Description of multiband.py

multiBand.py can create multi-color catalog based on the object file made by stack.py (Fig 1). In this section, the processing in each steps of multiBand.py is described.

Fig 1. Process of multiBand.py

1. Combining object catalogs in each filter（merge）

stack.py creates a detected object catalog for each filter（det-[filter]-[tract]-[patch].fits) . The fiest step of the process of multiBand.py is gathering these catalogs and making new one（mergeDet-[tract]-[patch].fits).

The object lists in mergeDet catalog are updated according to the following priority;

1. Select the detected object in the filter to which multiBand.py refers.
2. If there is an object within 1” of the peak of footprint in the reference filter, these two are considered as the same object.
3. Select the detected objects only in the second reference filter.
4. If there is an object within 1” of the peak of footrint in the second filter, these two are considered as the same object.
5. Select the detected objects only in the third reference filter.

For instance, the footprint and peaks shown in Fig 2 are identified in each filter. The objects (g: r: i) = (1,2,3: 1,2,3,4: 1,2,3,4) are detected and listed on det catalog. Now we assume that the order of referring is from i-, g-, to r-band. On mergeDet catalog, all detected objects in i-band are listed (i-band 1,2,3,4). At this time, if the distance of peaks between i-band object and the one in another filter is within 1”, these two objects are the same, so the object detected in the another filter is not added to mergeDet catalog. In case of Fig 2, (i-band 1/g-band 1), (i-band 2/g-band 2), and (r-band 1/i-band 4/r-band 3) are the same. Then the objects detected only in g-band are added. Object g-band 3 is considered to be the same as r-band 2. Finally the objects detected only on r-band (r-band 4) are listed. The final mergeDet catalog holds the objects i-band 1, 2, 3, 4, g-band 3, r-band 4 and their photometry parameters.

Detected footprints in each filter are also collected into mergeDet catalog. The footprint for mergeDet catalog is determined by combining (merging) footprints of all filters. In case of Fig 2, the footprint for mergeDet catalog is shown by grey dotted line.

Fig 2. Footprints and peaks detected in all filters

2. Photometry and positioning using mergeDet catalog（meas）

Photometry is proceeded again using potisional information listed on mergeDet catalog. meas-[filter]-[tract]-[patch].fits files are generated in this process.

3. Construct whole object catalog from meas catalogs（ref）

Next, ref-[tract]-[patch].fits files are made from meas catalogs in each filter. In this process, the results of meas catalogs of reference filter for each objects are gathered and summarized. This summary is ref catalog.

4. Generate multiband catalogs for each filter（forced_src）

The final step is to generate catalogs for each filter based on ref catalog parameters （forced_src-[filter]-[tract]-[patch].fits). If the parameters in meas catalog of first filter are not changed during creating ref catalog, the results of photometry is almost same between first meas and forced_src catalog.

Contents of mergeDet catalog

The parameters of mergeDet catalog objects varies greatly depending on the order of reference filter. In case of Fig 2, if the reference starts from r-, g-, to i-band, objects and photomery parameters for r-band 1, 2, 3, 4, g-band 1, and i-band 3 are added to mergeDet catalog.