B. S. Gaudi

The Ohio State University, Columbus, Ohio, United States

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Publications (232)886.68 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: NASA's proposed WFIRST-AFTA mission will discover thousands of exoplanets with separations from the habitable zone out to unbound planets, using the technique of gravitational microlensing. The Study Analysis Group 11 of the NASA Exoplanet Program Analysis Group was convened to explore scientific programs that can be undertaken now, and in the years leading up to WFIRST's launch, in order to maximize the mission's scientific return and to reduce technical and scientific risk. This report presents those findings, which include suggested precursor Hubble Space Telescope observations, a ground-based, NIR microlensing survey, and other programs to develop and deepen community scientific expertise prior to the mission.
    09/2014;
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    ABSTRACT: We present the analysis of the gravitational microlensing event OGLE-2013-BLG-0102. The light curve of the event is characterized by a strong short-term anomaly superposed on a smoothly varying lensing curve with a moderate magnification $A_{\rm max}\sim 1.5$. It is found that the event was produced by a binary lens with a mass ratio between the components is $q = 0.13$ and the anomaly was caused by the passage of the source trajectory over a caustic located away from the barycenter of the binary. From the analysis of the effects on the light curve due to the finite size of the source and the parallactic motion of the Earth, the physical parameters of the lens system are determined. The measured masses of the lens components are $M_{1} = 0.097 \pm 0.011~M_{\odot}$ and $M_{2} = 0.013 \pm 0.002~M_{\odot}$, which correspond to the upper and lower limits of brown dwarfs, respectively. The distance to the lens is $3.02 \pm 0.21~{\rm kpc}$ and the projected separation between the lens components is $0.80 \pm 0.04~{\rm AU}$. These physical parameters lie beyond the detection ranges of other methods, demonstrating that microlensing is a useful method in detecting very low-mass binaries.
    07/2014;
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    ABSTRACT: Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earth’s) and lies projected at ~0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planet’s temperature is much lower, <60 Kelvin, because the host star is only 0.10 to 0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host itself orbits a slightly more massive companion with projected separation of 10 to 15 AU. This detection is consistent with such systems being very common. Straightforward modification of current microlensing search strategies could increase sensitivity to planets in binary systems. With more detections, such binary-star planetary systems could constrain models of planet formation and evolution.
    Science 07/2014; 345(6192):46-49. · 31.20 Impact Factor
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    ABSTRACT: We report the discovery of MOA-2013-BLG-220Lb, which has a super-Jupiter mass ratio q = 3.01 ± 0.02 × 10--3 relative to its host. The proper motion, mu = 12.5 ± 1 mas yr--1, is one of the highest for microlensing planets yet discovered, implying that it will be possible to separately resolve the host within ~7 yr. Two separate lines of evidence imply that the planet and host are in the Galactic disk. The planet could have been detected and characterized purely with follow-up data, which has important implications for microlensing surveys, both current and into the Large Synoptic Survey Telescope (LSST) era.
    The Astrophysical Journal 07/2014; 790(1):14. · 6.73 Impact Factor
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    ABSTRACT: The Korean Microlensing Telescope Network (KMTNet) will consist of three 1.6m telescopes each with a 4 deg^{2} field of view (FoV) and will be dedicated to monitoring the Galactic Bulge to detect exoplanets via gravitational microlensing. KMTNet's combination of aperture size, FoV, cadence, and longitudinal coverage will provide a unique opportunity to probe exoplanet demographics in an unbiased way. Here we present simulations that optimize the observing strategy for, and predict the planetary yields of, KMTNet. We find preferences for four target fields located in the central Bulge and an exposure time of t_{exp} = 120s, leading to the detection of ~2,200 microlensing events per year. We estimate the planet detection rates for planets with mass and separation across the ranges 0.1 <= M_{p}/M_{Earth} <= 1000 and 0.4 <= a/AU <= 16, respectively. Normalizing these rates to the cool-planet mass function of Cassan (2012), we predict KMTNet will be approximately uniformly sensitive to planets with mass 5 <= M_{p}/M_{Earth} <= 1000 and will detect ~20 planets per year per dex in mass across that range. For lower-mass planets with mass 0.1 <= M_{p}/M_{Earth} < 5, we predict KMTNet will detect ~10 planets per year. We also compute the yields KMTNet will obtain for free-floating planets (FFPs) and predict KMTNet will detect ~1 Earth-mass FFP per year, assuming an underlying population of one such planet per star in the Galaxy. Lastly, we investigate the dependence of these detection rates on the number of observatories, the photometric precision limit, and optimistic assumptions regarding seeing, throughput, and flux measurement uncertainties.
    06/2014;
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    ABSTRACT: Characterizing a microlensing planet is done from modeling an observed lensing light curve. In this process, it is often confronted that solutions of different lensing parameters result in similar light curves, causing difficulties in uniquely interpreting the lens system, and thus understanding the causes of different types of degeneracy is important. In this work, we show that incomplete coverage of a planetary perturbation can also result in degenerate solutions even for events where the planetary signal is detected with a high level of statistical significance. We demonstrate the degeneracy for an actually observed event OGLE-2012-BLG-0455/MOA-2012-BLG-206. The peak of this high-magnification event $(A_{\rm max}\sim400)$ exhibits very strong deviation from a point-lens model with $\Delta\chi^{2}\gtrsim4000$. From detailed modeling of the light curve, we find that the deviation can be explained by four distinct solutions, i.e., two very different sets of solutions, each with a two-fold degeneracy. While the two-fold (so-called ``close/wide'') degeneracy is well-understood, the degeneracy between the radically different solutions is not previously known. The model light curves of this degeneracy differ substantially in the parts that were not covered by observation, indicating that the degeneracy is caused by the incomplete coverage of the perturbation. It is expected that the frequency of the degeneracy introduced in this work will be greatly reduced with the improvement of the current lensing survey and follow-up experiments and the advent of new surveys.
    The Astrophysical Journal 05/2014; 787(1):71. · 6.73 Impact Factor
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    ABSTRACT: The mass of the lenses giving rise to Galactic microlensing events can be constrained by measuring the relative lens-source proper motion and lens flux. The flux of the lens can be separated from that of the source, companions to the source, and unrelated nearby stars with high-resolution images taken when the lens and source are spatially resolved. For typical ground-based adaptive optics (AO) or space-based observations, this requires either inordinately long time baselines or high relative proper motions. We provide a list of microlensing events toward the Galactic Bulge with high relative lens-source proper motion that are therefore good candidates for constraining the lens mass with future high-resolution imaging. We investigate all events from 2004 -- 2013 that display detectable finite-source effects, a feature that allows us to measure the proper motion. In total, we present 20 events with mu >~ 8 mas/yr. Of these, 14 were culled from previous analyses while 6 are new, including OGLE-2004-BLG-368, MOA-2005-BLG-36, OGLE-2012-BLG-0211, OGLE-2012-BLG-0456, MOA-2012-BLG-532, and MOA-2013-BLG-029. In <~12 years the lens and source of each event will be sufficiently separated for ground-based telescopes with AO systems or space telescopes to resolve each component and further characterize the lens system. Furthermore, for the most recent events, comparison of the lens flux estimates from images taken immediately to those estimated from images taken when the lens and source are resolved can be used to empirically check the robustness of the single-epoch method currently being used to estimate lens masses for many events.
    03/2014;
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    ABSTRACT: Based on its high proper motion $\mu=12.5\pm 1\,\masyr$, MOA-2013-BLG-220Lb is the best candidate to date for a microlensing planet with a verifiable brown dwarf host. This candidacy can be partially tested immediately and more fully tested by $\sim 2021$, when the source and lens will have separated sufficiently to be resolved in high-resolution images even if the lens is at the bottom of the main sequence, and so extremely faint, $H\sim 24$. The planet-star mass ratio is $q=3.01\pm 0.02\times 10^{-3}$. The planet could have been detected and characterized purely with follow-up data. The potential to completely characterize planetary events from followup data has far-reaching implications for microlensing surveys, both current and into the LSST era.
    03/2014;
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    ABSTRACT: We present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius determined from finite-source effects, we estimate the physical parameters of the lens system. We find that the event was caused by a $2.73\pm 0.43\ M_{\rm J}$ planet orbiting a $0.44\pm 0.07\ M_{\odot}$ early M-type star. The distance to the lens is $4.97\pm 0.29$\ kpc and the projected separation between the host star and its planet at the time of the event is $3.45\pm 0.26$ AU. We find that the additional coverage provided by follow-up observations, especially during the planetary perturbation, leads to a more accurate determination of the physical parameters of the lens.
    The Astrophysical Journal 02/2014; 782(1):48. · 6.73 Impact Factor
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    ABSTRACT: The unique sensitivity of gravitational microlensing to low-mass planets at or beyond the snow line makes it an indispensable tool for understanding the distribution and formation mechanisms of exoplanets. The Korean Microlensing Telescope Network (KMTNet) consists of three 1.6m telescopes each with a 4 deg2 field of view and will be dedicated to monitoring the Galactic Bulge in order to detect exoplanets via gravitational microlensing. With its relatively large aperture, large field of view, high cadence, and near-complete longitudinal coverage of the Galactic Bulge for much of the microlensing observing season (early March through late October), KMTNet will provide the opportunity to probe exoplanet demographics in an unbiased and automated way. Here we present detailed simulations that optimize the observing strategy and predict the planetary yields of KMTNet for planets with mass greater than that of Mars, including those for solivagant planets.
    01/2014;
  • Matthew Penny, B. S. Gaudi
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    ABSTRACT: One of the primary goals of the Kepler mission is to determine the frequency of habitable terrestrial planets around sunlike stars (η_Earth). While there have already been estimates of the frequency of habitable planets orbiting M-dwarfs, the longer periods and larger-than-expected activity intrinsic stellar variability may make the estimates of η_Earth for sunlike stars substantially more uncertain. The gravitational microlensing survey of the AFTA-WFIRST mission will complement Kepler's search for warm and hot planets by characterizing the frequency of cold planets. While the majority of the host stars of the microlensing survey will be low-mass stars, AFTA-WFIRST is most sensitive to habitable planets around the sunlike hosts. I will introduce the microlensing survey of AFTA-WFIRST, and then focus on its ability to detect habitable planets and its synergies with Kepler. Specifically, I will discuss how results on the abundances of planets from Kepler and AFTA-WFIRST might be combined to interpolate into the habitable zone and thus obtain a more robust measurement of η_Earth.
    01/2014;
  • Matthew T. Penny, B. Scott Gaudi
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    ABSTRACT: The Wide Field InfraRed Survey Telescope (WFIRST) was the top ranked large space mission of the New Worlds, New Horizons Decadal Survey, and is currently under active study by NASA. Its primary instrument will be a large-format high-resolution near-infrared imager and slitless spectrometer. A primary goal of WFIRST will be to perform a high-cadence microlensing survey of the Galactic bulge to search for low-mass exoplanets beyond the ice line. We highlight some of the expected results of the WFIRST exoplanet survey. For example, the survey will probe the abundance of Earth-mass planets from less than 1 AU outwards, including free-floating planets. In its peak sensitivity range of ~2-5 AU, WFIRST will be sensitive to planets with masses lower than Mercury, and even down to the mass of Ganymede. Overall, WFIRST is expected to detect several thousand bound planets, in addition to several thousand free-floating planets. WFIRST will complete the exoplanet census begun by Kepler, enabling an unprecedented understanding of planetary systems and their formation.
    Proceedings of the International Astronomical Union 01/2014;
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    ABSTRACT: We are building an ultra-precise Doppler spectrometer for the Large Binocular Telescope (LBT) that operates at near-infrared wavelengths. The instrument, named iLocater, holds significant advantages over current and forth-coming Doppler designs. An R=110,000 spectrograph that operates in the Y-band, iLocater will receive a well-corrected beam from the LBT “extreme” adaptive optics system and use single-mode optical fibers to stabilize the instrument line spread function. With an input image 30 times smaller than comparable seeing-limited instruments (i.e., all Doppler radial velocity predecessors), iLocater will simultaneously achieve high spectral resolution, high spatial resolution, high throughput, and a compact optical design for low cost (affordable gratings). By working at the diffraction-limit, it is possible to circumvent, or ameliorate, many of the sources of noise common to seeing-limited spectrometers, including background contamination, thermal drifts, binary star interlopers, and pressure-induced changes in refractive index. Further, starlight received simultaneously from the LBT’s two separate telescope dishes may be used to monitor and remove internal systematic RV errors. iLocater will: identify "Earth-like" planets orbiting in the habitable-zone around nearby M-dwarf stars; perform the first systematic study of planet occurrence around binary stars as a function of their orbital separation; obtain the first spin-orbit orientation measurements of transiting terrestrial planets; and acquire essential follow-up observations for NASA's planned Transiting Exoplanet Survey Satellite (TESS) mission. In this poster, we present iLocater's design and science cases.
    01/2014;
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    ABSTRACT: We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of M_host ~ 4 Jupiter masses hosting a sub-Earth mass moon. The data are well fit by this exomoon model, but an alternate star+planet model fits the data almost as well. Nevertheless, these results indicate the potential of microlensing to detect exomoons, albeit ones that are different from the giant planet moons in our solar system. The argument for an exomoon hinges on the system being relatively close to the Sun. The data constrain the product M pi_rel, where M is the lens system mass and pi_rel is the lens-source relative parallax. If the lens system is nearby (large pi_rel), then M is small (a few Jupiter masses) and the companion is a sub-Earth-mass exomoon. The best-fit solution has a large lens-source relative proper motion, mu_rel = 19.6 +- 1.6 mas/yr, which would rule out a distant lens system unless the source star has an unusually high proper motion. However, data from the OGLE collaboration nearly rule out a high source proper motion, so the exoplanet+exomoon model is the favored interpretation for the best fit model. However, the alternate solution has a lower proper motion, which is compatible with a distant (so stellar) host. A Bayesian analysis does not favor the exoplanet+exomoon interpretation, so Occam's razor favors a lens system in the bulge with host and companion masses of M_host = 0.12 (+0.19 -0.06) M_solar and m_comp = 18 (+28 -100 M_earth, at a projected separation of a_perp ~ 0.84 AU. The existence of this degeneracy is an unlucky accident, so current microlensing experiments are in principle sensitive to exomoons. In some circumstances, it will be possible to definitively establish the low mass of such lens systems through the microlensing parallax effect. Future experiments will be sensitive to less extreme exomoons.
    12/2013;
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    ABSTRACT: We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11+/-0.01 M_{sun} and Mp = 9.2+/-2.2M_Earth, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at DL = 0.81 +/- 0.10 kpc with projected separation r = 0.92 +/- 0.16 AU. Because of the host's a-priori-unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its close host distance. We show that future high-resolution astrometric measurements could decisively resolve the remaining ambiguity of these solutions.
    The Astrophysical Journal 12/2013; 779:91. · 6.73 Impact Factor
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    ABSTRACT: Observations of accretion disks around young brown dwarfs have led to the speculation that they may form planetary systems similar to normal stars. While there have been several detections of planetary-mass objects around brown dwarfs (2MASS 1207-3932 and 2MASS 0441-2301), these companions have relatively large mass ratios and projected separations, suggesting that they formed in a manner analogous to stellar binaries. We present the discovery of a planetary-mass object orbiting a field brown dwarf via gravitational microlensing, OGLE-2012-BLG-0358Lb. The system is a low secondary/primary mass ratio (0.080 +- 0.001), relatively tightly-separated (~0.87 AU) binary composed of a planetary-mass object with 1.9 +- 0.2 Jupiter masses orbiting a brown dwarf with a mass 0.022 M_Sun. The relatively small mass ratio and separation suggest that the companion may have formed in a protoplanetary disk around the brown dwarf host, in a manner analogous to planets.
    The Astrophysical Journal 11/2013; 778:38. · 6.73 Impact Factor
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    ABSTRACT: We present secondary eclipse observations of the highly irradiated transiting brown dwarf KELT-1b. Using the Spitzer Space Telescope, we measure secondary eclipse depths of 0.195+/-0.010% at 3.6um and 0.200+/-0.012% at 4.5um, corresponding to a fairly grey color of [3.6]-[4.5]=0.07+/-0.11. Using four separate ground-based light curves, we find tentative evidence for the secondary eclipse in the z' band with a depth of 0.049+/-0.023%. These observations suggest that the amount of heat redistribution in the atmosphere to the night side is very low, and prefer a model in which there is no TiO inversion and a strong substellar hotspot. However, models with no TiO and a more mild hotspot, or with TiO absorption and complete dayside redistribution, are only marginally disfavored. The eclipse timings and durations indicate that the orbital eccentricity of KELT-1b is consistent with circular to better than a percent. These observations represent the first constraints on the atmospheric dynamics of a highly irradiated brown dwarf, and are interesting in the context of both the atmospheres of irradiated giant planets at high surface gravity, and the atmospheres of brown dwarfs that are dominated by external, rather than internal, energy. In particular, as compared to objects of similar temperature, KELT-1b has a [3.6]-[4.5]~0 color that is more similar to isolated brown dwarfs, as opposed to lower surface gravity exoplanets, which tend to have redder colors. Future phase curve observations at different wavelengths with Spitzer or JWST will provide important constraints on the precise amount of heat redistribution and the presence of a day-night TiO cold trap in the atmosphere of this unique transition object.
    The Astrophysical Journal 10/2013; 783(2). · 6.73 Impact Factor
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    ABSTRACT: We used Keck adaptive optics observations to identify the first planet discovered by microlensing to lie in or near the habitable zone, i.e., at projected separation $r_\perp=1.1\pm 0.1\,$AU from its $M_{L}=0.86\pm 0.06\,M_\odot$ host, being the highest microlensing mass definitely identified. The planet has a mass $m_p = 4.8\pm 0.3\,M_{\rm Jup}$, and could in principle have habitable moons. This is also the first planet to be identified as being in the Galactic bulge with good confidence: $D_L=7.7\pm 0.44$ kpc. The planet/host masses and distance were previously not known, but only estimated using Bayesian priors based on a Galactic model (Yee et al. 2012). These estimates had suggested that the planet might be a super-Jupiter orbiting an M dwarf, a very rare class of planets. We obtained high-resolution $JHK$ images using Keck adaptive optics to detect the lens and so test this hypothesis. We clearly detect light from a G dwarf at the position of the event, and exclude all interpretations other than that this is the lens with high confidence (95%), using a new astrometric technique. The calibrated magnitude of the planet host star is $H_{L}=19.16\pm 0.13$. We infer the following probabilities for the three possible orbital configurations of the gas giant planet: 53% to be in the habitable zone, 35% to be near the habitable zone, and 12% to be beyond the snow line, depending on the atmospherical conditions and the uncertainties on the semimajor axis.
    The Astrophysical Journal 10/2013; 780(1). · 6.73 Impact Factor
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    ABSTRACT: A planetary microlensing signal is generally characterized by a short-term perturbation to the standard single lensing light curve. A subset of binary-source events can produce perturbations that mimic planetary signals, thereby introducing an ambiguity between the planetary and binary-source interpretations. In this paper, we present analysis of the microlensing event MOA-2012-BLG-486, for which the light curve exhibits a short-lived perturbation. Routine modeling not considering data taken in different passbands yields a best-fit planetary model that is slightly preferred over the best-fit binary-source model. However, when allowed for a change in the color during the perturbation, we find that the binary-source model yields a significantly better fit and thus the degeneracy is clearly resolved. This event not only signifies the importance of considering various interpretations of short-term anomalies, but also demonstrates the importance of multi-band data for checking the possibility of false-positive planetary signals.
    08/2013;
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    ABSTRACT: We report the discovery of KELT-6b, a mildly-inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was confirmed using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V=10.38 host star (TYC 2532-556-1) is a mildly evolved, late-F star with T_eff=6102 \pm 43 K, log(g_*)=4.07_{-0.07}^{+0.04} and [Fe/H]=-0.28 \pm 0.04, with an inferred mass M_*=1.09 \pm 0.04 M_sun and radius R_*=1.58_{-0.09}^{+0.16} R_sun. The planetary companion has mass M_p=0.43 \pm 0.05 M_Jup, radius R_p=1.19_{-0.08}^{+0.13} R_Jup, surface gravity log(g_p)=2.86_{-0.08}^{+0.06}, and density rho_p=0.31_{-0.08}^{+0.07} g cm^{-3}. The planet is on an orbit with semimajor axis a=0.079 \pm 0.001 AU and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with circular, and has ephemeris of T_C(BJD_TDB)=2456347.79679 \pm 0.00036 and P=7.845631 \pm 0.000046 d. Equally plausible fits that employ empirical constraints on the host star parameters rather than isochrones yield a larger planet mass and radius by ~4-7%. KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458b by ~0.3 dex. Thus, the KELT-6 system is a metal-poor analog of HD 209458, and offers the unique opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images.
    08/2013;

Publication Stats

2k Citations
886.68 Total Impact Points

Institutions

  • 1996–2014
    • The Ohio State University
      • Department of Astronomy
      Columbus, Ohio, United States
  • 2013
    • Instituto de Astrofísica de Canarias
      San Cristóbal de La Laguna, Canary Islands, Spain
    • Vanderbilt University
      • Department of Physics and Astronomy
      Nashville, Michigan, United States
    • University of California, Santa Barbara
      Santa Barbara, California, United States
    • University of Florida
      • Department of Astronomy
      Gainesville, Florida, United States
  • 2012
    • Universidad de La Laguna
      • Department of Astrophysics
      San Cristóbal de La Laguna, Canary Islands, Spain
  • 2010
    • Fisk University
      • Department of Physics
      Nashville, Tennessee, United States
  • 2003–2008
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • Harvard University
      • Department of Astronomy
      Cambridge, Massachusetts, United States
  • 2007
    • University of California, Berkeley
      • Department of Astronomy
      Berkeley, California, United States
  • 2002
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States