D. C. Hines

Space Telescope Science Institute, Baltimore, Maryland, United States

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Publications (364)1043.77 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The James Webb Space Telescope (JWST) will enable a wealth of new scientific investigations in the near- and mid-infrared, with sensitivity and spatial/spectral resolution greatly surpassing its predecessors. In this paper, we focus upon Solar System science facilitated by JWST, discussing the most current information available concerning JWST instrument properties and observing techniques relevant to planetary science. We also present numerous example observing scenarios for a wide variety of Solar System targets to illustrate the potential of JWST science to the Solar System community. This paper updates and supersedes the Solar System white paper published by the JWST Project in 2010. It is based both on that paper and on a workshop held at the annual meeting of the Division for Planetary Sciences in Reno, NV, in 2012.
    No preview · Article · Feb 2016 · Publications of the Astronomical Society of the Pacific
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    ABSTRACT: The coronagraphic instrument (CGI) currently proposed for the Wide-Field Infrared Survey Telescope-Astrophysics Focused Telescope Assets (WFIRST-AFTA) mission will be the first example of a space-based coronagraph optimized for extremely high contrasts that are required for the direct imaging of exoplanets reflecting the light of their host star. While the design of this instrument is still in progress, this early stage of development is a particularly beneficial time to consider the operation of such an instrument. We review current or planned operations on the Hubble Space Telescope and the James Webb Space Telescope with a focus on which operational aspects will have relevance to the planned WFIRST-AFTA CGI. We identify five key aspects of operations that will require attention: (1) detector health and evolution, (2) wavefront control, (3) observing strategies/postprocessing, (4) astrometric precision/target acquisition, and (5) polarimetry. We make suggestions on a path forward for each of these items. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE).
    No preview · Article · Dec 2015
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    ABSTRACT: We present the first images of four debris disks observed in scattered light around the young (4--250 Myr old) M dwarfs TWA 7 and TWA 25, the K6 star HD 35650, and the G2 star HD 377. We obtained these images by reprocessing archival Hubble Space Telescope NICMOS coronagraph data with modern post-processing techniques as part of the Archival Legacy Investigation of Circumstellar Environments (ALICE) program. All four disks appear faint and compact compared with other debris disks resolved in scattered light. The disks around TWA 25, HD 35650, and HD 377 appear very inclined, while TWA 7's disk is viewed nearly face-on. The surface brightness of HD 35650's disk is strongly asymmetric. These new detections raise the number of disks resolved in scattered light around M and late-K stars from one (the AU Mic system) to four. This new sample of resolved disks enables comparative studies of heretofore scarce debris disks around low-mass stars relative to solar-type stars.
    Full-text · Article · Dec 2015
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    ABSTRACT: Polarimetric observations of comets have provided crucial insight into the composition and evolution of cometary dust particles. Herein, we present a brief overview of the polarization properties observed in comets, and some possible interpretations. We also discuss recent imaging polarimetry observations of C/2012 S1 (ISON) and 67 P/Churyumov-Gerasimenko using the Hubble Space Telescope. The observations of 67 P/Churyumov-Gerasimenko are of particular interest, as they were timed to be contemporary with the initial rendezvous of Rosetta and the subsequent landing of the probe Philae. We also outline some unanswered questions and future developments that will greatly enhance our ability to further leverage the power of polarimetry for cometary research.
    No preview · Article · Dec 2015 · Planetary and Space Science
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    ABSTRACT: The coronagraphic instrument currently proposed for the WFIRST-AFTA mission will be the first example of a space-based coronagraph optimized for extremely high contrasts that are required for the direct imaging of exoplanets reflecting the light of their host star. While the design of this instrument is still in progress, this early stage of development is a particularly beneficial time to consider the operation of such an instrument. In this paper, we review current or planned operations on the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST) with a focus on which operational aspects will have relevance to the planned WFIRST-AFTA coronagraphic instrument. We identify five key aspects of operations that will require attention: 1) detector health and evolution, 2) wavefront control, 3) observing strategies/post-processing, 4) astrometric precision/target acquisition, and 5) polarimetry. We make suggestions on a path forward for each of these items.
    Full-text · Article · Nov 2015
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    ABSTRACT: We examine the dispersion of the degree of linear polarization P in comets at phase angle ~90° where the maximum amplitude of positive polarization P max occurs. The range of polarization observed in comets is from 7% up to more than 30%, and this cannot be explained through depolarization by gaseous emissions. Instead, we suggest that the observed dispersion of P results from different properties in cometary dust. We simulate the spectral polarimetric observations of comets using model agglomerated debris particles. The vast majority of observations can be reproduced with a mixture of weakly absorbing and highly absorbing agglomerated debris particles, which obey the same power-law size distribution. Within this extremely simple approach, polarization at side-scattering angles in a given comet is governed by the relative abundance of weakly and strongly absorbing particles. We find that in comets with the highest polarization, the weakly absorbing particles appear in proportions of only 14–23% by volume; whereas, in comets with the lowest polarization P max , their abundance is much greater, 82–95%. We conclude that the polarization at side-scattering angles unambiguously measures the relative abundance of Mg-rich silicates and refractory organics or amorphous carbon in comets. We put forth a hypothesis that low P max could be an indicator for presence of a well-developed refractory surface layer covering cometary nucleus.
    Full-text · Article · Oct 2015 · Planetary and Space Science
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    ABSTRACT: The James Webb Space Telescope (JWST), as the largest space-based astronomical observatory with near- and mid-infrared instrumentation, will elucidate many mysterious aspects of comets. We summarize four cometary science themes especially suited for this telescope and its instrumentation: the drivers of cometary activity, comet nucleus heterogeneity, water ice in comae and on surfaces, and activity in faint comets and main-belt asteroids. With JWST, we can expect the most distant detections of gas, especially CO2, in what we now consider to be only moderately bright comets. For nearby comets, coma dust properties can be studied with their driving gases, measured simultaneously with the same instrument or contemporaneously with another. Studies of water ice and gas in the distant Solar System will help us test our understanding of cometary interiors and coma evolution. The question of cometary activity in main-belt comets will be further explored with the possibility of a direct detection of coma gas. We explore the technical approaches to these science cases and provide simple tools for estimating comet dust and gas brightness. Finally, we consider the effects of the observatory's non-sidereal tracking limits, and provide a list of potential comet targets during the first 5 years of the mission.
    No preview · Article · Oct 2015 · Publications of the Astronomical Society of the Pacific
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    ABSTRACT: In the 1980s, excess infrared emission was discovered around main-sequence stars; subsequent direct-imaging observations revealed orbiting disks of cold dust to be the source. These ' debris disks' were thought to be by-products of planet formation because they often exhibited morphological and brightness asymmetries that may result from gravitational perturbation by planets. This was proved to be true for the β Pictoris system, in which the known planet generates an observable warp in the disk. The nearby, young, unusually active late-type star AU Microscopii hosts a well-studied edge-on debris disk; earlier observations in the visible and near-infrared found asymmetric localized structures in the form of intensity variations along the midplane of the disk beyond a distance of 20 astronomical units. Here we report high-contrast imaging that reveals a series of five large-scale features in the southeast side of the disk, at projected separations of 10-60 astronomical units, persisting over intervals of 1-4 years. All these features appear to move away from the star at projected speeds of 4-10 kilometres per second, suggesting highly eccentric or unbound trajectories if they are associated with physical entities. The origin, localization, morphology and rapid evolution of these features are difficult to reconcile with current theories.
    No preview · Article · Oct 2015 · Nature
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    ABSTRACT: We analyze the first color and polarization images of Comet ISON (C/2012 S1) taken during two measurement campaigns of the Hubble Space Telescope (HST) on UTC 2013 April 10 and May 8, when the phase angle of Comet ISON was α ≈ 13.7 º and 12.2º, respectively. We model the particles in the coma using highly irregular agglomerated debris particles. Even though the observations were made over a small range of phase angle, the data still place significant constraints on the material properties of the cometary coma. The different photo-polarimetric responses are indicative of spatial chemical heterogeneity of coma in Comet ISON. For instance, at small projected distances to the nucleus (<500 km), our modeling suggests the cometary particles are composed predominantly of small, highly absorbing particles, such as amorphous carbon and/or organics material heavily irradiated with UV radiation; whereas, at longer projected distances (>1000 km), the refractive index of the particles is consistent with organic matter slightly processed with UV radiation, tholins, Mg-Fe silicates, and/or Mg-rich silicates contaminated with ~10% (by volume) amorphous carbon. The modeling suggests low relative abundances of particles with low material absorption in the visible, i.e., Im(m) <= 0.02. Such particles were detected unambiguously in other comets in the vicinity of nucleus through very strong negative polarization near backscattering (P ≈ –6%) and very low positive polarization (P ≈ 3–5%) at side scattering. These materials were previously attributed to Mg-rich silicates forming a refractory surface layer on the surface of cometary nuclei (Zubko et al., 2012). The absence of such particles in Comet ISON could imply an absence of such a layer on its nucleus.
    Full-text · Article · Aug 2015 · Planetary and Space Science
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    ABSTRACT: The imaging channel on the Mid-Infrared Instrument (MIRI) is equipped with four coronagraphs that provide high contrast imaging capabilities for studying faint point sources and extended emission that would otherwise be overwhelmed by a bright point-source in its vicinity. Such bright sources might include stars that are orbited by exoplanets and circumstellar material, mass-loss envelopes around post-main-sequence stars, the near-nuclear environments in active galaxies, and the host galaxies of distant quasars. This paper describes the coronagraphic observing modes of MIRI, as well as performance estimates based on measurements of the MIRI flight model during cryo-vacuum testing. A brief outline of coronagraphic operations is also provided. Finally, simulated MIRI coronagraphic observations of a few astronomical targets are presented for illustration.
    Full-text · Article · Aug 2015 · Publications of the Astronomical Society of the Pacific
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    ABSTRACT: We describe the operations concept and data reduction plan for the Mid- Infrared Instrument (MIRI) for the James Webb Space Telescope (JWST). The overall JWST operations concept is to use Observation Templates (OTs) to provide a straightforward and intuitive way for users to specify observations. MIRI has four OTs that correspond to the four observing modes: 1.) Imaging, 2.) Coronagraphy, 3.) Low Resolution Spectroscopy, and 4.) Medium Resolution Spectroscopy. We outline the user choices and expansion of these choices into detailed instrument operations. The data reduction plans for MIRI are split into three stages, where the specificity of the reduction steps to the observation type increases with stage. The reduction starts with integration ramps: stage 1 yields uncalibrated slope images; stage 2 calibrates the slope images; and then stage 3 combines multiple calibrated slope images into high level data products (e.g. mosaics, spectral cubes, and extracted source information). Finally, we give examples of the data and data products that will be derived from each of the four different OTs.
    Full-text · Article · Aug 2015 · Publications of the Astronomical Society of the Pacific
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    ABSTRACT: We report the presence of scattered light from dust grains located in the giant planet formation region of the circumbinary disk orbiting the ~20-Myr-old close (~0.045 AU separation) binary system V4046 Sgr AB based on observations with the new Gemini Planet Imager (GPI) instrument. These GPI images probe to within ~7 AU of the central binary with linear spatial resolution of ~3 AU, and are thereby capable of revealing dust disk structure within a region corresponding to the giant planets in our solar system. The GPI imaging reveals a relatively narrow (FWHM ~10 AU) ring of polarized near-infrared flux whose brightness peaks at ~14 AU. This ~14 AU radius ring is surrounded by a fainter outer halo of scattered light extending to ~45 AU, which coincides with previously detected mm-wave thermal dust emission. The presence of small grains that efficiently scatter starlight well inside the mm-wavelength disk cavity supports current models of planet formation that suggest planet-disk interactions can generate pressure traps that impose strong radial variations in the particle size distribution throughout the disk.
    Preview · Article · Mar 2015
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    ABSTRACT: Most stars form surrounded by dusty disks of circumstellar matter. Initially gas rich, these disks give birth to planetary systems through complex physical processes which are still poorly understood. Spatially resolved images of protoplanetary disks are essential to measure their physical properties and constrain the processes of planet formation. As protoplanets grow in mass, they can begin carving out regions cleared of smaller bodies, leading to complex transitional disk structures as planetary assembly progresses. Once primordial gas has dissipated, dynamical stirring can increase the relative velocities of remaining planetesimals and collisional accretion gives way to collisional destruction. Dust particles produced through collisional cascades will eventually be driven from the system by radiative forces or stellar winds; in quasi-equilibrium, the transient populations of dust give rise to debris disks that persist for tens or hundreds of millions of years. Debris disks are analogous to the zodiacal dust in our own solar system produced from comets, asteroids, and Kuiper Belt objects, though currently observable examples are generally younger and have higher optical depth than our solar system today. Throughout this evolution of circumstellar disks from protoplanetary to transitional to debris, starlight scatters from their constituent dust particles, and in doing so becomes polarized. This induced linear polarization, which can easily exceed values of more than 50%, renders polarimetry an especially potent tool for studying circumstellar disks. In recent years such observations have been extended to high angular resolution via diffraction-limited observations made with adaptive optics (AO) or using the Hubble Space Telescope (HST). In this chapter we concern ourselves particularly with spatially resolved imaging linear polarimetry of circumstellar disks, mostly at optical and near infrared (IR) wavelengths (Fig. 15.1). Broadly speaking, applications of imaging polarimetry to circumstellar disks fall into two classes: (1) Using polarization to gain increased sensitivity to faint circumstellar material against the background halo of relatively weakly polarized starlight. […]
    No preview · Chapter · Jan 2015
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    ABSTRACT: This article summarizes a workshop held on March, 2014, on the potential of the James Webb Space Telescope (JWST) to revolutionize our knowledge of the physical properties of exoplanets through transit observations. JWST’s unique combination of high sensitivity and broad wavelength coverage will enable the accurate measurement of transits with high signal-to-noise ratio (S/N). Most importantly, JWST spectroscopy will investigate planetary atmospheres to determine atomic and molecular compositions, to probe vertical and horizontal structure, and to follow dynamical evolution, i.e., exoplanet weather. JWST will sample a diverse population of planets of varying masses and densities in a wide variety of environments characterized by a range of host star masses and metallicities, orbital semi-major axes, and eccentricities. A broad program of exoplanet science could use a substantial fraction of the overall JWST mission. © 2014. The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A.
    No preview · Article · Dec 2014 · Publications of the Astronomical Society of the Pacific
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    ABSTRACT: This article summarizes a workshop held on March, 2014, on the potential of the James Webb Space Telescope (JWST) to revolutionize our knowledge of the physical properties of exoplanets through transit observations. JWST's unique combination of high sensitivity and broad wavelength coverage will enable the accurate measurement of transits with high signal-to-noise. Most importantly, JWST spectroscopy will investigate planetary atmospheres to determine atomic and molecular compositions, to probe vertical and horizontal structure, and to follow dynamical evolution, i.e. exoplanet weather. JWST will sample a diverse population of planets of varying masses and densities in a wide variety of environments characterized by a range of host star masses and metallicities, orbital semi-major axes and eccentricities. A broad program of exoplanet science could use a substantial fraction of the overall JWST mission.
    Full-text · Article · Nov 2014
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    ABSTRACT: We present the results of ongoing coronagraphic simulations aimed at designing strategies for optimizing oper- ations of the coronagraphs in the mid-infrared instrument (MIRI) on-board the James Webb Space Telescope (JWST). In particular, the adverse effects on the point spread function caused by the phase mask coronagraphs and the observatory slew accuracy are known to limit our ability to position stars at the center of the coron- agraph. Here, we investigate these two effects on our ability to perform target acquisition (TA) and consider different scenarios involving single and multiple acquisitions to mitigate them. We assess the performance of the coronagraphs under various slew accuracy models as well as noise sources. In general, we find that scenarios that require fewer acquisitions yield final positions with smaller dispersions but larger offsets. Our Single TA scenario yields the best repeatability for all three slew accuracy models that we considered although a dual Twin TA strategy generally yields more accurate centering. We also investigate the use of the contamination control cover (CCC) inside MIRI during TA of bright objects, and ways to mitigate the resulting latent images when the CCC is not used. Our results are expressed in terms of achieved contrast with simple, single reference star subtraction. Given our preliminary prescription for latency, our simulations suggest that the CCC need not be used except for very bright sources; detailed guidelines will require additional information on the latent image decay time scale. Furthermore, we find that contrast is dependent on the observatory slew accuracy at any wavelength. The highest contrast is achieved with the highest slew accuracy model, although the background photon noise limits the contrast at longer wavelengths.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: Coronagraphic Target Acquisition (TA) is an important factor that contributes to the contrast performance and typically depends on the coronagraph design. In the case of JWST, coronagraphic TAs rely on measuring the centroid of the star's point spread function away from the focal plane mask, and performing a small angle ma- neuver (SAM), to place the star behind the coronagraphic mask. Therefore, the accuracy of the TA is directly limited by the SAM accuracy. Typically JWST coronagraphic observations will include the subtraction of a reference (either a reference star, or a self-reference after a telescope roll). With such differential measurement, the reproducibility of the TA is a very important factor. We propose a novel coronagraphic observation concept whereby the reference PSF is first acquired using a standard TA, followed by coronagraphic observations of a reference star on a small grid of dithered positions. Sub-pixel dithers (5-10 mas each) provide a small reference PSF library that samples the variations in the PSF as a function of position relative to the mask, thus compen- sating for errors in the TA process. This library can be used for PSF subtraction with a variety of algorithms (e.g; LOCI or KLIP algorithms, Lafrenière et al. 2007; Soummer, Pueyo and Larkin 2012). These sub-pixel dithers are executed under closed-loop fine guidance, unlike a standard SAM that executes the maneuver in coarse point mode, which can result in a temporary target offset of 1 arcsecond and would bring the star out from behind the coronagraphic mask. We discuss and evaluate the performance gains from this observation scenario compared to the standard TA both for MIRI coronagraphs.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: When giant planets form, they grow by accreting gas and dust. HD 142527 is a young star that offers a scaled-up view of this process. It has a broad, asymmetric ring of gas and dust beyond \about 100 AU and a wide inner gap. Within the gap, a low-mass stellar companion orbits the primary star at just \about 12 AU, and both the primary and secondary are accreting gas. In an attempt to directly detect the dusty counterpart to this accreted gas, we have observed HD 142527 with the Gemini Planet Imager in polarized light at $Y$ band (0.95-1.14 \microns). We clearly detect the companion in total intensity and show that its position and photometry are generally consistent with the expected values. We also detect a point-source in polarized light that may be spatially separated by \about a few AU from the location of the companion in total intensity. This suggests that dust is likely falling onto or orbiting the companion. Given the possible contribution of scattered light from this dust to previously reported photometry of the companion, the current mass limits should be viewed as upper limits only. If the dust near the companion is eventually confirmed to be spatially separated, this system would resemble a scaled-up version of the young planetary system inside the gap of the transition disk around LkCa 15.
    Preview · Article · Jul 2014 · The Astrophysical Journal Letters
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    ABSTRACT: The present and next few years will see the arrival of several new coronagraphic instruments dedicated to the detection and characterization of planetary systems. These ground- and space-based instruments (Gemini/GPI, VLT/SPHERE, Subaru/ CHARIS, JWST NIRCam and MIRI coronagraphs among others), will provide a large number of new candidates, through multiple nearby-star surveys and will complete and extend those acquired with current generation instruments (Palomar P1640, VLT/NACO, Keck, HST). To optimize the use of the wealth of data, including non-detection results, the science products of these instruments will require to be shared among the community. In the long term such data exchange will significantly ease companion confirmations, planet characterization via different type of instruments (integral field spectrographs, polarimetric imagers, etc.), and Monte-Carlo population studies from detection and non-detection results. In this context, we initiated a collaborative effort between the teams developing the data reduction pipelines for SPHERE, GPI, and the JWST coronagraphs, and the ALICE (Archival Legacy Investigations of Circumstellar Environment) collaboration, which is currently reprocessing all the HST/NICMOS coronagraphic surveys. We are developing a standard format for the science products generated by high-contrast direct imaging instruments (reduced image, sensitivity limits, noise image, candidate list, etc.), that is directly usable for astrophysical investigations. In this paper, we present first results of this work and propose a preliminary format adopted for the science product. We call for discussions in the high-contrast direct imaging community to develop this effort, reach a consensus and finalize this standard. This action will be critical to enable data interchange and combination in a consistent way between several instruments and to stiffen the scientific production in the community.
    Full-text · Conference Paper · Jul 2014
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    ABSTRACT: Mid-infrared spectral observations Uranus acquired with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope are used to determine the abundances of C2H2, C2H6, CH3C2H, C4H2, CO2, and tentatively CH3 on Uranus at the time of the 2007 equinox. For vertically uniform eddy diffusion coefficients in the range 2200-2600 cm2 s-1, photochemical models that reproduce the observed methane emission also predict C2H6 profiles that compare well with emission in the 11.6-12.5 micron wavelength region, where the nu9 band of C2H6 is prominent. Our nominal model with a uniform eddy diffusion coefficient Kzz = 2430 cm2 sec-1 and a CH4 tropopause mole fraction of 1.6x10-5 provides a good fit to other hydrocarbon emission features, such as those of C2H2 and C4H2, but the model profile for CH3C2H must be scaled by a factor of 0.43, suggesting that improvements are needed in the chemical reaction mechanism for C3Hx species. The nominal model is consistent with a CH3D/CH4 ratio of 3.0+-0.2x10-4. From the best-fit scaling of these photochemical-model profiles, we derive column abundances above the 10-mbar level of 4.5+01.1/-0.8 x 10+19 molecule-cm-2 for CH4, 6.2 +- 1.0 x 10+16 molecule-cm-2 for C2H2 (with a value 24% higher from a different longitudinal sampling), 3.1 +- 0.3 x 10+16 molecule-cm-2 for C2H6, 8.6 +- 2.6 x 10+13 molecule-cm-2 for CH3C2H, 1.8 +- 0.3 x 10+13 molecule-cm-2 for C4H2, and 1.7 +- 0.4 x 10+13 molecule-cm-2 for CO2 on Uranus. Our results have implications with respect to the influx rate of exogenic oxygen species and the production rate of stratospheric hazes on Uranus, as well as the C4H2 vapor pressure over C4H2 ice at low temperatures.
    Full-text · Article · Jul 2014 · Icarus

Publication Stats

8k Citations
1,043.77 Total Impact Points

Institutions

  • 2011-2016
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
    • New Mexico State University
      • Department of Astronomy
      Las Cruces, New Mexico, United States
  • 2013
    • University of Concepción
      • Departamento de Astronomía
      Ciudad de Concepcion, Biobío, Chile
  • 2006-2011
    • The Space Science Institute
      Boulder, Colorado, United States
  • 2010
    • University of New Mexico
      • Department of Physics & Astronomy
      Albuquerque, New Mexico, United States
    • University of Cincinnati
      • Department of Physics
      Cincinnati, Ohio, United States
  • 2009
    • University of Texas at Austin
      • Department of Astronomy
      Austin, Texas, United States
    • University of Illinois, Urbana-Champaign
      • Department of Astronomy
      Urbana, Illinois, United States
  • 1997-2009
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
  • 2007
    • University of California, Los Angeles
      • Department of Physics and Astronomy
      Los Angeles, California, United States
    • California State University, Los Angeles
      • Department of Physics and Astronomy
      Los Angeles, California, United States
  • 2005
    • University of Colorado at Boulder
      Boulder, Colorado, United States
  • 2003
    • Arizona State University
      • School of Earth and Space Exploration
      Phoenix, Arizona, United States
  • 1998-1999
    • University of Hawaiʻi at Hilo
      Hilo, Hawaii, United States