these planets would look like, would they be boring cratered balls of rock or something a bit more interesting?

Michael :)
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Post #3by Evil Dr Ganymede » 16.06.2005, 07:39

Reading the paper, it seems the WD orbits the primary at about 21 AU, and the binary is between 2 - 8 Ga old assuming the star that formed the WD had 2-4 solar masses. (they say it could be 13-16 Ga old if the progenitor star for the WD had one solar mass, but that means the system is at least as old as the galaxy itself, or older than the universe! So it seems more likely that the progenitor was more massive).

The planet itself is at 0.11 AU from the primary, so it it'd probably be OK. It's quite clearly orbiting the K1 V primary, not the WD. As it is, the planet's blackbody temperature is about 645 K. If we assume the red giant was about 1000 sols luminosity, and that the K1 V and the red giant are illuminating the same hemisphere of the planet, then the blackbody temperature only goes up by about 12K. Not really enough to roast it much more than it already is being roasted anyway, in other words.

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Post #4by ajtribick » 16.06.2005, 22:50

Michael Kilderry wrote:boring cratered balls of rock


What's one of those when its in orbit around a main sequence star other than our sun? Given that we've only been finding gas giants so far (anyone got any values for molecular weight retained by the "hot Neptunes" such as Mu Arae d or Rho1 Cancri e, I'm not sure of the relevant formulae), terrestrial planets (including what you so dismissively term "boring cratered balls of rock") are the holy grail right now.

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Post #5by Michael Kilderry » 17.06.2005, 08:38

I wasn't saying that they were going to be boring, I was wondering if they would be interesting or not. :?

The first "boring cratered ball of rock" discovered may be interesting at first, but the novelty does wear off over time, for example, who talks about the Kuiper Belt object 1992 QB1 anymore?

Michael :)
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