Data Set Information
DATA_SET_NAME EARTH BASED CCD OBSERVATIONS V1.0
DATA_SET_ID EAR-C-CCD-3-RDR-GRIGG-SKJELL-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set includes ground-based images from several observers, all made using CDC instruments. The bulk of the images were obtained with the ESO CCD instrument and were submitted by Alexandra Rotundi for the team of Fulle, M. et al.(1993A). Data from Calor Alto were submitted by Boehnhardt and Matella; most of the data is described in Birkle and Boehnhardt (1992). Three pre-encounter images recorded at the AAO through narrow-band filters that measured H2O+ were were submitted by a group (Jones, et al.) from the Mullard Space Science Laboratory. Finally, a post-encounter image, a composite of five short exposures taken through a broad band red filter at ESO was submitted by Karl Joeckers et al. Parameters : The images from ESO were taken near perihelion in 1992 after the Giotto spacecraft had flown by the nucleus of comet 26P/Grigg-Skjellerup. These data were used to derive the radial distribution of light away from the nucleus. The original images were taken with a large field (1024 x 1024) CCD and used for this dust study. In the archive are cropped images (101 x 101). Calar Alto data were collected over a seven year-span for astrometric positions that would assist in the targeting of the Giotto spacecraft. Anomalies : The ESO data were sent with minimal FITS header and a separate ASCII description of the measurements. A FITS header, combining both sets of information, was constructed to detail the observations. Through e-mail contact with A. Rotundi, a proper observation time was assigned. The images from Calor Alto were sent as FITS files. Unfortunately, some discrepancies were detected in the FITS headers describing the data when compared to Birkle and Boehnhardt (1992). These were corrected after consultation with one of the submitters (H. Boehnhardt) as follows: 1. Images 26 and 27 from the original submission: Using the published information, two images, identified as 1987/05/24.86278 and 24.86707 respectively, have the wrong exposure, which were changed to 15 and 30 s. 2. Images 15 and 16, identified as 1991/09/12.18236 and 12.19242, should have the filter : V (and not R as in the submitted FITS header). 3. Image 18, identified as 1991/12/03.98953, has the wrong exposure, which has been changed to 400 s (and not 401 as given). 4. There was a general problem with the time specification. The FITS keyword indicated a midpoint time but comparison of data through 1991 indicates it is a start time expressed in decimal hours. In addition, the accuracy (in decimal hours) is quoted to 7 figures, which is unlikely. All accuracies have been rounded to 4 figures in the hour or 1 sec in time. 5. Image 10 was out of order with the other images on that date. Rearranging these images in time, shows that two images identified in the the published work as 1987/07/24.85777 and 24.86176 have the wrong decimal hours. The former also has the incorrect exposure. The correct value for this image in decimal hours is 20.5822 and exposure : 30 sec. For the latter image, the correct decimal hour is 20.6406. 6. The earliest three images have the wrong decimal hours (images 1,2,3). Using the published work and identifying the images by their exposures indicates that the correct identification and decimal hours should be: (1986/10/22) 22.21197 image 1, exp 525, dec hour : 5.0113 (1986/10/22) 22.22703 image 2, exp 485, dec hour : 5.3814 (1986/10/23) 23.08935 image 3, exp 800, dec hour : 2.0333 7. The corrections listed above were applied to the FITS headers in the following manner: The TIME-OBS keyword was replaced with TIMEUTH, with a description reading '/ UT start time given as decimal hours'. New corrected values were placed in the appropriate FITS header and the old value captured as a COMMENT. In addition, any changes to the exposure or filter were also captured as a COMMENT. Reduction : The data from both groups was processed using standard routines in MIDAS. The bias, flat field, and sky level were subtracted. Any unusual features are recorded in the FITS COMMENT or HISTORY fields. The data from ESO was reduced using the full image (1024 x 1024) before the cropped image was formed for the archive. Modification History : Before final submission of this data set to the PDS archive, all PDS labels and catalog files were brought up to current (PDS3) standards and the errata and addenda collected by personnel at the PDS Small Bodies Node were applied and added. -Anne Raugh, 11 September 2006
DATA_SET_RELEASE_DATE 1994-05-10T00:00:00.000Z
START_TIME 1986-10-22T05:00:41.000Z
STOP_TIME 1993-09-16T08:40:49.000Z
MISSION_NAME GIOTTO EXTENDED MISSION
MISSION_START_DATE 1990-01-01T12:00:00.000Z
MISSION_STOP_DATE 1992-01-01T12:00:00.000Z
TARGET_NAME 26P/GRIGG-SKJELLERUP 1 (1922 K1)
TARGET_TYPE COMET
INSTRUMENT_HOST_ID GEMGB
INSTRUMENT_NAME GROUND-BASED CCDS
INSTRUMENT_ID CCD
INSTRUMENT_TYPE CCD
NODE_NAME Small Bodies
ARCHIVE_STATUS SAFED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : Please consult the notes and comments in the FITS headers and PDS labels of the individual images for quality comments from the observers. In addition, the user should reference the publications relevant to each set of images.
CITATION_DESCRIPTION Unknown
ABSTRACT_TEXT This data set presents images of 26P/Grigg-Skjellerup obtained by various observers at several ground-based observatories using CCD instruments. These data have not been through the full PDS review process.
PRODUCER_FULL_NAME SMALL BODIES NODE
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