My local copy had an error in the FLASH parameter for one of the exposures. I'm not sure if the submitted phase II proposal had this error, but this one is correct. 871880979 ----- Attempting Submission 1 (Sun Aug 11 23:20:27 GMT 2024) ----- HST Phase II Proposal 17838 successfully submitted. Receipt: # 17838-1 ----- Attempting Submission 2 (Tue Aug 13 15:38:04 GMT 2024) ----- We propose Hubble imaging of the black hole candidate microlens system MOA-2019-BLG-284 in order to measure the astrometric microlensing signal and determine the lens system mass. Microlensing is the only method that can detect black holes that are isolated or in stable, non-accreting binary systems, so routine detection of black hole astrometric microlensing will provide a significant advance in our understanding of the formation of stellar mass black holes. Our proposed observations will determine if the MOA-2019-BLG-284 lens system is a rare stable binary system with a black hole primary or an isolated stellar mass black hole. This observing program is designed to address possible systematic errors in the astrometric measurements. We will also use the Hubble data to correct systematic errors in the ground-based photometry that determines the microlensing parallax. Since both astrometric microlensing and microlensing parallx measurements are needed to determine black hole masses, an understanding of systematic errors in both quantaties is needed for reliable mass measurements. The novel systematic error correction methods that we propose may be used to increase the sensitivity of future black hole mass measurements from astrometric and photometric microlensing. We request two visits per year of two orbits each, with one orbit to observe in each of the F814W and F606W passbands. This is 4 orbits per year for a total of 12 orbits over 3 years. We require a time series of data in both the F814W and F606W passbands for two reasons. First, we can get redundant astrometry measurements with two passband, and this will help to understand possible systematic astrometry errors. The two passbands will also provide a critical test of the possibility of models with binary source stars, since astrometric microlensing of binary source stars is generally color dependent. The spring and fall data are necessary in order to obtain a time series of observations with roll angles changing by 180 degrees every ~ 6 months. This will provide yearly imaging with PSF distortions due to CTE losses in nearly opposite directions in alternate visits. The roll angles used will be the same as two previous observing programs for this target (Bennett et al. 2020, Terry et al. 2021) in order to provide two long duration, independent data sets with nearly opposite directions of CCD charge transfer. The strongest astrometric microlensing signals are expected at twice the Einstein radius crossing time ( ~ 570 days) after the event peak, which will be in mid-2023 for MB19284. However, as Dominik & Sahu (2002) point out, it is necessary to make astrometric microlensing observations for a longer duration (at least 3 Einstein radius crossing times) to separate the astrometric microlensing signal from the linear proper motion of the source star. We propose observations over 3 cycles to obtain the last observation at 3.6 Einstein radius crossing times after the light curve peak. We request 18 exposures per orbit in the WFC3/UVIS F814W and F606W passbands to get good spatial sampling of the effective PSFs (Anderson and King 2000) and to avoid saturation. So, we select the UVIS2-C1K1C-SUB subarray to minimize PSF distortions due to the effects of CTE degradation. We require observations within two weeks of one of our May and September 2020 and 2021 observations in order to minimize the effect of parallax motion of our astrometric reference stars between visits in different years. The PI, Daivd Bennett is a Senior Research Scientist at University of Maryland and NASA Goddard Space flight Center, and he has led the first Hubble and Keck Laser Guide star programs to observe MOA-2019-BLG-284 in 2020. He also leads the software development for the exoplanet microlensing survey for the Nancy Grace Roman Space Telescope and is co-leader of an exoplanet microlensing high angular resolution follow-up group that had developed custom software to analyze Hubble and Keck AO data. The co-leader of this microlensing follow-up is Jean-Phillpe Beaulieu, a senior researcher at the Institut d'Astrophysique ds Paris and visiting faculty at University of Tasmania. The other members of this group (who do most of the work) include research scientist Aparna Bhattacharya, and postdocs Naoki Koshimoto, and Aikaterini Vandorou, at NASA Goddard, Joshua Blackman at the University of Tasmania, Clement Ranc at the University of Heidelberg, and Sean Terry at UC, Berkeley. Our team includes leaders from both the MOA and OGLE ground based microlensing survey groups. Bennett, Ian Bond Of Massey University In New Zealand, and Takahiro Sumi of Osaka University lead the MOA group. Bennett was the first to identify the systematic photometry errors due to color dependent atmospheric refraction, and Bennett and Bond developed methods to correct these systematic errors to the extent that these can be corrected without high angular resolution imaging. Our team includes OGLE group leader Andrzej Udalski, and OGLE group members Przemek Mroz and Jan Skowron, who led the analysis to remove a systematic photometry error due to the proper motion of a nearby star from the analysis of planetary microlensing event OGLE-2013-BLG-0341 (Gould et al. 2014). CoI Prof. Jessica Lu has expertise in high-precision astrometry both from ground-based adaptive optics and HST observations. Prof. Lu has used high-precision astrometry to study resolved stellar populations throughout the Milky Way, including showing evidence for a top-heavy IMF in the massive, young clusters in the Galactic Center and disk and conducting the first search for astrometric microlensing signals by black holes from the ground. Lu and her group also develop microlens modeling codes. Prof. Lu's student Casey Lam, built the microlens population synthesis code, PopSyCLE, and led one of the discovery papers for the first stellar mass black hole to be found by astrometric microlensing. Prof. Lu's postdoc and Co-PI Sean Terry also works on Dr. Lu's high precision astrometry group, and has led early astrometric and photometric analysis of the MOA-2019-BLG-284 black hole candidate. Our team also includes Jean-Phillpe Beaulieu, a senior researcher in CNRS, IAP and visiting faculty at University of Tasmania. Beaulieu has led the Keck AO observing effort that is done in close cooperation with our HST program. He has published numerous papers on microlensing follow-up observations including mass measurements of the first two planets found by microlensing to orbit a solar type star (Beaulieu et al. 2016). Stellar Physics and Stellar Types Stellar Populations and the Interstellar Medium 6 false false false false false false false false SUPPORTED STAR BULGE GRAVITATIONAL LENS K V-IV J2000 J2000 I = 15.97 +- 0.05 WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W 1723563324718 The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. /private/var/folders/79/rv_1w6j53vn8svxjqq2dc8gc0000gp/T/OPVisit13065220795928992924.xml (Tic-Visit :proposal-id 17838 :visit-id "01" :proposal-version -1 :trans-version "20240604" :date "13-Aug-2024 11:35:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 534736 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17838 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17838 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2637 :al-overhead-at-end 87 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3034 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17838 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2642 :al-overhead-at-end 87 :internal-dur-at-end 621 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3034 :pcs-gap 0 ) true 2 0 1723417673635 The scheduling data was generated by CASM 32.1.1. 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