8490( 2) - 05/14/99 14:22 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8490 Version: 2 Check-in Date: 13-May-1999 09:43:42 1.Proposal Title: Confirmation of a Gravitational Microlensing Black Hole Candidate ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/DD 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: David Bennett University of Notre Dame CoI: Sun Hong Rhie University of Notre Dame N CoI: Andrew Becker University of Washington N CoI: Andrew Drake Mount Stromlo and Siding Springs N Observatories ------------------------------------------------------------------------------------ 5. Abstract We propose to obtain WFPC2 images of gravitational microlensing event MACHO-96-BLG-5 in mid-1999 in an attempt to confirm the conclusion, based upon MACHO observations, that the lens is a black hole of about 20 solar masses. This event is the longest Galactic microlensing event yet observed with an Einstein diameter crossing time of 1700 days - about 4 times longer than the second longest event, and the microlensing fit to the lightcurve indicates that the lens has a mass of around 20 solar masses. This microlensing fit predicts that the lens will be magnified by a factor of 1.26 in July, 1999, and will be slowly decreasing after this. The DD observations we propose will allow us to observe the decreasing brightness of the lensed star and test the black hole microlensing model. ------------------------------------------------------------------------------------ 8490( 2) - 05/14/99 14:22 - [ 2] Observations Description ------------------------ We plan 4 160 sec exposures in F814W and 2 400 sec exposures using the F555W filter. The seperate exposures will be dithered for maximum angular resolution. Real Time Justification ----------------------- The requested observations of microlensing event MACHO-96-BLG-5 are time critical. The microlensing fit to the MSO and CTIO photometry of this event indicate that the lens is dark and has a mass of about 20 solar masses. Because the event is still in progress, it is possible to confirm crucial details of this lens fit with DD time WFPC2 observations.The magnification reached its peak at the end of 1996 and it is now decreasing. The source star is blended with unlensed neighbors, so that it contributes only 14% of the flux of the "star" seen in ground based images.Its current magnification is a factor of 1.29, and it will fall to 1.26 by early July. Due to the effects of blending, the magnification as seen from the ground will be only about 1.02, so HST observations are required to detect a significant magnification at present. By July, 2000, the magnification factor will be 1.12, and by July of 2001, the magnificationfactor will be 1.06. Thus, the DD observation proposed her e will allow a test of the microlensing model with observations at magnifications of 1.26 in July, 1999, 1.12 in July, 2000, and 1.06 in July, 2001 (assuming an allocation of 2 orbits in cycle 9). With 2-3% relative photometry between the different observations, the proposed DD time observation will allow a much more stringent test of the microlensing hypothesis than would bepossible with only observations in cycles 9 or greater. Calibration Justification ------------------------- none. Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: YES Media: 8MM_HI Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8490( 2) - 05/14/99 14:22 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MACHO-96-BLG STAR, BULGE RA=18H 5M 2.5S +/- 2", DEC=-27D J2000 V = 21.9+/-0.2 -5 42' 17" +/- 2" R = 21.1+/-0.2 8490( 2) - 05/14/99 14:22 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BEFORE 15-Oct-1999 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 MACHO-96-BL WFPC2 IMAGE PC1 F814W DITHER-TYPE=BOX,ATD-GAIN=15 1 160 S G-5 ------------------------------------------------------------------------------------------------------------------------------------ 20 MACHO-96-BL WFPC2 IMAGE PC1 F555W DITHER-TYPE=LINE,ATD-GAIN=15 1 400 S G-5 ------------------------------------------------------------------------------------------------------------------------------------ 8490( 2) - 05/14/99 14:22 - [ 5] Summary Form for Proposal 8490 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters DITHER-TYPE=BOX ATD-GAIN=15 DITHER-TYPE=LINE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 15-Oct-1999 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names MACHO-96-BLG-5 ------------------------------------------------------------------------------------------------------------------------------------