Photometric data from SDSS fits files

In summary, to make plots of photometric data from the SDSS, you will need to retrieve the photometric data from the "PhotoObj" in the SDSS and match it to the spectroscopic data stored in "SpecObjAll". This can be done by running a new query that retrieves the desired photometry (such as Petrosian or Model magnitudes) for each object using its object ID. An example query for retrieving ugriz model magnitudes, errors, and extinction for 10 objects is provided.
  • #1
kris2010
1
0
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?
 
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  • #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:
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)
 

1. What is photometric data from SDSS fits files?

Photometric data from SDSS fits files refers to the measurements of light intensity and color of astronomical objects obtained from images taken by the Sloan Digital Sky Survey (SDSS). These measurements are stored in a standardized file format known as Flexible Image Transport System (FITS) files.

2. How is photometric data collected and processed?

Photometric data is collected by the SDSS telescope and camera, which capture images of the night sky. These images are then processed using specialized software to measure the brightness and color of each object in the image. The processed data is then stored in FITS files for further analysis.

3. What types of objects are included in SDSS photometric data?

SDSS photometric data includes a wide range of astronomical objects, such as stars, galaxies, quasars, and other celestial bodies. The survey covers a large portion of the sky and has observed over 500 million objects since its inception.

4. How is photometric data used in scientific research?

Photometric data from SDSS is used by scientists to study the properties and behaviors of different astronomical objects. It can also be used to identify new objects or to track changes in the brightness and color of objects over time. This data is crucial for understanding the structure and evolution of the universe.

5. Is SDSS photometric data publicly available?

Yes, SDSS photometric data is publicly available and can be accessed through the SDSS website or through various online databases. The data is released periodically as new observations are made, allowing scientists from all over the world to use it for their research.

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