0 Assigned ID: 673 ----- Attempting Submission 1 (Fri Apr 10 18:53:35 GMT 2015) ----- Dither patters and chip have been modified to optimize the program. Pos targ is added to place the object of interest closer to the read out chip and as such minimize effect of CTE loss. FOV has been chosen to maximise area previously unboserved by HST. 1336271839 ----- Attempting Submission 1 (Thu Jul 23 21:15:11 GMT 2015) ----- ----- Attempting Submission 2 (Mon Nov 30 18:32:04 GMT 2015) ----- Possible Stellar Donor or Remnant for the Type Iax SN 2008ha White dwarf (WD) supernovae (SN) play a pivotal role in astrophysics, but are surprisingly poorly understood. We now know that not all exploding WDs are SN Ia. Some are SN Iax: low-energy stellar explosions that are similar to, but physically distinct from, SN Ia. Recent deep HST pre-explosion images reveal a blue source at the position of a SN Iax. This is the first detection of the progenitor system for a WD SN! Our favored interpretation is that this source is the helium star binary companion to the progenitor WD. Observations suggest, and theory predicts, that some SN Iax do not completely disrupt their WD progenitor stars, leaving behind a battered, bruised, and possibly very luminous remnant. In Cycle 20, we imaged the location of a nearby SN Iax, SN 2008ha, 4 years after explosion, and detected a luminous red source, S1, at the position of the SN. S1 could be (1) the companion star, possibly affected by the SN impact, (2) the luminous remnant star, which would be the first time such an object has ever been detected, or (3) a chance coincidence (although unlikely, it is not completely ruled out). A companion or remnant star is predicted to vary on years timescales, while an unrelated star should not vary. Basic assumptions suggest that a companion would brighten and a remnant would fade between our last observations and now. We propose to observe S1 with HST to measure its possible variability and distinguish between the possible scenarios. These measurements will result in deeper understanding of SN Iax, and all WD SN, and possibly reveal the second detected companion star to a thermonuclear SN or a completely new class of object (the remnant). We plan to obtain ACS/WFC images of the site of SN 2008ha in UGC 12682. HST resolution/depth is necessary to investigate the potential companion star or remnant (S1) of SN 2008ha and determine if it varies. Additional HST images will also improve our astrometric uncertainties and provide a more stringent limit on any association between S1 and SN 2008ha. As S1 was most strongly detected in F814W (F814W = 26.3 mag), our best chance to detect variability is to repeat observations in this filter. The energy input from radioactive decay would suggest a change of 1.5-1.9 mag between our previous observation and the various timing windows available for our target (as determined from APT). Therefore, we aim to have a 5 sigma limit of F814W = 28.2 mag, which orbit calculations from APT combined with ETC estimates suggest can be done in 5 HST orbits. A 10-point spiral dither pattern with a 0.2" spacing has been applied to these orbits in order to reduce issues with cosmic rays/hot pixels and to provide a subsampled combined image via astrodrizzle. F435W observations are required in order to detect a possible blue companion star similar to that of SN 2012Z. 3 HST orbits (again combining APT and ETC results) are required in order to investigate this possibility. For this filter we will use a 6-point spiral dither pattern with a 0.2" spacing. This pattern will again be used to create a subsampled drizzled image. Because of its better sensitivity, wide field of view, and correspondence to previous observations, ACS has been chosen over WFC3. To improve our astrometry, we have placed S1 in the South-West corner of the ACS FOV, increasing the FOV to the North-East, where there is currently no HST data. A roll angle between 60-70 degrees has been specified in order to maximize the currently non-covered FOV and provide a significant number of stars for alignment. For alignment purposes and the reduction of geometric distortion correction inaccuracies we request that both visit 1 and visit 2 have the same orient restriction. As the object in question may be variable we also request that visit 2 be taken no later than 7 days after visit 1. A timing requirement between the 14th of November 2015 and the 17th of January 2016 was put in place to optimize the exposure time, window length and roll angle coverage. We would like to look into using POS TARGS rather than using dither pattern containers to improve subsampling and acquire a better dither pattern. During the CS reviews we would like to receive comments on the advantages of POS TARGS verses the spiral dither pattern currently applied. HOT STARS 12 false false false false SUPPORTED STAR SUPERNOVA J2000 J2000 ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F814W POS-TARG DITHER 0.265 LINE 0.187 false false 69.05 4 20.67 ACS-WFC-DITHER-BOX 3 false POS-TARG DITHER 0.15 LINE false false 2 34.13 LINE 5 false Timing link suitability includes constraints ([02 After 01 by at most 7.0 days]) The scheduling data was generated by CASM 23.2. 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