16753( 6) - 10-Jun-2024 18:44:59 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16753 Version: 6 Check-in Time: 10-Jun-2024 18:44:59 STScI Edit Number: 2 Title The radius and magnetic field structure of the smallest white dwarf ------------------------------------------------------------------------------------ Type Cycle GO 29 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Ilaria Caiazzo Institute of Science and Technology Y Austria CoI: Dr. Kevin Burdge Massachusetts Institute of Technology N CoI: Prof. Boris T. Gaensicke The University of Warwick N CoI: Dr. Jeremy Heyl University of British Columbia N CoI: Dr. Harvey B. Richer University of British Columbia N CoI: Dr. Thomas A Prince California Institute of Technology N CoI: Prof. Shrinivas R. Kulkarni California Institute of Technology N CoI: Prof. Jim Fuller California Institute of Technology N CoI: Dr. Adela Kawka Curtin University N CoI: Dr. Stephane Vennes Australian National University N CoI: Prof. dayal tissa wickramasinghe Australian National University N CoI: Prof. Lilia Ferrario Australian National University N ------------------------------------------------------------------------------------ Abstract The white dwarf ZTF J1901+1458 is extreme in almost every regard: it rotates every 6.94 minutes, one of the shortest periods measured for an isolated white dwarf, it is threaded by a magnetic field of almost a billion Gauss, and is the smallest white dwarf for which a radius has been measured, with a size comparable to that of the Moon. The white dwarf is so compact, that it might be gravitationally unstable and headed toward collapse. The radius's measurement, however, hinges on assumptions on the white dwarf's spectral distribution that can only be verified by ultraviolet spectroscopy. Moreover, a UV spectrum will allow a detailed modeling of the white dwarf's magnetic field strength and morphology. ------------------------------------------------------------------------------------ Observations Description ------------------------ The purpose of this program is to study the SED and lightcurve of the white dwarf ZTF J1901+1458, as well as detect hydrogen absorption features in the far UV. ZTF J1901+1458 is the smallest white dwarf known (with a radius of about 2100 km), which shows signs of a very strong magnetic fields (almost a billion Gauss) and a variation in optical luminosity of about 3% over a period of 6.94 minutes. The proposed observations will allow us to constrain the surface temperature and radius of the white dwarf, as well as its magnetic field strength and structure. We ask for 4 orbits of COS spectroscopy and 6 orbits of STIS spectroscopy in the time-tag mode, so that we will obtain high signal-to-noise phase resolved spectra and UV lightcurves. For the COS observations, we ask for a different FP-POS in each orbit, for a total of 4. There are no time constraints on the observations, and the 4 visits can be scheduled separately. 16753( 6) - 10-Jun-2024 18:44:59 - [ 2] The Swift UVOT data for this white dwarf in the UV shows a flattening of the SED, in contrast to what we expect from a non magnetized white dwarf. For this reason, we cannot predict with high confidence the luminosity in the far UV. Thus, we employ two different models in the ETC: a flat spectrum normalized to the bluest UVOT filter, which correspond to the faintest hypothesis for the far UV, and the white dwarf spectrum that best fits both the optical and UV data, which predicts a higher number of counts. To be the most conservative, we use the flat spectrum to estimate the exposure times in the targeting mode of COS, while we employ the white dwarf spectrum to estimate the correct buffer times and the exposure times in the targeting mode of STIS. ------------------------------------------------------------------------------------ 16753( 6) - 10-Jun-2024 18:44:59 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ZTFJ1901+145 STAR, DA RA=19H01M32.8452S +/- J2000 V = 15.72 +/- 0.02 PS1 g 15.51, Swift U 8 0.0000256", DEC=+14D58'8.34" +/- 14.94, Swift UVW1 14.42, Swift UVM2 0.0000306" 14.40 Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016.0 0.00658105624768654 0.07255800000000001 0.0241538 ------------------------------------------------------------------------------------------------------------------------------------ 16753( 6) - 10-Jun-2024 18:44:59 - [ 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 ZTFJ1901+14 COS/FUV ACQ/PEA PSA G140L 1105 1 1.5 S (1.5 58 KXD S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ1901+14 COS/FUV ACQ/PEA PSA G140L 1105 NUM-POS=5, STEP-SIZE=0.9, 1 1.5 S (1.5 58 KD CENTER=FLUX-WT-FLR S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ZTFJ1901+14 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=260, FP-POS=1 1 2273 S 58 G see below (2268 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ZTFJ1901+14 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=260, FP-POS=2 1 2693 S 58 G (2693 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ1901+1458 1 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD ZTFJ1901+1458 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD ZTFJ1901+1458 3 COS/FUV TIME-TA PSA G140L 800 none none none none 1 2268.0 S G ZTFJ1901+1458 4 COS/FUV TIME-TA PSA G140L 800 none none none none 2 N/A G 16753( 6) - 10-Jun-2024 18:44:59 - [ 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 ZTFJ1901+14 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 1.1 S (1.1 58 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ1901+14 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=280 1 2165 S 58 -MAMA G (2165 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ZTFJ1901+14 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=280 1 2729 S 58 -MAMA G (2729 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ZTFJ1901+14 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=280 1 2729 S 58 -MAMA G see below (2704 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ1901+1458 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ZTFJ1901+1458 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ZTFJ1901+1458 3 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 2 N/A -MAMA G ZTFJ1901+1458 4 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 3 2704.0 S -MAMA G 16753( 6) - 10-Jun-2024 18:44:59 - [ 6] Visit: 03 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 ZTFJ1901+14 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 1.1 S (1.1 58 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ1901+14 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=280 1 2165 S 58 -MAMA G (2165 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ZTFJ1901+14 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=280 1 2729 S 58 -MAMA G (2729 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ZTFJ1901+14 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=280 1 2729 S 58 -MAMA G see below (2704 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ1901+1458 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ZTFJ1901+1458 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 N/A -MAMA G ZTFJ1901+1458 3 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 2 N/A -MAMA G ZTFJ1901+1458 4 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 3 2704.0 S -MAMA G 16753( 6) - 10-Jun-2024 18:44:59 - [ 7] Visit: 04 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 ZTFJ1901+14 COS/FUV ACQ/PEA PSA G140L 1105 1 1.5 S (1.5 58 KXD S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ1901+14 COS/FUV ACQ/PEA PSA G140L 1105 NUM-POS=5, STEP-SIZE=0.9, 1 1.5 S (1.5 58 KD CENTER=FLUX-WT-FLR S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ZTFJ1901+14 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=260, FP-POS=3 1 2273 S 58 G see below (2268 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ZTFJ1901+14 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=260, FP-POS=4 1 2693 S 58 G (2693 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ1901+1458 1 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD ZTFJ1901+1458 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD ZTFJ1901+1458 3 COS/FUV TIME-TA PSA G140L 800 none none none none 1 2268.0 S G ZTFJ1901+1458 4 COS/FUV TIME-TA PSA G140L 800 none none none none 2 N/A G 16753( 6) - 10-Jun-2024 18:44:59 - [ 8] Visit: R4 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 ZTFJ1901+14 COS/FUV ACQ/PEA PSA G140L 1105 1 1.5 S (1.5 58 KXD S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ1901+14 COS/FUV ACQ/PEA PSA G140L 1105 NUM-POS=5, STEP-SIZE=0.9, 1 1.5 S (1.5 58 KD CENTER=FLUX-WT-FLR S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ZTFJ1901+14 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=260, FP-POS=3 1 2273 S 58 G see below (2268 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ZTFJ1901+14 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=260, FP-POS=4 1 2693 S 58 G (2693 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ1901+1458 1 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD ZTFJ1901+1458 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD ZTFJ1901+1458 3 COS/FUV TIME-TA PSA G140L 800 none none none none 1 2268.0 S G ZTFJ1901+1458 4 COS/FUV TIME-TA PSA G140L 800 none none none none 2 N/A G 16753( 6) - 10-Jun-2024 18:44:59 - [ 9] Visit: R5 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 ZTFJ1901+14 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 1.1 S (1.1 58 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 ZTFJ1901+14 STIS/NUV TIME-TA 52X2 G230L 2376 BUFFER-TIME=280 1 2165 S 58 -MAMA G see below (2044 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 | ------------------------------------------------------------------------------------------------------------------------------------ ZTFJ1901+1458 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A ZTFJ1901+1458 2 STIS/NUV TIME-TA 52X2 G230L 2376 none none none none 1 2044.0 S -MAMA G 16753( 6) - 10-Jun-2024 18:44:59 - [ 10] Summary Form for Proposal 16753 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X2, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, ACQ/PEAKD, ACQ/PEAKXD, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=260, BUFFER-TIME=280, CENTER=FLUX-WT-FLR, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, NUM-POS=5, STEP-SIZE=0.9 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names ZTFJ1901+1458 ------------------------------------------------------------------------------------------------------------------------------------