12588( 11) - 18-Sep-2013 13:51:46 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12588 Version: 11 Check-in Time: 18-Sep-2013 13:51:46 STScI Edit Number: 6 Title Accurate Mass Determination of the Old White Dwarf G105-30 through Astrometric Microlensing ------------------------------------------------------------------------------------ Type Cycle GO 19 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kailash C. Sahu Space Telescope Science Institute Y CoI: Dr. Howard E. Bond The Pennsylvania State University N CoI: Dr. Jay Anderson Space Telescope Science Institute N CoI: Dr. Edmund Nelan Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract We propose to determine the mass of the cool, nearby, high-proper-motion white dwarf (WD) G 105-30 (LHS 1838) through astrometric microlensing. In a reprise of the famous 1919 solar eclipse that verified general relativity, G 105-30 will pass very close in front of a 19.5-mag background star in June 2012, with an impact parameter of only ~0.08 arcsec. As it passes in front, it will cause a relativistic deflection of the background star's image by >2 milliarcsec, an amount easily detectable with HST/WFC3. The gravitational deflection angle depends only on the distances and relative positions of the stars, and on the mass of the WD. Since the distance to G 105-30 is already known from an accurate parallax, and the relative positions can be determined precisely before the event, the astrometric measurement offers a unique and direct method to measure the mass of the WD to high accuracy (<5%, potentially <1% for favorable circumstances). One key astrophysical prediction for WDs is the existence of a mass-radius relation (MRR), which depends on the WD's core composition. Since the luminosity and distance of G 105-30 are known, its radius is known. Our measurements will thus provide a new, precise point in the MRR. The mass of G 105-30 is of special interest because it is an old and relatively massive WD, which would provide new constraints near the bottom of the WD cooling curve, currently being used to age-date stellar populations. ------------------------------------------------------------------------------------ Observations Description ------------------------ First, we need to know accurate locations and proper motions for G105-30 and the source star, in order to predict the precise circumstances of the event, including the date and impact parameter. We will use direct imaging with WFC3 to determine the astrometric parameters of G105-30, the source star, and the surrounding reference field. We need to know the time of closest approach as accurately as possible in order to schedule subsequent critical observations. We have a four-phase observing program: (1) In the first phase, we will obtain the HST observations needed to make the final predictions of the circumstances of the event (impact parameter and time of closest approach) with high accuracy. At the beginning of Cycle~19 we will image the field twice at about a 3-month separation for this purpose. 12588( 11) - 18-Sep-2013 13:51:46 - [ 2] (2) Based on the early Cycle~19 astrometry, we will refine the predicted dates between which the images will be blended, so that we will know the optimal observation dates just before and after those times. (3) We will obtain one more observation in cycle 19 just before the onset of blending (and before the peak of the microlensing), when the astrometric deflection is at its largest observable value. (If this epoch turns turns out to lie in the solar-avoidance interval, May--August 2012, we would make sure to obtain this observation just before the solar-avoidance interval.) (4) We will obtain 4 more observations after the peak of the microlensing, beginning just after the time when the source and the lens are no more blended. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12588( 11) - 18-Sep-2013 13:51:46 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 3 G105-30-SOUR STAR, GRAVITATIONAL RA=06H20M48.2000S +/- 0.1", J2000 V = 16.37 CE LENS DEC=+06D45'17.10" +/- 0.1" Reference Frame: ICRS Comments: The coordinates were calculated using POSS2 red image. The coordinates are that of the source that will be lensed by the WD. ------------------------------------------------------------------------------------------------------------------------------------ 12588( 11) - 18-Sep-2013 13:51:46 - [ 4] Visit: 01 Visit Requirements: ORIENT 258D TO 258 D; BEFORE 25-AUG-2011 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 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F606W 1 50 S (50 POS TARG 9.36, 8.22 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 40 S (40 SAME POS AS 1 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 3 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 100 S (100 SAME POS AS 1 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 4 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 100 S (100 POS TARG 19.62, 2.29 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 5 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 40 S (40 SAME POS AS 4 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 6 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F606W 1 20 S (20 SAME POS AS 5 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 7 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 40 S (40 POS TARG 3.44, 18.48 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 8 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 100 S (100 SAME POS AS 7 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 9 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F850LP 1 160 S (160 SAME POS AS 7 RCE S C-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 | ------------------------------------------------------------------------------------------------------------------------------------ G105-30-SOURCE 1 WFC3/UVI ACCUM UVIS2-2K F606W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 2 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 3 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 4 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB 12588( 11) - 18-Sep-2013 13:51:46 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ G105-30-SOURCE 5 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 6 WFC3/UVI ACCUM UVIS2-2K F606W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 7 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 8 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 9 WFC3/UVI ACCUM UVIS2-2K F850LP none none none none 1 N/A S 2C-SUB 12588( 11) - 18-Sep-2013 13:51:46 - [ 6] Visit: 02 Visit Requirements: BEFORE 07-SEP-2011 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 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 17.192, 9.849 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 13.746, 14.91 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 3 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 7.731, 16.052 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 4 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 2.67, 12.606 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 5 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 1.528, 6.591 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 6 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 4.974, 1.53 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 7 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 10.989, 0.388 RCE S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 8 G105-30-SOU WFC3/UVI ACCUM UVIS2-2K2 F814W 1 110 S (110 POS TARG 16.05 , 3.834 RCE S C-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 | ------------------------------------------------------------------------------------------------------------------------------------ G105-30-SOURCE 1 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 2 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 3 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 4 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 5 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 6 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB 12588( 11) - 18-Sep-2013 13:51:46 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ G105-30-SOURCE 7 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB G105-30-SOURCE 8 WFC3/UVI ACCUM UVIS2-2K F814W none none none none 1 N/A S 2C-SUB 12588( 11) - 18-Sep-2013 13:51:46 - [ 8] Visit: 04 Visit Requirements: ORIENT 275D TO 281 D; BETWEEN 30-SEP-2013 AND 18-OCT-2013 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 G105-30-SOU WFC3/UVI ACCUM UVIS2 F606W FLASH=10 1 40 S (40 POS TARG 0, 0 RCE S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 G105-30-SOU WFC3/UVI ACCUM UVIS2 F606W 1 500 S (500 POS TARG 0, 0; SPATIAL RCE S S) SCAN 0.0040, 1.8612 Degrees, Forward ------------------------------------------------------------------------------------------------------------------------------------ 3 G105-30-SOU WFC3/UVI ACCUM UVIS2 F606W 1 500 S (500 POS TARG 2, 0; SPATIAL RCE S S) SCAN 0.0040, 1.8612 Degrees, Forward ------------------------------------------------------------------------------------------------------------------------------------ 4 G105-30-SOU WFC3/UVI ACCUM UVIS2 F606W 1 500 S (500 POS TARG 0, 0; SPATIAL RCE S S) SCAN 0.0040, 88.091 Degrees, Forward ------------------------------------------------------------------------------------------------------------------------------------ 5 G105-30-SOU WFC3/UVI ACCUM UVIS2 F606W 1 500 S (500 POS TARG 0, 2; SPATIAL RCE S S) SCAN 0.0040, 88.091 Degrees, Forward ------------------------------------------------------------------------------------------------------------------------------------ 6 G105-30-SOU WFC3/UVI ACCUM UVIS2 F606W FLASH=10 1 40 S (40 POS TARG 2, 5 RCE S 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 | ------------------------------------------------------------------------------------------------------------------------------------ G105-30-SOURCE 1 WFC3/UVI ACCUM UVIS2 F606W none none none none 1 N/A S G105-30-SOURCE 2 WFC3/UVI ACCUM UVIS2 F606W none none none none 1 N/A S G105-30-SOURCE 3 WFC3/UVI ACCUM UVIS2 F606W none none none none 1 N/A S G105-30-SOURCE 4 WFC3/UVI ACCUM UVIS2 F606W none none none none 1 N/A S G105-30-SOURCE 5 WFC3/UVI ACCUM UVIS2 F606W none none none none 1 N/A S G105-30-SOURCE 6 WFC3/UVI ACCUM UVIS2 F606W none none none none 1 N/A S 12588( 11) - 18-Sep-2013 13:51:46 - [ 9] Summary Form for Proposal 12588 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2, UVIS2-2K2C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=10 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 07-SEP-2011, BEFORE 25-AUG-2011, BETWEEN 30-SEP-2013 AND 18-OCT-2013, ORIENT 258D TO 258 D, ORIENT 275D TO 281 D, POS TARG 0, 0, POS TARG 0, 2, POS TARG 1.528, 6.591, POS TARG 10.989, 0.388, POS TARG 13.746, 14.91, POS TARG 16.05 , 3.834, POS TARG 17.192, 9.849, POS TARG 19.62, 2.29, POS TARG 2, 0, POS TARG 2, 5, POS TARG 2.67, 12.606, POS TARG 3.44, 18.48, POS TARG 4.974, 1.53, POS TARG 7.731, 16.052, POS TARG 9.36, 8.22, SAME POS AS 1, SAME POS AS 4, SAME POS AS 5, SAME POS AS 7, SPATIAL SCAN 0.0040, 1.8612 Degrees, Forward, SPATIAL SCAN 0.0040, 88.091 Degrees, Forward ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W, F850LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names G105-30-SOURCE ------------------------------------------------------------------------------------------------------------------------------------