0 Assigned ID: 1170 ----- Attempting Submission 1 (Fri Sep 18 20:26:25 GMT 2015) ----- HST Phase I Proposal 1170 (stein_dd.apt) successfully submitted. Receipt: # 1170-1 ----- Attempting Submission 2 (Tue Sep 22 14:25:16 GMT 2015) ----- This attribute cannot have this value due to other choices: Optional_Parameter=BLADE The combination of attributes chosen is illegal. This attribute cannot have this value due to other choices: Optional_Parameter=BLADE=A The combination of attributes chosen is illegal. BLADE is not a valid selection Ready! -1851111682 ----- Attempting Submission 1 (Tue Sep 29 17:31:10 GMT 2015) ----- HST Phase II Proposal 14448 (14448_v1.apt) successfully submitted. Receipt: # 14448-1 ----- Attempting Submission 2 (Tue Sep 29 19:10:27 GMT 2015) ----- Ready! We request one orbit of WFC3 imaging of the nearby white dwarf (WD) Stein 2051B. In 2014 March, this WD passed very close to a faint background star, affording the opportunity to measure the relativistic deflection of its apparent position and thus determine the mass of the WD--the first application of this novel technique to the measurement of a stellar mass. We were awarded 7 orbits of HST time for WFC3 astrometry of the event. The deflection is clearly detected (at >3 sigma) in 3 of the epochs. Unfortunately, at the other 4 epochs, the background star (400 times fainter than the WD) was extremely close to the WD (inside the second Airy ring). In spite of strenuous efforts at PSF subtraction by our expert CoI, we have been unable to achieve high astrometric accuracy at these 4 epochs. Using only the 3 measured deflections, there is an ambiguity, resulting in two possible masses. One solution, at 0.71 Msun, is consistent with physical models for a CO-core WD, but the other, at 0.52 Msun, would imply an iron core. The latter would be inconsistent with most of our WD-formation theories, but oddly enough agrees with a ground-based mass derived by Strand in the 1980's based on an analysis of differential proper motions. Fortunately, the deflection is still detectable until ~2015 November, and as a bonus will now be in a different direction relative to the proper motion of the source. Thus one more observation, if taken before 2015 December, will both remove the ambiguity between the two mass solutions, and reduce the error bar on the correct mass. Hence we propose one orbit of DD time, to be obtained before 2015 December. This is a continuation of our program 13850. Since (I) proper motions of the source and reference stars have the largest uncertainty at this point, (ii) there is a clear science gain if we measure the position of the red dwarf with respect to the WD, (iv) the source is ~90 pixels away from the WD, we plan to observe in 2kx2k mode in F814W, so that we can have the maximum number of reference stars. We will take ~2 additional short exposures in F763M to get the position of the red dwarf. HOT STARS 0 AVAILABLE STAR DA This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. 1443556681493 56 /private/var/folders/56/c_jk44c970v8fj73rtx427cm0006v6/T/OPVisit5410421933720890452.xml ORIENT constraints are used to avoid diffraction spikes and bleed columns from Stein 2051A and B falling near the faint source star. (Tic-Visit :proposal-id 14448 :visit-id "01" :proposal-version -1 :trans-version "20150609" :date "29-Sep-2015 15:58:01.0" :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 703888 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14448 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14448 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3017 :al-overhead-at-end 170 :internal-dur-at-end 575 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3360.0 :pcs-gap 0 ) false 1 0