0 Assigned ID: 1837 ----- Attempting Submission 1 (Fri Apr 09 06:37:30 GMT 2021) ----- HST Phase I Proposal 1837 successfully submitted. Receipt: # 1837-1 ----- Attempting Submission 2 (Fri Apr 09 19:50:18 GMT 2021) ----- HST Phase I Proposal 1837 successfully submitted. Receipt: # 1837-2 ----- Attempting Submission 3 (Fri Apr 09 22:30:25 GMT 2021) ----- HST Phase I Proposal 1837 successfully submitted. Receipt: # 1837-3 ----- Attempting Submission 4 (Fri Apr 09 22:56:05 GMT 2021) ----- HST Phase I Proposal 1837 successfully submitted. Receipt: # 1837-4 ----- Attempting Submission 5 (Fri Apr 09 23:11:59 GMT 2021) ----- HST Phase I Proposal 1837 successfully submitted. Receipt: # 1837-5 ----- Attempting Submission 6 (Fri Apr 09 23:33:38 GMT 2021) ----- HST Phase I Proposal 1837 successfully submitted. Receipt: # 1837-6 ----- Attempting Submission 7 (Fri Apr 09 23:45:30 GMT 2021) ----- HST Phase I Proposal 1837 successfully submitted. Receipt: # 1837-7 FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser Added text to observing description and further clarified some comments, everything else is the same as original submission. 2074361455 ----- Attempting Submission 1 (Wed Jul 28 23:45:53 GMT 2021) ----- HST Phase II Proposal 16760 successfully submitted. Receipt: # 16760-1 ----- Attempting Submission 2 (Thu Jul 29 18:11:46 GMT 2021) ----- Ignoring warnings about FLASH, since new minimum UVIS image total background now recommended at least 20 e-/pix. First detection of an isolated stellar mass black hole with astrometric microlensing We propose to confirm the detection of the first isolated black hole (BH), OB110462. We analyzed archival HST data with improved astrometric techniques and demonstrate that the 3 sigma lower mass limit of OB110462 is 5 Msun, making it a solid BH detection. However, the allowed mass range of the BH is quite wide (68% CI of 9-31 Msun), due to the lack of sufficient time baseline of the archival data. We propose to obtain a new measurement of the target, now 10 years after the lensing event, in order to better constrain the baseline proper motion. This will allow the mass constraints of the BH to be improved by a factor of at least 2. This will provide the first mass measurement of an isolated BH, which will inform theoretical models of massive star death, the Milky Way BH mass distribution, and the population of BH-BH binaries discovered via gravitational waves. We will observe two additional epochs of OB110462 in order to increase our time baseline to more precisely measure its proper motion, and in turn its mass. In order to match past observations and better understand color-dependent astrometric effects, we will image using WFC3-UVIS in both F814W and F606W filters. For observations in each filter, we will dither a small amount 5-6 times to sample the pixel phase and maximize our SNR. We will also take our observations in the same ORIENT as the past observations to minimze astrometric systematics due to unmodeled camera distortion and seasonal effects. In terms of the possibility of HST going into reduced gyro mode (RGM), the astrometry technique we are using is not the spatial-scan technique, so will not be affected by RGM. In addition, our observations are more affected by systematic errors, not FWHM or SNR, and so nominal changes in these metrics due to RGM will not adversely affect the proposed observations. 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. Prof. Lu advises UC Berkeley graduate student Casey Lam, who has built the population synthesis codes and worked on high-precision astrometry with HST microlensing data. Stellar Physics and Stellar Types 6 false false false false false false false false SUPPORTED STAR BULGE J2000 J2000 WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W POS-TARG DITHER 0.13 LINE false false 6 45 SPIRAL 1 false POS-TARG DITHER 0.13 LINE false false 5 45 SPIRAL 2 false /g/lu/scratch/jlu/doc/proposals/hst/cycle29/ob110462/OP-cache/Cycle29_OB110462-v01.xml Timing link suitability includes constraints ([02 After 01 by 180.0 to 360.0 days]) The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. It would be strongly preferred that this visit be scheduled in October 2021 if possible, when ORIENT is between 88 and 96 degrees. (Tic-Visit :proposal-id 16760 :visit-id "01" :proposal-version -1 :trans-version "20210514" :date "28-Jul-2021 16:17:58.0" :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 774256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16760 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16760 :visit-id "01" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2780 :al-overhead-at-end 174 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3165 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16760 :visit-id "01" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2771 :al-overhead-at-end 170 :internal-dur-at-end 652 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3165 :pcs-gap 0 ) true 2 0 /g/lu/scratch/jlu/doc/proposals/hst/cycle29/ob110462/OP-cache/Cycle29_OB110462-v02.xml Timing link suitability includes constraints ([02 After 01 by 180.0 to 360.0 days]) The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. It would be strongly preferred that this visit be scheduled August 2022 or after, if possible, when ORIENT is between 88 to 96 degrees. (Tic-Visit :proposal-id 16760 :visit-id "02" :proposal-version -1 :trans-version "20210514" :date "28-Jul-2021 16:17:45.0" :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 774256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16760 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16760 :visit-id "02" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2780 :al-overhead-at-end 174 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3165 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16760 :visit-id "02" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2771 :al-overhead-at-end 170 :internal-dur-at-end 652 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3165 :pcs-gap 0 ) true 2 0