16782( 3) - 31-Jan-2023 11:50:32 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16782 Version: 3 Check-in Time: 31-Jan-2023 11:50:32 STScI Edit Number: 0 Title Discovering Isolated Stellar-Mass Black Holes Using Astrometric Microlensing ------------------------------------------------------------------------------------ Type Cycle GO 29 ------------------------------------------------------------------------------------ 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. 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. Andrzej Udalski Warsaw University N ------------------------------------------------------------------------------------ Abstract There should be ~100 million black holes (BHs) in our Galaxy, of which the majority should be single. Yet there has been no unambiguous detection of a solitary BH--not surprisingly, since they emit essentially no radiation. Astrometric microlensing--the relativistic deflection of light from a background star--is the only technique that can detect isolated BHs. HST has demonstrated its capability to measure such tiny deflections. A multi-year HST program of precision astrometry of long-duration microlensing events in the Galactic bulge is underway, aimed at the first detection of isolated BHs. This program has achieved clear detections of deflections in two events, consistent with non-luminous massive lenses. However, the timing of the observations was sub-optimal due to some guide-star failures and the HST gyro failure in 2018. As a result, there remains a degeneracy between deflection, parallax, and proper motion; an unusually slow-moving low-mass lens remains a possibility. One more observation of these two targets will resolve this degeneracy. Observations of another event had to be abandoned when HST revealed a blended source. Because of the 2018 HST gyro failure, initiation of two new events had to be delayed until 2019. These events are still ongoing and need a total of five orbits for completion. One of the BH candidate sources is extremely red, which can be best explained by a shell around the putative BH. A 1-orbit STIS spectrum, and a final WFC3 image in Cycle 29, will test this hypothesis. Thus a total of 9 orbits (7 in Cycle 28 and 2 in Cycle 29) are needed to achieve the original objectives of the program, and to confirm the potentially exciting findings. ------------------------------------------------------------------------------------ Observations Description ------------------------ WFC3 imaging to measure astrometric deflections. We will employ an observational strategy similar to that used in the GO-15318 program. We will image each field using WFC3/UVIS, primarily with the F814W filter, but also with F606W. In a rich stellar field such as the Galactic bulge, there is always a large 16782( 3) - 31-Jan-2023 11:50:32 - [ 2] number of reference stars available in the WFC3 field, even with the subarrays that we will use to avoid buffer dumps. This allows the highest possible astrometric accuracy. For the astrometric analysis, we will basically use procedures described in previous HST studies, including Anderson & King (2004) and Bellini (2014). Very similar techniques were used by Sahu et al. (2017) to detect the relativistic deflection of a background star by the nearby white dwarf Stein2051B, leading to a mass determination for this isolated object. STIS spectroscopy of OGLE-2017-BLG-328. We will use G750L with a 0.2" slit to obtain a classification spectrum of the source. This setting covers a wavelength range of 5240-10265 A. The STIS ETC indicates that a one-orbit exposure will reach a S/N per resolution element of ~22 at 7500 A, which is more than adequate for spectral classification and inference of the intrinsic color. As indicated in phase-I, we may have to re-adjust the orbit distribution for the targets based on the results from the first few observations. So the targets in vists 5 and 6 are specified as "DUMMY", which will be replaced with specific targets later on. ------------------------------------------------------------------------------------ 16782( 3) - 31-Jan-2023 11:50:32 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 8 OGLE-2017-BL EXT-STAR, A0-A3 III-I RA=17H41M35.9300S, J2000 V = 19.25 +/- 2 G-0302 DEC=-34D33'19.30" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 7 OGLE-2019-BL EXT-STAR, A0-A3 III-I RA=18H10M4.4700S, J2000 V = 19.25 +/- 2 G-1080 DEC=-27D52'1.40" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 16782( 3) - 31-Jan-2023 11:50:32 - [ 4] Visit: 01 Visit Requirements: ORIENT 251.93D TO 251.93 D; BETWEEN 15-MAR-2023 AND 29-MAR-2023 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 OGLE-2017-B WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=11 1 318 S (318 POS TARG 0, 0; GS ACQ LG-0302 S 1C-SUB S) SCENARIO BASE1B3 ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-2017-B WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=11 1 318 S (318 POS TARG 3.95, 0 LG-0302 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OGLE-2017-B WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=11 1 318 S (318 POS TARG 1.97, 3.42 LG-0302 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OGLE-2017-B WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=11 1 318 S (318 POS TARG -1.98, 3.42 LG-0302 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OGLE-2017-B WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=11 1 318 S (318 POS TARG -3.95, -0.02 LG-0302 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 6 OGLE-2017-B WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=11 1 318 S (318 POS TARG -1.96, -3.43 LG-0302 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 7 OGLE-2017-B WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=11 1 318 S (318 POS TARG 2.00, -3.41 LG-0302 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 | ------------------------------------------------------------------------------------------------------------------------------------ OGLE-2017-BLG-0302 1 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2017-BLG-0302 2 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2017-BLG-0302 3 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2017-BLG-0302 4 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2017-BLG-0302 5 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2017-BLG-0302 6 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2017-BLG-0302 7 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB 16782( 3) - 31-Jan-2023 11:50:32 - [ 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 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F814W CR-SPLIT=NO, FLASH=12 1 216 S (216 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO, FLASH=12 1 216 S (216 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO, FLASH=12 1 216 S (216 POS TARG 3.95, 0.1 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO, FLASH=12 1 216 S (216 POS TARG 2.79, 2.79 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO, FLASH=12 1 216 S (216 POS TARG 0, 3.95 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 6 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F814W CR-SPLIT=NO, FLASH=12 1 216 S (216 POS TARG 0, 3.95 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 7 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO, FLASH=12 1 216 S (216 POS TARG -2.79, 2.8 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 8 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO, FLASH=12 1 216 S (216 POS TARG -3.95, 0 LG-1080 S 1C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 9 OGLE-2019-B WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO, FLASH=12 1 216 S (216 POS TARG -2.68, -2.79 LG-1080 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 | ------------------------------------------------------------------------------------------------------------------------------------ OGLE-2019-BLG-1080 1 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2019-BLG-1080 2 WFC3/UVI ACCUM UVIS2-C1 F606W none none none none 1 N/A S K1C-SUB OGLE-2019-BLG-1080 3 WFC3/UVI ACCUM UVIS2-C1 F606W none none none none 1 N/A S K1C-SUB OGLE-2019-BLG-1080 4 WFC3/UVI ACCUM UVIS2-C1 F606W none none none none 1 N/A S K1C-SUB 16782( 3) - 31-Jan-2023 11:50:32 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ OGLE-2019-BLG-1080 5 WFC3/UVI ACCUM UVIS2-C1 F606W none none none none 1 N/A S K1C-SUB OGLE-2019-BLG-1080 6 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 N/A S K1C-SUB OGLE-2019-BLG-1080 7 WFC3/UVI ACCUM UVIS2-C1 F606W none none none none 1 N/A S K1C-SUB OGLE-2019-BLG-1080 8 WFC3/UVI ACCUM UVIS2-C1 F606W none none none none 1 N/A S K1C-SUB OGLE-2019-BLG-1080 9 WFC3/UVI ACCUM UVIS2-C1 F606W none none none none 1 N/A S K1C-SUB 16782( 3) - 31-Jan-2023 11:50:32 - [ 7] Summary Form for Proposal 16782 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO, FLASH=11, FLASH=12 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 15-MAR-2023 AND 29-MAR-2023, GS ACQ SCENARIO BASE1B3, ORIENT 251.93D TO 251.93 D, POS TARG -1.96, -3.43, POS TARG -1.98, 3.42, POS TARG -2.68, -2.79, POS TARG -2.79, 2.8, POS TARG -3.95, -0.02, POS TARG -3.95, 0, POS TARG 0, 0, POS TARG 0, 3.95, POS TARG 1.97, 3.42, POS TARG 2.00, -3.41, POS TARG 2.79, 2.79, POS TARG 3.95, 0, POS TARG 3.95, 0.1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names OGLE-2017-BLG-0302, OGLE-2019-BLG-1080 ------------------------------------------------------------------------------------------------------------------------------------