Gliese 86 system age

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Gliese 86 system age

Post by Lazarus on 29th March 2014, 2:47 pm

Fuhrmann et al., Astrophysical Journal (2014): "On the Age of Gliese 86"
http://iopscience.iop.org/0004-637X/785/1/68/

Seems that this is actually an old system (~10 Gyr), the low chromospheric age is probably due to mass/angular momentum accretion from the secondary. The progenitor mass of Gliese 86 B is estimated to be 1.11±0.05 solar masses.
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Re: Gliese 86 system age

Post by Shellface on 30th March 2014, 10:12 am

I recall literature indicating the system is kinematic a member of the thick disk, and it looks like spectroscopy confirms its age.

The discord between activity-derived ages and other methods of aging for stars with white dwarf companions is becoming an increasingly noticed phenomenon; I don't recall it being significantly physically evidenced prior to the discovery of HD 8049 B, but the effect has since been noted for HD 114174 (companion discovery paper here) and has now been characterised for Gliese 86. It will be interesting to find out what the limits to the separation between the main sequence star and the white dwarf are in order for this to take effect - maybe 40 Eridani, with two MS components at 35 and 400 AU from a white dwarf with a cooling age of ~0.1 Gyr, will be a useful test?

That mass for the WD progenitor puts the pre-evolution system as loosely similar to Alpha Centauri, though the differences in metallicity mean that neither system is a perfect proxy for the other. Still, it points the direction in which Alpha Cen will develop, I suppose! It also puts into perspective how weird Gliese 86 Ab is; how did such a massive object end up in a 16-day orbit in such an old system? Using the Alpha Cen proxy, B's protoplanetary disk is supposed to have been truncated at just outside the ice line, which pretty much cuts off giant planet formation; so how did at least 4 Jupiter masses end up coalescing in a similar system? Gliese 86 is certainly a system worth further study!

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Re: Gliese 86 system age

Post by Sirius_Alpha on 30th March 2014, 10:39 am

Perets points out that the planet at Gliese 86 Ab probably formed during/after the RGB phase of the system. Way back when this system was a mass-transfering binary, Gliese 86 B would have lost material to Gliese 86 A, producing a disk around the primary out of which "second generation" planets could form.

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Re: Gliese 86 system age

Post by Lazarus on 30th March 2014, 12:44 pm

I admit I've always liked the second generation planet scenario. One possibility is that the gas giant accreted onto an existing planet in the system. It suggests certain scenarios for science fiction/worldbuilding - imagine a habitable planet in a similar system slowly getting transformed into a gas giant as it accretes matter from a nearby red giant.
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Re: Gliese 86 system age

Post by Stalker on 30th March 2014, 1:59 pm

Il remind me of Jack Vance's Big Planet.

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