Daniel C. Fabrycky

UPMC, Pittsburgh, Pennsylvania, United States

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Publications (130)892.39 Total impact

  • Source
    Gwenaël Boué, Daniel C. Fabrycky
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    ABSTRACT: The stellar spin orientation relative to the orbital planes of multiplanet systems are becoming accessible to observations. For example, 55 Cancri is a system composed of 5 planets orbiting a member of a stellar binary for which a projected obliquity of 72+-12 deg relative to the orbit of the innermost planet has been reported (Bourrier & Hebrard 2014). This large obliquity has been attributed to the perturbation induced by the binary. Here we describe the secular evolution of similar systems and we discuss the case of the 55 Cancri system more deeply. We provide two different orbital configurations compatible with the currently available observations.
    10/2014;
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    Joshua N. Winn, Daniel C. Fabrycky
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    ABSTRACT: The basic geometry of the Solar System -- the shapes, spacings, and orientations of the planetary orbits -- has long been a subject of fascination as well as inspiration for planet formation theories. For exoplanetary systems, those same properties have only recently come into focus. Here we review our current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multiplanet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems.
    10/2014;
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    ABSTRACT: We present the discovery of KIC 9632895b, a 6.2 Earth-radius planet in a low-eccentricity, 240.5-day orbit about an eclipsing binary. The binary itself consists of a 0.93 and 0.194 solar mass pair of stars with an orbital period of 27.3 days. The plane of the planet's orbit is rapidly precessing, and its inclination only becomes sufficiently aligned with the primary star in the latter portion of the Kepler data. Thus three transits are present in the latter half of the light curve, but none of the three conjunctions that occurred during the first half of the light curve produced transits. The precession period is ~103 years, and during that cycle, transits are visible only ~8% of the time. This has the important implication that for every system like KIC 9632895 that we detect, there are ~12 circumbinary systems that exist but are not currently exhibiting transits. The planet's mass is too small to noticeably perturb the binary, consequently its mass is not measurable with these data; but our photodynamical model places a 1-sigma upper limit of 16 Earth masses. With a period 8.8 times that of the binary, the planet is well outside the dynamical instability zone. It does, however, lie within the habitable zone of the binary, and making it the third of ten Kepler circumbinary planets to do so.
    09/2014;
  • Gwenaël Boué, Daniel C. Fabrycky
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    ABSTRACT: The non-resonant secular dynamics of compact planetary systems are modeled by a perturbing function that is usually expanded in eccentricity and absolute inclination with respect to the invariant plane. Here, the expressions are given in a vectorial form which naturally leads to an expansion in eccentricity and mutual inclination. The two approaches are equivalent in most cases, but the vectorial one is specially designed for those cases where an entire quasi-coplanar system tilts to a large degree. Moreover, the vectorial expressions of the Hamiltonian and of the equations of motion are slightly simpler than those given in terms of the usual elliptical elements. We also provide the secular perturbing function in vectorial form expanded in semi-major axis ratio allowing for arbitrary eccentricities and inclinations. The interaction between the equatorial bulge of a central star and its planets is also provided, as is the relativistic periapse precession of any planet induced by the central star. We illustrate the use of this representation to follow the secular oscillations of the terrestrial planets of the solar system and for Kozai cycles which may take place in exoplanetary systems.
    The Astrophysical Journal 06/2014; 789(2):110. · 6.73 Impact Factor
  • Gwenaël Boué, Daniel C. Fabrycky
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    ABSTRACT: The stellar spin orientation relative to the orbital planes of multiplanet systems is becoming accessible to observations. Here, we analyze and classify different types of spin-orbit evolution in compact multiplanet systems perturbed by an inclined outer companion. Our study is based on classical secular theory, using a vectorial approach developed in a separate paper. When planet-planet perturbations are truncated at the second order in eccentricity and mutual inclination, and the planet-companion perturbations are developed at the quadrupole order, the problem becomes integrable. The motion is composed of a uniform precession of the whole system around the total angular momentum, and in the rotating frame, the evolution is periodic. Here, we focus on the relative motion associated with the oscillations of the inclination between the planet system and the outer orbit and of the obliquities of the star with respect to the two orbital planes. The solution is obtained using a powerful geometric method. With this technique, we identify four different regimes characterized by the nutation amplitude of the stellar spin axis relative to the orbital plane of the planets. In particular, the obliquity of the star reaches its maximum when the system is in the Cassini regime where planets have more angular momentum than the star and where the precession rate of the star is similar to that of the planets induced by the companion. In that case, spin-orbit oscillations exceed twice the inclination between the planets and the companion. Even if the mutual inclination is only 20°, this resonant case can cause the spin-orbit angle to oscillate between perfectly aligned and retrograde values.
    The Astrophysical Journal 06/2014; 789(2):111. · 6.73 Impact Factor
  • Gwenaël Boué, Daniel Fabrycky
    [Show abstract] [Hide abstract]
    ABSTRACT: The non-resonant secular dynamics of compact planetary systems are modeled by a perturbing function which is usually expanded in eccentricity and absolute inclination with respect to the invariant plane. Here, the expressions are given in a vectorial form which naturally leads to an expansion in eccentricity and mutual inclination. The two approaches are equivalent in most cases, but the vectorial one is specially designed for those where a quasi-coplanar system tilts as a whole by a large amount. Moreover, the vectorial expressions of the Hamiltonian and of the equations of motion are slightly simpler than those given in terms of the usual elliptical elements. We also provide the secular perturbing function in vectorial form expanded in semimajor axis ratio allowing for arbitrary eccentricities and inclinations. The interaction between the equatorial bulge of a central star and its planets is also provided, as is the relativistic periapse precession of any planet induced by the central star. We illustrate the use of this representation for following the secular oscillations of the terrestrial planets of the solar system, and for Kozai cycles as may take place in exoplanetary systems.
    05/2014;
  • Gwenaël Boué, Daniel Fabrycky
    [Show abstract] [Hide abstract]
    ABSTRACT: The stellar spin orientation relative to the orbital planes of multiplanet systems are becoming accessible to observations. Here, we analyze and classify different types of spin-orbit evolution in compact multiplanet systems perturbed by an inclined outer companion. Our study is based on classical secular theory, using a vectorial approach developed in a separate paper. When planet-planet perturbations are truncated at the second order in eccentricity and mutual inclination, and the planet-companion perturbations are developed at the quadrupole order, the problem becomes integrable. The motion is composed of a uniform precession of the whole system around the total angular momentum, and in the rotating frame, the evolution is periodic. Here, we focus on the relative motion associated to the oscillations of the inclination between the planet system and the outer orbit, and of the obliquities of the star with respect to the two orbital planes. The solution is obtained using a powerful geometric method. With this technique, we identify four different regimes characterized by the nutation amplitude of the stellar spin-axis relative to the orbital plane of the planets. In particular, the obliquity of the star reaches its maximum when the system is in the Cassini regime where planets have more angular momentum than the star, and where the precession rate of the star is similar to that of the planets induced by the companion. In that case, spin-orbit oscillations exceed twice the inclination between the planets and the companion. Even if mutual inclination is only ~ 20 deg, this resonant case can cause the spin-orbit angle to oscillate between perfectly aligned and retrograde values.
    05/2014;
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    Smadar Naoz, Daniel C. Fabrycky
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    ABSTRACT: Many close stellar binaries are accompanied by a far-away star. The "eccentric Kozai-Lidov" (EKL) mechanism can cause dramatic inclination and eccentricity fluctuations, resulting in tidal tightening of inner binaries of triple stars. We run a large set of Monte-Carlo simulations including the secular evolution of the orbits, general relativistic precession and tides, and we determine the semimajor axis, eccentricity, inclination and spin-orbit angle distributions of the final configurations. We find that the efficiency of forming tight binaries (<~16 d) when taking the EKL mechanism into account is ~ 21%, and about 4% of all simulated systems ended up in a merger event. These merger events can lead to the formation of blue-stragglers. Furthermore, we find that the spin-orbit angle distribution of the inner binaries carries a signature of the initial setup of the system, thus observations can be used to disentangle close binaries' birth configuration. The resulting inner and outer final orbits' period distributions, and their estimated fraction, suggests secular dynamics may be a significant channel for the formation of close binaries in triples and even blue stragglers.
    The Astrophysical Journal 05/2014; 793(2). · 6.73 Impact Factor
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    ABSTRACT: We establish the three-dimensional architecture of the KOI-1474 system to be eccentric yet with a low mutual inclination. KOI-1474b is a warm Jupiter at semi-major axis a = 0.370 +0.007/-0.006 AU with a large eccentricity (e=0.85 +0.08/-0.07) measured via the "photoeccentric effect." It exhibits transit timing variations induced by the non-transiting KOI-1474c, which we uniquely constrain to be a moderately eccentric (e=0.184 +/- 0.002), hierarchically-separated (a=1.68 +/- 0.03 AU) giant planet (7.3 +/- 0.4 MJup). We combine sixteen quarters of Kepler photometry, radial-velocity (RV) measurements from the HIgh Resolution Echelle Spectrometer (HIRES) on Keck, and improved stellar parameters that we derive from spectroscopy and asteroseismology. From the RVs, we measure the mass of inner planet to be 2.6 +/- 0.3 MJup and confirm its photometrically-measured eccentricity, refining the value to e=0.83 +/- 0.01. The RV acceleration is consistent with the properties of the outer planet derived from TTVs. We find that, despite their sizable eccentricities, the planets are coplanar to within 10 +8/-6 degrees, and therefore the inner planet's large eccentricity and close-in orbit are unlikely to be the result of Kozai migration. Moreover, even over many secular cycles, the inner planet's periapse is most likely never small enough for tidal circularization. Finally, we present and measure a transit time and impact parameter from four simultaneous ground-based light curves from 1m-class telescopes, demonstrating the feasibility of ground-based follow-up of Kepler giant planets exhibiting large TTVs.
    The Astrophysical Journal 04/2014; 791(2). · 6.73 Impact Factor
  • Jun Yang, Gwenael Boue, Daniel C. Fabrycky, Dorian S. Abbot
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    ABSTRACT: Planetary rotation rate is a key parameter in determining atmospheric circulation and hence the spatial pattern of clouds. Since clouds can exert a dominant control on planetary radiation balance, rotation rate could be critical for determining mean planetary climate. Here we investigate this idea using a three-dimensional general circulation model with a sophisticated cloud scheme. We find that slowly rotating planets (like Venus) can maintain an Earth-like climate at nearly twice the stellar flux as rapidly rotating planets (like Earth). This suggests that many exoplanets previously believed to be too hot may actually be habitable, depending on their rotation rate. The explanation for this behavior is that slowly rotating planets have a weak Coriolis force and long daytime illumination, which promotes strong convergence and convection in the substellar region. This produces a large area of optically thick clouds, which greatly increases the planetary albedo. In contrast, on rapidly rotating planets a much narrower belt of clouds form in the deep tropics, leading to a relatively low albedo. A particularly striking example of the importance of rotation rate suggested by our simulations is that a planet with modern Earth's atmosphere, in Venus' orbit, and with modern Venus' (slow) rotation rate would be habitable. This would imply that if Venus went through a runaway greenhouse, it had a higher rotation rate at that time.
    04/2014; 787(1).
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    ABSTRACT: Kepler-79 (KOI-152) has four planetary candidates ranging in size from 3.5 to 7 times the size of the Earth, in a compact configuration with orbital periods near a 1:2:4:6 chain of commensurability, from 13.5 to 81.1 days. All four planets exhibit transit timing variations with periods that are consistent with the distance of each planet to resonance with its neighbors. We perform a dynamical analysis of the system based on transit timing measurements over 1282 days of Kepler photometry. Stellar parameters are obtained using a combination of spectral classification and the stellar density constraints provided by light curve analysis and orbital eccentricity solutions from our dynamical study. Our models provide tight bounds on the masses of all four transiting bodies, demonstrating that they are planets and that they orbit the same star. All four of Kepler-79's transiting planets have low densities given their sizes, which is consistent with other studies of compact multiplanet transiting systems. The largest of the four, Kepler-79 d (KOI-152.01), has the lowest bulk density yet determined among sub-Saturn mass planets.
    03/2014; 785(1).
  • Man Hoi Lee, D. Fabrycky, D. N. C. Lin
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    ABSTRACT: The multiple-planet systems discovered by the Kepler mission show an excess of planet pairs with period ratios just wide of exact commensurability for first-order resonances like 2:1 and 3:2. In principle, these planet pairs could be in resonance if their orbital eccentricities are sufficiently small, because the width of first-order resonances diverges in the limit of vanishingly small eccentricity. We consider a widely-held scenario in which pairs of planets were captured into first-order resonances by migration due to planet-disk interactions, and subsequently became detached from the resonances, due to tidal dissipation in the planets. In the context of this scenario, we find a constraint on the ratio of the planet's tidal dissipation function and Love number that implies that some of the Kepler planets are likely solid. However, tides are not strong enough to move many of the planet pairs to the observed separations, suggesting that additional processes are at play.
    03/2014;
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    ABSTRACT: As part of the BANANA project (Binaries Are Not Always Neatly Aligned), we have found that the eclipsing binary CV Velorum has misaligned rotation axes. Based on our analysis of the Rossiter-McLaughlin effect, we find sky-projected spin-orbit angles of $\beta_{\rm p} = -52\pm6^{\circ}$ and $\beta_{\rm s}= 3\pm7^{\circ}$ for the primary and secondary stars (B2.5V $+$ B2.5V, $P=6.9$ d). We combine this information with several measurements of changing projected stellar rotation speeds ($v \sin i_{\star}$) over the last $30$ years, leading to a model in which the primary star's obliquity is $\approx65^{\circ}$, and its spin axis precesses around the total angular momentum vector with a period of about $140$ years. The geometry of the secondary star is less clear, although a significant obliquity is also implicated by the observed time variations in the $v \sin i_{\star}$. By integrating the secular tidal evolution equations backward in time, we find that the system could have evolved from a state of even stronger misalignment similar to DI Herculis, a younger but otherwise comparable binary.
    The Astrophysical Journal 03/2014; 785(2). · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of a transiting, Rp = 4.347+/-0.099REarth, circumbinary planet (CBP) orbiting the Kepler K+M Eclipsing Binary (EB) system KIC 12351927 (Kepler-413) every ~66 days on an eccentric orbit with ap = 0.355+/-0.002AU, ep = 0.118+/-0.002. The two stars, with MA = 0.820+/-0.015MSun, RA = 0.776+/-0.009RSun and MB = 0.542+/-0.008MSun, RB = 0.484+/-0.024RSun respectively revolve around each other every 10.11615+/-0.00001 days on a nearly circular (eEB = 0.037+/-0.002) orbit. The orbital plane of the EB is slightly inclined to the line of sight (iEB = 87.33+/-0.06 degrees) while that of the planet is inclined by ~2.5 degrees to the binary plane at the reference epoch. Orbital precession with a period of ~11 years causes the inclination of the latter to the sky plane to continuously change. As a result, the planet often fails to transit the primary star at inferior conjunction, causing stretches of hundreds of days with no transits (corresponding to multiple planetary orbital periods). We predict that the next transit will not occur until 2020. The orbital configuration of the system places the planet slightly closer to its host stars than the inner edge of the extended habitable zone. Additionally, the orbital configuration of the system is such that the CBP may experience Cassini-States dynamics under the influence of the EB, in which the planet's obliquity precesses with a rate comparable to its orbital precession. Depending on the angular precession frequency of the CBP, it could potentially undergo obliquity fluctuations of dozens of degrees (and complex seasonal cycles) on precession timescales.
    The Astrophysical Journal 01/2014; 784(1). · 6.73 Impact Factor
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    ABSTRACT: We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities for all of the transiting planets (41 of 42 have a false-positive probability under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than 3X the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify 6 planets with densities above 5 g/cc, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than ~2 R_earth. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).
    01/2014;
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    ABSTRACT: Over the course of the past three years, the peerless-quality data from the NASA Kepler mission has allowed us to confirm, for the first time, the existence of eight circumbinary planets. This dissertation talk presents my contribution to the field in terms of discovery and characterization of three circumbinary planetary systems (Kepler-47, Kepler-64, KIC12351927). Here I describe the unique observational signatures of circumbinary planets, the detection method and analysis tools we developed to characterize the systems, and the theoretical implications of our discoveries. The results of my work deliver important new insight into the nature of these remarkable objects and are paramount for our understanding of a) how planets form and evolve in multiple stellar systems and b) what type of binary stars can support circumbinary planets. Adding new members to the still small family of circumbinary planets has direct relevance for estimating the planetary census in the Galaxy, and for the extension of the concept of habitability to binary stars.
    01/2014;
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    ABSTRACT: The transit timing variation (TTV) technique has recently become a crucial method for determining the complete architectures (i.e., planet masses, orbital eccentricities, inclinations, and resonant properties) of extrasolar planetary systems. This technique has blossomed because of the Kepler mission's discovery of systems with multiple transiting planets and individual planets exhibiting very large TTVs. All of Kepler's results in this area so far have been for relatively short-period planets, but Kepler has also discovered dynamically-interacting systems with planets that have longer periods, similar to those of the Solar System. However, the ill-timed failure of the Kepler telescope has left us with an incomplete picture of these systems due to a lack of the required time baseline. Fortunately, Spitzer is positioned to leverage the unique potential that these planets offer, by extending the time baseline of transit observations. We propose to observe transits of seven Kepler-discovered planets in four particularly compelling systems to precisely determine their transit times. Combining the legacy Kepler transit times with the new times from Spitzer will give us the baseline that is needed to confirm and characterize these dynamically interacting systems of planets. This information will allow us to assess the complete architectures of these systems -- we will discover planets that do not transit and determine the masses and orbital properties of all the planets. For 6 planets in these systems, the TTVs will allow us to measure the planetary masses to better than 20%, which will approximately double the number of cool giant planets with known masses and radii. Several of the systems have mean-motion resonances between the planets, and characterizing these interactions yields information on the formation and migration of giant planets. The required precision and duration of these observations render Spitzer the only remaining instrument capable of such study.
    Spitzer Proposal. 11/2013;
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    ABSTRACT: Stars hosting hot Jupiters are often observed to have high obliquities, whereas stars with multiple coplanar planets have been seen to have low obliquities. This has been interpreted as evidence that hot-Jupiter formation is linked to dynamical disruption, as opposed to planet migration through a protoplanetary disk. We used asteroseismology to measure a large obliquity for Kepler-56, a red giant star hosting two transiting coplanar planets. These observations show that spin-orbit misalignments are not confined to hot-Jupiter systems. Misalignments in a broader class of systems had been predicted as a consequence of torques from wide-orbiting companions, and indeed radial velocity measurements revealed a third companion in a wide orbit in the Kepler-56 system.
    Science 10/2013; 342(6156):331-4. · 31.20 Impact Factor
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    ABSTRACT: KOI-152 is among the first known systems of multiple transiting planetary candidates (Steffen et al. 2010) ranging in size from 3.5 to 7 times the size of the Earth, in a compact configuration with orbital periods near a 1:2:4:6 chain of commensurability, from 13.5 days to 81.1 days. All four planets exhibit transit timing variations with periods that are consistent with the distance of each planet to resonance with its neighbors. We perform a dynamical analysis of the system based on transit timing measurements over 1282 days of \textit{Kepler} photometry. Stellar parameters are obtained with a combination of spectral classification and the stellar density constraints provided by light curve analysis and orbital eccentricity solutions from our dynamical study. Our models provide tight constraints on the masses of all four transiting bodies, demonstrating that they are planets and that they orbit the same star. All four of KOI-152's transiting planets have low densities given their sizes, consistent with other studies of compact multiplanet transiting systems. The largest of the four, KOI-152.01, has the lowest bulk density yet determined amongst sub-Saturn mass planets.
    10/2013;
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    ABSTRACT: The bounty of sub-Neptunes discovered by Kepler enables us to study a regime in planetary size and mass that is absent from the Solar System. This regime includes a transition from rocky planets to those with substantial amounts of volatiles-- in either ice mantles or deep atmospheres. Characterizing these worlds by their bulk densities can probe this transition, and this requires mass and radius determinations. Outside our solar system, there is a small sample of planets with known masses and radii, mostly hot jupiters whose radii are known from transit depths, and whose masses are determined from radial velocity spectroscopy (RV). In the absence of mass determinations via RV observations, transit timing variations (TTVs) offer a chance to probe perturbations between planets that pass close to one another or are near resonance, and hence dynamical fits to observed transit times can measure planetary masses and orbital parameters. Such modelling can probe planetary masses at longer orbital periods than RV targets, although not without some challenges. For example, in modeling pairwise planetary perturbations, a degeneracy between eccentricity and mass exists that limits the accuracy of mass determinations. Nevertheless, in several compact multiplanet systems, fitting complex TTV signals can break the degeneracy, permitting useful mass determinations. The precision in measuring the radius of a transiting planet rests on the uncertainty in the stellar radius, which is typically ~10% for targets with spectral follow-up. With dynamical fits, however, solutions for the orbital parameters including the eccentricity vectors can, alongside the transit lightcurves, tightly constrain the stellar density and radius. Revisiting the six-planet system of Kepler-11, our dynamical fits to TTVs, alongside spectroscopic data on the host star, reduced the stellar and hence planetary radius uncertainties to just 2%, permitting useful planetary density determinations. In the case of Kepler-11, planetary densities are lower than typical RV determinations in the same mass range. Other similar compact multi-planet systems follow the trend set by Kepler-11.
    10/2013;

Publication Stats

2k Citations
892.39 Total Impact Points

Institutions

  • 2014
    • UPMC
      Pittsburgh, Pennsylvania, United States
  • 2013–2014
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States
    • University of Illinois at Chicago
      Chicago, Illinois, United States
  • 2010–2014
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, California, United States
  • 2008–2014
    • Harvard-Smithsonian Center for Astrophysics
      • • Institute for Theory and Computation
      • • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2012
    • University of Notre Dame
      South Bend, Indiana, United States
    • California Institute of Technology
      • Department of Astronomy
      Pasadena, California, United States
    • San Diego State University
      • Department of Astronomy
      San Diego, CA, United States
  • 2005–2007
    • Princeton University
      • Department of Astrophysical Sciences
      Princeton, New Jersey, United States