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
$ 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
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
$ 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
c05 refers to the campaign number,
ch13 is the CCD channel number,
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