Issue |
A&A
Volume 452, Number 1, June II 2006
|
|
---|---|---|
Page(s) | 155 - 162 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20054198 | |
Published online | 17 May 2006 |
Mass segregation in rich LMC clusters from modelling of deep HST colour–magnitude diagrams
1
Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501–970, RS, Brazil e-mail: kerber@astro.iag.usp.br
2
Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, SP, Brazil
Received:
13
September
2005
Accepted:
10
January
2006
Aims.We used the deep colour–magnitude diagrams (CMDs) of five rich LMC clusters (NGC 1805, NGC 1818, NGC 1831, NGC 1868, and Hodge 14) observed with HST/WFPC2 to derive their present day mass function (PDMF) and its variation with position within the cluster.
Methods.The PDMF was parameterized as a power law in the
available main-sequence mass range of each cluster,
typically ; its slope
was determined at different positions spanning from the very centre out to
several core radii. The CMDs in the central regions of the
clusters were carefully studied earlier,
resulting in accurate age, metallicity, distance modulus, and reddening values.
The slope α (where Salpeter is 2.35)
was determined in annuli by following two distinct methods:
1) a power law fit to the PDMF obtained from the systemic luminosity
function (LF);
2) a statistical comparison between observed and model CMDs.
In the second case, α is a free input parameter in the CMD modelling
process where we incorporate photometric errors and
the effect of binarity as a fraction of unresolved binaries
(
%) with random pairing of masses from the same
PDMF.
Results.In all clusters, significant mass segregation is found from
the positional dependence of the PDMF slope:
for
and
Salpeter
inside
(except for Hodge 14, where
Salpeter for
).
The results are robust in the sense that they hold true for both methods used.
The CMD method reveals that unresolved binaries flatten the PDMF obtained
form the systemic LF, but this effect is smaller than the uncertainties
in the α determination.
For each cluster we estimated dynamical ages inside the core and for
the entire system.
In both cases we found a trend in the sense that older clusters have flatter
PDMF, consistent with a dynamical mass segregation and
stellar evaporation.
Key words: galaxies: star clusters / galaxies: Magellanic Clouds / stars: luminosity function, mass function / stars: Hertzsprung-Russell (HR) and C-M diagrams / methods: numerical
© ESO, 2006
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