12168( 4) - 26-Jan-2011 12:02:13 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12168 Version: 4 Check-in Time: 26-Jan-2011 12:02:13 STScI Edit Number: 1 Title The temperature, mass and chemical composition of the bare ONe white dwarf SDSS1102+4054 ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Boris T. Gaensicke The University of Warwick CoI: Dr. Detlev G. Koester Universitat Kiel N CoI: Dr. John Thorstensen Dartmouth College N CoI: Mr. Jonathan Girven The University of Warwick N ------------------------------------------------------------------------------------ Abstract SDSS1102+2054 is a cool white dwarf with a helium-dominated atmosphere that exhibits strong oxygen and carbon lines in its optical spectrum. The oxygen-to-carbon (O/C) abundance ratio implied by the line strengths is much larger than unity, which rules out out a carbon-oxygen core composition and provides strong evidence that SDSS1102+2054 is a naked oxygen-neon (ONe) core. Stellar evolution models predict that such extreme O/C abundance ratios are achieved only in the most massive stars that just avoid core-collapse, and we hence believe that SDSS1102+2054 descends from an intermediate mass star close to the 8-10Msun boundary between stars leaving behind either white dwarfs, or neutron stars. As such, this white dwarf has the potential to provide important constraints on our understanding of the evolution of intermediate mass stars, in particular testing predictions of mass loss, the efficiency of convective core mixing, and the relevant nuclear reaction rates. We propose to obtain intermediate-resolution HST/COS spectroscopy of SDSS1102+2054 to overcome the limitations of the available ground-based data and accurately measure its effective temperature, mass, and Mg abundance, and stringently test the current models of stellar evolution. ------------------------------------------------------------------------------------ Observations Description ------------------------ SDSS1102+2054 is the first cool white dwarf with a very oxygen (and carbon)-rich atmosphere. We need to obtain a low-res FUV/NUV spectrum to establish the spectral energy distribution, and from there determine the effective temperature of the star. This will be done by a combination of COS/G140L and COS/G230L observations. The G140L observations are spread over three orbits, and use two different FP-POS (1, 4) settings to deal with fixed pattern noise. The NUV range is sampled in two orbits with three G230L observations, centred on 2635A, 2950A, 3360A. The target is sufficiently faint to be acquired with NUV imaging, MIRRORA + PSA. Real Time Justification ----------------------- Calibration Justification ------------------------- 12168( 4) - 26-Jan-2011 12:02:13 - [ 2] Additional Comments ------------------- ------------------------------------------------------------------------------------ 12168( 4) - 26-Jan-2011 12:02:13 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSSJ110239. STAR, DZ RA=11H02M39.7300S +/- 0.1", J2000 V = 17.24 +/- 0.01 69+205439.4 DEC=+20D54'39.80" +/- 0.1" Reference Frame: ICRS Comments: No GALEX data at the position, this is a cool white dwarf with a predicted flux of 1.5e-14/erg/cm2/s/AA across the NUV, and rapidly dropping at lambda < 2000A. UPDATE - we have obtained a Swift UVOT UVW1 observation (Target ID=31907), which gvies a flux density [erg/s/cm^2/A] of 4.82 +/- 0.18 (stat) +/- 0.15 (sys) x 10^-16 at 2591A, i.e. about a factor ~3 lower than the predicted flux. I have updated the target acq exposure times from 7sec to 16sec. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.01194687338134168 -0.037200000000000004 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 12168( 4) - 26-Jan-2011 12:02:13 - [ 4] Visit: 01 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSSJ110239 COS/NUV ACQ/SEA PSA MIRRORA SCAN-SIZE=3, STEP-SIZE=1.767, 1 16 S .69+205439. RCH CENTER=FLUX-WT-FLR 4 Comments: COS.ta.004574 ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSSJ110239 COS/NUV ACQ/IMA PSA MIRRORA 1 16 S .69+205439. GE 4 Comments: COS.ta.004574 ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSSJ110239 COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=1500, FLASH=YES, 1 2071 S .69+205439. G FP-POS=1 4 Comments: COS.A331104 ------------------------------------------------------------------------------------------------------------------------------------ 4 SDSSJ110239 COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=1500, FLASH=YES, 1 1815 S .69+205439. G FP-POS=1 4 Comments: COS.A331104 ------------------------------------------------------------------------------------------------------------------------------------ 5 SDSSJ110239 COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=1029, FLASH=YES, 1 1029 S .69+205439. G FP-POS=4 4 Comments: COS.A331104 ------------------------------------------------------------------------------------------------------------------------------------ 6 SDSSJ110239 COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=1500, FLASH=YES, 1 2963 S .69+205439. G FP-POS=4 4 Comments: COS.A331104 ------------------------------------------------------------------------------------------------------------------------------------ 7 SDSSJ110239 COS/NUV TIME-TA PSA G230L 2635 BUFFER-TIME=1500, FLASH=YES 1 3000 S .69+205439. G 4 Comments: COS.A331100 ------------------------------------------------------------------------------------------------------------------------------------ 8 SDSSJ110239 COS/NUV TIME-TA PSA G230L 2950 BUFFER-TIME=1500, FLASH=YES 1 3000 S .69+205439. G 4 Comments: COS.A331095 ------------------------------------------------------------------------------------------------------------------------------------ 12168( 4) - 26-Jan-2011 12:02:13 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 9 SDSSJ110239 COS/NUV TIME-TA PSA G230L 3360 BUFFER-TIME=1500, FLASH=YES 1 3000 S .69+205439. G 4 Comments: COS.A331099 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSSJ110239.69+2054 1 COS/NUV ACQ/SEA PSA MIRRORA none none none none 1 N/A 39.4 RCH SDSSJ110239.69+2054 2 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A 39.4 GE SDSSJ110239.69+2054 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 N/A 39.4 G SDSSJ110239.69+2054 4 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A 39.4 G SDSSJ110239.69+2054 5 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A 39.4 G SDSSJ110239.69+2054 6 COS/FUV TIME-TA PSA G140L 1280 none none none none 3 N/A 39.4 G SDSSJ110239.69+2054 7 COS/NUV TIME-TA PSA G230L 2635 none none none none 4 N/A 39.4 G SDSSJ110239.69+2054 8 COS/NUV TIME-TA PSA G230L 2950 none none none none 5 N/A 39.4 G SDSSJ110239.69+2054 9 COS/NUV TIME-TA PSA G230L 3360 none none none none 6 N/A 39.4 G 12168( 4) - 26-Jan-2011 12:02:13 - [ 6] Summary Form for Proposal 12168 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, ACQ/SEARCH, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1029, BUFFER-TIME=1500, CENTER=FLUX-WT-FLR, FLASH=YES, FP-POS=1, FP-POS=4, SCAN-SIZE=3, STEP-SIZE=1.767 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names SDSSJ110239.69+205439.4 ------------------------------------------------------------------------------------------------------------------------------------