In the process of organizing the NOAO R-band
data for public distribution using Altas, IRSA
found several FITS-compliance issues with the
FITS image headers, in both the FLS NOAO and FLS
NOAO ELAIS datasets.
IRSA repaired the image headers using the
IRAF; the
format of the headers has been changed to bring
them into compliance with the FITS standard; the
technical content of the headers is unaltered.
Please note that the data distributed from NOAO
and the SSC ftp area DO NOT contain these
corrections.
The problem with the headers were as
follows:
- The "DATE-OBS" header entry (keyword name,
value and comment) was longer than the standard
allowed 80 characters. The comment line spilled
over to a new line in all the NOAO R-band FITS
headers. The entry looked like this:
DATE-OBS= '2000-05-06T09:56:52.0' / UT Date of Earliest Obs. Used In Com
bined Image
Since the comment was too long to fit on one line, it
appeared to the FITS library as two separate keywords. The part
that did not fit on the first line ("bined Image") was therefore
treated as a separate FITS keyword, "bined". To fix this problem,
the "DATE-OBS" keyword comment has been shortened as follows:
DATE-OBS= '2000-05-06T09:56:52.0' / UT Date of Earliest Obs. Used In Combined Im
The last word in the comment, "Image", was shorted to "Im" in
order to fit within the 80 character limit.
- Directly after the "TIME-OBS" header
keyword entry, there was a blank line before
the next header keyword entry. Our suspicion is
that the "TIME-OBS" header keyword entry was 81
characters and so the last character (blank
space or newline) created a blank line in the
header. We deleted this blank line from all the
FITS headers.
- Each header contained the keyword "SKY";
all the values for this keyword were set to 21
asterisks (********************). This value
was not a number, nor was it quoted to be a
string. Since IRSA had no knowledge of the
value of "SKY" for these data, we set the "SKY"
value to a string of asterisks
('********************'). By putting quotes
around the value "SKY", it became a legal FITS
keyword value. Please note that we do not know
the correct value for the "SKY" keyword; we
have simply made this change in order for the
header to be FITS-compliant.
- Similar to the problem listed above, a
number of other header keyword values were set
to 21 asterisks (********************). We
placed quotes around each of these strings,
making them FITS-compliant keyword values. Here
is a list of the FITS file names and header
keywords which had this problem:
FLS_fullfield_KPNO_R_v01.fits:EFFGAIN = ******************** / Conversion ...
FLS_fullfield_KPNO_R_v01.fits:SEEING = ******************** / Seeing ...
FLS_fullfield_KPNO_R_v01.fits:SKY = ******************** / Sky background
FLS_fullfield_KPNO_R_v01.fits:SKYSIG = ******************** / 1 sigma ...
FLS_fullfield_KPNO_R_v01.fits:DEPTH = ******************** / Approximate
FLS_fullfield_KPNO_R_v01.fits:MAGZERO = ******************** / R Kron-C ...
ELAIS_fullfield_KPNO_R_v01.fits:EFFGAIN = ******************** / Conversion ...
ELAIS_fullfield_KPNO_R_v01.fits:SEEING = ******************** / Seeing FWHM
ELAIS_fullfield_KPNO_R_v01.fits:SKY = ******************** / Sky background
ELAIS_fullfield_KPNO_R_v01.fits:SKYSIG = ******************** / 1 sigma ...
ELAIS_fullfield_KPNO_R_v01.fits:DEPTH = ******************** / Approximate
ELAIS_fullfield_KPNO_R_v01.fits:PROPOSAL= '******************' / Proposal
ELAIS_fullfield_KPNO_R_v01.fits:MAGZERO = ******************** / R Kron-C ...
We also noticed that there were extra blank
lines between the last COMMENT keyword ("COMMENT
2004, A.J., submitted.") and the "END" of each
header. This is not "wrong" in terms of FITS
compliance, but we wanted to make a note of it
here for completeness. We did not remove these
blank lines.
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