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TOPIC: HD189733


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Posts: 131433
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Hot Jupiters
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Title: Atmospheric Circulation of Hot Jupiters: A Review of Current Understanding
Authors: Adam P. Showman, Kristen Menou, James Y-K. Cho

Hot Jupiters are new laboratories for the physics of giant planet atmospheres. Subject to unusual forcing conditions, the circulation regime on these planets may be unlike anything known in the Solar System. Characterising the atmospheric circulation of hot Jupiters is necessary for reliable interpretation of the multifaceted data currently being collected on these planets. We discuss several fundamental concepts of atmospheric dynamics that are likely central to obtaining a solid understanding of these fascinating atmospheres. A particular effort is made to compare the various modelling approaches employed so far to address this challenging problem.

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RE: HD189733
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Title: Mapping the Atmospheres of Hot Jupiters
Authors: H. A. Knutson

We present the results of recent observations of phase-dependent variations in brightness designed to characterise the atmospheres of hot Jupiters. In particular, we focus on recent observations of the transiting planet HD 189733b at 8 micron using the Spitzer Space Telescope, which allow us to determine the efficiency of the day-night circulation on this planet and estimate the longitudinal positions of hot and cold regions in the atmosphere. We discuss the implications of these observations in the context of two other successful detections of more sparsely-sampled phase variations for the non-transiting systems upsilon And b and HD 179949b, which imply a potential diversity in the properties of the atmospheres of hot Jupiters. Lastly, we highlight several upcoming Spitzer observations that will extend this sample to additional wavelengths and more transiting systems in the near future.

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Title: Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
Authors: F. Pont, R. L. Gilliland, C. Moutou, F. Bouchy, T. M. Brown, D. Charbonneau, M. Mayor, D. Queloz, N. Santos, S. Udry
(Version v2)

We monitored three transits of the giant gas planet around the nearby K dwarf HD 189733 with the ACS camera on the Hubble Space Telescope. The resulting very-high accuracy lightcurve (signal-to-noise ratio near 15000 on individual measurements, 35000 on 10-minute averages) allows a direct geometric measurement of the orbital inclination, radius ratio and scale of the system: i = 85.68 ± 0.04, Rpl/R*=0.1572 ± 0.0004, a/R*=8.92 ± 0.09. We derive improved values for the stellar and planetary radius, R*=0.755 ± 0.011 Rsol, Rpl=1.154 ± 0.017 RJ, and the transit ephemerides, Ttr=2453931.12048 ± 0.00002 + n 2.218581 ± 0.000002. The HST data also reveal clear evidence of the planet occulting spots on the surface of the star. At least one large spot complex (>80000 km) is required to explain the observed flux residuals and their colour evolution. This feature is compatible in amplitude and phase with the variability observed simultaneously from the ground. No evidence for satellites or rings around HD 189733b is seen in the HST lightcurve. This allows us to exclude with a high probability the presence of Earth-sized moons and Saturn-type debris rings around this planet. The timing of the three transits sampled is stable to the level of a few seconds, excluding a massive second planet in outer 2:1 resonance.

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Title: The Rotation Period of the Planet-Hosting Star HD 189733
Authors: Gregory W. Henry, Joshua N. Winn

We present synoptic optical photometry of HD 189733, the chromospherically active parent star of one of the most intensively studied exoplanets. We have significantly extended the timespan of our previously reported observations and refined the estimate of the stellar rotation period by more than an order of magnitude: P = 11.953 ± 0.009 days. We derive a lower limit on the inclination of the stellar rotation axis of 56\arcdeg  (with 95% confidence), corroborating earlier evidence that the stellar spin axis and planetary orbital axis are well aligned.

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Title: Looking for Super-Earths in the HD 189733 System: A Search for Transits in Most Space-Based Photometry
Authors: Bryce Croll, Jaymie M. Matthews, Jason F. Rowe, Brett Gladman, Eliza Miller-Ricci, Dimitar Sasselov, Gordon A.H. Walker, Rainer Kuschnig, Douglas N.C. Lin, David B. Guenther, Anthony F.J. Moffat, Slavek M. Rucinski, Werner W. Weiss

We have made a comprehensive transit search for exoplanets down to ~1.5 - 2 Earth radii in the HD 189733 system, based on 21-days of nearly uninterrupted broadband optical photometry obtained with the MOST (Microvariability & Oscillations of STars) satellite in 2006. We have searched these data for realistic limb-darkened transits from exoplanets other than the known hot Jupiter, HD 189733b, with periods ranging from about 0.4 days to one week. Monte Carlo statistical tests of the data with synthetic transits inserted into the data-set allow us to rule out additional close-in exoplanets with sizes ranging from about 0.15 - 0.31 RJ (Jupiter radii), or 1.7 - 3.5 RE (Earth radii) on orbits whose planes are near that of HD 189733b. These null results constrain theories that invoke lower-mass hot Super-Earth and hot Neptune planets in orbits similar to HD 189733b due to the inward migration of this hot Jupiter. This work also illustrates the feasibility of discovering smaller transiting planets around chromospherically active stars.

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Title: A Spitzer Search for Water in the Transiting Exoplanet HD189733b
Authors: David Ehrenreich (IAP), Guillaume Hébrard (IAP), Alain Lecavelier Des Etangs (IAP), David K Sing (IAP), Jean-Michel Désert (IAP), François Bouchy (IAP), Roger Ferlet (IAP), Alfred Vidal-Madjar (IAP)

We present Spitzer Space Telescope observations of the extrasolar planet HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with the Infrared Array Camera. The system parameters, including planetary radius, stellar radius, and impact parameter are derived from fits to the transit light curves at both wavelengths. We measure two consistent planet-to-star radius ratios, (Rp/Rs)[3.6 µm] = 0.1560 ± 0.0008(stat) ± 0.0002(syst) and (Rp/Rs)[5.8 µm] = 0.1541 ± 0.0009(stat) ± 0.0009(syst), which include both the random and systematic errors in the transit baseline. Although planet radii are determined at 1%-accuracy, if all uncertainties are taken into account the resulting error bars are still too large to allow for the detection of atmospheric constituents like water vapour. This illustrates the need to observe multiple transits with the longest possible out-of-transit baseline, in order to achieve the precision required by transmission spectroscopy of giant extrasolar planets.
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Posts: 131433
Date:
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Title: Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
Authors: F. Pont, R. L. Gilliland. C. Moutou, F. Bouchy, T. M. Brown, D. Charbonneau, M. Mayor, D. Queloz, N. Santos, S. Udry

We monitored three transits of the giant gas planet around the nearby K dwarf HD 189733 with the ACS camera on the Hubble Space Telescope. The resulting very-high accuracy lightcurve (signal-to-noise ratio near 15000 on individual measurements, 35000 on 10-minute averages) allows a direct geometric measurement of the orbital inclination, radius ratio and scale of the system: i = 85.68 ± 0.04 R_{pl}/R_*=0.1572 ± 0.0004, a/R_*=8.92 ± 0.09. We derive improved values for the stellar and planetary radius, R_*=0.755 ± 0.011 R_{sun}, R_{pl}=1.154 ± 0.017 R_J, and the transit ephemerides, T_{tr}=2453931.12048 ± 0.00002 + n 2.218581 ± 0.000002. The HST data also reveal clear evidence of the planet occulting spots on the surface of the star. At least one large spot complex (> 80000 km) is required to explain the observed flux residuals and their colour evolution. This feature is compatible in amplitude and phase with the variability observed simultaneously from the ground. No evidence for satellites or rings around HD 189733b are seen in the HST lightcurve. This allows us to exclude with a high probability the presence of Earth-sized moons and Saturn-type debris rings around this planet. The timing of the three transits sampled is stable to the level of a few seconds, excluding a massive second planet in outer 2:1 resonance.

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Posts: 131433
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Title: Analysis of Spitzer Spectra of Irradiated Planets: Evidence for Water Vapour?
Authors: Jonathan J. Fortney, Mark S. Marley
(Version v2)

Published mid infrared spectra of transiting planets HD 209458b and HD 189733b, obtained during secondary eclipse by the InfraRed Spectrograph (IRS) aboard the Spitzer Space Telescope, are predominantly featureless. In particular these flux ratio spectra do not exhibit an expected feature arising from water vapour absorption short-ward of 10 um. Here we suggest that, in the absence of flux variability, the spectral data for HD 189733b are inconsistent with 8 um-photometry obtained with Spitzer's InfraRed Array Camera (IRAC), perhaps an indication of problems with the challenging reduction of the IRS spectra. The IRAC point, along with previously published secondary eclipse photometry for HD 189733b, are in good agreement with a one-dimensional model of HD 189733b that clearly shows absorption due to water vapour in the emergent spectrum. We are not able to draw firm conclusions regarding the IRS data for HD 209458b, but spectra predicted by 1D and 3D atmosphere models fit the data adequately, without adjustment of the water abundance or reliance on cloud opacity. We argue that the generally good agreement between model spectra and IRS spectra of brown dwarfs with atmospheric temperatures similar to these highly irradiated planets lends confidence in the modelling procedure.

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Posts: 131433
Date:
Transiting Exoplanet
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Eleven years ago, David Charbonneau was a new graduate student at Harvard University's astronomy department, eager to explore the birth of the universe.

"Then I learned of the incredible first discoveries that had just been announced in exoplanets" - David Charbonneau.

Those objects, the first planets found outside the solar system, prompted Charbonneau to drop the Big Bang like a hot potato. He's been hunting for exoplanets ever since.
Yet the orbs that piqued the imagination of Charbonneau and so many other astronomers in the mid-1990s were then little more than phantoms. Too small to be seen, each planet revealed its presence only because its gravitational pull made its parent star wobble a little. Astronomers could ascertain just two basic properties of each of these elusive planets: a minimum value for its mass and the time it takes to orbit its star.
Seven years ago, Charbonneau and his colleagues brought the first of these alien worlds out of the shadows. They measured how much light the planet blocked when it passed in front of, or transited, its parent star. Such minieclipses reveal a planet's true size and mass, while the filtering of starlight by its atmosphere shows what gases cling to the alien world.

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Posts: 131433
Date:
RE: HD189733
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Exoplanet Forecast: Hot and Wet
Image credit: NASA/JPL-Caltech/ESA/ Institute d'Astrophysique de Paris

This plot of data from NASA's Spitzer Space Telescope tells astronomers that a toasty gas exoplanet, or a planet beyond our solar system, contains water vapour.

Spitzer observed the planet, called HD 189733b, cross in front of its star at three different infrared wavelengths: 3.6 microns; 5.8 microns and 8 microns (see lime-coloured dots). For each wavelength, the planet's atmosphere absorbed different amounts of the starlight that passed through it. The pattern by which this absorption varies with wavelength matches known signatures of water, as shown by the theoretical model in blue.

+ High-resolution (JPEG 1Mb)

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