15871( 2) - 15-Jul-2019 17:11:41 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15871 Version: 2 Check-in Time: 15-Jul-2019 17:11:41 STScI Edit Number: 0 Title UV properties of the first known surviving companions of Type Ia supernovae ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Ken Shen University of California - Berkeley Y CoI: Prof. Boris T. Gaensicke The University of Warwick N CoI: Dr. Odette Fabiola Toloza The University of Warwick N Castillo CoI: Prof. Detlev G. Koester Universitat Kiel N CoI: Dr. Roberto Raddi Universitat Erlangen-Nurnberg N CoI: Prof. Ulrich Heber Universitat Erlangen-Nurnberg N CoI: Dr. JJ Hermes Boston University N CoI: Dr. Mark Hollands The University of Warwick N ------------------------------------------------------------------------------------ Abstract The study of Type Ia supernovae (SNe Ia) has undergone a revolution within the last year following the discovery of three extremely unique stars in Gaia's Data Release 2. Their hypervelocities (1000-2500 km/s), atmospheric compositions (predominantly C/O with contributions from Mg, Si, S, and Fe-group elements), inflated radii, and the kinematic association of one of the stars with a known SN remnant are all strong evidence that they are the former white dwarf (WD) secondaries in merging double WD systems in which the primary WD exploded as a SN Ia. While analysis of these paradigm-shifting stars in the optical is ongoing, a complete understanding is currently limited by degeneracies in the effective temperatures, surface gravities, and metal abundances. Near-ultraviolet spectroscopy is crucial to break these degeneracies. Our proposed ultraviolet observations of the brightest of these stars will allow for the derivation of its radius, mass, and bulk atmospheric composition, enabling constraints on the precise nucleosynthetic yields of the nearby explosion that polluted the surviving companion's surface as well as characterization of its current stellar structure. This will enable modeling of the future evolution of these stars, which will facilitate searches for more SN Ia survivors that will answer the decades-old mystery of the nature of SN Ia progenitors. ------------------------------------------------------------------------------------ Observations Description ------------------------ The primary goal of this proposal is to obtain the near-ultraviolet spectral energy distribution of this star. We choose the STIS G230L grating and the widest slit, 52x2, to ensure that we optimise the throughput and minimise possible slit flux losses. The observation sequence is straight-foward: two identical three-orbit visits, composed of an acquisition with the optical CCD and the FP28x50LP broadband filter, followed by G230L spectroscopy. ------------------------------------------------------------------------------------ 15871( 2) - 15-Jul-2019 17:11:41 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 D6-2 STAR, SDB RA=21H38M26.9972S +/- 0.0977", J2000 V = 17.0 +/- 0.1 GALEX NUV=19.57 DEC=+25D22'25.36" +/- 0.0757" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 0.0072592890602048345 0.240352 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 15871( 2) - 15-Jul-2019 17:11:41 - [ 3] Visit: 01 (STIS spectroscopy of D6-2) Visit Requirements: 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 D6-2 STIS/CCD ACQ F28X50LP MIRROR 1 2 S (2 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 D6-2 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=300 1 2177 S -MAMA G (2177 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 D6-2 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=300 1 2835 S -MAMA G (2835 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 D6-2 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=300 1 2810 S -MAMA G (2810 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 | ------------------------------------------------------------------------------------------------------------------------------------ D6-2 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A D6-2 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G D6-2 3 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 2 N/A -MAMA G D6-2 4 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 3 N/A -MAMA G 15871( 2) - 15-Jul-2019 17:11:41 - [ 4] Visit: 02 (STIS spectroscopy of D6-2) Visit Requirements: 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 D6-2 STIS/CCD ACQ F28X50LP MIRROR 1 2 S (2 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 D6-2 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=300 1 2177 S -MAMA G (2177 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 D6-2 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=300 1 2835 S -MAMA G (2835 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 D6-2 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=300 1 2810 S -MAMA G (2810 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 | ------------------------------------------------------------------------------------------------------------------------------------ D6-2 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A D6-2 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G D6-2 3 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 2 N/A -MAMA G D6-2 4 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 3 N/A -MAMA G 15871( 2) - 15-Jul-2019 17:11:41 - [ 5] Summary Form for Proposal 15871 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=300 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names D6-2 ------------------------------------------------------------------------------------------------------------------------------------