7406( 6) - 04/05/99 11:42 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7406 Version: 6 Check-in Date: 10-Aug-1998 15:00:05 1.Proposal Title: High-Resolution Imaging of Ejecta Knots in the Cassiopeia A SNR ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Robert Fesen Dartmouth College CoI: Alan Hurford Dartmouth College N CoI: David Matonick Dartmouth College N ------------------------------------------------------------------------------------ 5. Abstract The Cassiopeia A supernova remnant (SN ~eq1680 AD) exhibits optical emissions strong in O, S, Ar, and N lines indicating metal-rich ejecta and a high mass progenitor (>= 15 M_\odot). The remnant's highest velocity ejecta (V = 7, 000 -- 13, 000 km s^-1) consist of small, unresolved knots outside the main emission shell. These include fast-moving, nitrogen-rich knots and a well defined ``jet'' of O + S rich ejecta. Because many of these are moving nearly in the plane of the sky, they show relatively low radial velocities permitting the use of HST's narrow passband filters. This makes possible high-resolution images to investigate the spatial structure of a young SNR's high-velocity ejecta. We propose taking WFPC2 images of several of Cas A's high-velocity knots including ones from both the progenitor's outer (N-rich) and core (O+S rich) layers. Our goal is to better understand the structure and evolution of ejecta in young SNRs. These images should reveal ejecta structures down to spatial scales of 10^16 cm as well as any shock ionization features. Of particular interest is the nature of several knots which show elongated shapes or faint, clumpy trailing emission which could be evidence of mass ablation due to the interaction with ambient circumstellar/interstellar medium. ------------------------------------------------------------------------------------ 7406( 6) - 04/05/99 11:42 - [ 2] Observations Description ------------------------ Cas A lies well inside the CVZ and the orbit estimates below assume CVZ observations. Since the NW FMFs and the NE jet are separated by several arc minutes, they have been treated as two separate visits. In Visit 1, we will take four 2000 s exposures at the tip of the jet (see Fig. 2) in both S II and S III (F673N and F953N). Just one WFC CCD can cover more than a half dozen bright knots near the jet's tip and all those marked in Figure 2, but we will try positioning the WFPC2 so as to pick up other surrounding knots. Jet knots 2, 6, 9, 27, 73, and 74 have radial velocities of -160, +370, +400, -510, +210, and -420 respectively, meaning their S II and S III emissions will fall inside the filters' FWHMs (of course, their transverse velocities are >= 9000 km s^- 1). Typical S II LambdaLambda6716, 6731 fluxes for these knots (e.g. No. 73) is 1 - 2 * 10^-15 erg s^-1 cm^-2. Using the formula in the WFPC2 Handbook and the QT for the F673N Filter of 0.111 (Table 6.1), we estimate a target count rate of 2.9 cts/s integrated over the whole source. This would produce a S/N of 6 if spread over 1 sq arcsec in a single 2000 sec exposure. Due to cosmic rays and hot pixels, we will take two sets of two dithered frames. The same 2000 s exposure time will be used for the S III images. While the knots' S III emissions have not been measured, other Cas A FMK knots typically show S II/S II Lambda9531 around 10 (Hurford & Fesen 1996), quite sufficient to yield good knot detections. In addition, a set of two 100 s R-band images (F675W) will also be taken in order to permit star subtraction from the final S II and S III images. Calculating 7 min for GS ACQ and 2 min for filter changes, we estimate a total time requirement of 270 min or just under 3 CVZ orbits (checked with RPS2 software). In Visit 2, we will image the remnant's northwestern rim FMFs (see Fig. 3) using the F658N filter to detect N II Lambda6583. From published spectra, these knots have radial velocities ranging between +500 and +1100 km s^-1. These velocities will shift the knots' Lambda6583 emission 11 -- 24 Angstrom \ but still well within the F658N filter's peak transmission bandwidth (see WFPC Handbook, p217). The N II flux of knot 10 (Fig. 3) is around 1 * 10^- 15. Using 2000 s exposures, this flux yields similar count rates and S/N as for the jet FMKs described above. We will also take two sets of two exposures to remove cosmic rays and hot pixels. And again, a set of two 100 s R-band images (F675W) will also be taken in order to remove the stars from the final combined N II image. The total time for these observations is estimated to be 2 CVZ orbits. Real Time Justification ----------------------- None. None. Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 7406( 6) - 04/05/99 11:42 - [ 3] Data Distribution Paper Products: Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7406( 6) - 04/05/99 11:42 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CAS-A-JET ISM RA=23H 23M 53.5S +/-0.50S, 2000 V = 25.0+/-2.0 DEC=58D 50' 38.0" +/-3.0"ON SPECIFICATION FORMAT IS Comments: E(B-V)=1.60 +/-0.50 2 CAS-A-NW-A ISM RA=23H 23M 11.8S +/-0.50S, 2000 V = 25.0+/-2.0 DEC=58D 50' 59.0" +/-5.0" Comments: E(B-V)=1.60 +/-0.50 3 CAS-A-NW-B ISM RA=23H 23M 9.0S +/-0.50S, 2000 V = 25.0+/-2.0 DEC=58D 50' 25.0" +/-5.0" Comments: E(B-V)=1.60 +/-0.50 7406( 6) - 04/05/99 11:42 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 250D TO 260D 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 ------------------------------------------------------------------------------------------------------------------------------------ 101 CAS-A-JET WFPC2 IMAGE PC1 F673N CR-SPLIT=NO 3 1000 S ------------------------------------------------------------------------------------------------------------------------------------ 111 CAS-A-JET WFPC2 IMAGE WF3-FIX F673N CR-SPLIT=NO 3 1000 S ------------------------------------------------------------------------------------------------------------------------------------ 112 CAS-A-JET WFPC2 IMAGE WF3-FIX F673N CR-SPLIT=NO 3 1000 S POS TARG 0.50, 0.50 ------------------------------------------------------------------------------------------------------------------------------------ 121 CAS-A-JET WFPC2 IMAGE WF3-FIX F953N CR-SPLIT=NO 2 1000 S ------------------------------------------------------------------------------------------------------------------------------------ 131 CAS-A-JET WFPC2 IMAGE WF3-FIX F675W CR-SPLIT=NO 2 600 S ------------------------------------------------------------------------------------------------------------------------------------ 132 CAS-A-JET WFPC2 IMAGE WF3-FIX F675W CR-SPLIT=NO 2 600 S POS TARG 0.50, 0.50 ------------------------------------------------------------------------------------------------------------------------------------ 7406( 6) - 04/05/99 11:42 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 250D TO 260D 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 ------------------------------------------------------------------------------------------------------------------------------------ 201 CAS-A-NW-A WFPC2 IMAGE WF2-FIX F658N CR-SPLIT=NO 2 900 S ------------------------------------------------------------------------------------------------------------------------------------ 202 CAS-A-NW-A WFPC2 IMAGE WF2-FIX F658N CR-SPLIT=NO 2 900 S POS TARG 0.50, 0.50 ------------------------------------------------------------------------------------------------------------------------------------ 211 CAS-A-NW-A WFPC2 IMAGE WF2-FIX F675W CR-SPLIT=NO 3 500 S ------------------------------------------------------------------------------------------------------------------------------------ 221 CAS-A-NW-B WFPC2 IMAGE WF3-FIX F658N CR-SPLIT=NO 2 900 S ------------------------------------------------------------------------------------------------------------------------------------ 231 CAS-A-NW-B WFPC2 IMAGE WF3-FIX F675W CR-SPLIT=NO 2 700 S ------------------------------------------------------------------------------------------------------------------------------------ 7406( 6) - 04/05/99 11:42 - [ 7] Summary Form for Proposal 7406 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 WF3-FIX WF2-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 250D TO 260D CVZ POS TARG 0.50, 0.50 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F673N F953N F675W F658N ------------------------------------------------------------------------------------------------------------------------------------ Target Names CAS-A-JET CAS-A-NW-A CAS-A-NW-B ------------------------------------------------------------------------------------------------------------------------------------