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

Abstract

Aims. We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. Methods. We have computed full 3D LTE synthetic spectra based on 3D radiative hydrodynamic atmosphere models from the Stagger-grid in the ranges: T eff from 4000 to 7000 K, log g from 1.5 to 5.0, and [Fe/H], from −4.0 to +0.5. From the resulting intensities, we derived coefficients for the standard limb darkening laws considering a number of often-used photometric filters. Furthermore, we calculated theoretical transit light curves, in order to quantify the differences between predictions by the widely used 1D model atmosphere and our 3D models. Results. The 3D models are often found to predict steeper darkening towards the limb compared to the 1D models, mainly due to the temperature stratifications and temperature gradients being different in the 3D models compared to those predicted with 1D models based on the mixing length theory description of convective energy transport. The resulting differences in the transit light curves are rather small; however, these can be significant for high-precision observations of extrasolar transits, and are able to lower the residuals from the fits with 1D limb darkening profiles. Conclusions. We advocate the use of the new limb darkening coefficients provided for the standard four-parameter non-linear power law, which can fit the limb darkening more accurately than other choices.

Theoretical gravity and limb-darkening coefficients for the MOST satellite photometric system

“…The validity of Eq. (6) was confirmed in other papers on limbdarkening and very recently by Magic et al (2014) for 3D model atmospheres.…”

New view on exoplanet transits

“…The limb-darkening coefficients for a star with the stellar parameters of the Sun and for the visible range are listed in Table 3. Magic et al (2015) used the same RHD simulation as listed in our Table 1 to extract their coefficients. Moreover, we used the law of Claret to fit the average RHD profile 3D of Fig.…”

“…Magic et al (2015;red curve) and with the RHD 3D limb-darkening. Since the magnitude of the intensity variation in the light curve depends on the brightness contrast between the solar disk and Venus, it is noticeable that the RHD synthetic disk image differs from limb-darkening models with particular emphasis at the stellar limb.…”

“…5 and 6). The red and light blue curves represent the limbdarkening Magic et al (2015) and Claret (2000), respectively. In the end, the purple curve represents the limb-darkening carried out using Claret's law for the RHD 3D profile of Fig.…”

“…They have recently been employed (i) in predictions of differential spectroscopy during exoplanet transits to reconstruct spectra of small stellar surface portions that successively become hidden behind the planet (Dravins et al 2014); (ii) and to assess the transit light-curve effects of the limb-darkening issued from 3D RHD simulations with respect to 1D models (Magic et al 2015).…”