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2M1207b
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Title: The Young Planet-mass Object 2M1207b: a cool, cloudy, and methane-poor atmosphere
Authors: Travis S. Barman, Bruce Macintosh, Quinn M. Konopacky, Christian Marois

The properties of 2M1207b, a young (~ 8 Myr) planet-mass companion, have lacked a satisfactory explanation for some time. The combination of low luminosity, red near-IR colours, and L-type near-IR spectrum (previously consistent with Teff ~ 1600K) imply an abnormally small radius. Early explanations for the apparent underluminosity of 2M1207b invoked an edge-on disk or the remnant of a recent protoplanetary collision. The discovery of a second planet-mass object (HR8799b) with similar luminosity and colours as 2M1207b indicate that a third explanation, one of a purely atmospheric nature, is more likely. By including clouds, non-equilibrium chemistry and low-gravity, an atmosphere with effective temperature consistent with evolution cooling-track predictions is revealed. Consequently 2M1207b, and others like it, require no new physics to explain nor do they belong to a new class of objects. Instead they most likely represent the natural extension of cloudy substellar atmospheres down to low Teff and log(g). If this atmosphere only explanation for 2M1207b is correct, then very young planet-mass objects with near-IR spectra similar to field T dwarfs may be rare.

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First photograph of an exo planet
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Something bizarre orbiting a young, failed star 170 light-years from Earth may be the progeny of two protoplanets that collided and merged.
Given its hotter-than-expected temperature, dim luminosity, young age and location, the orbiting object, known as 2M1207B, should be a physical impossibility.
The collision hypothesis makes several predictions that astronomers can test. Chief among them is a low surface gravity, which depends on a planets mass and radius. To check this prediction, astronomers will need to get a better spectrum of 2M1207B. That's challenging because the object is very faint and very close to the brown dwarf 2M1207A.
While a planet collision may not be the correct explanation for the weirdness of 2M1207B, examples of colliding planets are likely to be found by the next generation of ground-based telescopes.

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2M1207B
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Two planets may have collided, merged
Astronomers have long puzzled over the mysterious object
An extrasolar planet about one-fourth the heft of Jupiter might have formed from the collision and merger of two planets, astronomers announced today.
Known as 2M1207B, the object orbits a brown-dwarf star called 2M1207A located 170 light-years from Earth and seen in the direction of the constellation Centaurus.

2M1207B

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RE: First photograph of an exo planet
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Title: An accurate distance to 2M1207Ab
Authors: C. Ducourant, R. Teixeira, G. Chauvin, G.Daigne, J.F. Le Campion, Inseok Song, B.Zuckerman

In April 2004 the first image was obtained of a planetary mass companion (now known as 2M1207 b) in orbit around a self-luminous object different from our own Sun (the young brown dwarf 2MASSW J1207334-393254, hereafter 2M1207 A). 2M1207 b probably formed via fragmentation and gravitational collapse, offering proof that such a mechanism can form bodies in the planetary mass regime. However, the predicted mass, luminosity, and radius of 2M1207 b depend on its age, distance, and other observables such as effective temperature. To refine our knowledge of the physical properties of 2M1207 b and its nature, we obtained an accurate determination of the distance to the 2M1207 A and b system by measurements of its trigonometric parallax at the milliarcsec level. With the ESO NTT/SUSI2 telescope, in 2006 we began a campaign of photometric and astrometric observations to measure the trigonometric parallax of 2M1207 A. An accurate distance (52.4 ± 1.1 pc) to 2M1207A was measured. From distance and proper motions we derived spatial velocities fully compatible with TWA membership. With this new distance estimate, we discuss three scenarios regarding the nature of 2M1207 b: (1) a cool (1150 ±150 K) companion of mass 4 ±1 M_{
m{Jup}}, (2) a warmer (1600 ±100 K) and heavier (8 ±2 M_{
m{Jup}}) companion occulted by an edge-on circum-secondary disk or (3) a hot protoplanet collision afterglow.

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A "failed star" with only 24 times the mass of Jupiter is the smallest known object to spout jets of matter from its poles, a phenomenon typically associated with much larger black holes and young stars.
The new finding, detailed in the current issue of Astrophysical Journal, confirms that a wide range of celestial objects is capable of generating such outflows.

"There are black holes that are 3 million solar masses spewing jets, and there's this thing, which is 2 percent of a solar mass, doing the same thing" - Ray Jayawardhana,  study team member, University of Toronto.

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2MASS1207-3932B
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Earth's Moon was created by an early collision with another large planetary body. It was a "chip off the old block." Mars captured its asteroidal moons as they passed by. But Jupiter made its own moons out of dust and gas remaining from its formation. Now, observations by astronomer Subhanjoy Mohanty of the Harvard-Smithsonian Centre for Astrophysics (CfA) and his colleagues provide the first direct evidence for a dusty disk around a distant planet that in mass would be Jupiter's "big brother."

"It is quite possible that moons or moonlets could form out of this disk, just as they have around the giant planets in our own solar system" - Subhanjoy Mohanty.

Mohanty presented the discovery today in a press conference at the 208th meeting of the American Astronomical Society. Other members of the team are Ray Jayawardhana (University of Toronto), Nuria Huélamo (ESO) and Eric Mamajek (CfA).
The team studied a planetary mass object known as 2MASS1207-3932B, which is located about 170 light-years from Earth in the direction of the constellation Centaurus. 2M1207B, as it is abbreviated, orbits a tiny brown dwarf star at a separation of about 40 astronomical units, or 3.7 billion miles - comparable to the size of Pluto's orbit. That separation is much larger than typical for binary brown dwarf systems. The wide separation may indicate that the duo formed in relative isolation, far from passing stars that could have pulled them apart.

"This system probably won't survive for long. It won't last 5 billion years like our solar system has. All it would take is for a more massive interloper star to come along and yank the planet away from the brown dwarf" - Eric Mamajek.

Observations by Mohanty's team showed that the brown dwarf has a mass of about 25 Jupiters and a temperature of 2600 K. Its companion 2M1207B weighs about 8 times Jupiter and has a temperature of 1600 K. Both objects are warm due to their young age of 5-10 million years, having retained the heat of formation.
Given those temperatures, the team then calculated the expected brightness of both objects. The brown dwarf matched predictions but its companion was about 8 times fainter than expected. After examining several potential causes, the team concluded that the only plausible explanation was the presence of an edge-on dusty disk that blocked most of the planet's light. The planet is seen only in light scattered from the disk.
Spectral analysis shows that 2M1207B is a gas giant like Jupiter with no solid surface. As a result, it would be a poor abode for life. Any moons that might form around it, however, could prove more hospitable.
The large mass of 2M1207B relative to the brown dwarf star poses a puzzle for planetary formation theories. Typical planets like those in our solar system are less than one-hundredth the size of the central star. In contrast, 2M1207B holds one-third as much mass as the brown dwarf.

"Mass ratios of that size are more typical for binary stars than for planetary systems. 2M1207B probably formed like a star, together with the brown dwarf, rather than from core accretion like giant planets around other stars"- Subhanjoy Mohanty .

Mohanty and his colleagues plan to study the polarisation of light from 2M1207B in order to investigate the inclination of its disk as well as the size of dust grains within the disk. Further studies await the next generation of large telescopes, such as the Giant Magellan Telescope and the Atacama Large Millimetre Array, which may be able to directly detect the disk around the planetary mass companion.

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RE: First photograph of an exo planet
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Half of the stars in our galaxy have a stellar companion. And yet, of the 130 or so currently known exoplanets (none of which are Earth-like), only about 20 of them are around so-called binaries.
The percentage may grow higher.
The current ratio is affected by an observational bias: planet hunters tend to avoid binaries because the star-star interactions can hide the planet signatures.
Scientists discussed the issue earlier this month at a gathering of exoplanet hunters at the Space Telescope Science Institute in Baltimore.
"A few years ago, it was thought that [binaries] were a very bad site to search for planets. So we carefully eliminated all binary stars from our sample." - Michel Mayor of the Observatoire de Geneve.
But planets may be just as likely around binaries as around single stars. Recent numerical simulations have shown that Earth-like planets, known as terrestrials, form readily in double star systems.
"The most significant thing we found is that terrestrial planets around certain close and wide binaries can look similar to planets around a single star." - Jack Lissauer of the NASA Ames Research Centre.
Wide binaries are those in which the two stars are separated by several astronomical units (AU), which is the distance between the Sun and the Earth. Planets could orbit around one of the pair, or each separately. So far, all the stellar binaries with exoplanets are wide binaries.
But close binaries, where the stars are less than about an AU apart, can potentially have planets in orbit around both stars. These planets, however, will be much harder to detect.
Lissauer and his collaborators have explored what binary star systems are favourable for planet formation. These limits could be useful in future planet searches.
The researchers used computer models that start with 14 large planet "embryos" and 140 smaller planetesimals in orbit around one star or both stars of a binary. Evolution of this material is influenced by gravity and collisions. The models are followed for the equivalent of about one billion years.
"All of our simulations have been able to form terrestrial planets." - Elisa Quintana, Ames researcher, who presented a poster on these results at the symposium.
But not all of the models produce planets around 1 AU, which is often thought to be the most likely habitable zone for life. Quintana varied how the two stars revolve around each other to see what configurations allowed for stable planet orbits inside 1 AU.
For wide binaries, Earth-like planets formed as long as the two stars came no closer than 7 AU. Quintana said that about 50 percent of known binaries meet this constraint.
The research group also ran simulations that mimicked Alpha Centauri – the nearest binary system to Earth, where the closest the two stars come is about 11 AU. The secondary star apparently acts like Jupiter does in our solar system – limiting how far out planets can form. The results showed several terrestrial planets were possible around either of the stars.
Planets have not yet been seen in the Alpha Centauri system, but small mass planets cannot yet be ruled out.
For close binaries, if the two stars are about 0.1 AU apart, the planets that form are indistinguishable from those seen in simulations with only one star. But as this separation increases, or the orbit becomes highly non-circular, it is harder for Earth-like planets to exist.
"Perturbations from the stellar motions can eject matter into space or into one of the stars." - Elisa Quintana.
The simulation results can inform observers which binaries might be better targets for their telescopes.
That said, it will not be easy to see a planet around a binary, especially those where the stars are close to each other. Most planets have been found by the radial velocity technique that searches for Doppler shifts in the light spectra of stars.
"Finding the wobble from a planet in a stellar spectrum is hard enough without having another star orbiting the one you are looking at." - Elisa Quintana.
An alternative way of detecting planets is to look for the eclipse, or transit, of a planet in front of a star. Lissauer said that transiting searches could potentially discover planets around close binaries, but "there are complications."
For one thing, two stars are putting out light, so the eclipse of one star is less noticeable. Also, the transit searches look for certain patterns of dimming and brightening of a star. If there are two stars in a tight orbit, this pattern will be different, so special algorithms will be needed.
But there are situations where a binary could provide an advantage for detecting planets. If the two stars eclipse each other, a planet could change when this eclipse happens.
"If the timing of the eclipses is not periodic, maybe a planet is to blame." - Jack Lissauer
Besides the possibility of transit timing, eclipsing binaries make good targets because planets – if they exist – will likely orbit in the same plane as the two stars – meaning they will also eclipse the stars at some point.
Which of these detection methods will be most likely to find the first double sun planet? Lissauer is unwilling to say.
"Predictions are tricky because they deal with the future."


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European and American scientists say they have photographed a planet outside the Solar System for the first time.
The European Southern Observatory group said the red image is the first direct shot of a planet around another star. The planet, known as 2M1207b, is about five times the size of Jupiter and is orbiting at a distance nearly twice as far as Neptune is from our Sun.The parent star and planet are more than 200 light-years away near the southern constellation of Hydra. There has been a lot of competition among astronomers to secure the first direct picture of an exoplanet. When the ESO group first released the picture last September there was doubt over whether the star and planet were gravitationally bound. But follow-up images taken at the Very Large Telescope facility in Chile show the two objects are moving together.


http://www.eso.org/outreach/press-rel/pr-2005/images/phot-14a-05-preview.jpg



"Our new images are quite convincing. This really is a planet - the first planet that has ever been imaged outside of our Solar System...Given the rather unusual properties of the 2M1207 system, the giant planet most probably did not form like the planets in our Solar System. Instead it must have formed the same way our Sun formed, by gravitational collapse of a cloud of gas and dust." - Gael Chauvin, Eso astronomer.
It is extremely difficult for current technology to detect exoplanets - let alone get a clear shot of one. All of the 130 or so exoplanets so far discovered have been found using indirect methods - looking for changes in the properties of stars (ie brightness or movement) that can be explained only by the presence of a planet. The star has the uninspiring catalogue number 2M1207A. It is a brown dwarf, or "failed star" - an object whose mass of hydrogen and helium has failed to trigger the nuclear reactions that would make it shine brightly like normal stars.
At the time of 2M1207b's discovery, it was impossible to prove that the red speck caught in the original images was not a background object, such as an unusual galaxy or a peculiar cool star. The new observations show with high confidence that the two objects are moving together and hence are gravitationally bound.
"The two objects - the giant planet and the young brown dwarf - are moving together; we have observed them for a year, and the new images essentially confirm our 2004 finding." - Benjamin Zuckerman, UCLA professor of physics and astronomy.


However, what everybody wants is a direct image of a rocky planet like Earth circling another star. But this will not come until we get the next generation of super-telescopes capable of resolving such small, faint objects.


http://www.eso.org/outreach/press-rel/pr-2005/pr-12-05.html



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