16251( 4) - 11-Aug-2020 11:56:52 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16251 Version: 4 Check-in Time: 11-Aug-2020 11:56:52 STScI Edit Number: 2 Title Accurate Mass Determination of the Nearby Single White Dwarf L145-141 (LAWD 37) through Astrometric Microlensing ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kailash C. Sahu Space Telescope Science Institute Y CoI: Dr. Jay Anderson Space Telescope Science Institute N CoI: Dr. Andrea Bellini Space Telescope Science Institute N CoI: Dr. Pierre Bergeron Universite de Montreal N CoI: Dr. Vasily Belokurov University of Cambridge N CoI: Dr. Howard E. Bond The Pennsylvania State University N CoI: Dr. Thomas M. Brown Space Telescope Science Institute N CoI: Dr. Annalisa Calamida Space Telescope Science Institute N CoI: Dr. Stefano Casertano Space Telescope Science Institute N CoI: Dr. Martin Dominik University of St. Andrews N CoI: Prof. Wyn Evans University of Cambridge N CoI: Dr. Noe Kains Barnard College N CoI: Mr. Jonas Klueter Astronomisches Rechen-Institut Heidelberg N CoI: Mr. Peter McGill University of Cambridge N CoI: Dr. Martin Bo Nielsen New York University Abu Dhabi N CoI: Dr. Edmund Nelan Space Telescope Science Institute N CoI: Dr. Richard Smart Osservatorio Astronomico di Torino N CoI: Dr. Leigh Smith University of Cambridge N CoI: Dr. Joachim Wambsganss Astronomisches Rechen-Institut Heidelberg N CoI: Dr. Daniel Bramich New York University Abu Dhabi N ------------------------------------------------------------------------------------ Abstract White dwarf (WD) is the final stage for a vast majority of stars, and WDs are important in a variety of astrophysical and galactic contexts. However, there are surprisingly few WDs with direct mass measurements, all of them in binaries. It has been reported recently that the fifth-nearest WD, L145-141 (LAWD 37), will pass closely in front of a background star in late 2019, with an impact parameter of only 380 milliarcsec. As it passes in front, the WD will relativistically deflect the light from the background star, providing a unique opportunity for direct measurement of the WD's mass. The gravitational deflection angle depends only on the distances and relative positions of the stars, and on the mass of the WD. Since the distances and positions can be determined precisely before the event, the astrometric measurement offers a direct method to measure the mass of the WD to high accuracy (~2.5%). Precision HST astrometry was recently used to measure the astrometric deflection caused by the nearby white dwarf Stein 2051B, and thus measure its mass--the first application of this technique outside the solar system. We now propose to repeat this experiment for a second WD. Relativistic astrometric microlensing is the only available model-independent technique for determining the mass of a single WD. Our target is of special interest because it is the second-nearest single WD (after van 16251( 4) - 11-Aug-2020 11:56:52 - [ 2] Maanen's Star). Our measurement will be the first model-independent mass measurement of a single WD, and will add to the surprisingly small number of accurate model-independent mass determinations for WDs--a key element in testing the theoretical mass-radius relation. ------------------------------------------------------------------------------------ Observations Description ------------------------ We have tweaked the observing strategy that was used in program GO-14448 to determine the mass of Stein 2051B, in order to improve the accuracy even further. At each epoch, we will obtain images in WFC3/UVIS F814W (I-band). The contrast between source and lens is best in this filter, and its PSF is well characterized. We will use a 2kx2k subarray to ensure that there are enough reference stars within the field, yet interruptions for buffer dumps will be unnecessary. At one epoch we will also obtain a few frames in F555W (V -band) in order to estimate the spectral types of the source and reference stars, and thus refine their distance estimates. Since the astrometric deflection measurements are differential, it is important to measure them at several epochs, including close to the baseline and the peak. In addition, there must be enough epochs to independently solve for the proper motions and parallaxes of the reference stars and source. These considerations dictate our proposal to observe at 8 epochs beginning in April 2019. ------------------------------------------------------------------------------------ 16251( 4) - 11-Aug-2020 11:56:52 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LAWD-37-SOUR STAR, K III-I RA=11H45M51.2650S +/- 0.1", J2000 V = 18.46 CE DEC=-64D50'35.87" +/- 0.1" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 2 LAWD-37-OFFS EXT-STAR, DC RA=11H45M50.9500S, J2000 V = 19 ET DEC=-64D50'41.50" Reference Frame: ICRS Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 16251( 4) - 11-Aug-2020 11:56:52 - [ 4] Visit: 53 Visit Requirements: ORIENT 181.99D TO 182.01 D; BETWEEN 16-SEP-2020 AND 19-SEP-2020 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 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20, BLADE=A 1 1.5 S (1.5 POS TARG 0, 0; GS ACQ SET S 1C-SUB S) SCENARIO BASE1B3; SEQ 1-19 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 SAME POS AS 1 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG 3.56, 0 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG 3.08, 1.78 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 5 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 1.5 S (1.5 POS TARG 1.77, 3.08 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 6 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 SAME POS AS 5 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 7 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG -0.01, 3.55 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 8 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG -1.79, 3.07 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 9 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 1.5 S (1.5 POS TARG -3.09, 1.77 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 10 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 SAME POS AS 9 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 11 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG -3.55, -0.02 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 12 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG -3.07, -1.79 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 13 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 1.5 S (1.5 POS TARG -1.76, -3.09 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 14 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 SAME POS AS 13 SET S 1C-SUB S) 16251( 4) - 11-Aug-2020 11:56:52 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------ 15 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG 0.02, -3.55 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 16 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG 1.8, -3.07 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 17 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 1.5 S (1.5 POS TARG 3.09, -1.75 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 18 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 SAME POS AS 17 SET S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 19 LAWD-37-OFF WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=18 1 85 S (85 POS TARG 0, 0 SET S 1C-SUB 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 | ------------------------------------------------------------------------------------------------------------------------------------ LAWD-37-OFFSET 1 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 2 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 3 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 4 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 5 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 6 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 7 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 8 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 9 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 10 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 11 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 12 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB 16251( 4) - 11-Aug-2020 11:56:52 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ LAWD-37-OFFSET 13 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 14 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 15 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 16 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 17 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 18 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB LAWD-37-OFFSET 19 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB 16251( 4) - 11-Aug-2020 11:56:52 - [ 7] Summary Form for Proposal 16251 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BLADE=A, FLASH=18, FLASH=20 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 16-SEP-2020 AND 19-SEP-2020, GS ACQ SCENARIO BASE1B3, ORIENT 181.99D TO 182.01 D, POS TARG -0.01, 3.55, POS TARG -1.76, -3.09, POS TARG -1.79, 3.07, POS TARG -3.07, -1.79, POS TARG -3.09, 1.77, POS TARG -3.55, -0.02, POS TARG 0, 0, POS TARG 0.02, -3.55, POS TARG 1.77, 3.08, POS TARG 1.8, -3.07, POS TARG 3.08, 1.78, POS TARG 3.09, -1.75, POS TARG 3.56, 0, SAME POS AS 1, SAME POS AS 13, SAME POS AS 17, SAME POS AS 5, SAME POS AS 9, SEQ 1-19 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names LAWD-37-OFFSET ------------------------------------------------------------------------------------------------------------------------------------