15431( 2) - 21-Nov-2017 13:55:21 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15431 Version: 2 Check-in Time: 21-Nov-2017 13:55:21 STScI Edit Number: 0 Title GD492: a nearby hypervelocity emissary from a thermonuclear supernova event ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Roberto Raddi The University of Warwick Y CoI: Prof. Detlev G. Koester Universitat Kiel N CoI: Mr. Mark Hollands The University of Warwick N CoI: Prof. Boris T. Gaensicke The University of Warwick Y CoI: Dr. Nicola Gentile-Fusillo The University of Warwick N CoI: Dr. Dean Townsley University of Alabama N CoI: Dr. JJ Hermes University of North Carolina at Chapel N Hill ------------------------------------------------------------------------------------ Abstract GD 492 is a nearby hypervelocity white dwarf with a unique chemical composition displaying the nucleosynthesis fingerprints of C-, O-, and Si- burning. From our ground-based optical spectroscopy, we determine a He-dominated atmosphere, but loaded with a large amount of Ne, Mn, O (30, 5, 1%, by mass, respectively) and traces of ten other elements. The large space velocity, exceeding the Galactic escape velocity, and the considerable alpha enhancements strongly suggest that GD 492 is an exotic white dwarf remnant of a failed Type Ia supernova. The super-Solar Mn/Fe ratio provides evidence that this partial thermonuclear explosion occurred in a single-degenerate binary. Through kinematic analysis, we constrained the supernova event to have occurred most likely < 10 Myr ago, at a nearby Galactic disc location towards the Carina arm. Here we apply for five HST orbits to obtain high-quality STIS near-ultraviolet spectroscopy of GD492 which we will use to: (1) accurately measure the effective temperature, which is significantly affected by the currently unconstrained amount of ultraviolet line blanketing. Together with the forthcoming Gaia DR2 parallax, this measurement will also tightly constrain the radius and mass of GD 492. (2) unambiguously measure the bulk atmospheric composition, i.e. the Ne/He ratio; determine the degree of C-burning through the detection of (or placing a firm upper limit on) the C-abundance; and derive significantly improved constraints on O- and Si- burning via more accurate abundance measurements of Mn, S, and Ni. Both scientific goals critically require space-based ultraviolet spectroscopy. ------------------------------------------------------------------------------------ Observations Description ------------------------ The goal of these observations is to obtain a high S/N spectrum of the target star, GD492. The star has a moderate, but well known proper motion, and is in a 15431( 2) - 21-Nov-2017 13:55:21 - [ 2] sparse field, so acquisition with the STIS CCD should be straightforward. We were awarded five orbits, but as requested, we split the observations into a two and a three-orbit visit to facilitate the scheduling of the observations. We would be equally happy should it be possible to schedule the observations as a single five-orbit visit, as that would give us an extra ~650sec on-target, but the difference in the total S/N is too small to request a single five-orbit visit. Please attempt to schedule the observations in one of the Dec/Jan/Mar to ensure the spectroscopy is available in time for the Gaia Data Release 2, which will provide an accurate parallax. ------------------------------------------------------------------------------------ 15431( 2) - 21-Nov-2017 13:55:21 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 GD-492 STAR, DZ RA=14H06M35.4460S, J2000 V = 15.506 +/- 0.093 GALEX DEC=+74D18'58.06" FUV=21.051+-0.299 GALEX NUV=18.605+-0.058 Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.014229550678895761 0.1449 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 15431( 2) - 21-Nov-2017 13:55:21 - [ 4] Visit: 02 (GD492 - 3 orbit visit) 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 GD-492 STIS/CCD ACQ F28X50LP MIRROR 1 1 S (1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 GD-492 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=625 1 2661 S -MAMA G (2661 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 GD-492 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=625 1 3310 S -MAMA G (3310 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 GD-492 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=625 1 3310 S -MAMA G (3310 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 | ------------------------------------------------------------------------------------------------------------------------------------ GD-492 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A GD-492 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G GD-492 3 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 2 N/A -MAMA G GD-492 4 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 3 N/A -MAMA G 15431( 2) - 21-Nov-2017 13:55:21 - [ 5] Visit: 03 (GD492 - 2 orbit visit) 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 GD-492 STIS/CCD ACQ F28X50LP MIRROR 1 1 S (1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 GD-492 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=625 1 2661 S -MAMA G (2661 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 GD-492 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=625 1 3310 S -MAMA G (3310 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 | ------------------------------------------------------------------------------------------------------------------------------------ GD-492 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A GD-492 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G GD-492 3 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 2 N/A -MAMA G 15431( 2) - 21-Nov-2017 13:55:21 - [ 6] Summary Form for Proposal 15431 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=625 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names GD-492 ------------------------------------------------------------------------------------------------------------------------------------