6780( 7) - 09/10/96 09:51 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6780 Version: 7 Check-in Date: 10-Sep-1996 09:46:33 1.Proposal Title: Spectroscopy and Imaging of a New Globular Cluster Planetary Nebula ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle INTERSTELLAR MEDIUM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: GEORGE JACOBY KITT PEAK NATIONAL OBSERVATORY CoI: Laura Fullton Space Telescope Science Institute N CoI: Jon Morse University of Colorado N ------------------------------------------------------------------------------------ 6. Abstract We found the third (and probably last) PN to be associated with a Galactic globular cluster in NGC 6441. Optical spectra indicate an unexpectedly severe oxygen depletion (O/Fe ~ - 0.8). Ionization models (CLOUDY) indicate that oxygen at higher ionization stages may account for half of the depletion. HST observations are requested to (1) obtain UV spectra of the nebula to constrain models further and to determine directly the contributions from unseen higher stages of ionization of oxygen, while measuring carbon and nitrogen abundances, and (2) image the nebula at high resolution to ascertain its degree of disruption by the ISM. Neither the UV spectra nor the high resolution imaging can be done with ground-based telescopes. The optically derived O/Fe is 30-40* smaller than seen in the M15 PN or in field stars. This ratio impacts the ages derived for clusters where the field star assumption is used. Stellar dredge-up theory does not account for a depletion of oxygen this extreme. There is a small chance that the NGC 6441 PN is NOT a member of the cluster; its velocity differs from the cluster by ~ 20 km/s. This difference could be due to an interaction with the ISM. Direct images of the nebula are requested to examine the morphology. An interaction will be evident by the presence of a bow shock or by displacement of the ``central'' star from the nebula center. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will obtain HAlpha (F656N) and [OIII] (F502N) images of the PN in NGC 6441 with the PC to (1) provide EARLY ACQUISITION images for pointing information, and (2) ascertain its degree of distortion that might result from an interaction with the ISM, (3) identify any ionization dependent structures. We choose to image primarily in HAlpha rather than OIII since the flux is slightly higher and the throughput better at the red wavelength, resulting in a 2* improvement and the primary goal of the imaging is to prepare for the spectroscopy. Short continuum exposures (F675W, F547M) are required to subtract stellar sources from the faint nebular image. The images are necessary for the spectroscopy since we wish to avoid as many stars as possible while collecting as much nebular light as we can. Stars can be the limiting noise source if the aperture is poorly placed. Exposure times for the PC imaging (assuming 7.1 min for acquisition and 5.25 min for orbit 2 and 3 re-acquisition) allow for 6 exposures at Halpha of 600s each in orbits 1 and 2, 5 F675W red continuum exposures of 23s each at the end of orbits 1 and 2. Two exposures of 2s through F675W are also needed to avoid saturating our FOS offset star. Orbit 3 was originally intended to begin the FOS spectroscopy in a second visit, but the SAA limits our 9 orbits for spectroscopy to 8 orbits; consequently, we have moved one orbit to enhance the imaging science. Orbit 3 provides for 2 [OIII] exposures of 1000s each and 2 green continuum exposures of 80s and 2 of 20s each. For a nebula flux of F_HAlpha = 3* 10^-15 ergs/cm^2/s/arcsec^2, based on our spectroscopy, the S/N per PC pixel over the 3900s of Halpha on- band exposures will exceed 2.5 per pixel. The total continuum exposures have an effective throughput 50* higher, so only 1.3 minutes are required to match the on-band image; however, 2 minutes total are requested to avoid degradation of the on-band image when subtracting the continuum. Similar arguments apply at [OIII], although the final S/N will be about 30% lower due to the lower system throughput at 5007A. Three spectral setups are needed to tie into the ground- based spectra. Only the blue spectrum (grating G160L) is time consuming, as a consequence of the weak lines of nitrgoen and the lower system throughput. This region of the spectrum, requiring 5 orbits, is crucial: it provides the most constraints on the photo-ionization models through the lines of NV (1240), OIV (1402), NIV (1487), CIV (1549), NIII (1747), HeII (1640), OIII (1663), CIII (1909), and NeIV 2422. Shorter exposures with gratings G270H and G400H will tie into the optical spectrum via NeIII (3868), HGamma (4340), and HeII (4686) which are all strong lines. The exposure time in the blue (1150-2510) is calculated to yield a good measurement (SNR ~ 5) for extinction (E(B-V)=0.5) affected lines as weak as 25\\% of HBeta (F^obs_HBeta = 0.6 * 10^-15 ergs/cm^2/s/arcsec) integrated over aperture 1.0 (0.86" round). Photo- ionization models indicate that the high excitation nitrogen lines will be this weak. With this goal, all FOS data can be obtained in 1 visit. Acquisition for FOS can be performed by a peak-up on a nearby star, followed by a small blind offset to the nebula position. Absolute positioning is not critical. Peaking up on the nebula is NOT desired, as the aperture may be pulled off the optimum nebular position to a continuum source. \\medskip begintabularlll WFPC2 & Primary Orbits:3 & Exposures:10 (3900s in HAlpha,2.3 min in R, 2800s in [OIII], 320s in Green, total) , FOS Acq + G400H & Primary Orbits:1 & Exposures:2 1700s, FOS G400H + G270H (ReD) & Primary Orbits:1 & Exposures:3 (1000s + 1220s) , FOS G270H (ReD) & Primary Orbits:1 & Exposures:1 (2480s) , FOS G160L (BLue) & Primary Orbits:1 & Exposures:1 (2110s) , FOS G160L (BLue) & Primary Orbits:1 & Exposures:1 (2500s) , FOS G160L (BLue) & Primary Orbits:1 & Exposures:2 2500s, FOS G160L (BLue) & Primary Orbits:2 & Exposures:2 (2500s each orbit) , endtabular \\medskip The switch from red to blue detectors can be done at the end of target visibility for the G270H grating to minimize loss of exposure time during the orbit commencing the G160L grating observations. Real Time Justification ----------------------- None We are submitting a proposal to CTIO for deeper optical spectra and near- IR spectra (out to 9532 Angstrom) to assist in constraining the photo- ionization models at the low excitation species end. Calibration Justification ------------------------- Additional Comments ------------------- Please ensure that WFPC-2 EARLY/ACQ imaging is scheduled well in advance of FOS spectroscopy. ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6780( 7) - 09/10/96 09:51 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6441-PN STELLAR RA=17H50M10.88S +/- 0.1S, DEC=- 2000 V=+30 V = 19.8+/-0.5 CLUSTER,GLOBULAR 37D03'27.1" +/- 1", PLATE- SURF-LINE(4861)=6+/-2e-16 CLUSTER,ISM,PLANETARY ID=060H NEBULA 2 NGC6441- STAR RA=17H50M11.2916S +/- 0.05S, 2000 V=+30 V = 16.3+/-0.1 OFFSET DEC=-37D03'35.71" +/- 1", PLATE- B-V = 1.60+/-0.1 ID=060H Comments: Magnitude, color and position determined from EARLY/ACQ images. 3 NGC6441- ISM,PLANETARY R=10.91", PA=328.188D, FROM 2 2000 V=+30 SURF-LINE(4861)=6+/-2e-16 POSN1 NEBULA,KNOT Comments: Knot determined from WFPC2 EARLY/ACQ images. 6780( 7) - 09/10/96 09:51 - [ 2] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: EARLY/ACQ images to identify target for FOS spectroscopy. Best ORIENT is 210D but this may be unschedulable and is NOT critical WFPC2 observations must be scheduled as early as possible to allow time for analysis and scheduling of FOS orbits in the August or October windows, the last chances before FOS disappears. We therefore request the WFPC2 images to be obtained in the April/May cycle 5 window. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6441-PN WFPC2 IMAGE PC1-FIX F656N CR-SPLIT=0.5 1 1200 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6441-PN WFPC2 IMAGE PC1-FIX F656N CR-SPLIT=NO 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6441-PN WFPC2 IMAGE PC1-FIX F675W CR-SPLIT=0.5 1 46 S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6441-PN WFPC2 IMAGE PC1-FIX F675W CR-SPLIT=NO 1 23 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6441-PN WFPC2 IMAGE PC1-FIX F656N CR-SPLIT=0.5 1 1200 S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6441-PN WFPC2 IMAGE PC1-FIX F656N CR-SPLIT=NO 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6441-PN WFPC2 IMAGE PC1-FIX F675W CR-SPLIT=0.5 1 46 S ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6441-PN WFPC2 IMAGE PC1-FIX F675W CR-SPLIT=0.5 1 6 S ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC6441-PN WFPC2 IMAGE PC1-FIX F547M CR-SPLIT=NO 1 80 S ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6441-PN WFPC2 IMAGE PC1-FIX F547M CR-SPLIT=NO 1 80 S ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6441-PN WFPC2 IMAGE PC1-FIX F547M CR-SPLIT=0.5 1 40 S ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC6441-PN WFPC2 IMAGE PC1-FIX F502N 1 2000 S ------------------------------------------------------------------------------------------------------------------------------------ 6780( 7) - 09/10/96 09:51 - [ 3] Visit: 02 Visit Requirements: ON HOLD FOR 1 On Hold Comments: Hold visit 2 for 2 months (assuming Visit 1 can be scheduled during the April/May/June windows) so that NGC6441-POSN1 coordinates can be verified from WFPC2 EARLY/ACQ images. Additional Comments: Acquire offset star with BIN/ACQ, do 1-stage peak-up, offset to PN position, then run through exposures. Take WAVEs during earth occultation. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 101 NGC6441-OFF FOS/RD ACQ/BIN 4.3 MIRROR FAINT=1210 1 16 S ONBOARD ACQ FOR 102 SET ARY Comments: Shorter exposure and higher FAINT value in order to exclude nearby stars from being detected. ------------------------------------------------------------------------------------------------------------------------------------ 102 NGC6441-OFF FOS/RD ACQ/PEA 0.3 MIRROR SEARCH-SIZE-X=4,SEARCH-SIZE-Y=4, 1 10 S ONBOARD ACQ FOR 103-111 SET K SCAN-STEP-X=.17,SCAN-STEP-Y=.17 Comments: Exposure time is compromise between critical and non-critical peak-up; good enough for 1.0-PAIR. ------------------------------------------------------------------------------------------------------------------------------------ 103 NGC6441-POS FOS/RD ACCUM 1.0-PAI G400H STEP-PATT=SINGLE 1 600 S N1 R-A ------------------------------------------------------------------------------------------------------------------------------------ 104 WAVE FOS/RD ACCUM 1.0-PAI G400H 3238-47 STEP-PATT=SINGLE 1 DEF R-A 81 Comments: During occultation. ------------------------------------------------------------------------------------------------------------------------------------ 105 NGC6441-POS FOS/RD ACCUM 1.0-PAI G400H STEP-PATT=SINGLE 1 1500 S N1 R-A ------------------------------------------------------------------------------------------------------------------------------------ 106 NGC6441-POS FOS/RD ACCUM 1.0-PAI G270H STEP-PATT=SINGLE 1 800 S N1 R-A ------------------------------------------------------------------------------------------------------------------------------------ 107 WAVE FOS/RD ACCUM 1.0-PAI G270H 2222-32 STEP-PATT=SINGLE 1 DEF R-A 77 Comments: During occultation. ------------------------------------------------------------------------------------------------------------------------------------ 108 NGC6441-POS FOS/RD ACCUM 1.0-PAI G270H STEP-PATT=SINGLE 1 2500 S N1 R-A ------------------------------------------------------------------------------------------------------------------------------------ 109 NGC6441-POS FOS/BL ACCUM 1.0-PAI G160L STEP-PATT=SINGLE 1 7200 S N1 R-A ------------------------------------------------------------------------------------------------------------------------------------ 110 WAVE FOS/BL ACCUM 1.0-PAI G160L 1140-25 STEP-PATT=SINGLE 1 DEF R-A 08 Comments: During occultation. ------------------------------------------------------------------------------------------------------------------------------------ 111 NGC6441-POS FOS/BL ACCUM 1.0-PAI G160L STEP-PATT=SINGLE 1 5000 S N1 R-A ------------------------------------------------------------------------------------------------------------------------------------ 6780( 7) - 09/10/96 09:51 - [ 4] Summary Form for Proposal 6780 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 FOS/RD FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ/BINARY ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=0.5 CR-SPLIT=NO FAINT=1210 SCAN-STEP-Y=.17 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ON HOLD FOR 1 ONBOARD ACQ FOR 102 ONBOARD ACQ FOR 103-111 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F656N F675W F547M F502N MIRROR G400H G270H G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6441-PN NGC6441-OFFSET NGC6441-POSN1 WAVE ------------------------------------------------------------------------------------------------------------------------------------