Flatiron Institute Center for Computational Astrophysics Pre-Doctoral Program

Important Dates
  • Application deadline
  • Applicant notification
  • Fellowship start date (approx.)
Contact Info
  • Please send inquiries
    about the program to ccainfo@flatironinstitute.org

Purpose

The Center for Computational Astrophysics (CCA) at the Flatiron Institute is a vibrant research center in the heart of New York City with the mission of creating new computational frameworks that allow scientists to analyze big astronomical datasets and to understand complex, multi-scale physics in a cosmological context.

The CCA Pre-Doctoral Program will enable graduate student researchers from institutions around the world to participate in the CCA mission by collaborating with CCA scientists for a period of 5 months on site. With this opportunity, the selected group of researchers will be able to participate in the many events at the CCA and interact with CCA scientists working on a variety of topics in computational astrophysics (including both numerical simulations and sophisticated analyses of observational data), thereby deepening and broadening their skill sets.

Application

CCA Pre-Doctoral Program participants will be employed for up to 5 months at the CCA as Research Analysts during the fall (September through January). More information about this paid position is available on the application page, which can be accessed by clicking ‘Apply Now’.

Research Analysts will collaborate with one or more CCA scientists on a project of mutual interest. Potential applicants can find a list of projects proposed by possible CCA mentors by going to the mentors tab above. Alternatively, applicants may propose a project related to the interests of one or more of the CCA mentors listed. Before applying, applicants must contact one or more potential mentors to discuss the project of interest in detail and specify the selected mentor(s) in the research proposal.

Deadline

Applications for the Research Analyst position should be submitted here by May 31. Applicants will be notified about the status of their applications by July 15.

Supporting material for the application includes the following:

  • CV and publication list
  • Description of previous research experience (not to exceed two pages)
  • Research proposal of not more than 2 pages outlining planned work at CCA
  • Three (3) letters of recommendation submitted confidentially by the letter writers to ccapredoc@flatironinstitute.org. One letter must be from the applicant’s PhD supervisor and must explicitly approve the applicant’s possible participation in the Pre-Doctoral Program

Contact Info
Please send inquiries about the program to ccainfo@flatironinstitute.org

Read More
Important Dates
  • Application deadline
  • Applicant notification
  • Fellowship start date (approx.)
Contact Info
  • Please send inquiries
    about the program to ccainfo@flatironinstitute.org

Application
FPVP participants will be employed for up tospend 6 months at the CCA as Research Analysts either during the fall (September through February) or spring (March through August) [we may want to rethink these dates]. More information about the Research Analyst position is available from the link in the Deadline section. The selected researchers will receive support for living expenses in NYC ($4000/month from the CCA, intended to supplement their normal salaries from their home institutions).

Research Analysts FPVP participants will collaborate with one or more CCA scientists a project of mutual interest. Potential applicants can find a list of projects proposed by possible CCA mentors here [link]. Alternately, applicants may propose a project related to the interests of one or more of the CCA mentors listed on the same list. Before applying, applicants must contact one or more potential mentors to discuss the project of interest in detail and specify the selected mentor(s) on the application form.

Deadline
Applications for the Research Analyst position can be submitted (link, here) by May 15 [??]. Applicants will be notified about the status of their applications by June 15.

Supporting material for the application includes the following:
Research statement (<=3 pages)
A brief description of the proposed project (goals, codes and datasets involved, etc.) (<1 page)
CV
Publication list
1-3 letters of reference

Contact Info
Please send inquiries about the program to [email].

Important Dates
  • Application deadline
  • Applicant notification
  • Fellowship start date (approx.)
Contact Info
  • Please send inquiries
    about the program to ccainfo@flatironinstitute.org

 

Simone Aiola

 

Multifrequency Analysis of Millimeter Sources with ACT Data

 

The Atacama Cosmology Telescope is a high-resolution millimeter polarimeter in the Atacama Desert in Chile that is designed to observe the oldest light in the universe, the cosmic microwave background (CMB).  The high-fidelity sky maps made at multiple frequencies over 40 percent of the sky also contain the non-primordial imprint of bright millimeter sources, such as active galactic nuclei (AGNs) and dusty star-forming galaxies (DSFGs).  These sources represent both a wealth of astrophysical information and a contaminant to the primordial signal we want to observe.

 

Using multifrequency data from the ACT telescope, we will constrain the properties of the different source populations, their polarization and their clustering, and make accurate predictions and simulations for upcoming experiments, such as the Simons Observatory.

 

Ruth Angus

 

  1. The evolution of debris disks may provide constraints on the characteristic timescales of exoplanet migration and giant impacts. The student will work with Trevor David and Ruth Angus to leverage large data sets (TESS, Gaia and WISE) to measure gyrochronology ages of debris disk hosts and trace the evolution of disk parameters for a larger statistical sample than has been possible previously.

 

  1. (CCA co-mentor: Melissa Ness) Large-scale spectroscopic surveys along with advances from the Solar-twin community are enabling the calibration of stellar ages based on spectral line diagnostics with higher fidelity than has been previously possible. The student will work with Trevor David, Ruth Angus, Melissa Ness and Megan Bedell to derive empirical stellar age relations and measure the ages of exoplanet host stars from high-resolution spectra. With accurate and self-consistent ages for a large sample of exoplanet hosts, the student will then search for evolutionary trends in planet parameters.

 

Phil Armitage

 

Phil Armitage is interested in theoretical and computational studies of protoplanetary disks, the formation and dynamics of planetary systems and accretion astrophysics in high-energy environments such as AGN and tidal disruption events.

 

Matteo Cantiello
 
I work on computational stellar physics. My main interest is the physics of stellar interiors and its impact on the life and death of stars. Interested students can work on 1D (MESA and GYRE) and multi-D (Dedalus and ATHENA++) problems related to e.g. stellar convection, rotational mixing, stellar magnetic fields, stellar mass loss and asteroseismology. I am particularly interested in massive stars and their properties prior to collapse. Besides the computational aspect, projects will likely have a connection to observations through Gaia, TESS, archival Kepler data and LIGO/Virgo. A few possible projects are listed below; please inquire for more details. Prospective students are also welcome to submit their own ideas for collaboration.
 

  • – Modeling stellar planetary ingestions
    (Computations: MESA. Data: Kepler, TESS, and LSST)
  • – Modeling stellar convection and magnetism in stars
    (Computations: Dedalus/ATHENA++. Data: TESS, BRITE, and Gaia. In collaboration with Keaton Burns, Yanfei Jiang, and Daniel Lecoanet)
  • – Modeling and detecting stellar spots in OBA stars
    (Computations: MESA, Dedalus, and Starry. Data: Kepler, BRITE, and TESS. In collaboration with Rodrigo Luger and Dan Foreman Mackey)
  • – The stellar magneto-rotational instability
    (Computations: MESA. Data: #Asteroseismology and Kepler)
  • – Interaction of internal gravity waves with strong magnetic fields in the core of red giant stars
    (Computations: Dedalus. Data: #Asteroseismology and Kepler. In collaboration with Daniel Lecoanet and Keaton Burns)
  • – Exotic stellar evolution in AGN disks
    (Computations: MESA and ATHENA++. Possible collaboration with Yanfei Jiang)

 

James Cho

 

My broad research interests: hydro and MHD waves, vortex dynamics and turbulence — both computational and analytical. I am also interested in topological and algebraic techniques for data analysis and solving differential equations.

 

Specifically, I would be interested in working with a student on any of the below (in addition to things that fit with the broader interests mentioned above):

 

  • simulations of weakly and strongly ionized planetary and stellar general circulation, climate (including coupling to radiative transfer)
  • simulations of hydro and MHD protoplanetary/accretion disks (wave-mean flow interaction, turbulence and radiative transfer coupling; with Phil Armitage)
  • MHD convection simulations of giant planets, brown dwarfs and stellar interiors
  • applications of topological data analysis, group and/or homotopy analyses of differential equations of astrophysics, or algebraic structures of equations of astrophysics — all involving some numerical computation

 

Dan Foreman-Mackey

 

Mapping the Surface of Io with Moon-Moon Occultations

(CCA co-mentor: Rodrigo Luger)

 

Although Galileo provided high-resolution images of Io in the 1990s, the surface of this Jovian moon is constantly changing due to its extreme volcanic activity. In particular the location, duty cycle and other properties of the major volcanoes are still an area of active investigation, as they can inform models of the planet’s interior and details of its tidal interaction with Jupiter. In this project we will use the “starry” code package  to construct time-variable two-dimensional maps of the surface of Io from the many moon-moon and Jupiter-moon occultations that have been observed to date. In addition to constraining fundamental properties of the surface and interior of Io, this project will pave the way for mapping exoplanets from secondary eclipses observed with JWST, and for future missions.

 

Robust Detection and Characterization of Radial Velocity Exoplanet Systems

 

There are many new extreme-precision radial velocity spectrographs coming online in the next few years, and if these projects are to be successful, it is crucial that we develop methods for robustly detecting and characterizing radial velocity exoplanets. The two main classes of detection algorithms are frequentist hypothesis testing and Bayesian model comparison. There are significant disagreements between and within these classes of algorithms, but there exists a simpler technique that can be used to bridge this gap: parameter estimation. This project will involve developing and applying a method for high-dimensional parameter estimation using state-of-the-art probabilistic inference techniques for radial velocity time series, as well as deriving and testing models for the impact of stellar variability on the radial velocity measurements. The result will be a set of recommendations for best practices and a high-impact software package for exoplanet detection and characterization.

 

Shy Genel

 

We will study the properties of galaxies in the environments of massive groups, clusters and proto-clusters over a broad range of redshifts around z~1 using the IllustrisTNG300 cosmological hydrodynamical simulation, which is uniquely positioned for this purpose due to its combination of volume and resolution. This study will provide predictions and theoretical context for upcoming surveys that will probe these rare environments, such as WAVES@4MOST/VISTA (Driver et al., 2019) and PFS@Subaru (Takada et al., 2014). The focus will be on galaxy mass, sSFR, color, morphological type and AGN activity in relation to group membership and to the location in and properties of these over-dense environments. Discussion of additional project ideas in numerical galaxy formation will be welcome.

 

Chris Hayward

 

The Contribution of Obscured AGN to Thermal Dust Emission in the Far-Infrared

(CCA co-mentor: Daniel Anglés-Alcázar)

 

The conventional wisdom is that thermal far-infrared (FIR) emission from cold dust is powered by star formation rather than AGN, making the bolometric FIR luminosity an excellent star formation rate (SFR) tracer. The primary reason for this assumption is that the dust in the AGN torus is hot, and thus does not contribute significantly to the spectral energy distribution longward of approximately 60 microns. However, emission from a sufficiently deeply obscured AGN can, in principle, heat host-galaxy dust at kiloparsec scales, resulting in cold dust and consequently significant FIR emission; this effect is not captured by standard AGN torus models. Performing radiative transfer on galaxy simulations entails a unique opportunity to probe the effects of an AGN on host-galaxy dust emission, because by comparing otherwise identical simulations with and without AGN, one can directly quantify the dust emission that is powered by the AGN rather than star formation. This project will involve performing radiative transfer on galaxy simulations from the Feedback in Realistic Environments (FIRE) project to investigate whether obscured AGN can lead to significant FIR emission. If so, one important implication would be that the FIR luminosity cannot be considered a robust SFR tracer for galaxies that host luminous AGN, and many results in the literature would have to be revised.

 

Do Modern Galaxy Simulations Sufficiently Resolve the Dusty ISM?

 

Performing radiative transfer on galaxy simulations enables predicting observables from hydrodynamical simulations, and thus more directly comparing theory and observations. Unfortunately, the “sub-grid” structure of the dust typically represents a significant uncertainty in such calculations, requiring one to rely on a sub-grid model of the dust distribution, thereby limiting the predictive power of such calculations. However, given the high mass (particle mass < 100 Msun) and spatial (<1 pc) resolution attainable in state-of-the-art cosmological zoom simulations, which enables resolving massive giant molecular clouds, it is possible we can now sufficiently resolve the dusty ISM, and no longer need to employ a sub-grid dust attenuation model. This project will entail performing radiative transfer on cosmological zoom simulations from the Feedback in Realistic Environments (FIRE) project to test whether this is indeed the case.

 

Additionally, I would be interested in mentoring a student on a project connected to any of my areas of research, so please email me if you have an ongoing project or project idea related to one or more of the following topics:

 

  • – Radiative transfer, dust and predicting observables from simulations
  • – Stellar feedback, turbulence and outflows
  • – Galactic magnetic fields
  • – Black hole accretion and feedback (with Daniel Anglés-Alcázar)
  • – Circumgalactic medium (CGM) and the physics of multiphase gas (with Drummond Fielding)
  • – Infrared/submillimeter-selected galaxies

 

Shirley Ho

 

Combining Physics and Deep Learning

 

The project is one of the most challenging and interesting projects at the interface of physics and machine learning. Physicists have spent ages accumulating “physical intuition” through their training. Machine learning has recently been touted as probably able to learn “science” without the guide of humans or scientists for scientific problems. This project will aim to combine physical intuition and the power of machine learning — in particular, deep learning — to make better learned models in astrophysical applications.

 

Space Weather and Deep Learning

 

We aim to develop and apply novel deep-learning methods to compare space-weather observational data and simulations. To predict space weather would require understanding the global state of terrestrial magnetospheres in the presence of magnetic reconnection, shocks and turbulence, with micro- and macro-scales coupled self-consistently. It is a very demanding task that has been difficult to attack with traditional methods. We will approach this problem with novel deep-learning methods, especially at the interface between simulations and observations of space weather.

 

David Hogg

(CCA co-mentor: Megan Bedell)

 

Extreme-precision radial velocity (EPRV) measurements are a crucial part of exoplanet discovery and follow-up, but many data-analysis challenges exist along the path from observed spectra to inferred planetary orbits. A visiting graduate student could work with Megan Bedell and David W. Hogg on related projects, including (a) the application of data-driven EPRV pipeline “wobble” to near-infrared spectra or (b) information theory-based tests of various observing strategies for the mitigation of stellar noise in EPRV measurements.

 

Mordecai-Mark Mac Low

 

  1. Gaia has revealed the dynamics of nearby brown dwarfs and low mass stars with unprecedented detail. Understanding how such stars are ejected from their parent clusters will provide initial conditions for modeling their kinematics in the field. We have developed a hybrid MHD/N-body code, based on the integration of FLASH and ph4 in the AMUSE software framework, that follows collisional stellar dynamics in the presence of dense gas, including a detailed treatment of stellar feedback through winds, supernovas and ionizing radiation. The project would involve running models of open cluster formation including formation of objects down to the brown dwarf regime and examining their phase-space distribution after gas expulsion.

 

  1. The Laser Interferometer Gravitational Wave Observatory (LIGO) detected mergers of black holes more massive than expected from the evolution of massive stars and occurring toward the upper end of the predicted range of frequency. Standard channels, such as mergers at the centers of globular clusters, may be insufficient to explain these observations. Interactions of black holes from stars in the massive clusters found at the centers of galaxies with the gas disks around supermassive black holes in active galactic nuclei provide an efficient alternative channel. Making concrete predictions from this channel requires study of the migration of stellar mass black holes through such disks, along with accompanying improvement of models of the disks and interactions of stellar mass black holes with the disk gas. This will involve running simulations with the Pencil and Athena++ MHD codes in order to measure migration rates and how disk properties evolve.

 

In addition to the above, I am potentially interested in projects on planet formation (particularly the interactions of solid objects with gas disks), star formation, the structure and dynamics of the interstellar medium, galactic outflows and black holes embedded in AGN disks.

 

Sigurd Naess

 

Rescuing the ACT Daytime Data

 

The Atacama Cosmology Telescope (ACT) is a cosmic microwave background (CMB) telescope in the Atacama Desert in Chile with a 6m primary mirror and approximately five times higher resolution than Planck.

 

Six seasons of data (roughly 100 TB) are available, but so far only the nighttime data have been used. The daytime data are languishing because the telescope beam (point spread function) changes during the course of a day, and we don’t understand the pattern of those changes. However, a subset of the data hit strong radio sources like active galactic nuclei, and each time this happens, we get an instantaneous map of the beam shape, allowing us to track the beam shape changes over time.

 

There are clear patterns here, but so far we don’t have a predictive model. The goal is to build such a model, and answer the question “What classes of shapes does the beam take, and when?” This problem is perfectly suited to machine learning and has a large scientific payout, effectively doubling the statistical power of a state-of-the-art CMB observatory.

 

Solar System Objects with ACT

 

The Atacama Cosmology Telescope (ACT) is a cosmic microwave background (CMB) telescope in the Atacama Desert in Chile with a 6m primary mirror and approximately five times higher resolution than Planck.

 

This high resolution (for a CMB experiment, anyway) means that it is also sensitive to cold faint bodies in our solar system, especially large and remote ones, where it could be competitive with large optical telescopes. The reason for this is that optical telescopes rely on reflected sunlight, which falls off as 1/r4, with r being the distance of the object from the sun, while ACT is sensitive to the heat radiated from the body, which for objects that still retain their heat of formation goes as 1/ r2.

 

A perfect example of such an object is the hypothetical Planet 9, a roughly Neptune-size planet at approximately 500 AU distance, with an expected intrinsic brightness temperature of 69 K at 150 GHz. Taking into account dilution of the signal by ACT’s angular resolution, it should be visible as a 48–109 µK point source depending on where it is in its orbit. For comparison, the typical ACT noise level is currently 5–33 µK per beam across 40 percent of the sky. So a discovery is possible if we’re lucky.

 

But since it’s such a faint object, integration over multiple years of data will be necessary, and this is complicated by both the object’s own movement and Earth’s parallax making it move across the sky. If not accounted for, this would smear out the signal far below detectability. Only vague predictions exist for the orbit of the planet, so we will need to find an efficient way to explore the likelihood.

 

Aside from Planet 9, ACT can also see some closer objects like the largest asteroids in the asteroid belt, like Ceres. It is not competitive with optical telescopes for detecting new objects here, but they represent guaranteed targets with known orbits on which to test methods.

 

Variable Point Sources with ACT

 

The Atacama Cosmology Telescope (ACT) is a cosmic microwave background (CMB) telescope in the Atacama Desert in Chile, with a 6m primary mirror and approximately five times higher resolution than Planck, that surveys 40 percent of the sky every day.

 

High resolution means that ACT detects thousands of point sources, many of which are highly variable, and the high cadence means that we can follow their brightness changes from day to day for bright sources and on weekly timescales for fainter ones. We have six years of data waiting to be analyzed (though the first three years cover less of the sky). As far as I know, this is the microwave dataset with the largest number of variable point sources available.

 

The main challenge in the analysis is disentangling instrument variability from source variability, such as gain drift, beam changes and pointing errors. This could be done by looking for coherent changes across multiple point sources, or perhaps even by calibrating against the CMB itself on short timescales. Fits can be performed in both the time domain and pixel space, each of which comes with different trade-offs.

 

Melissa Ness

 

Data-Driven Mapping of Galaxies to Obtain Individual Chemical Abundances

 

This project will derive mean abundances from the integrated stellar spectra of MUSE galaxies using a stellar library based on LAMOST stars. Using a catalog of 4.5 million stars from the LAMOST survey across the full extent of the Teff-log g plane, with measured abundances and stellar parameters, this project will aim to build an algorithm that uses these stellar spectra to infer the mean parameters and abundances for integrated MUSE spectra, given a mass-weighted combination of LAMOST stars that comprise it.

 

Does Tidal Binary Interaction Drive Lithium Production in Stars?

 

Recently, Casey et al. (2019) discovered over 2,000 lithium-enhanced red giant stars in the LAMOST survey that span a range of parameter space along the red giant branch. Their work concluded that the distribution of these stars across the giant branch rules out the leading explanation for lithium-rich stars as being tied to a particular evolutionary time in a red giant’s life. Instead, Casey et al. (2019) have proposed that stars must become Li-enhanced due to extra mixing driven by binary interaction. We find a significant number of Li-rich stars in the GALAH survey, which have TESS observations that enable rotation periods to be determined for these stars. If Li-enhancements measured in stars are due to binary interaction, we expect to find anomalously high rotation periods for these stars compared with a photometric and parametrically identical control sample, which this project will test.

 

 

Sasha Philippov

 

My main research area is relativistic plasma astrophysics. Interested students may work on subjects including (but not limited to) kinetic plasma simulations of pulsars, binary neutron star and black hole magnetospheres and astrophysical jets. These first-principles simulations are instrumental for understanding plasma production, particle acceleration and emission of nonthermal photons in the environments of compact objects. I’m also broadly interested in production of coherent radio emission in the universe, ranging from solar radio bursts to pulsar radio emission and the enigmatic fast radio bursts.

 

Rachel Somerville

 

A variety of projects can be developed depending on students’ interests, related to understanding galaxy formation and evolution using semi-analytic models, numerical simulations, statistical techniques and multiwavelength observations.

 

Stephanie Tonnesen

 

I am interested in using wind-tunnel simulations of ram pressure stripping to understand how this process may quench galaxies. I am also interested in the physics of gas in the tail. What sets the rate of mixing and cooling in stripped gas as it interacts with the ICM?

 

I am also interested in studying how the large-scale environment may affect the IGM — for example, the temperature and structure of filaments. We would look for any effects in the publicly available large cosmological simulations.

 

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