Quantum unified theory applied to Ly

New quantum calculations for the Lyβ, Lyγ, Lyδ profiles perturbed by electron collisions are obtained from the unified one-perturber theory in the exact resonance approximation (Tran-Minh et al. 1975, J. Phys. B: Atom. Molec. Phys., 8, 1810; Feautrier et al. [CITE], J. Phys. B: Atom. Molec. Phys., 9, 1871). This accounts for the-long range dipole interaction. The profiles are obtained by summing the partial contributions of each total angular momentum LT. It appears that there is a threshold $L_{\min}$ below which some eigenchannels become complex and are not well described by the exact resonance method. To overcome this problem, the contribution of the first angular momenta is estimated by taking into account the real eigenvalues and by neglecting the complex ones. Estimation of the error due to this systematic underestimation of the profile is given. Density effects due to the Debye screening are found in the near wings

Coherent Redistribution in the Doppler Core of the O VI 1032 Å Line in the Solar Wind Acceleration Region

International audienc

Work in progress in Atomic Physics at the Meudon Observatory in relation with the Study of the Solar Activity

International audienc

Asymmetric shocks in χ\chi Cyg observed with linear spectropolarimetry

Aims: From a coherent interpretation of the linear polarisation detected in the spectral lines of the Mira star $\chi$ Cyg, we derive information about the dynamics of the stellar photosphere, including pulsation. Methods: From spectropolarimetric observations of $\chi$ Cyg, we perform careful analysis of the polarisation signals observed in atomic and molecular lines, both in absorption and emission, using the radiative transfer in the polarisation context, through two mechanisms: intrinsic polarisation and continuum depolarisation. We also explain the observed line doubling phenomenon in terms of an expanding shell in spherical geometry, which allows us to pinpoint the coordinates over the stellar disk with enhanced polarisation. Results: We find that the polarised spectrum of $\chi$ Cyg is dominated by intrinsic polarisation, with a negligible continuum depolarisation. The observed polarised signals can only be explained by assuming that this polarisation is locally enhanced by velocity fields. During the pulsation, radial velocities are not homogeneous over the disk. We map these regions of enhanced velocities. Conclusions: We have set an algorithm to distinguish in any stellar spectra of linear polarisation the origin of this polarisation and the way to increase signal by coherently adding many lines with an appropriated weight. Applied to the Mira star $\chi$ Cyg, we reached the unexpected result that during the pulsation, velocities are radial but not homogeneous over the disk. The reason for these local velocity enhancements are probably related to the interplay between the atmospheric pulsation dynamics and the underlying stellar convection