27 research outputs found
Coherent thermal radiation of Fabry-Perot resonator structures
The coherent thermal radiation from semiconductor plane-parallel resonator
structures is investigated both theoretically and experimentally. The coherent properties
of thermal radiation from these objects are manifested by sharp spectral lines and wellpronounced
lobe-like directional patterns. We investigated the dependences of the
intensities of spectral lines and the angular distribution of thermal radiation on optical
parameters of the structures. New optical effects are presented, namely, the modulation
of the coherent thermal radiation spectrum by an external magnetic field and a uniaxial
pressure
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Coherent scattering effects in the polarizing properties of the Galilean satellites of Jupiter
Dependence of the aerosol component of optical thickness and the relative concentration of methane on depth in atmospheres of giant planets
Astronomical observations and monitoring surveys of the Earth from the surface or from the Moon’s orbit and their ground support
On the efficiency of polarization measurements while studying aerosols in the terrestrial atmosphere
Mechanism for the addition of acetals to vinyl alkyl ethers in the presence of lewis acids
HYDRO2GEN: Non-thermal hydrogen Balmer and Paschen emission in solar flares generated by electron beams
Aims. Sharp rises of hard X-ray (HXR) emission accompanied by H↵ line profiles with strong red-shifts up to 4 Å from the central wavelength, often observed at the onset of flares with the Specola Solare Ticinese Telescope (STT) and the Swedish Solar Telescope (SST), are not fully explained by existing radiative models. Moreover, observations of white light (WL) and Balmer continuum emission with the Interface Region Imaging Spectrograph (IRIS) reveal strong co-temporal enhancements and are often nearly cospatial with HXR emission. These effects indicate a fast effective source of excitation and ionisation of hydrogen atoms in flaring atmospheres associated with HXR emission. In this paper we investigate electron beams as the agents accounting for the observed hydrogen line and continuum emission.
Methods. Flaring atmospheres are considered to be produced by a 1D hydrodynamic response to the injection of an electron beam defining their kinetic temperatures, densities, and macro velocities. We simulated a radiative response in these atmospheres using a fully non-local thermodynamic equilibrium (NLTE) approach for a 5-level plus continuum hydrogen atom model, considering its excitation and ionisation by spontaneous, external, and internal diffusive radiation and by inelastic collisions with thermal and beam electrons. Simultaneous steady-state and integral radiative transfer equations in all optically thick transitions (Lyman and Balmer series) were solved iteratively for all the transitions to define their source functions with the relative accuracy of 105. The solutions of the radiative transfer equations were found using the L2 approximation. Resulting intensities of hydrogen line and continuum emission were also calculated for Balmer and Paschen series.
Results. We find that inelastic collisions with beam electrons strongly increase excitation and ionisation of hydrogen atoms from the chromosphere to photosphere. This leads to an increase in Lyman continuum radiation, which has high optical thickness, and after the beam is off it governs hydrogen ionisation and leads to the long lasting order of magnitude enhancement of emission in Balmer and Paschen continua. The ratio of Balmer-to-other-continuum head intensities are found to be correlated with the initial flux of the beam. The height distribution of contribution functions for Paschen continuum emission indicate a close correlation with the observations of heights of WL and HXR emission reported for limb flares. This process also leads to a strong increase of wing emission (Stark’s wings) in Balmer and Paschen lines, which is superimposed on large red-shifted enhancements of H↵-H line emission resulting from a downward motion by hydrodynamic shocks. The simulated line profiles are shown to fit the observations for various flaring events closely