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Photometric data from SDSS fits files

  1. Jul 1, 2010 #1
    I have fits files from the Sloan Digital Sky Survey (SDSS) and I have been able to make plots of the spectral data in the spSpec files. I would like to make similar plots for comparison using the photometric(ugriz) data but I'm not sure where to find it. I believe it should be somewhere in the folder I downloaded from SDSS which contains a series of spSpec & spAtlas files along with a file for main_gals, spObj and spPlate. So which one of these fits files has what I need to make plots of photometric data?
  2. jcsd
  3. Aug 18, 2010 #2
    Hi, I don't know if this is too late for you, but here's the outline of what you need to do:

    1. The photometric data is stored as "PhotoObj" in the SDSS, spectroscopic data is stored in SpecObjAll (check the schema)
    2. If you have spectroscopic data, for each (galaxy?) (star?) you should have an object ID - this should be called bestObjID - ie the best spectra taken for that object. This is matched to the Photometric objID. If you don't have object id's, it's probably easier to re-submit the query to get them.
    3. Run a new query (CAS) that retrieves ugriz photometry for the data you already have, by adding a "WHERE xx.bestObjID = yy.objID"

    So... you should first of all ask yourself what type of photometry you want: Petrosian, Model, Kron, aperture? If you don't know, or are not sure, and your targets are galaxies, IMHO go for Model magnitudes, though Petrosian is possibly better for more local (galactic) targets.

    Here's an example snippet that gets ugriz model mags, their errors and their extinction (Schlegel 1998?), as well as their spectroscopic redshift:

    Code (Text):

    SELECT        TOP 10 p.objID, p.ra,p.dec, s.z as specz, s.zerr as specz_error,
                  p.modelMag_u,p.modelMag_g, p.modelMag_r, p.modelMag_i, p.modelMag_z,
                  p.modelMagErr_u, p.modelMagErr_g, p.modelMagErr_r, p.modelMagErr_i, p.modelMagErr_z,
                  p.extinction_u as extinction_u, p.extinction_g as extinction_g, p.extinction_r as extinction_r,
                  p.extinction_i as extinction_i, p.extinction_z as extinction_z
    FROM PhotoObjAll as p, SpecObjAll as s

    WHERE (p.objID = s.bestObjID)
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