15897( 3) - 04-Dec-2019 19:04:10 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15897 Version: 3 Check-in Time: 04-Dec-2019 19:04:10 STScI Edit Number: 0 Title ZTF J1539+5027: the Shortest Period Eclipsing White Dwarf Binary ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Mr. Kevin Burdge California Institute of Technology Y CoI: Prof. Boris T. Gaensicke The University of Warwick N CoI: Dr. Thomas A Prince California Institute of Technology N CoI: Prof. Tom R. Marsh The University of Warwick N CoI: Prof. David L. Kaplan University of Wisconsin - Milwaukee N CoI: Prof. Shrinivas R. Kulkarni California Institute of Technology N CoI: Dr. Michael W. Coughlin California Institute of Technology N CoI: Prof. Jim Fuller California Institute of Technology N CoI: Dr. Odette Fabiola Toloza The University of Warwick N Castillo ------------------------------------------------------------------------------------ Abstract Here, we propose to obtain high resolution ultraviolet spectroscopy using COS on the shortest eclipsing binary system known, the double white dwarf binary ZTF J1539+5027 (submitted to Nature). This deeply eclipsing binary system has an orbital period of 6.91 minutes and exhibits a rapid orbital decay due to the emission of gravitational radiation. The binary emits gravitational waves near the peak of the Laser Interferometer Space Antenna's (LISA) sensitivity, making it one of the strongest LISA gravitational wave sources, with detection expected within the first week of operations. We are requesting Hubble's unique capability to obtain high resolution far-ultraviolet spectroscopy because the more compact white dwarf in this system is 50, 000K despite its short cooling age, suggesting heating via accretion; however, no signs of accretion have been detected in the optical or X-ray. If we fail to detect metal lines visible uniquely in the UV, we will be able place an upper limit on the accretion rate to a level 8 orders of magnitude below what is currently possible in the X-ray or optical, ruling out the possibility that this white dwarf is currently heated by ongoing mass-transfer. If we detect metal lines, we will measure the accretion rate, obtain precise radial velocity semi-amplitudes of the components. Additionally, by using Lyman absorption lines as well as the ratio of metal lines (if present), we will be able to accurately measure the temperature of the primary, refining the distance estimate to the system. Finally, by obtaining a high SNR ultraviolet lightcurve, we will constrain the temperature ratio of the two components. ------------------------------------------------------------------------------------ Observations Description ------------------------ This program will obtain time-resolved intermediate resolution spectroscopy of the ultra-short-period eclipsig double-white dwarf binary to (1) determine an accurate effective temperature of the hotter white dwarf from it's Ly alpha absorption profile 15897( 3) - 04-Dec-2019 19:04:10 - [ 2] (2) construct a far-ultraviolet eclipse light curve to model the stellar radii (3) probe for photospheric metal lines arising from accretion from the companion The target acqusition is done via near-UV imaging. However, as the primary, which totally dominates the ultraviolet flux, is eclipsed every 7min, we need to implement an ephemeris timing constraint to avoid that the target acquisition occurs during primary eclipse. We split this ten-orbit program into two five-orbit visits, using the 1291A and 1222A central wavelengths to maximise the total wavelength range covered: extending the blue Ly alpha wing, and covering the Si IV 1393/1403A resonance lines. We will achieve a combined signal-to-noise ratio of ~20 in the overlapping region. The time-tagged photon stream will be used to construct average spectra on the 7min orbital period of the system, and far-ultraviolet light curves in at least two wavelength bands . ------------------------------------------------------------------------------------ 15897( 3) - 04-Dec-2019 19:04:10 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ZTFJ153932.1 STAR, DA RA=15H39M32.1588S +/- J2000 V = 20.2 +/- 0.2 GALEX FUV=18.75 6+502738.8 0.0006649", DEC=+50D27'38.78" NUV=19.33 +/- 0.0007122" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -3.5741605041423783E-4 -0.003823 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 15897( 3) - 04-Dec-2019 19:04:10 - [ 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ZTFJ153932. COS/NUV ACQ/IMA PSA MIRRORA 1 60 S (60 16+502738.8 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=9497, FP-POS=3 1 2508 S 16+502738.8 G (2508 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=9497, FP-POS=4 1 2967 S 16+502738.8 G (2967 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=9497, FP-POS=3 1 2967 S 16+502738.8 G (2967 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=9497, FP-POS=4 1 2967 S 16+502738.8 G (2967 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=9497, FP-POS=3 1 2967 S 16+502738.8 G (2967 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ153932.16+50273 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A 8.8 GE ZTFJ153932.16+50273 2 COS/FUV TIME-TA PSA G130M 1291 none none none none 1 N/A 8.8 G ZTFJ153932.16+50273 3 COS/FUV TIME-TA PSA G130M 1291 none none none none 2 N/A 8.8 G ZTFJ153932.16+50273 4 COS/FUV TIME-TA PSA G130M 1291 none none none none 3 N/A 8.8 G ZTFJ153932.16+50273 5 COS/FUV TIME-TA PSA G130M 1291 none none none none 4 N/A 8.8 G ZTFJ153932.16+50273 6 COS/FUV TIME-TA PSA G130M 1291 none none none none 5 N/A 8.8 G 15897( 3) - 04-Dec-2019 19:04:10 - [ 5] Visit: 02 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 ZTFJ153932. COS/NUV ACQ/IMA PSA MIRRORA 1 60 S (60 16+502738.8 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1222 BUFFER-TIME=9497, FP-POS=3 1 2493 S 16+502738.8 G (2493 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1222 BUFFER-TIME=9497, FP-POS=4 1 2967 S 16+502738.8 G (2967 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1222 BUFFER-TIME=9497, FP-POS=1 1 2967 S 16+502738.8 G (2967 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1222 BUFFER-TIME=9497, FP-POS=2 1 2967 S 16+502738.8 G (2967 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 ZTFJ153932. COS/FUV TIME-TA PSA G130M 1222 BUFFER-TIME=9497, FP-POS=3 1 2967 S 16+502738.8 G (2967 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ153932.16+50273 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A 8.8 GE ZTFJ153932.16+50273 2 COS/FUV TIME-TA PSA G130M 1222 none none none none 1 N/A 8.8 G ZTFJ153932.16+50273 3 COS/FUV TIME-TA PSA G130M 1222 none none none none 2 N/A 8.8 G ZTFJ153932.16+50273 4 COS/FUV TIME-TA PSA G130M 1222 none none none none 3 N/A 8.8 G ZTFJ153932.16+50273 5 COS/FUV TIME-TA PSA G130M 1222 none none none none 4 N/A 8.8 G ZTFJ153932.16+50273 6 COS/FUV TIME-TA PSA G130M 1222 none none none none 5 N/A 8.8 G 15897( 3) - 04-Dec-2019 19:04:10 - [ 6] Summary Form for Proposal 15897 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=9497, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G130M, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names ZTFJ153932.16+502738.8 ------------------------------------------------------------------------------------------------------------------------------------