BLUE STRAGGLER STARS IN SAGITTARIUS GLOBULAR CLUSTERS Nov 06, 2012

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.

The data: BV photometry, Danish

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.

Structural properties:

Structural properties: cont. Sgr main body clusters

BS stars selection: Contamination taken into account in a statistical way

BS radial distribution: Not segregated Segregated Not segregated

BS specific frequency: Sgr Main Body contamination ????

BS cumulative distribution: Anderson-Darling test 60 % 0.4 % 44 % 75%

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.

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)

BS in Galactic Old Open Clusters Carraro, Boffin, Ahumada, Beccari, Davies, Monaco

BS in Galactic Old Open Clusters

 FLAMES (blue setup) + UVES  Multi-epoch ( typically 3 epochs)  Improving membership, improving statististics, finding pathological cases  In the middle between micro- and macro-economy