Slide 1

BLUE STRAGGLER STARS IN SAGITTARIUS GLOBULAR CLUSTERS Nov 06, 2012 Slide 2 The context: Sgr offers a different environment to study the BS phenomenon: Star clusters associated with Sgr exhibit wide variations of age, structural and dynamical properties, and metallicity. Slide 3 The data: BV photometry, Danish telescope @LaSilla Slide 4 The Color-Magnitude Diagrams: Arp 2 and Terzan 8 are Sgr genuine members, NGC 5634 and Palomar 12 are stripped clusters, now floating in the MW halo. Slide 5 Structural properties: Slide 6 Structural properties: cont. Sgr main body clusters Slide 7 BS stars selection: Contamination taken into account in a statistical way Slide 8 BS radial distribution: Not segregated Segregated Not segregated Slide 9 BS specific frequency: Sgr Main Body contamination ???? Slide 10 BS cumulative distribution: Anderson-Darling test 60 % 0.4 % 44 % 75% Slide 11 Conclusions: The main idea of this study was to use BS as test- particle to probe the parent cluster dynamical status; Their distribution nicely correlates with the King parameters of the parent clusters; Special care must be taken since contamination from Sgr Main Body can complicate significantly the interpretation. Slide 12 BS in Galactic Old Open Clusters Open clusters seem to possess the largest frequency of BS (see Yazan talk) There is a trend of having more BS at decreasing total luminosity and increasing age (De Marchi et al. 2006) Membership is a challenge (see Javier talk) Slide 13 BS in Galactic Old Open Clusters Carraro, Boffin, Ahumada, Beccari, Davies, Monaco Slide 14 BS in Galactic Old Open Clusters Slide 15 FLAMES (blue setup) + UVES Multi-epoch ( typically 3 epochs) Improving membership, improving statististics, finding pathological cases In the middle between micro- and macro-economy