15954( 2) - 19-Jul-2019 14:59:32 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15954 Version: 2 Check-in Time: 19-Jul-2019 14:59:32 STScI Edit Number: 0 Title The first pulsating white dwarf in an eclipsing binary ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Steven Gary Parsons University of Sheffield Y CoI: Dr. Stuart Littlefair University of Sheffield N CoI: Prof. Vik Dhillon University of Sheffield N CoI: Prof. Tom R. Marsh The University of Warwick N CoI: Prof. Boris T. Gaensicke The University of Warwick N CoI: Dr. JJ Hermes Boston University N ------------------------------------------------------------------------------------ Abstract White dwarfs are the end states of all stars less massive than 8-10 solar masses. Encrypted inside these stellar remnants is a record of the evolutionary history of the progenitor stars, providing a wealth of information about the evolution of stars, star formation, and the age of a variety of stellar populations. However, the internal structure and composition of white dwarfs are hidden by their high gravities, which causes all elements, apart from hydrogen and helium, to settle out of their atmospheres. An exciting system has recently been discovered, the first pulsating white dwarf in an eclipsing binary. Both binary modeling and asteroseismology of the pulsation periods are available to reveal the core composition of this roughly 0.35 solar-mass stellar remnant. Current modeling can constrain the radius of this white dwarf to around 5%, but by constraining the limb darkening via the temperature of the primary we can obtain a factor of five improvement to roughly 1% uncertainty. Only by measuring the temperature of the hotter star in the binary with COS FUV spectroscopy can we unlock the full potential of this unique system to accurately constrain the core composition of a 0.35 solar-mass white dwarf, accurately testing whether it has a helium-, carbon-oxygen, or even hybrid core composition. It will serve as a powerful benchmark to empirically constrain the core composition of low-mass stellar remnants and investigate the effects of close binary evolution on the internal structure of white dwarfs. ------------------------------------------------------------------------------------ Observations Description ------------------------ The goal of this proposal is to obtain phase-resolved far-ultraviolet spectroscopy of the eclipsing double-white dwarf binary SDSS1152+0248. This data will be used to (1) measure the effective temperature and surface gravity from the well-calibrated COS/G140L spectrum, and (2) obtain high-quality far-ultraviolet light curves of the primay eclipse, from which we will measure the stellar radii. The target will be acquired using COS/NUV imaging, followed by time-tagged COS/G140L spectroscopy. During the primary eclipse, the ultraviolet flux will drop dramitcally, hence we need to ensure via a phase constraint that the 15954( 2) - 19-Jul-2019 14:59:32 - [ 2] target acqusition occurs outside the primary eclipse. The ephemeris is HJD(UTC) = 2457461.1502539(10) + 0.09986526542(10)E and we need to acquire somewhere in the phase interval 0.15 - 0.85. In principle, the phase constraint only applies to the first exposure, the short NUV acquisition image - however, the scheduling software doesn't cope well with periods shorter than the visit duration. Therefore we provide APT with three times the orbital period, 0.3994610617, and the phase window 0.05 - 0.285. This will probably reduce the number of scheduling opportunities by a factor three as well - if that becomes a problem, we need to re-think the strategy again. APT warns about the inefficien sequence of the FP-POS changes, but that's not a problem as we switch FP-POS during Earth occultation. ------------------------------------------------------------------------------------ 15954( 2) - 19-Jul-2019 14:59:32 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SDSS-J115219 STAR, DA RA=11H52M19.9989S +/- 0.05", J2000 V = 17.880 +/- 0.001 .99+024814.4 DEC=+02D48'14.43" +/- 0.05" FUV=17.962+/-0.069, NUV=18.270+/-0.048 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 0.002279996466684361 -0.009862 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 15954( 2) - 19-Jul-2019 14:59:32 - [ 4] Visit: 01 Visit Requirements: Period 0.3994610617 D AND ZERO-PHASE HJD2457461.1510218 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 SDSS-J11521 COS/NUV ACQ/IMA PSA MIRRORA 1 15 S (15 PHASE 0.05 TO 0.285 9.99+024814 GE S) .4 ------------------------------------------------------------------------------------------------------------------------------------ 2 SDSS-J11521 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=2000, FP-POS=3 1 2376 S 9.99+024814 G (2376 S) .4 ------------------------------------------------------------------------------------------------------------------------------------ 3 SDSS-J11521 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=2000, FP-POS=4 1 2776 S 9.99+024814 G (2776 S) .4 ------------------------------------------------------------------------------------------------------------------------------------ 4 SDSS-J11521 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=2000, FP-POS=1 1 2776 S 9.99+024814 G (2776 S) .4 ------------------------------------------------------------------------------------------------------------------------------------ 5 SDSS-J11521 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=2000, FP-POS=2 1 2776 S 9.99+024814 G (2776 S) .4 ------------------------------------------------------------------------------------------------------------------------------------ 6 SDSS-J11521 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=2000, FP-POS=3 1 2776 S 9.99+024814 G (2776 S) .4 ------------------------------------------------------------------------------------------------------------------------------------ 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-J115219.99+024 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A 814.4 GE SDSS-J115219.99+024 2 COS/FUV TIME-TA PSA G140L 800 none none none none 1 N/A 814.4 G SDSS-J115219.99+024 3 COS/FUV TIME-TA PSA G140L 800 none none none none 2 N/A 814.4 G SDSS-J115219.99+024 4 COS/FUV TIME-TA PSA G140L 800 none none none none 3 N/A 814.4 G SDSS-J115219.99+024 5 COS/FUV TIME-TA PSA G140L 800 none none none none 4 N/A 814.4 G SDSS-J115219.99+024 6 COS/FUV TIME-TA PSA G140L 800 none none none none 5 N/A 814.4 G 15954( 2) - 19-Jul-2019 14:59:32 - [ 5] Summary Form for Proposal 15954 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=2000, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PHASE 0.05 TO 0.285, Period 0.3994610617 D AND ZERO-PHASE HJD2457461.1510218 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names SDSS-J115219.99+024814.4 ------------------------------------------------------------------------------------------------------------------------------------