This proposal aims to make the first detection of isolated stellar-mass black holes (BHs) in the Milky Way, and to determine their masses. Until now, the only directly measured BH masses have come from radial-velocity measurements of X-ray binaries. Our proposed method uses the astrometric shifts that occur when a Galactic-bulge microlensing event is caused by a BH lens. Out of the hundreds of bulge microlensing events found annually by the OGLE and MOA surveys, a few are found to have very long durations (>200 days). It is generally believed that the majority of these long-duration events are caused by lenses that are isolated BHs. To test this hypothesis, we will carry out high-precision astrometry of 5 long-duration events, using the ACS/HRC camera. The expected astrometric signal from a BH lens is >1.4 mas, at least 7 times the demonstrated astrometric precision attainable with the HRC. This proposal will thus potentially lead to the first unambiguous detection of isolated stellar-mass BHs, and the first direct mass measurement for isolated stellar-mass BHs through any technique. Detection of several BHs will provide information on the frequency of BHs in the Galaxy, with implications for the slope of the IMF at high masses, the minimum mass of progenitors that produce BHs, and constraints on theoretical models of BH formation.

We will select long-duration events which do not show any light contribution from the lens. In addition, the events should have reasonably high amplifications which will ensure that the centroid shift is close to zero at the peak amplification, and will facilitate detection of the parallax signal and hence the distance estimate for the lens. It is easy to identify long-duration events and to determine their time of peak amplification well before the actual peak. Our group includes members of the microlensing survey teams who have access to the survey data for proper selection of such events. To guard against the possibility that the geometric distortion may be dependeant on the location on the detector; we will position the target at different locations along close-to-central-x-axis of the of the detector. We will take most images in a single filter, but also take a small number of images in a different filter to check the color dependenacy, if any, of the astrometric shift. We will try to take as many images as possible in a single ORIENT for better astrometri accuracy. However, maintaining a single ORIENT may not be possible for all the observations. Since almost all of our targets are close to the ecliptic, we plan to use the same orient for nearly half of the year, and then flip it by 180 deg. HOT STARS 12 false 0.0 0.0 false false false false false false AVAILABLE STAR BULGE GRAVITATIONAL LENS J2000 17 30 0.0000 -29 00 0.00 J2000 STAR BULGE GRAVITATIONAL LENS J2000 17 30 0.0000 -29 00 0.00 J2000 STAR BULGE GRAVITATIONAL LENS J2000 17 30 0.0000 -29 00 0.00 J2000 STAR GRAVITATIONAL LENS J2000 17 30 0.0000 -29 00 0.00 J2000 STAR GRAVITATIONAL LENS J2000 17 30 0.0000 -30 00 0.00 J2000 ACS/HRC Imaging No No F814W ACS/HRC Imaging No No F555W ACS/HRC Imaging No No F814W ACS/HRC Imaging No No F555W ACS/HRC Imaging No No F814W ACS/HRC Imaging No No F555W ACS/HRC Imaging No No F814W ACS/HRC Imaging No No F555W ACS/HRC Imaging No No F814W ACS/HRC Imaging No No F555W 1282533896000 90.0 (Tic-Visit :proposal-id 11707 :visit-id "01" :proposal-version -1 :trans-version "20100218" :date "11-Aug-2010 03:34:52.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 985744 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2821 :al-overhead-at-end 216 :internal-dur-at-end 500 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. 1254377203000 95.0 (Tic-Visit :proposal-id 11707 :visit-id "05" :proposal-version -1 :trans-version "20090130" :date "04-Jul-2009 09:53:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 985744 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2777 :al-overhead-at-end 218 :internal-dur-at-end 500 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. 1255918657000 95.0 (Tic-Visit :proposal-id 11707 :visit-id "06" :proposal-version -1 :trans-version "20090702" :date "07-Oct-2009 20:03:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 985744 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2817 :al-overhead-at-end 216 :internal-dur-at-end 500 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1284340262000 90.0 (Tic-Visit :proposal-id 11707 :visit-id "02" :proposal-version -1 :trans-version "20100218" :date "07-Sep-2010 12:53:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1126560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2374 :al-overhead-at-end 218 :internal-dur-at-end 654 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3275 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1275881131000 270.0 (Tic-Visit :proposal-id 11707 :visit-id "10" :proposal-version -1 :trans-version "20100218" :date "26-May-2010 15:27:47.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1126560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "10" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2774 :al-overhead-at-end 218 :internal-dur-at-end 654 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1277086203000 318.0 (Tic-Visit :proposal-id 11707 :visit-id "09" :proposal-version -1 :trans-version "20100218" :date "09-Jun-2010 09:17:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 704112 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "09" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2868 :al-overhead-at-end 216 :internal-dur-at-end 500 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1280106546000 90.0 (Tic-Visit :proposal-id 11707 :visit-id "04" :proposal-version -1 :trans-version "20091209" :date "01-Jul-2010 15:10:53.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 704112 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2833 :al-overhead-at-end 216 :internal-dur-at-end 500 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1269281208000 275.0 (Tic-Visit :proposal-id 11707 :visit-id "07" :proposal-version -1 :trans-version "20100218" :date "09-Mar-2010 14:36:30.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 844944 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2871 :al-overhead-at-end 216 :internal-dur-at-end 654 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. 1276528323000 275.0 (Tic-Visit :proposal-id 11707 :visit-id "08" :proposal-version -1 :trans-version "20091209" :date "01-Jun-2010 09:09:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 844944 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "08" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2746 :al-overhead-at-end 216 :internal-dur-at-end 654 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 18.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11707 :visit-id "11" :proposal-version -1 :trans-version "20100218" :date "05-Oct-2010 13:15:43.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 844944 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11707 :visit-id "11" :obset-id "11" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11707 :visit-id "11" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2844 :al-overhead-at-end 216 :internal-dur-at-end 654 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) false 1 0