Several typos corrected.1264765338Assigned ID: 4
----- Attempting Submission 1 (Fri Feb 07 15:56:29 GMT 2020) -----
HST Phase I Proposal 4 successfully submitted.
Receipt: # 4-1
----- Attempting Submission 2 (Fri Feb 07 17:25:38 GMT 2020) -----
HST Phase I Proposal 4 successfully submitted.
Receipt: # 4-2This is being resubmitted because of schedulability problems. I have expanded the timing range to allow observations earlier in September. It is critical that
the observations be done before the end of October. If this doesn't work, I can drastically reduce the requested observation time per oribt, but I would then
then like to request additional orbits to make up for the lost time. If we would have been made away of this schedulability issue before the proposal was
submitted, we would have requested more orbits.1669039308----- Attempting Submission 1 (Wed Feb 19 03:02:57 GMT 2020) -----
HST Phase II Proposal 16067 successfully submitted.
Receipt: # 16067-1
----- Attempting Submission 2 (Wed Aug 26 20:32:12 GMT 2020) -----Mass Measurement of Isolated Black Hole Candidate MOA-2019-BLG-284L via Lensed Image SeparationWe propose a novel method to measure the mass of the MOA-2019-BLG-284 microlens, which is a black hole candidate due to its extremely long Einstein radius crossing time of 890 days and its low microlensing parallax amplitude. The microlensing parallax is well measured due to the multiyear event duration, and the duration of the event is long enough to suggest a lens mass of more than 20 solar masses. This event will be passing through its peak magnification during 2020, which should allow the measement of a slight image elongation due to the separation of the two relatively bright lensed images. Furthermore, the direction of this elongation will rotate during the year, with a total rotation of about 53 degrees over the course of our proposed observations from March to September, 2020. This rotation will confirm that the image elongation is indeed a gravitational lensing effect. If successful, these observations will determine the lens mass and open a new window on the, as yet unmeasured, isolated black hole population of our Galaxy. This method can be futher exploited by JWST, which shoud be able to make such measurements with higher sensitivity than HST.The observations that we propose are challenging, but if successful, they will open a new window on the population of black holes in our Galaxy and likely contribute to the first ever Galactic census of black holes. We have based our sensitivity estimates on the best stellar separation measurement that has been done in the Galactic bulge with HST, and we have scaled them to account for our much detected photon count. This results in a factor of 3.2 improvement over the previous best measurement. In order to achieve such an improvement, we require significant redundancy so that we can test for and correct systematic errors. Therefore, we have proposed independent measurements in two passbands and three separate visits to measure the expected rotation of the elongated blended image.
We request three visits of two orbits each, with one orbit to observe in each of the F814W and F606W passbands. Three visits are needed in order to measure the rotation of the image orientation. We request 16 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 this means that will be unable to do parallel, full-frame buffer dumps. However, our target is relatively bright, so we want a large enough area to ensure a sufficient number of stars with a similar color and brightness to our target that can be used to construct precise PSF models and calibrate the data. So, we select the UVIS2-C1K1C-SUB subarray to obtain ~25 stars within 0.6 in magnitude and V-I color from the target.
To minimize systematic errors that might interfere with our measurements, we require that each of the visits impose the same pixel grid orientation on the sky. It is not possible to observe our target with exactly the same pixel orientation in two visits separated by ~200 days, so we request orientations that differ by a 180 degree orientation for the first and third visits in order to have the pixel grids lined up between the different visits. It is also not possible to observe our target between May 29 and June 28, so we request our second visit shortly before May 29 or shortly after June 28, with an orientation that is identical to that of the first or third visit.The PI, Daivd Bennett is a Senior Research Scientist at University of Maryland and NASA Goddard Space flight Center, and he has led the development of the methods for measuring small separations between micolens source and lens star with the first such measurement for a planetary system
(Bennett et al. 2006) and the first theoretical paper discussing the the methods to be used for these measurements. Starting from the HST analysis methods developed by CoI Jay Anderson for HST astrometric, Bennett has worked with postdoc Aparna Bhattacharya to develop analysis methods to measure the brightness and separation of unresolved lens and source stars. This method has been quite successful, and it has been able to measure the separation and magnitude of stars in HST V and I-band images when the separations were as small as 12 mas. Our method the state-of-the-art in the field, and no other group has been able to duplicate this work.
Our team includes leaders from both the MOA and OGLE ground based microlensing survey group: Bennett, and Ian Bond Of Massey University In New Zealand lead the MOA group along with Takahiro Sumi, and Andrzej Udalski leads OGLE.
CoI Prof. J. 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, and her student, Casey Lam, built the microlens population synthesis code, PopSyCLE.
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 Populations and the Interstellar Medium0falseSUPPORTEDSTARBULGEGRAVITATIONAL LENSK V-IVJ2000J2000I = 16.3 +- 0.10WFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF555WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF555WWFC3/UVISImagingNoNoF814WWFC3/UVISImagingNoNoF555WThe scheduling data was generated by CASM 28.2.CASM was run in Phase II mode.1584113581000269.0(Tic-Visit
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