In order to manage the data, two "cron" jobs run every morning on arpc55.
15 07 * * * ~/polar\_bear/pbt\_imgname >> ~/polar\_bear/pbt\_cronjobs.logThis job reads the file creation time for each image and creates a new filename in the form:
ccc\_yyyymmdd\_hhmmss.fitwhere ccc = camera number, yyyy = year, mm = month, dd = day, hh = hour, mm = minutes, ss = seconds.
pbt_imgname could be made redundant by modifying runstarlight.py to name images as they are recorded
30 07 * * * ~/polar\_bear/pbt\_clean >> ~/polar\_bear/pbt_cronjobs.logThis job reads through every file and identifies the number of stars visible on each image. The following files are deleted. All files taken during "daylight" hours (the script currently has to be told when these change). All files with fewer than c. 100 stars are deleted. All files with more than c. 15000 stars are deleted - these are files with a fixed pattern noise obtained either when the cameras were switched off or when they were exposed in daylight and hence completely saturated.
The remaining files are moved to a folder called /starlight/yyyymmdd_ccc
deleted files are currently not deleted, but moved to a folder /starlight/spocn/bucket/ until pbt_clean is proven to be working optimally.
BUG pbt_clean currently puts all frames from the same calendar date into the same folder. This applies to dates since sometime in May. The original design was to put all frames from the same night into the same folder, with the calendar date corresponding to the date on which the night started ** Needs fixing **
Data may be easily inspected using any image viewing programme which recognises FITS file formats. The most useful are those designed for working with astronomical images including
gaia (Starlink)
ds9 (SAOImage)
It is worth checking random images through the night to check that the pre-processing was successful. It is also worth updating the observing log ''regularly'', including any helpful comments about observing conditions and so on. This provides an extremely valuable record when it comes to process the data and assess photometry extracted many months subsequently.
The observing log is at /starlight/pbt_data_checklist.ods
This can be saved as xhtml and viewed online
-- eg PBT Observing Log
To Be Done The observing log should be updated automatically by the various tasks it reports The xhtml version needs to be automatically updated from the base version
pbt_phot carries out the primary tasks of fixing every fits file, subtracting a bias frame, and dividing by a normalised flat field. It subsequently inspects each image and, if > 500 stars are present, it proceeds to compute an astrometric solution using solve_field. Photometry is extracted for every star on the image using sextractator. This script is run once per day and per camera.
doitall loops over days and cameras and runs pbt_phot once for each. It is useful, for example,
to process one month's data at a time.
Output from these procedures is placed in
The contents of a typical ''.phot'' file are as follows, with the contents of each column described in the file header.
<code>
# NUMBER Running object number
# X_WORLD Barycenter position along world x axis [deg]
# Y_WORLD Barycenter position along world y axis [deg]
# X_IMAGE Object position along x [pixel]
# Y_IMAGE Object position along y [pixel]
# FLUX_ISO Isophotal flux [count]
# FLUXERR_ISO RMS error for isophotal flux [count]
# MAG_ISO Isophotal magnitude [mag]
# MAGERR_ISO RMS error for isophotal magnitude [mag]
# ISOAREA_IMAGE Isophotal area above Analysis threshold [pixel**2]
# THETA_IMAGE Position angle (CCW/x) [deg]
# FLAGS Extraction flags
# FWHM_IMAGE FWHM assuming a gaussian core [pixel]
# ELONGATION A_IMAGE/B_IMAGE
# ELLIPTICITY 1 - B_IMAGE/A_IMAGE
1 2.6088554331e+02 8.4757096415e+01 71.732 2.193 26932.68 1568.236 -11.0757 0.0632 25 9.0 10 7.23 2.212 0.548
2 6.9714854344e+01 8.5533229347e+01 1955.691 1.421 60127.55 2060.075 -11.9477 0.0372 43 2.9 10 12.06 4.703 0.787
3 2.9235591789e+02 8.9215386720e+01 968.514 2.352 7620.165 829.88 -9.7049 0.1183 7 82.5 8 4.63 2.699 0.629
4 5.5533041071e+01 8.8652372113e+01 1336.880 2.609 8140.638 830.1935 -9.7766 0.1108 7 -74.6 8 4.21 4.078 0.755
5 2.7727718642e+02 8.8804697414e+01 874.732 8.085 6000.606 767.9739 -9.4455 0.1390 6 25.1 0 3.51 1.421 0.296
6 1.7168476705e+01 8.9484622646e+01 1143.247 7.747 5302.679 701.2766 -9.3112 0.1436 5 -12.7 0 2.47 1.204 0.169
</code>Thus each file contains one photometric measurement for each star identified on one image. The star may potentially be identified from the image position in world coordinates (columns 2 and 3). The user should be aware of the ''extraction flags'' column (12), the magnitude error column (9) and the FWHM column (13).