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Welcome to the home page of Douglas Burke. I am an Astrophysicist at the Chandra X-ray Center, a part of the Smithsonian Astrophysical Observatory at the Harvard-Smithsonian Center for Astrophysics.

Twitter and the AAS

[New] Unfortunately I'm not going to be able to do my usual Twitter analysis of AAS 227. Let me know if you are planning to do so and I'll add a link here, and can act as a resource for tips and tricks if needed!

I've started a "hobby" of analysing the Twitter feed from AAS meetings. Here's the current list:

Notebooks & presentations

Here's a collection of notebooks and presentations. The information presented should be considered to be in the public domain unless explicitly noted otherwise.


This is a set of notebooks playing around with simple cosmology-related calculations as an excuse to try out IHaskell.

  1. Angular Diameter Distance
  2. This time with units
  3. K corrections with a dimensional twist
  4. a FITSfull of ARF


These are ipython notebooks showing off Sherpa (and other parts of CIAO):

  1. A simple sherpa fit, showing how to use the standalone version of Sherpa.

  2. A set of examples, available on GitHub, showing off the standalone version of Sherpa, but the code can also be used in the CIAO version:

    1. Writing your own user model, in this case fitting the CDF with a Gamma distribution.

      May 26, 2015

    2. Writing an "integrated" user model, which uses the data from the previous notebook but fits the histogram of the data with the PDF of a Gamma distribution, which requires handling "integrated" data sets (i.e. those with a lower and upper edge for each bin of the independent axis).

      June 4, 2015

    3. Plotting using the "low-level" interface, which shows how plots can be made when using the direct, object, interface (rather than the sherpa.astro.ui or sherpa.ui modules).

      June 5, 2015

    4. Extending existing models (and an example of using XSPEC models), which shows how to write a user model that extends the behavior of an existing model (in this case, subtracting a model from itself with different parameter values). It also shows how to build the XSPEC module, and so use the XSPEC models from standalone Sherpa.

      June 16, 2015

    5. Simulating 2D data with a dash of error analysis, which uses the object API to simulate a 2D model (i.e. an image), fit it, and calculate errors on the parameters. This can be thought of as an extension of the previous notebooks that show how to replicate the functionality of the high-level UI layer using the object API (it also marks the start of me using the term "object API" for what I previously referred to as the "low-level API").

      June 19, 2015

    6. Simulating and fitting a 2D image (this time with a Bayesian approach), which is based on the previous notebook, this time showing how you can use the Monte Carlo Markov Chain (MCMC) analysis module in Sherpa (that is, the Bayesian Low-Count X-ray Spectral (pyBLoCXS) module). This notebook is mainly intended to show how to do this, rather than explain why (or the differences between the various frequentist and Bayesian methods for coming up with an error estimate).

      June 22, 2015

  3. Trying out Sherpa and ChIPS, which incorporates much of what I learnt in:
    1. Plotting with ChIPS
    2. Errors, Tracebacks, and Sherpa
    3. Logging messages and Sherpa
    4. HTML output (niver views)
    5. Interactive editing of values

Astronomy & Python

Various talks advertising Python to Astronomers:

  1. A quick - and highly biased - tour of Python for X-ray Astronomy presented at the COSPAR Capacity Building Workshop, 'Advanced School on X-ray', Ensenada, Mexico, November 2014
  2. What is Python?, part of a series of presentations based on the Practical Python for Astronomers course which we repurposed for the SAO REU Summer Intern program.

Scientific stuff

I am interested in using clusters of galaxies to elucidate the evolution of structure in the Universe. Or some-such high-fallutin one-line research description. A more accurate view of my research interests - which also cover galaxy evolution and studies of the major baryonic components in the Universe - can be found by perusing my ORCID profile ORCID logo or see what “impact” ImpactStory logo my research has made.

I thought-up, designed, wrote, and maintain the What is Chandra doing? site, which shows what Chandra is observing now, as well as allowing you to look at past observations, and how they are related. I am particularly fond of some of the visualizations in the Explore page, such as the correlation between the proposal area (e.g. Galaxy Clusters) and the types of objects that are observed. If nothing else, it shows: how nebulous some of our concepts are; how Astronomers are not taught to think of archival purposes when setting up observations (e.g. the choice of the target name field); and how hard it is to extract useful meaning from the data.

There is also my Southern SHARC survey page, which provides machine-readable (ASCII format) versions of the data in Burke et al. 2003, "The Southern SHARC Catalogue: a ROSAT survey for distant galaxy clusters".

Recently - for a very vague definition of the term - some of my time has been spent on projects related to the Virtual Observatory, in particular how semantic-web technologies can be used to improve the use of the data that is now available to us (and that is changing the way we do science if you believe Wired). There is a report now available on my study of faceted browsing and its application to Astronomical searches in the VO era. A simple demo (using the Exhibit framework) shows a facet-based view of the Chandra Short-Term schedule. This work has lead me to collaborate with the SAO/NASA Astrophysics Data System Digital Library on using semantics and enhanced search techniques as part of its nascent ADS Labs effort.

For more information on Semantic Astronomy and AstroInformatics, see the Practical AstroInformatics web site, in particular its conferences and workshops page. I was on the organizing committee for the Practical Semantic Astronomy Workshop 2009, on the Programme Committee for the Web Semantics in Action: Web 3.0 in e-Science workshop at the 5th IEEE International Conference on e-Science, which was in Oxford, UK (December 9-11, 2009), and an organizer of the Practical Astroinformatics: An Emerging Discipline special session at the 115th AAS meeting in Washington, DC (January 3-7, 2010). I have served on the Program Committee for the NASA Conference on Intelligent Data Undertanding (CIDU), which doesn't seem to have a nice home page to link to!

Press releases and news items:

Scientific stuff (moribund)

This section is for projects which are now out of date, or unmaintained, or perpetually on the back burner.

I tried an experiment in "live-blogging" some Chandra data analysis, in honor of Open-Access Week (#OAWeek). Unfortunately the CIAO release came along and stopped this in its track; I hope to get back to this in 2013. Which I obviously failed at ...

I created the AstroMOAT server to investigate whether "semantic tagging" can be coupled to the work done to create Astronomical vocabularies.

I ran the Chandra Twitter feed; more information can be found from it's home page, although it is very out of date, since the feed has been taken over by the Chandra Public Outreach group. I also created a timeline of Chandra discoveries and events which uses the SIMILE Timeline widget, but this has not been updated for a long time.

Obligatory geek stuff

I use (well, used) PDL - an "IDL-like" set of packages for perl - to do some of my scientific stuff. I wrote the support for "bad-values" (i.e. PDL::BadValues and PDL::Bad) in PDL, as well as provide bug-fixes and updates to the whole module. If you are interested in PDL, or wonder what it can do for you, then have a look at some success stories or read about PDL, Perl 5, and Perl 6 in Perl 6 Now: The Core Ideas Illustrated With Perl 5.

I use the CIAO software package, so you should too. I released, in May 2010, the download_chandra_obsid script that simplifies downloading public datasets from the Chandra Data Archive; this is now available as part of the CIAO contributed software package so you should already have it.

I have recently taken over maintenance of the Swish semantic-web toolkit package for Haskell. You can get to the repository and bug tracker on the bitbucket site, or read about it in the May 2011 Haskell Communities and Activities Report.

See my perl pages for some useful astronomy-related software for perl (these packages are feeling a bit neglected, so if you want to take over maintaining any of them please contact me):

If you are interested in an editor for XML, in particular for text-orientated formats such as DocBook, then you should look at the Conglomerate editor. I provided some bug fixes and feature enhancements to the display widgets.

Obligatory weather stuff

Select for Cambridge, Massachusetts Forecast or try the weather forecast from

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