emilio j. alfaro (iaa-csic) on behalf ges- wg1 young clusters in the gaia-eso survey palermo, may...
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Emilio J. Alfaro (IAA-CSIC) on behalf GES-WG1
Young Clusters in the Gaia-ESO SurveyPalermo, May 20, 2014
What is a cluster member for GES?
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The problem
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The problem
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The problem
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The problem
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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.
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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 [Geisler et al. 2012; Carraro et al. 2012] (double BHB; Na:O correlation) [Carraro et al. 2012, 2013] (Bulge Cluster?)
NGC 6791
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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
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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] –
Orion Nebula Cluster
NGC 2264
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(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
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Massive Star Forming Region W5-East [Chavarría et al. 2014]
Pipe’s cores distribution[Alfaro et al. 2014]
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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.
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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.
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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.
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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
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Rho Ophiuchi [Michiel Cottaar & Michael Meyer] P89 P93
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Blanco 1 [Despina Hatzidimitriou]
Several Photometric Studies:
Westerlund et al 1988 (UBVRI Cousins)Moraux et al. 2007 (I, z)Mermilliod et al. 2008 (UBV)
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Blanco 1 [Despina Hatzidimitriou]
B-V = 0.44 + 2.53 (I-z)V-I = 0.10 + 3.51 (I-z)
Working Transformation Equations
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Blanco 1 [Despina Hatzidimitriou]
59 cluster members selected with Pro(RV) > 0.8 from Mermilliod et al. (2008)
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Blanco 1
Selection by Photometry and Proper Motion Data excluding those stars being outliers in any of the data sets.
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First Observing Period
Number Clusters
P88 6 NGC 2516, Tr 20, NGC 2264, Γ 2 Vel, Cha I, NGC 3293
P89+P90 20 Ρ Oph, NGC 2547, Be 81, NGC 6705, NGC 4815, IC 4665, NGC 6633,IC 2944, Be 44, NGC 6530, Tr 23, NGC 3532, IC 2602, NGC 6611, Λ Ori, IC 2391, NGC 3766,NGC 6802, Ruprecht 134, NGC 2509
P91 3 NGC 6259, Blanco 1, Pismis 18
P92 4 NGC 2243, Be 25, NGC 2415 A+B, Tr 14+16/Coll 228
P93 1 NGC 6005
P94 6 Be 21, Be31, Be 36, NGC 2232, NGC 2420, Tr 5
In progressReady to be observed Completed
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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.