Publications (19)12.05 Total impact
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Article: 0.94 - 2.42 micron ground-based transmission spectra of the hot-Jupiter HD-189733b
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ABSTRACT: We present here new transmission spectra of the hot Jupiter HD-189733b using the SpeX instrument on the NASA Infrared Telescope Facility. We obtained two nights of observations where we recorded the primary transit of the planet in the J-, H- and K-bands simultaneously, covering a total spectral range from 0.94 to 2.4 micron. We used Fourier analysis and other de-trending techniques validated previously on other datasets to clean the data. We tested the statistical significance of our results by calculating the auto-correlation function, and we found that, after the detrending, white noise dominates at most frequencies. Additionally, we repeated our analysis on the out-of-transit data only, showing that the residual telluric contamination is well within the error bars. While these techniques are very efficient when multiple nights of observations are combined together, our results prove that even one good night of observations is enough to provide statistically meaningful data, which might appear counterintuitive given the daunting accuracy to be achieved. Our observed spectra are consistent with space-based data recorded in the same wavelength interval by multiple instruments, indicating that ground-based facilities are becoming a viable and complementary option to spaceborne observatories. The best fit to the features in our data was obtained with water vapour. Our error bars are not small enough to address the presence of additional molecules.12/2012; -
Article: Characterizing the Atmospheres of Transiting Planets with a Dedicated Space Telescope
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ABSTRACT: Exoplanetary science is one of the fastest evolving fields of today's astronomical research, continuously yielding unexpected and surprising results. Ground-based planet-hunting surveys, together with dedicated space missions such as Kepler and CoRoT, are delivering an ever-increasing number of exoplanets, over 690, and ESA's Gaia mission will escalate the exoplanetary census into the several thousands. The next logical step is the characterization of these new worlds. What is their nature? Why are they as they are? Use of the Hubble Space Telescope and Spitzer Space Telescope to probe the atmospheres of transiting hot, gaseous exoplanets has opened perspectives unimaginable even just 10 years ago, demonstrating that it is indeed possible with current technology to address the ambitious goal of characterizing the atmospheres of these alien worlds. However, these successful measurements have also shown the difficulty of understanding the physics and chemistry of these exotic environments when having to rely on a limited number of observations performed on a handful of objects. To progress substantially in this field, a dedicated facility for exoplanet characterization, able to observe a statistically significant number of planets over time and a broad spectral range will be essential. Additionally, the instrument design (e.g., detector performances, photometric stability) will be tailored to optimize the extraction of the astrophysical signal. In this paper, we analyze the performance and tradeoffs of a 1.2/1.4 m space telescope for exoplanet transit spectroscopy from the visible to the mid-IR. We present the signal-to-noise ratio as a function of integration time and stellar magnitude/spectral type for the acquisition of spectra of planetary atmospheres for a variety of scenarios: hot, warm, and temperate planets orbiting stars ranging in spectral type from hot F- to cooler M-dwarfs. Our results include key examples of known planets (e.g., HD 189733b, GJ 436b, GJ 1214b, and Cancri 55 e) and simulations of plausible terrestrial and gaseous planets, with a variety of thermodynamical conditions. We conclude that even most challenging targets, such as super-Earths in the habitable zone of late-type stars, are within reach of an M-class, space-based spectroscopy mission.The Astrophysical Journal 01/2012; 746(1):45. · 6.02 Impact Factor -
Article: Characterising the Atmospheres of Transiting Planets with a Dedicated Space Telescope
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ABSTRACT: Exoplanetary science is among the fastest evolving fields of today's astronomical research. Ground-based planet-hunting surveys alongside dedicated space missions (Kepler, CoRoT) are delivering an ever-increasing number of exoplanets, now numbering at ~690, with ESA's GAIA mission planned to bring this number into the thousands. The next logical step is the characterisation of these worlds: what is their nature? Why are they as they are? The use of the HST and Spitzer Space Telescope to probe the atmospheres of transiting hot, gaseous exoplanets has demonstrated that it is possible with current technology to address this ambitious goal. The measurements have also shown the difficulty of understanding the physics and chemistry of these environments when having to rely on a limited number of observations performed on a handful of objects. To progress substantially in this field, a dedicated facility for exoplanet characterization with an optimised instrument design (detector performance, photometric stability, etc.), able to observe through time and over a broad spectral range a statistically significant number of planets, will be essential. We analyse the performances of a 1.2/1.4m space telescope for exoplanet transit spectroscopy from the visible to the mid IR, and present the SNR ratio as function of integration time and stellar magnitude/spectral type for the acquisition of spectra of planetary atmospheres in a variety of scenarios: hot, warm, and temperate planets, orbiting stars ranging in spectral type from hot F to cool M dwarfs. We include key examples of known planets (e.g. HD 189733b, Cancri 55 e) and simulations of plausible terrestrial and gaseous planets, with a variety of thermodynamical conditions. We conclude that even most challenging targets, such as super-Earths in the habitable-zone of late-type stars, are within reach of a M-class, space-based spectroscopy mission.11/2011; -
Conference Proceeding: Characterising Super Earths With The EChO Spacemission Concept
AAS/Division for Extreme Solar Systems Abstracts; 09/2011 -
Article: Ground-based NIR emission spectroscopy of HD189733b
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ABSTRACT: We investigate the K and L band dayside emission of the hot-Jupiter HD 189733b with three nights of secondary eclipse data obtained with the SpeX instrument on the NASA IRTF. The observations for each of these three nights use equivalent instrument settings and the data from one of the nights has previously reported by Swain et al (2010). We describe an improved data analysis method that, in conjunction with the multi-night data set, allows increased spectral resolution (R~175) leading to high-confidence identification of spectral features. We confirm the previously reported strong emission at ~3.3 microns and, by assuming a 5% vibrational temperature excess for methane, we show that non-LTE emission from the methane nu3 branch is a physically plausible source of this emission. We consider two possible energy sources that could power non-LTE emission and additional modelling is needed to obtain a detailed understanding of the physics of the emission mechanism. The validity of the data analysis method and the presence of strong 3.3 microns emission is independently confirmed by simultaneous, long-slit, L band spectroscopy of HD 189733b and a comparison star.04/2011; -
Article: NICMOS transmission spectroscopy of HD 189733b: controversy becomes confirmation
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ABSTRACT: Spectral features corresponding to methane and water opacity were reported based on spectroscopic observations of HD 189733b with Hubble/NICMOS. Recently, these data, and other NICMOS exoplanet spectroscopy measurements, have been reexamined in Gibson et al. 2010, who claim that the features in the transmission spectra are due to uncorrected systematic errors and not molecular opacities. We examine the methods used by the Gibson team and show that, contrary to their claim, their results for the transmission spectrum of HD 189733b are in fact in agreement with the original results. In the case of HD 189733b, the most significant problem with the Gibson approach is a poorly determined instrument model, which causes (1) an increase in the formal uncertainty and (2) instability in the minimization process; although Gibson et al. do recover the correct spectrum, they cannot identify it due to the problems caused by a poorly determined instrument model. In the case of XO-1b, the Gibson method is fundamentally flawed because they omit the most important parameters from the instrument model. For HD 189733b, the Gibson team did not omit these parameters, which explains why they are able to reproduce previous results in this case, although with poor SNR. Comment: 11 pages, 4 figures, submitted to MNRAS11/2010; -
Article: Probing the terminator region atmosphere of the Hot-Jupiter XO-1b with transmission spectroscopy
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ABSTRACT: We report here the first infrared spectrum of the hot-Jupiter XO-1b. The observations were obtained with NICMOS instrument onboard the Hubble Space Telescope during a primary eclipse of the XO-1 system. Near photon-noise-limited spectroscopy between 1.2 and 1.8 micron allows us to determine the main composition of this hot-Jupiter's planetary atmosphere with good precision. This is the third hot-Jupiter's atmosphere for which spectroscopic data are available in the near IR. The spectrum shows the presence of water vapor (H2O), methane (CH4) and carbon dioxide (CO2), and suggests the possible presence of carbon monoxide (CO). We show that the published IRAC secondary transit emission photometric data are compatible with the atmospheric composition at the terminator determined from the NICMOS spectrum, with a range of possible mixing-ratios and thermal profiles; additional emission spectroscopy data are needed to reduce the degeneracy of the possible solutions. Finally, we note the similarity between the 1.2-1.8 micron transmission spectra of XO-1b and HD 209458b, suggesting that in addition to having similar stellar/orbital and planetary parameters the two systems may also have a similar exoplanetary atmospheric composition. Comment: ApJ accepted, 4 figures02/2010; -
Article: Water, Methane, and Carbon Dioxide Present in the Dayside Spectrum of the Exoplanet HD 209458b
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ABSTRACT: Using the NICMOS instrument on the Hubble Space Telescope, we have measured the dayside spectrum of HD 209458b between 1.5 and 2.5 μm. The emergent spectrum is dominated by features due to the presence of methane (CH4) and water vapor (H2O), with smaller contributions from carbon dioxide (CO2). Combining this near-infrared spectrum with existing mid-infrared measurements shows the existence of a temperature inversion and confirms the interpretation of previous photometry measurements. We find a family of plausible solutions for the molecular abundance and detailed temperature profile. Observationally resolving the ambiguity between abundance and temperature requires either (1) improved wavelength coverage or spectral resolution of the dayside emission spectrum or (2) a transmission spectrum where abundance determinations are less sensitive to the temperature structure.The Astrophysical Journal 10/2009; 704(2):1616. · 6.02 Impact Factor -
Article: Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b
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ABSTRACT: We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5 microns using the NICMOS instrument on the Hubble Space Telescope. The emergent spectrum contains significant modulation, which we attribute to the presence of molecular bands seen in absorption. We find that water (H2O), carbon monoxide (CO), and carbon dioxide (CO2) are needed to explain the observations, and we are able to estimate the mixing ratios for these molecules. We also find temperature decreases with altitude in the ~0.01 < P < ~1 bar region of the dayside near-infrared photosphere and set an upper limit to the dayside abundance of methane (CH4) at these pressures.01/2009; -
Article: Water in HD 209458b's atmosphere from 3.6 - 8 microns IRAC photometric observations in primary transit
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ABSTRACT: The hot Jupiter HD 209458b was observed during primary transit at 3.6, 4.5, 5.8 and 8.0 microns using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We detail here the procedures we adopted to correct for the systematic trends present in the IRAC data. The light curves were fitted including limb darkening effects and fitted using Markov Chain Monte Carlo and prayer-bead Monte Carlo techniques, finding almost identical results. The final depth measurements obtained by a combined Markov Chain Monte Carlo fit are at 3.6 microns, 1.469 +- 0.013 % and 1.448 +- 0.013 %; at 4.5 microns, 1.478 +- 0.017 % ; at 5.8 microns, 1.549 +- 0.015 % and at 8.0 microns 1.535 +- 0.011 %. Our results clearly indicate the presence of water in the planetary atmosphere. Our broad band photometric measurements with IRAC prevent us from determining the additional presence of other other molecules such as CO, CO2 and methane for which spectroscopy is needed. While water vapour with a mixing ratio of 10^-4-10^-3 combined with thermal profiles retrieved from the day-side may provide a very good fit to our observations, this data set alone is unable to resolve completely the degeneracy between water abundance and atmospheric thermal profile.arXiv. 01/2009; astro-ph.EP. -
Article: The mid-infrared spectrum of the transiting exoplanet HD 209458b
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ABSTRACT: We report the spectroscopic detection of mid-infrared emission from the transiting exoplanet HD 209458b. Using archive data taken with the Spitzer/IRS instrument, we have determined the spectrum of HD 209458b between 7.46 and 15.25 microns. We have used two independent methods to determine the planet spectrum, one differential in wavelength and one absolute, and find the results are in good agreement. Over much of this spectral range, the planet spectrum is consistent with featureless thermal emission. Between 7.5 and 8.5 microns, we find evidence for an unidentified spectral feature. If this spectral modulation is due to absorption, it implies that the dayside vertical temperature profile of the planetary atmosphere is not entirely isothermal. Using the IRS data, we have determined the broad-band eclipse depth to be 0.00315 +/- 0.000315, implying significant redistribution of heat from the dayside to the nightside. This work required development of improved methods for Spitzer/IRS data calibration that increase the achievable absolute calibration precision and dynamic range for observations of bright point sources. Comment: 35 pages, 12 figures, revised version accepted by the Astrophysical Journal02/2007; -
Article: Cryogenic Delay Line for Long-Baseline Interferometry in the Far-Infrared
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ABSTRACT: We discuss the design, current status, and ongoing development of a cryogenic delay line for long-baseline direct-detection interferometry in the far-infrared.05/2004; -
Article: Keck Interferometer Nuller Data Reduction and On-Sky Performance
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ABSTRACT: We describe the Keck Interferometer nuller theory of operation, data reduction, and on-sky performance, particularly as it applies to the nuller exozodiacal dust key science program that was carried out between 2008 February and 2009 January. We review the nuller implementation, including the detailed phasor processing involved in implementing the null-peak mode used for science data and the sequencing used for science observing. We then describe the Level 1 reduction to convert the instrument telemetry streams to raw null leakages, and the Level 2 reduction to provide calibrated null leakages. The Level 1 reduction uses conservative, primarily linear processing, implemented consistently for science and calibrator stars. The Level 2 processing is more flexible, and uses diameters for the calibrator stars measured contemporaneously with the interferometer’s K-band cophasing system in order to provide the requisite accuracy. Using the key science data set of 462 total scans, we assess the instrument performance for sensitivity and systematic error. At 2.0 Jy we achieve a photometrically-limited null leakage uncertainty of 0.25% rms per 10 minutes of integration time in our broadband channel. From analysis of the Level 2 reductions, we estimate a systematic noise floor for bright stars of ~0.2% rms null leakage uncertainty per observing cluster in the broadband channel. A similar analysis is performed for the narrowband channels. We also provide additional information needed for science reduction, including details on the instrument beam pattern and the basic astrophysical response of the system, and references to the data reduction and modeling tools. -
Article: Water in the atmosphere of HD 209458b from 3.6–8 μm IRAC photometric observations in primary transit
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ABSTRACT: The hot Jupiter HD 209458b was observed during primary transit at 3.6, 4.5, 5.8 and 8.0 μm using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We describe the procedures we adopted to correct for the systematic effects present in the IRAC data and the subsequent analysis. The light curves were fitted including limb-darkening effects and fitted using Markov Chain Monte Carlo and prayer-bead Monte Carlo techniques, obtaining almost identical results. The final depth measurements obtained by a combined Markov Chain Monte Carlo fit are at 3.6 μm, 1.469 ± 0.013 and 1.448 ± 0.013 per cent; at 4.5 μm, 1.478 ± 0.017 per cent; at 5.8 μm, 1.549 ± 0.015 per cent; and at 8.0 μm, 1.535 ± 0.011 per cent. Our results clearly indicate the presence of water in the planetary atmosphere. Our broad-band photometric measurements with IRAC prevent us from determining the additional presence of other molecules such as CO, CO_2 and methane for which spectroscopy is needed. While water vapour with a mixing ratio of 10^(-4) to 10^(-3) combined with thermal profiles retrieved from the day side may provide a very good fit to our observations, this data set alone is unable to resolve completely the degeneracy between water abundance and atmospheric thermal profile. -
Article: Cryogenic delay line for far-IR interferometry in space
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ABSTRACT: We discuss the design, current status, and ongoing development of a cryogenic delay line for long-baseline direct-detection interferometry in the far-infrared.36:173-176. -
Article: Differential phase mode with the Keck Interferometer
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ABSTRACT: We will describe the differential phase mode of the Keck Interferometer. The scientific goal of this mode is the direct detection and spectroscopic characterization of hot, Jupiter mass planets. We will describe the effect caused by the relative color difference between the planet and the parent star and the observational technique, which utilizes two-color phase reference interferometry in the near to mid-infrared.194:89. -
Article: Detection of Extra-solar Planets with the Keck Interferometer
Proceedings of the International Astronomical Union 202:471. -
Article: The Keck Interferometer: Instrument Overview and Proposed Science
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ABSTRACT: The Keck Interferometer project will link the two 10m Keck telescopes and 4 1.8m outrigger telescopes in an infrared interferometric array. We will give details of the proposed form for the instrument and report on current progress with design and construction. The key science programs consist of nulling detection of exo-zodiacal light, multi-color phase differencing detection of hot jupiters, astrometric searches for jupiter to uranus mass planets orbiting nearby stars, and general interferometric imaging. We will give details how the key science programs can be achieved with the proposed instrument, and show the results expected to be generated by these science programs.194:256. -
Article: The mid-infrared spectrum of the transiting exoplanet HD 209458b
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ABSTRACT: We report the spectroscopic detection of mid-infrared emission from the transiting exoplanet HD 209458b. Using archive data taken with the Spitzer IRS instrument, we have determined the spectrum of HD 209458b between 7.46 and 15.25 μm. We have used two independent methods to determine the planet spectrum, one differential in wavelength and one absolute, and find the results are in good agreement. Over much of this spectral range, the planet spectrum is consistent with featureless thermal emission. Between 7.5 and 8.5 μm, we find evidence for an unidentified spectral feature. If this spectral modulation is due to absorption, it implies that the dayside vertical temperature profile of the planetary atmosphere is not entirely isothermal. Using the IRS data, we have determined the broadband eclipse depth to be 0.00315 ± 0.000315, implying significant redistribution of heat from the dayside to the nightside. This work required the development of improved methods for Spitzer IRS data calibration that increase the achievable absolute calibration precision and dynamic range for observations of bright point sources.
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2009–2012
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California Institute of Technology
- Jet Propulsion Laboratory
Pasadena, CA, USA
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