15864( 3) - 13-Feb-2020 17:52:27 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15864 Version: 3 Check-in Time: 13-Feb-2020 17:52:27 STScI Edit Number: 1 Title Is the Type Ic supernova progenitor WS35 a white dwarf merger product? ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Goetz Graefener Universitat Bonn, Argelander Institute for Y Astronomy CoI: Dr. Vasilii V. Gvaramadze Sternberg State Astronomical Institute N CoI: Dr. Norbert Langer Universitat Bonn, Argelander Institute for N Astronomy CoI: Prof. Richard Ignace East Tennessee State University N CoI: Dr. Tomer Shenar Katholieke Universiteit Leuven N CoI: Prof. Hugues Sana Katholieke Universiteit Leuven N CoI: Dr. Josiah Schwab University of California - Santa Cruz N ------------------------------------------------------------------------------------ Abstract We propose to obtain UV spectroscopy of the newly discovered emission-line star WS35 with HST/STIS, which was found in the center of a hydrogen-free infrared nebula. Its pure C-O-Ne surface composition, high surface temperature of 200, 000 K, and luminosity of 40, 000 Lsun imply it is an immediate progenitor of a Type Ic supernova. Optical spectra show an unprecedented, supernova-like velocity of its wind, 16, 000 km/s, whose kinetic energy exceeds the photon energy implied by WS35's luminosity. This argues for the wind acceleration being aided by a strong magnetic field and rapid rotation. It has thus been suggested that WS35 is the result of a recent white dwarf merger exceeding the Chandrasekhar mass, caught during its brief evolution from merging to collapse. We aim to test this scenario using FUV/NUV spectra of WS35, which allow to assess the velocity profile of its wind, and thereby provide a clear diagnostic of the wind acceleration mechanism. The proposed STIS UV spectroscopy will further provide unprecedented information on the surface chemical composition that is not accessible from optical spectra, in particular on the so far unconstrained neon abundance. Our results will shed new light on the formation of Type Ic supernovae, constrain the origin of Type Ia supernovae in the double-degenerate scenario, and trial the idea of generating strong magnetic fields in stellar mergers. ------------------------------------------------------------------------------------ Observations Description ------------------------ We obtained 10 HST orbits to observe WS35 with STIS long-slit spectroscopy in low spectral resolution with gratings G140L in the FUV and G230L in the NUV. We wish to obtain data for two epochs to constrain a possible binary nature of the object. We further use time-tag mode to get information on short-term variability, which could be of the order of 5min. We split our observing time in two visits with 5 orbits each. With an integration time of 7051s per visit in the NUV and 7645s per visit in the FUV we obtain a minimum S/N of 20 per visit in the relevant wavelength ranges 15864( 3) - 13-Feb-2020 17:52:27 - [ 2] (~1600-3000A in the NUV, and ~1250-1600A in the FUV, cf. ETC runs STIS.sp.1368104 and STIS.sp.1368105). For time-tag mode we chose buffer times that are roughly a factor three lower than the ETC recommendations to be safe against uncertainties in the source flux and the interstellar extinction (which is included in our uploaded model spectrum). We adopt the standard 52"x0.2" slit. For target acquisition we use a standard point source acquisition. ------------------------------------------------------------------------------------ 15864( 3) - 13-Feb-2020 17:52:27 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WS35 STAR, WOLF RAYET RA=00H53M11.2100S, J2000 V = 15.23 DEC=+67D30'2.10" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the 2MASS database. ------------------------------------------------------------------------------------------------------------------------------------ 15864( 3) - 13-Feb-2020 17:52:27 - [ 4] Visit: 01 Visit Requirements: AFTER 06-SEP-2020:00:00:00 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 WS35 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 1 S (1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 WS35 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=320 1 1000 S -MAMA G see below (2562 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 WS35 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=320 1 1000 S -MAMA G see below (3156 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 WS35 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=320 1 1000 S -MAMA G see below (1333 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 WS35 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=2000 1 1000 S -MAMA G see below (1333 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 WS35 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=2000 1 1000 S -MAMA G see below (3156 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 WS35 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=2000 1 1000 S -MAMA G see below (3156 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 | ------------------------------------------------------------------------------------------------------------------------------------ WS35 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A WS35 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 2562.0 S -MAMA G WS35 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 2 3156.0 S -MAMA G WS35 4 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 3 1333.0 S -MAMA G WS35 5 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 3 1333.0 S -MAMA G 15864( 3) - 13-Feb-2020 17:52:27 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ WS35 6 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 4 3156.0 S -MAMA G WS35 7 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 5 3156.0 S -MAMA G 15864( 3) - 13-Feb-2020 17:52:27 - [ 6] Visit: 02 Visit Requirements: AFTER 06-SEP-2020:00:00:00 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 WS35 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 1 S (1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 WS35 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=320 1 1000 S -MAMA G see below (2562 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 WS35 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=320 1 1000 S -MAMA G see below (3156 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 WS35 STIS/NUV TIME-TA 52X0.2 G230L 2376 BUFFER-TIME=320 1 1000 S -MAMA G see below (1333 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 WS35 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=2000 1 1000 S -MAMA G see below (1333 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 WS35 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=2000 1 1000 S -MAMA G see below (3156 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 WS35 STIS/FUV TIME-TA 52X0.2 G140L 1425 BUFFER-TIME=2000 1 1000 S -MAMA G see below (3156 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 | ------------------------------------------------------------------------------------------------------------------------------------ WS35 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A WS35 2 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 1 2562.0 S -MAMA G WS35 3 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 2 3156.0 S -MAMA G WS35 4 STIS/NUV TIME-TA 52X0.2 G230L 2376 none none none none 3 1333.0 S -MAMA G WS35 5 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 3 1333.0 S -MAMA G 15864( 3) - 13-Feb-2020 17:52:27 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ WS35 6 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 4 3156.0 S -MAMA G WS35 7 STIS/FUV TIME-TA 52X0.2 G140L 1425 none none none none 5 3156.0 S -MAMA G 15864( 3) - 13-Feb-2020 17:52:27 - [ 8] Summary Form for Proposal 15864 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=2000, BUFFER-TIME=320 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 06-SEP-2020:00:00:00 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names WS35 ------------------------------------------------------------------------------------------------------------------------------------