Astrometric calibration

In this tutorial you will astrometrically calibrate the ReducedScienceFrames (i.e., de-biased and flatfielded science frames) from the previous tutorial.

Find ReducedScienceFrames to run astrometry on

1. In a previous exercise, you reduced some RawScienceFrames, resulting in the creation of ReducedScienceFrames. Construct a list of these frames.

   Instruction: Use information in HOW-TO Query the database from Python to construct a query that contains your and only your ReducedScienceFrames.

   Answer (1):
   awe> t = '2012-06-01T08:51:44'
   awe> q = ReducedScienceFrame.template.start == dateutil.parser.parse(t)
   awe> frames = q.project_only().user_only()
   awe> len(frames)
   <some number of frames>
   
   Answer (2):
   # Alternatively, you can look for ReducedScienceFrames that you made less
   # than 20 minutes ago:
   
   # Use current UTC minus datetime.timedelta(days, seconds, microseconds).
   awe> date = datetime.datetime.utcnow() - datetime.timedelta(0, 20*60, 0)
   awe> q = (ReducedScienceFrame.creation_date > date).user_only()
   

Derive astrometric calibration

1. Derive astrometry by creating AstrometricParameters objects for the ReducedScienceFrames.

   Instruction: Use information in HOW-TO Derive an astrometric solution to re-derive the AstrometricParameters for your ReducedScienceFrames.

   Answer:
   awe> filenames = [f.filename for f in frames]
   awe> dpu.run('Astrometry', instrument='OMEGACAM', red_filenames=filenames, C=1)
   

   or (note that this command selects the most recent, valid ReducedScienceFrames for the specified template and chip, which may be frames made by someone other than yourself)

   awe> dpu.run('Astrometry', instrument='OMEGACAM', template='2012-06-01T08:51:44',
                chip='ESO_CCD_#65', C=1)
   

2. Examine the attributes of an AstrometricParameters object.

   Instruction: Use the dir() method to see the attributes of interest (usually in all capital letters).

   Answer:
   awe> ap = (AstrometricParameters.reduced == frames[0])[0]
   awe> dir(ap)
   ['CD1_1', 'CD1_2', 'CD2_1', 'CD2_2', 'CRPIX1', 'CRPIX2', 'CRVAL1', 'CRVAL2', 'CTYPE1', 'CTYPE2', 'FITERRS', 'FITPARMS', 'INCONSISTENT_SOLUTION', 'MEAN_DDEC', 'MEAN_DDEC_OVERLAP', 'MEAN_DRA', 'MEAN_DRA_OVERLAP', 'NFITPARM', 'NO_SOLUTION_FOUND', 'NREF', 'NREF_TOO_HIGH', 'NREF_TOO_LOW', 'N_OVERLAP', 'N_OVERLAP_TOO_HIGH', 'N_OVERLAP_TOO_LOW', 'PREASTROM_FAILED', 'PROCESS_TIME', 'PV1_0', 'PV1_1', 'PV1_10', 'PV1_2', 'PV1_3', 'PV1_4', 'PV1_5', 'PV1_6', 'PV1_7', 'PV1_8',...
   awe> ap.NREF
   ...
   awe> ap.RMS
   ...
   awe> ap.SEEING
   ...
   

Visually inspect astrometry

1. Display the quality control plot for the AstrometricParameters object.

   Instruction: Follow the instructions in HOW-TO Inspect an astrometric solution to inspect the astrometric solution for one of your ReducedScienceFrames.

   Answer:
   awe> ap.inspect()