5977( 7) - 11/22/95 13:40 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5977 Version: 7 Check-in Date: ********** 1.Proposal Title: Cometary Forms in the Helix Nebula ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Interstellar Medium GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: C. Robert O'Dell Department of Space Physics and Astronomy, Rice University CoI: Arthur D. Code University of Wisconsin N ------------------------------------------------------------------------------------ 6. Abstract The nature of the cometary forms seen in the Helix Nebula, NGC 7293 are an unresolved puzzle. The fact that this is the closest of the planetary nebulae indicates that we may be seeing a phenomenon simply unresolved in the more distant planetaries. The interpretation of these forms ranges from the straightforward explanation of their being instabilities, to interpretations having far greater impact, such as being remnants of the extended envelope of the precursor star, to being components of an Oort Cloud of comets formed when the precursor star was created. The emission line filter images that we propose for the WFPC2 would provide direct and quantitative information that will allow resolution of the nature of these objects. ------------------------------------------------------------------------------------ 5977( 7) - 11/22/95 13:40 - [ 2] Observations Description ------------------------ Our observing program is in two parts, the first of which is to obtain an F631N (OI) image of the same portion of NGC 7293 that we will have imaged in F658N (NII), F656N (H-Alpha), and F502N (OIII) as part of our GTO programs. We can predict the resulting image as Code's 1000 second image in F658N gave a peak count for the cometary forms of 60 counts above the background. We propose using one orbit on this source, NGC7293-N, which will allow a total exposure time of 2000 seconds with three images, thus allowing good cosmic ray subtraction. The Warner and Rubin (1975, ApJ, 198,593) low spatial resolution spectroscopy indicate an average photon ratio for OI 6300 Angstroms over NII 6584 Angstroms of 0.32, thus predicting peak counts of 38 per pixel. We expect the peaks to be larger than this because the OI should be more sharply concentrated than NII. The second part of the observing program is to obtain a complete set of emission line images of a southerly portion of NGC 7293 (NGC7293-S). Since this region has not been imaged before, we will need to spend one orbit for each filter. Each will involve a triple exposure to allow good cosmic ray correction and the total exposure times will be F658N(2400 seconds), F656N(2400 seconds), F631N(2400seconds) and F502N(2000 seconds). The shorter time for F502N reflects the fact that it will be made on the first visit to NGC7293-S, where initial guidestar acquisition time is needed. Unlike other planetary nebulae the OIII line is very comparable to NII (0.92 times), so that the long exposure is needed in order to give a sufficient signal to noise ratio (ten) because one is looking for the effects of extinction by the Comets of the background nebular emission. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5977( 7) - 11/22/95 13:40 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PK36-57D1W ISM,PLANETARY RA=22H 29M 37.72S +/- 0.02S, 2000 SURF-LINE(6563) = 1.1 +/- 0.1 E-10 NEBULA,COMETARY DEC=-20D 47' 58.47" +/- 1" NEBULA,KNOT Comments: Surface brightness given is for the entire line. 2 PK36-57D1E ISM,PLANETARY RA=22H 29M 45.19S +/- 0.02S, 2000 SURF-LINE(6563) = 1.1 +/- 0.1 E-10 NEBULA,COMETARY DEC=-20D 48' 08.9" +/- 1" NEBULA,KNOT Comments: Surface brightness given is for the entire line. 5977( 7) - 11/22/95 13:40 - [ 4] Visit: 01 Visit Requirements: ORIENT 252D TO 254D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PK36-57D1W WFPC2 IMAGE WF4-FIX F631N CLOCKS=NO, CR- 3 500S NO SPLIT SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 PK36-57D1W WFPC2 IMAGE WF4-FIX F547M CLOCKS=NO, CR- 2 100S NO SPLIT SAME POS AS 1 SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 5977( 7) - 11/22/95 13:40 - [ 5] Visit: 02 Visit Requirements: ORIENT 69D TO 69D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 3 PK36-57D1E WFPC2 IMAGE WFALL F656N CLOCKS=NO, CR- 3 600S NO SPLIT SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 4 PK36-57D1E WFPC2 IMAGE WFALL F631N CLOCKS=NO, CR- 3 700S NO SPLIT SAME POS AS 3 MAX DUR 150% SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 5 PK36-57D1E WFPC2 IMAGE WFALL F658N CLOCKS=NO, CR- 3 700S NO SPLIT SAME POS AS 3 MAX DUR 150% SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 6 PK36-57D1E WFPC2 IMAGE WFALL F502N CLOCKS=NO, CR- 3 600S NO SPLIT SAME POS AS 3 SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 7 PK36-57D1E WFPC2 IMAGE WFALL F547M CLOCKS=NO, CR- 2 100S NO SPLIT SAME POS AS 3 SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 5977( 7) - 11/22/95 13:40 - [ 6] Summary Form for Proposal 5977 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CLOCKS=NO CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Interstellar Medium ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 252D TO 254D NO SPLIT NO SPLIT SAME POS AS 1 ORIENT 69D TO 69D NO SPLIT SAME POS AS 3 MAX DUR 150% NO SPLIT SAME POS AS 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F631N F547M F656N F658N F502N ------------------------------------------------------------------------------------------------------------------------------------ Target Names PK36-57D1W PK36-57D1E ------------------------------------------------------------------------------------------------------------------------------------