11311( 9) - 23-Jan-2008 18:14:04 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11311 Version: 9 Check-in Time: 23-Jan-2008 18:14:04 STScI Edit Number: 6 Title The high-amplification microlensing event OGLE-2007-BLG-224: a substellar lens in the Galactic disk or a low-mass stellar lens in the halo? ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO/DD 15 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Kailash Sahu Space Telescope Science Institute CoI: Dr. David P. Bennett University of Notre Dame N CoI: Dr. Andrew Gould The Ohio State University Research N Foundation CoI: Dr. Martin Dominik University of St. Andrews N CoI: Dr. Andrzej Udalski Warsaw University N CoI: Dr. Takahiro Sumi Nagoya University N ------------------------------------------------------------------------------------ Abstract OGLE-2007-BLG-224/MOA-2007-BLG-163 is a remarkable microlensing event towards the Galactic bulge, which peaked on May 12, 2007. The light curve reached a peak magnification of ~3700, which is the highest magnification ever observed. The color and magnitude of the source indicate that it is a G-dwarf in the Galactic bulge, and source radius crossing time of t* = 8.2 minutes implies that the lens-source relative proper motion is 45 mas/yr. This indicates that the lens must either be a very nearby brown dwarf, or a halo star. The HST observations proposed here provide a very good chance to distinguish between these two possibilities and to determine the distance and mass of the lens. If it is a nearby brown dwarf, it is likely to be associated with a high-proper-motion star that is found close to the source. HST observations taken at two epochs will resolve out the geocentric and the heliocentric the proper-motions, thus providing unambiguous proof that it is a substellar lens. If the lens is a halo star, then it should be detectable as it separates from the source star over the next year. This would be the first definitive detection of a lens star in the Galatic halo and it would help to resolve the long running controversy over whether a significant fraction of the microlensing events seen towards the Magellanic Clouds are due to lens objects in the halo. Thus, it will either be the first clear proof of a substellar lens in the Galactic disk, or the first clear detection of a halo lens. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will use WFPC2 to image the field in V and I filters, with the object placed in the PC chip. Given its magnitude of I~18.1, we will require about ~(5 +5) min exposures in V and I filters, which should allow us to see fainter objects in the field without saturating the source. We will also use NICMOS/NIC1 to image the field in J and H bands. The observations will be repeated about 8 months later. Note that the galactic bulge can be observed from about February to June, which allows the observations to be taken 8 months apart, in the 2-gyro mode. Real Time Justification 11311( 9) - 23-Jan-2008 18:14:04 - [ 2] ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 11311( 9) - 23-Jan-2008 18:14:04 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 OGLE-2007-BL EXT-STAR, G V-IV RA=18H05M41.0500S +/- 0.1", J2000 V = 17.5 +/- 0.5 G-224 DEC=-28D45'36.20" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 11311( 9) - 23-Jan-2008 18:14:04 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFPC2-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.3535 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 45.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type NIC-SPIRAL-DITH Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.334461 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 45.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 11311( 9) - 23-Jan-2008 18:14:04 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 324.0D TO 325.0 D; BETWEEN 11-JUN-2007:00:00:00 AND 12-JUN-2007:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 OGLE-2007-B WFPC2 IMAGE PC1 F814W 1 400.0 S PATTERN 1 1-2 LG-224 ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-2007-B WFPC2 IMAGE PC1 F555W 1 400.0 S LG-224 ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ OGLE-2007-BLG-224 1 WFPC2 IMAGE PC1 F814W 1 none none none 1 N/A OGLE-2007-BLG-224 1 WFPC2 IMAGE PC1 F814W 2 none none none 1 N/A OGLE-2007-BLG-224 2 WFPC2 IMAGE PC1 F555W 1 none none none 1 N/A OGLE-2007-BLG-224 2 WFPC2 IMAGE PC1 F555W 2 none none none 1 N/A 11311( 9) - 23-Jan-2008 18:14:04 - [ 6] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 11-JUN-2007:00:00:00 AND 12-JUN-2007:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 OGLE-2007-B NIC1 MULTIAC NIC1 F110W NSAMP=14, SAMP-SEQ=STEP128 1 DEF PATTERN 2 1-2 LG-224 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-2007-B NIC1 MULTIAC NIC1 F160W NSAMP=14, SAMP-SEQ=STEP128 1 DEF LG-224 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ OGLE-2007-BLG-224 1 NIC1 MULTIAC NIC1 F110W 1 none none none 1 N/A CUM OGLE-2007-BLG-224 1 NIC1 MULTIAC NIC1 F110W 2 none none none 1 N/A CUM OGLE-2007-BLG-224 2 NIC1 MULTIAC NIC1 F160W 1 none none none 1 N/A CUM OGLE-2007-BLG-224 2 NIC1 MULTIAC NIC1 F160W 2 none none none 1 N/A CUM 11311( 9) - 23-Jan-2008 18:14:04 - [ 7] Visit: 03 Visit Priority: Visit Requirements: ORIENT 324.01D TO 324.02 D; BETWEEN 08-JUN-2008:00:00:00 AND 15-JUN-2008:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 OGLE-2007-B WFPC2 IMAGE PC1 F814W 1 400.0 S GSPAIR LG-224 S9SO000634F2S9SR000110F1 ; PATTERN 1 1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-2007-B WFPC2 IMAGE PC1 F555W 1 400.0 S LG-224 ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ OGLE-2007-BLG-224 1 WFPC2 IMAGE PC1 F814W 1 none none none 1 N/A OGLE-2007-BLG-224 1 WFPC2 IMAGE PC1 F814W 2 none none none 1 N/A OGLE-2007-BLG-224 2 WFPC2 IMAGE PC1 F555W 1 none none none 1 N/A OGLE-2007-BLG-224 2 WFPC2 IMAGE PC1 F555W 2 none none none 1 N/A 11311( 9) - 23-Jan-2008 18:14:04 - [ 8] Visit: 04 Visit Priority: Visit Requirements: ORIENT 316.1846D TO 316.1846 D; BETWEEN 08-JUN-2008:00:00:00 AND 15-JUN-2008:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 OGLE-2007-B NIC1 MULTIAC NIC1 F110W NSAMP=13, SAMP-SEQ=STEP128 1 DEF GSPAIR LG-224 CUM S9SO000653F2S9SR000087F3 ; GS ACQ SCENARIO BASE1T3; PATTERN 2 1-2 ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-2007-B NIC1 MULTIAC NIC1 F160W NSAMP=14, SAMP-SEQ=STEP128 1 DEF LG-224 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ OGLE-2007-BLG-224 1 NIC1 MULTIAC NIC1 F110W 1 none none none 1 N/A CUM OGLE-2007-BLG-224 1 NIC1 MULTIAC NIC1 F110W 2 none none none 1 N/A CUM OGLE-2007-BLG-224 2 NIC1 MULTIAC NIC1 F160W 1 none none none 1 N/A CUM OGLE-2007-BLG-224 2 NIC1 MULTIAC NIC1 F160W 2 none none none 1 N/A CUM 11311( 9) - 23-Jan-2008 18:14:04 - [ 9] Summary Form for Proposal 11311 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures NIC1, PC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC1, WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=13, NSAMP=14, SAMP-SEQ=STEP128 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 08-JUN-2008:00:00:00 AND 15-JUN-2008:00:00:00, BETWEEN 11-JUN-2007:00:00:00 AND 12-JUN-2007:00:00:00, GS ACQ SCENARIO BASE1T3, GSPAIR S9SO000634F2S9SR000110F1, GSPAIR S9SO000653F2S9SR000087F3, ORIENT 316.1846D TO 316.1846 D, ORIENT 324.01D TO 324.02 D, ORIENT 324.0D TO 325.0 D, PATTERN 1 1-2, PATTERN 2 1-2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W, F160W, F555W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names OGLE-2007-BLG-224 ------------------------------------------------------------------------------------------------------------------------------------