Extracting specific star data from Gaia DR2?

Question

I would like to extract all Gaia DR2 sources which have six-parameter solutions as well as their radial velocities and effective temperatures. Is this possible as DR2 only specifies that there are 1,331,909,727 sources with parameters?

Answer 1

You can do this via VizieR (main site at CDS, Strasbourg, France linked; worldwide mirrors are available). You can search by catalog name from that form or enter I/345/gaia2 to get the specific catalog table we want. Assuming you have no other constraints other than what you specified in your question, we can enter the following into the constraint fields:

• Set Solved to =31 (this says to only select sources with all 5 astrometric parameters fitted - see the "Note 14" link off to the side)
• Set RV to != (this says to only return results with a non-null radial velocity)
• Set fPriam to =100001 (this says to only return results from the astrophysical parameter estimation that are close to the stellar locus, have good colors and within the training sets for $T_{eff}$ and extinction. This is (unusually) not well documented or linked within VizieR; I looked this value up by experimenting and consulting this table in the Gaia-DR2 data documentation))

There may well be other constraints on fields that you will want to apply for your problem, particularly if you want well-measured sources and/or good parallaxes; you will need to consult the Gaia-DR2 release documentation. More info on how to apply constraints within VizieR is given by a pop-up help at the top of the form (where it says 'Query by constraints?' which links to this page.

Finally, under Preferences along the left hand side, you will want to change the max number of rows to 'unlimited' and change the output format to something that will be directly download and not rendered by the browser (it crashed the tab in Firefox when I tried it with the default HTML table and unlimited results). Using a FITS binary table, I got a 1.1GB FITS table with 5,797,861 rows when I did this. You may want to look at using cdsclient (linked at the top of the query form) or other programmatic solutions e.g. Astropy's Astroquery for Vizier if you are doing this regularly and are comfortable with some programming.