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Exoplanet Discoveries, discussion of the latest finds
Guest_PhilCo126_*
post Apr 21 2009, 11:10 AM
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Well-known exoplanet researcher Dr Michel Mayor ( discoverer of Peg 51b with Dr Didier Queloz in 1995 ) today announced the discovery of the lightest exoplanet found so far. The planet, e, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist:
http://www.eso.org/public/outreach/press-r...9/pr-15-09.html

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belleraphon1
post Oct 19 2009, 01:32 PM
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32 New Exoplanets Found - 10/19/09 ESO release

"Today, at an international ESO/CAUP exoplanet conference in Porto, the team who built the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for ESO's 3.6-metre telescope, reports on the incredible discovery of some 32 new exoplanets, cementing HARPS's position as the worlds foremost exoplanet hunter. This result also increases the number of known low-mass planets by an impressive 30%. Over the past five years HARPS has spotted more than 75 of the roughly 400 or so exoplanets now known"

http://www.eso.org/public/outreach/press-r...9/pr-39-09.html

From searching Extrasolar Planets Encyclopedia catalog I find 6 of the new planets seem to be Neptune mass or less.
http://exoplanet.eu/catalog-all.php?&m...de=-7&more=

BD-082823b at .045 Jmass
GJ 433b at .019 Jmass
GJ 667Cb at .018 Jmass
HD 1255995b at .045 Jmass
HD 215497b at .017Jmass
HD 90156b .055Jmass

Craig
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Julius
post Oct 20 2009, 11:10 AM
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How can they be so sure that the super earths detected represent one planetary body ie.could it not be that 8 earth masses could represent 2 terrestrial planets and other planetary dust the likes of asteroids in orbit round the parent star?!
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qraal
post Oct 20 2009, 11:27 AM
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QUOTE (Julius @ Oct 20 2009, 10:10 PM) *
How can they be so sure that the super earths detected represent one planetary body ie.could it not be that 8 earth masses could represent 2 terrestrial planets and other planetary dust the likes of asteroids in orbit round the parent star?!


Because the radial velocity detection method detects a periodic signal that only a planet can cause - though some data is too patchy to be sure we're seeing one planet and not two. A diffuse asteroid belt would produce a symmetric 'tug' on the star it orbits, thus producing no radial velocity signal.
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Greg Hullender
post Oct 20 2009, 07:47 PM
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There's a branch of mathematics called "Fourier Analysis" which, among other things, let's you take a complex signal and break it into a collection of sine waves. It's pretty cool, if you haven't seen it before.

So if there's just one planet, then the velocity plot ought to be a pretty clean simple sine wave over time. If there are multiple planets (let's say three) around the same star, then it'll be a mess, but a fourier analysis ought to result in just three sine curves and very little else.

--Greg

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tfisher
post Oct 22 2009, 12:30 AM
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QUOTE (Greg Hullender @ Oct 20 2009, 02:47 PM) *
So if there's just one planet, then the velocity plot ought to be a pretty clean simple sine wave over time. If there are multiple planets (let's say three) around the same star, then it'll be a mess, but a fourier analysis ought to result in just three sine curves and very little else.


I'm afraid this skips over a few important complexities. One is that with eccentric orbits (which are common!), the radial velocity signal of a planet is not a single sine wave, but may have significantly different shape. Another problem is that in reality we never have continuous or even a complete discrete series of radial velocity observations of a given target. Instead of seeing a continuous curve, we just have a non-uniformly spaced discrete sampling from the curve. So Fourier analysis can't really be directly applied to work out the component curves. A third problem is that there is a lot of noise in the observed radial velocities, coming from stellar activity of the host star and limitations of the observation instruments. In many cases (smaller, more distant planets or younger, more active stars) this noise is of a similar or even much greater strength to the signals we are looking for.

You can get a really good understanding of all of this playing with the amazing "systemic console" free tool for fitting candidate planetary systems to radial velocity datasets. You can get this at oklo.org. I highly recommend it!
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Greg Hullender
post Oct 22 2009, 02:26 AM
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QUOTE (tfisher @ Oct 21 2009, 05:30 PM) *
I'm afraid this skips over a few important complexities.

Fair enough. I still maintain that a Fourier Transform would work fine for a system whose planets had circular orbits and ought to be a great way to eliminate the high-frequency noise in any case, but, yeah, I agree it won't be very good for elliptical orbits.
QUOTE (tfisher @ Oct 21 2009, 05:30 PM) *
You can get a really good understanding of all of this playing with the amazing "systemic console" free tool for fitting candidate planetary systems to radial velocity datasets. You can get this at oklo.org. I highly recommend it!

This is pretty cool. Without actually downloading the program, is there a link to a document that describes the actual algorithms they're using? From what I could glean from their blog, it could be anything from Expectation Maximization to Markov Chain Monte Carlo.

Thanks!

--Greg
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Hungry4info
post Oct 22 2009, 12:33 PM
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QUOTE (Greg Hullender @ Oct 21 2009, 08:26 PM) *
This is pretty cool. Without actually downloading the program, is there a link to a document that describes the actual algorithms they're using? From what I could glean from their blog, it could be anything from Expectation Maximization to Markov Chain Monte Carlo.
There's a paper describing Systemic in such level of detail here.
http://arxiv.org/abs/0907.1675


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Greg Hullender
post Oct 22 2009, 05:31 PM
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QUOTE (Hungry4info @ Oct 22 2009, 04:33 AM) *
There's a paper describing Systemic in such level of detail here.
http://arxiv.org/abs/0907.1675

Excellent! Thank you very much!

This paper's a pretty good read, if you've got the math for it, and offers a very comprehensive answer to the original question. A point they mentioned that I hadn't thought about before is that they don't yet make relativistic corrections, which actually ought to matter considering how many of these planets are in very close orbits. It'll be fun to see what happens once they start to get their hands on the Kepler data.

--Greg
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imipak
post Oct 23 2009, 06:47 PM
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'Spherical cow' now has it's very own Wikipedia entry smile.gif


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Guest_PhilCo126_*
post Dec 5 2009, 05:47 PM
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Team of Astronomers using Japanese Subaru Telescope at Mauna Kea - Hawaii makes major discovery: GJ 758 B


http://www.princeton.edu/main/news/archive...tion=topstories
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Hungry4info
post Dec 6 2009, 04:00 AM
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I'm quite unsure as to why this is being made into such a big deal. The mass of the two objects are quite unconstrained (and in the case of c, it's not even known for sure if it's bound to the system). Even the minimum mass of 10 M_J for B is so high that it's hard to say for sure that this object would be a planet. Also, another object like this was imaged at 1RXS J160929.1-210524 with a mass of 8 M_J, but it's unknown if the object is bound to the system.


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centsworth_II
post Dec 6 2009, 07:15 AM
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QUOTE (Hungry4info @ Dec 5 2009, 11:00 PM) *
I'm quite unsure as to why this is being made into such a big deal....
I'm not surprised that a site titled "News at Princeton" would make a big deal of any new discovery involving a Princeton scientist. How big a deal anyone else makes of it is up to them.

It is the first discovery of a new instrument and validates its usefulness in imaging sub-stellar objects orbiting stars. That seems pretty exciting to me. Isn't this just the second time such a feat has been accomplished?
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ngunn
post Dec 6 2009, 11:57 AM
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On a different topic, I've not noticed discussion here of the planets/lithium anticorrelation announced a few weeks back.
http://www.eso.org/public/outreach/press-r...9/pr-42-09.html

Thinking about what could create a planetary system and also flush a star clean of lithium led me to the idea of a self-ejecting supernova companion. A little digging tracked that idea back 65 years to Fred Hoyle and it seems to have been seriously considered by at least some astronomers in the intervening time. It appears towards the end of this free sample page:
http://resources.metapress.com/pdf-preview...mp;size=largest

Any thoughts?
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Hungry4info
post Dec 6 2009, 02:26 PM
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QUOTE ("centsworth_II")
Isn't this just the second time such a feat has been accomplished?


Maybe not the second, if you count 51 Sagittae B (first brown dwarf discovered around a sun-like star, in 2002, directly imaged) and 54 Piscium B (from 2006, also directly imaged). Spectral types G1V and K0V, respectively, with true masses of ~50 M_J for both objects. But I can see why such a high mass would cause these sub-stellar companions to be sort-of ignored. I guess it all depends on perspective. Epsilon Indi also has a pair of imaged brown dwarfs.

ngunn,

According to recent papers on the current theories, which the authors admit are incomplete, tidal interactions of a planet with its host star allow mixing of the stellar interior. This lets lithium descend deeper into the star than possible without the presence of a planetary companion. The lithium gets roasted alive and no longer shows up in stellar spectra.

The lithium anti-correlation is only applicable to a very narrow temperature range of about 100 K on either side of the temperature of Sol. M, K, F and A stars do not seem to have this trend (the population of planets around A stars is mostly inferred from the detection of planets around stars that have evolved and cooled to become cool giant stars, while too few planets are known to exist around OB stars).

Interestingly, sun-like stars with close stellar companions do not seem to have this anti-correlation. If stellar mixing is the cause, then one would expect stellar companions would do better at that than planetary companions. The orbits of close stellar companions are statistically indistinguishable from the orbits of planetary companions.

Another idea is that a star will magnetically interact with its protoplanetary disk and somehow allow the lithium to be transported deeper into the star and destroyed that way.


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