13421( 4) - 03-Jul-2013 17:35:59 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13421 Version: 4 Check-in Time: 03-Jul-2013 17:35:59 STScI Edit Number: 1 Title CSS 41177: an eclipsing double white dwarf binary ------------------------------------------------------------------------------------ Type Cycle GO 21 ------------------------------------------------------------------------------------ Investigators Contact? PI: Ms. Madelon C.P. Bours The University of Warwick Y CoI: Prof. Thomas R. Marsh The University of Warwick Y CoI: Prof. Boris T. Gaensicke The University of Warwick N CoI: Dr. Steven G. Parsons Valparaiso University N ------------------------------------------------------------------------------------ Abstract The overwhelming majority of stellar remnants are white dwarfs. Despite their abundance and importance to, amongst others, Galactic age determinations and our understanding of type Ia supernovae fewer than a dozen white dwarfs have model-independent measurements of fundamental parameters like mass and radius. A major limitation on the observational side is that such parameters are extremely difficult to determine in a model-independant way for single white dwarfs. Close white dwarf binaries can provide these important tests. The largest class of white dwarf binaries in the Galaxy are the detached double white dwarfs, which are becoming increasingly popular as the progenitor systems of Type Ia supernovae. In recent years four eclipsing double white dwarfs have been found, creating the opportunity for precision mass and radius measurements of two white dwarfs at once. Our target, CSS 41177, contains two extremely low-gravity white dwarfs with very different temperatures, presenting us with a unique chance to test the existing mass-radius relation at its extremes. Here we propose a 2 orbit HST/COS FUV observation of CSS 41177, to accurately determine the temperature and surface gravity of the hot white dwarf. Through the flux ratio from the light curve this will at the same time constrain those of the cool white dwarf. Therefore it will allow us to add two more white dwarfs with accurate parameters to the short list of white dwarfs for which precise masses and radii are known. Note: The proposed observations are part of the doctoral thesis of Ms. Madelon C.P. Bours. ------------------------------------------------------------------------------------ Observations Description ------------------------ The aim of the observation is to obtain a far-ultraviolet spectrum of a double-degenerate DA white dwarf. The sequence is straight-forward: target acquisition in dispersed light, followed by G140L spectroscopy using all four FP-POS positions. Real Time Justification ----------------------- 13421( 4) - 03-Jul-2013 17:35:59 - [ 2] Calibration Justification ------------------------- Additional Comments ------------------- As this is part of Ms Bours PhD work, it would be very helpful if the observations could be scheduled early in Cycle 21. ------------------------------------------------------------------------------------ 13421( 4) - 03-Jul-2013 17:35:59 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSS-J100559 STAR, DA RA=10H05M59.1200S +/- 0.1", J2000 V = 17.3 +/- 0.1 .10+224932.2 DEC=+22D49'32.48" +/- 0.1" Reference Frame: ICRS Comments: The target was observed with GALEX, at m(fuv)=16.72 +/- 0.04 (AB) and m(nuv)=16.98 +/- 0.03 (AB). Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.0014176866831940543 -0.013300000000000001 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 13421( 4) - 03-Jul-2013 17:35:59 - [ 4] Visit: 01 Visit Requirements: Period 0.1160154352 D AND ZERO-PHASE HJD2455936.84389534 On Hold Comments: Additional Comments: This double white dwarf is eclipsing. Even though the eclipse lasts only ~minutes, we implement a phase constraint for this visit to avoid that the target acq. is done during the eclipse. FYI, a similar procedure has been successfully used in a number of visits in program 12870. 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 SDSS-J10055 COS/FUV ACQ/PEA PSA G140L 1105 1 11 S (11 PHASE 0.2 TO 0.8 9.10+224932 KXD S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSS-J10055 COS/FUV ACQ/PEA PSA G140L 1105 STEP-SIZE=0.9, NUM-POS=5, 1 11 S (11 9.10+224932 KD CENTER=DEF S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSS-J10055 COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=1062, FLASH=YES, 1 1162 S 9.10+224932 G FP-POS=1 (1162 S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 4 SDSS-J10055 COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=1200, FLASH=YES, 1 1200 S 9.10+224932 G FP-POS=2 (1200 S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 5 SDSS-J10055 COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=1320, FLASH=YES, 1 1428 S NEW OBSET 9.10+224932 G FP-POS=3 see below .2 (1426 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 SDSS-J10055 COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=1425, FLASH=YES, 1 1425 S 9.10+224932 G FP-POS=4 (1425 S) .2 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSS-J100559.10+224 1 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A 932.2 KXD SDSS-J100559.10+224 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A 932.2 KD SDSS-J100559.10+224 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A 932.2 G SDSS-J100559.10+224 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A 932.2 G 13421( 4) - 03-Jul-2013 17:35:59 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ SDSS-J100559.10+224 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 1426.0 S 932.2 G SDSS-J100559.10+224 6 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A 932.2 G 13421( 4) - 03-Jul-2013 17:35:59 - [ 6] Summary Form for Proposal 13421 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAKD, ACQ/PEAKXD, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1062, BUFFER-TIME=1200, BUFFER-TIME=1320, BUFFER-TIME=1425, CENTER=DEF, FLASH=YES, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, NUM-POS=5, STEP-SIZE=0.9 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements NEW OBSET, PHASE 0.2 TO 0.8, Period 0.1160154352 D AND ZERO-PHASE HJD2455936.84389534 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names SDSS-J100559.10+224932.2 ------------------------------------------------------------------------------------------------------------------------------------