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mkline55
2012-Dec-03, 08:28 PM
ESO1132 (http://en.wikipedia.org/wiki/SDSS_J102915%2B172927), also referred to as SDSS J102915+172927 or Caffau's star, had the lowest metallicity of any known star at the time of its discovery. If that were all I heard about it, I'd wonder if it were a population III star, and how far away it was. While it has the hypothesised metallicity of a pop III star, it's location is surprisingly right here in the Milky Way. It's estimated age is somewhere around the age of the Milky Way at 13 Gyr. In all that time, however, it has not evolved to have a higher metal content, it has not acquired a significant metal content, nor has it exploded, as pop III stars are supposed to have done in the first few hundred million years.

Google search came up with a variety of explanations, so I don't know if there is a mainstream concensus about how eso1132 came to be, but I'd like to know if there is. If not, then I'd like to know the opinions of other readers.

ngc3314
2012-Dec-03, 09:06 PM
It's not a pop III star - they would start with zero content of anything heavier than lithium. At that mass, the interior is not fully convective, so the surface abundances essentially reflect what it started with rather than having been increased by core fusion; metal content should be increased in an individual star only by pretty rare interactions with more evolved companions, since accretion or the interstellar medium is such a small factor even in the galactic disk. It's in the Milky Way because thats the only place where we can find stars that old (since they're very faint except in the brief red-giant phase). And with a mass that low, it won't blow up and is still close to the main sequence.

To my mind, what's most interesting is that unlike many of the other very-low-metallicity stars found so far, its iron-peak abundances are about as low relative to solar as the CNO elements. That pushes it at least close to the critical metal abundance below which the fine-structure far-IR emission lines of C and O will no longer cool collapsing interstellar gas toward higher densities. Making ow-mass stars in that low-abundance regime is still theoretically difficult (not that we actually know anything empirically about real Pop III stars at this point anyway).

mkline55
2012-Dec-04, 03:06 PM
Thanks, NGC3314. I am researching various publicly-available sources, and haven't run into the convection agrument yet. Can you point me to a publication?

I've found an eso document here (http://www.eso.org/public/archives/releases/sciencepapers/eso1132/eso1132.pdf), that descibes the object in greater detail, but suggests that under current theory, this object should not exist. Several scattered blogs discuss the object. An article here (http://www.space.com/12788-impossible-star-defies-theory.html) on space.com discusses the object but offers no theory as to how it could exist. An article here (http://arxiv.org/pdf/1203.4234v1.pdf) discusses how the object might have formed from the dust of supernovas from the first stars, but does not offer much as to why it remains unchanged (perhaps the convection argument may apply). A technical paper here (http://arxiv.org/pdf/1203.2607.pdf) seems to suggest in the discussion section that the lithium originally present during the formation of this star was possibly destroyed by its fast rotation or high turbulance.

mkline55
2013-Jan-02, 02:52 PM
I don't know if there is a mainstream concensus about how eso1132 came to be, but I'd like to know if there is. If not, then I'd like to know the opinions of other readers.

While I had hoped to receive additional responses within 30 days, I'll settle for a consensus of one, and assume that ngc3314 has provided the best and only possible answer. Thanks.

sjw40364
2013-Jan-20, 05:23 PM
Umm, they havnt a clue and are throwing out anything as way of explanation? Of course all these theories are untestable, so every theory is correct or wrong, take your pick. You might research our Sun, metals were found in our sun long before helium on every spectra ever done, and helium was first thought to be a form of sodium when finally discovered as it had never been observed yet. Only after being observed here on earth in experiments, was it finally observed on the Sun. And it is the ionized form of helium, which they don't bother to tell you has only been observed during electrical events. Take all that as you will.