Four new objects announced, three transiting planets and something peculiar from CoRoT a "compact brown dwarf" - or is it...
Four new planetary objects were announced this week: XO-5b is a normal "hot Jupiter" in a 4 day orbit around a solar like G star, maybe slightly bloated.;
CoRoT announced two hot Jupiters CoRoT-Exo4b and CoRoT-Exo5b 9 and 4 day orbits, respectively, around F stars, and both are undermassive and bloated - which is interesting, something going on there, although it could be selection effect dominated, since the bloated planets have the deepest transits are easiest to find in quick look at the transit time series.
F stars are a bit hotter and more massive than the sun and their planetary systems are somewhat underexplored.
I'm not sure what to make of CoRoT-Exo3b though: it is a 20 Jupiter mass object, in a 4 day orbit around a G0V solar like main sequence star; the star basically has solar metallicity.
The radius of CoRoT-Exo3b is 0.82 +0.15-0.05 Jupiter radii.
The object is twenty times more massive than Jupiter, but has a smaller reported radius.
The sucker is enormously dense. Mean density twice that of platinum!
The CoRoT team is referring to it as a "compact brown dwarf", which is technically correct, the mass is too high for a planet, but the radius too small for a brown dwarf.
The density is inexplicable - here is the CoRoT communique announcing it - I very much want to see the radial velocity confirmation data, although 20 Jupiter masses at 4d period around a 13th magnitude star should be quite solid.
Can you get a Jupiter mass metal core? Around a solar metallicity G star?
Is this some sort of ablated object - if so, ablated by what?
I'd go science fictional on this thing, but it is hard to think of anything useful to do with a thing like this...
PS: As Alastair mentions in the comments, this could be a product of collision between, presumably ~ 10 Jupiter mass objects, with the object losing some of the hydrogen envelope in the process; or it could have been in a closer orbit, with shorter orbital period, and lost some atmosphere before moving further out.
Or, it is just on the somewhat extreme end of the brown dwarf spread.
The other news, is that CoRoT has δm/m ~ 5*10-4 - though they don't say what S/N for how long an integration time...
That is to say, they can see stars dimming by one part in two thousand as a small planet passes in front of the star blocking a small fraction of the star's light.
This is pretty good sensitivity, allowing CoRoT to detect quite small planets.
The formal detection threshold for CoRoT at this precision is 1.7 Earth radii.
Corresponding to a mass of 5 Earth masses if the density is similar to Earth's - rock is not very compressible in this range, so this is not a bad estimate.
Of course getting radial velocity confirmation for 5 earth mass transit candidates at 12th magnitude is kinda hard...
This is quite interesting.
The Brown Dwarf calculator from Burrows at Arizona suggests the radius is not too crazy for an old brown dwarf - the numbers quoted are at the high end of the error range, but they could be consistent with a 6-8 billion year old brown dwarf, which is not implausible for a slightly sub-solar G star.
Might need to push a little bit on the error bars, but this could just be a quiet old and cold brown dwarf with a normal degenerate core, maybe a bit on the dense side as the spread in density for low mass brown dwarfs goes.
Or our radius-mass relationship for brown dwarfs could be a little bit off, which would be important, as it would mean the mass estimates for brown dwarfs with no direct mass measurements are too high.
Most known brown dwarfs have brightness and colour/spectral measurments and the radius and hence masses are inferred from the effective temperature from the colour and hence the surface area of the brown dwarf from the luminousity, assuming we know the distance also.
If that is wrong, and brown dwarfs tend to be denser than estimated from models, then we are overestimating most of the brown dwarf masses - low mass brown dwarfs are slightly bigger.
Or, the brown dwarf cooling models are wrong and they cool more rapidly than predicted becoming denser with age than expected from models.
Something to sort out.
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Look at: Structure and evolution of super-Earth to super-Jupiter exoplanets. I. Heavy element enrichment in the interior, Baraffe et al. 2008
http://adsabs.harvard.edu/abs/2008arXiv0802.1810B
They describe methods of getting up to 25 Mj planet cores.
Basically collide two Jupiters, and lose the light atmospheres in the process ...
I hadn't expected to see test cases so soon.
Looking forward to seeing the actual data.
It may re-open the debate as to what is a planet, based on formation mechanism(s) rather than fusion, etc.
"That's no moon. It's a space station."
A caution to getting too excited about COROT--I've heard rumors from a transit person that there's a lot of trouble with systematics in the photometry, which could ruin that really high precision. I haven't found anything obviously out there on the intertubes though, so take this with a grain of salt. The results so far are pretty interesting.
Hm, that is interesting.
It is hard for any secular trend to mask true periodic signals, but could miss stuff.
'course when they go back for a second look at the first long stare field any real signal should start accumulating
To get science fictional, I can speculate on 4th generation solar systems, on brown dwarfs with small black holes at their cores, and stuff like that -- not capable of getting past peer review, but maybe of tempting Dr. Stanley Schmidt at Analog.
http://scottaaronson.com/blog/?p=328#comment-20443
# Scott Says:
Comment #4 May 24th, 2008 at 1:59 am
Incidentally, here's a challenge that I issue to any and all readers:
Why is the age of the Earth â and of life on Earth â of the same order as the age of the entire universe? Why isn't one measured in billions of years and the other in quadrillions? Can you tell me an anthropic story that will make me a little less surprised by this?
(The Bousso et al. story seems to be silent about this particular coincidence, since it takes everything other than Î as given.)
=====================
Dear Prof. Scott Aaronson,
There is a first generation of stars, formed from primordial hydrogen (with a little helium and a tiny amount of lithium).
Some of them blow up and expel the material that makes a second generation of stars, that nucleosynthesize the hydrogen and the little helium into what astronomers alone call metals (anything heavier than helium, especially carbon, nitrogen, oxygen, silicon, phosphorus, sulfur, and the like). Those elements are also what makes terrestrial planets, people, and computers.
Some of those second generation stars go supernova and eventually yield new planets and third generation stars.
There are not likely any significant fraction of fourth generation stars. But after quadrillion of years, per your question, there would be.
The composition of ourselves and our our planet and our instruments suggest an anthropic argument for why our sun is on the order of magnitude the age of the universe, but roughly a third that amount,
rather than a thousandth or millionth.
I link to the Scott Anderson thread, even though it is infected by the dangerous cult of defamatory plagiarists surrounding the citation-careless philosopher Nick Bostrom, who stole Transhumanism away from its founders and whose followers have denied my existence and that of two of my distinguished co-authors.
But never mind the loons, who keep losing their tax-exempt status, moving to another state, and starting over. My question to this thread is: what would a 4th generation planet look like?