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Manipulating VOTables with TOPCAT and STILTS

This presentation introduces TOPCAT, a powerful GUI for manipulating VOTables, and STILTS, its underlying library for filtering and converting tables. Developed by Mark Taylor as part of the Starlink project, TOPCAT allows users to easily access and analyze data from various VO sources. Learn how to load, convert, and filter astronomical data using practical examples and explore advanced features like histogram creation, cross-correlations, and synthetic columns. Master the capabilities of TOPCAT and STILTS to enhance your astronomical data analysis skills.

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Manipulating VOTables with TOPCAT and STILTS

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  1. Manipulating VOTables with TOPCAT and STILTS Tom McGlynn

  2. What are TOPCAT and STILTS? • STILTS is a powerful library that enables users to filter and convert tables in VOTable and other popular formats. • TOPCAT is a user interface built on top of STILTS with extensive GUI and graphics capabilities. • All written by Mark Taylor (Bristol University/UK) originally as part of the Starlink project. • This demo uses TOPCAT but the underlying functionality is available through the STILTS library (in Java). • There are some other standalone commands built on STILTS (e.g., votcopy). • There is a TOPCAT chapter in the NVO book.

  3. Starting TOPCAT • In the standard distribution as command ‘topcat’ • Note capabilities to download data from various VO and other data sources. • Remember to run setup first! • Files used in this presentation: Download these (Twiki doesn’t let TOPCAT read them directly) • http://nvo-twiki.stsci.edu/twiki/pub/Main/NVOSS2008Sched/spocs.csv • http://nvo-twiki.stsci.edu/twiki/pub/Main/NVOSS2008Sched/spocs.xml • http://nvo-twiki.stsci.edu/twiki/pub/Main/NVOSS2008Sched/exostars.xml This URL can be used directly • http://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=messier

  4. Starting and loading a URL

  5. Table loaded successfully

  6. Getting to and from VOTables • Converting to VOTables from CSV Load spocs.csv (available on Twiki) Save as spocs.xml (VOTable) Can covert into many formats. • Converting VOTables to CSV Load http://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=messier Save as CSV Portal tools may work better in handling data in non-standard formats.

  7. Convert to a CSV file

  8. After loading CSV convert to VOTable

  9. The table browser

  10. Filtering data using TOPCAT • Show SPOCS table (view/tabledata) • Create a subset (view/row subsets/+) • Enter name=Sunlike • Enter criterion Teff>5720 && Teff<5820 && log_g>4.34 && log_g<4.54 && M_H>-0.1 && M_H <0.1 • Should create subset with ~30 rows. • Show with Views/Table data/Apply Subset/Sunlike • We can use column names or $number. • A sample can be saved in any of the supported formats.

  11. Creating a subset

  12. Histograms • Click on histogram • Note which subsets are showing and click on all • Change column to VMAG • Note both all and sunlike data.

  13. Histograms

  14. Plots • X/Y display • Ensure that full sample is shown. • Change parameters to Teff/Age • Zoom around sun location • Create new sample from plot (third box from right) • Note region selection tool (fourth from right)

  15. X-Y plots

  16. Creating a subset graphically

  17. 3-D Graphics/Synthetic columns • 3-d displays (change third axis to something interesting in box) • Creating new columns: column metadata/+ • Name = AppMag • Expr = Vmag – 5*log10(Dist/10) [note striping error] • Note function browser • New columns can be used anywhere and show up on output

  18. 3-D plots

  19. Creating a new column

  20. Correlations using TOPCAT • Load • SPOCS table • EXOStars table • Click on double match • Cross-correlate by position: • Find all the SPOCS stars that have exoplanets

  21. Cross-correlations

  22. Viewing the correlation

  23. Saving the correlated data.

  24. Many more capabilities Direct access to VO enabled services Density plots Column data conversions Hundreds of functions usable in creating columns PLASTIC/SAMP communication with other tasks Joining tables Stacked plots or spherical plots Table statistics …

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