What is a cluster member for GES?

1. What is a cluster member for GES? Emilio J. Alfaro (IAA-CSIC) on behalf GES-WG1 Young Clusters in the Gaia-ESO Survey Palermo, May 20, 2014

2. The problem

3. The problem

4. The problem

5. The problem

6. What is a cluster? • Apparent concentration of stars in the sky, born from the same molecular cloud, sharing the same chemical composition, the same distance (cluster radius <<< distance to cluster) and the same age, and moving as a whole with respect to the Sun with a low internal velocity dispersion (connected to the cluster gravitational stability). • The above definition is a mixture of phenomenological aspects and physical properties (so, not a very good definition). • Some clusters diverge, in one or various aspects, from this description.

7. Abnormal Clusters • Disk Clusters with Multiple Populations: • Trumpler 20 [Platais et al. 2012; Donati et al. 2014](multiple populations discarded) • Berkeley 39 [Bragaglia et al. 2012] (multiple populations discarded) • Melotte 66 [Carraro et al. 2014](multiple populations discarded) NGC 6791 • - NGC 6791 [Geisler et al. 2012; Carraro et al. 2012](double BHB; Na:O correlation) [Carraro et al. 2012, 2013](Bulge Cluster?)

8. Abnormal Clusters • Disk Clusters with Multiple Populations: • - NGC 6791 [Geisler et al. 2012; Carraro et al. 2012](double BHB; Na:O correlation) [Carraro et al. 2012, 2013](Bulge Cluster?) NGC 6791

9. Abnormal Clusters • Kinematic Substructures: • NGC 2264 [Fürész et al. 2006; Dobson et al. 2013] • Orion Nebula Cluster [Fürész et al. 2008] • Gamma Velorum [Jeffries et al. 2014] • NGC 2548 (hint of kinematic substructure; much older cluster)[Alfaro et al. 2014] • M 67 (!?)[Vereshchagin et al. 2014] NGC 2264 Orion Nebula Cluster

10. (Not so) Abnormal Clusters • Spatial Substructures: • Many disk stellar clusters show a high degree of internal structure [i.e. Cartwright & Whitworth 2004] • Internal Structure as defined by Q parameter increases with cluster age (weak correlation) [Schmeja et al. 2008, 2010; Sánchez & Alfaro 2009; Sánchez et al. 2010; Vallenari 2012] • Cluster Fractal Dimension (for those objects with Q<0.8) increases with cluster age (strong correlation) [Sánchez & Alfaro 2009] • Many embedded clusters and proto-stellar cores show filamentary spatial distributions

11. Massive Star Forming Region W5-East [Chavarría et al. 2014] Pipe’s cores distribution [Alfaro et al. 2014]

12. What is a cluster member? Stars in the cluster area accomplishing the following conditions: • Cluster members should be spatially distributed more densely than field stars are. That includes the third dimension (distance to the Sun). • The same for one, some, or all velocity components in the kinematic space. • CMDs of cluster members should fit a single isochrone at a given distance (the same distance for any CM combination). • Metallicity and Chemical abundances for cluster members should present a common value with a low internal dispersion (mainly due to observational errors), but taking chemical evolution (e.g. Li depletion) into account.

13. What to do with GES clusters? After many discussions the answer arrived to • The main objective is the drawing up of a list of stars in the cluster field that are considered probable members upon the basis of their photometry and kinematics. • Both the final list and the procedure to follow should be adjusted to the following general rules: a) Homogeneity: the procedure ought to be as homogeneous as possible even if the data are not and the clusters under study have very different observational characteristics. b) Simplicity: the tools utilized for this should be universal, easily accessible for the panel members. c) Completeness: only those stars considered with certainty as non-members should be excluded from the final list.

14. What to do with GES clusters? After many discussions the answer arrived to • The main objective is the drawing up of a list of stars in the cluster field that are considered probable members upon the basis of their photometry and kinematics. • Both the final list and the procedure to follow should be adjusted to the following general rules: a) Homogeneity: the procedure ought to be as homogeneous as possible even if the data are not and the clusters under study have very different observational characteristics. b) Simplicity: the tools utilized for this should be universal, easily accessible for the panel members. c) Completeness: only those stars considered with certainty as non-members should be excluded from the final list. We are not looking for stars guilty of being cluster members, but for suspect ones.

15. The procedure • The position within the “cluster locus” in CMDs • Defined from an “apparent” cluster sequence • Defined as a fiducial line drawn by the known cluster members • With the help of the best isochrone • The spatial boundary of the cluster (not well known in many cases) • Detection of kinematic outliers • N > 20 “bona fide” cluster members from RV or specific proper motion analysis • Matching with working proper motion catalogues • Searching for systemic dispersion • Looking for outliers

16. Rho Ophiuchi [Michiel Cottaar & Michael Meyer] P89  P93

17. Blanco 1 [Despina Hatzidimitriou] Several Photometric Studies: Westerlund et al 1988 (UBVRI Cousins) Moraux et al. 2007 (I, z) Mermilliod et al. 2008 (UBV)

18. Blanco 1 [Despina Hatzidimitriou] Working Transformation Equations B-V = 0.44 + 2.53 (I-z) V-I = 0.10 + 3.51 (I-z)

19. Blanco 1 [Despina Hatzidimitriou] 59 cluster members selected with Pro(RV) > 0.8 from Mermilliod et al. (2008)

20. Blanco 1 Selection by Photometry and Proper Motion Data excluding those stars being outliers in any of the data sets.

21. In progress Ready to be observed Completed

22. By way of conclusion • We have designed and developed a methodology for selecting the target stars in GES clusters, based upon a conservative approach to the problem. • Sometime we can apply it, but each cluster is a peculiar case. • In order to check the ratio of success (a single example), see Mayte Costado’s poster.