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WISE, a mission that will find ALL the neighbours
Guest_PhilCo126_*
post Nov 27 2009, 08:42 AM
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Greg, the onboard frozen Hydrogen is expected to last 10 months, allowing WISE to map most of the sky a second time in order to see what has changed. So only a partial 2nd survey should be possible...
Launch is now set to 9th December smile.gif
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Greg Hullender
post Nov 27 2009, 06:48 PM
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I guess I'm counting on even that number having some safety factor in it. :-)

Something else I've thought about recently is that two observations six months apart aren't enough to characterize an orbit. Even if it finds thousands of new asteroids, the fact that we can't observe them from the ground seems to limit the immediate usefulness of the data. Or perhaps it's hoped it could justify a followup mission a few years later? Or maybe just offer good initial targets for Pan-STARRS.

My personal hope is still that it finds a brown-dwarf companion to the sun that offers some explanation for things like the orbit of Sedna and the abrupt edge of the Kuiper belt -- not to mention a REALLY great flagship mission target. And even if not, WISE ought to be able to absolutely rule out the possibility of such a thing.

We're probably still a good year away from any results, I guess. Unless they really DO find that brown dwarf.

--Greg
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ngunn
post Nov 27 2009, 10:22 PM
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When is a brown dwarf a black dwarf? When it no longer emits any visible light at all? If they find any of those nearby I think Herschel will be on the case.
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nprev
post Nov 27 2009, 10:39 PM
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I always thought that a black dwarf was a completely burned-out star, normally a former white dwarf...considerably more massive than a brown dwarf.


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ngunn
post Nov 27 2009, 10:56 PM
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Probably right. I just wanted to make the point that WISE could discover objects close to room temperature. Would it really be appropriate to call them brown dwarfs? If the term 'black dwarf' is to be confined to cooled white dwarfs then we need a new name for cooled brown dwarfs and other objects that were never even hot enough to be brown for any length of time but could still turn up in IR surveys.
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Reed
post Nov 28 2009, 12:14 AM
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QUOTE (Greg Hullender @ Nov 27 2009, 10:48 AM) *
Something else I've thought about recently is that two observations six months apart aren't enough to characterize an orbit.

Existing and future narrow angle instruments should be able to follow up on them. You'd never get Herschel, Keck or VLT time for a large area survey, but they are definitely candidates for followup.
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Guest_PhilCo126_*
post Nov 28 2009, 10:34 AM
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It isn't just two obsevations six months apart;
There’ll be sufficient overlap, so that each position in the sky gets eight or more independent exposures on successive orbits. wink.gif
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nprev
post Nov 28 2009, 10:48 AM
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Thing is, what if we have a companion brown dwarf about a 0.5 LY out with an orbital period of 100,000 years or so? Finding such a thing should be easy with WISE, but it may take a decade or more to confirm that it's probably in orbit around the Sun, even longer to derive a decent ephemeris. The problem isn't frequency of observation, it's very low orbital velocities for distant objects.

New Horizons is still trying to work out ephemeris uncertainties for Pluto because it hasn't been observed for even half an orbit since its discovery.


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Greg Hullender
post Nov 28 2009, 06:52 PM
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Proxima Centauri is 0.21 ly from the Alpha A/B barycenter, and even after 100 years, we're still not QUITE sure it's actually orbiting the other two.

http://en.wikipedia.org/wiki/Proxima_Centauri

I'd hope we'd do a BIT better with an object nominally orbiting our own sun, but it'd still take a while. Even with the overlapping observations, I think the trouble with the WISE data will be that it spans just one year. Of course, something that barely moves after one year (like a remote brown dwarf) probably won't get lost easily, but an Earth-crossing asteroid might well be hard to find again.

As for black dwarfs, the Universe probably isn't old enough for any to exist yet:

http://en.wikipedia.org/wiki/Black_dwarf

There are already known brown dwarfs with estimated temperatures as low as 500K:

http://en.wikipedia.org/wiki/Brown_dwarf#D...gh_mass_planets

It seems plausible that smaller, cooler ones exist and even might be more plentiful than regular stars, given the mass/frequency curve we seem to see everywhere else in the universe. WISE could well find LOTS of brown dwarfs closer to the sun than (say) 4 light years.

I guess we'll know in eighteen months or so!

--Greg


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NGC3314
post Nov 29 2009, 04:03 AM
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If the IR broadband signature for brown dwarfs really is distinctive enough, candidates can be followed up with large ground-based telescopes once WISE points them out. That would give much higher angular resolution as well as time baseline. One of the bumper-sticker descriptions of WISE (back when it was NGSS, which someone thought would be too confusing compared to NGST which is now JWST) was that it should discover both the most luminous galaxies and our nearest stellar neighbors; practically something for everybody.
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DFinfrock
post Nov 30 2009, 06:24 PM
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QUOTE (Greg Hullender @ Nov 28 2009, 06:52 PM) *
WISE could well find LOTS of brown dwarfs closer to the sun than (say) 4 light years.


I can't wait to begin the exoplanet surveys for all of those local brown dwarfs!

David
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Guest_PhilCo126_*
post Dec 10 2009, 10:31 AM
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Launch postponed: The WISE launch is currently scheduled for no earlier than Saturday, December 12th, at 6:09:33 am pacific, from Vandenberg Air Force Base in CA...
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ElkGroveDan
post Dec 10 2009, 03:36 PM
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...and even that doesn't look likely at this point.


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Holder of the Tw...
post Dec 10 2009, 11:32 PM
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We might want to lower our expectations just a bit for finding brown dwarfs closer than Proxima. There is a distinct possibility for finding none at all.
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ElkGroveDan
post Dec 11 2009, 01:05 AM
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At least not until after it launches anyway. Which is now set for Sunday the 13th. I'll miss that one, but if it gets bumped over to Monday or Tuesday I might be able to make it again.


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