News: Water Vapour From a Star !

[CraigS]

"Recipe for water: Just add starlight"
http://www.physorg.com/news202577650.html

"ESA's (European Space Agency) Herschel infrared space observatory has discovered that ultraviolet starlight is a key ingredient for making water in the atmosphere of some stars. It is the only explanation for why a dying star is surrounded by a gigantic cloud of hot water vapour. These new results will be published tomorrow in Nature."
....
"This suggests that the water is being created by a previously unsuspected chemical process where ultraviolet radiation from interstellar space is breaking up the carbon monoxide and releasing oxygen atoms that can then react with hydrogen to form water molecules."
...
"The discovery of water vapour from the outflowing wind of a carbon star has required a complete re-evaluation of our models for the chemical processes in such flows"

The water vapour is being formed at about 1000 degrees C !!
Boy, this theory rework really IS going to get them into hot water !

Cheers

[CraigS]

I'm very sceptical about this one ..

How on earth can the H=O bonds stay together close to a star ?
They don't mention in the article how close the vapour is to the star surface but irrespective of that, how do the bonds stay intact at 1000 degrees ? What about the radiation outflows, etc ?

I'll have to read up more on this one.
Seems to be an advert for the super-human "Herschel team".

Cheers

[renormalised (Carl)]

The water is most likely being protected by the sooty outgassings of the star. Carbon stars stellar winds are full of carbon particles, that's almost like a soot that can absorb a lot of the radiation being given off by the star. Some carbon stars are that sooty, they radiate mostly in the IR. Their visible light is nearly completely absorbed by the sooty "atmosphere" and re-radiated in the IR. That soot also protects more delicate molecules by shielding them from UV, heat etc. Prevents them from breaking up.

You also have to remember this...1000C at 1 atm is far different from 1000C in a vacuum. At 1atm, because of the vast numbers of molecules and atoms present, the radiative transfer of heat is far more efficient than what it is in a vacuum...despite the presence of the star's outflows, that gas is still a much better vacuum than we can achieve here on Earth.

[CraigS]

Article says:

"Observations with the PACS and SPIRE spectrometers have shown that water vapour is being formed deep down near the surface of the star; a place where it was previously thought to be impossible."

”The new Herschel observations have shown that the water is being formed much closer to the star itself, at temperatures approaching 1000oC."

So, I wouldn't have thought the soot would provide much protection if the water is forming closer to the star than the soot.

Their explanation seems to be the gaps in the soot cloud allows external UV to stimulate the formation of the H2O.

So, if the H2O is close to the star, I would've thought it would be getting pummelled by star radiation, plasma bursts, ion flows, etc.

I guess it all depends on how close the H2O is to the star (and they seem to have left that bit out in the explanation .... and I can't find any original paper).

Frustrating.

Cheers

[renormalised (Carl)]

I haven't read the paper either....so it's forming close to the star.

Problem with their interpretation is that UV dissociates water molecules, so there must be another mechanism allowing the water to form. The UV does split up CO and allows O to combine with H, the conventional reaction is this...

CO + UV light= C +O

O + H2 = H2O

However the water has to be masked in order to not be dissociated itself, otherwise you get what you typically see in carbon stars and that's an OH maser in the atmospheres of the stars...

H2O + UV = OH + H

The maser is caused by the heat/radiation making the OH molecules radiate in the microwave region.

Being close to the star is exactly where that water will get pummeled by all that you mentioned.

[renormalised (Carl)]

Here's some papers which should shed some light....

http://arxiv.org/abs/astro-ph/0107212

http://arxiv.org/abs/astro-ph/0302103

http://arxiv.org/abs/astro-ph/0407153

[CraigS]

Thanks Carl.

I don't think we're going to answer this one, as the guys who came up with it don't understand it either. (Ie: 'its a first'). I think the papers you cite provide the current theories, which seem now to have been challenged by this discovery.

The guys who wrote the article seem to be versed in the H2O-from-comet theory and the UV-from-the-star being filtered by the soot theory as well.

Perhaps its all a question of what happens, where (in terms of proximity to the star and the soot) .. the carbon closer to the star does get dissociated, then recombines with H2 and forms H2O in areas where it is 'sootiest' (ie: soot clumps), then as they move out more, the cloud (providing the shielding) gets thinner in some places and then they get UV'd by interstellar UV and drift off as OH and H, as per usual.

All a question of the clumpiness of the soot and the distance from the star?

Don't know.

Cheers

[renormalised (Carl)]

In carbon stars, the carbon when it's in close to the star, just like every other molecule and atom there, is essentially in its ionised state. It's only once the carbon drifts out from the star does it condense into tiny soot particles, much like the dust in the ISM and about the same size. As I was saying previously, these guys have to account for the fact that UV light (although around a carbon star there isn't too much of that to begin with) dissociates water molecules. If this UV is coming from interstellar space, as the article says, then we have to have a source somewhere close by, preferably a rather hot star...O or B preferably.

I don't think this has challenged current theory as it has added another layer of complexity to the problem. It still think they need to nut this one through a bit more before they can say anything definitively about what's happening.

[Steffen]

I wonder whether all this vapour is causing global warming of the star's atmosphere

Cheers
Steffen.

[renormalised (Carl)]

Probably, or someone left the heater on