Processing Feder Image Files

Overview

How header processing occurs

The intent is that this processing will happen automatically within 24 hours of the data being uploaded to physics.mnstate.edu. The actual processing will be done on a OSX-based machine (currently esne-bide.mnstate.edu) with the results passed back up to physics.mnstate.edu.

After processing, the raw data files will be compressed and will remain on the physics server.

Purpose of the header processing

The purpose of the header processing is to:

• Modify or add keywords to the FITS header to make working with other software easier:
  • Standardize names instead using the MaxIm DL defaults (e.g. RA and Dec instead of OBJCTRA and OBJCTDEC)
  • Set IMAGETYP to IRAF default
  • Add convenient keywords that MaxImDL does not always include (e.g. AIRMASS, HA, LST)
  • Add keywords indicating the overscan region, if any, in the image.
• Add astrometry to the FITS header so that RA/Dec can be extracted/displayed for sources in the image.
• Add object names to the HEADER where possible.
• Identify images that need manual action to add any of the information above.
• Create a table of images in each directory with columns for several FITS header keywords to facilitate indexing of images taken at Feder.

Running the software

The underlying python functions are run with a few convenience scripts to accomplish each of the steps above. They would typically be run in this order:

• run_patch to do a first round of header patching that puts site information, LST, airmass (where appropriate) and RA/Dec information (where appropriate) into the files. See Header processing for details.
• run_triage (details at Summary table) to:

• generate a table summarizing properties of images in a directory. Each image is one row in the table and the columns are keywords from the FITS headers.
• create files with lists of images missing key information.

• Fix any problems identified by run_triage. The script quick_add_keys_to_file may be useful for this; it is an easy way to add/modify the values of keywords in FITS headers from the command line; see details at Quickly modify FITS headers. After fixing these problems you may need to re-run patch, particularly if you have added pointing information or changed the IMAGETYP of any of the images.
• run_astrometry to use astrometry.net to add WCS (astrometry) information to the file. See Astrometry for details. Note that this requires a local installation of astrometry.net.
• If desired, run_triage again to regenerate the table of image information.

Detailed documentation of the individual scripts is available here.

Details

Header patching

The keywords that are currently added/modified by patch_headers for all files are:

IMAGETYP: Type of image
LATITUDE: [degrees] Observatory latitude
LONGITUD: [degrees east] Observatory longitude
ALTITUDE: [meters] Observatory altitude
LST: Local Sidereal Time at start of observation
JD-OBS: Julian Date at start of observation
MJD-OBS: Modified Julian date at start of observation
OSCAN: True if image has overscan region
OSCANAX: Overscan axis, 1 is NAXIS1, 2 is NAXIS 2
OSCANST: Starting pixel of overscan region

The keywords that are currently added/modified by patch_header for light files only are:

RA: Approximate RA at EQUINOX
DEC: Approximate DEC at EQUINOX
OBJECT: Target of the observations
HA: Hour angle
AIRMASS: Airmass (Sec(Z)) at start of observation
ALT-OBJ: [degrees] Altitude of object, no refraction
AZ-OBJ: [degrees] Azimuth of object, no refraction

Some keywords are purged from the original headers because I don’t trust the values that MaxImDL v5 puts in:

OBJECT
JD
JD-HELIO
OBJCTALT
OBJCTAZ
OBJCTHA
AIRMASS