----- Attempting Submission 1 (Thu Jul 03 00:24:22 GMT 2008) ----- Phase II Proposal 11609 (ngc6266.15_day_window.apt) successfully submitted. ----- Attempting Submission 2 (Thu Jul 03 00:25:28 GMT 2008) ----- Assigned ID: 927 ----- Attempting Submission 1 (Sat Mar 08 00:56:25 GMT 2008) ----- The existence of intermediate-mass black holes (IMBHs) in star clusters has been predicted by a variety of theoretical arguments and, more recently, by several large, realistic sets of collisional N-body simulations. Establishing their presence or absence at the centers of globular clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of the supermassive black holes (BHs) that inhabit the centers of most large, luminous galaxies. Observationally, the unambiguous signature of a massive central BH would be the discovery of central, unresolved X-ray or radio emission that is not consistent with more common stellar-mass accreting objects or pulsars. Yet, due to the largely uncertain details of accretion modeling, a precise mass determination of a central BH must necessarily come from stellar dynamics. This goal has not been achieved to date at the centers of Galactic globular clusters because of lack of adequate data as well as the use of too simplified methods of analysis. This situation can be overcome today through the combination of HST proper-motion measurements and state-of-the-art dynamical models specifically designed to take full advantage of this type of dataset. In this project, we will use two HST orbits to obtain another epoch of observations of NGC 6266. This cluster has photometric and structural properties that are consistent with current theoretical expectations for a cluster harboring an IMBH. Even more importantly, it is the only Galactic globular cluster for which there exists a detection of radio emission coincident with the cluster's core, and with a flux density that appears to rule out a stellar or binary origin. The goal of our project is to obtain proper motion measurements to either confirm an IMBH in this cluster and measure its mass, or to set limits to its mass and existence.

The success of this project hinges on accurate astrometric measurements for a large number of stars in the center of a globular cluster. The first epoch observations that we will use were taken with ACS/WFC in F435W as part of GO-10120. We will use WFC3 to obtain another epoch of data, producing a time baseline of 5 years. The advantages of this choice of instrument include a larger field of view than that of ACS/HRC (important to adequately constrain the floor level of the mass-to-light ratio at intermediate distances during the dynamical modeling), a smaller pixel size than the ACS/WFC (thus producing even better astrometry and allowing any necessary deblending of the 1st epoch images), and avoiding the CTE effects that the ACS CCDs suffer from after seven years on orbit. In order to suppress bright giants, we will take measurements in the F390W filter using the WFC3, which provides the best compromise between crowding issues and reasonable exposure times. Using the WFC3 ETC, we find that individual exposure times of around 420 sec do not produce any significant amount of saturation, and we plan to obtain about ten (10) such exposures to achieve the necessary signal-to-noise ratio. Shorter exposures are not an efficient approach, since this would force the instrument to dump the buffers before another exposure can start. Four (4) short, 35 sec exposures will be taken in order to perform astrometry around stars saturated on the longer exposures. We align our central fields with the edges of the ACS/WFC field of the first epoch in order to maximize the number of stars in common between the two epochs. Therefore, the target RA and DEC that we use for pointing do not correspond exactly with the catalogued center of the cluster. This choice of orientation constrains the window of schedulability to two weeks in the month of June, 2009. For dithering, we use a custom-made pattern of large offsets from our central pointing, designed to randomize any systematic errors related to the location of the stars on the detector as well as make independent estimates of the internal position uncertainties. RESOLVED STELLAR POPULATIONS 12 false 0.0 0.0 false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. M62 J2000 17 01 12.6000 -30 06 44.50 J2000 WFC3/UVIS Imaging No No F390W The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /Users/visitor/Desktop/OP-cache/ngc6266-v01.xml 1215024043982 (Tic-Visit :proposal-id 11609 :visit-id "01" :proposal-version -1 :trans-version "20080624" :date "02-Jul-2008 11:40:40.0" :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 4042496 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11609 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11609 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2815 :al-overhead-at-end 118 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3152 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11609 :visit-id "01" :orbit-number 2 :pcs-time 195 :si-vis-utilization 2955 :al-overhead-at-end 118 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3152 :pcs-gap 0 ) true 2 0