Supernovae (SNe) have a profound effect on galaxies, and have been used recently as precise cosmological probes, resulting in the Nobel-recognized discovery of the accelerating Universe. They are clearly very important events deserving of intense study. Yet, even with over 5900 known SNe, we know relatively little about the stars which give rise to these powerful explosions. The main limitation has been the lack of spatial resolution in pre-SN imaging data. However, since 1999 our team has been at the vanguard of directly identifying SN progenitor stars in HST images. From this exciting line of study, the emerging trend from 7 detections for Type II-Plateau SNe is that their progenitors appear to be relatively low mass (8 to 20 Msun) red supergiants, although more cases are needed. Additionally, we have identified the possibly yellow supergiant progenitors of two likely Type II-Linear SNe. Also, one case indicates that the progenitors of Type II-narrow SNe may be related to luminous blue variables. However, the nature of the progenitors of Type Ib/c SNe, a subset of which are associated with the amazing gamma-ray bursts, remains ambiguous. Furthermore, we remain in the continually embarrassing situation that we still do not yet know which progenitor systems explode as Type Ia SNe, which are currently being used for precision cosmology. In Cycles 16 and 17 we had great success with our approved ToO programs. We therefore propose to build on that success by determining the identities of the progenitors of 4 SNe within, generally, about 20 Mpc, which we expect to occur during Cycle 20, through ToO observations using WFC3/UVIS. We plan for four ToO triggers during Cycle 20. If we detect one or more candidate stellar objects within a 1-sigma positional uncertainty in ACS, WFPC2, or WFC3 pre-supernova archival image(s), we will request a trigger to pinpoint the location of the SN in the pre-SN images and attempt to confirm the progenitor candidate. Our plan is to image with WFC3/UVIS, to provide the highest possible spatial resolution. Our strategy, generally, is to acquire several short-exposure dithered images in V (F555W, 10-s) or I (F814W, 30-s), for the 3 core-collapse visits (which will likely best match with the available archival image data), and in U (F336W, 20-s) or B (F438W, 20-s) for a putative, nearby (<10 Mpc) SN Ia visit, since these SNe will likely be too bright in redder bands, but fade more rapidly in the blue. The initial Phase II observations are meant to be representative of a typical trigger. Each of the four possible ToOs has an initial placeholder position of RA(J2000)=0, Dec(J2000)=0. We will likely request triggers when the SN is still fairly bright, depending on its age at discovery, but limit this, generally, to m >14 mag. We therefore may alter exposure times and bands, depending on the expected brightness of a given SN when it is scheduled and depending on the bands of the pre-SN images available for the SN site in the HST archive. This may also result in changes in the dither strategy for a given visit. The ToOs are not intended to be high-impact, and will be requested to occur after 2 to 3 weeks from discovery, so there should be no disruption of normal scheduling. RESOLVED STELLAR POPULATIONS 0 false false 0.0 0.0 false false false SUPPORTED STAR SUPERNOVA TYPE II J2000 J2000 STAR SUPERNOVA TYPE IB J2000 J2000 STAR SUPERNOVA TYPE IB J2000 J2000 STAR SUPERNOVA TYPE IB J2000 J2000 WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 1 false POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 2 false POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 3 false The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. 1373874186000 100.53204103443318 (Tic-Visit :proposal-id 12888 :visit-id "01" :proposal-version -1 :trans-version "20130502" :date "28-Jun-2013 08:47:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 463440 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12888 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12888 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2563 :al-overhead-at-end 83 :internal-dur-at-end 543 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2997 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. 1373879721000 118.99337873862942 (Tic-Visit :proposal-id 12888 :visit-id "02" :proposal-version -1 :trans-version "20130502" :date "20-Aug-2013 11:24:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 481264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12888 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12888 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2665 :al-overhead-at-end 83 :internal-dur-at-end 562 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3015 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. 1378108778000 100.58923320312618 (Tic-Visit :proposal-id 12888 :visit-id "03" :proposal-version -1 :trans-version "20130502" :date "20-Aug-2013 11:53:53.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 285200 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12888 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12888 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2663 :al-overhead-at-end 83 :internal-dur-at-end 348 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3015 :pcs-gap 0 ) false 1 0 Pending ToO activation. The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12888 :visit-id "04" :proposal-version -1 :trans-version "20130502" :date "30-Sep-2013 11:54:49.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1154992 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12888 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12888 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2671 :al-overhead-at-end 123 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3015 :pcs-gap 0 ) false 1 0