Changed cycle from 19 to 20. DCT ----- Attempting Submission 5 (Tue Jul 10 23:36:11 GMT 2012) ----- It's all fine. This is the second part of a proposal to add six new white dwarfs (WDs) to the mass-radius relation for WDs, thus providing a stringent new test of our understanding of WD physics. The first part (12594) observed white dwarf binaries G107-70 and WD 1818+126. This proposal observes WD1639+153 as it achieve its maximum projected component separation (0.13") between August 2013 and Feb 2014. For the past several years, we have had underway programs of HST/FGS astrometry of three close visual binaries in which both components are WDs. The astrometry is yielding precise, model-independent dynamical masses for these six WDs. To complete the investigation, we need to obtain flux-calibrated spectra of the individual WDs in these binaries, which, combined with the accurate parallaxes from the FGS data, yield the radii. All three binaries are too close together for individual spectra to be obtained from the ground, but they can be obtained easily with STIS. By using an optimal telescope roll angle, we can obtain both spectra simultaneously in a single STIS exposure. Two of the binaries are bright enough to obtain the spectra in one orbit. Our faintest target requires 2 orbits to obtain the necessry S/N on the V=17.4 secondary. In order to observe the closest of the binaries at maximum separation (WD 1639+153 at 0.132"), its observation should be done a few months after the beginning of Cycle 20. We propose to use HST/STIS to obtain low resolution broad-band spectroscopy & photometry of the six WD stars in our three DD binary systems. From the FGS observations of these binaries we know precisely the component position angle and separation at a given time. With this knowledge, for each binary we propose to align the binary position angle with the 52"x2" STIS long slit (to within 1 degree) by specification of a date-dependent HST ORIENT, and place the object near the center of the aperture, using the STIS target acquisition capability. A peak-up will not be needed for the 2" wide slit. The stars will be observed using the G430L and the G750L low resolution elements, with a CR-SPLIT = 2, and a 2-point dither along the slit in the spatial direction, of 0.650", to accomodate the widest binary in this proposal (G107-70, sep = ~450 mas at the proposed observing time. In accordance with guidance from the STIS INS HDBK, we obtain CCD flats with the G750L to calibrate away the red fringing. HOT STARS 12 false 0.0 0.0 false false false false SUPPORTED STAR DC Target coordinates are updated from observed "miss distance" in the FGS observations (dRA= +1", dDec = +0.8"). This is a binary system with sep = 0.430", PA = 269.9 deg, and dmag = 0.3 at epoch Feb 2012. J2000 J2000 STAR DC binary system with sep = 173", PA = 189.5 deg, dmag = 0.9, at epoch Nov, 2011. J2000 J2000 STAR DC This target will be observed by the "Cycle 20 continuation proposal" associated with this proposal. We wish to wait for the projected separation of the binary components to approach apastron (0.132"), which occurs in early Cycle 20. We retain the target in this proposal for bookkeeping purpose. J2000 J2000 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G750L 7751 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G750L 7751 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G750L 7751 POS-TARG DITHER 0.6350 LINE false false 2 90.0 STIS-ALONG-SLIT 1 false The scheduling data was generated by CASM 20.0. CASM was run in Phase II mode. Optimal orientation (133 deg) for aligning binary position angle with spatial direction of 52x2 slit has no guide stars. The selection of 127 deg (has guide stars) will be acceptable. (Tic-Visit :proposal-id 13059 :visit-id "01" :proposal-version -1 :trans-version "20111111" :date "09-Jul-2012 12:37:30.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 221248 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13059 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13059 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2802 :al-overhead-at-end 0 :internal-dur-at-end 688 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3249 :pcs-gap 0 ) false 1 0 binary star system, sep = 0.6", dmag = 0.3, PA =