Abstract
We deal with granular intensity fluctuations in the Sun and how they are caused by temperature fluctuations. We calculate temperature response functions RFT(λ,z) in the solar photosphere. We apply the Diagonal Element Lambda Operator (DELO) method to calculate the response functions for the continuum (λλ = 380nm-2.5 µ). LTE is assumed throughout. It is demonstrated that, within the framework of the linear approximation, the H − continuum absorption plays an important role for the formation of the fluctuations in continuum images. It counteracts substantially the intensity fluctuations caused by variations of the Planck function. The temperature response functions are used to calculate, for three models of temperature fluctuations, the continuum intensity contrasts and their formation height for the above wavelength range.
Highlights
We deal with granular intensity fluctuations in the Sun and how they are caused by temperature fluctuations
It is a widespread believe that the fluctuation of the granular intensity pattern on the Sun can be approximated by the simple relation δIλ/Iλ = δBλ/Bλ with Bλ being the Planck function
In the linear approximation with δBλ ∝ δT, the observation of δIλ would give a good proxy to δT at some optical depth τλ ≈ cos θ, the latter according to the Eddington-Barbier relation
Summary
In the linear approximation with δBλ ∝ δT , the observation of δIλ would give a good proxy to δT at some optical depth τλ ≈ cos θ, the latter according to the Eddington-Barbier relation. Such reasonning falls short on two grounds: 1) It neglects the opacity changes due to temperature changes. We restrict ourselves to the linear regime from which one can already gain insight into the formation of intensity fluctuations, without the need to refer to complex non-linear calculations For this purpose, it is appropriate to calculate temperature response functions RFT(λ, z) for a given mean solar atmospheric model.
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