In this proposal we intend to firmly identify the chemical species responsible for the UV and UV-optical color differences exhibited by the multiple stellar populations harboured by two Galactic globular clusters: omega Centauri and 47 Tucanae, one with highly helium enriched sub-populations (omega Centauri), the other not. We plan to collect ultraviolet STIS spectra for stars in the crowded cores of the clusters, where HST photometry is already available for thousands of stars in more than 10 filters, from F225W to F850LP. This WFC3+ACS photometric database has allowed us to show that UV colors are remarkably effective in separating the different cluster sub-populations, and with the proposed STIS spectroscopy we can quantify the chemical abundance differences among such sub-populations, most notably in Nitrogen and Oxygen. The resulting calibration of the UV colors in terms of CNO abundances will provide a new effective tool for the chemical characterization of large numbers of globular cluster stars belonging to the various sub-populations in each cluster, and to better isolate the specific role of the helium abundance. The plan is to observe at least one star for each of the main principal stellar sub-populations in each of the two clusters. These objects are selected on the basis of their accurate photometry and astrometry already in hand, based on existing UV-HST images.

Two stars per slit. i.e. tight constrains on the ORIENT. Two or three dither along the slit. WFC3/UVIS parallel observations in F438W, F336W, and F275W. ACS/WFC parallel observations in F475W, and F814W. RESOLVED STELLAR POPULATIONS 12 false 0.0 0.0 0.0 false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. and then edited. J2000 J2000 STIS/CCD Spectroscopic No No G430L 4300 STIS/NUV-MAMA Spectroscopic No No G230L 2376 WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W STIS/CCD Spectroscopic No No G430L 4300 WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W STIS/CCD Spectroscopic No No G430L 4300 WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. wCen(CCD): SGBred + SGBblue (Tic-Visit :proposal-id 12580 :visit-id "01" :proposal-version -1 :trans-version "20110509" :date "06-Jul-2011 10:01:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 6523936 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12580 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12580 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3058 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12580 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3169 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12580 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3169 :al-overhead-at-end 116 :internal-dur-at-end 1460 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) false 3 0 The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. wCen(CCD): SGBblack + SGBgreen (Tic-Visit :proposal-id 12580 :visit-id "02" :proposal-version -1 :trans-version "20110509" :date "06-Jul-2011 10:23:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 6523936 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12580 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12580 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3058 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12580 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3169 :al-overhead-at-end 116 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12580 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3169 :al-overhead-at-end 116 :internal-dur-at-end 1440 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) false 3 0 The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. 47Tuc(CCD): SGBb + SGBf + (SGBa) (Tic-Visit :proposal-id 12580 :visit-id "03" :proposal-version -1 :trans-version "20110509" :date "05-Jul-2011 21:33:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 4181376 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12580 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12580 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3312 :al-overhead-at-end 116 :internal-dur-at-end 354 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3645 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12580 :visit-id "03" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3423 :al-overhead-at-end 115 :internal-dur-at-end 1400 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3645 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. 47Tuc(CCD+MAMA): HBb + HBf (Tic-Visit :proposal-id 12580 :visit-id "04" :proposal-version -1 :trans-version "20110509" :date "05-Jul-2011 21:41:57.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 4351360 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12580 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12580 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3295 :al-overhead-at-end 116 :internal-dur-at-end 80 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3645 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12580 :visit-id "04" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3404 :al-overhead-at-end 110 :internal-dur-at-end 1415 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3645 :pcs-gap 0 ) true 2 0