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Analysis of Colour-Magnitude Diagrams of Rich LMC Clusters: NGC 1831

Published online by Cambridge University Press:  03 August 2017

Basílio X. Santiago
Affiliation:
Inst. de Física, Univ. Federal do RS, Av. Bento Gonçalves, 9500, Porto Alegre, RS 91501-970, Brazil
Leandro Kerber
Affiliation:
Inst. de Física, Univ. Federal do RS, Av. Bento Gonçalves, 9500, Porto Alegre, RS 91501-970, Brazil
Rodrigo Castro
Affiliation:
Inst. de Física, Univ. Federal do RS, Av. Bento Gonçalves, 9500, Porto Alegre, RS 91501-970, Brazil
Mark Wilkinson
Affiliation:
Inst. of Astronomy, Madingley Rd, Cambridge, CB3 0HA, UK
Richard de Grijs
Affiliation:
Inst. of Astronomy, Madingley Rd, Cambridge, CB3 0HA, UK
Rachel Johnson
Affiliation:
Inst. of Astronomy, Madingley Rd, Cambridge, CB3 0HA, UK
Gerry Gilmore
Affiliation:
Inst. of Astronomy, Madingley Rd, Cambridge, CB3 0HA, UK
Sylvie Beaulieu
Affiliation:
University of Victoria, Victoria, B.C., Canada, V8W 3P6

Abstract

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We present a preliminary analysis of a deep colour-magnitude diagram of NGC 1831, a rich cluster in the LMC. The data were obtained with HST/WFPC2 in the F555W and F814W filters, reaching m555 ⋍ 25 mag. Efficient use of the two-dimensional distribution of data was made by comparing the observed colour-magnitude diagram with model ones. We discuss the process used in accounting for field star contamination and sampling incompleteness in the data. We also describe the algorithm used in building artificial diagrams from model isochrones and the statistical method used in comparing model and data colour-magnitude diagrams. From these comparisons we infer a metallicity Z = 0.008 and a low value, fbin ⋍ 0.25, for the global binary fraction of NGC 1831. We also rule out ages τ ≲ 500 Myr and mass function slope values α ≳ 2.

Type
Part 4. Star Cluster Formation and Evolution: Theory and Observation
Copyright
Copyright © Astronomical Society of the Pacific 2002 

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