Umbral chromospheric fine structure and umbral flashes modelled as one: The corrugated umbra

Evidence for Fine Structure in the Chromospheric Umbral Oscillation

Novel spectro-polarimetric observations of the He I multiplet are used to explore the dynamics of the chromospheric oscillation above sunspot umbrae. The results presented here provide strong evidence in support of the two-component model proposed by Socas-Navarro et al. According to this model, the waves propagate only inside channels of sub-arcsecond width (the “active” component), whereas th...

The Umbral Refinement Equation

Algebras and the Umbral Calculus ∗

We apply Baxter algebras to the study of the umbral calculus. We give a characterization of the umbral calculus in terms of Baxter algebra. This characterization leads to a natural generalization of the umbral calculus that include the classical umbral calculus in a family of λ-umbral calculi parameterized by λ in the base ring.

A study on Ca II 854.2 nm emission in a sunspot umbra using a thin cloud model

In the present work, we introduce and explain a method of solution of the radiative transfer equation based on a thin cloud model. The efficiency of this method to retrieve dynamical chromospheric parameters from Stokes I profiles of Ca II 854.2 nm line showing spectral emission is investigated. The analyzed data were recorded with the Crisp Imaging Spectro-Polarimeter (CRISP) at Swedish 1-m So...

Formal Calculus and Umbral Calculus

We use the viewpoint of the formal calculus underlying vertex operator algebra theory to study certain aspects of the classical umbral calculus. We begin by calculating the exponential generating function of the higher derivatives of a composite function, following a very short proof which naturally arose as a motivating computation related to a certain crucial “associativity” property of an im...