5 research outputs found
The Gaia–ESO Survey: dynamical models of flattened, rotating globular clusters
We present a family of self-consistent axisymmetric rotating globular cluster models which are fitted to spectroscopic data for NGC 362, NGC 1851, NGC 2808, NGC 4372, NGC 5927 and NGC 6752 to provide constraints on their physical and kinematic properties, including their rotation signals. They are constructed by flattening Modified Plummer profiles, which have the same asymptotic behaviour as classical Plummer models, but can provide better fits to young clusters due to a slower turnover in the density profile. The models are in dynamical equilibrium as they depend solely on the action variables. We employ a fully Bayesian scheme to investigate the uncertainty in our model parameters (including mass-to-light ratios and inclination angles) and evaluate the Bayesian evidence ratio for rotating to non-rotating models. We find convincing levels of rotation only in NGC 2808. In the other clusters, there is just a hint of rotation (in particular, NGC 4372 and NGC 5927), as the data quality does not allow us to draw strong conclusions. Where rotation is present, we find that it is confined to the central regions, within radii of R ≤ 2rh. As part of this work, we have developed a novel q-Gaussian basis expansion of the line-of-sight velocity distributions, from which general models can be constructed via interpolation on the basis coefficients.This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’ Istruzione, dell’ Università ’ e della Ricerca (MIUR) in the form of the grant ‘Premiale VLT 2012’
Atomic data for the Gaia-ESO Survey
We describe the atomic and molecular data that were used for the abundance
analyses of FGK-type stars carried out within the Gaia-ESO Survey. We present
an unprecedented effort to create a homogeneous line list, which was used by
several abundance analysis groups to calculate synthetic spectra and equivalent
widths. The atomic data are accompanied by quality indicators and detailed
references to the sources. The atomic and molecular data are made publicly
available in electronic form. In general experimental transition probabilities
were preferred but theoretical values were also used. Astrophysical gf-values
were avoided due to the model-dependence of such a procedure. For elements
whose lines are significantly affected by hyperfine structure or isotopic
splitting a concerted effort has been made to collate the necessary data for
the individual line components. We also performed a detailed investigation of
available data for line broadening due to collisions with neutral hydrogen
atoms. Synthetic spectra calculated for the Sun and Arcturus were used to
assess the blending properties of the lines. Among a subset of over 1300 lines
of 35 elements in the wavelength ranges from 475 nm to 685 nm and from 850 nm
to 895 nm we identified about 200 lines of 24 species which have accurate
gf-values and are free of blends in the spectra of the Sun and Arcturus. For
the broadening due to collisions with neutral hydrogen we recommend data based
on Anstee-Barklem-O'Mara theory, where available, and to avoid lines of neutral
species otherwise. Theoretical broadening data by R.L. Kurucz should be used
for Sc II, Ti II, and Y II lines. For ionised rare-earth species the Uns\"old
approximation with an enhancement factor of 1.5 for the line width can be used.
Desirable improvements in atomic data were identified for a number of species,
including Al I, S I, Cr II, Na I, Si I, Ca II, and Ni I