Contact Binary Ages?

[Dollan]

Hi folks...

Is there a common age range for contact binaries? My purpose is to place a habitable planet about the contact binary AE Phoenicis, but I can find no information on its age. If one can have a contact binary that is at least 4 billion years old, then I'm willing to fudge it -- unless there is some information somewhere on that star's possible age that someone might be aware of.

Thanks!

...John...

[Malenfant]

Is there a common age range for contact binaries? My purpose is to place a habitable planet about the contact binary AE Phoenicis, but I can find no information on its age. If one can have a contact binary that is at least 4 billion years old, then I'm willing to fudge it -- unless there is some information somewhere on that star's possible age that someone might be aware of.

I'll need some more info... do you know anything about the stars in that specific binary? Masses? Is one a giant or not? spectral types? Things like that can narrow it down.

I know that some contact binaries can physically merge - I think they're called W UMa systems (ER Vulpeculae types are what happens just before that) - which usually involve two main sequence stars that spiral into eachother by magnetic braking and end up forming a single star.

It really depends on what the individual stars are though, as far as I'm aware there's no "common age" for all contact binaries. If you can give me all the info you have on those I can probably tell you something about them.

[Dollan]

Yeah, I should have posted that, sorry....

Spectrum: G1 V and G2 V
Masses: 1.366 and 0.629
Temp.: 5700 K (I'm not certain if this is just for the A component or both combined, or both seperately).
Period: 0.36237274 days
It *is* a W UMa overcontact binary.

Considering the masses and spectral types, I don't think they would be older than 5 billion years, but if they're younger than, say, 3.5 billion years (and that's stretching it in my opinion) I doubt advanced multicellular forms (to say nothing of intelligence) would have arisen.

...John...

[Malenfant]

Yeah, I should have posted that, sorry....

Spectrum: G1 V and G2 V
Masses: 1.366 and 0.629

Hm, if those masses are correct then something crazy is going on there... a 0.629 solar mass star can't possibly be a G2 V. I suspect the temperature and spectral type being determined by the outer envelope there (apparently this happens a lot), and what's really inside that is a mid-K V star. The spectral types can be very misleading here.

Considering the masses and spectral types, I don't think they would be older than 5 billion years, but if they're younger than, say, 3.5 billion years (and that's stretching it in my opinion) I doubt advanced multicellular forms (to say nothing of intelligence) would have arisen.

My suspicion from what you've said here is that it's probably a very young system - the prototype system itself (W UMa) is estimated to be only about 100-500 million years old according to http://adsabs.harvard.edu/abs/1974MNRAS.168...31W . So I'd be surprised if these contact binaries were generally over a billion years old...

[Dollan]

Somewhere, in my Google, etc. search that lasted most of the morning, I remember seeing a reference to an F8 V star, but not having found it again I discarded it.

Drat. I need to find another star.... Known of a good Solar twin beyond 150 light years?

**goes back to dredging through the HabCat**

...John...

[ajtribick]

...then again, this article says that most contact binaries are found in clusters over a billion years old - though it doesn't say whether these are main sequence stars or not, nor is it clear how long the stars have been in the contact binary stage.

[Malenfant]

It also doesn't give a maximum age for how old they can be though...

It really depends on a lot of factors. Did the stars start off further apart and eventually get close enough (through gravitational or magnetic braking) to touch? Can contact binaries remain in stable orbits over time or is their ultimate fate always to merge into one star? Did one or both stars expand into a giant and overflow their roche lobes? When they're talking about 'contact binaries' are they just talking about the full-blown examples where both stars are surrounded by a common envelope, or are they also including 'semi-detached' systems where only one star has overflowed its roche lobe?

I'd still think that they're going to be young systems, based on what I've seen about the long-term stability of such systems. A contact system with type V stars might get older than a billion years but probably not THAT much older. And the age of a system where one or both stars are giants that have overflowed the roche lobes depends on the masses of the stars and how long it took for them to reach their Giant stages...

[ajtribick]

Apparently the Geneva-Copenhagen survey (which includes age estimates) has an entry for AE Phoenicis (at least, SIMBAD gives a reference to it), but I haven't checked whether the tables are still available, or whether AE Phoenicis is in there.

[Cormoran]

I have the tables...

AE Phoenicis is also known as HD 9528 (apparently)

Its given age is given at 9.1 Gigayears, with a lower limit of 4.1 and a higher limit of 13.3

Big margin of error there I know

Cormie

[selden]

The Geneva Copenhagen Survey catalog is available on the Vizier catalog server at
http://vizier.u-strasbg.fr/viz-bin/Cat?V/117

You can query it for specific entries or you can download the whole thing.

[ajtribick]

Thanks for that Cormoran.

Another reference to throw into the mix here: Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation.

From the abstract:

Dispersions in the velocity space indicate a 5.47-Gyr kinematical age for the FCB group. Compared with the field chromospherically active binaries (CABs), presumably detached binary progenitors of the contact systems, the FCB group appears to be 1.61 Gyr older. Assuming an equilibrium in the formation and destruction of CAB and W UMa systems in the Galaxy, this age difference is treated as an empirically deduced lifetime of the contact stage. Because the kinematical ages (3.21, 3.51, 7.14 and 8.89 Gyr) of the four subgroups of the FCB group are much longer than the 1.61-Gyr lifetime of the contact stage, the pre-contact stages of the FCB group must dominantly be producing the large dispersions.

So we have a lifetime of the contact stage of 1.61 Gyr, so presumably for most of its lifetime it was an RS Canum Venaticorum star, which probably wasn't a healthy environment (superflares).

[Malenfant]

Interesting, that's older than I thought! I'll have to peruse those articles later...

[ajtribick]

Actually all this has made me think up this scenario...

Two stars start off as an RS CVn system, with a planet in the habitable zone. Life on the planet doesn't get very advanced because of superflare activity. However W UMa stars are less active than RS CVn ones, so let's have the system undergo a transition to a W UMa binary a few billion years in (magnetic braking or something might do this). The lessened activity allows a Cambrian-explosion style evolutionary radiation on the planet.

Not sure if this is possible (especially with regard to luminosity changes on going from an RS CVn system to a W UMa binary), or what would happen when the W UMa system finally coalesces a billion years or so later.