Solar granulation from photosphere to low chromosphere observed in Ba II 4554 Å line

Abstract

Aims. The purpose of this paper is to characterize the statistical properties of solar granulation in the photosphere and low chromosphere up to 650 km. Methods.We use velocity and intensity variations obtained at different atmospheric heights from observations in Ba ii 4554 Å. The observations were done during good seeing conditions at the VTT at the Observatorio del Teide on Tenerife. The line core forms rather high in the atmosphere and allows granulation properties to be studied at heights that have been not accessed before in similar studies. In addition, we analyze the synthetic profiles of the Ba ii 4554 Å line by the same method computed taking NLTE effects into account in the 3D hydrodynamical model atmosphere. Results. We suggest a 16-column model of solar granulation depending on the direction of motion and on the intensity contrast measured in the continuum and in the uppermost layer. We calculate the heights of intensity contrast sign reversal and velocity sign reversal. We show that both parameters depend strongly on the granulation velocity and intensity at the bottom photosphere. The larger the two parameters, the higher the reversal takes place in the atmosphere. On average, this happens at about 200-300 km. We suggest that this number also depends on the line depth of the spectral line used in observations. Despite the intensity and velocity reversal, about 40% of the column structure of granulation is preserved up to heights around 650 km.

Properties of oscillatory motions in a facular region

“…We keep the division into the sub-domains since the φ(T, V) histograms naturally split into these four regimes. dataset was taken in June 2004 at the VTT and was used in our earlier work (Kostik et al 2009). The details of the observations can be found in that paper.…”

The Small-scale Structure of Photospheric Convection Retrieved by a Deconvolution Technique Applied to Hinode/SP Data

“…We believe that the reason behind this behavior is the photospheric temperature stratification, in which, towards higher layers, the intensity contrast in the granulation becomes smaller and eventually reverses, i.e., reversed granulation is seen. In this layer, dark blue-shifted granules are surrounded by bright red-shifted intergranular lanes (Kostik et al 2009). The transition from the normal granulation to the reversed one occurs at roughly 130 to 140 km according to the numerical simulations of Wedemeyer et al (2004) and Cheung et al (2007) and at roughly 140 km in the observational work of Ruiz Cobo et al (1996).…”

The Third Signature of Granulation in Bright-Giant and Supergiant Stars

“…In regions where the velocity gradients are large, we are forced to deal with averages. Should we wish to actually scale from the solar velocities, we have numerous choices, e.g., Jin et al (2009), Nordlund et al (2009, Kostik et al (2009), de la Cruz Rodriguez (2011, which leads to some ambiguity. On the other hand, if one is computing models, internal consistency then dictates that the model for the star has the observed scale factor compared to the model for the Sun.…”