A grid of MARCS model atmospheres for late-type stars

Abstract

Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. This includes "CN-cycled" models with C/N = 4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 ≤ ξ t ≤ 5 km s −1 . We also list thermodynamic quantities (T , P g , P e , ρ, partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with planeparallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying.Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate "rules of thumb" concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.

Improved constraints on the expansion rate of the Universe up to z ∼ 1.1 from the spectroscopic evolution of cosmic chronometers

“…We found that, in the range of D4000 n relevant for our analysis, while the absolute values of D4000 n are different, the slopes are not strongly dependent on the α-enhancement, with a percentage difference between 2% and 8% 6 . This results is confirmed also studying single stellar population models based on MARCS theoretical libraries [99], using solar metallicity and [α/F e] = 0, 0.4 (Claudia Maraston, private communication); in this case the difference in D4000 n is extremely small, on average only ∼ 0.5%, with a percentage variation in the slope of ∼ 8%. As a final remark, it has to be considered also that since in our analysis we consider the most massive ETGs, these galaxies will have quite similar enhancements, so that considering this effect will not introduce an additional systematic error, but just a shift in the slope.…”

Tracing the evolution of the Galactic bulge with chemodynamical modelling of alpha-elements

“…The atmospheric models were obtained by interpolation in the grid of MARCS LTE models (Gustafsson et al 2008). The spectrum synthesis code used is described in Barbuy et al (2003) and Coelho et al (2005).…”

VLT/FLAMES spectroscopy of red giant branch stars in the Carina dwarf spheroidal galaxy

“…We used a grid of OSMARCS atmosphere models in spherical symmetry (Gustafsson et al, 2008) Spite (1967) and continuously improved since then. Abundances were first computed for each individual line and the uncertainties on the EW measurements given by DAOSPEC are propagated into uncertainties on individual abundances.…”