The recent discovery by our group of an unexpectedly bright end of the white-dwarf (WD) luminosity function (LF) of the metal-rich, old open cluster NGC 6791 casts serious doubts on our understanding of the physical process which rules the formation and the cooling of WDs. It is clear at this point that the theory badly needs more observations. Here we propose WFC3/UVIS and ACS/WFC HST observations reaching the bottom end of the WD LF, for the first time in a solar-metallicity, 2.5-Gyr-old, populous open cluster: NGC 6819.

This is also a two-epoch astrometric program. The first epoch is in this Cycle17, for which we were allocated with 8 orbits. It is important to collect the first epoch data as soon as possible (ideally before the end of 2008, or as soon as possible in any case) so to enlarge the time-base-line when the second epoch will be collected (4 orbits in Cycle 19). RESOLVED STELLAR POPULATIONS 12 false 0.0 0.0 false false false false SUPPORTED STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the NED database. + plus a shift J2000 J2000 WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F814W ACS/WFC Imaging No No F814W Same orient constraint links visits (01 02 03 04) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12669 :visit-id "01" :proposal-version -1 :trans-version "20110509" :date "16-Jun-2011 15:15:34.0" :trans-errors '(:WARNINGS 4 :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 2296400 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12669 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12669 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3008 :al-overhead-at-end 116 :internal-dur-at-end 1019 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3341 :pcs-gap 0 ) false 1 0 Same orient constraint links visits (01 02 03 04) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12669 :visit-id "02" :proposal-version -1 :trans-version "20110509" :date "16-Jun-2011 15:13:30.0" :trans-errors '(:WARNINGS 1 :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 2296400 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12669 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12669 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3008 :al-overhead-at-end 116 :internal-dur-at-end 1019 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3341 :pcs-gap 0 ) false 1 0 Same orient constraint links visits (01 02 03 04) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12669 :visit-id "03" :proposal-version -1 :trans-version "20110509" :date "16-Jun-2011 15:13:52.0" :trans-errors '(:WARNINGS 4 :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 2296400 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12669 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12669 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3008 :al-overhead-at-end 116 :internal-dur-at-end 1019 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3341 :pcs-gap 0 ) false 1 0 Same orient constraint links visits (01 02 03 04) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12669 :visit-id "04" :proposal-version -1 :trans-version "20110509" :date "16-Jun-2011 15:14:02.0" :trans-errors '(:WARNINGS 4 :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 2296400 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12669 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12669 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3008 :al-overhead-at-end 116 :internal-dur-at-end 1019 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3341 :pcs-gap 0 ) false 1 0