Data Set Information
DATA_SET_NAME PHOTOMETRY OF IO AND EUROPA DURING SL9 IMPACT FLASHES
DATA_SET_ID EAR-J/SA-HSOTP-2-EDR-SL9-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION The data producer originally supplied a data set description. However, a lien from the peer review requested a more detailed description. PDS-SBN enhanced the description with information provided in an unpublished paper about these data by Woodney et al. (1998) [WOODNEYETAL1998]. Data Set Overview: This data set contains digitized photometry of the reflections off Io and Europa of the impact fireballs produced as the D, E, K, and N fragments of comet D/Shoemaker-Levy 9 hit the atmosphere of Jupiter. The data were acquired during the predicted impact period for each fragment, from 17 through 20 July 1994. Observations ------------ The following paragraphs were paraphrased from Woodney et al. (1998) [WOODNEYETAL1998]. At Mt. Singleton in West Australia, the University of Maryland/Perth Observatory team used a high-speed occultation timing photometer and a 14-inch Celestron to look for flashes off Io or Europa during the expected impact times of the D, E, K, N and P2 fragments. During the D, E, N, and P2 impacts, Io was observed, while Europa was the target for the K impact. This fragment was predicted to illuminate Europa while the moon was in eclipse with Jupiter, possibly making the satellite temporarily visible from Earth. The flashes from Io were expected to be small compared to the reflected solar component (one to ten percent), so the best opportunity to observe an effect was during an eclipse. The photometer had a bi-alkali photocathode, and the observations were made with no filter. The resultant bandpass of the whole system ranged from 312 to 615 nanometers, with an effective wavelength of 453 nanometers. The team obtained continuous light curves of Io at the predicted times of the impacts of fragments D and E. Mechanical problems during the impacts of K, N and P2 left large gaps in the temporal coverage. This severely limits the usefulness of these data. In particular, the P2 data were not included in this data set because this coverage was very sparse. Therefore, only the following impact data are included in this data set: Start Stop Impact Date UTC UTC Target Observing Notes ------ ------ ----- ----- --------------- ------------------------------ D Jul 17 11:30 12:00 Io Photometric sky E Jul 17 14:45 15:15 Io Photometric sky, some wind K Jul 19 10:07 11:10 Eclipsed Europa Mechanical problems, data gaps N Jul 20 10:10 10:21 Io Mechanical problems, data gaps A set of calibration observations was recorded around impact D. These data are also included in this data set. For each observation the appropriate moon or calibration source was centered in a 30-arcsecond aperture. The observer tracked the moon by looking through a 5-inch finder scope and using a hand paddle to drive the telescope. This method, combined with the Jovian scattered light, is one of the larger sources of error in the photometer data. Motion of the moon within the aperture caused variations on the order of five percent as more or less scattered light entered the aperture. For each observing run, a voltage-to-frequency converter was used to record the following data onto a four-track audiotape: 1. Data counts from the target, recorded as a frequency 2. WWV time signals (http://tf.nist.gov/timefreq/index.html) 3. A 60Hz reference signal 4. Voice comments of the observers To optimize the system for detecting small events, the gain for the voltage-to-frequency converter as high as possible, which caused the sunlit satellites to be near the saturation point. When the converter saturated, the frequency went to zero, which led to low values for all saturations when the data were digitized. During data collection, the observers recorded the UTC time associated with selected second ticks from the WWV and the 60Hz reference signal so that data could be synchronized. Results from Impact D --------------------- The following paragraphs are paraphrased from Woodney et al. (1998) [WOODNEYETAL1998]. During impact D, the team observed a sunlit Io. The team had hoped to hoped to observe the flash as a percentage increase in the brightness of the moon. Data acquired near the time of the D impact are the best set obtained by the team. The sky was photometric, tracking was good, and there were no mechanical failures. No flashes were large enough to be seen on a strip chart produced at the time of the observation. However, the digitized data were carefully inspected for the several minutes around the time of the first infrared precursor flash reported by the observers at the Anglo-Australian Telescope (AAT). At 11:54:20 UT, 26 seconds before the infrared precursor flash was observed at the AAT, a small rise is seen in the digitized data. The signal rises to about 7 percent above the average over three seconds, plateaus for almost two seconds, then quickly drops back. While this event seems too long to be noise, the team could not conclusively determine if any reflection off Io of the D impact flash was observed. Results from Impact E --------------------- The following paragraphs are paraphrased from Woodney et al. (1998) [WOODNEYETAL1998]. During impact E, the team observed a sunlit Io. Again, observing conditions were good but the photometer data included many saturations which made it difficult to analyze for evidence of flashes. However, At the IAU meeting in August 1994, N. Raghavan, of the Nehru Planetarium in New Delhi, reported photographing a flash off Io which started at 15:14:42 UT and lasted three seconds. The team reanalyzed the digitized, high-speed photometer data and found saturations from 15:14:40 to 15:14:46. Since the saturations occur at the same time as the suggested flash, it is possible that the flash caused the last few seconds of saturated data. Assuming the flash was as the saturation level, the team estimated it to be 15 percent of the brightness of Io. It is important to note that the start and stop times given in the time-sychronized table for impact E are 11 minutes sooner than those reported by Woodney et al. 1998 [WOODNEYETAL1998]. PDS-SBN could not reconcile either set of times with the UTC of the possible, saturated flash from impact E reported above. The data table for impact E should be used with caution. Results from Impact K --------------------- The following paragraphs are paraphrased from Woodney et al. (1998) [WOODNEYETAL1998]. The team proposed impact K would provide the best chance to observe a flash because the target, Europa, was in eclipse with Jupiter during the event. There was not reflected sunlight to overwhelm a lower intensity flash. While data for this event are similar in quality to the data for E, there are many saturations caused by scattered light from Jupiter entering the aperture. The team was not able to find evidence of a flash in these data. Results from Impact N --------------------- During impact N, the team observed a sunlit Io but high winds and equipment failures resulted in sparse, poor quality data. However, these data could be digitized and are included in this data set. Processing: For each observing run, the following data were recorded directly onto a four-track audiotape: 1. Raw data counts from the target as produced the photometer, then recorded as a frequency 2. WWV time signals, including seconds ticks 3. A 60Hz reference signal 4. Voice comments of the observers The audiotapes were digitized in the fall of 1994 at Lowell Observatory. Each four-track audiotape was digitized, at a rate of approximately 100 samples per second. The outputs from this process are ASCII tables which contain only two columns: 1) Column 1 contains time stamps produced by the digitization process. It contains a series of ones and zeros. Each occurrence of a one represents the beginning of one second of time, corresponding to a specific clock time as recorded on the audiotape. The WWV time signals were used when available. For the K fragment, the WWV was not strong enough on the audiotape for the voice track was used. For samples between the seconds ticks, the digitization process output a zero in this column. There are approximately 99 samples between each second. For the first record, the digitization process output a value other than zero or one in this column. For the time-synchronized version of a table (see the explanation below), the process output a number greater than 63000 in this column to mark the start of the time-synchronized samples. 2) Column 2 provides the intensity of the digitized raw data numbers. Tapes were generally digitized twice: Once with the time reference beginning at an exact UT time (this is the time-synchronized version as noted in the label) and once with the time reference beginning at the start of the data. By comparing the two, the exact timing of the entire data set can be determined. If there was not a clear WWV signal for a data set, or exact timing was not important for a set of observations such as calibrations, there may not be a time-synched digitization for that data set. The data provided in this data set are raw and have not been processed beyond the digitization procedure described above. Woodney et al. (1998) [WOODNEYETAL1998] provide a recipe for converting the observed flux increases into flash luminosities. Parameters: The following naming convention is used for the ASCII data tables that contain data from impact D, E, K, or N: TABLfns.TAB where f : D for impact D data E for impact E data K for impact K data N for impact N data n : 1 or 2 for the first or second half of a set of observations s : T for the time-synchronized version of the impact data; if T is not present, data file is not time-synchronized Two calibration tables were provided: TABLD1.TAB and TABL2D1.TAB. While these tables contain observations of standard stars, the data provider did not list the targets. These calibration tables are not time-synchronized. TABL2D1.TAB is simply a second digitization of TABLD1.TAB that appears to be noise. In addition to the impact and calibration tables, three tables of unspecified targets are provided: TABL1.TAB, TABL11.TAB, and TABL12.TAB. These data were used to test the digitization of the data using different gains. TABL12.TAB has the correct gain.
DATA_SET_RELEASE_DATE 1999-12-31T00:00:00.000Z
START_TIME 1994-07-17T11:30:00.000Z
STOP_TIME 1994-07-20T10:21:00.000Z
MISSION_NAME COMET SL9/JUPITER COLLISION
MISSION_START_DATE 1993-01-01T12:00:00.000Z
MISSION_STOP_DATE 1996-01-01T12:00:00.000Z
TARGET_NAME J1 IO
J2 EUROPA
TARGET_TYPE SATELLITE
INSTRUMENT_HOST_ID MTSC14
INSTRUMENT_NAME HIGH SPEED OCCULTATION TIMING PHOTOMETER
INSTRUMENT_ID HSOTP
INSTRUMENT_TYPE PHOTOMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview: These data were peer-reviewed in 2002. During the review it was noted these data are unique and should be archived. Reviewers indicated these completely raw data could be reduced if someone was determined to do so. Data Coverage and Quality: Data from impacts D and E data cover the times of the impact events and are reliable. However, mechanical problems during K and N impacts left large gaps in the time coverage that severely limits the usefulness of these data. For each observation the moon was centered in a thirty-arcsecond aperture. An observer looking through a five-inch finder scope manually tracked the target by using a hand paddle. This tracking method, combined with the Jovian scattered light is one of the larger sources of error in the photometer data. Motion of the moon within the aperture caused variations on the order of 5 percent as more or less scattered light entered the aperture. The moon was also occasionally lost from the aperture for brief periods. Additionally there was no protection from the wind for the telescope and this caused some interference with tracking. Specifically, the numerous saturations seen in the data for impact E are attributed to wind buffeting the telescope during these observations. The wind made it difficult to keep Io centered in the aperture, resulting in strong contamination by scattered light from Jupiter. Since the detector was working very close to its limit, this additional light was enough to saturate the detector. Also, for impact E, the start and stop times given in the time- sychronized table included in this data set are 11 minutes sooner than those reported by Woodney et al. 1998 [WOODNEYETAL1998]. PDS-SBN could not reconcile either set of times with the UTC of the possible, saturated flash from impact E reported by Woodney et al. 1998 [WOODNEYETAL1998]. Therefore, the data table for impact E should be used with caution. Finally, an unsynchronized and a time-synchronized data table were provided for impacts D, K, and N. For impact E, only a time-synchronized data table was provided. Limitations: One must be careful when interpreting these data. Most, if not all changes in these light curves may be due to tracking problems. To optimize the system for detecting small events, the gain for the voltage-to-frequency converter was set as high as possible, which caused the sunlit satellites to be near the saturation point. When the converter saturated, the frequency went to zero, which led to low values for all saturations when the data were digitized. Therefore, this is an ambiguity between low values due to saturations and low values due to the loss of the satellite from the aperture. Values that are below the sky level are clearly saturated. However, some portion of all low spikes that are still above the sky can be attributed to either saturation or loss of a portion of the moon from the aperture. The data provided in this data set are raw. While Woodney et al. (1998) [WOODNEYETAL1998] provide a recipe for converting the observed flux increases into flash luminosities, there is not clear description of the steps required to calibrate the raw data.
CITATION_DESCRIPTION Woodney, L.M., PHOTOMETRY OF IO AND EUROPA DURING WITH SL9 IMPACT FLASHES, EAR-J/SA-HSOTP-2-EDR-SL9-V1.0, 2002.
ABSTRACT_TEXT This data set contains digitized photometry of the reflections off Io and Europa of the impact fireballs produced as the D, E, K, and N fragments of comet D/Shoemaker-Levy 9 hit Jupiter's atmosphere.
PRODUCER_FULL_NAME LAURA M. WOODNEY
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