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TOPIC: HD189733
Blobrana


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HD 189733b
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Title: Disequilibrium Carbon, Oxygen, and Nitrogen Chemistry in the Atmospheres of HD 189733b and HD 209458b
Authors: Julianne I. Moses, Channon Visscher, Jonathan J. Fortney, Adam P. Showman, Nikole K. Lewis, Caitlin A. Griffith, Megan Shabram, A. James Friedson, Mark S. Marley, Richard S. Freedman

We have developed 1-D photochemical and thermochemical kinetics and diffusion models for the transiting exoplanets HD 189733b and HD 209458b to study the effects of disequilibrium chemistry on the atmospheric composition of "hot Jupiters." Here we investigate the coupled chemistry of neutral carbon, hydrogen, oxygen, and nitrogen species, and we compare the model results with existing transit and eclipse observations. We find that the vertical profiles of molecular constituents are significantly affected by transport-induced quenching and photochemistry, particularly on cooler HD 189733b; however, the warmer stratospheric temperatures on HD 209458b can help maintain thermochemical equilibrium and reduce the effects of disequilibrium chemistry. For both planets, the methane and ammonia mole fractions are found to be enhanced over their equilibrium values at pressures of a few bar to less than a mbar due to transport-induced quenching, but CH_4 and NH_3 are photochemically removed at higher altitudes. Atomic species, unsaturated hydrocarbons (particularly C_2H_2), some nitriles (particularly HCN), and radicals like OH, CH_3, and NH_2 are enhanced overequilibrium predictions because of quenching and photochemistry. In contrast, CO, H_2O, N_2, and CO_2 more closely follow their equilibrium profiles, except at pressures \lta 1 microbar, where CO, H_2, and N_2 are photochemically destroyed and CO_2 is produced before its eventual high-altitude destruction. The enhanced abundances of HCN, CH_4, and NH_3 in particular are expected to affect the spectral signatures and thermal profiles HD 189733b and other, relatively cool, close-in transiting exoplanets. We examine the sensitivity of our results to the assumed temperature structure and eddy diffusion coefficientss and discuss further observational consequences of these models.

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Blobrana


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Posts: 131433
Date:
HD189733b
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Title: Polarised reflected light from the exoplanet HD189733b: First multicolour observations and confirmation of detection
Authors: S. V. Berdyugina, A. V. Berdyugin, D. M. Fluri, V. Piirola

We report first multicolour polarimetric measurements (UBV bands) for the hot Jupiters HD189733b and confirm our previously reported detection of polarisation in the B band (Berdyugina et al. 2008). The wavelength dependence of polarisation indicates the dominance of Rayleigh scattering with a peak in the blue B and U bands of ~10^-4±10^-5 and at least a factor of two lower signal in the V band. The Rayleigh-like wavelength dependence, detected also in the transmitted light during transits, implies a rapid decrease of the polarization signal toward longer wavelengths. Therefore, the nondetection by Wiktorowicz (2009), based on a measurement integrated within a broad passband covering the V band and partly B and R bands, is inconclusive and consistent with our detection in B. We discuss possible sources of the polarisation and demonstrate that effects of incomplete cancellation of stellar limb polarisation due to starspots or tidal perturbations are negligible as compared to scattering polarisation in the planetary atmosphere. We compare the observations with a Rayleigh-Lambert model and determine effective radii and geometrical albedos for different wavelengths. We find a close similarity of the wavelength dependent geometrical albedo with that of the Neptune atmosphere, which is known to be strongly influenced by Rayleigh and Raman scattering. Our result establishes polarimetry as a reliable means for directly studying exoplanetary atmospheres.

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Blobrana


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RE: HD189733
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Title: A new look at NICMOS transmission spectroscopy of HD189733, GJ-436 and XO-1: no conclusive evidence for molecular features
Authors: Neale P. Gibson (1,2), Frederic Pont (2), Suzanne Aigrain (1,2) ((1) University of Oxford, (2) University of Exeter)

We present a re-analysis of archival HST/NICMOS transmission spectroscopy of three exoplanet systems; HD 189733, GJ-436 and XO-1. Detections of several molecules, including H20, CH4 and CO2, have been claimed for HD 189733 and XO-1, but similarly sized features are attributed to systematic noise for GJ-436. The data consist of time-series grism spectra covering a planetary transit. After extracting light curves in independent wavelength channels, we use a linear decorrelation technique account for instrumental systematics (which is becoming standard in the field), and measure the planet-to-star radius ratio as a function of wavelength. For HD 189733, the uncertainties in the transmission spectrum are significantly larger than those previously reported. We also find the transmission spectrum is considerably altered when using different out-of-transit orbits to remove the systematics, when some parameters are left out of the decorrelation procedure, or when we perform the decorrelation with quadratic functions rather than linear functions. Given that there is no physical reason to believe the baseline flux should be modelled as a linear function of any particular set of parameters, we interpret this as evidence that the linear decorrelation technique is not a robust method to remove systematic effects from the light curves for each wavelength channel. For XO-1, the parameters measured to decorrelate the light curves would require extrapolation to the in-transit orbit to remove the systematics, and we cannot reproduce the previously reported results. We conclude that the resulting NICMOS transmission spectra are too dependent on the method used to remove systematics to be considered robust detections of molecular species in planetary atmospheres, although the presence of these molecules is not ruled out.

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Blobrana


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HD 189733b
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Title: The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
Authors: E. Agol, N. B. Cowan (University of Washington, Kavli Institute for Theoretical Physics, UCSB), H. A. Knutson (UC Berkeley, Kavli Institute for Theoretical Physics, UCSB), D. Deming (NASA Goddard Space Flight Centre), J. H. Steffen (Fermilab), G. W. Henry (Tennessee State University), D. Charbonneau (Harvard-Smithsonian Center for Astrophysics)

We present observations of seven transits and seven eclipses of the transiting planet system HD 189733 taken with Spitzer IRAC at 8 microns. We use a new correction for the detector ramp variation with a double-exponential function. Our main findings are: (1) an upper limit on the variability of the day-side planet flux of 2.7% (68% confidence); (2) the most precise set of transit times measured for a transiting planet, with an average accuracy of 3 seconds; (3) a lack of transit-timing variations, excluding the presence of second planets in this system above 20% of the mass of Mars in low-order mean-motion resonance at 95% confidence; (4) a confirmation of the planet's phase variation, finding the night side is 64% as bright as the day side, as well as an upper limit on the night-side variability of 17% (68% confidence); (5) a better correction for stellar variability at 8 micron causing the phase function to peak 3.5 hrs before secondary eclipse, confirming that the advection and radiation timescales are comparable at the 8 micron photosphere; (6) variation in the depth of transit, which possibly implies variations in the surface brightness of the portion of the star occulted by the planet, posing a fundamental limit on non-simultaneous multi-wavelength transit absorption measurements of planet atmospheres; (7) a measurement of the infrared limb-darkening of the star, in agreement with stellar atmosphere models; (8) an offset in the times of secondary eclipse of 69 sec, which is mostly accounted for by a 31 sec light travel time delay and 33 sec delay due to the shift of ingress and egress by the planet hot spot; this confirms that the phase variation is due to an offset hot spot on the planet; (9) a retraction of the claimed eccentricity of this system due to the offset of secondary eclipse; and (10) high precision measurements of the parameters of this system.

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Blobrana


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RE: HD189733
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Pune can take pride in the recent discovery by National Aeronautics and Space Administrations (NASA) and some eminent scientists of renowned universities of molecules of chemical elements of a planet that is 63 light years away from the Earth as the research, published in the acclaimed science journal Nature, mentions Azam Thatte, a city researcher.
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Blobrana


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Posts: 131433
Date:
HD 189733b
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Astronomers have used a new ground-based technique to study the atmospheres of planets outside our Solar System.
The work could assist the search for Earth-like planets with traces of organic, or carbon-rich, molecules.
Astronomers spotted evidence of methane gas in the atmosphere of an exoplanet.
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Blobrana


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Title: A Search for molecules in the atmosphere of HD 189733b
Authors: J.R. Barnes, Travis S. Barman, H.R.A. Jones, R.J. Barber, Brad M.S. Hansen, L. Prato, E.L. Rice, C.J. Leigh, A. Collier Cameron, D.J. Pinfield

We use signal enhancement techniques and a matched filter analysis to search for the K band spectroscopic absorption signature of the close orbiting extrasolar giant planet, HD 189733b. With timeseries observations taken with NIRSPEC at the Keck II telescope, we investigate the relative abundances of H2O and carbon bearing molecules, which have now been identified in the dayside spectrum of HD 189733b. We detect a candidate planet signature with a low level of significance, close to the ~153 km/s velocity amplitude of HD 189733b. However, some systematic variations, mainly due to imperfect telluric line removal, remain in the residual spectral timeseries in which we search for the planetary signal. The robustness of our candidate signature is assessed, enabling us to conclude that it is not possible to confirm the presence of any planetary signal which appears at Fp/F* contrasts deeper than the 95.4 per cent confidence level. Our search does not enable us to detect the planet at a contrast ratio of Fp/F* = 1/1920 with 99.9 per cent confidence. We also investigate the effect of model uncertainties on our ability to reliably recover a planetary signal. The use of incorrect temperature, model opacity wavelengths and model temperature-pressure profiles have important consequences for the least squares deconvolution procedure that we use to boost the S/N ratio in our spectral timeseries observations. We find that mismatches between the empirical and model planetary spectrum may weaken the significance of a detection by ~30-60 per cent, thereby potentially impairing our ability to recover a planetary signal with high confidence.

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Blobrana


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Posts: 131433
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HD189733b
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Title: Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS
Authors: David K. Sing, J.-M. Desert, A. Lecavelier des Etangs, G. E. Ballester, A. Vidal-Madjar, V. Parmentier, G. Hebrard, G. W. Henry

We present Hubble Space Telescope near-infrared transit photometry of the nearby hot-Jupiter HD189733b. The observations were taken with the NICMOS instrument during five transits, with three transits executed with a narrowband filter at 1.87 microns and two performed with a narrowband filter at 1.66 microns. Our observing strategy using narrowband filters is insensitive to the usual HST intra-orbit and orbit-to-orbit measurement of systematic errors, allowing us to accurately and robustly measure the near-IR wavelength dependence of the planetary radius. Our measurements fail to reproduce the Swain et al. absorption signature of atmospheric water below 2 microns at a 5-sigma confidence level. We measure a planet-to-star radius contrast of 0.15498±0.00035 at 1.66 microns and a contrast of 0.15517±0.00019 at 1.87 microns. Both of our near-IR planetary radii values are in excellent agreement with the levels expected from Rayleigh scattering by sub-micron haze particles, observed at optical wavelengths, indicating that upper-atmospheric haze still dominates the near-IR transmission spectra over the absorption from gaseous molecular species at least below 2 microns.

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Blobrana


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Posts: 131433
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RE: HD189733
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HD 189733b transiting its parent star (artist's impression)


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Blobrana


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Posts: 131433
Date:
HD 189733
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Title: Stellar activity of planetary host star HD 189733
Authors: I. Boisse, C. Moutou, A. Vidal-Madjar, F. Bouchy, F. Pont, G. Hébrard, X. Bonfils, B. Croll, X. Delfosse, M. Desort, T. Forveille, A.-M. Lagrange, B. Loeillet, C. Lovis, J. M. Matthews, M. Mayor, F. Pepe, C. Perrier, D. Queloz, J. F. Rowe, N. C. Santos, D. Ségransan, S. Udry
(Version v2)

Extra-solar planet search programs require high-precision velocity measurements. They need to study how to disentangle radial-velocity variations due to Doppler motion from the noise induced by stellar activity. We monitored the active K2V star HD 189733 and its transiting planetary companion that has a 2.2-day orbital period. We used the high-resolution spectrograph SOPHIE mounted on the 1.93-m telescope at the Observatoire de Haute-Provence to obtain 55 spectra of HD 189733 over nearly two months. We refined the HD 189733b orbit parameters and put limits on the eccentricity and on a long-term velocity gradient. After subtracting the orbital motion of the planet, we compared the variability of spectroscopic activity indices to the evolution of the radial-velocity residuals and the shape of spectral lines. The radial velocity, the spectral-line profile and the activity indices measured in HeI (5875.62 \AA), Halpha (6562.81 \AA) and the CaII H&K lines (3968.47 \AA and 3933.66 \AA, respectively) show a periodicity around the stellar rotation period and the correlations between them are consistent with a spotted stellar surface in rotation. We used such correlations to correct for the radial-velocity jitter due to stellar activity. This results in achieving high precision on the orbit parameters, with a semi-amplitude K = 200.56 ±0.88 m.s-1 and a derived planet mass of M_{P}=1.13 ±0.03 M_{Jup}.

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