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TOPIC: Extrasolar Planets
Blobrana


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Posts: 131433
Date:
TrES-2
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"The Transatlantic Exoplanet Survey (TrES) is a network of telescopes, Sleuth, PSST and STARE, that is used to search the skies for gas giants orbiting other stars that occassionaly cross the disk of the stars. The TrES team had our first successful detection of such a transiting planet with the discovery of TrES-1. We are pleased to announce the discovery of our second planet, TrES-2, which is the most massive of the known nearby transiting planets."

Details of TrES-2, the Star
Position: 19h 07m 14.03s +49d 18m 59.3s (J2000)
V Magnitude: 11.4 magnitudes
Spectral Type: G0V
Mass: 1.08 solar masses
Radius: 1.00 solas masses

Details of TrES-2, the Planet
Orbital Period: 2.47063 days
Semi-Major Axis: 0.0367 AU = 5.5 million kilometers
Orbital Inclination: 83.9 degrees
Mass: 1.28 Jupiter masses
Radius: 1.24 Jupiter radii

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Title: TrES–2: The First Transiting Planet in the Kepler Field
Authors: Francis T. O’Donovan, David Charbonneau, Georgi Mandushev, Edward W. Dunham, David W. Latham, Guillermo Torres, Alessandro Sozzetti, Timothy M. Brown, John T. Trauger, Juan A. Belmonte, Markus Rabus, Jos´e M. Almenara, Roi Alonso, Hans J. Deeg, Gilbert A. Esquerdo, Emilio E. Falco,
Lynne A. Hillenbrand, Anna Roussanova, Robert P. Stefanik, Joshua N. Winn

We announce the discovery of the second transiting hot Jupiter discovered
by the Trans-atlantic Exoplanet Survey. The planet, which we dub TrES–2, or-
bits the nearby star GSC03549–02811 every 2.47063 days. From high-resolution spectra, we determine that the star has Teff = 5960 ±100K and log g = 4.4 ±0.2, implying a spectral type of G0V and a mass of 1.08+0.11 -0.05 Solar Masses. High-precision radial velocity measurements confirm a sinusoidal variation with the period and phase predicted by the photometry, and permit us to rule out the presence of line bisector variations that would indicate that the spectroscopic orbit is spurious. We estimate a planetary mass of 1.28+0.09 -0.04MJup. We model B, r, R, and I photometric timeseries of the 1.4%-deep transits and find a planetary radius of 1.24+0.09 -0.06 RJup. This planet lies within the field of view of the NASA Kepler mission, ensuring that hundreds of upcoming transits will be monitored with exquisite precision and permitting a host of unprecedented investigations.

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Blobrana


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Posts: 131433
Date:
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Astronomers sing a network of amateur-sized telescopes called the Trans-Atlantic Exoplanet Survey (TrES), have found an extrasolar planet orbiting a Sun-like star just 750 light years from Earth, in the constellation Draco, that exhibits the most ideal geometry known for studying the planet's composition and atmosphere.
The astronomers watched for small dips in a star's brightness produced when a planet passes in front of it and block some of its light.
The team determined that it is slightly larger than Jupiter, with about 1.3 times the giant planet's mass and 1.2 times its radius. It also orbits around its host star in just 2.5 days in an orbit 10 times smaller than Mercury's around the Sun.

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Blobrana


L

Posts: 131433
Date:
RE: Extrasolar Planets
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A new planet with nearly three times the mass of Jupiter has been detected orbiting the bright star, Pollux, one of the Gemini twins.
While the 200 extra-solar planets discovered so far have been around fairly inconspicuous stars, Pollux is the 16th brightest star in the sky and can be easily seen from all places on Earth.
The discovery of planets orbiting stars other than the Sun continues at the rate of nearly one a week. The planet discovered around Pollux has the mass of 2.9 Jupiters and orbits the star in 590 days.
The discovery was made independently by two teams of astronomers using the so-called Doppler method, a method of detecting the tiny wobble in the motion of the parent star caused by the planet.

The Doppler method is the most successful planet detection method but because larger planets cause a bigger wobble, the method tends to find large planets in orbits relatively close to their stars. These systems may not be typical.
Doppler observations need to be carried out on many stars over a period of years with a large telescope. The technology needed to measure such small stellar motions was only developed 15 years ago.
In another development, a team of planet-hunters at Geneva Observatory have announced the discovery of two more planets orbiting the southern hemisphere star Mu Arae, which is known to have two planets.

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Blobrana


L

Posts: 131433
Date:
HD160691
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A fourth exoplanet, HD160691e, has been added to the HD160691 (mu Ara) star system.

HD160691d 0.09 AU 0.044 Mj
HD160691e 0.92 AU 0.522 Mj
HD160691b 1.50 AU 1.670 Mj
HD160691c 4.17 AU 3.100 Mj


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Blobrana


L

Posts: 131433
Date:
RE: Extrasolar Planets
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Title: Evolution of Giant Planets in Eccentric Disks
Authors: Gennaro D'Angelo, Stephen H. Lubow, Matthew R. Bate

Researchers investigate the interaction between a giant planet and a viscous circumstellar disk by means of high-resolution, two-dimensional hydrodynamical simulations. They consider planet masses that range from 1 to 3 Jupiter masses (Mjup) and initial orbital eccentricities that range from 0 to 0.4.
The researchers find that a planet can cause eccentricity growth in a disk region adjacent to the planet's orbit, even if the planet's orbit is circular. Disk-planet interactions lead to growth in a planet's orbital eccentricity. The orbital eccentricities of a 2 Mjup and a 3 Mjup planet increase from 0 to 0.11 within about 3000 orbits. Over a similar time period, the orbital eccentricity of a 1 Mjup planet grows from 0 to 0.02. For a case of a 1 Mjup planet with an initial eccentricity of 0.01, the orbital eccentricity grows to 0.09 over 4000 orbits. Radial migration is directed inwards, but slows considerably as a planet's orbit becomes eccentric. If a planet's orbital eccentricity becomes sufficiently large, e > ~0.2, migration can reverse and so be directed outwards. The accretion rate towards a planet depends on both the disk and the planet orbital eccentricity and is pulsed over the orbital period. Planet mass growth rates increase with planet orbital eccentricity. For e~0.2 the mass growth rate of a planet increases by approximately 30% above the value for e=0. For e > ~0.1, most of the accretion within the planet's Roche lobe occurs when the planet is near the apocentre. Similar accretion modulation occurs for flow at the inner disk boundary which represents accretion toward the star.

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Blobrana


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Posts: 131433
Date:
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Title: Extrasolar Planets: A Galactic Perspective
Author: I. N. Reid

The host stars of extrasolar planets tend to be metal-rich. We have examined the data for these stars for evidence of trends in other galactic parameters, without success. However, several ESP hosts are likely to be members of the thick disk population, indicating that planet formation has occurred throughout the full lifetime of the Galactic disk. We briefly consider the radial metallicity gradient and age-metallicity relation of the Galactic disk, and complete a back-of-the envelope estimate of the likely number of solar-type stars with planetary companions with 6 < R < 10 kpc.

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Blobrana


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Posts: 131433
Date:
M Dwarf GJ436
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Title: The M Dwarf GJ 436 and its Neptune-Mass Planet
Authors: H. L. Maness, G. W. Marcy, E. B. Ford, P. H. Hauschildt, A. T. Shreve, G. B. Basri, R. P. Butler, S. S. Vogt

We determine stellar parameters for the M dwarf GJ 436 that hosts a Neptune-mass planet. We employ primarily spectral modelling at low and high resolution, examining the agreement between model and observed optical spectra of five comparison stars of type, M0-M3. Modelling high resolution optical spectra suffers from uncertainties in TiO transitions, affecting the predicted strengths of both atomic and molecular lines in M dwarfs. The determination of Teff, gravity, and metallicity from optical spectra remains at ~10%. As molecules provide opacity both in lines and as an effective continuum, determining molecular transition parameters remains a challenge facing models such as the PHOENIX series, best verified with high resolution and photometric spectra. Our analysis of GJ 436 yields an effective temperature of Teff = 3350 ± 300 K and a mass of 0.44 solar masses. New Doppler measurements for GJ 436 with a precision of 3 m/s taken during 6 years improve the Keplerian model of the planet, giving a minimum mass, M sin i = 0.0713 Mjup = 22.7 Mearth, period, P = 2.6439 d, and e = 0.16 ± 0.02. The noncircular orbit contrasts with the tidally circularised orbits of all close-in exoplanets, implying either ongoing pumping of eccentricity by a more distant companion, or a higher Q value for this low-mass planet. The velocities indeed reveal a long term trend, indicating a possible distant companion.

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Blobrana


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Posts: 131433
Date:
OGLE-2003-BLG-235L
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The Hubble Space Telescope has for the first time identified the parent star of a distant planet (system name OGLE-2003-BLG-235L/MOA-2003-BLG-53L) in the constellation Sagittarius, discovered in 2003 through ground-based gravitational microlensing.


Position (2000): R.A. 18h 05m 16s.36 Dec. -28° 53' 42".0

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Blobrana


L

Posts: 131433
Date:
OGLE-2003-BLG-235
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In 2003, astronomers discovered a planet (OGLE-2003-BLG-235b) outside our solar system by measuring the way light from a distant star warped around the new world's host star.
But it took two more years of telescope observations to see the host star. Using NASA's Hubble Space Telescope, astronomers have for the first time identified the parent star of distant planet discovered through gravitational microlensing.
The new finding is due to appear later this month in Astrophysical Journal Letters.

OGLE-2003-BLG-235b
Credit NASA / ESA / Notre Dame / Rice U.

This is a Hubble Space Telescope view of a small region of our galaxy where the host star to a gravitationally lensed planet is located. The star is identified by the crosshatch at the centre of the frame. An enlarged image of the target (lower left inset) reveals the light of two stars: a foreground star and a background star superimposed on each other. The background star is the brighter, solar-type star, and the foreground star is the fainter star.

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Blobrana


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Posts: 131433
Date:
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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

We present the results of HST observations of the host star for the first definitive 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 ~6mas 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 ~0.7mas between the centroid of this source in the F814W and F435W filter bands. We 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) M_solar and a planet mass of M_p = 2.6 (+0.8/-0.6) M_Jup 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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