New electron density diagnostic line ratios are presented for the O iv 2s22p 2P–2s2p24P and S iv 3s23p 2P–3s3p24P intercombination lines around 1400Å. A comparison of these with observational data for the symbiotic star RR Telescopii (RR Tel), obtained with the Space Telescope Imaging Spectrograph (STIS), reveals generally very good agreement between theory and observation. However the S iv2P3/2–4P1/2 transition at 1423.824Å is found to be blended with an unknown feature at 1423.774 Å. The linewidth for the latter indicates that the feature arises from a species with a large ionization potential. In addition, the S iv2P1/2–4P3/2 transition at 1398.044 Å is identified for the first time (to our knowledge) in an astrophysical source other than the Sun, and an improved wavelength of 1397.166 Å is measured for the O iv2P1/2–4P3/2 line. The O iv and S iv line ratios in a sunspot plume spectrum, obtained with the Solar Ultraviolet Measurements of the Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory, are found to be consistent, and remove discrepancies noted in previous comparisons of these two ions.

We report on many electrostatic nonlinear structures, namely, soliton, explosive, shocklike, and periodic waves, which may exist due to the dynamics of different ion species in Titan's ionosphere. Using the latest available observations of Titan at an altitude of ≈ 1300 km, the main ion components are HCNH+, C2H5+, and C3H5+. The dynamics of these waves are described by the Korteweg–de Vries (KdV) equation. Using the G′/G–expansion method, we obtain a class of solutions that elucidate these nonlinear structures. As the wave amplitude increases, both the width and velocity of the wave deviate from the prediction of the KdV equation. To describe the waves of larger amplitude, the higher-order dispersion has to be taken into account. The G′/G–expansion method is used, for the first time, to solve the KdV equation with higher-order dispersion. We compare between both KdV and higher-order dispersive KdV solutions, i.e., soliton, explosive, shocklike, and periodic waves.

Nonlinear solitary waves are investigated for a plasma system at the night side of Titan’s ionosphere. The plasma model consists of three positive ions, namely C2H , HCNH+, and C3H , as well as Maxwellian electrons. The basic set of fluid equations is reduced to a Korteweg de-Vries (KdV) equation and linear inhomogeneous higher order KdV (LIHO-KdV) equation. The solitary wave solutions of both equations are obtained using a renormalization method. The solitary waves’ existence region and the wave profile are investigated, and their dependences on the plasma parameters at the night side of Titan’s ionosphere are examined. The solitary waves’ phase velocities are subsonic or supersonic, and the propagating pulses are usually positive. The effect of higher-order corrections on the perturbation theory is investigated. It is found that the higher-order contribution makes the amplitude slightly taller, which is suitable for describing the solitary waves when the amplitude augments.

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We investigate the nonlinear ion-acoustic solitary waves for a plasma model in the dayside of ionosphere of Titan. The system of the plasma is composed of three positive ions, namely HCNH⁺, C₂H₅⁺, and CH₅⁺, isothermal electrons and streaming solar wind particles (i.e. protons and electrons). The dynamics of the ion-acoustic waves is described by Korteweg de-Vries (KdV) equation. The analysis has been done by using a reductive perturbation method. The solitary wave solution is obtained and the effects of solar wind parameters on the pulses profile are examined. Furthermore, the effects of the relevant physical parameters on the profiles of soliton waves are investigated. It is found that only positive pulses are existing and there is not any negative pulses. The soliton amplitude increases with the increase of the phase velocity λ and the relative density protons-to-HCNH⁺. Also, it was found that the pulses decrease with the increase of the relative density C₂H₅⁺-to-HCNH⁺ and temperature ratio protons-to-electrons.