7300( 2) - 05/23/97 10:57 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7300 Version: 2 Check-in Date: 23-May-1997 10:56:51 1.Proposal Title: Hyperfine Induced Transitions as Probes of Low Density Plasmas ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR EJECTA GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: TOMAS BRAGE UNIVERSITY OF LUND CoI: Charles R. Proffitt Computer Sciences Corporation N CoI: Philip Judge High Altitude Observatory, National Center N for Atmospheric Research ------------------------------------------------------------------------------------ 6. Abstract Hyperfine induced (HPF) transitions in ^13C, ^29Si, and N may provide a sensitive density diagnostic for low density plasmas, as well as a way to measure carbon and silicon isotope ratios. As it is impossible to measure such small transition probabilites in laboratory sources, we propose to detect the HPF line of N IV, Lambda1483.32 Angstrom, in the low density planetary nebulae NGC 3918. Sucessful detection of this line would verify the predictions of atomic theory, and when combined with a previous non-detection of the ^13C III HPF line (Lambda1906.7 Angstrom) in this source, would yield an upper limit to the ^13C/^12C ratio. ------------------------------------------------------------------------------------ 7300( 2) - 05/23/97 10:57 - [ 2] Observations Description ------------------------ Optical and IUE data for this nebula were discussed by Clegg et al. The observed flux in the HST/GHRS large aperture spectrum of the C III IC line is about 3times10^-12 ergs/cm^2/sec. H-Beta images of the nebula show that emission over the central 8 arc-seconds diameter is relatively flat with contours that are roughly circular, and we will take the mean surface brightness of the center of the nebulae in C III to be this flux divided by the area of the HRS LSA. We will estimate the flux of the other lines of interest by assuming that their flux relative to C III is the same as in IUE spectra of the nebulae (i.e. N IV is about 1/10th, and that of Si III is 1/100th of the intensity of C III). When we combine this with the predicted isotopic ratios and the relative intensities of the HPF and intercombination lines, we find that the predicted surface brightness of the N IV lines is as follows:, ION Lambda (Angstrom) IC HPF Line widths ergs/cm^2/sec/"^2 (Angstroms) N IV 1486 1e -13 0.25e-13, 0.4 A direct estimate using the IUE spectra gives similar fluxes. Using the G140M with the 52*0.1" aperture, a S/N of 3 in each spatial resolution element with an exposure of 4180 seconds, and there should be about 100 spatial resolution elements across the source. This should allow a clear detection of the HPF line in the spatially integrated spectrum. Allowing for target acquisition and overheads we request 3 orbits to execute this observation. As the nebulae is roughly circular, the orientation of the slit is not relevant for our purposes. For the acquisition, we take the total O III flux given by Kouhotek et al (1981, A&AS, 44, 325) of 1.4e-9 erg/cm^2/sec, and assume a 10" diameter, giving a mean surface brightness of 4.5e-12 erg/cm^2/sec/"^2. A simulated line profile input into the spectrographic ETC yields 1500 cnts/pixel in a 30 second exposure. This allows a generous margin of error for localized brightness enhancements before saturating the CCD. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Charles R. Proffitt*Code 681/CSC*Goddard Space Flight Center*Greenbelt, MD 20771 Ship Via: Email: proffitt@figaro.gsfc.nasa.gov ------------------------------------------------------------------------------------ 7300( 2) - 05/23/97 10:57 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3918 ISM,PLANETARY NEBULA RA=11H 50M 17.84S +/- 0.04S,DEC= J2000 SURF-LINE(5007)=4.5+/-2e-12 -57D 10' 56.3" +/- 0.3",PLATE- SURF(V) = 13.5+/-1 ID=06PS SURF-LINE(1483)=1+/-0.3e-13 SURF-CONT(1470)=1+/-0.3e-15 W-LINE(1483)=0.24+/-0.1 W-LINE(5007)=0.8+/-0.2 7300( 2) - 05/23/97 10:57 - [ 4] Visit: 01 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC3918 STIS/C ACQ F28X50O MIRROR CHECKBOX=21, 1 30 S ONBOARD ACQ FOR 20,30,40 CD III DIFFUSE-CENTER=FLUX-CENTROID, ACQTYPE=DIFFUSE ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC3918 STIS/F ACCUM 52X0.2 G140M 1470 1 2153 S EXPAND UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC3918 STIS/F ACCUM 52X0.2 G140M 1470 1 2790 S EXPAND UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC3918 STIS/F ACCUM 52X0.2 G140M 1470 1 2790 S EXPAND UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7300( 2) - 05/23/97 10:57 - [ 5] Summary Form for Proposal 7300 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CHECKBOX=21 DIFFUSE-CENTER=FLUX-CENTROID ACQTYPE=DIFFUSE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR EJECTA ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 20,30,40 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3918 ------------------------------------------------------------------------------------------------------------------------------------