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TOPIC: Extrasolar Planets


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Posts: 131433
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RE: Extrasolar Planets
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Title: The Structure of Jupiter, Saturn, and Exoplanets: Key Questions for High-Pressure Experiments
Authors: Jonathan J. Fortney

Jonathan J. Fortney gives an overview of our current understanding of the structure of gas giant planets, from Jupiter and Saturn to extrasolar giant planets. He focus on addressing what high-pressure laboratory experiments on hydrogen and helium can help to elucidate about the structure of these planets.

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Posts: 131433
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200 Extrasolar Planets
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Planet detectives have now found a total of 200 planets orbiting nearby stars.
A little more than a decade ago, that number was zero. Since that time, planet detections have confirmed astronomers' suspicions stretching back centuries, along with many a space opera writer's plot outline.

The latest detections, announced in the July 20 edition of The Astrophysical Journal, come courtesy of the leading planet detection team led by Geoff Marcy of the University of California, Berkeley, and Paul Butler of the Carnegie Institution of Washington (D.C.) They bring the total to 200 such detections, according to the Extrasolar Planet Encyclopedia maintained by Jean Schneider of the Paris Observatory, a clearinghouse for planet announcements.

The Marcy team's paper unveils five new planets, all orbiting stars 50 to 200 light years away, close by galactic standards. They were detected by the "radial velocity" method the team pioneered, which detects the subtle back-and-forth wobble of a star caused by gravitational tugs of a circling planet. The method is biased towards finding big, close-in planets, which create more powerful and quickly detected tugs. This held true for the new detections: The smallest planet is about one-third the mass of Jupiter and the largest is likely about three times bigger than Jupiter, the King of Planets in our solar system. Jupiter weighs almost 318 times as much as Earth.
But the study goes beyond just announcing the new planets to look at all the known "exoplanets" orbiting within 200 parsecs, about 650 light years, of Earth. Some of these close planets, 167 in all, were spotted by "transit" detection, spotting the dip in light caused by a planet orbiting in front of their star.
A key finding of the paper is that there are likely many more lightweight planets (meaning lighter than Jupiter — like Earth) out there waiting to be detected. Even with the bias of the radial velocity method toward jumbo planets, the numbers pile up in the study's catalogue at the low end of the scale.

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RE: Extrasolar Planets
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The steady discovery of giant planets orbiting stars other than our sun has heightened speculation that there could be Earth-type worlds in nearby planetary systems capable of sustaining life. Now researchers running computer simulations for four nearby systems that contain giant planets about the size of Jupiter have found one that could have formed an Earth-like planet with the right conditions to support life.

A second system is likely to have a belt of rocky bodies the size of Mars or smaller. The other two, the models show, do not have the proper conditions to form an Earth-size planet. Each system lies within 250 light years of Earth (a light year is about 5.88 trillion miles). Astronomers already have found evidence that each system contains at least two giant planets about the mass of Jupiter, which have migrated close to their stars, perhaps as close as Mercury is to the sun.
For each of the four systems, the researchers conducted 10 computerized simulations that placed small planet embryos, or protoplanets, in the system to see if they are able to gather more material and form a true planet the size of Earth. Each simulation assumed the same conditions in the planetary system except that the position and mass of each protoplanet was altered slightly, said Sean Raymond, a postdoctoral researcher at the University of Colorado, who took part in the work while he was an astronomy doctoral student at the University of Washington.
Raymond is lead author of a paper describing the research published in June in the Astrophysical Journal. Co-authors are Rory Barnes, a postdoctoral researcher at the University of Arizona who also took part in the work while a UW astronomy doctoral student, and Nathan Kaib, a UW doctoral student in astronomy. The work was funded by the National Aeronautics and Space Administration, NASA's Astrobiology Institute and the National Science Foundation.

"It's exciting that our models show a habitable planet, a planet with mass, temperature and water content similar to Earth's, could have formed in one of the first extrasolar multi-planet systems detected" - Rory Barnes.

Recent studies show many known extrasolar planetary systems have regions stable enough to support planets ranging from the mass of Earth to that of Saturn. The UW models tested planet formation in systems called 55 Cancri, HD 38529, HD 37124 and HD 74156. The researchers assumed the systems are complete and the orbits of their giant planets are well established. They also assumed conditions that might allow formation of small bodies that could develop into rocky, Earth-like planets.
In the models, the scientists placed moon-sized planet embryos between giant planets and allowed them to evolve for 100 million years. With those assumptions, they found terrestrial planets formed readily in 55 Cancri, sometimes with substantial water and orbits in the system's habitable zone. They found HD 38529 is likely to support an asteroid belt and Mars-sized or smaller bodies but no notable terrestrial planets. No planets formed in HD 37124 and HD 74156.

"What surprised me the most was to see the system that only formed planets the size of Mars or smaller. Anything that grew too big would be unstable, so there was an accumulation of a lot of smaller protoplanets maybe one-tenth the size of Earth" - Sean Raymond.

It was significant, Kaib said, that the models showed conditions could remain stable enough for 100 million years so that a planetary embryo would have a chance to gather more substance and develop into a body the size of the moon or Mars.

"In our early system, that's probably what our inner solar system looked like, with hundreds of bodies that size" - Nathan Kaib

Extrasolar planets have been discovered with increasing frequency in recent years because of techniques that detect giant planets by their gravitational effect on their parent stars. It is uncertain how the giant planets evolve, but they are thought to form far away from their host stars and then migrate inward, pushed by the gas discs from which they formed. If the migration occurs late in the system's development, the giant planets might destroy most of the materials needed to build Earth-like planets, Raymond said. He noted that while the presence of giant planets is fairly well established, it will be some time before it is possible to detect much smaller Earth-sized planets around other stars.

For another recent paper, Raymond ran more than 450 computer simulations to map giant planet orbits that allow Earth-like planets to form. If a giant planet is too close it will prevent rocky material from amassing into an Earth-sized planet. That study showed that only about 5 percent of the known giant-planet systems are likely to have Earth-like planets. But because of long observation times and sensitive equipment needed to detect planets the size of Saturn and Jupiter, it is possible there could be many planetary systems such as ours in this galaxy.

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Posts: 131433
Date:
Exoplanet Catalogue
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Title: Catalogue of Nearby Exoplanets
Authors: R. P. Butler, J. T. Wright, G. W. Marcy, D. A Fischer, S. S. Vogt, C. G. Tinney, H. R. A. Jones, B. D. Carter, J. A. Johnson, C. McCarthy, A. J. Penny

Researchers present a catalogue of nearby exoplanets.. It contains the 172 known low mass companions with orbits established through radial velocity and transit measurements around stars within 200 pc. They include 5 previously unpublished exoplanets orbiting the stars HD 11964, HD 66428, HD 99109, HD 107148, and HD 164922. The researchers update orbits for 90 additional exoplanets including many whose orbits have not been revised since their announcement, and include radial velocity time series from the Lick, Keck, and Anglo-Australian Observatory planet searches. Both these new and previously published velocities are more precise here due to improvements in their data reduction pipeline, which they applied to archival spectra.
The researchers present a brief summary of the global properties of the known exoplanets, including their distributions of orbital semimajor axis, minimum mass, and orbital eccentricity.

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See also http://exoplanets.org/

-- Edited by Blobrana at 13:05, 2006-07-24

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Posts: 131433
Date:
Planetary Mass Candidates with Disks
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Title: Spectroscopy of Young Planetary Mass Candidates with Disks
Authors: Ray Jayawardhana, Valentin D. Ivanov

It is now well established that many young brown dwarfs exhibit characteristics similar to classical T Tauri stars, including infrared excess from disks and emission lines related to accretion. Whether the same holds true for even lower mass objects, namely those near and below the Deuterium-burning limit, is an important question. Here we present optical spectra of six isolated planetary mass candidates in Chamaeleon II, Lupus I and Ophiuchus star-forming regions, recently identified by Allers and collaborators to harbour substantial mid-infrared excesses. Our spectra, from ESO's Very Large Telescope and New Technology Telescope, show that four of the targets have spectral types in the ~M9-L1 range, and three of those also exhibit H_alpha. Their luminosities are consistent with masses of ~5-15 M_{Jupiter} according to models of Chabrier, Baraffe and co-workers, thus placing these four objects among the lowest mass brown dwarfs known to be surrounded by circum-sub-stellar disks. Our findings bolster the idea that free-floating planetary mass objects could have infancies remarkably similar to those of Sun-like stars and suggest the intriguing possibility of planet formation around primaries whose masses are comparable to those of extra-solar giant planets. Another target appears to be a brown dwarf (~M8) with prominent H_alpha emission, possibly arising from accretion. The sixth candidate is likely a background source, underlining the need for spectroscopic confirmation.

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Posts: 131433
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RE: Extrasolar Planets
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Title: Detecting a Rotation in the Epsilon Eridani Debris Disc
Authors: C. J. Poulton, J. S. Greaves and A. C. Cameron

Researchers from the University of St. Andrews, Scotland, have found evidence that the ring of dust around nearby Epison Eridani is rotating.

ABSTRACT
The evidence for a rotation of the Epsilon Eridani debris disc is examined. Data at 850 µm wavelength were previously obtained using the Submillimetre Common User Bolometer Array (SCUBA) over periods in 1997-1998 and 2000-2002. By χ² fitting after shift and rotation operations, images from these two epochs were compared to recover proper motion and orbital motion of the disc. The same procedures were then performed on simulated images to estimate the accuracy of the results.
Minima in the χ² plots indicate a motion of the disc of approximately 0.6'' per year in the direction of the star’s proper motion. This underestimates the true value of 1'' per year, implying that some of the structure in the disc region is not associated with Epsilon Eridani, originating instead from background galaxies. From the χ² fitting for orbital motion, a counterclockwise rotation rate of about 2.75° per year is deduced. Comparisons with simulated data in which the disc is not rotating show that noise and background galaxies result in approximately Gaussian fluctuations with a standard deviation ±1.5.
per year. Thus counterclockwise rotation of disc features is supported at approximately a 2-σ level, after a 4-year time difference. This rate is faster than the Keplerian rate of 0.65° per year for features at about 65 AU from the star, suggesting their motion is tracking a planet inside the dust ring.

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Posts: 131433
Date:
HD62509 planet
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Title: Confirmation of the Planet Hypothesis for the Long-period Radial Velocity Variations of Beta Geminorum
Authors: A.P. Hatzes, W.D. Cochran, M. Endl E.W. Guenther, S.H. Saar, G.A.H. Walker, S. Yang, M. Hartmann, M. Esposito, D.B. Paulson

Researchers present precise stellar radial velocity measurements for the K giant star Beta Gem spanning over 25 years. These data show that the long period low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. An examination of the Ca II K emission, spectral line shapes from high resolution data (R = 210,000), and Hipparcos photometry show no significant variations of these quantities with the RV period. These data confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). An orbital solution assuming a stellar mass of 1.7 Solar masses yields a period, P = 589.6 days, a minimum mass of 2.3 Jupiter Masses, and a semi-major axis, and a = 1.6 AU. The orbit is nearly circular (e = 0.02). Beta Gem is the seventh intermediate mass star shown to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common.

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A 2.3 (± 0.45) Jupiter mass planet has been found orbiting around the orange giant star Pollux (Beta Geminorum).
This is the first known planet orbiting around a first magnitude star.

The planet orbits the star at a distance of 1.64 AU in a circular orbit.
The planet was first suspected by Hatzes & Cochran in 1993.

Name HD 62509b
Discovered in 2006
Mass 2.3 (± 0.45) MJ
Semi major axis 1.64 (± 0.27) AU
Orbital period 589.64 (± 0.81) days
Eccentricity 0.02 (± 0.03)
Omega 534.58 (± 95.65) deg.
Tperi 2447739.02 (± 4.5)


Pollux is 33.72 light-years away in the constellation Gemini, is a variable giant orange K star. Evidence has been found for a a hot, outer, magnetically supported corona around the star.
The star is known to be an X-ray emitter.

Position(2000): RA 07 45 18.95 Dec +28 01 34.3

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Posts: 131433
Date:
Planemos
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Forget our traditional ideas of where a planetary system forms — new research led by a University of Toronto astronomer reveals that planetary nurseries can exist not only around stars but also around objects that are themselves not much heftier than Jupiter. It suggests that miniature versions of the solar system may circle objects that are some 100 times less massive than our sun.

That’s the dramatic conclusion of two studies being presented today at the American Astronomical Society meeting in Calgary by Professor Ray Jayawardhana and his colleagues. The new findings show that objects only a few times more massive than Jupiter are born with disks of dust and gas, the raw material for planet making. Research done by Jayawardhana’s group and others in recent years had shown that disks are common around failed stars known as “brown dwarfs”. Now, they report, the same appears to be true for their even punier cousins, sometimes called planetary mass objects or “planemos.” These objects, discovered within the past five years, have masses similar to those of extra-solar planets, but they are not in orbit around stars — instead, they float freely through space.

Now that we know of these planetary mass objects with their own little infant planetary systems, the definition of the word ‘planet’ has blurred even more. In a way, the new discoveries are not too surprising — after all, Jupiter must have been born with its own disk, out of which its bigger moons formed ” - Professor Ray Jayawardhana , associate professor of astronomy and astrophysics.

Unlike Jupiter, however, these planemos are not circling stars. In the first study, Jayawardhana and Valentin Ivanov of the European Southern Observatory (ESO) in Chile used two of ESO's telescopes — the 8.2-metre Very Large Telescope and the 3.5-metre New Technology Telescope — to obtain optical spectra of six candidates identified recently by researchers at the University of Texas at Austin. Two of the six turned out to have masses between five to 10 times that of Jupiter while two others are a tad heftier, at 10 to 15 times Jupiter’s mass. All four of these objects are just a few million years old and are located in star-forming regions about 450 light-years from Earth. The planemos show infrared emission from dusty disks that may evolve into miniature planetary systems over time.

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Posts: 131433
Date:
OGLE-2003-BLG-235
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Title: Identification of the OGLE-2003-BLG-235/MOA-2003-BLG-53 Planetary Host Star
Authors: David P. Bennett, Jay Anderson, Ian A.Bond, Andrzej Udalski, Andrew Gould

Researchers present the results of Hubble Space Telescope (HST) observations of the source star for the first clear extrasolar planet detected by microlensing. The light curve model for this event predicts that the lens star should be separated from the source star by ~6 mas at the time of the HST images. If the lens star is a late G, K or early M dwarf, then it will be visible in the HST images as an additional source of light that is blended with the source image.
Unless the lens and source have exactly the same colours, its presence will also be revealed by a systematic shift between centroids of the source plus lens in different filter bands. The HST data indicates both of these effects: the HST source that matches the position of the source star is 0.21 magnitudes brighter in the ACS/HRC-F814W filter than the microlensing model predicts, and there is an offset of ~0.7 mas between the centroid of this source in the F814W and F435W filter bands.
The researchers conclude the planetary host star has been detected in these HST images, and this identification of the lens star enables a complete solution of the lens system. The lens parameters are determined with a Bayesian analysis, averaging over uncertainties in the measured parameters, interstellar extinction, and allowing for the possibility of a binary companion to the source star. This yields a stellar mass of M_* = 0.63 (+0.07/-0.09) solar masses and a planet mass of M_p = 2.6 (+0.8/-0.6} Jupiter masses, at an orbital separation of 4.3 (+2.5/-0.8) AU. Thus, the lens system resembles our own Solar System, with a planet of ~3 Jupiter-masses in a Jupiter-like orbit around a star of two-thirds of a Solar mass. These conclusions can be tested with future HST images, which should reveal a broadening of the blended source-plus-lens point spread function due to the relative lens-source proper motion.

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