15918( 3) - 17-Apr-2020 15:17:09 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15918 Version: 3 Check-in Time: 17-Apr-2020 15:17:09 STScI Edit Number: 1 Title Accurate physical parameters of an orphan runaway white dwarf ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Roberto Raddi Universitat Politecnica de Catalunya Y CoI: Dr. Mark Hollands The University of Warwick Y CoI: Prof. Detlev G. Koester Universitat Kiel N CoI: Prof. Boris T. Gaensicke The University of Warwick N CoI: Dr. Odette Fabiola Toloza The University of Warwick N Castillo CoI: Dr. Ken Shen University of California - Berkeley N CoI: Prof. Ulrich Heber Universitat Erlangen-Nurnberg N CoI: Dr. JJ Hermes Boston University N ------------------------------------------------------------------------------------ Abstract Recent discoveries have been revolutionising the field of thermonuclear supernovae with the identification of a new family of remarkable stars that, like their prototype LP 40-365, are suggested to be the former accreting white dwarfs that likely survived to peculiar (possibly Type Iax) supernova explosions. Their element abundance pattern shows ONeMg-dominated atmospheres, presenting large traces of partial Si-burning, iron-peak elements, which are heavily produced in near Chandrasekhar-mass thermonuclear explosions. Thanks to the accurate parallaxes of the Second Data Release of Gaia, these stars are confirmed as inflated low-mass white dwarfs that have been ejected with velocities in the range of 600 km/s. The observational evidence collected so far strongly suggests these stars were the former white dwarf accretors in single-degenerate binaries, which were partly burned by the explosions that unbound the binaries they belonged to. Near- and far-ultraviolet spectroscopy is crucial to precisely measure key properties of these stars, as this wavelength range enables to accurately measure their effective temperature leading to improved determinations of their atmospheric bulk composition and, in combination with Gaia parallaxes, their radii and masses. The proposed target is the hottest and the brightest star of this family, enabling a favorable perspective on the likely earliest phases of their formation. Hence, the HST observations will allow us to gain deeper insight in the evolutionary status and formation mechanisms of these stars via comparison with theoretical models. ------------------------------------------------------------------------------------ Observations Description ------------------------ The primary goal of this proposal is to obtain the far- and near-ultraviolet spectral energy distribution of this star. We choose the STIS G140L/G230L gratings and the widest slit, 52x2, to ensure that we optimise the throughput and minimise possible slit flux losses. The observation sequence is straight-foward: acquisition with the optical CCD and the FP28x50LP broadband filter, one orbit of STIS/G230L spectroscopy, and two orbits of STIS/G140L spectroscopy. 15918( 3) - 17-Apr-2020 15:17:09 - [ 2] ------------------------------------------------------------------------------------ 15918( 3) - 17-Apr-2020 15:17:09 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 J1825-3757 STAR, SDB RA=18H25M22.1500S, J2000 V = -48 V = 13.270 GALEX NUV = 14.6 DEC=-37D57'26.10" 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 -0.00317915329088156 -0.143 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 15918( 3) - 17-Apr-2020 15:17:09 - [ 4] Visit: 01 (STIS spectroscopy of J1825-3757) 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 J1825-3757 STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S (0.5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 J1825-3757 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=200 1 2218 S -MAMA G (2218 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J1825-3757 STIS/FUV TIME-TA 52X2 G140L 1425 BUFFER-TIME=600 1 2830 S -MAMA G (2830 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J1825-3757 STIS/FUV TIME-TA 52X2 G140L 1425 BUFFER-TIME=600 1 2830 S -MAMA G (2830 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 | ------------------------------------------------------------------------------------------------------------------------------------ J1825-3757 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A J1825-3757 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G J1825-3757 3 STIS/FUV TIME-TA 52X2 G140L 1425 none none none none 2 N/A -MAMA G J1825-3757 4 STIS/FUV TIME-TA 52X2 G140L 1425 none none none none 3 N/A -MAMA G 15918( 3) - 17-Apr-2020 15:17:09 - [ 5] Visit: 02 (STIS spectroscopy of J1825-3757) 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 J1825-3757 STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S (0.5 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 J1825-3757 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=200 1 2218 S -MAMA G (2218 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J1825-3757 STIS/FUV TIME-TA 52X2 G140L 1425 BUFFER-TIME=600 1 2830 S -MAMA G (2830 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J1825-3757 STIS/FUV TIME-TA 52X2 G140L 1425 BUFFER-TIME=600 1 2830 S -MAMA G (2830 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 | ------------------------------------------------------------------------------------------------------------------------------------ J1825-3757 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A J1825-3757 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G J1825-3757 3 STIS/FUV TIME-TA 52X2 G140L 1425 none none none none 2 N/A -MAMA G J1825-3757 4 STIS/FUV TIME-TA 52X2 G140L 1425 none none none none 3 N/A -MAMA G 15918( 3) - 17-Apr-2020 15:17:09 - [ 6] Summary Form for Proposal 15918 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=200, BUFFER-TIME=600 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names J1825-3757 ------------------------------------------------------------------------------------------------------------------------------------