Final Data Product

[AlexaVillaume]

So the final data product from the get_photometry() function in UCD_Photometry is a catalog for however many images you passed to that function. The fun stuff comes after all of that is generated and right now is in main().

Be advised that I don't have this functioning automatically yet. But I have it set up for NGC4621. We read the catalog into a tree, take the coordinates that we know of the ucds and query the tree to return back the magnitude, the fwhm, anything...Do you see how that works?

If we have multiple bands we can cross correlate the catalogs to make a final catalog.

What still needs to be added is correcting for the zero point on these images. So, the calcZeropoint function returns the median offset between the magnitudes in the Subaru catalog and the magnitudes in SDSS. Then we correct the Subaru images by that offset.

You should try changing the main function so that it works for your M80 function (comment out the get_photometry call at the beginning, you already have the catalog no need to repeat that step) while I work on getting calcZeropoint set up for you to test. I'll let you know when the new version is pushed.

[AlexaVillaume]

Okay so I can slapped something together just so we can test things. Pull the UCD_Photometry and change the main function to work for your data set. So, because you only have one band of data remove the second band of data steps that I use, change the catalog names, the UCD coordinates, etc...

I included the calczeropoint function (again, you need astropy and astroquery for that function to run), I print out the zeropoint for each band and then I correct just the magnitudes specific to the UCD. I'm going to eventually correct all the magnitudes for each of the sources but I need to give some thought on the best way to do that.

Note that I'm going to make major overhauls to this main function but this is just for now so we can test calcZeropoint and you can see what sort of things you can do with the quadtree.

[vincepota-zz]

Hi Alexa, I'm going to test this code out. did you change the code recently? I'm a bit confused at the moment.

1.We have a catalogue for each band. 2.We want to calibrate the magnitudes to SDSS. 3.We want to match the three bands and get a final catalogue.

The first point seems to work fine, except for a few minor issues, like not efficient clean-up.

The second point is what I'm going to test. Question: Do you match the whole subaru catalogue with SDSS? We should try match only the brightest point sources in SDSS with the brightest in Subaru. We usually use 18<mag<22 from SDSS (stellar objects only). We match the output with our subaru catalogue and then we take the weighted average of the difference between the two. Then we subtract the result off the subaru magnitudes.

The third point is work in progress.. is it correct?

I don't understand what you mean when you say: "We read the catalog into a tree"

[AlexaVillaume]

Hey Vince - I moved your zero point error to a new issue. I'm trying to keep these issues very narrow, this is only a discussion about what we want the final data product to be. That will only be finding a solution to the bug. It's easier to keep track of things that way.

[AlexaVillaume]

You might as well pull everything again, I can't remember what's different.

I'll address your second point in the calcZeropoint thread.

The third point is sort of a work in progress. All the tools to do the matching are in place, I just have to write the function and test it. The tree is a special data structure that I wrote to optimize sorting and querying two dimensional data. When I say "we red the catalog into a tree" it's just like reading a catalog into an array, it's just a different data structure. Does that make sense?