We propose deep WFPC2 and NICMOS observations to search for optical companions to binary millisecond pulsar (MSPs) in two Globular Clusters (GCs): Terzan 5 and NGC6266. Terzan 5 has the largest MSP population of any GC: 33 MSP (17 in binary systems) have been discovered up to now in this stellar system. NGC6266 ranks fifth among the GC for wealth of MSPs but it is the only one in which all the (six) detected MSPs are in binary systems. Only 5 optical counterparts to binary MSP companions are known in GCs (two of them have been discovered by our group): hence even the addition of a few new identifications are crucial to investigate the variety of processes occurring in binary MSPs in dense environment. The observations proposed here would easily double/triple the existing sample of known MSP companions, allowing the first meaningful study of the phenomena which drive the formation and evolution of these exotic systems. Moreover, since most of binary MSP in GC are formed via stellar interactions in the high density regions of the cluster, the determination of the nature of the companion and the incidence of this collisionally induced population have a significant impact on our knowledge of the cluster dynamics. Even more interesting, the study of the optical companions to NSs in a GC allows to derive tighter constraints (than those obtainable for NS binaries in the galactic field) on the properties (mass, orbital inclination and so on) of the compation star. This has, in turn, an intrisic importance for fundamental physics since it offers the opportunity of measuring the mass of the NS and hence to put constraints to the equation of state of matter at nuclear equilibrium density.

We propose to perform deep broad-band photometry to investigate the MSP companion in two clusters: (1) TERZAN 5 : (a) NICMOS observations of the cluster core (with NIC2) are planned in two filters (F110W and F160W). These observations are organized in two visits (VISIT1 and VISIT2) each visit will last two orbits (one orbit per filter). We request VISIT2 be executed at least after 5 orbits from VISIT1 to check for object variability. Parallel observations with NIC1/WFPC2 are also planned. (b) WFPC2 observations of the cluster are planned in two filters (F606W and F814W). These observations are organized in 3 visits (VISIT3-VISIT5), two orbits per visit (one orbit per filter). We request VISIT4 be executed at least 5 orbits after VISIT3 and VISIT5 at least 5 orbits after VISIT4, in order to check for variability. Parallel observations with NIC3 are also planned. (2) NGC6266: WFPC2 observations of the cluster are planned in two filters (F656N and F439W). The observations are organized in 3 visits (VISIT6-VISIT8), the first two visits (VISIT6 and VISIT7) have been enterely devoted to obtain long exposures (1200 sec) in the H_alpha filter. In VISIT8 one orbit per filter is planned. We request VISIT7 be executed at least 5 orbits after VISIT6 and VISIT8 at least 5 orbits after VISIT7, in order to check for variability. Parallel observations with NIC3 are also planned. RESOLVED STELLAR POPULATIONS 12 false 0.0 false false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER BULGE This is 4" N and 6" E with respect to the cluster center J2000 17 48 5.0000 -24 46 45.00 J2000 STELLAR CLUSTER GLOBULAR CLUSTER centered on PSR-B J2000 17 01 12.6000 -30 06 44.00 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This is 8" W and 3"S with respect to the cluster center J2000 00 00 0.0000 +00 00 0.00 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F625W NIC1 Imaging No No F110W NIC1 Imaging No No F160W NIC2 Imaging No No F110W NIC2 Imaging No No F160W WFPC2 Imaging No F606W WFPC2 Imaging No F814W WFPC2 Imaging No F439W WFPC2 Imaging No F675W POS-TARG DITHER 0.559017 LINE 0.559017 false false 143.130096 4 26.56505 WFPC2-BOX 1 false (Tic-Visit :proposal-id 10845 :visit-id "01" :proposal-version -1 :trans-version "20061210" :date "03-Mar-2007 17:01:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 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