0 ----- Attempting Submission 1 (Sun Jul 17 01:38:09 GMT 2016) ----- Our HST/COS survey for the photospheric pollution by planetary debris undisputably demonstrates that at least 25% of white dwarfs host an evolved planetary system. The debris discs holding the material that accretes onto the white dwarf are produced by the tidal disruption of asteroids, and are observed in nearly 40 systems by infrared excess emission from micron-sized dust. In a small number of cases, we have also detected double-peaked Ca II 860 nm emission lines from a metal-rich gaseous disc in addition to photospheric pollution and circumstellar dust. Our ground-based monitoring of the brightest of these systems, SDSS J1228+1040, over the last eleven years shows a dramatic morphological change in the emission line profiles on the time-scale of years. The evolution of the line profiles is consistent with the precession of an eccentric disc on a period of ~25 years, indicating a recent dynamical interaction within the underlying dust disc. This could either be related to the initial circularisation of the disc, or a secondary impact onto an existing disc. We expect that the accretion rate onto the white dwarf varies on the same timescale as the Ca II emission lines, and there is the tantalising possibility to detect changes in the bulk abundances, if the impact of a planetesimal with a different bulk abundance stirred up the disc. We request a small amount of COS time to monitor the debris abundances over the next three HST Cycles to test this hypothesis, and bolster our understanding of the late evolution of planetary systems. We request the 3 visits to be spaced as equally apart as possible over the 3 years, as we require the multiple observations for time-resolved spectroscopy of the absorption lines present in the UV. DEBRIS DISKS 12 false true false false false false SUPPORTED STAR DA DISK EXTRA-SOLAR PLANETARY SYSTEM NO SDSSJ1228+1040 has been observed three times with COS (HST programs 11561, 12906, and the first of this monitoring proposal in March 2016) - no bright object limit concerns. J2000 J2000 GALEX FUV=15.62 +/- 0.02 GALEX NUV=15.85 +/- 0.02 COS/FUV Spectroscopic No No G130M 1291 1468319297260 /Volumes/Storage/PhD_files/proposals/HST_2015/OP-cache/14813_epoch2-v01.xml The scheduling data was generated by CASM 24.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 14813 :visit-id "01" :proposal-version -1 :trans-version "20160601" :date "12-Jul-2016 11:28:16.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 539424 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14813 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14813 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2885 :al-overhead-at-end 0 :internal-dur-at-end 38 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3218 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14813 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2996 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3218 :pcs-gap 0 ) true 2 0 Target acquisition based on an uploaded WD model spectrum that has been scale to the COS data from a previous observation.