Thanks to CS and PC for reminding me to make the changes. 1. Added ORIENT constraints to make sure that the diffarction spikes don't affect the source stars. 2. Restricted the observing window to about 1 week around 28th March 2013, since the allowed ORIENTs change with time. -1948427865 ----- Attempting Submission 7 (Tue Nov 13 19:35:14 GMT 2012) ----- Already run. We propose to determine the mass of our nearest neighbor, Proxima Centauri, using the novel technique of astrometric microlensing. Proxima is a dM6e star, with an estimated mass of about 0.12 Msun, lying at a distance of 1.3 pc and having a large proper motion of 3.8 arcsec/yr. In a reprise of the famous 1919 solar eclipse that verified general relativity, Proxima will pass in front of a pair of 18th-magnitude background stars in 2015, affording us two independent opportunities to measure the relativistic deflection. The first passage will occur in May 2015 (impact parameter 1.5 arcsec), and the second in June 2015 (impact parameter 1.4 arcsec). As Proxima passes in front, it will cause a relativistic deflection of the background stars' images by ~0.5 milliarcsec, an amount readily detectable with HST/WFC3. The gravitational deflection angle depends only upon the distances and relative positions of the stars, and the mass of the lens (Proxima). Since the distance to Proxima is well known from accurate parallax measurements, and the relative stellar positions can be determined precisely before the event, the astrometric measurement offers a unique and direct method to measure the mass of a single, isolated star. We anticipate better than 10% accuracy for the mass determination. The mass of Proxima is of special interest because it is the nearest M dwarf, representing the most common type of star in the Galaxy, for which the mass-luminosity relation is still uncertain at present. The first epoch observations will be taken in a few different filters (F475W, F555W, F606W, F814W) to better characterize the spectral type of the source. Subsequent observations will be taken mainly in 2 filters (F606W and F814W). We will obtain one short (0.5 sec) exposure to get an unsaturated image of Proxima, in order to register its position. The other exposures will be of 90 to 200 sec durations, so that the source stars will have a S/N & 300 in each exposure. We can obtain about 10 such exposures in each orbit, at 2 dither positions, which would be adequate to achieve the astrometric accuracy required for the project. COOL STARS 12 false 0.0 0.0 false false false false SUPPORTED STAR K V-IV This object was updated to the SOURCE that Proxima-Cen is going to lens. At present, the source and proxima-cen are separated by about 10.5 arcsec, and this separation will slowly decrease to 1.5 arcsec in 2015. J2000 J2000 WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F475W The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. 1349052293000 146.1071580685101 (Tic-Visit :proposal-id 12985 :visit-id "01" :proposal-version -1 :trans-version "20120802" :date "18-Sep-2012 12:59:43.0" :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 703872 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12985 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12985 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3177 :al-overhead-at-end 174 :internal-dur-at-end 190 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3511 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 20.2. CASM was run in Phase II mode. /private/var/folders/vq/vqHvVK0yGlWAHXOSHPkI9U++4D2/-Tmp-/OPVisit8772295664188108596.xml 1352833819285 (Tic-Visit :proposal-id 12985 :visit-id "02" :proposal-version -1 :trans-version "20121031" :date "13-Nov-2012 14:10:19.0" :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 703872 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12985 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12985 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3157 :al-overhead-at-end 174 :internal-dur-at-end 190 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3511 :pcs-gap 0 ) true 1 0