Hydrogen Hα Line Research Articles

Hα Emission in the Giant Components of RS CVn Systems

The Hα line of hydrogen is a very powerful tool for the study of the solar chromosphere (plages, flares, prominences). Although it is difficult to derive in a simple way quantitative information, like chromospheric temperature and electron density, because of the very extensive depth of its formation and the very complex mechanism of excitation, Hα has been successfully used to study the chromospheres of active stars (Herbig, 1985). Moreover this diagnostic has proved to be very useful for the study of surface inhomogeneities and transient phenomena like flares in systems of the RS CVn type and other active stars (Bopp, 1981; Bopp et al., 1988; Fraquelli, 1982).With the aim of investigating the behaviour of chromospheric activity, we have undertaken an extensive monitoring of Hα emission in a selected group of RS CVn binaries (Strassmeier et al., 1988). We report here preliminary results of the observations obtained in 1988–1989.

Time-resolved spectroscopic measurement of anode plasma in magnetically-insulated diode

A new diagnostic technique has been developed for the time-resolved spectroscopic measurement of anode plasma in a single-current-feed magnetically-insulated iondiode. From the measurement of Stark broadening of Hα line of hydrogen, we have estimated the electron density to be 4 ∼ 5 × 1016 cm−3 using the pulse-power generator, ‘ETIGO-I’, typically operated with diode voltage, 550 and 600 kV, diode current, 36 and 53 kA, and pulse width ∼ 90 ns (FWHM of diode current). Assuming local thermodynamic equilibrium, we have estimated the electron temperature to be l·9∼2·4eV from the measurement of light intensity ratio of successive ionization stages of carbon. The expansion velocity of the anode plasma has been found to be 4∼4·5cm/μS.

Stark broadening of the Hα line of hydrogen at low densities: quantal and semiclassical results

Stark profiles of the H alpha lines of hydrogen are computed at low densities (from 1010 to 1013 cm-3) in the 'impact' theory. By a comparison with quantal results the authors show that a simple semiclassical perturbational approach with appropriate cutoffs is sufficient to give accurate profiles in the line centre. Neglecting the natural broadening and the fine-structure effects, they prove that the electronic broadening is negligible and that the profile has a Lorentzian shape, and they give an analytical expression of the half width.

Potential models of the unipolar sunspot magnetic field

The potential models of the unipolar sunspot magnetic field are calculated on the basis of magnetographic measurements of the magnetic field made in the three spectral lines of different intensities, Hα, Cai λ6103 and Fei λ4808. The computed distributions of the magnetic field vector are compared with actual distributions observed at these three levels. It is shown that the electric current density in the spot reaches values up to 105 CGSE in the volume contained between formation depths of two pairs of lines, Fei λ4808-Cai λ6103 and Fei λ4808 - Hα. Therefore, the magnetic field of the spot deviates strongly from a potential configuration. To the contrary, at higher levels, in the semi-infinite volume restricted at the bottom by the hydrogen Hα-line, the field appears to be quite close to a potential one.