Corrected an error in the keywords. Assigned ID: 938 ----- Attempting Submission 1 (Sat Feb 27 00:41:55 GMT 2010) ----- HST Phase I Proposal 938 (macho_179a.apt) successfully submitted. ----- Attempting Submission 2 (Sat Feb 27 03:35:12 GMT 2010) ----- HST Phase I Proposal 938 (macho_179a.apt) successfully submitted. ----- Attempting Submission 1 (Sat Jun 19 17:17:43 GMT 2010) ----- Detection and Mass Measurement of an Isolated Brown Dwarf 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.
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 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. COOL STARS 12 false 0.0 0.0 false false false false false false SUPPORTED STAR BROWN DWARF G V-IV R = 20.38 +/- 0.05 J2000 18 08 58.4000 -26 08 8.00 J2000 WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F110W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F625W WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F110W POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false POS-TARG DITHER 0.636 LINE false false 2 41.788 WFC3-IR-DITHER-LINE 2 false /Users/bennett/Documents/HST/cycle18_ph2/OP-cache/macho_179a_ph2-v01.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12232 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "18-Jun-2010 20:20:12.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 3899600 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12232 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12232 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2762 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12232 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2885 :al-overhead-at-end 0 :internal-dur-at-end 692 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 2 0 /Users/bennett/Documents/HST/cycle18_ph2/OP-cache/macho_179a_ph2-v02.xml The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12232 :visit-id "02" :proposal-version -1 :trans-version "20100505" :date "18-Jun-2010 20:22:11.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 3899600 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12232 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12232 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2762 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12232 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2885 :al-overhead-at-end 0 :internal-dur-at-end 692 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3257 :pcs-gap 0 ) true 2 0