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TOPIC: Extrasolar Planets
Blobrana


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RE: Extrasolar Planets
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Exoplanets are of high interest, not only because questions regarding alien life in the universe have accompanied humanity for a long time, but also because studying exoplanetary systems allows to study the past and the future of our own solar system.
The first exoplanet was discovered 15 years ago: it was part of a rather "exotic" system with 3 planets orbiting the millisecond pulsar PSR1257+12. A pulsar is an extremely compact object that is produced by a supernova (SN) explosion when the mass of the collapsed star is not big enough to produce a black hole. As it is difficult to imagine that planets can survive a SN explosion, it is much more likely that the pulsar's planets formed after the SN explosion.
Detection of the pulsars's planets was performed using the so-called "timing method", which consists in measuring the small differences in the arrival times of the photons due to the changing distance of the pulsar from us, because it is rotating around the barycentre of the system.
Three years later, Mayor & Queloz  detected an exoplanet orbiting the star 51 Pegasi, a main sequence star burning hydrogen in its core (like our sun). This discovery was obtained using the more popular method of the radial velocities (RVs), ie, measuring the Doppler shift of the spectral lines of the star induced, again, by the orbital motion of the star around the barycentre of the system.
The discovery of 51 Pegasi b (this is the name of the planet), opened an exciting season of several new discoveries so that today more than 250 exoplanet candidates are known. Most of them were found using the RV method, even though exoplanets are currently detected also through transits (an attractive method for when we observe large numbers of stars as in the case of the COROT and Kepler space missions), microlensing, and direct imaging. As well, most exoplanet candidates orbit main sequence stars.
In the last years, first discoveries of planets around stars in evolutionary phases different from the main sequence were reported. When their core hydrogen runs out, main sequence stars undergo a red giant expansion that modifies the planetary orbits and can easily reach and engulf the inner planets. The same will happen to the planets of our solar system in about 5 Gyr, and the fate of the Earth is matter of debate. Recently, a few planets orbiting red giant stars have been found. However, what happens to the inner planets at the maximum red giant expansion or after is largely unknown.

For this reason, to detect a planet around a post-red giant star is of high interest; in particular, when this planet, V 391 Peg b, is relatively close to its parent star at 1.7 astronomical units (AU; 1 AU being the mean distance between Earth and sun).
The star, V 391 Peg, is an old star, with an age of presumably ~10 Gyr or more, that has already experienced the red giant expansion, at the end of which explosive helium ignition took place in its core (the so-called "helium flash").

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Blobrana


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Astronomers may be on the brink of discovering a second Earth-like planet, a find that would add fresh impetus to the search for extraterrestrial life, according to a leading science journal.
Planet hunters have spotted more than 200 planets beyond our solar system, but the vast majority are hot, Jupiter-sized planets that would dwarf the Earth and are almost certainly lifeless.
Writing in the US journal Science, astronomers from six major centres, including Nasa, Harvard and the University of Colorado, outline how advances in technology suggest scientists are on the verge of being able to detect the presence of small, rocky planets, much like our own, around distant stars for the first time. The planets are considered the most likely havens for extraterrestrial life.

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Blobrana


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The Gemini Deep Planet Survey - First Results
A Canada-US-UK team led by David Lafrenière and René Doyon of the University of Montreal has released the first results from the Gemini Deep Planet Survey (GDPS), a near-infrared adaptive optics search for giant planets and brown dwarfs around 85 nearby young stars. The observations, made with the ALTAIR/NIRI adaptive optics system at the Gemini North telescope, are aimed at constraining the population of Jupiter-mass planets with orbits that have a semi-major axis in the range of 10-300 astronomical units (AU). This work constitutes a first step toward the detection of the population of outer giant planets around other stars.

Source

Title: The Gemini Deep Planet Survey -- GDPS
Authors: David Lafreniere, Rene Doyon, Christian Marois, Daniel Nadeau, Ben R. Oppenheimer, Patrick F. Roche, Francois Rigaut, James R. Graham, Ray Jayawardhana, Doug Johnstone, Paul G. Kalas, Bruce Macintosh, Rene Racine
(Version v2)

We present the results of the Gemini Deep Planet Survey, a near-infrared adaptive optics search for giant planets and brown dwarfs around nearby young stars. The observations were obtained with the Altair adaptive optics system at the Gemini North telescope and angular differential imaging was used to suppress the speckle noise of the central star. Detection limits for the 85 stars observed are presented, along with a list of all faint point sources detected around them. Typically, the observations are sensitive to angular separations beyond 0.5" with 5-sigma contrast sensitivities in magnitude difference at 1.6 micron of 9.5 at 0.5", 12.9 at 1", 15.0 at 2", and 16.5 at 5". For the typical target of the survey, a 100 Myr old K0 star located 22 pc from the Sun, the observations are sensitive enough to detect planets more massive than 2 Mjup with a projected separation in the range 40-200 AU. Second epoch observations of 48 stars with candidates (out of 54) have confirmed that all candidates are unrelated background stars. A detailed statistical analysis of the survey results, yielding upper limits on the fractions of stars with giant planet or low mass brown dwarf companions, is presented. Assuming a planet mass distribution dN/dm m^{-1.2} and a semi-major axis distribution dN/da a^{-1}, the 95% credible upper limits on the fraction of stars with at least one planet of mass 0.5-13 Mjup are 0.28 for the range 10-25 AU, 0.13 for 25-50 AU, and 0.093 for 50-250 AU. The 95% credible interval for the fraction of stars with at least one brown dwarf companion having a semi-major axis in the range 25-250 AU is 0.019 (-0.015/+0.083), irrespective of any assumption on the mass and semi-major axis distributions. The stars HD 14802, HD 166181, and HD 213845 have been resolved into binaries for the first time.

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Blobrana


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Title: Inevitability of Plate Tectonics on Super-Earths
Authors: Diana Valencia (1), Richard J. O'Connell (1), Dimitar D. Sasselov (2) ((1) Earth and Planetary Sciences, Harvard University, (2) Harvard-Smithsonian Centre for Astrophysics)

The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favourably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.

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Blobrana


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GJ436b
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Title: Characterisation of the hot Neptune GJ 436b with Spitzer and ground-based observations
Authors: B.-O. Demory (1,7), M. Gillon (1,2), T. Barman (3), X. Bonfils (4), M. Mayor (1), T. Mazeh (5), D. Queloz (1), S. Udry (1), F. Bouchy (8), X. Delfosse (6), T. Forveille (6), F. Mallmann (7), F. Pepe (1), C. Perrier (6) ((1) Observatoire de Geneve, Universite de Geneve, Switzerland; (2) Institut d'Astrophysique et de Geophysique, Universite de Liege, Belgium; (3) Lowell Observatory, Flagstaff, AZ, USA; (4) Observatorio Astronomico de Lisboa, Lisboa, Portugal; (5) School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Israel; (6) Laboratoire d'Astrophysique de Grenoble, Universite J. Fourier, Grenoble, France; (7) Observatoire Francois-Xavier Bagnoud - OFXB, Saint-Luc, Switzerland; (8) Institut d'Astrophysique de Paris, Universite Pierre & Marie Curie, Paris, France)
(Version v3)

We present Spitzer Space Telescope infrared photometry of a secondary eclipse of the hot Neptune GJ436b. The observations were obtained using the 8-micron band of the InfraRed Array Camera (IRAC). The data spanning the predicted time of secondary eclipse show a clear flux decrement with the expected shape and duration. The observed eclipse depth of 0.58 mmag allows us to estimate a blackbody brightness temperature of T_p = 717 ± 35 K at 8 microns. We compare this infrared flux measurement to a model of the planetary thermal emission, and show that this model reproduces properly the observed flux decrement. The timing of the secondary eclipse confirms the non-zero orbital eccentricity of the planet, while also increasing its precision (e = 0.14 ±  0.01). Additional new spectroscopic and photometric observations allow us to estimate the rotational period of the star and to assess the potential presence of another planet.

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Blobrana


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Planets in Binary Stellar Systems
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Title: Microlensing Detections of Planets in Binary Stellar Systems
Authors: Dong-Wook Lee, Chung-Uk Lee, Byeong-Gon Park, Sun-Ju Chung, Young-Soo Kim, Ho-Il Kim, Cheongho Han

We demonstrate that microlensing can be used for detecting planets in binary stellar systems. This is possible because in the geometry of planetary binary systems where the planet orbits one of the binary component and the other binary star is located at a large distance, both planet and secondary companion produce perturbations at a common region around the planet-hosting binary star and thus the signatures of both planet and binary companion can be detected in the light curves of high-magnification lensing events. We find that identifying planets in binary systems is optimised when the secondary is located in a certain range which depends on the type of the planet. The proposed method can detect planets with masses down to one tenth of the Jupiter mass in binaries with separations <~ 100 AU. These ranges of planet mass and binary separation are not covered by other methods and thus microlensing would be able to make the planetary binary sample richer.

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Blobrana


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HD 74156d
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HD 74156d.kmz
Google Sky file

-- Edited by Blobrana at 16:16, 2008-01-12

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Blobrana


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Posts: 131433
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RE: Extrasolar Planets
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Title: Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope
Authors: Jacob L. Bean, Barbara E. McArthur, G. Fritz Benedict, Amber Armstrong

We report the discovery of a third planetary mass companion to the G0 star HD 74156. High precision radial velocity measurements made with the Hobby-Eberly Telescope aided the detection of this object. The best fit triple Keplerian model to all the available velocity data yields an orbital period of 347 days and minimum mass of 0.4 M_Jup for the new planet. We determine revised orbital periods of 51.7 and 2477 days, and minimum masses of 1.9 and 8.0 M_Jup respectively for the previously known planets. Preliminary calculations indicate that the derived orbits are stable, although all three planets have significant orbital eccentricities (e = 0.64, 0.43, and 0.25). With our detection, HD 74156 becomes the eighth normal star known to host three or more planets. Further study of this system's dynamical characteristics will likely give important insight to planet formation and evolutionary processes.

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Blobrana


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Blobrana


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Beta Geminorum
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Title: The Discovery of Stellar Oscillations in the Planet Hosting Giant Star Beta Geminorum
Authors: Artie P. Hatzes, Mathias Zechmeister

We present the results of a long time series of precise stellar radial velocity measurements of the planet hosting K giant star Beta Geminorum. A total of 20 hours of observations spanning three nights were obtained and the radial velocity variations show the presence of solar-like stellar oscillations. Our period analysis yields six significant pulsation modes that have frequencies in the range of 30 - 150 microHz. The dominant mode is at a frequency of 86.9 microHz and has an amplitude of 5.3 m/s. These values are consistent with stellar oscillations for a giant star with a stellar mass of approximately 2 solar masses. This stellar mass implies a companion minimum mass of 2.6 Jupiter masses. Beta Gem is the first planet hosting giant star in which multi-periodic stellar oscillations have been detected. The study of stellar oscillations in planet hosting giant stars may provide an independent, and more accurate determination of the stellar mass.

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