Example: M67 mosaic

The K2 mission observed the open cluster M67 as part of Campaign 5. The data on the cluster is available only as a series of Target Pixel Files (TPFs) that each cover only a part of the cluster. In this example we will mosaic these into single images.

First, we need to create a list of the Target Pixel Files (TPFs) that we wish to mosaic. The easiest way to do this is to use the k2mosaic list tool, which outputs a list of TPF urls for a given channel and campaign.

We know that, during Campaign 5, M67 fell on CCD channel #13. Let’s run the tpflist tool to identify the TPFs on this channel and save the output to list-of-target-pixel-files.txt:

$ k2mosaic tpflist 5 13 > list-of-target-pixel-files.txt

If you inspect the output, you will find that it simply contains a list of TPF URLs, one per line:

$ head list-of-target-pixel-files.txt
http://archive.stsci.edu/missions/k2/target_pixel_files/c5/200000000/08000/ktwo200008644-c05_lpd-targ.fits.gz
http://archive.stsci.edu/missions/k2/target_pixel_files/c5/200000000/08000/ktwo200008645-c05_lpd-targ.fits.gz
http://archive.stsci.edu/missions/k2/target_pixel_files/c5/200000000/08000/ktwo200008646-c05_lpd-targ.fits.gz
...

If you have a local copy of the desired data, e.g. downloaded through the archive’s K2 Data Search interface, then you can simply build a list using the unix ls command, e.g.:

$ ls /path/to/directory/*fits.gz > list-of-target-pixel-files.txt

Having obtained a list of input files, we can now hand this list to the k2mosaic mosaic tool to combine them into single FITS images.

Caution: by default, the mosaic command will create a FITS image for each cadence, of which there are typically several thousands. This will be slow. Let’s start by creating a FITS image for a specific cadence first, by providing the optional --cadence argument:

$ k2mosaic mosaic --cadencec 110000 list-of-tpf-urls.txt

The above command will download the required TPF files (if needed) and create a new FITS images called k2mosaic-c05-ch13-cad110000.fits, where c05 refers to the campaign number, ch13 is the CCD channel number, and cad110000 refers to the unique K2 cadence number. The result should look like this:

TODO: insert image.

The range of cadence numbers for a given campaign can be obtained from the data release notes.

You are now ready to produce images for all cadences, by running:

$ k2mosaic mosaic list-of-tpf-urls.txt

This will create additional files called k2mosaic-c05-ch13-cadxxxxxx.fits.