The young Galactic remnant Cas A provides perhaps our clearest look at the explosion of a high mass, core-collapse supernova. Two opposing streams or "jets" of high-velocity debris extending outward along its northeastern and southwestern limbs have expansion velocities more than twice that of the remnant's bright main shell. Interpretation of these NE-SW jets has been controversial. However, SN debris located at the farthest tip of the NE jet has been found to be S,Ar,Ca-rich but O-poor suggesting an origin deep inside the progenitor possibly due to an overturning of layers as predicted in some aspherical explosion models. Recent WFC3/IR images taken of the NE jet revealed a far richer debris field than previously realized, with ejecta knots found out to the very edge of the camera's FOV. This leaves uncertain the jet's true maximum velocity and total kinetic energy. The lack of a complete census of the jet's structure and kinematics critically limits understanding on the nature of these puzzling kinematic and chemically distinct features. We propose to obtain WFC3/IR images of the remnant's NE jet out beyond existing HST images to complete a survey of its S-rich ejecta and explore the presence of even higher-velocity, Fe-rich ejecta predicted by supernova models. Detection of very high-velocity Fe-rich material in the jet would represent a breakthrough in our understanding of Cas A and core-collapse supernovae in general. The aim of this project is to obtain WFC3/IR images of two regions near the young supernova remnant, Cassiopeia A, in two filters: the F098M filter to detect [S III] 9069, 9531 and [S II] 10250-10,400 emission lines, while the F160N filter images will detect [Fe II] 1.64 emission from Fe-rich ejecta. Two adjacent and slightly overlapping fields will be imaged in both filters. We will employ a four point dither pattern for these images. The features we are trying to detect are small (0.5" or less) emission blobs using the F098M filter, and eitehr small ejecta knots/blobs of patches of diffuse emission in the F164N images. These images will serve as the first set of images to be combined with a nearly identical set of images taken in Cycle 25. Stellar Physics 6 false false false false false false SUPPORTED ISM EJECTA EMISSION LINE NEBULA YES J2000 J2000 ISM EJECTA EMISSION LINE NEBULA YES J2000 J2000 WFC3/IR Imaging No No F098M WFC3/IR Imaging No No F164N WFC3/IR Imaging No No F098M WFC3/IR Imaging No No F164N POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false 1499802966899 /private/var/folders/12/j8rygdwn2yj3__vvrb1vl5600000gr/T/OPVisit4239249674893621934.xml Timing link suitability includes constraints ([Group (01 02) Within 60.0 days]) The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15361 :visit-id "01" :proposal-version -1 :trans-version "20170613" :date "11-Jul-2017 15:56:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 2089056 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15361 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15361 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3040 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3449 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15361 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3024 :al-overhead-at-end 0 :internal-dur-at-end 443 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3449 :pcs-gap 0 ) true 2 0 1499802968010 Timing link suitability includes constraints ([Group (01 02) Within 60.0 days]) The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. /private/var/folders/12/j8rygdwn2yj3__vvrb1vl5600000gr/T/OPVisit2821241543273180999.xml (Tic-Visit :proposal-id 15361 :visit-id "02" :proposal-version -1 :trans-version "20170613" :date "11-Jul-2017 15:56:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 2089056 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15361 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15361 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3040 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3449 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15361 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3024 :al-overhead-at-end 0 :internal-dur-at-end 443 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3449 :pcs-gap 0 ) true 2 0