Updated phase 2 for second-epoch observations in August 2009 with ACS (Visit 02) and WFC3/IR (Visit 04). We have applied our one "banked" orbit to Visit 02. The changes were based on our first-epoch measurements of the supernova, which has faded faster than expected. ----- Attempting Submission 4 (Tue Jun 23 17:08:20 GMT 2009) ----- Errors refer only to Visits 01 and 03, which have already been completed. Observing the IR Catastrophe in a Deflagration Type Ia Supernova Our lack of understanding of Type Ia supernova (SN Ia) explosions limits our confidence in their use for cosmology. While there is broad agreement that these objects represent the explosions of white dwarfs, the details of the explosion mechanism are not well-understood. Recently, we have identified an internally homogeneous subclass of SNe Ia whose photometric and spectroscopic peculiarities make them quite distinct from normal SNe Ia. Models suggest we may be seeing the result of an explosion with a subsonic burning front, called a deflagration. We propose to test SN Ia models by obtaining late-time photometry for SN 2008A, a recent, nearby example of this subclass, using ACS and WFC3 on HST. We will accurately measure the late-time photometric decline rate and spectral energy distribution (SED). These observations will allow us to test whether the ejecta contain the large amount of oxygen predicted by certain models. We also aim to detect major evolution of the SED expected due to the "IR catastrophe," a change in the dominant cooling mechanism in the ejecta, as generically predicted by models but only hinted at by current observations.
We aim to constrain the SED of SN 2008A with HST observations at two epochs as the supernova fades: February-March 2009 (400 days after SN maximum light), and June-August 2009 (550 days after maximum). Using optical and near-infrared data, we will measure the SN decline rate and look for color signatures of the "infrared catastrophe" predicted by models. The timing of the two epochs corresponds to the available observability windows for SN 2008A in cycle 17. **REVISED** (current version June 23, 2009) Because of the time-sensitive nature of these observations and the delay in SM4, we have revised the proposal so that our first epoch observations use WFPC2 instead of ACS and WFC3/IR. Thus they can still be scheduled in early 2009; we have opened the observing window from 2009-Jan-15 to 2009-Mar-31 to facilitate two-gryo mode visibility. Because NICMOS will not be available for the first epoch data, we have switched visit03 to WFPC2. Our second-epoch observations (August 2009) have been revised based on the first-epoch data in which we found the SN to be about 1 magnitude fainter than the nominal prediction. We have updated visits 02 and 04 using the new information. We have structured the observations in 4 visits: In the first optical epoch we will observe with WFPC2 in four filters: F555W, F622W, F791W, and F850LP; corresponding to ground-based Vriz. Based on extrapolations of the current data and inferences from other SN 2002cx-like SNe Ia (including our recent cycle 16 experience with SN 2005hk), we anticipate SN 2008A will have V = 23.5, r = 22.5, i = 22.0, and z = 22.0 mag in the first epoch, with an uncertainty of about 1 mag. To meaningfully constrain models, we must achieve S/N >= 10 in all bands, even in the pessimistic case (1 mag below the prediction). The WFPC2 exposure time calculator indicates this can be done comfortably in two orbits, and we can fill the orbits with exposures of 1000, 800, 900, and 1200 seconds in F555W, F622W, F791W, and F850LP, respectively. We will employ the recommended two-point dither to remove cosmic rays and hot pixels; these have been input using POS TARG offsets to minimize telescope motions. We will put the SN on the PC chip, offset towards the readout amplifier to minimize CTE effects. [COMPLETED] In the first epoch (but a separate visit, visit 03 which was formerly NICMOS) we will also add 350 seconds of F850LP exposure to increase the sensitivity, as well as 1500 seconds of dithered F439W exposure to increase the wavelength range of the SED. [COMPLETED] In the second optical epoch (VISIT 02), we will observe with ACS/WFC in three filters: F555W, F625W, and F775W, and we anticipate SN 2008A will have V = 26.5, r = 26.4, and i = 25.3 at that time, with an uncertainty of 0.5 mag. We will fill four orbits, with total exposures of 3750, 3530, and 2484 seconds in F555W, F625W, and F775W, respectively, with box-dithered observations. In this epoch, the ORIENT restrictions (which overlap entirely the available roll ranges) lead us to use the WFC1 aperture to avoid a nearby bright star (HD 9983, V=7.6, about 2 arcmin to the southwest). In the infrared (VISIT 04), we expect J = 25.0 +/- 1 mag for SN 2008A, and require three orbits using WFC3/IR. We use a four-point box dither in each orbit, with the boxes offset slightly from orbit to orbit, near the standard IR aperture. In orbits 2 and 3 we use a standard dither pattern with SPARS50, NSAMP=15 readout. In the first orbit we use specific POS TARG offsets so that we can have two NSAMP=14 and two NSAMP=15 exposures to optimally fill the shorter available exposure time. This yields a total exposure of 8336 seconds. The supernova will be too faint for our originally planned F160W observations. HOT STARS 12 false 0.0 0.0 false false false false false SUPPORTED EXT-STAR SUPERNOVA TYPE IA fading J2000 01 38 17.3800 +35 22 13.70 J2000 ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F625W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F850LP ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F625W ACS/WFC Imaging No No F775W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.265 LINE 0.187 false false 69.05 4 20.67 ACS-WFC-DITHER-BOX 1 false POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 2 false The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /Users/saurabh/proposals/hst.cycle17.sn08A/apt-addorbit/OP-cache/addorbit-v01.xml 1235013710000 56.628366531990906 (Tic-Visit :proposal-id 11590 :visit-id "01" :proposal-version -1 :trans-version "20090130" :date "23-Jun-2009 12:32:20.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 358528 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11590 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11590 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2940 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11590 :visit-id "01" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2940 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /Users/saurabh/proposals/hst.cycle17.sn08A/apt-addorbit/OP-cache/addorbit-v02.xml ORIENT range avoids bright star to the southwest (Tic-Visit :proposal-id 11590 :visit-id "02" :proposal-version -1 :trans-version "20090130" :date "23-Jun-2009 12:31:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 4547584 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11590 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11590 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2974 :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 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11590 :visit-id "02" :orbit-number 2 :pcs-time 195 :si-vis-utilization 3113 :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 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11590 :visit-id "02" :orbit-number 3 :pcs-time 195 :si-vis-utilization 3112 :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 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11590 :visit-id "02" :orbit-number 4 :pcs-time 195 :si-vis-utilization 3114 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) true 4 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /Users/saurabh/proposals/hst.cycle17.sn08A/apt-addorbit/OP-cache/addorbit-v03.xml 1235163336000 55.8114067944189 (Tic-Visit :proposal-id 11590 :visit-id "03" :proposal-version -1 :trans-version "20090130" :date "23-Jun-2009 12:32:21.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11590 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11590 :visit-id "03" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2940 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /Users/saurabh/proposals/hst.cycle17.sn08A/apt-addorbit/OP-cache/addorbit-v04.xml (Tic-Visit :proposal-id 11590 :visit-id "04" :proposal-version -1 :trans-version "20090130" :date "23-Jun-2009 11:37:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 3307696 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11590 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11590 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2940 :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 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11590 :visit-id "04" :orbit-number 2 :pcs-time 195 :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 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11590 :visit-id "04" :orbit-number 3 :pcs-time 195 :si-vis-utilization 3040 :al-overhead-at-end 0 :internal-dur-at-end 516 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) true 3 0