Cannot find file \System\Volumes\Data\solaris\user1\williamj\hst\work\cycle23\C:\Users\hkito\Documents\projects\telescope_proposals\HST\Cycle29_mid\late_time_spec_draft3.pdf0Assigned ID: 2568
----- Attempting Submission 1 (Tue Sep 28 15:05:17 GMT 2021) -----0----- Attempting Submission 1 (Wed Dec 15 09:43:15 GMT 2021) -----
----- Attempting Submission 2 (Thu Jun 23 10:45:35 GMT 2022) -----A spectroscopic study of the Type Ia supernova near-infrared plateauWe 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 to explosion as well as the evolution of the SN ejecta.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.Drs. Lluis Galbany, Or Graur, Griffin Hosseinzadeh, Andy Howell, Saurabh Jha, Kate Maguire, Curtis McCully, and Adam G. Riess are all expert supernova (SN) observers. Dr. Graur has used HST+WFC3 to lead several experiments similar to the one proposed here, with SN 2012cg (Graur et al. 2016), SN 2015F (Graur et al. 2018a), ASASSN-14lp (Graur et al. 2018b), SN 2014J (Graur 2019), and several SNe Ia in the near-infrared (Graur et al. 2020). Dr. Maguire and Ms. Deckers ar experienced in obtaining and analyzing near-infrared spectra of SNe. Dr. Russell Ryan is an expert in the reduction and analysis of WFC3 grism spectra. Drs. Jha and Riess have a long record of observing SNe with HST. Drs. McCully, Hosseinzadeh, and Howell form the core of the Las Cumbres Observatory's Global Supernova Project, which has provided early-time observations of the SNe in this proposal. Dr. Michael M. Shara is an expert in HST observations of various types of transients. Dr. David R. Zurek is an expert in the processing of HST images. Drs. Robert Fisher, Andrew Fullard, Wolfgang Kerzendorf, Ivo R. Seitenzahl, and Stuart Sim are experts in the theory of SN explosions and nucleosynthesis; Drs. Fisher, Kerzendorf, and Seitenzahl specifically have expertise in the theory of the late-time behavior of SNe Ia. Finally, Dr. Armin Rest is a world leader in the detection and analysis of light echoes. Dr. Or Graur will serve as PI of this program, and Dr. Saurabh Jha will serve as its US administrative Co-I.Stellar Physics and Stellar Types3falsefalsefalsefalsefalsetruefalseSUPPORTEDEXT-STARSUPERNOVA TYPE IANOJ2000J2000EXT-STARSUPERNOVA TYPE IANOJ2000J2000WFC3/IRSpectroscopicNoNoG141WFC3/IRImagingNoNoF160WWFC3/IRSpectroscopicNoNoG141WFC3/IRImagingNoNoF160WPOS-TARGDITHER0.636LINEfalsefalse241.788WFC3-IR-DITHER-LINE1falseThe scheduling data was generated by CASM 30.3.CASM was run in Phase II mode.C:\Users\hkito\AppData\Local\Temp\OPVisit10934423995629339941.xml(Tic-Visit
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