14244( 4) - 30-Nov-2015 18:42:07 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14244 Version: 4 Check-in Time: 30-Nov-2015 18:42:07 STScI Edit Number: 1 Title Possible Stellar Donor or Remnant for the Type Iax SN 2008ha ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Ryan Foley University of Illinois at Urbana - Y Champaign CoI: Prof. Lars Bildsten University of California - Santa Barbara N CoI: Dr. Wen-fai Fong University of Arizona N CoI: Dr. Rebekah Hounsell University of Illinois at Urbana - Y Champaign CoI: Dr. Saurabh W. Jha Rutgers the State University of New Jersey N CoI: Dr. Dan Kasen Lawrence Berkeley National Laboratory N CoI: Dr. Curtis McCully Las Cumbres Observatory Global Telescope N Network CoI: Dr. Gautham Narayan National Optical Astronomy Observatory, N AURA CoI: Dr. Armin Rest Space Telescope Science Institute N CoI: Dr. Maximillian Stritzinger Aarhus University N ------------------------------------------------------------------------------------ Abstract 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). 14244( 4) - 30-Nov-2015 18:42:07 - [ 2] ------------------------------------------------------------------------------------ Observations Description ------------------------ 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. 14244( 4) - 30-Nov-2015 18:42:07 - [ 3] ------------------------------------------------------------------------------------ 14244( 4) - 30-Nov-2015 18:42:07 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SN-2008HA STAR, SUPERNOVA RA=23H34M52.6900S +/- 0.1", J2000 V = 27 DEC=+18D13'35.40" +/- 0.1" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 14244( 4) - 30-Nov-2015 18:42:07 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.265 Line_Spacing 0.187 Coordinate_Frame POS-TARG Pattern_Orient 20.67 Angle_Between_Sides 69.05 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 5 Primary_Pattern Secondary_Pattern Pattern_Type LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.15 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 34.13 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 14244( 4) - 30-Nov-2015 18:42:07 - [ 6] Visit: 01 Visit Requirements: SCHED 30%; ORIENT 60D TO 70 D; BETWEEN 14-NOV-2015:00:00:00 AND 17-JAN-2016:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SN-2008HA ACS/WFC ACCUM WFC2 F435W 1 1250 S POS TARG 60, -15; (5202 S) PATTERN 3 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 SN-2008HA ACS/WFC ACCUM WFC2 F435W 1 1200 S POS TARG 60.1125, see below -14.8875; PATTERN 5 2 (2702 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SN-2008HA 1 ACS/WFC ACCUM WFC2 F435W 1 none none none 1 N/A SN-2008HA 1 ACS/WFC ACCUM WFC2 F435W 2 none none none 1 N/A SN-2008HA 1 ACS/WFC ACCUM WFC2 F435W 3 none none none 2 1351.0 S SN-2008HA 1 ACS/WFC ACCUM WFC2 F435W 4 none none none 2 1351.0 S SN-2008HA 2 ACS/WFC ACCUM WFC2 F435W 1 none none none 3 1351.0 S SN-2008HA 2 ACS/WFC ACCUM WFC2 F435W 2 none none none 3 1351.0 S 14244( 4) - 30-Nov-2015 18:42:07 - [ 7] Visit: 02 Visit Requirements: SCHED 30%; SAME ORIENT AS 01; AFTER 01 BY 0 D TO 7 D; BETWEEN 14-NOV-2015:00:00:00 AND 17-JAN-2016:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SN-2008HA ACS/WFC ACCUM WFC2 F814W 1 1250 S POS TARG 60, -15; (5202 S) PATTERN 3 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 SN-2008HA ACS/WFC ACCUM WFC2 F814W 1 1200 S POS TARG 59.8875, see below -15.1125; PATTERN 3 2 (5404 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN-2008HA ACS/WFC ACCUM WFC2 F814W 1 1200 S POS TARG 60.1125, see below -14.8875; PATTERN 5 3 (2702 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SN-2008HA 1 ACS/WFC ACCUM WFC2 F814W 1 none none none 1 N/A SN-2008HA 1 ACS/WFC ACCUM WFC2 F814W 2 none none none 1 N/A SN-2008HA 1 ACS/WFC ACCUM WFC2 F814W 3 none none none 2 1351.0 S SN-2008HA 1 ACS/WFC ACCUM WFC2 F814W 4 none none none 2 1351.0 S SN-2008HA 2 ACS/WFC ACCUM WFC2 F814W 1 none none none 3 1351.0 S SN-2008HA 2 ACS/WFC ACCUM WFC2 F814W 2 none none none 3 1351.0 S SN-2008HA 2 ACS/WFC ACCUM WFC2 F814W 3 none none none 4 1351.0 S SN-2008HA 2 ACS/WFC ACCUM WFC2 F814W 4 none none none 4 1351.0 S SN-2008HA 3 ACS/WFC ACCUM WFC2 F814W 1 none none none 5 1351.0 S SN-2008HA 3 ACS/WFC ACCUM WFC2 F814W 2 none none none 5 1351.0 S 14244( 4) - 30-Nov-2015 18:42:07 - [ 8] Summary Form for Proposal 14244 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 0 D TO 7 D, BETWEEN 14-NOV-2015:00:00:00 AND 17-JAN-2016:00:00:00, ORIENT 60D TO 70 D, PATTERN 3 1, PATTERN 3 2, PATTERN 5 2, PATTERN 5 3, POS TARG 59.8875, -15.1125, POS TARG 60, -15, POS TARG 60.1125, -14.8875, SAME ORIENT AS 01, SCHED 30% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F435W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN-2008HA ------------------------------------------------------------------------------------------------------------------------------------