Physical parameters of a mid-latitude streamer during the declining phase of the solar cycle

Abstract

Context. Investigating the physical properties of solar coronal streamers is important for understanding their role in the global magnetic structure of the extended solar atmosphere, as well as in the generation of the slow solar wind. Aims. We hope to contribute as completely as possible to the ongoing SOHO instruments campaign devoted to the study of the physical characteristics of coronal streamers at various heliocentric distances. Results. Electron densities and temperatures, H i and O vi kinetic temperatures, and outflow velocities were derived from the line intensities and widths, as well as from the O vi line intensity ratio in the 1.6−5 R range of heights, limited to the central region of the streamer. To our knowledge, the H i outflow velocities obtained in this work are the first ones determined inside a streamer structure. They are significantly lower than those of the O vi ions. This, together with the O vi kinetic temperatures that are much higher than the H i ones, suggest that the absorption of Alfvén waves at the ion cyclotron frequency might also occur inside streamers. Methods. We analyzed ultraviolet H iConclusions. In comparison with other streamers described in the literature, the structure examined in this work generally exhibits lower electron density and neutral hydrogen kinetic temperature. Conversely, the O vi kinetic temperature and outflow velocity radial profiles are consistent with the results for the other examined streamers.

Mapping the coronal hydrogen temperature in view of the forthcoming coronagraph observations by Solar Orbiter

“…We derive the H i temperature component T starting from the T ⊥ values obtained by the fitting procedure discussed in Sect. 2, and properly adopting the values of anisotropy found by Cranmer et al (1999) and Spadaro et al (2007). The results are shown in Figs.…”

“…5 as a function of the heliocentric distance. More recently Spadaro et al (2007) determined the physical parameters of a mid-latitude streamer during the declining phase of the solar cycle. They used a bi-Maxwellian distribution for the emitting ions in the Doppler dimming computation and found that the component of the H i temperature parallel to the magnetic field results in a factor of 1.3 smaller than the respective perpendicular component, independent of height (see Fig.…”

“…Cranmer et al 1999;Spadaro et al 2007). This condition can be formally described by a bi-Maxwellian distribution with two different temperature components T ⊥ and T (see details in Allen et al 1998) for the emitting particles moving along directions perpendicular and parallel to the magnetic field lines, respectively.…”

“…13 0, 45, 180, 225 2004 for some selected coronal structures (see e.g. Dolei et al 2015;Spadaro et al 2007;Susino et al 2008), despite the huge amount of the Lyα data obtained by UVCS. The aim of this work is to exploit all the potential of the UVCS Lyα database by systematically analysing the observations referring to a lot of polar, mid-latitude and equatorial structures at different phases of the solar activity.…”

Visible light and ultraviolet observations of coronal structures: physical properties of an equatorial streamer and modelling of the F corona

“…In so doing, the solar wind outflow velocity turns out to be the only free parameter in the theoretical modelling of the Lyα intensity for the first time. It is worthwhile noting that in the past the extent of the streamer along the LOS has just been assumed (see Spadaro et al 2007;Susino et al 2008).…”