Proposal_Information ! Section 4 Title: Cometary Forms in the Helix Nebula Proposal_Category: GO Scientific_Category: Interstellar Medium Cycle: 5 Investigators PI_name: C. Robert O'Dell PI_Institution: Department of Space Physics and Astronomy, Rice University CoI_Name: Arthur D. Code CoI_Institution: University of Wisconsin Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) 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. Questions ! Free format text (please update) Observing_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: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number:1 Target_Name:PK36-57D1W Alternate_Names:NGC7293 Description:ISM,PLANETARY NEBULA,COMETARY NEBULA,KNOT Position:RA=22H 29M 37.72S +/- 0.02S, DEC=-20D 47' 58.47" +/- 1" Equinox:2000 Flux:SURF-LINE(6563) = 1.1 +/- 0.1 E-10 Comments:Surface brightness given is for the entire line. Fixed_Targets ! Section 5.1 Target_Number:2 Target_Name:PK36-57D1E Alternate_Names:NGC7293 Description:ISM,PLANETARY NEBULA,COMETARY NEBULA,KNOT Position:RA=22H 29M 45.19S +/- 0.02S, DEC=-20D 48' 08.9" +/- 1" Equinox:2000 Flux:SURF-LINE(6563) = 1.1 +/- 0.1 E-10 Comments:Surface brightness given is for the entire line. Visits ! Section 6 Visit_Number:1 Visit_Requirements:ORIENT 252D TO 254D On_Hold_Comments: Visit_Comments: Exposure_Number:1 ! Section 6.5 Target_Name:PK36-57D1W Config:WFPC2 Opmode:IMAGE Aperture:WF4-FIX Sp_Element:F631N Wavelength: Optional_Parameters:CLOCKS=NO, CR-SPLIT=NO Number_of_Iterations:3 Time_Per_Exposure:500S Special_Requirements:NO SPLIT ! Section 7.2 Comments: Exposure_Number:2 ! Section 6.5 Target_Name:PK36-57D1W Config:WFPC2 Opmode:IMAGE Aperture:WF4-FIX Sp_Element:F547M Wavelength: Optional_Parameters:CLOCKS=NO, CR-SPLIT=NO Number_of_Iterations:2 Time_Per_Exposure:100S Special_Requirements:NO SPLIT SAME POS AS 1 Comments: Visits ! Section 6 Visit_Number:2 Visit_Requirements:ORIENT 69D TO 69D On_Hold_Comments: Visit_Comments: Exposure_Number:3 ! Section 6.5 Target_Name:PK36-57D1E Config:WFPC2 Opmode:IMAGE Aperture:WFALL Sp_Element:F656N Wavelength: Optional_Parameters:CLOCKS=NO, CR-SPLIT=NO Number_of_Iterations:3 Time_Per_Exposure:600S Special_Requirements:NO SPLIT ! Section 7.2 Comments: Exposure_Number:4 ! Section 6.5 Target_Name:PK36-57D1E Config:WFPC2 Opmode:IMAGE Aperture:WFALL Sp_Element:F631N Wavelength: Optional_Parameters:CLOCKS=NO, CR-SPLIT=NO Number_of_Iterations:3 Time_Per_Exposure:700S Special_Requirements:NO SPLIT SAME POS AS 3 MAX DUR 150% Comments: Exposure_Number:5 ! Section 6.5 Target_Name:PK36-57D1E Config:WFPC2 Opmode:IMAGE Aperture:WFALL Sp_Element:F658N Wavelength: Optional_Parameters:CLOCKS=NO, CR-SPLIT=NO Number_of_Iterations:3 Time_Per_Exposure:700S Special_Requirements:NO SPLIT SAME POS AS 3 MAX DUR 150% Comments: Exposure_Number:6 ! Section 6.5 Target_Name:PK36-57D1E Config:WFPC2 Opmode:IMAGE Aperture:WFALL Sp_Element:F502N Wavelength: Optional_Parameters:CLOCKS=NO, CR-SPLIT=NO, Number_of_Iterations:3 Time_Per_Exposure:600S Special_Requirements:NO SPLIT SAME POS AS 3 Comments: Exposure_Number:7 ! Section 6.5 Target_Name:PK36-57D1E Config:WFPC2 Opmode:IMAGE Aperture:WFALL Sp_Element:F547M Wavelength: Optional_Parameters:CLOCKS=NO, CR-SPLIT=NO, Number_of_Iterations:2 Time_Per_Exposure:100S Special_Requirements:NO SPLIT SAME POS AS 3 Comments: Data_Distribution ! Defaults indicated; change if desired Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 ! Only astronomers with very old 9- ! track tape drives should consider ! a blocking factor of 1 Ship_To: PI_address Ship_Via: UPS ! UPS (2-day) or OVERNIGHT ! Overnight shipping done at PI expense Recipient_Email: ! Needed if Ship_To: is not PI_Address