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Bayesian Analysis Of Two Stellar Populations In Galactic Globular Clusters I: Statistical And Computational Methods, David Stenning, Ted Von Hippel, Rachel Wagner-Kaiser, Elliot Robinson, David Van Dyk, Ata Sarajedini, Nathan Stein
Bayesian Analysis Of Two Stellar Populations In Galactic Globular Clusters I: Statistical And Computational Methods, David Stenning, Ted Von Hippel, Rachel Wagner-Kaiser, Elliot Robinson, David Van Dyk, Ata Sarajedini, Nathan Stein
Ted von Hippel
We develop a Bayesian model for globular clusters composed of multiple stellar populations, extend- ing earlier statistical models for open clusters composed of simple (single) stellar populations (e.g., van Dyk et al. 2009; Stein et al. 2013). Specifically, we model globular clusters with two populations that differ in helium abundance. Our model assumes a hierarchical structuring of the parameters in which physical properties|age, metallicity, helium abundance, distance, absorption, and initial mass|are common to (i) the cluster as a whole or to (ii) individual populations within a cluster, or are unique to (iii) individual stars. An adaptive Markov chain Monte Carlo …
Bayesian Analysis Of Two Stellar Populations In Galactic Globular Clusters – Iii. Analysis Of 30 Clusters, R. Wagner-Kaiser, D. C. Stenning, A Sarajedini, Ted Von Hippel, D. A. Van Dyk, E. Robinson, W. H. Jefferys
Bayesian Analysis Of Two Stellar Populations In Galactic Globular Clusters – Iii. Analysis Of 30 Clusters, R. Wagner-Kaiser, D. C. Stenning, A Sarajedini, Ted Von Hippel, D. A. Van Dyk, E. Robinson, W. H. Jefferys
Ted von Hippel
We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of 30 Galactic globular clusters to characterize two distinct stellar populations. A sophisticated Bayesian technique is employed to simultaneously sample the joint posterior distribution of age, distance, and extinction for each cluster, as well as unique helium values for two populations within each cluster and the relative proportion of those populations. We find the helium differences among the two populations in the clusters fall in the range of ∼0.04 to 0.11. Because adequate models varying in carbon, nitrogen, and oxygen are not presently available, we …