12232( 2) - 28-Jun-2010 16:00:09 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12232 Version: 2 Check-in Time: 28-Jun-2010 16:00:09 STScI Edit Number: 0 Title Detection and Mass Measurement of an Isolated Brown Dwarf ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. David P. Bennett University of Notre Dame CoI: Dr. Michael C. Liu University of Hawaii N CoI: Mr. Trent J. Dupuy University of Hawaii N ------------------------------------------------------------------------------------ Abstract We propose observations that are likely to detect the brown dwarf lens object for microlensing event MACHO-179-A, which was observed observed by the MACHO collaboration some 15 years ago. The strong microlensing parallax signal seen in the light curve and follow-up Keck adaptive optics images imply that the lens is a brown dwarf within about 300 parsecs. If the lens object is at least as massive as 0.015 Solar masses at an age of 1 Gyr or 0.03 Solar masses at an age of 10 Gyr, these observations will detect the lens and measure its relative lens-source proper motion. The relative proper motion can be combined with the microlensing parallax measurement and a precise WFC3/UVIS measurement of the source star brightness to yield a mass measurement of the source star to 3% or better. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose WFC3/IR observations in two visits of two orbits each separated by about six months. If the source is not extremely faint, these should yield a parallax measurement for the brown dwarf. This should provide confirmation of our understanding of the microlensing event because the distance to the brown dwarf lens is also determined by eq. 2 of the phase 1 proposal. In order to maximize our photometric and astrometric sensitivity we seek dithered observations with as many pointings as possible and as many reads as possible without triggering the inefficiency of serial buffer dumps. This leads to the choice of the SPARS25 observing sequence with NSAMP = 15, which have a duration of 352.9 seconds, which is just enough to allow parallel buffer dumps. In two orbits, we have time for 14 SPARS25, SAMP = 15, observing sequences, so request 2 sets of 4-point box dither patterns in the F127M passband and one 4-point box dither pattern plus a 2-point line dither pattern in the F110W passband. If our brown dwarf target is > 0.04M? or is relatively young, then the F110W observations will provide a greater S/N than the F127M observations, but if the brown dwarf is near our proposed magnitude limit, then the F127M observations will provide a higher S/N than F110W. This would be true for an isolated brown dwarf, but the mass-distance relation implied by eqs. 1 and 2 (of the phase 1 proposal) implies that a faint brown dwarf will be slightly less than 0.4?? away from the source, and this means that the PSF wing of the source star image 12232( 2) - 28-Jun-2010 16:00:09 - [ 2] will interfere with the detection of the brown dwarf. However, with the F127M filter, the source star-brown dwarf contrast is improved by a factor of ~ 6, and the background from the source star at a distance of 0.38?? is well below the background from other sources. As a result, we are able to detect a J = 26.5 brown dwarf lens at a S/N ~ 6. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12232( 2) - 28-Jun-2010 16:00:09 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 MACHO-179-A STAR, BROWN DWARF, G RA=18H08M58.4150S +/- 0.5", J2000 V = 21.63 +/- 0.05 R = 20.38 +/- 0.05 V-IV DEC=-26D08'7.58" +/- 2.0" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 12232( 2) - 28-Jun-2010 16:00:09 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.636 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 41.788 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 12232( 2) - 28-Jun-2010 16:00:09 - [ 5] Visit: 01 Visit Requirements: BETWEEN 04-SEP-2010:00:00:00 AND 16-OCT-2010:23:59:59 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 MACHO-179-A WFC3/IR MULTIAC IR F127M SAMP-SEQ=SPARS25, NSAMP=15 2 DEF PATTERN 1 1 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 MACHO-179-A WFC3/IR MULTIAC IR F110W SAMP-SEQ=SPARS25, NSAMP=15 1 DEF PATTERN 1 2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 MACHO-179-A WFC3/IR MULTIAC IR F110W NSAMP=15, SAMP-SEQ=SPARS25 1 DEF PATTERN 2 3 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 | ------------------------------------------------------------------------------------------------------------------------------------ MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 1 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 1 none 2 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 2 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 2 none 2 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 3 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 3 none 2 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 4 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 4 none 2 none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 1 none none none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 2 none none none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 3 none none none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 4 none none none 2 N/A CUM MACHO-179-A 3 WFC3/IR MULTIAC IR F110W 1 none none none 2 N/A CUM 12232( 2) - 28-Jun-2010 16:00:09 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ MACHO-179-A 3 WFC3/IR MULTIAC IR F110W 2 none none none 2 N/A CUM 12232( 2) - 28-Jun-2010 16:00:09 - [ 7] Visit: 02 Visit Requirements: BETWEEN 28-FEB-2011:00:00:00 AND 10-APR-2011:23:59:59 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 MACHO-179-A WFC3/IR MULTIAC IR F127M SAMP-SEQ=SPARS25, NSAMP=15 2 DEF PATTERN 1 1 CUM ------------------------------------------------------------------------------------------------------------------------------------ 2 MACHO-179-A WFC3/IR MULTIAC IR F110W SAMP-SEQ=SPARS25, NSAMP=15 1 DEF PATTERN 1 2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 3 MACHO-179-A WFC3/IR MULTIAC IR F110W NSAMP=15, SAMP-SEQ=SPARS25 1 DEF PATTERN 2 3 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 | ------------------------------------------------------------------------------------------------------------------------------------ MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 1 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 1 none 2 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 2 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 2 none 2 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 3 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 3 none 2 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 4 none 1 none 1 N/A CUM MACHO-179-A 1 WFC3/IR MULTIAC IR F127M 4 none 2 none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 1 none none none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 2 none none none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 3 none none none 2 N/A CUM MACHO-179-A 2 WFC3/IR MULTIAC IR F110W 4 none none none 2 N/A CUM MACHO-179-A 3 WFC3/IR MULTIAC IR F110W 1 none none none 2 N/A CUM 12232( 2) - 28-Jun-2010 16:00:09 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ MACHO-179-A 3 WFC3/IR MULTIAC IR F110W 2 none none none 2 N/A CUM 12232( 2) - 28-Jun-2010 16:00:09 - [ 9] Summary Form for Proposal 12232 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=15, SAMP-SEQ=SPARS25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 04-SEP-2010:00:00:00 AND 16-OCT-2010:23:59:59, BETWEEN 28-FEB-2011:00:00:00 AND 10-APR-2011:23:59:59, PATTERN 1 1, PATTERN 1 2, PATTERN 2 3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W, F127M ------------------------------------------------------------------------------------------------------------------------------------ Target Names MACHO-179-A ------------------------------------------------------------------------------------------------------------------------------------