Plasma diagnostic of a solar prominence from hydrogen and helium resonance lines

We present the first comparison of profiles of H et He resonance lines observed by SUMER with theoretical profiles computed with our non-LTE radiative transfer code. We use the H I Lyman-beta, H I Lyman-epsilon, and He I 584 A lines. Our code allows us to obtain the plasma parameters in prominences in conjunction with a multi-line, multi-element set of observations. The plasma temperature in the prominence core is ~ 8600 K and the pressure is 0.03 dyn/cm^2. The Ly-beta line is formed in a higher temperature region (more than 11000 K).Comment: 2 pages, 2 color figures. Proceedings of SF2A, Semaine de l'Astrophysique Francaise, Journees de la SF2A 2006, Pari

Diagnostics of active and eruptive prominences through hydrogen and helium lines modelling

In this study we show how hydrogen and helium lines modelling can be used to make a diagnostic of active and eruptive prominences. One motivation for this work is to identify the physical conditions during prominence activation and eruption. Hydrogen and helium lines are key in probing different parts of the prominence structure and inferring the plasma parameters. However, the interpretation of observations, being either spectroscopic or obtained with imaging, is not straightforward. Their resonance lines are optically thick, and the prominence plasma is out of local thermodynamic equilibrium due to the strong incident radiation coming from the solar disk. In view of the shift of the incident radiation occurring when the prominence plasma flows radially, it is essential to take into account velocity fields in the prominence diagnostic. Therefore we need to investigate the effects of the radial motion of the prominence plasma on hydrogen and helium lines. The method that we use is the resolution of the radiative transfer problem in the hydrogen and helium lines out of local thermodynamic equilibrium. We study the variation of the computed integrated intensities in H and He lines with the radial velocity of the prominence plasma. We can confirm that there exist suitable lines which can be used to make a diagnostic of the plasma in active and eruptive prominences in the presence of velocity fields.Comment: 5 pages, 4 colour figure

Effect of motions in prominences on the helium resonance lines in the extreme ultraviolet

<b>Context</b>: Extreme ultraviolet resonance lines of neutral and ionised helium observed in prominences are difficult to interpret as the prominence plasma is optically thick at these wavelengths. If mass motions are taking place, as is the case in active and eruptive prominences, the diagnostic is even more complex. <b>Aims</b>: We aim at studying the effect of radial motions on the spectrum emitted by moving prominences in the helium resonance lines and at facilitating the interpretation of observations, in order to improve our understanding of these dynamic structures. <b>Methods</b>: We develop our non-local thermodynamic equilibrium radiative transfer code formerly used for the study of quiescent prominences. The new numerical code is now able to solve the statistical equilibrium and radiative transfer equations in the non-static case by using velocity-dependent boundary conditions for the solution of the radiative transfer problem. This first study investigates the effects of different physical conditions (temperature, pressure, geometrical thickness) on the emergent helium radiation. <b>Results</b>: The motion of the prominence plasma induces a Doppler dimming effect on the resonance lines of HE i and HE ii. The velocity effects are particularly important for the HE ii λ 304 Å line as it is mostly formed by resonant diffusion of incident radiation under prominence conditions. The HE i resonance lines at 584 and 537 Å also show some sensitivity to the motion of the plasma, all the more when thermal emission is not too important in these lines. We also show that it is necessary to consider partial redistribution in frequency for the scattering of the incident radiation. Conclusions.This set of helium lines offers strong diagnostic possibilities that can be exploited with the SOHO spectrometers and with the EIS spectrometer on board the Hinode satellite. The addition of other helium lines and of lines from other elements (in particular hydrogen) in the diagnostics will further enhance the strength of the method

Modelling of helium spectrum in solar prominences

No abstract available

The helium spectrum in moving solar prominences

No abstract available

Optical determination and identification of organic shells around nanoparticles: application to silver nanoparticles

We present a simple method to prove the presence of an organic shell around silver nanoparticles. This method is based on the comparison between optical extinction measurements of isolated nanoparticles and Mie calculations predicting the expected wavelength of the Localized Surface Plasmon Resonance of the nanoparticles with and without the presence of an organic layer. This method was applied to silver nanoparticles which seemed to be well protected from oxidation. Further experimental characterization via Surface Enhanced Raman Spectroscopy (SERS) measurements allowed to identify this protective shell as ethylene glycol. Combining LSPR and SERS measurements could thus give proof of both presence and identification for other plasmonic nanoparticles surrounded by organic shells

Prediction of line intensity ratios in solar prominences

No abstract available

Line profiles and intensity ratios in prominence models with a prominence to corona interface

In this work we study the hydrogen, helium and calcium spectra emitted by a one-dimensional prominence model in magneto-hydrostatic equilibrium. The prominence slab consists of two parts: a cool core where the plasma is optically thick for some lines, and a prominence-to-corona transition region (PCTR) with a strong temperature gradient. The models are defined by 5 parameters: temperature, pressure, slab thickness, microturbulent velocity and altitude. We solve the NLTE radiative transfer equations for all optically thick transitions. We present line ratios between infrared, optical and EUV lines, as well as line profiles. We show that the presence of a PCTR, where both collisional and radiative excitations are important, affects H, He, and Ca populations and emergent lines in different manners

Oracle-based optimization applied to climate model calibration

In this paper, we show how oracle-based optimization can be effectively used for the calibration of an intermediate complexity climate model. In a fully developed example, we estimate the 12 principal parameters of the C-GOLDSTEIN climate model by using an oracle-based optimization tool, Proximal-ACCPM. The oracle is a procedure that finds, for each query point, a value for the goodness-of-fit function and an evaluation of its gradient. The difficulty in the model calibration problem stems from the need to undertake costly calculations for each simulation and also from the fact that the error function used to assess the goodness-of-fit is not convex. The method converges to a ‘best fit' estimate over 10 times faster than a comparable test using the ensemble Kalman filter. The approach is simple to implement and potentially useful in calibrating computationally demanding models based on temporal integration (simulation), for which functional derivative information is not readily availabl