Review of PDS archive of 28 Sgr Occultation Dataset
Cathy Olkin
January 1, 2004
I have experimented with the files on the 28 Sgr occultation archive CD and only have minor comments. I have read in some of the data files, looked to make sure that key information is in the headers (such as latitude and longitude of the observatories, wavelength of the observations, etcÉ). The dataset appears complete. The minor issues that I encountered are outlined below:
REFERENCE_KEY_ID = NICHOLSONETAL1991
REFERENCE_KEY_ID = NICHOLSONETAL1995
REFERENCE_KEY_ID = TAYLOR1983
Done.
2. In IRTF_D~1.CAT: There is confusion regarding the photometric conditions during the occultation:
In ÒData Set OverviewÓ It says:
Data include occultation profiles for both ingress
and egress. Observations began well after ring ingress had
commenced capturing part of the C Ring only. However they span the
entire ring egress under excellent conditions.
Later under ÒPROCESSINGÓ (#4), it says:
For the approximately last half of the egress observations, cloud
cover significantly affected the observations. Ring features can
still be detected, but the observing team judged that absolute
flux values are not valid. These data are flagged as non-photometric in the resampled data files.
Were the observing conditions ÒexcellentÓ or cloudy during the last half of egress.
The same sentence also occurs in the same section of the LICK1M~1.CAT file, the MCD27M~1.CAT file. Check other similar files to see if the sentence was accidently left in all files of this type.
Corrected.
ÒThe stellar RA & DEC given above are from FRENCHETAL 1993, and are suitable
for astrometry. The stellar magnitudes, determined from photometric
observations obtained at Palomar in 1988, are 1.27 at 3.8 microns and 1.48
at 2.2 microns. The star is described in detail in TAYLOR1983. A total of
64,000 raw frames were recorded, each with an integration time of 0.15
seconds. Observing conditions became partly cloudy during egress
observations of the B and A rings; consequently, the photometric quality of
these observations is not as good as for the corresponding ingress
observations. Absolute timing was achieved by chopping with the secondary
mirror exactly 2 arcsec north for exactly 2 sec (13.3 frames)at intervals of
1 minute, and for exactly 4 sec on the hour, using trigger pulses from a
crystal-oscillator continuously synchronized with shortwave radio time
signals from WWVB. Absolute occultation timing was reconstructed with an
accuracy of 0.05 sec. This observation is described in FRENCHETAL1993, and
NICHOLSONETAL2000."
I believe this may be another section of text that was inadvertently left in later files of the same type.
Corrected.
RING_EVENT_START_TIME = 1989-07-03T07:21:23.45
RING_EVENT_STOP_TIME = 1989-07-03T08:15:11.53
START_TIME = 1989-07-03T08:36:25.07
STOP_TIME = 1989-07-03T09:30:13.07
If I assume that the start time and stop time are the beginning and end times of data collection, then this station should have recorded no data (as the data collection started after the ring event stop time). Do these times mean something other than what I have assumed?
RING_EVENT_XXXX_TIME Ð gives the time at the ring plane
XXXX_TIME Ð gives the time the data was acquired at the observatory. The differences between the corresponding times are the Saturn to Earth light travel time.
In addition Dr. Olkin identified numerous minor errors on printout of various files.
All have been addressed.