C. J. Cyganowski

University of St Andrews, Saint Andrews, Scotland, United Kingdom

Are you C. J. Cyganowski?

Claim your profile

Publications (47)191.73 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. However, individually these observations provide limited constraints on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Towards the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH3CCH and CH3CN seem to always trace a lukewarm (T ≈ 60 K) and a hot (T > 100 K) complex chemistry, respectively. These spatial trends are consistent with abundance–temperature correlations of four representative complex organics – CH3CCH, CH3CN, CH3OCH3 and CH3CHO – in a large sample of complex molecule hosts mined from the literature. Together, these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, and may provide information about its formation history.
    Faraday Discussions 08/2014; 168. · 3.82 Impact Factor
  • Source
    T. R. Hunter, C. L. Brogan, C. J. Cyganowski, K. H. Young
    [Show abstract] [Hide abstract]
    ABSTRACT: Using the SMA and VLA, we have imaged the massive protocluster NGC6334I(N) at high angular resolution (0.5"~650AU) from 6cm to 0.87mm, detecting 18 new compact continuum sources. Three of the new sources are coincident with previously-identified water masers. Together with the previously-known sources, these data bring the number of likely protocluster members to 25 for a protostellar density of ~700 pc^-3. Our preliminary measurement of the Q-parameter of the minimum spanning tree is 0.82 -- close to the value for a uniform volume distribution. All of the (nine) sources with detections at multiple frequencies have SEDs consistent with dust emission, and two (SMA1b and SMA4) also have long wavelength emission consistent with a central hypercompact HII region. Thermal spectral line emission, including CH3CN, is detected in six sources: LTE model fitting of CH3CN(J=12-11) yields temperatures of 72-373K, confirming the presence of multiple hot cores. The fitted LSR velocities range from -3.3 to -7.0 km/s, with an unbiased mean square deviation of 2.05 km/s, implying a dynamical mass of 410+-260 Msun for the protocluster. From analysis of a wide range of hot core molecules, the kinematics of SMA1b are consistent with a rotating, infalling Keplerian disk of diameter 800AU and enclosed mass of 10-30 Msun that is perpendicular (within 1 degree) to the large-scale bipolar outflow axis. A companion to SMA1b at a projected separation of 0.45" (590AU; SMA1d), which shows no evidence of spectral line emission, is also confirmed. Finally, we detect one 218.440GHz and several 229.7588GHz Class-I methanol masers.
    The Astrophysical Journal 05/2014; 788(2). · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Large-scale Spitzer surveys of the Galactic plane have yielded a new tracer of massive young stellar objects (MYSOs) that are actively accreting and driving outflows: extended emission in the IRAC 4.5 μm band, believed to arise from shocked molecular gas. The GLIMPSE catalog of extended 4.5 μm sources (called EGOs, Extended Green Objects, for the common coding of 3-color IRAC images) is a unique sample, well-suited for studying the initial stages of massive star formation and establishing an observation-based MYSO evolutionary sequence. In this proceeding, we present results from extensive recent high-resolution Submillimeter Array (SMA) and Very Large Array (VLA) observations of EGOs at cm-mm wavelengths, including maser, molecular line, and continuum studies. These observations often reveal (proto)clusters that exhibit chemical and evolutionary diversity.
    11/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We explore the evolutionary diversity of the massive protocluster NGC 6334 I using comparable sub-arcsecond resolution (~600 AU at 1.6 kpc) imaging from centimeter to submillimeter wavelengths. Using the recently upgraded Jansky Very Large Array (VLA) at 6 cm, 1.5 cm, and 0.7 cm and the A and B configurations, we have detected all four members of the massive millimeter protocluster NGC 6334 I in at least one centimeter wavelength. We also find a new continuum source (JVLA1) detected only at 6 cm which coincides with the group of water masers located north of SMA1. Combined with Submillimeter Array (SMA) imaging at 1.3 mm and 0.86 mm, we analyze the continuum emission from each object, disentangling the dust component from the various types of free-free emission where possible. We briefly summarize the relative evolutionary state of all the objects in light of these latest images of the continuum, molecular line, and maser emission.
    07/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Spitzer surveys of the inner Galactic Plane (GLIMPSE I & II) revealed a promising new diagnostic for identifying actively accreting (proto)stars: extended excess emission in the IRAC 4.5 micron band, believed to trace shocked molecular gas in active protostellar outflows. We will present initial results from our search for extended excess 4.5 micron sources in the outer Galaxy GLIMPSE360 survey, focusing on the area of the survey associated with the Perseus arm.
    06/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Based on astrochemical theory, the complex molecular composition around high-mass YSOs should evolve from the outer envelope in toward the central hot region as a sequence of temperature dependent chemical pathways are activated in ices and in the gas-phase. The resulting complex molecules have been broadly classified into three generations dependent on the temperature (<25, >25, and >100 K) required for formation. We combine IRAM 30m and Submillimeter Array observations to explore the spatial distribution of organic molecules around the high-mass young stellar object NGC 7538 IRS9, whose weak complex molecule emission previously escaped detection, quantifying the emission and abundance profiles of key organic molecules as a function of distance from the central protostar. We find that emission from N-bearing organics and saturated O-bearing organics present large increases in emission around 8000 AU and R<3000 AU, while O-bearing molecules and hydrocarbons do not. The increase in flux from some complex molecules in the envelope, around 8000 AU or 25 K, is consistent with recent model predictions of an onset of complex ice chemistry at 20-30 K. The emission increase for some molecules at R<3000 AU suggests the presence of a weak hot core, where thermal ice evaporation and hot gas-phase chemistry drives the chemistry. Complex organics thus form at all radii and temperatures around this protostar, but the composition changes dramatically as the temperature increases, which is used to constrain the chemical generation(s) to which different classes of molecule belong.
    The Astrophysical Journal 05/2013; 771(2). · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of a Nobeyama 45 m H2O maser and NH3 survey of all 94 northern GLIMPSE extended green objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5 μm emission. We observed the NH3(1,1), (2,2), and (3,3) inversion lines, and detected emission toward 97%, 63%, and 46% of our sample, respectively (median rms ~ 50 mK). The H2O maser detection rate is 68% (median rms ~ 0.11 Jy). The derived H2O maser and clump-scale gas properties are consistent with the identification of EGOs as young MYSOs. To explore the degree of variation among EGOs, we analyze subsamples defined based on mid-infrared (MIR) properties or maser associations. H2O masers and warm dense gas, as indicated by emission in the higher-excitation NH3 transitions, are most frequently detected toward EGOs also associated with both Class I and II CH3OH masers. Ninety-five percent (81%) of such EGOs are detected in H2O (NH3(3,3)), compared to only 33% (7%) of EGOs without either CH3OH maser type. As populations, EGOs associated with Class I and/or II CH3OH masers have significantly higher NH3 line widths, column densities, and kinetic temperatures than EGOs undetected in CH3OH maser surveys. However, we find no evidence for statistically significant differences in H2O maser properties (such as maser luminosity) among any EGO subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane Survey, we find no correlation between isotropic H2O maser luminosity and clump number density. H2O maser luminosity is weakly correlated with clump (gas) temperature and clump mass.
    The Astrophysical Journal 01/2013; 764(1):61. · 6.73 Impact Factor
  • Claudia Cyganowski, C. L. Brogan, T. R. Hunter, Q. Zhang
    [Show abstract] [Hide abstract]
    ABSTRACT: I will describe a survey of protocluster evolution conducted with the Submillimeter Array (SMA), in 1.3 mm line and continuum emission. The survey targets a representative sample of ~10 GLIMPSE Extended Green Objects (EGOs), identified by their extended 4.5 micron emission in IRAC images. EGOs are a unique sample, targeting a crucial stage of massive star and cluster formation: when rapid accretion must be ongoing and the final masses of the (proto)stars are yet to be determined. The wide-bandwidth SMA observing setup includes outflow tracers (CO, SiO) and indicators of chemistry and evolutionary state; the angular resolution is sufficient to distinguish multiplicity and chemical differentiation on cluster scales 3 12,000 AU at a typical distance of 4 kpc). I will present initial results from the SMA survey, focusing on (proto)stellar multiplicity and clustering scales and evidence for chemical/evolutionary diversity within protoclusters. I will complement the SMA survey results with Karl G. Jansky Very Large Array (VLA) cm continuum data. Support for this work was provided by an NSF Astronomy and Astrophysics Postdoctoral Fellowship to C. Cyganowski under award AST-1003134.
    01/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Physical parameters for 5106 visually identified infrared bubbles, located in Spitzer GLIMPSE/MIPSGAL data. (2 data files).
    VizieR Online Data Catalog. 11/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of a Nobeyama 45-m water maser and ammonia survey of all 94 northern GLIMPSE Extended Green Objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5 micron emission. We observed the ammonia (1,1), (2,2), and (3,3) inversion lines, and detect emission towards 97%, 63%, and 46% of our sample, respectively (median rms ~50 mK). The water maser detection rate is 68% (median rms ~0.11 Jy). The derived water maser and clump-scale gas properties are consistent with the identification of EGOs as young MYSOs. To explore the degree of variation among EGOs, we analyze subsamples defined based on MIR properties or maser associations. Water masers and warm dense gas, as indicated by emission in the higher-excitation ammonia transitions, are most frequently detected towards EGOs also associated with both Class I and II methanol masers. 95% (81%) of such EGOs are detected in water (ammonia(3,3)), compared to only 33% (7%) of EGOs without either methanol maser type. As populations, EGOs associated with Class I and/or II methanol masers have significantly higher ammonia linewidths, column densities, and kinetic temperatures than EGOs undetected in methanol maser surveys. However, we find no evidence for statistically significant differences in water maser properties (such as maser luminosity) among any EGO subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane Survey, we find no correlation between isotropic water maser luminosity and clump number density. Water maser luminosity is weakly correlated with clump (gas) temperature and clump mass.
    10/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present high angular resolution Submillimeter Array (SMA) and Karl G. Jansky Very Large Array (VLA) observations of the massive protocluster G18.67+0.03. Previously targeted in maser surveys of GLIMPSE Extended Green Objects (EGOs), this cluster contains three Class I methanol maser sources, providing a unique opportunity to test the proposed role of Class I masers as evolutionary indicators for massive star formation. The millimeter observations reveal bipolar molecular outflows, traced by 13CO(2-1) emission, associated with all three Class I maser sources. Two of these sources (including the EGO) are also associated with 6.7 GHz Class II methanol masers; the Class II masers are coincident with millimeter continuum cores that exhibit hot core line emission and drive active outflows, as indicated by the detection of SiO(5-4). In these cases, the Class I masers are coincident with outflow lobes, and appear as clear cases of excitation by active outflows. In contrast, the third Class I source is associated with an ultracompact HII region, and not with Class II masers. The lack of SiO emission suggests the 13CO outflow is a relic, consistent with its longer dynamical timescale. Our data show that massive young stellar objects associated only with Class I masers are not necessarily young, and provide the first unambiguous evidence that Class I masers may be excited by both young (hot core) and older (UC HII) MYSOs within the same protocluster.
    The Astrophysical Journal Letters 10/2012; 760(2). · 6.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated six H II regions with infrared, bright rimmed bubble or cometary morphology, in search of quantitative evidence for triggered star formation, both collect and collapse and radiatively driven implosion. We identified and classified 458 Young Stellar Objects (YSOs) in and around the H II regions. YSOs were determined by fitting a collection of radiative transfer model spectral energy distributions (SEDs) to infrared photometry for a large sample of point sources. We determined areas where there exist enhanced populations of relatively unevolved YSOs on the bright rims of these regions, suggesting that star formation has been triggered there. We further investigated the physical properties of the regions by using radio continuum emission as a proxy for ionizing flux powering the H II regions, and 13CO (1-0) observations to measure masses and gravitational stability of molecular clumps. We used an analytical model of collect and collapse triggered star formation, as well as a simulation of radiatively driven implosion, and thus we compare the observed properties of the molecular gas with those predicted in the triggering scenarios. Notably, those regions in our sample that show evidence of cometary, or "blister," morphology are more likely to show evidence of triggering. Keywords: HII regions -- ISM: bubbles -- Stars: formation -- Stars: protostars
    The Astronomical Journal 10/2012; 144(6). · 4.97 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have used the recently-upgraded Karl G. Jansky Very Large Array (JVLA) to conduct a K-band (~24 GHz) study of 22 massive young stellar objects in 1.3 cm continuum and a comprehensive set of diagnostic lines. This survey is unique in that it samples a wide range of massive star formation signposts simultaneously for the first time. In this proceeding we present preliminary results for the 11 sources in the 2-4 kpc distance bin. We detect compact NH3 cores in all of the fields, with many showing emission up through the (6,6) transition. Maser emission in the 25 GHz CH3OH ladder is present in 7 of 11 sources. We also detect non-thermal emission in the NH3 (3,3) transition in 7 of 11 sources.
    Proceedings of the International Astronomical Union 07/2012; 8(S287):497-501.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Large-scale Spitzer surveys of the Galactic plane have yielded a new diagnostic for massive young stellar objects (MYSOs) that are actively accreting and driving outflows: extended emission in the IRAC 4.5 μm band, believed to trace shocked molecular gas. Maser studies of these extended 4.5 μm sources (called EGOs, Extended Green Objects, for the common coding of 3-color IRAC images) have been and remain crucial for understanding the nature of EGOs. High detection rates in VLA CH3OH maser surveys provided the first proof that EGOs were indeed MYSOs driving outflows; our recent Nobeyama 45-m survey of northern EGOs shows that the majority are associated with H2O masers. Maser studies of EGOs also provide important constraints for the longstanding goal of a maser evolutionary sequence for MYSOs, particularly in combination with high resolution (sub)mm data. New SMA results show that Class I methanol masers can be excited by both young (hot core) and evolved (ultracompact HII region) sources within the same massive star-forming region.
    Proceedings of the International Astronomical Union 07/2012; 8(S287):127-132.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a new catalogue of 5,106 infrared bubbles created through visual classification via the online citizen science website 'The Milky Way Project'. Bubbles in the new catalogue have been independently measured by at least 5 individuals, producing consensus parameters for their position, radius, thickness, eccentricity and position angle. Citizen scientists - volunteers recruited online and taking part in this research - have independently rediscovered the locations of at least 86% of three widely-used catalogues of bubbles and H ii regions whilst finding an order of magnitude more objects. 29% of the Milky Way Project catalogue bubbles lie on the rim of a larger bubble, or have smaller bubbles located within them, opening up the possibility of better statistical studies of triggered star formation. Also outlined is the creation of a 'heat map' of star-formation activity in the Galactic plane. This online resource provides a crowd-sourced map of bubbles and arcs in the Milky Way, and will enable better statistical analysis of Galactic star-formation sites.
    Monthly Notices of the Royal Astronomical Society 01/2012; 424(4). · 5.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of deep, high angular resolution Very Large Array (VLA) surveys for radio continuum emission towards a sample of 14 GLIMPSE Extended Green Objects (EGOs). Identified as massive young stellar object (MYSO) outflow candidates based on their extended 4.5 micron emission in Spitzer images, the EGOs in our survey sample are also associated with 6.7 GHz Class II and/or 44 GHz Class I methanol masers. No continuum is detected at 3.6 or 1.3 cm towards the majority (57%) of our targets (median rms ~0.03 and 0.25 mJy/beam). Only two EGOs are associated with optically thin emission consistent with ultracompact/compact HII regions. Both of these sources exhibit cm-wavelength multiplicity, with evidence that one of the less-evolved members may be driving the 4.5 micron outflow. Most of the other cm-wavelength EGO counterparts are weak (< 1 mJy), unresolved, undetected at 1.3 cm, and characterized by intermediate spectral indices consistent with hypercompact (HC) HII regions or ionized winds or jets. One EGO cm counterpart, likely an optically thick HC HII region, is detected only at 1.3 cm and is associated with hot core line emission and water and 6.7 GHz methanol masers. The results of our exceptionally sensitive survey indicate that EGOs signify an early stage of massive star formation, before photoionizing feedback from the central MYSO significantly influences the (proto)cluster environment. Actively driving outflows (and so, presumably, actively accreting), the surveyed EGOs are associated with significant clump-scale gas reservoirs, providing sufficient material for sustained, rapid accretion.
    The Astrophysical Journal 09/2011; 743. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have performed a 1.3 cm survey of 24 massive young stellar objects (MYSOs) using the Expanded Very Large Array. The sources in the sample exhibit a broad range of massive star formation signposts including infrared dark clouds (IRDCs), ultra-compact H II (UC H II) regions, and extended 4.5 μm emission in the form of extended green objects (EGOs). In this work, we present results for G35.03+0.35 which exhibits all of these phenomena. We simultaneously image the 1.3 cm NH3 (1,1) through (6,6) inversion lines, four CH3OH transitions, two H recombination lines, plus continuum at 0.05 pc resolution. We find three areas of thermal NH3 emission, two within the EGO (designated as the NE and SW cores) and one toward an adjacent IRDC. The NE core contains a UC H II region (CM1) and a candidate hyper-compact H II region (CM2). A region of non-thermal, likely masing NH3 (3,3) and (6,6) emission is coincident with an arc of 44 GHz CH3OH masers. We also detect two new 25 GHz Class-I CH3OH masers. A complementary Submillimeter Array 1.3 mm continuum image shows that the distribution of dust emission is similar to the lower-lying NH3 lines, all peaking to the NW of CM2, indicating the likely presence of an additional MYSO in this protocluster. By modeling the NH3 and 1.3 mm continuum data, we obtain gas temperatures of 20-220 K and masses of 20-130 M ☉. The diversity of continuum emission properties and gas temperatures suggests that objects in a range of evolutionary states exist concurrently in this protocluster.
    The Astrophysical Journal Letters 08/2011; 739(1):L16. · 6.35 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of a GBT survey of NH3(1,1), (2,2), (3,3) lines towards 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic longitudes in the inner Galaxy. We have detected the NH3(1,1) line towards 72% of our targets (456), demonstrating that the high column density features identified in the BGPS and other continuum surveys accurately predict the presence of dense gas. We have determined kinematic distances and resolved the distance ambiguity for all BGPS sources detected in NH3. The BGPS sources trace the locations of the Scutum and Sagittarius spiral arms, with the number of sources peaking between Galactocentric radii of 4-5 kpc. We measure the physical properties of each source and find that depending on the distance, BGPS sources are primarily clumps, with some cores and clouds. We have examined the physical properties as a function of Galactocentric distance, and find a mean gas kinetic temperature of 15.6 K, and that the NH3 column density and abundance decrease by nearly an order of magnitude between Galactocentric radii of 3 - 11 kpc. Comparing sources at similar distances demonstrates that the physical properties are indistinguishable, which suggests a similarity in clump structure across the Galactic disk. We have also compared the BGPS sources to criteria for efficient star formation presented independently by Heiderman et al. and Lada et al., and massive star formation presented by Kauffmann et al. 48% of our sample should be forming stars (including massive stars) with high efficiency, and 87% contain subregions that should be efficiently forming stars. Indeed, we find that 67% of the sample exhibit signs of star formation activity based on an association with a mid-IR source.
    The Astrophysical Journal 08/2011; 741(2). · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have performed a 1.3 centimeter survey of 24 massive young stellar objects (MYSOs) using the Expanded Very Large Array (EVLA). The sources in the sample exhibit a broad range of massive star formation signposts including Infrared Dark Clouds (IRDCs), UCHII regions, and extended 4.5 micron emission in the form of Extended Green Objects (EGOs). In this work, we present results for G35.03+0.35 which exhibits all of these phenomena. We simultaneously image the 1.3 cm ammonia (1,1) through (6,6) inversion lines, four methanol transitions, two H recombination lines, plus continuum at 0.05 pc resolution. We find three areas of thermal ammonia emission, two within the EGO (designated the NE and SW cores) and one toward an adjacent IRDC. The NE core contains an UCHII region (CM1) and a candidate HCHII region (CM2). A region of non-thermal, likely masing ammonia (3,3) and (6,6) emission is coincident with an arc of 44 GHz methanol masers. We also detect two new 25 GHz Class I methanol masers. A complementary Submillimeter Array 1.3 mm continuum image shows that the distribution of dust emission is similar to the lower-lying ammonia lines, all peaking to the NW of CM2, indicating the likely presence of an additional MYSO in this protocluster. By modeling the ammonia and 1.3 mm continuum data, we obtain gas temperatures of 20-220 K and masses of 20-130 solar. The diversity of continuum emission properties and gas temperatures suggest that objects in a range of evolutionary states exist concurrently in this protocluster.
    06/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We propose to re-observe and enhance the original GLIMPSE survey region by following the Galactic warp at a Galactocentric distance of 13 kpc to survey the far outer Galaxy. The new survey will cover longitudes of 15 < l l > -95, with a latitude width of 2.5 degrees; 55% of the survey will overlap with GLIMPSE, and 45% will cover new territory. The survey strategy of 3 HDR visits on each sky position will increase the dynamic range over GLIMPSE by a factor of 13 on the faint end and 3 on the bright end. The survey will be enhanced by several complementary surveys at near-IR, mid-IR, far-IR, submm, and radio wavelengths. Deep GLIMPSE will allow us to map stellar Galactic structure out to the edge of the stellar disk; map star formation and H II regions in the far outer Galaxy; improve our estimate of the star formation rate (SFR) of the Galaxy and study the SFR as a function of Galactocentric distance; study low-mass as well as high-mass star formation in the Galactic plane and determine stellar mass functions and evolutionary timescales of YSOs as a function of stellar mass and environment; continue to catalog PAH bubbles, IRDCs, YSO outflows, stellar clusters, external galaxies, brown dwarfs, and more; and search for dwarf galaxies hidden by the Galactic midplane.
    Spitzer Proposal. 05/2011;

Publication Stats

658 Citations
191.73 Total Impact Points

Institutions

  • 2014
    • University of St Andrews
      Saint Andrews, Scotland, United Kingdom
  • 2008–2014
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 2007–2010
    • University of Wisconsin, Madison
      • Department of Astronomy
      Mississippi, United States
  • 2003
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States