Jonathan J. Fortney

University of California, Santa Cruz, Santa Cruz, California, United States

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Publications (339)1563.75 Total impact

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    ABSTRACT: Interpreting the spectra of brown dwarfs is key to determining the fundamental physical and chemical processes occurring in their atmospheres. Powerful Bayesian atmospheric retrieval tools have recently been applied to both exoplanet and brown dwarf spectra to tease out the thermal structures and molecular abundances to understand those processes. In this manuscript we develop a significantly upgraded retrieval method and apply it to the SpeX spectral library data of two benchmark late T-dwarfs, Gl570D and HD3651B, to establish the validity of our upgraded forward model parameterization and Bayesian estimator. Our retrieved metallicities, gravities, and effective temperature are consistent with the metallicity and presumed ages of the systems. We add the carbon-to-oxygen ratio as a new dimension to benchmark systems and find good agreement between carbon-to-oxygens ratio derived in the brown dwarfs and the host stars. Furthermore, we have for the first time unambiguously determined the presence of ammonia in the low-resolution spectra of these two late T-dwarfs. We also show that the retrieved results are not significantly impacted by the possible presence of clouds, though some quantities are significantly impacted by uncertainties in photometry. This investigation represents a watershed study in establishing the utility of atmospheric retrieval approaches on brown dwarf spectra.
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    ABSTRACT: Detailed characterization of exoplanets has begun to yield measurements of their atmospheric properties that constrain the planets' origins and evolution. For example, past observations of the dayside emission spectrum of the hot Jupiter WASP-12b indicated that its atmosphere has a high carbon-to-oxygen ratio (C/O $>$ 1), suggesting it had a different formation pathway than is commonly assumed for giant planets. Here we report a precise near-infrared transmission spectrum for WASP-12b based on six transit observations with the Hubble Space Telescope/Wide Field Camera 3. We bin the data in 13 spectrophotometric light curves from 0.84 - 1.67 $\mu$m and measure the transit depths to a median precision of 51 ppm. We retrieve the atmospheric properties using the transmission spectrum and find strong evidence for water absorption (7$\sigma$ confidence). This detection marks the first high-confidence, spectroscopic identification of a molecule in the atmosphere of WASP-12b. The retrieved 1$\sigma$ water volume mixing ratio is between $10^{-5}-10^{-2}$, which is consistent with C/O $>$ 1 to within 2$\sigma$. However, we also introduce a new retrieval parameterization that fits for C/O and metallicity under the assumption of chemical equilibrium. With this approach, we constrain C/O to $0.5^{+0.2}_{-0.3}$ at $1\,\sigma$ and rule out a carbon-rich atmosphere composition (C/O$>1$) at $>3\sigma$ confidence. Further observations and modeling of the planet's global thermal structure and dynamics would aid in resolving the tension between our inferred C/O and previous constraints. Our findings highlight the importance of obtaining high-precision data with multiple observing techniques in order to obtain robust constraints on the chemistry and physics of exoplanet atmospheres.
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    ABSTRACT: Recently, spectral retrieval has proven to be a powerful tool for constraining the physical properties and atmospheric compositions of extrasolar planet atmospheres from observed spectra, primarily for transiting objects but also increasingly for directly imaged planets and brown dwarfs. Despite its strengths, this approach has been applied to only about a dozen targets. Determining the abundances of the main carbon and oxygen-bearing compounds in a planetary atmosphere can lead to the C/O ratio of the object, which is crucial in understanding its formation and migration history. We present a retrieval analysis on the published near-infrared spectrum of {\kappa} And b, a directly imaged substellar companion to a young B9 star. We fit the emission spectrum model utilizing a Markov Chain Monte Carlo algorithm. We estimate the abundance of water vapor, and its uncertainty, in the atmosphere of the object. We also place upper limits on the abundances of carbon dioxide and methane and constrain the pressure-temperature profile of the atmosphere. We compare our results to studies that have applied model retrieval on multiband photometry and emission spectroscopy of hot Jupiters (extrasolar giant planets with orbital periods of several days) and the directly imaged giant planet HR 8799b. We find that the water abundances of the hot Jupiters and the two directly imaged planets inhabit overlapping regions of parameter space and that their P-T profiles are qualitatively similar, despite the wide range of effective temperatures and incident stellar fluxes for these objects.
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    ABSTRACT: (Abridged) NASA's Kepler mission has provided several thousand transiting planet candidates, yet only a small subset have been confirmed as true planets. Therefore, the most fundamental question about these candidates is the fraction of bona fide planets. Estimating the rate of false positives of the overall Kepler sample is necessary to derive the planet occurrence rate. We present the results from two large observational campaigns that were conducted with the Spitzer telescope during the the Kepler mission. These observations are dedicated to estimating the false positive rate (FPR) amongst the Kepler candidates. We select a sub-sample of 51 candidates, spanning wide ranges in stellar, orbital and planetary parameter space, and we observe their transits with Spitzer at 4.5 microns. We use these observations to measures the candidate's transit depths and infrared magnitudes. A bandpass-dependent depth alerts us to the potential presence of a blending star that could be the source of the observed eclipse: a false-positive scenario. For most of the candidates (85%), the transit depths measured with Kepler are consistent with the depths measured with Spitzer as expected for planetary objects, while we find that the most discrepant measurements are due to the presence of unresolved stars that dilute the photometry. The Spitzer constraints on their own yield FPRs between 5-40%, depending on the KOIs. By considering the population of the Kepler field stars, and by combining follow-up observations (imaging) when available, we find that the overall FPR of our sample is low. The measured upper limit on the FPR of our sample is 8.8% at a confidence level of 3 sigma. This observational result, which uses the achromatic property of planetary transit signals that is not investigated by the Kepler observations, provides an independent indication that Kepler's false positive rate is low.
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    ABSTRACT: We use a planetary albedo model to investigate variations in visible wavelength phase curves of exoplanets. The presence of clouds on these exoplanets significantly alters their planetary albedo spectra. We confirm that non-uniform cloud coverage on the dayside of tidally locked exoplanets will manifest as changes to the magnitude and shift of the phase curve. In this work, we first investigate a test case of our model using a Jupiter-like planet, at temperatures consistent to 2.0 AU insolation from a solar type star, to consider the effect of H2O clouds. We then extend our application of the model to the exoplanet Kepler-7b and consider the effect of varying cloud species, sedimentation efficiency, particle size, and cloud altitude. We show that, depending on the observational filter, the largest possible shift of the phase curve maximum will be 2-10 deg for a Jupiter-like planet, and up to 30 deg (0.08 in fractional orbital phase) for hot-Jupiter exoplanets at visible wavelengths as a function of dayside cloud distribution with a uniformly averaged thermal profile. Finally, we tailor our model for comparison with, and confirmation of, the recent optical phase-curve observations of Kepler-7b with the Kepler space telescope. The average planetary albedo can vary between 0.1-0.6 for the 1300 cloud scenarios that were compared to the observations. We observe that smaller particle size and increasing cloud altitude have a strong effect on increasing albedo. In particular, we show that a set of models where Kepler-7b has roughly half of its dayside covered in small-particle clouds high in the atmosphere, made of bright minerals like MgSiO3 and Mg2SiO4, provide the best fits to the observed offset and magnitude of the phase-curve, whereas Fe clouds are found to have too dark to fit the observations.
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    ABSTRACT: [Abridged] We have only been able to comprehensively characterize the atmospheres of a handful of transiting planets, because most orbit faint stars. TESS will discover transiting planets orbiting the brightest stars, enabling, in principle, an atmospheric survey of 10^2 to 10^3 bright hot Jupiters and warm sub-Neptunes. Uniform observations of such a statistically significant sample would provide leverage to understand---and learn from---the diversity of short-period planets. We argue that the best way to maximize the scientific returns of TESS is with a follow-up space mission consisting of a ~1 m telescope with an optical--NIR spectrograph: it could measure molecular absorption for non-terrestrial planets, as well as eclipses and phase variations for the hottest jovians. Such a mission could observe up to 10^3 transits per year, thus enabling it to survey a large fraction of the bright (J<11) TESS planets. JWST could be used to perform detailed atmospheric characterization of the most interesting transiting targets (transit, eclipse, and---when possible---phase-resolved spectroscopy). TESS is also expected to discover a few temperate terrestrial planets transiting nearby M-Dwarfs. Characterizing these worlds will be time-intensive: JWST will need months to provide tantalizing constraints on the presence of an atmosphere, planetary rotational state, clouds, and greenhouse gases. Future flagship missions should be designed to provide better constraints on the habitability of M-Dwarf temperate terrestrial planets.
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    ABSTRACT: We explored two aspects of the problem of characterizing cool extrasolar giant planets in scattered optical light with a space based coronagraph. First, for a number of the known radial velocity (RV) giants we computed traditional forward models of their atmospheric structure and clouds, given various input assumptions, and computed model albedo spectra. Such models have been computed before, but mostly for generic planets. Our new models demonstrate that there is likely interesting spectral diversity among those planets that are most favorable for direct detection. Second, we applied a powerful Markov Chain Monte Carlo (MCMC) retrieval technique to synthetic noisy data of cool giants to better understand how well various atmospheric parameters--particularly molecular abundances and cloud properties--could be constrained. This is the first time such techniques have been applied to this problem. The process is time consuming, so only a dozen or so cases could be completed in the limited time available. Nevertheless the results clearly show that even at S/N ~ 5, scientifically interesting and valuable conclusions can be drawn about the properties of giant planet atmospheres from noisy spectra. We find that atmospheric abundances are best constrained when the planet gravity is bounded. Thus direct imaging observations of known radial velocity planets are extremely valuable as limits on a target planet's gravity can be obtained from astrometric imaging and reflectivity and mass-radius relationship arguments (for mass and radius, respectively). Further retrieval studies are clearly warranted and would be valuable to help guide instrument design decisions.
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    ABSTRACT: Context. Astrometric monitoring of directly-imaged exoplanets allows the study of their orbital parameters and system architectures. Because most directly-imaged planets have long orbital periods (>20 AU), accurate astrometry is challenging when based on data acquired on timescales of a few years and usually with different instruments. The LMIRCam camera on the LBT is being used for the LEECH survey to search for and characterize young and adolescent exoplanets in L' band, including their system architectures. Aims. We first aim to provide a good astrometric calibration of LMIRCam. Then, we derive new astrometry, test the predictions of the orbital model of 8:4:2:1 mean motion resonance proposed by Go\'zdziewski & Migaszewski, and perform new orbital fitting of the HR 8799 bcde planets. We also present deep limits on a putative fifth planet interior to the known planets. Methods. We use observations of HR 8799 and the Theta1 Ori C field obtained during the same run in October 2013. Results. We first characterize the distortion of LMIRCam. We determine a platescale and a true north orientation for the images of 10.707 +/- 0.012 mas/pix and -0.430 +/- 0.076 deg, respectively. The errors on the platescale and true north orientation translate into astrometric accuracies at a separation of 1 of 1.1 mas and 1.3 mas, respectively. The measurements for all planets are usually in agreement within 3 sigma with the ephemeris predicted by Go\'zdziewski & Migaszewski. The orbital fitting based on the new astrometric measurements favors an architecture for the planetary system based on 8:4:2:1 mean motion resonance. The detection limits allow us to exclude a fifth planet slightly brighter/more massive than HR 8799 b at the location of the 2:1 resonance with HR 8799 e (~9.5 AU) and about twice as bright as HR 8799 cde at the location of the 3:1 resonance with HR 8799 e (~7.5 AU).
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    ABSTRACT: WD0137-349 is a white dwarf-brown dwarf binary system in a 116 minute orbit. We present radial velocity observations and multiwaveband photometry from V, R and I in the optical, to J, H and Ks in the near-IR and [3.6], [4.5], [5.8] and [8.0] microns in the mid-IR. The photometry and lightcurves show variability in all wavebands, with the amplitude peaking at [4.5] microns, where the system is also brightest. Fluxes and brightness temperatures were computed for the heated and unheated atmosphere of the brown dwarf (WD0137-349B) using synthetic spectra of the white dwarf using model atmosphere simulations. We show that the flux from the brown dwarf dayside is brighter than expected in the Ks and [4.5] micron bands when compared to models of irradiated brown dwarfs with full energy circulation and suggest this over-luminosity may be attributed to H2 fluorescence or H3+ being generated in the atmosphere by the UV irradiation.
    Monthly Notices of the Royal Astronomical Society 12/2014; 447(4). DOI:10.1093/mnras/stu2721 · 5.23 Impact Factor
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    ABSTRACT: Jupiter's atmosphere has been observed to be depleted in helium (Yatm~0.24), suggesting active helium sedimentation in the interior. This is accounted for in standard Jupiter structure and evolution models through the assumption of an outer, He-depleted envelope that is separated from the He-enriched deep interior by a sharp boundary. Here we aim to develop a model for Jupiter's inhomogeneous thermal evolution that relies on a more self-consistent description of the internal profiles of He abundance, temperature, and heat flux. We make use of recent numerical simulations on H/He demixing, and on layered (LDD) and oscillatory (ODD) double diffusive convection, and assume an idealized planet model composed of a H/He envelope and a massive core. A general framework for the construction of interior models with He rain is described. Despite, or perhaps because of, our simplifications made we find that self-consistent models are rare. For instance, no model for ODD convection is found. We modify the H/He phase diagram of Lorenzen et al. to reproduce Jupiter's atmospheric helium abundance and examine evolution models as a function of the LDD layer height, from those that prolong Jupiter's cooling time to those that actually shorten it. Resulting models that meet the luminosity constraint have layer heights of about 0.1-1 km, corresponding to ~10,-20,000 layers in the rain zone between ~1 and 3-4.5 Mbars. Present limitations and directions for future work are discussed, such as the formation and sinking of He droplets.
    Monthly Notices of the Royal Astronomical Society 12/2014; 447(4). DOI:10.1093/mnras/stu2634 · 5.23 Impact Factor
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    ABSTRACT: WASP-10b, a non-inflated hot Jupiter, was discovered around a K-dwarf in a near circular orbit ($\sim $$0.06$). Since its discovery in 2009, different published parameters for this system have led to a discussion about the size, density, and eccentricity of this exoplanet. In order to test the hypothesis of a circular orbit for WASP-10b, we have observed its secondary eclipse in the Ks-band, where the contribution of planetary light is high enough to be detected from the ground. Observations were performed with the OMEGA2000 instrument at the 3.5-meter telescope at Calar Alto (Almer\'ia, Spain), in staring mode during 5.4 continuous hours, with the telescope defocused, monitoring the target during the expected secondary eclipse. A relative light curve was generated and corrected from systematic effects, using the Principal Component Analysis (PCA) technique. The final light curve was fitted using a transit model to find the eclipse depth and a possible phase shift. The best model obtained from the Markov Chain Monte Carlo analysis resulted in an eclipse depth of $\Delta F$ of $0.137\%^{+0.013\%}_{-0.019\%}$ and a phase offset of $\Delta \phi $ of $-0.0028^{+0.0005}_{-0.0004}$. The eclipse phase offset derived from our modeling has systematic errors that were not taken into account and should not be considered as evidence of an eccentric orbit. The offset in phase obtained leads to a value for $|e\cos{\omega}|$ of $0.0044$. The derived eccentricity is too small to be of any significance.
    Astronomy and Astrophysics 12/2014; DOI:10.1051/0004-6361/201423509 · 4.48 Impact Factor
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    ABSTRACT: Until recently, WASP-43b was an unfamiliar name within a sea of confirmed transiting exoplanets. However, it is now one of the most intensely scrutinized exoplanets to date, joining the ranks of exoplanet archetypes HD 209458b and HD 189733b. In an in-depth investigation into this hot Jupiter's atmospheric composition and circulation, we dedicated 61 HST orbits to obtain a spectroscopic phase curve (the first of its kind with any telescope) from 1.1 to 1.7 microns. With the recent publication of our findings in Science and ApJL, WASP-43b is becoming the subject of numerous theoretical and observational follow-up investigations. Last cycle, we were awarded 26 hours of DDT to observe the transmission, dayside emission, and phase-resolved emission of WASP-43b at 4.5 microns. Here we propose to complete our IR spectrum by repeating our high-precision measurement at 3.6 microns. Data from just one Spitzer channel does not allow for a direct comparison with other Spitzer phase-curve targets and is insufficient to achieve our goals. This is because it is the flux variation between the two Spitzer channels (in conjunction with the HST data) that will enable us to determine the oxygen and carbon abundances in the planet's atmosphere, measure the variation of hot spot offset as a function of altitude, and resolve competing hypotheses on the large day-night WFC3 flux variations. This final point is particularly important because, up until now, Spitzer has been our only window into these planets' day-night contrasts and HST is telling us a different story. With exoplanet phase curves sure to be one of the main enduring Spitzer legacies, we must connect what we have learned from Spitzer to current and future HST data so that we can properly interpret these important measurements of benchmark exoplanets. This will allow us to connect all phase-curve measurements under one theory and predict future spectroscopic results with JWST.
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    ABSTRACT: We propose to observe full orbit phase curves, at 3.6um and 4.5um, of the transiting brown dwarf KELT-1b. KELT-1b is a 27MJ object on a short 1.2 day (29.2 hour) orbit around a bright (V=10.8) F5V star. This system is unique, in that it contains the only known highly irradiated brown dwarf on which it is possible to perform high precision atmospheric measurements, due to KELT-1b's short orbital period and the brightness of its host star. Future work to observationally and theoretically understand the properties of irradiated brown dwarfs will, therefore, rely on our ability to measure the properties of KELT-1b and its atmosphere. Furthermore, a comparison of KELT-1b's Spitzer phase curves to those of similarly irradiated giant planets offers the best possible test of the role of surface gravity in atmospheric circulation. Besides its one-of-a-kind status as an irradiated brown dwarf, KELT-1b is one of the best possible targets for phase curve observations. There are only seven transiting extrasolar giant planets or brown dwarfs with shorter orbital periods (<1.2 days), and all but one (WASP-18b) are around stars at least a magnitude fainter (V>11.8). Our proposed observations will therefore require a relativity low amount of Spitzer time compared to other phase curve proposals (74.5 hours for both bands), and will give very high signal-to-noise ratio (SNR) detections of the phase modulation (estimated SNR of 56 to 74). Our observations will yield one of the best defined phase curve measurements conducted by Spitzer: we estimate a SNR for the phase curve of KELT-1b similar to that achieved on WASP-18b, and a SNR 4 to 5 times higher than the next highest SNR achieved, for the phase curve of HD189733b.
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    ABSTRACT: We have conducted a search for high proper motion brown dwarfs using multi-epoch all-sky mid-infrared images from the WISE satellite. Through this work, we have discovered an object with a parallactic distance of 2.3 pc and a temperature of 250 K, making it the 4th closest neighbor of the Sun, and the coldest known brown dwarf. Because of its extreme proximity and temperature, it represents an unparalleled laboratory for studying planet-like atmospheres in an unexplored temperature regime. We propose to photometrically monitor this object with IRAC to 1) detect and characterize water ice clouds in its atmosphere via the short-term variations induced during rotation and 2) constrain the long-term evolution of its clouds across a period of months.
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    ABSTRACT: Condensate clouds play a critical role in shaping the emergent spectra of both brown dwarfs and gas giant planets. Our understanding of the vertical structure and horizontal distribution of these clouds remains limited, however, because we typically lack the multi-epoch observations required to study the disk-integrated emergent spectrum modulated by the brown dwarf's rotation. Variability studies can be used to advance our understanding of the three dimensional structure of brown dwarf atmospheres but simultaneous, multi-wavelength observations with broad spectral coverage are required. Noticeably absent from all variability studies of brown dwarfs to date are the Y dwarfs which are the coolest brown dwarfs currently known (Teff < 450 K). Our Cycle 9 Spitzer program has shown that Y dwarfs do indeed show variability in the mid-infrared, but to date no near-infrared variability has been detected. We therefore propose an HST/Spitzer case study of the Y0.5 dwarf WISE 1405+5534. We will obtain simultaneous F105W, F125W, [3.6] and [4.5] photometry of this dwarf and compare the light curves to predictions of partly cloudy model atmospheres. These observations will not only provide critical information for dynamical models of brown dwarf atmospheres but also directly inform the interpretation and characterization of cool gas giant exoplanets detected with the next generation of high-contrast imagers like the Gemini Planet Imager (GPI) and the SPHERE instrument for the VLT.
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    ABSTRACT: We propose to obtain two new eclipses of WASP-1b and full-orbit phase curves of CoRoT-2b and WASP-5b at both 3.6 and 4.5 micron. Unlike other short-period planets, these three have emission spectra poorly fit by spectral models of varying complexity (blackbody, self-consistent radiative transfer, or spectral retrieval). This misfit trio has only benefited from single eclipse observations in the crucial Spitzer bandpasses, only one has Spitzer transit depths, and none have had their thermal phase variations measured. The scenarios invoked to explain their unusual eclipse spectra range from high-altitude optical absorbers, silicate clouds near the photosphere, stellar accretion, and detector systematics; all of these hypotheses are testable with the proposed observations. We will establish robust 3.6 and 4.5 micron eclipse measurements by observing two new eclipses of all three planets in each channel. The full-orbit observations of CoRoT-2b and WASP-5b will also allow us to (1) determine their Bond albedo and heat transport efficiency, (2) compare dayside and nightside mid-IR colors, (3) further constrain their atmospheric opacity via transit spectroscopy, and (4) discriminate between astrophysical and atmospheric scenarios for the inscrutable eclipse spectra. Misfits often provide the most leverage for understanding phenomena, and we expect these observations to greatly enhance our understanding or hot Jupiter atmospheres.
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    ABSTRACT: The Kepler mission and radial-velocity surveys have revealed that super-Earth exoplanets are not only ubiquitous in our galaxy but also very diverse in terms of physical properties. However, very little is known about their nature because of the paucity of suitable targets amenable to detailed characterization. Two super-Earths, GJ1214b and 55Cnc e, orbit stars that are bright enough to enable detailed atmospheric and interior composition studies, which are crucial to improve our understanding of this class of exoplanets. As of today, 55Cnc e is the only super Earth amenable to occultation and phase curve infrared photometry, as well as a prime target to understand the nature of highly irradiated super Earths. In the past two years, Spitzer observations of 55 Cnc e resulted in photometric lightcurves of unprecedented quality, thanks to the brightness of its host star. We propose an observing program of 180 hours to pursue this effort. Our main goal is to determine whether 55 Cnc e harbors an atmosphere or not. We propose to obtain four orbital phase curves of 55 Cnc e at 4.5 microns and four other at 3.6 microns. Our observations will unambiguously determine whether 55 Cnc e is volatile-poor or volatile-rich. We will also measure for the first time the 3D climate patterns in a super-Earth atmosphere. Finally, our program will deliver precise transit, occultation and phase-curve photometry that will constitute an important legacy regarding the characterization of a super-Earth exoplanet, well in advance of JWST.
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    ABSTRACT: Exoplanet phase curves provide a wealth of information about atmospheric dynamics, energetics, and chemistry. Phase curves have been observed for relatively few planets, yet the current small sample already hints at the inadequacy of current atmospheric models. Our ultimate goal of understanding the global circulation patterns and their relation to atmospheric chemistry requires a larger and more homogenous sample. Here, we propose to more than double the sample of hot Jupiters with high S/N phase observations by targeting seven bright systems. Combined with the powerful new technique of high-resolution infrared Doppler spectroscopy, our observations will enable an unprecedented comparative study to relate global circulation patterns to atmospheric chemistry, and ultimately to facilitate retrieval of global abundance and temperature maps of extrasolar planets. The planets in our sample represent the best objects to leverage both space-based phase curves and ground-based spectroscopy in a combined analysis. Spectroscopic observations break the inclination degeneracy that plagued earlier non-transiting phase variations, while phase curves provide crucial information about the planetary thermal continuum that is lost in the inherently relative spectroscopic analysis. Our program uses Spitzer's recently-validated snapshot-phase curve mode to obtain high-precision photometry on long timescales with low data volumes and high scheduling flexibility, and our new retrieval approach will become a critical capability in an era of measurements at higher S/N and spectral resolution with JWST and Extremely Large ground-based telescopes.
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    ABSTRACT: We propose a joint Spitzer+HST program to explore the frontier of exoplanet atmosphere dynamics. We will pursue a multi-wavelength approach to create detailed maps of the thermal structure of two of the best target hot Jupiters. First, we will perform secondary eclipse mapping for WASP-18b with Spitzer at 4.5 microns to complement existing Spitzer+HST phase curve observations. The combination of these data will yield the first ever map of an exoplanet's thermal structure as a function of latitude, longitude, and altitude, and provide a benchmark for 3D atmospheric circulation models of highly irradiated planets. Second, we will use a new technique pioneered by our team to observe full-orbit phase curves for WASP-103b with Spitzer and HST/WFC3. These observations will reveal the planet's phase-resolved emission spectrum and determine the global temperature-pressure profile and atmospheric composition, as well as its heat redistribution and Bond albedo. This program will significantly expand the sample of thoroughly characterized exoplanets and enable comparative planetology beyond the Solar System. Spitzer and HST are the facilities that have made the strongest contributions to our understanding of exoplanet atmospheres thus far, and we are now in a position to combine their powers in a strategic way to yield unprecedentedly detailed characterization of hot Jupiter atmospheric dynamics. This program will set the stage for even more precise investigations that will be possible with JWST.
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    ABSTRACT: HAT-P-20b is a giant exoplanet that orbits a metal-rich star. The planet itself has a high total density, suggesting that it may also have a high metallicity in its atmosphere. We analyze two eclipses of the planet in each of the 3.6- and 4.5 micron bands of Warm Spitzer. These data exhibit intra-pixel detector sensitivity fluctuations that were resistant to traditional decorrelation methods. We have developed a simple, powerful, and radically different method to correct the intra-pixel effect for Warm Spitzer data, which we call pixel-level decorrelation (PLD). PLD corrects the intra-pixel effect very effectively, but without explicitly using - or even measuring - the fluctuations in the apparent position of the stellar image. We illustrate and validate PLD using synthetic and real data, and comparing the results to previous analyses. PLD can significantly reduce or eliminate red noise in Spitzer secondary eclipse photometry, even for eclipses that have proven to be intractable using other methods. Our successful PLD analysis of four HAT-P-20b eclipses shows a best-fit blackbody temperature of 1134 +/-29K, indicating inefficient longitudinal transfer of heat, but lacking evidence for strong molecular absorption. We find sufficient evidence for variability in the 4.5 micron band that the eclipses should be monitored at that wavelength by Spitzer, and this planet should be a high priority for JWST spectroscopy. All four eclipses occur about 35 minutes after orbital phase 0.5, indicating a slightly eccentric orbit. A joint fit of the eclipse and transit times with extant RV data yields e(cos{omega}) = 0.01352 (+0.00054, -0.00057), and establishes the small eccentricity of the orbit to high statistical confidence. Given the existence of a bound stellar companion, HAT-P-20b is another excellent candidate for orbital evolution via Kozai migration or other three-body mechanism.

Publication Stats

7k Citations
1,563.75 Total Impact Points

Institutions

  • 2008–2015
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States
  • 2014
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
  • 2001–2014
    • The University of Arizona
      • Department of Planetary Sciences
      Tucson, Arizona, United States
  • 2013
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States
    • Yale University
      • Department of Astronomy
      New Haven, Connecticut, United States
    • University of California, San Diego
      • Department of Physics
      San Diego, California, United States
  • 2011–2013
    • University of Florida
      • Department of Astronomy
      Gainesville, Florida, United States
    • National Optical Astronomy Observatory
      Tucson, Arizona, United States
    • University College London
      • Department of Physics and Astronomy
      London, ENG, United Kingdom
  • 2004–2013
    • NASA
      • Space Science and Astrobiology Division
      Washington, West Virginia, United States
  • 2012
    • Massachusetts Institute of Technology
      • Department of Earth Atmospheric and Planetary Sciences
      Cambridge, Massachusetts, United States
    • University of California, Los Angeles
      • Department of Physics and Astronomy
      Los Angeles, California, United States
  • 2010–2011
    • University of the Pacific (California - USA)
      Stockton, California, United States
  • 2007–2008
    • SETI Institute
      Mountain View, California, United States
    • Purdue University
      West Lafayette, Indiana, United States