6792( 7) - 11/07/96 15:39 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6792 Version: 7 Check-in Date: 07-Nov-1996 15:37:05 1.Proposal Title: Planetary Nebulae With Supporting Infrared Data ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle INTERSTELLAR MEDIUM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Robert Rubin NASA AMES RESEARCH CENTER CoI: Patrick Harrington UNIVERSITY OF MARYLAND N CoI: Reginald Dufour RICE UNIVERSITY N ------------------------------------------------------------------------------------ 6. Abstract Recent work has shown that nebular abundances derived from recombination lines are up to a factor of five larger than those obtained from the traditional optical/UV collisionally excited lines. These can be brought into agreement at the higher value if large unexplained temperature fluctuations (t^2) exist. We have been granted observing time on ISO to do IR spectroscopy of two planetary nebulae (PNs) to address this problem. The ISO line data and cospatial optical/UV spectra (including high dispersion IUE), will permit the measurement of the average N_e, T_e, and t^2 for several ionic species not possible previously. This provides information on how t^2 depends on level of ionization or excitation of the gas. Here we propose to complement the above macroscopic knowledge by observing the same PNs with several WFPC2 narrow filters in order to understand the origin of physical conditions on the microscopic scale (~ 0.1''). With the significantly improved resolution afforded by HST, there will be new knowledge of the morphology, stellar wind -- gas interactions, and N_e structure. More realistic photoionization and dynamical models should result. Our goals are to understand the conditions within the nebulae and the physical origin of the inferred T_e variations, and to find a prescription for determining reliable nebular abundances - fundamental to understanding the chemical evolution of the Galaxy. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our program is based on obtaining WFPC2 images of two PNs for which we have been awarded Infrared Space Observatory (ISO) time. The objects are NGC 6210 and NGC 6818. Irrespective of the ISO contribution, this program is of interest. The detailed structure and morphology of the sources will be enormously enhanced by the WFPC2 imaging. We will use a single field center for each of the PNs to take images with several narrow-band filters that cover emission lines of interest. Individual filters are listed as well as the dominant line they are designed to cover. The science objective for the various filters is briefly discussed. Imagery in one continuum band, F547M, is planned as this is crucial in order to take out the continuum contribution to the all- important [OIII] 4363 A line being imaged by the F437N filter. It is imperative in order that we may accomplish the chief scientific objective of getting T_e from F(4363)/F(5007) ratio maps. Exposure times are listed for our highest priority object NGC 6210 unless mentioned otherwise. These are based on measurements of Acker et al. (1989) except where noted. S(H Beta) = 8.63E-13 erg/cm^2-s-(square)". For NGC 6818, calculations of the time for the set of filters have been made also based on existing emission line observations (private communication Siek Hyung). Exposure times and S/N per pixel are based on the pixel size of the WFC. We plan 2 orbits for each PN. F375N [OII] 3727 -- Our time estimate is based on data of Aller & Czyzak (1983) for NGC 6210. A S/N ~ 10 per pixel is reached in ~460 sec. This filter is used ONLY for NGC 6210. F437N [OIII] 4363 -- This is a very important diagnostic line. As such, we plan the longest exposure of 2400 sec, that will provide S/N >~ 20 per pixel. We do 3 iterations of 800 sec for better removal of CRs. For all other filters, just 2 exposures are needed for CR removal. F487N H Beta 4861 -- A S/N >30 per pixel is reached in ~320 sec. F502N [OIII] 5007 -- A S/N >100 per pixel is reached in ~320 sec. F547M continuum -- We chose an exposure time of 320 sec, which should provide better S/N than in the narrow filters and allow an accurate subtraction of the continuum. F656N H Alpha 6563 -- A S/N >100 per pixel is reached in ~320 sec. The ratios of these lines will provide the following science: Reddening through H Alpha/H Beta; Images in F487N and F547M provide a measure of H Beta, with an accurate subtraction of the continuum. Together with the image in F656N, this permits derivation of point-to-point reddening via H Alpha/H Beta, which is important for making small-scale extinction corrections to line ratios involving lines over a large wavelength range. Electron temperature (T_e) through the excellent diagnostic [OIII] 4363/5007; As a further probe (that is based on stronger lines than 4363), if highly deviant temperatures exist, we would expect to see this as local fluctuations in the 5007/H Beta ratio. The proximity of wavelengths makes this ratio ideal, because it is very insensitive to variable reddening. For NGC 6210 only, we have time in the second orbit to obtain images in F375N (3727). By using this imagery in conjunction with the F502N (5007), ionization state OII/OIII information is obtained. For NGC 6818: We compare the H Beta surface brightness according to the entries in the Catalog of Galactic PN (Acker et al. 1992). Thus the H Beta surface brightness is down by a factor 2.4 compared with NGC 6210. Even so, because this PN is higher excitation and T_e [OIII] (12900 K Rola & Stasinska 1994) than NGC 6210, we can do 4 narrow filters plus F547M in 2 orbits with a S/N of at least 10 per WFC pixel. Real Time Justification ----------------------- An important aspect of this program is the opportunity to combine cospatial data over a large wavelength range. Thus, the two orbits per source need to be consecutive. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6792( 7) - 11/07/96 15:39 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6210-WF ISM, Planetary Nebula RA=16H 42M 23.65S +/- 0.01S, 1950 V = -36 B-V = -0.22 DEC=23D 53' 29.0" +/- 1" TYPE=O6 V = 12.66+/-0.1 SURF-LINE(6563)=2.6+/-0.53e-12 SURF-LINE(5007)=9.9+/-2.0e-12 SURF-LINE(4861)=8.6+/-1.7e-13 SURF-LINE(4363)=6.9+/-1.4e-14 SURF-LINE(3727)=3.9+/-0.78e-13 2 NGC6818-WF ISM, Planetary Nebula RA=19H 41M 08.67S +/- 0.01S, 1950 V = -13 B = 16.9 DEC=-14D 16' 26.2" +/- 1" TYPE=WNB? SURF-LINE(6563)=1.1+/-0.21e-12 SURF-LINE(5007)=5.3+/-1.1e-12 SURF-LINE(4861)=3.5+/-0.70e-13 SURF-LINE(4363)=7.8+/-1.6e-14 SURF-CONT(5000)=1.0+/-0.4e-14 6792( 7) - 11/07/96 15:39 - [ 2] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: This is long axis ORIENT 70 +/-20, along U2/V2 diagonal, Also acceptable is 180D shift or long axis ORIENT 250 +/-20 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6210-WF WFPC2 IMAGE WF3-FIX F437N CLOCKS=YES,CR-SPLIT=NO 3 800.0 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6210-WF WFPC2 IMAGE WF3-FIX F487N CR-SPLIT=NO 1 160.0 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6210-WF WFPC2 IMAGE WF3-FIX F487N CR-SPLIT=NO 1 160.0 S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6210-WF WFPC2 IMAGE WF3-FIX F502N CR-SPLIT=NO,ATD-GAIN=15 2 160.0 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6210-WF WFPC2 IMAGE WF3-FIX F547M CR-SPLIT=NO 2 160.0 S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6210-WF WFPC2 IMAGE WF3-FIX F656N CR-SPLIT=NO,ATD-GAIN=15 2 160.0 S ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6210-WF WFPC2 IMAGE WF3-FIX F375N CLOCKS=YES,CR-SPLIT=NO 1 260.0 S ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6210-WF WFPC2 IMAGE WF3-FIX F375N CLOCKS=YES,CR-SPLIT=NO 1 200.0 S ------------------------------------------------------------------------------------------------------------------------------------ 6792( 7) - 11/07/96 15:39 - [ 3] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: This is major axis ORIENT 105 +/-20, along U2/V2 diagonal, Also acceptable is 180D shift or long axis ORIENT 285 +/-20 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC6818-WF WFPC2 IMAGE WF3-FIX F437N CLOCKS=YES,CR-SPLIT=NO 3 800.0 S ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC6818-WF WFPC2 IMAGE WF3-FIX F487N CLOCKS=YES,CR-SPLIT=NO 2 260.0 S ------------------------------------------------------------------------------------------------------------------------------------ 23 NGC6818-WF WFPC2 IMAGE WF3-FIX F502N CR-SPLIT=NO,ATD-GAIN=15 2 160.0 S ------------------------------------------------------------------------------------------------------------------------------------ 24 NGC6818-WF WFPC2 IMAGE WF3-FIX F547M CR-SPLIT=NO 2 120.0 S ------------------------------------------------------------------------------------------------------------------------------------ 25 NGC6818-WF WFPC2 IMAGE WF3-FIX F656N CLOCKS=YES,CR-SPLIT=NO, 2 260.0 S ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ 6792( 7) - 11/07/96 15:39 - [ 4] Summary Form for Proposal 6792 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CLOCKS=YES CR-SPLIT=NO ATD-GAIN=15 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F437N F487N F502N F547M F656N F375N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6210-WF NGC6818-WF ------------------------------------------------------------------------------------------------------------------------------------