Two sets of H, He, and Ca+ emission lines were observed in a quiescent prominence simultaneously with the VTT and the Gregory telescope on Tenerife. At the same time, SUMER took two scans of low-ionized EUV emission lines.

The emission ratios of Ca+–to–Balmer lines from ground vary little in the prominence, indicating a largely constant gas-pressure. In contrast, the ratio of He–to–Balmer from the ground shows the (known) increase toward the prominence borders, indicating higher temperature there. Similarly, the two-dimensional distributions of the ratios S IV/N II and C III/He I show pronounced bright prominence rims.

The reduced He 537Å and He 584Å line widths are 2.6 and 3.6 times larger, respectively, than those of He D3 and He 3888Å. Explaining this by the optical thickness yields τ0 = 104 and τ0 = 2 · 105 for the two EUV lines. The total He 584 emission amounts to 13 watt/m2 ster in the main prominence body where the D3 line yields 4 watt/m2 ster; existing models, however, predict a factor 0.18.

The widths of simultaneously observed optical lines with different atomic weights yield thermal and non-thermal broadening parameters of Tkin ≈ 8000 K and 2.5 < ξ < 6.5 km/s. The EUV lines, however, show line widths which correspond to much higher temperatures and non-thermal velocities. Assuming for each ion the corresponding ionization temperature, the line widths require non-thermal velocities of 15–40 km/s which is similar to values for the quiet corona.

We report results on solar prominences from our observations of the November 3, 1994 total solar eclipse from the North Chile alteplano. From the military base at Putre, we used our transportable CCD camera and telescope, as well as support photographic digitised observations from Putre and Parinacota volcano. The variation of density and equivalent temperature were derived in coronal holes (plumes and interplumes) and in equatorial streamers. We obtained images from the inner to the outer corona, as well as low-resolution spectra of prominences and of the inner corona. We present the analysis of images and spectra of prominences in the Balmer, He I and Ca II lines, and in the Thomson scattered continuum.

On September 21, 1996 a filament located in a region close to an enhanced network was observed with the SOHO SUMER and CDS instruments. Four Lyman lines have been detected (Lδ, Lϵ, L-6, L-7) by SUMER in the raster mode. We have corrected the spectral data for flatfield and destreching and made wavelength and absolute intensity calibrations. In all these lines we detect a central absorption and an asymmetry in the intensity of the two peaks. Preliminary NLTE computations indicate that these Lyman profiles and their absolute intensities can be reproduced with the existing models provided that we take into account a prominence-corona transition region (PCTR).

We demonstrate how the angle-dependent redistribution function can be incorporated into the 2-D transfer modelling of solar prominences. Some preliminary numerical simulations have been performed and we present their results by comparing the emergent hydrogen Lα line profiles computed with the angle-averaged and angle-dependent redistributions.

We present new slab models for quiescent prominences in which both the condition of magnetohydrostatic equilibrium as well as NLTE are fulfilled. Using the Kippenhahn-Schlüter model, a unique relation between the components of the magnetic field on one hand and the gas pressure and width on the other is established for a given uniform temperature. We construct a grid of such NLTE models and compare them with the set of isothermal-isobaric models of Gouttebroze et al. (1993).

We have analyzed a set of spectra of Hα and CaII H & K lines taken from a quiescent prominence with the G1 CCD camera attached to a 25 cm coronagraph at the Norikura Coronal Station, the National Astronomical Observatory of Japan. From these lines we have determined temperature, turbulent velocity and electron density at various locations on the prominence. The final analysis shows that the averaged temperature of the prominence is about 8600K with mean turbulent velocity of 7.5 km/s and with a mean electron density of < ne > = 2.4×1010cm−3.

This study focusses on the less studied aspects of filaments evolution: the coupling of two or more filaments to form a complex filament and also the split of one such filament into many components. This phenomenon was first observed by d’Azambuja – we apply statistical mathematical methods to obtain evolutionary sequences and detect the complex filaments.

We review the observed characteristics of co-rotating clouds of neutral hydrogen recently detected in rapidly rotating, chromospherically active late-type stars and commonly termed “stellar prominences”. Their observed properties are placed in an overall interpretive framework and compared to standard solar prominences.

We present Hα observations of two rapidly-rotating G2 dwarfs in the Alpha Persei cluster and of AB Dor, a young K0 dwarf. All three stars have projected rotational velocities of about 90 km s−1 and axial rotation periods ranging from 11 to 15 hours. He 520 and AB Dor show very clear transient features that move through the profile. The most likely explanation for these features is that they are huge prominences in co-rotation with the star. We also use the recently developed technique of least squares deconvolution to present simultaneous dynamic profiles of the stars’ photospheric lines which show the locations of the surface spots. This technique has allowed us to extend our studies to a greater range of stars.

We study the stability of an idealised model of stellar prominences. We find that surface fields of a few hundred gauss are required to hold them in a stable equilibrium.

We present results from the analysis of spectra of the fast rotating active giant star FK Comae Berenices. The extended emission is interpreted as arising in giant active loops and prominences. The absorption is due to a shell of cold and dense gas (like solar filaments).

Extensive observational background exists about the presence of cool material clouds embedded in the stellar coronae of rapidly rotating, late-type stars. Observations of such clouds in HKAqr (Gliese 890) and HD 197890 suggest that the clouds are at heights smaller than the star’s corotation radius and could be looked at as a phenomenon similar to that of solar prominences. Recent observations of solar prominences have reinforced the evidence about their fibril structure made of many long, thin magnetic flux tubes making angles about 25 degrees with the direction of the filament channel, with only the central 10–20% of the magnetic flux tubes filled with cool matter, which can produce a depression at the summits of the flux tubes. Then, assuming a similar structure for the stellar cool clouds, we have looked for the physical characteristics of such stellar prominences, i.e. the size of the flux tube depression, the density, temperature, half-width and supported mass of the cool region, taking into account gravity variation with height and centrifugal acceleration, since such clouds have been detected at great heights within stellar coronae belonging to rapid rotators.

A time series of Hα spectra of the rapidly rotating star HK Aqr has been analyzed. Evidence is found for the presence of cool clouds which are in co-rotation with the star. The cloud velocities, as derived from the clouds’ absorption features, can be used to put constraints on the clouds’ co-latitudes and their distances from the star using a so-called visibility diagram. For HK Aqr most clouds are at distances of 2–3 stellar radii and do not extend beyond the co-rotation radius. By using a simple radiative transfer model, we demonstrate that for most stars the presence of clouds affects the whole Hα profile and does not result in discrete absorptions. Only clouds near rapidly rotating stars, with an inclination close to 90°, will cause discrete absorption features. The cool cloud plasma can form when a temperature inversion is created at the apex of a stellar-sized coronal loop because of reduced coronal heating at large distances from the star. It is likely that the cloud condensations are related to inverse polarity filaments because, near rapidly rotating stars, the axial current in normal polarity filaments decreases with height and has to change sign at the co-rotation radius.

Channels share with their filaments in a hemispheric dependance for the orientation of their axial magnetic fields. This property has significant implications for models of filaments. In support of new model-building exercises, this review examines known signatures of channels, presents evidence that emerging flux plays a key role in creating a new filament channel, and compares channels which form in the belts of active latitudes with those formed closer to the poles.

We present a model of the transport of photospheric and coronal magnetic fields with the aim of explaining the observed global pattern of dextral and sinistral filaments on the quiet sun. The model is based on the assumption that the axial field in a filament channel originates in the surrounding coronal arcade. The model predicts that switchbacks in the polarity inversion line have opposite chirality on the two arms of the switchback: the higher latitude “lead” arm has sinistral (dextral) orientation in the North (South), while the lower latitude “return” arm has dextral (sinistral) orientation. This is in conflict with prominence observations which show that the chirality is the same on the two arms of a switchback. The model predicts the wrong sign of the axial field in polar crown filaments. This suggests that axial field in quiescent filaments are not produced by differential rotation acting on the surrounding coronal arcades.

From a direct comparison, we find that filament channels are more easily detected in He I λ1083 than in Hλ, particularly for polar crown filaments. He I 1083 nm filament channels appear to coincide with the outer boundaries of Yohkoh/SXT X-ray cavities.

A fast multigrid method to calculate the linear force-free field for a prescribed photospheric flux distribution is outlined. This is used to examine an idealized model of a filament channel. The magnetic fields, for a number of different field strengths and positions, are calculated and the height up to which field lines connect along the channel is examined. This is shown to strongly depend on the value of the helicity of the system. A possible explanation, in terms of the global helicity of the system, is suggested for the dextral/sinistral hemispheric pattern observed in filament channels.

A series of numerical simulations are presented for formation of solar prominences. We have investigated the dynamic and thermodynamic evolution of coronal plasma in response to photospheric horizontal motions. In three different setups of field configurations and footpoint motions, different types of prominences are found to be formed by thermal instability.

Numerical 3D resistive MHD experiments are used to investigate the dynamical properties of a quadrupolar magnetic field, as the two dipolar regions are pushed together. A current concentration is formed between the approaching flux concentrations and, when reconnection starts, material is lifted against gravity. As it rises the material spreads out along the polarity inversion line and forms a prominence-like structure.

Over the years few examples of the formation of filament channels or filaments have been observed. One such example was recently seen by Gaizauskas et al. (1997). This paper constructs force-free models of the main stages of formation.