9238( 3) - 11/20/01 10:59 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9238 Version: 3 Check-in Date: 20-Nov-2001 10:59:07 1.Proposal Title: The Spatial and Ionization Structure of Cas A's Metal-Rich Ejecta ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Robert Fesen Dartmouth College CoI: Dr. Kazimierz Borkowski North Carolina State University N CoI: Dr. Roger Chevalier University of Virginia N CoI: Dr. Steve Lawrence Columbia University N CoI: Dr. Jon Morse University of Colorado N CoI: Dr. Sidney van den Bergh DAO N ------------------------------------------------------------------------------------ 5. Abstract Cassiopeia A (Cas A) is the prototype for the class of young, oxygen-rich SNRs containing material moving at several thousand km s^-1 and exhibiting extreme O and Si-group (Si, S, Ar, and Ca) abundances due to nuclear processing in a massive star. Several basic properties of the remnant are not well understood including shock dynamics of the ejecta, UV and optical line emission mechanisms, and the puzzling organization of its optical knots into large ring-like structures. Here we propose the first high-resolution mapping of this important remnant using WFPC2. Our goal is to survey the small-scale spatial and ionization structures in these metal-rich ejecta, then use these results to test reverse shock and CSM-interaction hydrodynamic and line emission models. We have selected filters which will permit imaging of the remnant's full +/-6000 km s^-1 expansion velocity in both high and low ionization emission lines of sulfur and oxygen. These data will provide spatial information at scales down to 0.001 pc and distinguish oxygen from sulfur rich emission knots and filaments. Because Cas A's ejecta knots have large proper motions of 0.2''-0.5'' yr^-1 and exhibit significant structural changes on timescales of just a few years, we would like to re-image the remnant during Cycle 10 in order to detect and measure spatial and ionization changes. ------------------------------------------------------------------------------------ 9238( 3) - 11/20/01 10:59 - [ 2] Observations Description ------------------------ We are proposing WFPC2 imaging of three sections of the Cas A remnant, namely the NE, NW, and Southern rims. This can be accomplished in three pointings in which two can have the same orientation (ORIENT). The two northern sections of the remnant, containing the bulk of the remnant's optical emission, can be well covered by the WF2, WF3, and WF4 chips in two pointings where one is 180 degrees rotated from the first. These two combined WFPC2 images cover an area approximately 300 * 150 arcsec with some overlap, more than enough to image Cas A's 250 * 120 arcsec northern emission shell. The remnant's southern emission rim can be imaged in just one pointing using either the WF2--WF3 or WF3--WF4 pairs of chips to cover the bright E--W emission band (see Fig 2). We intend to image each of these remnant sections (NE, NW, S) in four filters selected to isolate the ejecta's emission in oxygen and sulfur line emissions. To gain the maximum resolution from these WFC images (i.e., 0.05''), we will take two sets of twin images, dithered in both x and y by 2.5 pixels. This should eliminate the majority of cosmic rays and detector hot pixels. Based on ground-based imaging and the WFPC1 images, we estimate we need a S/N of ~ 5 per pixel for each of the four filter images in order to detect fine scale structures with high confidence. We have estimated exposure times using the WFPC2 exposure calculator on the STScI website and then checked these estimates against the archival WFPC1 images taken using narrow nebula filters. For example: For the F450W filter on one of Cas A's brighter knots (5 * 10^-14 erg cm^-2 s^-1 arcsec^-2; from Hurford & Fesen 1996), we obtain 1770 e^- per pixel and a S/N of 39.5 for 4 * 1000 sec exposures. The archival S II images for the brighter low velocity filaments give comparable numbers. For the fainter, more typical knots, which are roughly 20 times fainter, we will get a S/N of 5.4. Similarly, using the F850LP filter and a combined S III 9061 + 9531 knot flux of around 5 * 10^-15 erg cm^-2 s^-1 arcsec^-2 for a typical knot, we will get a S/N of 4.7 from 4 * 1000 sec images. Somewhat shorter exposure times are required for the F675W filter due to the detection of several strong lines (especially S II LambdaLambda6716, 6731) and for the F657N filter due to the strength of the N II Lambda6583 lines in the QSFs. At a Dec. of +58.7 degrees, Cas A lies well within the CVZ and we have calculated total orbit requirements assuming CVZ orbits. Using the RPS2 calculator, four 500 sec F657N and four 700 sec F675W images plus four 1000 sec exposures in both F450W and F850LP filters can be taken within 3 CVZ orbits for each target position. The total time requested for the three remnant pointings is therefore 9 CVZ orbits. , Summary:, N II & H -alpha ------ Filter F657N: 2 sets of 500 x 2 dithered images. , O I, O II, & S II-- Filter F675W: 2 sets of 700 s x 2 dithered images. , O III & O II -------- Filter F450W: 2 sets of 1000 s x 2 dithered images. , S III & S II --------- Filter F850LP: 2 sets of 1000 s x 2 dithered images. , = 3 CVZ orbits on each position. Three positions in two visits. Grand total = 9 orbits. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9238( 3) - 11/20/01 10:59 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CAS-A-NE ISM RA=23H 23M 38.0S +/-0.50S, 2000 V = 25.0+/-2.0 DEC=58D 49' 46.0" +/-3.0" Coordinate Source: HST_IMAGE Comments: E(B-V)=1.60 +/-0.50 2 CAS-A-NW ISM RA=23H 23M 29.0S +/-0.50S, 2000 V = 25.0+/-2.0 DEC=58D 49' 9.0" +/-5.0" Coordinate Source: HST_IMAGE Comments: E(B-V)=1.60 +/-0.50 3 CAS-A-SW ISM RA=23H 23M 30.0S +/-0.50S, 2000 V = 25.0+/-2.0 DEC=58D 47' 42.0" +/-3.0" Coordinate Source: HST_IMAGE Comments: E(B-V)=1.60 +/-0.50 9238( 3) - 11/20/01 10:59 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 44.9D TO 45.1D CVZ 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 ------------------------------------------------------------------------------------------------------------------------------------ 111 CAS-A-NE WFPC2 IMAGE WF4 F850LP CR-SPLIT=NO 2 700 S ------------------------------------------------------------------------------------------------------------------------------------ 112 CAS-A-NE WFPC2 IMAGE WF4 F850LP CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 121 CAS-A-NE WFPC2 IMAGE WF4 F450W CR-SPLIT=NO 2 700 S ------------------------------------------------------------------------------------------------------------------------------------ 122 CAS-A-NE WFPC2 IMAGE WF4 F450W CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 131 CAS-A-NE WFPC2 IMAGE WF4 F675W CR-SPLIT=NO 2 500 S ------------------------------------------------------------------------------------------------------------------------------------ 132 CAS-A-NE WFPC2 IMAGE WF4 F675W CR-SPLIT=NO 2 500 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 151 CAS-A-NE WFPC2 IMAGE WF3 F675W CR-SPLIT=NO 2 400 S POS TARG 12.0, -18.0 ------------------------------------------------------------------------------------------------------------------------------------ 152 CAS-A-NE WFPC2 IMAGE WF3 F675W CR-SPLIT=NO 2 400 S POS TARG 12.5, -18.5 ------------------------------------------------------------------------------------------------------------------------------------ 155 CAS-A-NE WFPC2 IMAGE WF3 F850LP CR-SPLIT=NO 2 500 S POS TARG 12.0, -18.0 ------------------------------------------------------------------------------------------------------------------------------------ 156 CAS-A-NE WFPC2 IMAGE WF3 F850LP CR-SPLIT=NO 2 500 S POS TARG 12.5, -18.5 ------------------------------------------------------------------------------------------------------------------------------------ 9238( 3) - 11/20/01 10:59 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 44.9D TO 45.1D CVZ 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 ------------------------------------------------------------------------------------------------------------------------------------ 211 CAS-A-NW WFPC2 IMAGE WF3 F850LP CR-SPLIT=NO 2 700 S ------------------------------------------------------------------------------------------------------------------------------------ 212 CAS-A-NW WFPC2 IMAGE WF3 F850LP CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 221 CAS-A-NW WFPC2 IMAGE WF3 F450W CR-SPLIT=NO 2 700 S ------------------------------------------------------------------------------------------------------------------------------------ 222 CAS-A-NW WFPC2 IMAGE WF3 F450W CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 231 CAS-A-NW WFPC2 IMAGE WF3 F675W CR-SPLIT=NO 2 500 S ------------------------------------------------------------------------------------------------------------------------------------ 232 CAS-A-NW WFPC2 IMAGE WF3 F675W CR-SPLIT=NO 2 500 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 251 CAS-A-NW WFPC2 IMAGE WF2 F675W CR-SPLIT=NO 2 500 S ------------------------------------------------------------------------------------------------------------------------------------ 252 CAS-A-NW WFPC2 IMAGE WF2 F675W CR-SPLIT=NO 2 500 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 253 CAS-A-NW WFPC2 IMAGE WF2 F450W CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 254 CAS-A-NW WFPC2 IMAGE WF2 F450W CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 255 CAS-A-NW WFPC2 IMAGE WF2 F850LP CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 256 CAS-A-NW WFPC2 IMAGE WF2 F850LP CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 9238( 3) - 11/20/01 10:59 - [ 6] Visit: 03 Visit Priority: Visit Requirements: ORIENT 44.9D TO 45.1D CVZ 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 ------------------------------------------------------------------------------------------------------------------------------------ 311 CAS-A-SW WFPC2 IMAGE WF2 F850LP CR-SPLIT=NO 2 700 S ------------------------------------------------------------------------------------------------------------------------------------ 312 CAS-A-SW WFPC2 IMAGE WF2 F850LP CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 321 CAS-A-SW WFPC2 IMAGE WF2 F450W CR-SPLIT=NO 2 700 S ------------------------------------------------------------------------------------------------------------------------------------ 322 CAS-A-SW WFPC2 IMAGE WF2 F450W CR-SPLIT=NO 2 700 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 331 CAS-A-SW WFPC2 IMAGE WF2 F675W CR-SPLIT=NO 2 500 S ------------------------------------------------------------------------------------------------------------------------------------ 332 CAS-A-SW WFPC2 IMAGE WF2 F675W CR-SPLIT=NO 2 500 S POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 9238( 3) - 11/20/01 10:59 - [ 7] Summary Form for Proposal 9238 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WF4 WF3 WF2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 44.9D TO 45.1D CVZ POS TARG 0.5, 0.5 POS TARG 12.0, -18.0 POS TARG 12.5, -18.5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F850LP F450W F675W ------------------------------------------------------------------------------------------------------------------------------------ Target Names CAS-A-NE CAS-A-NW CAS-A-SW ------------------------------------------------------------------------------------------------------------------------------------