2022 Sagan Summer Workshop

Exoplanet Science in the Gaia Era

Hands-On Sessions

Background References

Hands-on Session Descriptions

Monday, July 25: Accessing the Gaia Catalog

The Gaia Data Release 3 (DR3), on June 13, 2022, will be the largest and richest resource on fundamental properties of stars. These properties are essential in the characterization of exoplanets, thus being comfortable with extracting the relevant information from the Gaia catalog is important.

In this hands-on session you will learn how to access the Gaia catalog data through the Gaia archive's Astronomical Data Query Language (ADQL) query interface and programmatically in Python. For more information on ADQL and accessing the Gaia data archive, please see their Demos and Tutorials page. Topics covered:

  • Basic ADQL queries
  • Complex queries to combine data from several Gaia DR3 tables
  • Cross matching of an exoplanet host sample to Gaia DR3, using: tools available in the Gaia archive; Topcat; or Python
  • Accessing multidimensional data in Gaia DR3, such as the lightcurves of candidate transiting exoplanets
Tuesday, July 26: Visualizing Gaia Data

Exploring a large and complex data set such as Gaia DR3 is made easier through modern visualization tools that can quickly render plots of large amounts of data and that allow linking different views of the same data.

In this hands-on session you will explore the Gaia Catalog of Nearby Stars (GCNS) using Glue.

Topics covered:

  • Plot the observational Hertzprung-Russell diagram (HRD) for the GCNS
  • Do the same for different volume-limited or magnitude limited samples
  • Use the techniques learned in the first hands-on session to extract exoplanet host star data and overlay these on the observations HRDs
  • Make plots of different quantities for the same sample of stars and use Glue's data-linking capabilities to explore the relations between the plotted quantities; for example, what is the spatial distribution of a sample of stars selected from a color-magnitude diagram?
Wednesday, July 27: Orbital Fits using Orvara

Participants will install and use the open-source code Orvara to fit the mass and orbit of a known brown dwarf around a main-sequence star. Three complementary types of data will be available:

  1. absolute astrometry from Hipparcos and Gaia
  2. relative astrometry from direct imaging
  3. radial velocities

Participants will either install the code themselves or use a setup with Google Colab. The goals of this session are to:

  • obtain an orbital fit
  • estimate the convergence of that fit, and
  • to assess the reliability of the results using the chi squared values of the residuals.

Participants should be able to produce a chain from Markov Chain Monte Carlo, discard an appropriate amount from the beginning as burn-in, and plot all of the results. If there is time remaining, the fit can be repeated omitting one form of data, e.g. relative astrometry from imaging, and assessing the changes in the fit and the ability to predict the location of a companion in advance of imaging.

Thursday, July 28: Orbital Fitting Group Projects

This session will expand on orbit fitting and mass measurements and will be more open-ended. Data for several systems will be supplied: some will have only two of the three data types (absolute astrometry, relative astrometry, and radial velocities), some will have more than one companion, and some will not allow for a satisfactory orbital fit.

Participants will work in groups to explore these systems, including

  1. predicting the current locations of companions;
  2. assessing evidence for underestimated uncertainties or additional companions;
  3. implementing priors on masses where appropriate;
  4. diagnosing and achieving convergence;
  5. explaining degeneracies and covariances in the orbital parameters.

In-person attendees will give short, informal presentations on their group projects on Friday afternoon of the workshop.


Workshop Code of Conduct.

2022 Workshop home page

(last updated April 27th, 2022 10:15:13)