Observations of X-ray transients have posed crucial constraints to the processes and evolution of accretion disks in LMXB populations. Yet, the data to constrain the transient behavior of the most luminous BH LMXBs does not exist to date. We propose to study this rare component of the LMXB population, by observing the giant Virgo elliptical NGC4649 with ACIS-S (twice for 100 ks each). The extraordinarily rich population of ~58 BH candidates with LX> 2 1038 erg s-1 (40 with LX> 3 1038 erg s-1) of this galaxy provides the ideal sample for this study.

The primary observations with ACS/WFC are designed for photometry in F475W and F850LP of globular clusters in the massive elliptical galaxy NGC 4649. These observations complement deep Chandra imaging and the goal is to cross-match X-ray sources with HST-identified clusters. The use of two filters gives color information used to estimate rough metallicities of the clusters. For each filter we use two exposures and a simple line dither to cover the chip gap and correct pixel-level defects and cosmic rays. Given 54 min of visibility per orbit, 34 min are available after overheads for science exposures. Exposure times of 810 sec in F475W and 1200 sec in F850LP give approximately equal signal-to-noise in the two bands. NGC 4649 has one archival ACS pointing. The five additional pointings in this proposal, arranged in a quasi-mosaic, cover the remainder of the Chandra field of view (excepting foreground spiral in the northwest corner). The need to match both Chandra and the existing HST imaging in a mosaic leads to the restrictive orientation requirements. As described in the original proposal, we will make coordinated parallel observations with WFC3/IR in F160W during the latter part of each orbit. This will allow improved metallicity estimates for a subset of clusters. 12 false 0.0 0.0 false false false false SUPPORTED GALAXY ELLIPTICAL J2000 12 43 40.2000 +11 33 8.90 J2000 GALAXY ELLIPTICAL J2000 12 43 40.2000 +11 33 8.90 J2000 GALAXY ELLIPTICAL J2000 12 43 40.2000 +11 33 8.90 J2000 GALAXY ELLIPTICAL J2000 12 43 40.2000 +11 33 8.90 J2000 GALAXY ELLIPTICAL J2000 12 43 40.2000 +11 33 8.90 J2000 WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F850LP POS-TARG DITHER 3.011 LINE false false 2 85.28 ACS-WFC-DITHER-LINE 1 false The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12369 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "22-Sep-2010 13:41:52.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1624336 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12369 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12369 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2910 :al-overhead-at-end 0 :internal-dur-at-end 965 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) false 1 0 (Tic-Visit :proposal-id 12369 :visit-id "02" :proposal-version -1 :trans-version "20100505" :date "22-Sep-2010 13:44:03.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1624336 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12369 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12369 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2910 :al-overhead-at-end 0 :internal-dur-at-end 965 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) false 1 0 (Tic-Visit :proposal-id 12369 :visit-id "03" :proposal-version -1 :trans-version "20100505" :date "22-Sep-2010 13:45:27.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1624336 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12369 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12369 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2910 :al-overhead-at-end 0 :internal-dur-at-end 965 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) false 1 0 (Tic-Visit :proposal-id 12369 :visit-id "04" :proposal-version -1 :trans-version "20100505" :date "22-Sep-2010 13:47:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 3248688 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12369 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 12369 :visit-id "04" :obset-id "A4" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12369 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2910 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12369 :visit-id "04" :orbit-number 2 :pcs-time 333 :si-vis-utilization 2910 :al-overhead-at-end 0 :internal-dur-at-end 1041 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) false 2 0