17397( 5) - 05-Jul-2024 14:48:45 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17397 Version: 5 Check-in Time: 05-Jul-2024 14:48:45 STScI Edit Number: 1 Title Confirming the first isolated dark stellar remnant candidate discovered by interferometric microlensing ------------------------------------------------------------------------------------ Type Cycle GO/DD 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Subo Dong Peking University Y CoI: Dr. Andrew Gould The Ohio State University N CoI: Dr. Przemek Mroz Warsaw University N CoI: Dr. Antoine Merand European Southern Observatory - Germany N CoI: Dr. Jinyi Shangguan Max Planck Institute for Extraterrestrial N Physics ------------------------------------------------------------------------------------ Abstract We propose to confirm an isolated dark stellar remnant candidate identified based on the recently established method of VLTI-GRAVITY interferometric microlensing. The present mass measurement of the lens (2.20^{+0.31}_{-0.23} Msun) is consistent with either a neutron star or a low-mass black hole in the so-called "mass gap", and it will improve to a much better precision of ~5% when the complete light curve becomes available in 2024. However, the lens can also be a normal star blended with the microlensed red giant source, and the possibility of a luminous lens can only be definitively distinguished from a dark lens with the proposed HST observations. If the lens is confirmed to be dark by HST, it will be the first isolated low-mass dark stellar remnant having a mass measurement, with exciting potential implications on the physics of compact objects and their formation pathways. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will use the UVIS channel of WFC3 to image the target in both F555W (V) and F814W (I) at two epochs. (An adjustment is made from F606W to F555W proposed in Phase 1 to yield a more precise result.) The first epoch is very time-critical, and the sooner it is executed, the higher the magnification for leveraging the blended flux constraint. The upcoming available window is in August 2023, and if possible, it should be scheduled by mid-August when the event is magnified with A~1.2. The scheduling of first epoch should absolutely be no later than October 2023 when the event is still magnified with A=1.1. The second epoch needs to be scheduled in 2024 when the event returns to the baseline. The UVIS2-C1K1C-SUB subarray mode will be used to avoid buffer dumps, optimize observing efficiency, and minimize the CTE effects. For the first epoch (~Aug 15), we expect the target to be at (V, I) ~ (18.7, 15.2), after making careful magnitude calibrations. We plan to take multiple 17397( 5) - 05-Jul-2024 14:48:45 - [ 2] exposures for each filter to mitigate the possible effects of CRs, artifacts, or imperfectly subtracted hot pixels. For F555W and F814W, seven and five exposures will be taken, respectively. For each exposure, we use ETC to ensure obtaining sufficient SNR and also the peak pixel being well below saturation. We will follow the 7-point and 5-point dithering patterns in Instrument Science Report WFC3 2020-07 (Anderson 2020). The seven/five points spread the target around in the pixel phase to obtain a well-sampled image for optimizing high-precision photometry. The second epoch has the same observing strategy as the first epoch to optimize differential photometry. ------------------------------------------------------------------------------------ 17397( 5) - 05-Jul-2024 14:48:45 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 KMT-2023-BLG STAR, K III-I RA=17H31M42.6125S, J2000 V = 18.7 +/- 0.2 I ~ 15.2+/-0.1 -0025 DEC=-30D46'17.02" Reference Frame: ICRS Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016.0 1.5851670579270261E-4 -0.005642 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17397( 5) - 05-Jul-2024 14:48:45 - [ 4] Visit: 01 Visit Requirements: BETWEEN 01-AUG-2023:00:00:00 AND 31-OCT-2023:00:00:00 On Hold Comments: Additional Comments: This visit must be made as soon as possible, by mid-August 2023 if at all possible, but absolutely no later than October 2023. 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 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0, 0 G-0025 S 1C-SUB see below (231 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.0894, 0.3341 G-0025 S 1C-SUB see below (231 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.1785, 0.1908 G-0025 S 1C-SUB see below (231 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.2679, 0.5249 G-0025 S 1C-SUB see below (231 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.3173, 0.3591 G-0025 S 1C-SUB see below (231 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.4100, 0.6967 G-0025 S 1C-SUB see below (231 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.5024, 0.5158 G-0025 S 1C-SUB see below (231 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0, 0 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 9 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.1719, 0.1837 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 10 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.3437, 0.3674 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 17397( 5) - 05-Jul-2024 14:48:45 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.4760, 0.5286 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 12 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.6544, 0.6796 G-0025 S 1C-SUB see below (25 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 | ------------------------------------------------------------------------------------------------------------------------------------ KMT-2023-BLG-0025 1 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 231.0 S S K1C-SUB KMT-2023-BLG-0025 2 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 231.0 S S K1C-SUB KMT-2023-BLG-0025 3 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 231.0 S S K1C-SUB KMT-2023-BLG-0025 4 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 231.0 S S K1C-SUB KMT-2023-BLG-0025 5 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 231.0 S S K1C-SUB KMT-2023-BLG-0025 6 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 231.0 S S K1C-SUB KMT-2023-BLG-0025 7 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 231.0 S S K1C-SUB KMT-2023-BLG-0025 8 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 9 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 10 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 11 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 12 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB 17397( 5) - 05-Jul-2024 14:48:45 - [ 6] Visit: 02 Visit Requirements: ORIENT 34.6D TO 104.6 D; ORIENT 124.6D TO 194.6 D; ORIENT 214.6D TO 284.6 D; ORIENT 304.6D TO 14.6 D; BETWEEN 01-FEB-2024:00:00:00 AND 31-OCT-2025:00:00:00 On Hold Comments: Additional Comments: We apply various Orient constraints to avoid diffraction spikes landing near our target. 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 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0, 0 G-0025 S 1C-SUB see below (211 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.0894, 0.3341 G-0025 S 1C-SUB see below (211 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.1785, 0.1908 G-0025 S 1C-SUB see below (211 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.2679, 0.5249 G-0025 S 1C-SUB see below (211 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.3173, 0.3591 G-0025 S 1C-SUB see below (211 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.4100, 0.6967 G-0025 S 1C-SUB see below (211 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F555W FLASH=14 1 236 S POS TARG 0.5024, 0.5158 G-0025 S 1C-SUB see below (209 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0, 0 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 9 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.1719, 0.1837 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 10 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.3437, 0.3674 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 17397( 5) - 05-Jul-2024 14:48:45 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 11 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.4760, 0.5286 G-0025 S 1C-SUB see below (25 S) ------------------------------------------------------------------------------------------------------------------------------------ 12 KMT-2023-BL WFC3/UVI ACCUM UVIS2-C1K F814W FLASH=20 1 30 S POS TARG 0.6544, 0.6796 G-0025 S 1C-SUB see below (25 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 | ------------------------------------------------------------------------------------------------------------------------------------ KMT-2023-BLG-0025 1 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 211.0 S S K1C-SUB KMT-2023-BLG-0025 2 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 211.0 S S K1C-SUB KMT-2023-BLG-0025 3 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 211.0 S S K1C-SUB KMT-2023-BLG-0025 4 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 211.0 S S K1C-SUB KMT-2023-BLG-0025 5 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 211.0 S S K1C-SUB KMT-2023-BLG-0025 6 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 211.0 S S K1C-SUB KMT-2023-BLG-0025 7 WFC3/UVI ACCUM UVIS2-C1 F555W none none none none 1 209.0 S S K1C-SUB KMT-2023-BLG-0025 8 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 9 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 10 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 11 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB KMT-2023-BLG-0025 12 WFC3/UVI ACCUM UVIS2-C1 F814W none none none none 1 25.0 S S K1C-SUB 17397( 5) - 05-Jul-2024 14:48:45 - [ 8] Summary Form for Proposal 17397 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=14, FLASH=20 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-AUG-2023:00:00:00 AND 31-OCT-2023:00:00:00, BETWEEN 01-FEB-2024:00:00:00 AND 31-OCT-2025:00:00:00, ORIENT 124.6D TO 194.6 D, ORIENT 214.6D TO 284.6 D, ORIENT 304.6D TO 14.6 D, ORIENT 34.6D TO 104.6 D, POS TARG 0, 0, POS TARG 0.0894, 0.3341, POS TARG 0.1719, 0.1837, POS TARG 0.1785, 0.1908, POS TARG 0.2679, 0.5249, POS TARG 0.3173, 0.3591, POS TARG 0.3437, 0.3674, POS TARG 0.4100, 0.6967, POS TARG 0.4760, 0.5286, POS TARG 0.5024, 0.5158, POS TARG 0.6544, 0.6796 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names KMT-2023-BLG-0025 ------------------------------------------------------------------------------------------------------------------------------------