17000( 2) - 23-Jun-2022 13:41:20 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17000 Version: 2 Check-in Time: 23-Jun-2022 13:41:20 STScI Edit Number: 0 Title A spectroscopic study of the Type Ia supernova near-infrared plateau ------------------------------------------------------------------------------------ Type Cycle GO 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Or Graur University of Portsmouth Y CoI: Dr. Kate Maguire University of Dublin, Trinity College N CoI: Dr. Michael Shara American Museum of Natural History N CoI: Dr. David R. Zurek American Museum of Natural History N CoI: Dr. Adam Riess The Johns Hopkins University N CoI: Dr. Armin Rest Space Telescope Science Institute N CoI: Dr. Stuart A. Sim The Queen's University of Belfast N CoI: Dr. Russell E. Ryan Jr. Space Telescope Science Institute N CoI: Dr. Saurabh W. Jha Rutgers the State University of New Jersey N CoI: Dr. Dale Andrew Howell Las Cumbres Observatory Global Telescope N Network CoI: Dr. Griffin Hosseinzadeh University of Arizona N CoI: Dr. Curtis McCully Las Cumbres Observatory Global Telescope N Network CoI: Dr. Lluis Galbany Institute of Space Sciences (CSIC-IEEC) N CoI: Dr. Ivo Rolf Seitenzahl University of New South Wales N CoI: Dr. Wolfgang E Kerzendorf Michigan State University N CoI: Dr. Robert Fisher University of Massachusetts Dartmouth N CoI: Ms. Maxime Deckers University of Dublin, Trinity College N CoI: Dr. Andrew Giles Fullard Michigan State University N ------------------------------------------------------------------------------------ Abstract We ask for 6 WFC3 orbits to obtain G141 grism spectra of two Type Ia supernovae (SNe Ia) in order to ascertain why the newly-discovered near-infrared (NIR) year-long plateau at ~150-500 days comes to an end. SNe Ia have long been used as standard candles to measure extragalactic distances and constrain cosmology, yet the nature of their progenitor stars and the physics behind their explosions remain open questions. The recent discovery of the NIR plateau highlights just how much we still have to learn about the physics of these explosions. In this proposal, we aim to learn why the NIR plateau comes to an end at ~450-500 days past maximum light. The discoverers of the plateau proposed that a change in the dominant ionization state of the SN ejecta, from singly-ionized to neutral iron-group lines, may be the cause. However, this explanation rests on a dubious detection of neutral iron lines in a low signal-to-noise (S/N) grism spectrum of a single SN Ia at 600 days. We will obtain higher S/N spectra of two brighter SNe Ia and optimize the orients of our observations to properly subtract any contamination from the bright host galaxies of our targets. This will allow us to unambiguously detect any [Fe I] lines in our spectra, if they exist. By visiting our targets at additional, earlier epochs along the plateau we will also determine whether such [Fe I] lines exist along the plateau, something that could not be done with previous, ground-based spectra where these lines fell in atmospheric absorption bands. The results of our observations will provide fresh constraints on the chemical composition of the progenitors prior 17000( 2) - 23-Jun-2022 13:41:20 - [ 2] to explosion as well as the evolution of the SN ejecta. ------------------------------------------------------------------------------------ Observations Description ------------------------ In this program, we will obtain WFC3/IR G141 grism spectra of two bright Type Ia supernovae. Each supernova will be visited when it is roughly 300, 450-500, and 600 days beyond maximum light. In each visit, one orbit will be devoted mostly to a G141 observation. The rest will go to an F160W direct image required to reduce the grism data. Four of the orbits will be used in Cycle 29, while two more orbits will be used in Cycle 30 (for the last visit to each supernova). This program relies on an interplay of timing and rotation angle. On one hand, the spectra should be taken at specific phases of the evolution of the superonvae. On the other, to reduce the contamination of galaxy background light, the are specific orent ranges that would be optimal for this program. The timing requests in this proposal have taken both of these aspects into account. Were HST to transition into reduced-gyro operations, we would need to look into the possibility of rescheduling our visits to make the best of the new situation. If notified of this in advance, we will promptly evaluate what changes we would need to make and re-submit our phase II. ------------------------------------------------------------------------------------ 17000( 2) - 23-Jun-2022 13:41:20 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SN2021JAD EXT-STAR, SUPERNOVA RA=05H33M22.1800S, J2000 V = 20 TYPE IA DEC=-21D57'6.50" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 2 SN2021PIT EXT-STAR, SUPERNOVA RA=03H44M30.1700S, J2000 V = 19 TYPE IA DEC=-44D37'57.10" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 17000( 2) - 23-Jun-2022 13:41:20 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.636 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 41.788 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17000( 2) - 23-Jun-2022 13:41:20 - [ 5] Visit: 05 (SN2021jad - decline) Visit Requirements: ORIENT 71D TO 75 D; BETWEEN 24-JAN-2023:00:00:00 AND 31-JAN-2023:00:00:00 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 SN2021JAD WFC3/IR MULTIAC GRISM1024 F160W NSAMP=8, SAMP-SEQ=SPARS25 1 DEF CUM (177.936 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN2021JAD WFC3/IR MULTIAC GRISM1024 G141 NSAMP=12, SAMP-SEQ=SPARS100 1 DEF PATTERN 1 2 CUM (2205.872 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN2021JAD WFC3/IR MULTIAC GRISM1024 F160W NSAMP=8, SAMP-SEQ=SPARS25 1 DEF POS TARG 0.474, 0.424 CUM (177.936 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN2021JAD 1 WFC3/IR MULTIAC GRISM102 F160W none none none none 1 N/A CUM 4 SN2021JAD 2 WFC3/IR MULTIAC GRISM102 G141 1 none none none 1 N/A CUM 4 SN2021JAD 2 WFC3/IR MULTIAC GRISM102 G141 2 none none none 1 N/A CUM 4 SN2021JAD 3 WFC3/IR MULTIAC GRISM102 F160W none none none none 1 N/A CUM 4 17000( 2) - 23-Jun-2022 13:41:20 - [ 6] Visit: 06 (SN2021pit - decline) Visit Requirements: ORIENT 84D TO 88 D; BETWEEN 12-FEB-2023:00:00:00 AND 21-FEB-2023:00:00:00 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 SN2021PIT WFC3/IR MULTIAC GRISM1024 F160W NSAMP=10, SAMP-SEQ=SPARS25 1 DEF CUM (227.937 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SN2021PIT WFC3/IR MULTIAC GRISM1024 G141 NSAMP=12, SAMP-SEQ=SPARS100 1 DEF PATTERN 1 2 CUM (2205.872 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 SN2021PIT WFC3/IR MULTIAC GRISM1024 F160W NSAMP=9, SAMP-SEQ=SPARS25 1 DEF POS TARG 0.474, 0.424 CUM (202.936 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 | ------------------------------------------------------------------------------------------------------------------------------------ SN2021PIT 1 WFC3/IR MULTIAC GRISM102 F160W none none none none 1 N/A CUM 4 SN2021PIT 2 WFC3/IR MULTIAC GRISM102 G141 1 none none none 1 N/A CUM 4 SN2021PIT 2 WFC3/IR MULTIAC GRISM102 G141 2 none none none 1 N/A CUM 4 SN2021PIT 3 WFC3/IR MULTIAC GRISM102 F160W none none none none 1 N/A CUM 4 17000( 2) - 23-Jun-2022 13:41:20 - [ 7] Summary Form for Proposal 17000 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures GRISM1024 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=10, NSAMP=12, NSAMP=8, NSAMP=9, SAMP-SEQ=SPARS100, SAMP-SEQ=SPARS25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 12-FEB-2023:00:00:00 AND 21-FEB-2023:00:00:00, BETWEEN 24-JAN-2023:00:00:00 AND 31-JAN-2023:00:00:00, ORIENT 71D TO 75 D, ORIENT 84D TO 88 D, PATTERN 1 2, POS TARG 0.474, 0.424 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W, G141 ------------------------------------------------------------------------------------------------------------------------------------ Target Names SN2021JAD, SN2021PIT ------------------------------------------------------------------------------------------------------------------------------------