27. Datalink: Remote processing

Datalink also lets you declare processing services. SODA is a special set of parameters applicable to astronomical images (CIRCLE, POLYGON, TIME, BAND,… ).

Save a lot of time by only downloading cutouts of the object you’re interested in:

roi = SkyCoord.from_name('Mira')
for rec in svc.run_sync(
    "SELECT access_url, access_format FROM ivoa.obscore"
    " WHERE obs_collection='HDAP'"
    "AND 1=CONTAINS(CIRCLE('ICRS', {}, {}, 0.05),"
    "s_region)".format(roi.ra.deg, roi.dec.deg)):
    processed = rec.processed(
        circle=(roi.ra.deg, roi.dec.deg, 0.05))

[See datalink-soda.py]

Problems

(1)

Warning: Doesn’t work with pyVO as of Feb 2018

CALIFA is a collection of spectral cubes (i.e., an array of small-band images) of galaxies; there is a datalink-enabled TAP table (califadr3.cubes) listing the cubes on the TAP service http://dc.g-vo.org/tap.

Use TOPCAT to inspect the tables belonging to califadr3; in particular note the objects table that you can join with cubes via the califaid column. Now write a program that gets images of Sd galaxies in their Hα light.

Hints:

Use the Hubble type in the hubtyp column of califadr3’s objects table. Use a TOPCAT query to see how Hubble types are written.
The cubes come in three different setups. Only look at COMB for this exercise (this avoids duplicate data).
Hα is at 656.25 nm. For the low redshifts we’re talking about here, use λ_lab = (1 + z)λ₀ to compute the wavelength in the lab frame (and don’t worry about vacuum vs. air wavelengths for this exercise).
You’ll need to select the obs_publisher_did and mime columns for datalink to work. Use califaid to generate file names.
To cut out by wavelength, use SODA’s BAND parameter (future versions of pyVO will have better facilities to inspect the parameters the services support and the ranges applicable to a given dataset). It’s in meters of (vaccuum) wavelength.
To cut out just a single pixel in wavelength, just use the same upper and lower bound.

Answer

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Markus Demleitner, Hendrik Heinl