I. de Pater

Delft University of Technology, Delft, South Holland, Netherlands

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Publications (388)700.06 Total impact

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    Full-text · Article · Dec 2015 · Astronomy and Astrophysics
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    ABSTRACT: Context. Observing Jupiter's synchrotron emission from the Earth remains today the sole method to scrutinize the distribution and dynamical behavior of the ultra energetic electrons magnetically trapped around the planet (because in-situ particle data are limited in the inner magnetosphere). Aims. We perform the first resolved and low-frequency imaging of the synchrotron emission with LOFAR at 127 MHz. The radiation comes from low energy electrons (~1-30 MeV) which map a broad region of Jupiter's inner magnetosphere. Methods (see article for complete abstract) Results. The first resolved images of Jupiter's radiation belts at 127-172 MHz are obtained along with total integrated flux densities. They are compared with previous observations at higher frequencies and show a larger extent of the synchrotron emission source (>=4 $R_J$). The asymmetry and the dynamic of east-west emission peaks are measured and the presence of a hot spot at lambda_III=230 {\deg} $\pm$ 25 {\deg}. Spectral flux density measurements are on the low side of previous (unresolved) ones, suggesting a low-frequency turnover and/or time variations of the emission spectrum. Conclusions. LOFAR is a powerful and flexible planetary imager. The observations at 127 MHz depict an extended emission up to ~4-5 planetary radii. The similarities with high frequency results reinforce the conclusion that: i) the magnetic field morphology primarily shapes the brightness distribution of the emission and ii) the radiating electrons are likely radially and latitudinally distributed inside about 2 $R_J$. Nonetheless, the larger extent of the brightness combined with the overall lower flux density, yields new information on Jupiter's electron distribution, that may shed light on the origin and mode of transport of these particles.
    Full-text · Article · Nov 2015
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    ABSTRACT: Technique: We present a method to determine the pressure at which significant cloud opacity is present between 2 and 6 bars on Jupiter. We use: a) the strength of a Fraunhofer absorption line in a zone to determine the ratio of reflected sunlight to thermal emission, and b) pressure-broadened line profiles of deuterated methane (CH3D) at 4.66 microns to determine the location of clouds. We use radiative transfer models to constrain the altitude region of both the solar and thermal components of Jupiter's 5-micron spectrum. Results: For nearly all latitudes on Jupiter the thermal component is large enough to constrain the deep cloud structure even when upper clouds are present. We find that Hot Spots, belts, and high latitudes have broader line profiles than do zones. Radiative transfer models show that Hot Spots in the North and South Equatorial Belts (NEB, SEB) typically do not have opaque clouds at pressures greater than 2 bars. The South Tropical Zone (STZ) at 32 degrees S has an opaque cloud top between 4 and 5 bars. From thermochemical models this must be a water cloud. We measured the variation of the equivalent width of CH3D with latitude for comparison with Jupiter's belt-zone structure. We also constrained the vertical profile of water in an SEB Hot Spot and in the STZ. The Hot Spot is very dry for P<4.5 bars and then follows the water profile observed by the Galileo Probe. The STZ has a saturated water profile above its cloud top between 4 and 5 bars.
    Full-text · Article · Aug 2015 · The Astrophysical Journal
  • K. Kumar · I. de Pater · M.R. Showalter
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    ABSTRACT: We explored the hypothesis that Mab’s anomalous orbital motion, as deduced from Hubble Space Telescope (HST) data (Showalter, M.R., Lissauer, J.J. [2006]. Science (New York, NY) 311, 973–977), is the result of gravitational interactions with a putative suite of large bodies in the μ-ring. We conducted simulations to compute the gravitational effect of Mab (a recently discovered Uranian moon) on a cloud of test particles. Subsequently, by employing the data extracted from the test particle simulations, we executed random walk simulations to compute the back-reaction of nearby perturbers on Mab. By generating simulated observation metrics, we compared our results to the data retrieved from the HST. Our results indicate that the longitude residual change noted in the HST data ( deg) is well matched by our simulations. The eccentricity variations ( ) are however typically two orders of magnitude too small. We present a variety of reasons that could account for this discrepancy. The nominal scenario that we investigated assumes a perturber ring mass of 1 (Mab’s mass) and a perturber ring number density of 10 perturbers per 3 (Mab’s Hill radius). This effectively translates to a few tens of perturbers with radii of approximately 2–3 km, depending on the albedo assumed. The results obtained also include an interesting litmus test: variations of Mab’s inclination on the order of the eccentricity changes should be observable. Our work provides clues for further investigation into the tantalizing prospect that the Mab/μ-ring system is undergoing re-accretion after a recent catastrophic disruption.
    No preview · Article · Jul 2015 · Icarus
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    L.A. Sromovsky · I. de Pater · P.M. Fry · H.B. Hammel · P. Marcus
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    ABSTRACT: We imaged Uranus in the near infrared from 2012 into 2014, using the Keck/NIRC2 camera and Gemini/NIRI camera, both with adaptive optics. We obtained exceptional signal to noise ratios by averaging 8-16 individual exposures in a planet-fixed coordinate system. noise-reduced images revealed many low-contrast discrete features and large scale cloud patterns not seen before, including scalloped waveforms just south of the equator. In all three years numerous small (600-700 km wide) and mainly bright discrete features were seen within the north polar region (north of about 55\deg N). Over 850 wind measurements were made, the vast majority of which were in the northern hemisphere. These revealed an extended region of solid body rotation between 62\deg N and at least 83\deg N, at a rate of 4.08$\pm0.015$\deg/h westward relative to the planet's interior (radio) rotation of 20.88\deg/h westward. Near-equatorial speeds measured with high accuracy give different results for waves and small discrete features, with eastward drift rates of 0.4\deg/h and 0.1\deg/h respectively. The region of polar solid body rotation is a close match to the region of small-scale polar cloud features, suggesting a dynamical relationship. While winds at high southern latitudes (50\deg S - 90\deg S) are unconstrained by groundbased observations, a recent reanalysis of 1986 Voyager 2 observations by Karkoschka (2015, Icarus 250, 294-307) has revealed an extremely large north-south asymmetry in this region, which might be seasonal. Greatly increased activity was seen in 2014, including the brightest ever feature seen in K' images (de Pater et al. 2015, Icarus 252, 121-128). Over the 2012-2014 period we identified six persistent discrete features. Three were tracked for more than two years, two more for more than one year, and one for at least 5 months and continuing.
    Preview · Article · Jun 2015 · Icarus
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    ABSTRACT: The Large Binocular Telescope Interferometer mid-infrared camera, LMIRcam, imaged Io on the night of 2013 December 24 UT and detected strong M-band (4.8 μ m) thermal emission arising from Loki Patera. The 22.8 m baseline of the Large Binocular Telescope provides an angular resolution of ∼32 mas (∼100 km at Io) resolving the Loki Patera emission into two distinct maxima originating from different regions within Loki’s horseshoe lava lake. This observation is consistent with the presence of a high-temperature source observed in previous studies combined with an independent peak arising from cooling crust from recent resurfacing. The deconvolved images also reveal 15 other emission sites on the visible hemisphere of Io including two previously unidentified hot spots.
    No preview · Article · Apr 2015 · The Astronomical Journal
  • I. de Pater · J.J. Lissauer
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    ABSTRACT: An authoritative introduction for graduate students in the physical sciences, this award-winning textbook explains the wide variety of physical, chemical, and geological processes that govern the motions and properties of planets. This updated second edition has been revised and improved while maintaining its existing structure and organization. Many data tables and plots have been updated to account for the latest measurements. A new Appendix focuses on recent discoveries since the second edition was first published. These include results from Cassini, Kepler, MESSENGER, MRO, LRO, Dawn at Vesta, Curiosity, and others, as well as many ground-based observatories. With over 300 exercises to help students apply the concepts covered, this textbook is ideal for graduate courses in astronomy, planetary science and earth science, and well suited as a reference for researchers. Color versions of many figures, movie clips supplementing the text, and other resources are available at www.cambridge.org/depater.
    No preview · Book · Jan 2015
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    ABSTRACT: From STIS observations of Uranus in 2012, we found that the methane volume mixing ratio declined from about 4% at low latitudes to about 2% at 60 deg N and beyond. This is similar to that found in the south polar regions in 2002, in spite of what appears to be strikingly different convective activity in the two regions. Keck and HST imaging observations close to equinox imply that the depletions were simultaneously present in 2007, suggesting they are persistent features. The depletions appear to be mainly restricted to the upper troposphere, with depth increasing poleward from about 30 deg N, reaching ~4 bars at 45 deg N and perhaps much deeper at 70 deg N. The latitudinal variations in degree and depth of the depletions are important constraints on models of meridional circulation. Our observations are qualitatively consistent with previously suggested circulation cells in which rising methane-rich gas at low latitudes is dried out by condensation and sedimentation of methane ice particles as the gas ascends to altitudes above the methane condensation level, then is transported to high latitudes, where it descends and brings down methane depleted gas. Since this cell would seem to inhibit formation of condensation clouds in regions where clouds are actually inferred from spectral modelling, it suggests that sparse localized convective events may be important in cloud formation. The small-scale latitudinal variations we found in the effective methane mixing ratio between 55 deg N and 82 deg N have significant inverse correlations with zonal mean latitudinal variations in cloud reflectivity in near-IR Keck images taken before and after the HST observations. If the CH4/H2 absorption ratio variations are interpreted as local variations in para fraction instead of methane mixing ratio, we find that downwelling correlates with reduced cloud reflectivity.
    No preview · Article · Aug 2014 · Icarus
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    ABSTRACT: Aims. We examine Very Large Array (VLA) observations of Jupiter to present evidence of fluctuations in the emission produced by the electron belt in January 2001. Investigating the source of fluctuations will provide new opportunities to discuss the scenarios of temporal changes in Jupiter's synchrotron radiation (i.e., the electron belt) in future data analysis and modeling work. Methods. To discuss the electron belt dynamics during the Cassini flyby of Jupiter. we compare the radio measurements from 2-3 January 2001 with VLA observations obtained on 20-21 December 1988, when viewing geometry and array configuration are comparable. All data are scaled to a standard Earth-Jupiter distance of 4.04 AU for comparison purposes. Brightness distribution maps with identical spatial resolutions and cartography of the equatorial radiation are constructed and examined at the wavelengths of 21 cm and 90 cm. Results. Rotation-averaged maps show that the emission from the equatorial zones of maximum intensity is weaker by 5-40%. but the brightness distribution is spatially more extended on 2-3 January 2001. resulting in a total emission at both wavelengths stronger by similar to 35%. Between observation periods, the brightness distributions are observed to evolve differently during the planet rotation. Tomographic reconstructions of the equatorial radiation support our conclusion that the electron belt population was differently distributed around the planet in December 1988 and January 2001. Conclusions, Our analysis of VLA data sets suggests that the spatial distribution of the electron belt on 2-3 January 2001 is different from that usually observed. Our knowledge of solar activity at the time of the Cassini flyby of Jupiter suggests that the emission from the electron radiation belt was responding to external influences, most likely to solar wind structures rather than to solar radio flux, on a timescale of days to a couple of weeks. Combined results from a multisource data analysis including spacecraft and radio observations are needed to confirm this relationship.
    No preview · Article · Aug 2014 · Astronomy and Astrophysics
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    ABSTRACT: The Large Binocular Telescope (LBT) houses two 8.4-meter mirrors separated by 14.4 meters on a common mount. Coherent combination of these two AO-corrected apertures via the LBT Interferometer (LBTI) produces Fizeau interferometric images with a spatial resolution equivalent to that of a 22.8-meter telescope and the light- gathering power of single 11.8-meter mirror. Capitalizing on these unique capabilities, we used LBTI/LMIRcam to image thermal radiation from volcanic activity on the surface of Io at M-Band (4.8 μm) over a range of parallactic angles. At the distance of Io, the M-Band resolution of the interferometric baseline corresponds to a physical distance of ~135 km, enabling high-resolution monitoring of Io volcanism such as ares and outbursts inaccessible from other ground-based telescopes operating in this wavelength regime. Two deconvolution routines are used to recover the full spatial resolution of the combined images, resolving at least sixteen known volcanic hot spots. Coupling these observations with advanced image reconstruction algorithms demonstrates the versatility of Fizeau interferometry and realizes the LBT as the first in a series of extremely large telescopes.
    Full-text · Conference Paper · Jul 2014
  • H. A. Fuqua · G. T. Delory · I. de Pater · R. E. Grimm
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    ABSTRACT: We use transient within low nightside ARTEMIS magnetic field measurements with forward modeling to constrain the electrical conductivity of the lunar interior.
    No preview · Article · Feb 2014
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    ABSTRACT: Thermal models to FORCAST observations of Comet ISON (r_h = 1.2 AU) at 11, 19 and 32 µm show the coma has a steep size distribution of carbon-rich 0.7-1-µm grains.
    No preview · Article · Feb 2014
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    ABSTRACT: Images of Jupiter at 5 microns reveal a dynamic range of about 20 in thermal emission between the hottest Hot Spots and the lowest flux regions on the planet. The Great Red Spot is dark at 5 microns due to thick clouds, but imaging alone does not reveal which cloud layers are responsible for attenuating this radiation. Initial expectations were that upper level clouds were sufficiently opaque that structure at the water cloud level would be completely hidden. Fortunately, this is not the case. We used NIRSPEC on the Keck telescope and CSHELL on the Infrared Telescope Facility to spectrally resolve line profiles of CH3D and other molecules on Jupiter in order to derive the pressure of the line formation region in the 5-micron window. Deuterated methane is a good choice for studying cloud structure because methane and its isotopologues do not condense on Jupiter. Variations in CH3D line shape with position on Jupiter are therefore ONLY due to cloud structure rather than due to changes in gas mole fraction. By aligning the slit east/west on Jupiter, we sampled the Great Red Spot and a Hot Spot 7 arcsec to the west. The profile of the CH3D lines is very broad in the Hot Spot due to collisions with up to 8 bars of H2, where unit optical depth due to collision induced H2 opacity occurs. The extreme width of these CH3D features implies that Hot Spots do not have significant cloud opacity where water is expected to condense. This is consistent with the Galileo probe results. Within the Great Red Spot, the line profiles are substantially narrower than in the Hot Spot, but they are broader than would be expected if they were formed in a column above an opaque cloud at 0.7 bars (NH3) or 2 bars (NH4SH). The best fit to the line shape of CH3D requires an opaque cloud at 5 bars, which we identify as being a water cloud. Gaseous H2O is clearly evident in the Great Red Spot, which provides independent evidence that we are sounding deep in Jupiter’s atmosphere. A combination of Keck and IRTF data will allow us to retrieve NH3, PH3, and gaseous H2O inside the Hot Spot and within the Great Red Spot. This technique can be applied to study the deep cloud structure anywhere on Jupiter whether or not upper level clouds are present.
    No preview · Article · Oct 2013
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    ABSTRACT: On 28 September 2012, Hubble's Space Telescope Imaging Spectrograph (STIS) observed Uranus (GO 12894, L. Sromovsky PI). The result is a hyperspectral data cube of one half of the planet with spectral coverage of 300-1000 nm. The observations were designed to characterize latitudinally (from about 50 deg S to the north pole) the vertical structure of aerosols and global distribution of methane after the planet's 2007 equinox. These observations form a unique counterpart to similar observations made in 2002 (GO 9035, E. Karkoschka PI) when Uranus' south pole was in view. In 2002, Uranus was found to have a depletion of methane in southern mid-to-high latitudes (Karkoschka and Tomasko 2009, Icarus 202, 287-309; Sromovsky et al. 2011, Icarus 215, 292-312). Characterizing this distribution is possible by the simultaneous sounding of both hydrogen and methane spectral absorption regions (hydrogen CIA peaks near 825 nm). As Uranus' northern hemisphere came into view, it became apparent from near-IR observations of the troposphere (sensing to about 10 bars), that the north and south hemispheres were asymmetric in brightness, and that unexpectedly rapid seasonal changes were taking place (Sromovsky et al. 2009, Icarus 203, 265-286). The north polar region also has what appear to be many small convective features poleward of 60 deg N, in stark contrast to the south polar region (Sromovsky et al. 2012, Icarus 220, 694-712). Sromovsky et al. 2012 speculated this difference could be due to a seasonally-forced methane abundance asymmetry. However, 2007 NICMOS F108N and Keck NIRC2 PaBeta (1271 nm) equinox imagery suggest that the north polar region is also depleted in methane, as do 2009 IRTF SpeX observations (Tice et al. 2013, Icarus 223, 684-698). We can now confirm this northern hemispheric methane depletion appears symmetric rather than a seasonal phenomenon, thanks to the new STIS observations with an excellent view of Uranus northern latitudes. We will also present preliminary results of radiative transfer modeling of the current vertical structure of aerosols, and compare the current state to that of 2002. This work was supported by STScI and the NASA Planetary Astronomy program.
    No preview · Article · Oct 2013
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    ABSTRACT: We present models of the Uranian atmosphere and rings based on near-infrared (H- and K-band) observations of Uranus taken with the OSIRIS integral field spectrograph at the W.M. Keck Observatory in 2010 and 2011. In July 2010 we observed the Uranian atmosphere with spatial and spectral resolution at latitudes ranging from the north polar region to mid southern latitudes. We demonstrate radiative transfer models used to characterize the properties and vertical & latitudinal distribution of clouds and hazes. We also present spectra of a discrete cloud feature observed in July 2011, alongside radiative transfer models used to constrain the cloud altitude and properties. Finally, we present near-infrared spectra of the Uranian ring system, which we find to be gray. We determined ring particle reflectivities for each ring group based on this data, and find reflectivities consistent with previous results with the exception of the 456 ring group, which we find to be slightly fainter.
    No preview · Article · Oct 2013
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    ABSTRACT: We report on observations of Neptune's rings, arcs and inner moons as obtained by the Hubble Space Telescope during 2004-2009. These are the only Earth-based observations of the ring system obtained at visual wavelengths, permitting direct photometric comparison with the Voyager images. This allows us to determine quantitatively how the arcs have evolved from the time they were first imaged. Of the four arcs identified in 1989, the leading two have vanished, but the trailing two appear to have remained quite stable. New analysis of the images has also revealed a small moon, S/2004 N 1, orbiting between Proteus and Larissa. The body has a mean motion of 378.907 +/- 0.001 degrees per day, corresponding to semimajor axis 105,283 km. Its V magnitude is 26.5 +/- 0.3, suggesting a radius of ~ 10 km if its albedo is ~ 10%, comparable to that of the other inner moons. Tentative detections of Naiad, the smallest moon discovered by Voyager, will also be discussed.
    No preview · Article · Oct 2013
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    ABSTRACT: Previous studies using data from Pioneer Venus suggested that oxygen ion escape flux may be enhanced by orders of magnitude during Interplanetary Coronal Mass Ejections. However, this large enhancement has been ambiguous in Venus Express ion data - with some analyses showing no flux enhancement or a small enhancement (within 2 times undisturbed cases). One possible explanation is that high escape flux may be due to high dynamic pressure in the solar wind, and the dynamic pressure has been lower during the VEX time period. So, we focus on ICMEs with the largest dynamic pressure and with VEX sampling of the escaping ions during the sheath of the ICMEs (during which the highest dynamic pressures in the solar wind occur). We will show the characteristics of these large events measured by VEX, and compare them to the largest ICMEs measured by PVO. We will then discuss estimates of the oxygen ion escape flux during these events.
    No preview · Article · Oct 2013
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    ABSTRACT: Observations of Jupiter by a large number of amateurs have resulted in the discovery of three fireballs in its atmosphere produced by the impacts of small objects. The fireballs were detected on June 3, 2010, August 20, 2010 and September 10, 2012. The light-curves of these atmospheric airbursts provide a measure of the masses and sizes of the impacting objects and the statistical significance of the three events can be examined from knowledge of the large pool of Jupiter observations by the global community of amateur astronomers. These objects are in the category of 5-20 m sizes depending on their density and release energies comparable to the recent Chelyabinsk airburst. Current biases in observations of Jupiter suggest a rate of similar impacts of 18-160 per year.
    Full-text · Article · Sep 2013 · Astronomy and Astrophysics
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    ABSTRACT: CBET 3586 available at Central Bureau for Astronomical Telegrams.
    No preview · Article · Jul 2013
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    S. H. Luszcz-Cook · I. de Pater · M. Wright
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    ABSTRACT: We present maps of Neptune in and near the CO (2-1) rotation line at 230.538 GHz. These data, taken with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) represent the first published spatially-resolved maps in the millimeter. At large (~5 GHz) offsets from the CO line center, the majority of the emission originates from depths of 1.1-4.7 bar. We observe a latitudinal gradient in the brightness temperature at these frequencies, increasing by 2-3 K from 40 degrees N to the south pole. This corresponds to a decrease in the gas opacity of about 30% near the south pole at altitudes below 1 bar, or a decrease of order a factor of 50 in the gas opacity at pressures greater than 4 bar. We look at three potential causes of the observed gradient: variations in the tropospheric methane abundance, variations in the H2S abundance, and deviations from equilibrium in the ortho/para ratio of hydrogen. At smaller offsets (0-213 MHz) from the center of the CO line, lower atmospheric pressures are probed, with contributions from mbar levels down to several bars. We find evidence of latitudinal variations at the 2-3% level in the CO line, which are consistent with the variations in zonal-mean temperature near the tropopause found by Conrath et al. (1998) and Orton et al. (2007).
    Preview · Article · Jun 2013 · Icarus

Publication Stats

4k Citations
700.06 Total Impact Points

Institutions

  • 2008-2015
    • Delft University of Technology
      • Faculty of Aerospace Engineering (AE)
      Delft, South Holland, Netherlands
  • 1984-2015
    • University of California, Berkeley
      • • Department of Astronomy
      • • Department of Statistics
      Berkeley, California, United States
  • 2010
    • Boston University
      • Center for Space Physics
      Boston, Massachusetts, United States
  • 2006
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2005-2006
    • SETI Institute
      Mountain View, California, United States
  • 2004
    • Stanford University
      • Graduate School of Business
      Palo Alto, California, United States
    • W. M. Keck Observatory
      Hilo, Hawaii, United States
    • University of California, Santa Cruz
      • Center for Adaptive Optics
      Santa Cruz, California, United States
    • Lowell Observatory
      Lowell, Massachusetts, United States
  • 2002
    • The French Aeropace Lab ONERA
      Paliseau, Île-de-France, France
  • 2000
    • NASA
      Вашингтон, West Virginia, United States
  • 1999
    • Bay Area Research University
      Palm Bay, Florida, United States
  • 1992
    • University of Chicago
      Chicago, Illinois, United States
  • 1990
    • University of Iowa
      • Department of Physics and Astronomy
      Iowa City, Iowa, United States
  • 1983-1984
    • The University of Arizona
      • Department of Chemistry and Biochemistry (College of Science)
      Tucson, Arizona, United States
    • NSF
      Ann Arbor, Michigan, United States
  • 1982-1983
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 1980
    • Leiden University
      Leyden, South Holland, Netherlands