The Stagger-grid: A grid of 3D stellar atmosphere models

I. Methods and general properties^⋆,⋆⋆

¹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
e-mail: magic@mpa-garching.mpg.de
² Research School of Astronomy & Astrophysics, Cotter Road, Weston ACT 2611, Australia
³ StarPlan, Natural History Museum of Denmark/Niels Bohr Institute, Øster Voldgade 5–7, 1350 Copenhagen, Denmark
⁴ JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309, USA
⁵ Laboratoire Lagrange, UMR 7293, CNRS, Observatoire de la Côte d’Azur, Université de Nice Sophia-Antipolis, Nice, France
⁶ Department of Physics & Astronomy, Michigan State University, East Lansing, MI 48824, USA

Received: 11 February 2013
Accepted: 10 July 2013

Abstract

Aims. We present the Stagger-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. This grid of 3D models is intended for various applications besides studies of stellar convection and atmospheres per se, including stellar parameter determination, stellar spectroscopy and abundance analysis, asteroseismology, calibration of stellar evolution models, interferometry, and extrasolar planet search. In this introductory paper, we describe the methods we applied for the computation of the grid and discuss the general properties of the 3D models as well as of their temporal and spatial averages (here denoted ⟨3D⟩ models).

Methods. All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~ 220 grid models range in effective temperature, T_eff, from 4000 to 7000  K in steps of 500  K, in surface gravity, log g, from 1.5 to 5.0 in steps of 0.5 dex, and metallicity, [Fe/H], from − 4.0 to + 0.5 in steps of 0.5 and 1.0  dex.

Results. We find a tight scaling relation between the vertical velocity and the surface entropy jump, which itself correlates with the constant entropy value of the adiabatic convection zone. The range in intensity contrast is enhanced at lower metallicity. The granule size correlates closely with the pressure scale height sampled at the depth of maximum velocity. We compare the ⟨3D⟩ models with currently widely applied one-dimensional (1D) atmosphere models, as well as with theoretical 1D hydrostatic models generated with the same EOS and opacity tables as the 3D models, in order to isolate the effects of using self-consistent and hydrodynamic modeling of convection, rather than the classical mixing length theory approach. For the first time, we are able to quantify systematically over a broad range of stellar parameters the uncertainties of 1D models arising from the simplified treatment of physics, in particular convective energy transport. In agreement with previous findings, we find that the differences can be rather significant, especially for metal-poor stars.