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COROT planets
Tom Womack
post May 3 2007, 02:20 PM
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http://news.bbc.co.uk/1/hi/sci/tech/6611557.stm

is reporting that Corot has found its first planet. I can't find an arxiv paper about this, or even a press release, but there are many here better at squirreling out data releases than me.

1.3Mj, 1.8Rj so it's a very inflated planet, 1.5-day orbit around a 'star quite similar to the Sun' might account for that. In the Monoceros field (Corot is now pointing at the Scutum/Aquila field).
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ustrax
post May 3 2007, 04:53 PM
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Here's ESA's release.


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Guest_Sunspot_*
post May 3 2007, 04:54 PM
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And according to this New Scientist article COROT could be up to 30 times more sensitive than it's original design specification.

http://space.newscientist.com/article/mg19...ized-prize.html
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Guest_AlexBlackwell_*
post May 3 2007, 06:38 PM
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Emily has a new blog entry. Also, I'm not sure if it's mentioned here or not, but there is a new, related paper in press with Icarus:

Could we identify hot Ocean-Planets with CoRoT, Kepler and Doppler velocimetry?
Icarus, In Press, Accepted Manuscript, Available online 1 May 2007,
F. Selsis, B. Chazelas, P. Bordé, M. Ollivier, F. Brachet, M. Decaudin, F. Bouchy, D. Ehrenreich, J.-M. Grießmeier, H. Lammer, et al.
1.5 Mb PDF preprint

This post has been edited by AlexBlackwell: May 3 2007, 06:43 PM
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Rakhir
post May 3 2007, 09:11 PM
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And the CNES release (in French).
http://www.cnes.fr/web/5891-corot-decouvre...exoplanete-.php
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stevesliva
post May 3 2007, 10:05 PM
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I've been wondering, is there any reason to think that the orbital planes of other solar systems [in specific directions] will be aligned in such a way that we'll see more eclipses than total randomness would dictate?

Are there going to be tantalizing glimpses of transits that don't reoccur within reasonable timeframes?
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Tom Womack
post May 4 2007, 10:58 AM
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QUOTE (stevesliva @ May 3 2007, 11:05 PM) *
I've been wondering, is there any reason to think that the orbital planes of other solar systems [in specific directions] will be aligned in such a way that we'll see more eclipses than total randomness would dictate?

Are there going to be tantalizing glimpses of transits that don't reoccur within reasonable timeframes?


The Corot photometry is wonderfully stable, and looks as if it can pick up eclipses on a single occurrence rather than having to do a phased integral; Jupiter's diameter is 1/10 of the Sun, so a Jupiter transit would be a 1% drop in light, which Corot would pick up very happily, It would last (I think) jupiter_orbital_period * (sun_diameter / 2*pi*jupiter_orbit_diameter) = 4330 days * 1.4e6 km / (6.28 * 778e6km) = 1.25 days.

I don't think there's much that dims a star in a spectrally-uniform way with a flat bottom and that kind of ingress and egress period, so you would really see it in the data. I don't know how long Corot will last, it's working in the optical spectrum so doesn't have cryogens to exhaust, and it doesn't have to do very complicated station-keeping so the fuel should last reasonably, but two Jupiter-years is maybe a little long to expect, and the cadence where it looks at Monocerus for six months and Scutum for six months starts to be troublesome at the longer periods.

I'm looking forward to seeing the low-mass and long-period bits of phase space get populated, and to hearing complaints that there's not enough high-resolution-spectrograph time available to follow up all the transit detections!
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Greg Hullender
post May 4 2007, 07:32 PM
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Steve: The Kepler guys figure about 1/2 percent of stars with planets will be aligned enough for us to see transits -- assuming random alignment.

http://kepler.nasa.gov/sci/basis/character.html

Wikipedia claims 10%, but in this case I think I know whom to believe.

http://en.wikipedia.org/wiki/Methods_of_de...#Transit_method

I've also wondered whether this will REALLY be random, but I note that so far very few observed planets are transiting -- no surprise given only 200-odd extrasolar planets so far.

So I guess we can say that, if it's not random, it's not hugely skewed either.

I note also that Kepler claims they can detect Jovian-sized transits from a single event; it's only for Earth-sized transits that it needs to see three events to be sure.

--Greg
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Jyril
post May 5 2007, 12:08 AM
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10% claim should be true in the case of hot Jupiters. For more distantly orbiting planets, the value is of course considerably lower.

"Planets with small orbits" says Wikipedia so it's apparently correct if not clear.


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Olvegg
post May 5 2007, 10:08 AM
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0.5% is for Earth-like orbits around Sun-like stars.
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stevesliva
post May 7 2007, 11:07 PM
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QUOTE (Greg Hullender @ May 4 2007, 03:32 PM) *
I note also that Kepler claims they can detect Jovian-sized transits from a single event; it's only for Earth-sized transits that it needs to see three events to be sure.

Interesting. Hopefully Kepler prospers for a good many many years then!

Also that 0.5% figure is both plenty high, yet depressing in the regard that 99.5% will still be hidden from this technique. But it's no doubt conservative. I again wonder how many "near misses" will be detectable. Should be great to see.
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Greg Hullender
post May 9 2007, 03:04 AM
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Steve: What is more interesting about the 0.5% number is that it is independent of the distance of the star; at first it would seem that the further away it is, the less likely a planet is to be lined up so as to transit, but it turns out this is not the case. (Play with the geometry a bit and see.)

Of course the further away a star is, the harder it will be to tell that there was a transit; geometry can't fix that!

--Greg
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edstrick
post May 9 2007, 08:27 AM
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The fundamental purpose of missions like Corot and Keplar (and "Ogle" type searches for lensing events as well as whatever transits they catch) is to establish the statistical patterns of planetary system occurrence.

Star: 1) What mass stars, 2) what metallicity stars 3) what environment stars (disk, halo, globulars.. ) 4) what age stars. (yes. the last 3 are all significantly correlated)

Planet: Mass, Diameter, thus (density and gross composition)

Orbit: Toasty, close, distant, eccentric vs circular.

Before we build EITHER of the Terrestrial Planet Finder mission, we need a good model of how many there will be of what sizes -- around what mass and metallicity stars -- in what orbits -- in the solar neighborhood.

If we design and fly an inadequate TPF and find 3 barely-quasi-terrestrial planets for a budget of 3 billion dollars. Uh.......

If we know a 1.5 billion dollar TPF will find 2 or 3 dozen substantially terrestrialish planets (.8 to 1.5 earth mass, similar stellar insolation), it may fly a lot sooner than that 3 billion doller mission.

And... even though we'll not see a good spectrum or hardly anything from most terrestrial size or so planets Keplar and Corot may find, we'll get fabulous understanding of the population of planets out there and the type of planetary systems they are part of that we only half or quarter get from the doppler surveys.
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Mongo
post May 9 2007, 01:28 PM
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QUOTE (Greg Hullender @ May 9 2007, 03:04 AM) *
Steve: What is more interesting about the 0.5% number is that it is independent of the distance of the star; at first it would seem that the further away it is, the less likely a planet is to be lined up so as to transit, but it turns out this is not the case. (Play with the geometry a bit and see.)


Are you sure about this? The width of the 'band' of sky that can see a transit is the same width as the diameter of the primary as seen from the planet, hence a planet twice as close as another will be visible as transiting from twice the area of sky. The 0.5% number comes from the fact that a planet in a habitable orbit should have its primary subtend about 0.5 degree -- which actually suggests that its transit should be visible from about 0.44% of the sky. A planet ten times closer would have its primary subtend about 5%, so its transit would be visible over about 4.4% of the sky, and so on.

Bill
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Greg Hullender
post May 9 2007, 11:44 PM
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Mongo: You're correct, if "distance of the star" means "from the exoplanet," but I meant "from Earth." A star 50 light years away is (all other things being equal) just as likely as one 5 light years away to have a transiting planet. Maybe that's obvious, but it surprised me at first.

--Greg
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