Benjamin Johnson

Models+Data

Astronomy

I'm a Research Associate at the Center for Astrophysics | Harvard & Smithsonian. My current work is inferring star and galaxy properties in the nearby and distant universe from their spectral energy distributions (SEDs) and appearance in images.

I help build generative physical models and use I use advanced statistical techniques to compare the models' predictions to piles of astronomical data obtained with big chunks of glass and metal in space.

I have worked as an astronomer and data analyst for 20 years, six of them in Cambridge, England and Paris, France. My experience includes operating ground-based telescopes in the US and Chile and working with data from several satellite telescopes, including Hubble, Galex, and Spitzer.

See some of my projects

Code

I've worked on this software, and I hope you can use it. Mostly it's in Python.

  • prospector: Inference from full spectral fitting combined with photometry, using state-of-the-art stellar population synthesis models, MCMC sampling and flexible noise modeling including Gaussian processes.
  • sedpy: Python tools for working with astronomical spectral energy distributions, especially filter projections, with a flexible system for adding new filters. Also includes tools for dust extinction and attenuation and basic photometry modules. 
    
    from matplotlib.pyplot import *
    from sedpy import observate
    filterlist = observate.load_filters(['sdss_u','sdss_i'])
    mags = observate.getSED(wave, spec, filterlist)
    plot([f.wave_effective for f in filterlist], mags)
  • python-FSPS: Python bindings to Charlie Conroy's FSPS stellar population synthesis models.
  • forcepho: Forward image modeling galaxies and Bayesian inference of galaxy shape and flux parameters using HMC
  • hmc: A simple Hamiltonian Monte Carlo sampler, written in Python and Fortran.

...and more! See my github repos for some others.

Projects

Science research and otherwise ...

  • The Contributions of Women to 20th Century Physics :
    A peer reviewed database describing fundamental contributions of women to Physics, which I worked on as an undergrad.
  • GMACS :
    A database of matched UV (GALEX) through Far-IR photometry of 1000 galaxies from the SDSS main galaxy spectroscopic sample, compiled and analyzed for my Ph.D thesis.
  • LVL, KINGFISH
  • H3 Survey :
    A spectroscopic survey of stars in the halo of the Milky Way.