J. M. Moran

Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States

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Publications (394)1597.73 Total impact

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    ABSTRACT: Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. These magnetic fields would naturally give rise to the observed synchrotron emission in galaxy cores and to the formation of relativistic jets, but no observations to date have been able to resolve the expected horizon-scale magnetic-field structure. We report interferometric observations at 1.3-millimeter wavelength that spatially resolve the linearly polarized emission from the Galactic Center supermassive black hole, Sagittarius A*. We have found evidence for partially ordered fields near the event horizon, on scales of ~6 Schwarzschild radii, and we have detected and localized the intra-hour variability associated with these fields.
    Full-text · Article · Dec 2015 · Science
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    ABSTRACT: We report on 230 GHz (1.3 mm) VLBI observations of M87 with the Event Horizon Telescope using antennas on Mauna Kea in Hawaii, Mt. Graham in Arizona and Cedar Flat in California. For the first time, we have acquired 230 GHz VLBI interferometric phase information on M87 through measurement of closure phase on the triangle of long baselines. Most of the measured closure phases are consistent with 0$^{\circ}$ as expected by physically-motivated models for 230 GHz structure such as jet models and accretion disk models. The brightness temperature of the event-horizon-scale structure is $\sim 1 \times 10^{10}$ K derived from the compact flux density of $\sim 1$ Jy and the angular size of $\sim 40 $ $\rm \mu$as $\sim$ 5.5 $R_{{\rm s}}$, which is broadly consistent with the peak brightness of the radio cores at 1-86 GHz located within $\sim 10^2$ $R_{{\rm s}}$. Our observations occurred in the middle of an enhancement in very-high-energy (VHE) $\rm \gamma$-ray flux, presumably originating in the vicinity of the central black hole. Our measurements, combined with results of multi-wavelength observations, favor a scenario in which the VHE region has an extended size of $\sim$20-60 $R_{{\rm s}}$.
    Full-text · Article · May 2015 · The Astrophysical Journal
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    ABSTRACT: We report new observations with the Very Large Array, Atacama Large Millimeter Array, and Submillimeter Array at frequencies from 1.0 to 355 GHz of the Galactic Center black hole, Sagittarius A*. These observations were conducted between October 2012 and November 2014. While we see variability over the whole spectrum with an amplitude as large as a factor of 2 at millimeter wavelengths, we find no evidence for a change in the mean flux density or spectrum of Sgr A* that can be attributed to interaction with the G2 source. The absence of a bow shock at low frequencies is consistent with a cross-sectional area for G2 that is less than $2 \times 10^{29}$ cm$^2$. This result fits with several model predictions including a magnetically arrested cloud, a pressure-confined stellar wind, and a stellar photosphere of a binary merger. There is no evidence for enhanced accretion onto the black hole driving greater jet and/or accretion flow emission. Finally, we measure the millimeter wavelength spectral index of Sgr A* to be flat; combined with previous measurements, this suggests that there is no spectral break between 230 and 690 GHz. The emission region is thus likely in a transition between optically thick and thin at these frequencies and requires a mix of lepton distributions with varying temperatures consistent with stratification.
    Full-text · Article · Feb 2015 · The Astrophysical Journal
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    ABSTRACT: We present high angular resolution (∼0.3 arcsec) submillimeter continuum (0.85 mm) and line observations of the O-type protostar IRAS 16547−4247 carried out with the Atacama Large Millimeter/Submillimeter Array (ALMA). In the 0.85 mm continuum band, the observations revealed two compact sources (with a separation of 2 arcsec), one of them associated with IRAS 16547−4247, and the other one to the west. Both sources are well-resolved angularly, revealing a clumpy structure. On the other hand, the line observations revealed a rich variety of molecular species related to both continuum sources. In particular, we found a large number of S-bearing molecules, such as the rare molecule methyl mercaptan (CH3SH). At scales larger than 10 000 au, molecules (e.g. SO2 or OCS) mostly with low-excitation temperatures in the upper states (Ek ≲ 300 K) are present in both millimeter continuum sources, and show a south-east–north-west velocity gradient of 7 km s− 1 over 3 arcsec (165 km s−1 pc−1). We suggest that this gradient probably is produced by the thermal (free–free) jet emerging from this object with a similar orientation at the base. At much smaller scales (about 1000 au), molecules with high-excitation temperatures (Ek ≳ 500 K) are tracing a rotating structure elongated perpendicular to the orientation of the thermal jet, which we interpret as a candidate disc surrounding IRAS 16547−4247. The dynamical mass corresponding to the velocity gradient of the candidate to disc is about 20 M⊙, which is consistent with the bolometric luminosity of IRAS 16547−4247.
    Full-text · Article · Nov 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40$\alpha$, H42$\alpha$, and H50$\beta$ emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562$-$3959. The HRLs exhibit Voigt profiles, a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need a high-velocity component. The Lorentzian line wings imply electron densities of $5\times10^7$ cm$^{-3}$ on average. In addition, we detect SO and SO$_2$ emission arising from a compact ($\sim3000$ AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.
    Full-text · Article · Oct 2014 · The Astrophysical Journal
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    ABSTRACT: Formation of Super Massive Black Hole (SMBH) at the center of galaxy is a big quest on the evolution process of galaxy. Very Long Baseline Interferometry (VLBI) observations are now capable to confirm directly the existence of SMBH by detecting the shadow image of it. VLBI could also provide a chance to see merging SMBHs. Sub-millimeter VLBI group in ASIAA is planning to provide a new VLBI station to give better performance of the submm VLBI network. The promising site is in Greenland, where it is expected to make single dish observations at THz regions.
    No preview · Article · Oct 2013
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    ABSTRACT: We report results from 5-day VLBI observations of the well-known quasar 3C 279 at 1.3 mm (230 GHz) in 2011. The measured nonzero closure phases on triangles including stations in Arizona, California and Hawaii indicate that the source structure is spatially resolved. We find an unusual inner jet direction at scales of $\sim$1 parsec extending along the northwest-southeast direction (PA = $127^{\circ}\pm3^{\circ}$), as opposed to other (previously) reported measurements on scales of a few parsecs showing inner jet direction extending to the southwest. The 1.3 mm structure corresponds closely with that observed in the central region of quasi-simultaneous super-resolution VLBA images at 7 mm. The closure phase changed significantly on the last day when compared with the rest of observations, indicating that the inner jet structure may be variable on daily timescales. The observed new direction of the inner jet shows inconsistency with the prediction of a class of jet precession models. Our observations indicate a brightness temperature of $\sim 8\times10^{10}$ K in the 1.3 mm core, much lower than that at centimeter wavelengths. Observations with better uv coverage and sensitivity in the coming years will allow the discrimination between different structure models and will provide direct images of the inner regions of the jet with 20--30 $\mu$as (5--7 light months) resolution.
    Full-text · Article · May 2013 · The Astrophysical Journal
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    ABSTRACT: We report results from 1.3 mm VLBI observations of AGN jets with the Event Horizon Telescope focusing on the southern blazar 1921-293. We show the first 1.3 mm VLBI model image of 1921-293 using closure phase techniques obtained with four telescopes at three observatories: the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in Hawaii, the Arizona Radio Observatory's Submillimeter Telescope (SMT) in Arizona, and two telescopes of the Combined Array for Research in Millimeterwave Astronomy (CARMA) in California in April 2009. With the greatly improved resolution compared with previous observations and robust closure phase measurement, the inner jet structure of 1921-293 was spatially resolved. The inner jet extends to the northwest along a position angle of -53° degree at a distance of 0.38 mas from the tentatively identified core, in agreement with the inner jet structure inferred from lower frequencies, and making a position angle difference of ~80° with respect to the cm-jet. The size of the compact core is 0.15 pc with a brightness temperature of 1.2 ×1011 K. Compared with those measured at lower frequencies, the low brightness temperature may argue in favor of the decelerating jet model or particle-cascade models. Some results for another blazar 3C 279 will also be presented.
    No preview · Article · Jan 2013
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    ABSTRACT: Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by the accretion of matter onto supermassive black holes. Although the measured width profiles of such jets on large scales agree with theories of magnetic collimation, the predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations, at a wavelength of 1.3 millimeters, of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 ± 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.
    Full-text · Article · Sep 2012 · Science
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    ABSTRACT: We present the first 1.3 mm (230 GHz) very long baseline interferometry model image of an AGN jet using closure phase techniques with a four-element array. The model image of the quasar 1924-292 was obtained with four telescopes at three observatories: the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in Hawaii, the Arizona Radio Observatory's Submillimeter Telescope (SMT) in Arizona, and two telescopes of the Combined Array for Research in Millimeterwave Astronomy (CARMA) in California in April 2009. With the greatly improved resolution compared with previous observations and robust closure phase measurement, the inner jet structure of 1924-292 was spatially resolved. The inner jet extends to the northwest along a position angle of $-53^\circ$ at a distance of 0.38\,mas from the tentatively identified core, in agreement with the inner jet structure inferred from lower frequencies, and making a position angle difference of $\sim 80^{\circ}$ with respect to the cm-jet. The size of the compact core is 0.15\,pc with a brightness temperature of $1.2\times10^{11}$\,K. Compared with those measured at lower frequencies, the low brightness temperature may argue in favor of the decelerating jet model or particle-cascade models. The successful measurement of closure phase paves the way for imaging and time resolving Sgr A* and nearby AGN with the Event Horizon Telescope.
    Full-text · Article · Aug 2012 · The Astrophysical Journal Letters
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    Diego J. Muñoz · Daniel P. Marrone · James M. Moran · and R. Rao
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    ABSTRACT: We report the first detections of circularly polarized emission at submillimeter wavelengths from the compact radio source and supermassive black hole candidate Sgr A* at a level of 1.2% ± 0.3% at 1.3 mm wavelength (230 GHz) and 1.6% ± 0.3% at 860 μm (345 GHz) with the same handedness, left circular polarization (LCP), as observed at all lower frequencies (1.4-15 GHz). The observations, taken with the Submillimeter Array in multiple epochs, also show simultaneous linear polarization (LP) at both wavelengths of about 6%. These properties differ sharply from those at wavelengths longer than 1 cm (frequencies below 30 GHz), where weak circular polarization (CP) (~0.5%) dominates over LP, which is not detected at similar fractional limits. We describe an extensive set of tests to ensure the accuracy of our measurements. We find no CP in any other source, including the bright quasar 1924-292, which traces the same path on the sky as Sgr A* and therefore should be subject to identical systematic errors originating in the instrument frame. Since a relativistic synchrotron plasma is expected to produce little CP, the observed CP is probably generated close to the event horizon by the Faraday conversion process. We use a simple approximation to show that the phase shift associated with Faraday conversion can be nearly independent of frequency, a sufficient condition to make the handedness of CP independent of frequency. Because the size of the τ = 1 surface changes by more than an order of magnitude between 1.4 and 345 GHz, the magnetic field must be coherent over such scales to consistently produce LCP. To improve our understanding of the environment of SgrA* critical future measurements includes determining whether the Faraday rotation deviates from a λ2 dependence in wavelength and whether the circular and linear components of the flux density are correlated.
    Full-text · Article · Jan 2012 · The Astrophysical Journal
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    ABSTRACT: VLBI observations at a wavelength of 1.3mm have confirmed structure in SgrA* on scales of just a few Schwarzschild radii [1]. More sensitive observations in the next few years, if sufficiently sensitive, could confirm a tentative detection of time variable structures [2] predicted by models of flaring activity in SgrA*. A key improvement in sensitivity is provided by the deployment and commissioning of a VLBI phased array processor at the Submillimeter Array (SMA) on Mauna Kea. This new instrument enables the SMA and the neighboring single dish submillimeter telescopes, CSO and JCMT, to contribute to future VLBI observations with all their collecting area.
    Preview · Conference Paper · Sep 2011
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    ABSTRACT: Sagittarius A*, the ~4 x 10^6 solar mass black hole candidate at the Galactic Center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength Very Long Baseline Interferometry (VLBI). We report on 1.3 mm wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the ARO/SMT on Mt. Graham in Arizona, and two telescopes of the CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924-292 were observed over three consecutive nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3 mm VLBI interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable role in determining the structure of emission near the event horizon of Sgr A*.
    Full-text · Article · Nov 2010 · The Astrophysical Journal Letters
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    ABSTRACT: We report a study of the H30α line emission at 1.3 mm from the region around Sgr A* made with the Submillimeter Array at a resolution of 2'' over a field of 60'' (2 pc) and a velocity range of -360 to +345 km s–1. This field encompasses most of the Galactic center's "minispiral." With an isothermal homogeneous H II model, we determined the physical conditions of the ionized gas at specific locations in the Northern and Eastern Arms from the H30α line data along with Very Large Array data from the H92α line at 3.6 cm and from the radio continuum emission at 1.3 cm. The typical electron density and kinetic temperature in the minispiral arms are 3-21×104 cm–3 and 5000-13,000 K, respectively. The H30α and H92α line profiles are broadened due to the large velocity shear within and along the beam produced by dynamical motions in the strong gravitational field near Sgr A*. We constructed a three-dimensional model of the minispiral using the orbital parameters derived under the assumptions that the gas flows are in Keplerian motion. The gas in the Eastern Arm appears to collide with the Northern Arm flow in the "Bar" region, which is located 0.1-0.2 pc south of and behind Sgr A*. Finally, a total Lyman continuum flux of 3 × 1050 photons s–1 is inferred from the assumption that the gas is photoionized and the ionizing photons for the high-density gas in the minispiral arms are from external sources, which is equivalent to ~250 O9-type zero-age-main-sequence stars.
    Full-text · Article · Oct 2010 · The Astrophysical Journal
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    ABSTRACT: We report the results from observations of H30$\alpha$ line emission in Sgr A West with the Submillimeter Array at a resolution of 2\arcsec and a field of view of about 40\arcsec. The H30$\alpha$ line is sensitive to the high-density ionized gas in the minispiral structure. We compare the velocity field obtained from H30$\alpha$ line emission to a Keplerian model, and our results suggest that the supermassive black hole at Sgr A* dominates the dynamics of the ionized gas. However, we also detect significant deviations from the Keplerian motion, which show that the impact of strong stellar winds from the massive stars along the ionized flows and the interaction between Northern and Eastern arms play significant roles in the local gas dynamics. Comment: 4 pages, 2 figures
    Full-text · Article · Feb 2010
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    ABSTRACT: Based on spectroscopic signatures, about one-third of known H2O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These "disk maser candidates" are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v sys < 20, 000 km s–1). The remaining three disk maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, and NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 km s–1. Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses ((2-7) ×107M ☉) and mean disk radii (0.2-0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGNs are relatively distant (10,000 km s–1 <v sys < 15, 000 km s–1), and fractional error in a derived Hubble constant, due to peculiar motion of the galaxies, would be small. As signposts of highly inclined geometries at galactocentric radii of ~0.1-1 pc, disk masers also provide robust orientation references that allow analysis of (mis)alignment between AGNs and surrounding galactic stellar disks, even without extensive interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies. This provides independent support for conclusions that in late-type galaxies, central engine accretion disks and galactic plane orientations are not correlated.
    Preview · Article · Nov 2009 · The Astrophysical Journal
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    ABSTRACT: We present VLA 1.3 cm radio continuum and water maser observations as well as SMA SO$_2$ (226.300 GHz) and 1.3 mm dust continuum observations toward the massive star formation region IRAS 16547-4247. We find evidence of multiple sources in the central part of the region. There is evidence of a rotating structure associated with the most massive of these sources, traced at small scales (~50 AU) by the water masers. At large scales (~1000 AU) we find a velocity gradient in the SO2 molecular emission with a barely resolved structure that can be modeled as a rotating ring or two separate objects. The velocity gradients of the masers and of the molecular emission have the same sense and may trace the same structure at different size scales. The position angles of the structures associated with the velocity gradients are roughly perpendicular to the outflow axis observed in radio continuum and several molecular tracers. We estimate the mass of the most massive central source to be around 30 solar masses from the velocity gradient in the water maser emission. The main source of error in this estimate is the radius of the rotating structure. We also find water masers that are associated with the large scale molecular outflow of the system, as well as water masers that are associated with other sources in the region. Our results suggest that the formation of this source, one of the most luminous protostars or protostellar clusters known, is taking place with the presence of ionized jets and disk-like structures. Comment: 26 pages, 7 figures
    Full-text · Article · Jun 2009 · The Astrophysical Journal
  • Diego Munoz · D. Marrone · J. Moran
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    ABSTRACT: We report the detection of circularly polarized (CP) emission from the compact radio source Sagittarius A* at a level of 1.5% at a frequency of 235 GHz (1.4 mm). Sgr A* is associated with the supermassive black hole (SMBH) in the Galactic Center. The observations, taken with the Submillimeter Array (SMA) on 03/31/2007, also show a linearly polarized (LP) component of 7%. The snr of our detection of CP is about 14. Before our measurements, CP had only been detected at frequencies between 1.4 and 15 GHz (21 and 2 cm) at levels
    No preview · Article · May 2009
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    E. E. Bloemhof · J. M. Moran · and M. J. Reid
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    ABSTRACT: Intrinsic morphologies of interstellar OH maser-emitting gas condensations have been measured, for the first time, at two distinct epochs. The shapes and orientations of these maser condensations, in the vicinity of the ultracompact H II region W3(OH), are remarkably persistent from one epoch to the next despite significant position shifts. These observations provide the first direct evidence that the motions measured are due to actual physical movement of discrete clumps of maser-emitting matter, rather than to some sort of nonkinematic effect, such as traveling excitation phenomena or chance realignments of coherency paths through the masing gas. The kinematic assumption is crucial to astrophysical applications of maser proper-motion measurements, including distance determinations and studies of source dynamics. The shapes of the OH maser spots in W3(OH) show a tendency to be elongated in a direction parallel to the shock front delineated by radio continuum maps of the H II region, supporting the picture in which masers are formed in compressed gas behind the shock front.
    Preview · Article · Jan 2009 · The Astrophysical Journal
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    ABSTRACT: We report high angular resolution observations at λ = 7 mm of the hypercompact (HC) H II regions G34.26 + 0.15 A and B. The images and the intensity profiles obtained give possible evidence of limb brightening, which may indicate the existence of inner "holes" in the ionized gas. These "holes" were previously inferred from a study of the spectra and angular sizes at different frequencies from lower angular resolution observations. Using a spherical ionized model bounded by an inner and an outer radii with an electron density gradient ne ∝ r –α, we can reproduce the 7 mm intensity profile, spectral energy distribution, and observed angular sizes of both sources. These models indicate inner radii R 1 ~ 400 AU, outer radii R 2 ~ 1000 AU, and shallow density gradients with slopes α ~ 0.3-1.0. These profiles are similar in physical size and shape to those found recently for the HC H II regions G24.78+0.08 A1 and G28.20 – 0.04N. Therefore, at least four HC H II regions seem to have thick shells of ionized gas with fractional widths, (R 2 – R 1)/R 2 ~ 0.1-0.6, in contrast with the thin ionized shells expected in the case of shells swept up by stellar winds. More observations are needed to determine the origin of these thick ionized shells and their frequency of occurrence in the HC H II region stage.
    Full-text · Article · Jan 2009 · The Astrophysical Journal

Publication Stats

10k Citations
1,597.73 Total Impact Points


  • 1981-2015
    • Harvard-Smithsonian Center for Astrophysics
      • • Smithsonian Astrophysical Observatory
      • • Institute for Theory and Computation
      Cambridge, Massachusetts, United States
  • 2010
    • University of Chicago
      • Kavli Institute for Cosmological Physics
      Chicago, Illinois, United States
  • 1980-2005
    • University of California, Berkeley
      • • Department of Astronomy
      • • Radio Astronomy Laboratory
      Berkeley, California, United States
  • 2003
    • University of Tasmania
      • School of Mathematics & Physics
      Hobart Town, Tasmania, Australia
  • 1995-1996
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
    • National Astronomical Observatory of Japan
      • Astronomy Data Center
      Edo, Tōkyō, Japan
  • 1989
    • University of Santiago, Chile
      • Departamento de Economía
      CiudadSantiago, Santiago Metropolitan, Chile
  • 1977-1983
    • Harvard University
      Cambridge, Massachusetts, United States
    • California Institute of Technology
      Pasadena, California, United States
  • 1966-1983
    • Massachusetts Institute of Technology
      • Research Laboratory of Electronics
      Cambridge, Massachusetts, United States
  • 1977-1981
    • University of Massachusetts Amherst
      Amherst Center, Massachusetts, United States
  • 1979
    • Max Planck Institute for Radio Astronomy
      Bonn, North Rhine-Westphalia, Germany
  • 1978
    • Cambridge College
      Cambridge, Massachusetts, United States
  • 1976-1978
    • University of Toronto
      Toronto, Ontario, Canada
  • 1975
    • University of Maryland, College Park
      CGS, Maryland, United States