Christopher J. Campo

Keele University, Newcastle-under-Lyme, England, United Kingdom

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Publications (19)83.3 Total impact

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    ABSTRACT: WASP-8b has 2.18 times Jupiter's mass and is on an eccentric (e = 0.31) 8.16 day orbit. With a time-averaged equilibrium temperature of 948 K, it is one of the least-irradiated hot Jupiters observed with the Spitzer Space Telescope. We have analyzed six photometric light curves of WASP-8b during secondary eclipse observed in the 3.6, 4.5, and 8.0 μm Infrared Array Camera bands. The eclipse depths are 0.113% ± 0.018%, 0.069% ± 0.007%, and 0.093% ± 0.023%, respectively, giving respective brightness temperatures of 1552, 1131, and 938 K. We characterized the atmospheric thermal profile and composition of the planet using a line-by-line radiative transfer code and a Markov-chain Monte Carlo sampler. The data indicated no thermal inversion, independently of any assumption about chemical composition. We noted an anomalously high 3.6 μm brightness temperature (1552 K); by modeling the eccentricity-caused thermal variation, we found that this temperature is plausible for radiative timescales less than ~102 hr. However, as no model spectra fit all three data points well, the temperature discrepancy remains as an open question.
    The Astrophysical Journal 04/2013; 768(1):42. · 6.73 Impact Factor
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    ABSTRACT: We report the detection of UCF-1.01, a strong exoplanet candidate with a radius 0.66 +/- 0.04 times that of Earth (R_{\oplus}). This sub-Earth-sized planet transits the nearby M-dwarf star GJ 436 with a period of 1.365862 +/- 8x10^{-6} days. We also report evidence of a 0.65 +/- 0.06 R_{\oplus} exoplanet candidate (labeled UCF-1.02) orbiting the same star with an undetermined period. Using the Spitzer Space Telescope, we measure the dimming of light as the planets pass in front of their parent star to assess their sizes and orbital parameters. If confirmed, UCF-1.01 and UCF-1.02 would be called GJ 436c and GJ 436d, respectively, and would be part of the first multiple-transiting-planet system outside of the Kepler field. Assuming Earth-like densities of 5.515 g/cm^3, we predict both candidates to have similar masses (~0.28 Earth-masses, M_{\oplus}, 2.6 Mars-masses) and surface gravities of ~0.65 g (where g is the gravity on Earth). UCF-1.01's equilibrium temperature (T_{eq}, where emitted and absorbed radiation balance for an equivalent blackbody) is 860 K, making the planet unlikely to harbor life as on Earth. Its weak gravitational field and close proximity to its host star imply that UCF-1.01 is unlikely to have retained its original atmosphere; however, a transient atmosphere is possible if recent impacts or tidal heating were to supply volatiles to the surface. We also present additional observations of GJ 436b during secondary eclipse. The 3.6-micron light curve shows indications of stellar activity, making a reliable secondary eclipse measurement impossible. A second non-detection at 4.5 microns supports our previous work in which we find a methane-deficient and carbon monoxide-rich dayside atmosphere.
    The Astrophysical Journal 07/2012; 755(1). · 6.73 Impact Factor
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    ABSTRACT: We report detection of thermal emission from the exoplanet WASP-19b at 3.6, 4.5, 5.8 and 8.0 micron. We used the InfraRed Array Camera on the Spitzer Space Telescope to observe two occultations of WASP-19b by its host star. We combine our new detections with previous measurements of WASP-19b's emission at 1.6 and 2.09 micron to construct a spectral energy distribution of the planet's dayside atmosphere. By comparing this with model-atmosphere spectra, we find that the dayside atmosphere of WASP-19b lacks a strong temperature inversion. As WASP-19 is an active star (log RHK = -4.50 +/- 0.03), this finding supports the hypothesis of Knutson, Howard & Isaacson (2010) that inversions are suppressed in hot Jupiters orbiting active stars. The available data are unable to differentiate between a carbon-rich and an oxygen-rich atmosphere.
    Monthly Notices of the Royal Astronomical Society 12/2011; 430(4). · 5.52 Impact Factor
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    ABSTRACT: WASP-14b belongs to a class of highly irradiated hot Jupiters (Teq = 1866 K) with a mass of 7.3 \pm 0.5 MJ and a radius of 1.28 \pm 0.08 RJ . With a mean density of 4.6 gcm-3, this transiting planet is one of the densest known to date (Joshi et al. 2009), for planets with periods less than 3 days. We present analytic light-curve models for three Spitzer secondary eclipses, Keplerian orbital model, estimates of infrared brightness temperatures, and constraints on atmospheric composition and thermal structure. Although extremely irradiated, WASP-14b does not show any distinctive evidence of a thermal inversion, based on existing observations. In addition, the observations indicate low day-night redistribution (fr<0.25) and are consistent with chemical compositions at nearly solar abundances. We confirm a significant eccentricity of e = 0.087 \pm 0.002 and refine other orbital parameters.
    The Astrophysical Journal 11/2011; · 6.73 Impact Factor
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    ABSTRACT: The transiting exoplanet WASP-18b was discovered in 2008 by the Wide Angle Search for Planets project. The Spitzer Exoplanet Target of Opportunity Program observed secondary eclipses of WASP-18b using Spitzer's Infrared Array Camera in the 3.6 μm and 5.8 μm bands on 2008 December 20, and in the 4.5 μm and 8.0 μm bands on 2008 December 24. We report eclipse depths of 0.30% ± 0.02%, 0.39% ± 0.02%, 0.37% ± 0.03%, 0.41% ± 0.02%, and brightness temperatures of 3100 ± 90, 3310 ± 130, 3080 ± 140, and 3120 ± 110 K in order of increasing wavelength. WASP-18b is one of the hottest planets yet discovered—as hot as an M-class star. The planet's pressure-temperature profile most likely features a thermal inversion. The observations also require WASP-18b to have near-zero albedo and almost no redistribution of energy from the day side to the night side of the planet.
    The Astrophysical Journal 11/2011; 742(1):35. · 6.73 Impact Factor
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    ABSTRACT: We report the detection of thermal emission at 4.5 and 8 micron from the planet WASP-17b. We used Spitzer to measure the system brightness at each wavelength during two occultations of the planet by its host star. By combining the resulting light curves with existing transit light curves and radial velocity measurements in a simultaneous analysis, we find the radius of WASP-17b to be 2.0 Rjup, which is 0.2 Rjup larger than any other known planet and 0.7 Rjup larger than predicted by the standard cooling theory of irradiated gas giant planets. We find the retrograde orbit of WASP-17b to be slightly eccentric, with 0.0012 < e < 0.070 (3 sigma). Such a low eccentricity suggests that, under current models, tidal heating alone could not have bloated the planet to its current size, so the radius of WASP-17b is currently unexplained. From the measured planet-star flux-density ratios we infer 4.5 and 8 micron brightness temperatures of 1881 +/- 50 K and 1580 +/- 150 K, respectively, consistent with a low-albedo planet that efficiently redistributes heat from its day side to its night side.
    Monthly Notices of the Royal Astronomical Society 01/2011; 416(3). · 5.52 Impact Factor
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    ABSTRACT: We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity, leading to an estimate of the tidal Love number and an assessment of the degree of central concentration in the planetary interior. An initial ground-based secondary-eclipse phase reported by López-Morales et al. (0.510 ± 0.002) implied eccentricity at the 4.5σ level. The spectroscopic orbit of Hebb et al. has eccentricity 0.049 ± 0.015, a 3σ result, implying an eclipse phase of 0.509 ± 0.007. However, there is a well-documented tendency of spectroscopic data to overestimate small eccentricities. Our eclipse phases are 0.5010 ± 0.0006 (3.6 and 5.8 μm) and 0.5006 ± 0.0007 (4.5 and 8.0 μm). An unlikely orbital precession scenario invoking an alignment of the orbit during the Spitzer observations could have explained this apparent discrepancy, but the final eclipse phase of López-Morales et al. (0.510 ±+0.007 –0.006) is consistent with a circular orbit at better than 2σ. An orbit fit to all the available transit, eclipse, and radial-velocity data indicates precession at <1σ; a non-precessing solution fits better. We also comment on analysis and reporting for Spitzer exoplanet data in light of recent re-analyses.
    The Astrophysical Journal 01/2011; 727(2):125. · 6.73 Impact Factor
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    ABSTRACT: The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O ≥ 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T > 2,500 K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.
    Nature 01/2011; 469(7328):64-7. · 38.60 Impact Factor
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    ABSTRACT: Exoplanet WASP-12b has a period of 1.09 days and is close enough to its G0 star that, if eccentric, its orbital precession period of a few decades could be measureable in just a few years with high-precsion secondary eclipse measurements. We observed four secondary eclipses of WASP-12b with the Spitzer Space Telescope separated by several years. Combined with ground-based transit and radial-velocity measurements, we find a small eccentricity but no measurable precession. However, the eclipse depths have S/N as high as 29, among the highest ever obtained. The brightness temperatures are 3000 K, allowing atmospheric characterization at a nearly unprecedented level, especially when combined with the ground-based, near-infrared eclipses of Croll et al. Our analysis used a Markov-Chain Monte Carlo method to explore the space of thermal profiles and molecular abundances of CO, CH4, H2O, CO2, and included also collision-induced absorption and TiO/VO. It calculated over 4 million spectra and integrated them over the seven secondary eclipse bandpasses to compare to the observations. We will present the results at the meeting.
    01/2011;
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    ABSTRACT: We present our analysis of six Spitzer Space Telescope secondary eclipse observations of WASP-8b at 3.6, 4.5, and 8.0 μm. We derived light-curves, determined the planet's day-side infrared emission, and characterized the planet's atmosphere. We found a solar chemical composition, the absence of a thermal inversion layer, and a low energy redistribution over its surface.
    Boletin de la Asociacion Argentina de Astronomia La Plata Argentina. 01/2011;
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    ABSTRACT: The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior as opposed to a silicate-dominated composition as found on Earth, and the atmospheres can also differ from those in the Solar System. The solar C/O is 0.54. Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b that reveals C/O >= 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapor and enhanced in methane by over two orders of magnitude each compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T > 2,500 K) of WASP-12b lacks a prominent thermal inversion, or a stratosphere, and has very efficient day- night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres. Comment: Discovery of the first carbon-rich planet. To be published in Nature online on 9 Dec 2010. Accepted version is posted here. Please see published paper for final version with minor proof edits
    12/2010;
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    ABSTRACT: WASP-14b is a hot Jupiter planet (Y. C. Joshy et al. 2009, MNRAS 392, 1532-1538) with mass (7.3 Jupiter masses) and density (4.6 g/cm3) that exceed those of most known extrasolar planets. It is very close to its host star (semimajor axis = 0.036 AU), giving it a typical equilibrium temperature of 1800 K for 0 albedo, circular orbit, and uniform reemission. In addition, its significant orbital eccentricity (0.09) suggests the possibility of a companion planet. All of the above makes this object very interesting for atmospheric study. Spitzer program 60021 (H. Knutson, PI) obtained a secondary eclipse light curve at 3.6 microns on 2010-03-19 and the Spitzer Exoplanet Target of Opportunity Program (program 50517, J. Harrington, PI) obtained eclipse data at 4.5 and 8.0 microns on 2009-03-18. Analytic light curve models fit the data using a Metropolis-Hastings Markov Chain Monte Carlo (MCMC) algorithm that incorporates corrections for systematic effects. We present estimates of infrared brightness temperatures and constraints on atmospheric composition and thermal structure. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech.
    10/2010;
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    ABSTRACT: The Spitzer Exoplanet Target-of-Opportunity program has observed the secondary eclipses of several planets in suspected eccentric orbits around their host stars. The midpoint time determined from each observation can be combined with radial velocity (RV) and transit data to provide improved sets of orbital parameters for a given exoplanet. The orbital phase of the midpoint can be used to establish lower limits on the eccentricity (particularly on ecosomega, where e is eccentricity and omega is the argument of periastron) that are independent of RV data. Multiple midpoints can be used to detect parameter variation. We present results for WASP-12b (e < 0.06), WASP-14b (e 0.087), WASP-18b (e 0.0088), GJ 436b (e 0.1368), and HAT-P-13b; discussion of techniques of joint orbital modeling, including methods of detecting apsidal motion; dynamical implications for selected systems; and the role of amateur observers as sources of exoplanet data. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA, which provided support for this work.
    10/2010;
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    ABSTRACT: WASP-12b is one of the largets planets yet discovered, with an inflated radius of 1.79 Rjup. It also lies in very close proximity to its G-type star, with a semi-major axis of 0.0229 AU and orbital period of only 1.09 days. It is one of the hottest exoplanets discovered to date as well, with an equilibrium temperature of 2516 K for zero albedo and uniform redistribution of incident flux. We observed four secondary eclipses of the WASP-12b using Spitzer's Infrared Array Camera (IRAC), which yielded six separate eclipse lightcurves over the IRAC wavelengths (2x3.6, 2x4.5, 5.8, and 8.0 mum). From these observations, we are able to constrain the planet's orbital and atmospheric properties, such as eccentricity, atmospheric composition, and thermal structure. The secondary eclipse photometry is presented along with our analysis. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA, which provided support for this work.
    10/2010;
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    ABSTRACT: The transiting exoplanet WASP-18b was discovered in 2008 by the Wide Angle Search for Planets (WASP) project. The Spitzer Exoplanet Target of Opportunity Program observed secondary eclipses of WASP-18b using Spitzer's Infrared Array Camera (IRAC) in the 3.6 micron and 5.8 micron bands on 2008 December 20, and in the 4.5 micron and 8.0 micron bands on 2008 December 24. We present a pressure-temperature profile, eclipse depths and brightness temperatures of WASP-18b, which is one of the hottest planets yet discovered, as hot as an M-dwarf star. These observations are part of the Spitzer Exoplanet Target of Opportunity program, which observes eclipses and transits of new exoplanets. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA, which provided support for this work.
    09/2010; 42:1063.
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    ABSTRACT: We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity. The ground-based secondary eclipse phase reported by Lopez-Morales et al. (0.510 +/- 0.002) implies eccentricity at the 4.5\sigma level, and the spectroscopic orbit of Hebb et al. has eccentricity 0.049 +/- 0.015, a 3\sigma result, and predicts an eclipse phase of 0.509 +/- 0.007. Our eclipse phases are 0.5012 +/- 0.0006 (3.6 and 5.8 micron) and 0.5007 +/- 0.0007 (4.5 and 8.0 micron). These values are inconsistent with the ground-based data, but marginally consistent with the spectroscopic orbit. Considering the unlikely possibility that precession brought the long axis of the orbit into alignment during our observations, a model considering these points and transit times from professional and amateur observers estimates orbital precession at \omega = 0.02 +/- 0.01 deg/d. This implies a tidal Love number, k2p, of 0.15 +/- 0.08, indicating a very centrally condensed planet. However, if the orbit is actually eccentric, we have observed it at a remarkably special time to find eclipse phases consistent with apsidal alignment. Future observations can decide between these possibilities. Comment: 6 pages, 3 figures, electronic supplements to appear with published paper.
    03/2010;
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    ABSTRACT: HD 149026b is a Saturn-sized, transiting exoplanet that orbits a metal-rich star. Its 80 M⊕ of heavy elements exceed the solar system's entire complement, making it one of the most exotic worlds yet detected. We present secondary eclipses of HD 149026b observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8, and 16 μm. Taken under the Spitzer Exoplanet Target of Opportunity program and other programs, these data provide constraints on the planet's emission spectrum and temperature. As a small planet orbiting a relatively large and bright star, HD 149026b is a challenging target. We will discuss a variety of observing methods (including preflash and preburn) and Spitzer systematic models used to recover the planetary signal. A companion talk by Hardy et al. will provide constraints on the eccentricity and argument of periapsis due to the precise phase of secondary eclipse. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA, which provided support for this work.
    08/2009; 41.
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    ABSTRACT: We observed two secondary eclipses of the transiting exoplanet HAT-P-7b, which resides in the Kepler field of view. These observations were made using the Infrared Array Camera on the Spitzer Space Telescope. HAT-P-7b is a hot Jupiter that lies approximately 0.04 AU from its parent star. It has an approximately circular orbit and an equilibrium temperature of 2730K assuming immediate re-radiation of incident flux and 0 Bond albedo. We observed an eclipse of this planet at 3.6 and 5.8 µm on 28 October 2008 and at 4.5 and 8 µm on 30 October 2008. We will present estimates of infrared brightness temperatures and the use of a preflash to stabilize detector levels prior to observing the event. A companion talk by Hardy et al. will provide constraints on the eccentricity and argument of periapsis due to the precise phase of secondary eclipse. These observations are part of the Spitzer Exoplanet Target of Opportunity program, which observes eclipses and transits of new exoplanets. Spitzer is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA, which provided support for this work.
    01/2009;
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    ABSTRACT: We have recently discovered the first carbon-rich planetary atmosphere. In this talk, we will present the atmospheric composition and temperature structure of this exoplanet, along with the modeling technique that revealed the exotic atmosphere. We used a Bayesian analysis to constrain the atmospheric properties of this exoplanet based on broadband photometric observations. Carbon-rich planets present a new regime in atmospheric chemistry and temperature structure, planetary interiors, planet formation, and astrobiology. We will discuss these various aspects and their observable signatures.

Publication Stats

160 Citations
83.30 Total Impact Points

Institutions

  • 2013
    • Keele University
      • Department of Physics and Astrophysics
      Newcastle-under-Lyme, England, United Kingdom
  • 2011–2012
    • University of Central Florida
      • Department of Physics
      Orlando, Florida, United States
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States