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, etc…). The dataset appears complete. The minor issues that I encountered are outlined below:

 

 

1. In the REF.CAT file, the following references were missing:

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 “Data Set Overview” 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 “PROCESSING” (#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 “excellent” 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.

 

3. I found the following paragraph in both “IRT_EPD.LBL” and “ES2_EPD.LBL”. I doubt that both the IRTF and ESO datasets had all these things in common.

 

“The 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.

 

4. In the ES1_EGB.LBL files the following times are given:

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       – gives the time at the ring plane

XXXX_TIME                                    – 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.