I have updated the Phase 2 to Cycle 25. -2041823148 ----- Attempting Submission 6 (Fri Jul 14 16:18:57 GMT 2017) ----- Fomalhaut, a young nearby A4V star, is surrounded by an inclined dust debris belt, directly imaged in optical scattered light with HST. The proper motion and parallax of Fomalhaut will move this belt across an 18.5 magnitude background star in the next decade. This presents a unique and fortuitous opportunity to probe the dust structure and confirm disk dynamical theory to unprecedented resolution. In Cycle-21 we obtained HST/STIS spectra of the background star during the diffuse phase of the debris disk occultation. We propose obtaining HST/STIS spectra during the thick (Cycle-24 to 26), and pristine (~2021 with JWST) phases of occultation as the debris disk moves across the target background star. This is a rare opportunity to measure - for the first time - the dust optical depth structure in a known planet-forming system, providing a valuable constraint on current planet formation theories. This experiment will act as a pathfinder for this type of science for future observations with JWST and future ELTs. We will use STIS] in Cycle-24, 25, and 26 to observe a 18.5 magnitude background star as it passes behind the Fomalhaut debris disk. We will obtain a quick (2 s) image with STIS 50CORON MIRVIS for preimaging photometry of the background star. In the same orbit, we will switch to STIS G750L for the remaining time (~31 minutes). Extrasolar Planets and Planet Formation 0 false false false true false false SUPPORTED STAR G V-IV The offset of this target may be updated, depending on when the observation is scheduled. J2000 STAR A0-A3 V-IV J2000 STIS/CCD Spectroscopic No No G750L 7751 STIS/CCD Spectroscopic No No G750L 7751 STIS/CCD Spectroscopic No No G750L 7751 1500049016067 /private/var/folders/xy/skmjt2_j6_l_q0pqk8pxc4xw0005jq/T/OPVisit2550472634157778505.xml The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. First we will acquire Fomalhaut and then offset to the 18.5 magnitude background star. (Tic-Visit :proposal-id 15297 :visit-id "01" :proposal-version -1 :trans-version "20170613" :date "14-Jul-2017 09:16:46.0" :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 258064 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15297 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15297 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2887 :al-overhead-at-end 0 :internal-dur-at-end 847 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3225 :pcs-gap 0 ) true 1 0 Acquire Fomalhaut This is following the proposal ID 8788 pre-imaging of the same background star. The spectrum of the background star will be compared with ID:13434 and ID:8788 datasets.