D3 Line Research Articles

Altitude Heterogeneity of Magnetic Fields and Doppler Velocities in the Area of Seismic Source of a Strong Solar Flare from Data in Helium, Sodium, and Nickel Lines

Measurements of magnetic fields near seismic sources during solar flares are vital for understanding the dynamics of solar activity. We used spectropolarimetric observations of the X17.2/4B solar flare on 28 October 2003, over a wavelength interval of 43 Å, including the D3, D2, D1, and Ni I 5892.88 Å lines, to analyze the Stokes I ± V profiles. Effective magnetic fields within 0.5–1.5 kG were measured in the D1, D2, and D3 lines at different flare locations, with the photospheric Ni I 5892.88 Å line showing a weaker field of below 0.5 kG. The D3 line showed rapid plasma descents of up to 11 km/s, in contrast to the slower velocities within 2.3 km/s observed in other lines. The differing amplitudes in the I + V and I − V profiles indicated potential non-Zeeman polarization effects. Secondary Stokes V peaks were also detected up to 8 Å from the D3 emission core. Significant altitudinal inhomogeneity in the magnetic field strengths was detected, possibly indicating the local magnetic collapse, facilitating the Lorentz-force driven mechanism of the seismic source excitation.

Linear Polarization of the Helium D3 Line by Accelerated Protons in the Solar Chromosphere

Linear Polarization of the Helium D3 Line by Accelerated Protons in the Solar Chromosphere

Unique spectral manifestations around the D3 line observed in the region close to the seismic source of a large solar flare

ABSTRACT The main goal of our research is to search for super-strong magnetic fields in active processes on the Sun. Our method is based on Stokes V spectro-polarimetry in a wide spectral range from −14 Å to +29 Å relative to the D3 He i line. The object of the study is the area of a seismic source in the large solar flare on 2003 October 28 of the X17.2/4B class. The novelty of our study: we found characteristic spectral manifestations – secondary Stokes V peaks – far from D3 line, at distances of several angstroms. These secondary peaks have the following features: (a) their amplitudes reach 4 per cent – almost an order of magnitude more than previously detected in other flares, (b) in the general picture, the sign of the circular polarization changes when passing through the D3 centre, and (c) narrower spectral peculiarities were found at distances of +4.0, +6.3, and +8.5 Å, where the polarization sign also changes sharply. This unusual feature likely results from significant factors in the area of the seismic source, including substantial descending plasma velocities which exceed 400 km s−1 and, perhaps, super-strong magnetic fields.

First Metis Detection of the Helium D3 Line Polarization in a Large Eruptive Prominence

Metis on board Solar Orbiter is the space coronagraph developed by an Italian–German–Czech consortium. It is capable of observing solar corona and various coronal structures in the visible-light (VL) and UV (hydrogen Lyα) channels simultaneously for the first time. Here we present observations of a large eruptive prominence on 2021 April 25–26, in the VL, taken during the mission cruise phase, and demonstrate that apart from the broadband continuum emission, which is due to the Thomson scattering on prominence electrons, we detect a significant radiation in the neutral-helium D3 line (587.6 nm), which lies within the Metis VL passband. We show how the prominence looks like in Stokes I, Q, and U. We consider two extreme cases of the prominence magnetic field, and we separate the Stokes I and Q signals pertinent to Thomson scattering and to the D3 line. The degree of linear polarization of the D3 line (both Q and U) indicates the presence of the prominence magnetic field; hence Metis can serve as a magnetograph for eruptive prominences located high in the corona.

Search for superstrong magnetic fields in active processes on the Sun using spectro-polarimetry within 15 Å around the D3 line

ABSTRACT We critically review our previous results on this topic based on the following main points: (i) substantially larger wavelength range around the D3 line was investigated – up to ±15 Å instead of ±2.5 Å in comparison with the previous version of our study, and (ii) greater volume of observational data was analysed, including one X limb flare, additionally. Overall, our study concerns the 2004 July 12 active prominence and the 2014 June 10 limb flare of X1.5 class. For named limb flare, we found reliable and oppositely polarized secondary peaks of the V parameter located at distances of −4.5 and +2.7 Å from the line center. If these features are interpreted as manifestations of the magnetic splitting of the line together with its Doppler shift, then the corresponding magnetic field is ≈2.2 × 105 G, and the radial velocity −46 km s−1. Similar spectral manifestations were also found in the active prominence. For comparison with the theory, the spectral features of the Paschen–Baсk effect at magnetic fields up to 100 kG were studied too. It turned out that the theoretical width of the splitting components is relatively small, 0.3 Å, while the width of the observed peaks is sometimes much larger. On the basis of model calculations, it is shown that in some cases an alternative explanation of the observational data is possible, which includes much weaker magnetic fields (5.5–7.1 kG), but significant macroscopic velocities of different signs, at the level of 50–60 km s−1.

Prominence detection and chromosphere feature on the prototype RS CVn of active binary systems

ABSTRACT We present a study of high-resolution spectra of RS Canum Venaticorum (RS CVn), a prototype of active binary systems. Our data were obtained from 1998 to 2017 using different telescopes. We analyse the chromospheric activity indicators $\rm{Ca~{\small II}}$ IRT, Hα, $\rm{Na~{\small I}}$ D1, D2 doublet, $\rm{He~{\small I}}$ D3, and Hβ using a spectral subtraction technique. The chromospheric emission stems mainly from the K2 IV primary star, while the F5 V secondary star only shows weak emission features in a few of our spectra. We find excess absorption features in the subtracted Hα lines and other activity indicators from spectra taken near primary eclipse, which we ascribe to prominence-like material associated with the primary star. We estimate size limits of these tentative prominences based on the geometry of the binary system, and investigate the physical properties of the strongest prominence. An optical flare, characterized by $\rm{He~{\small I}}$ D3 line emission, together with stronger emission in other activity lines, was detected. The flare energy is roughly comparable to strong flares observed on other RS CVn-type stars. The chromospherically active longitudes of RS CVn most frequently appear near the two quadratures of the system and display changes between observing runs, which indicates an ongoing evolution of its active regions.

Revised physical parameters and study on magnetic activities for the eclipsing binary USNO-B1.0 1387-0467554

ABSTRACT We present optimized physical parameters of the active eclipsing binary system USNO-B1.0 1387-0467554 discovered recently in Yunnan–Hong Kong wide-field photometric (YNHK) survey, based on the analysis of its two colour light curves and low resolution spectra obtained at Yunnan Observatories, China. Its spot distributions are derived by means of the Wilson–Devinney code, using photometric data of the YNHK survey from 2016 to 2021. There exist active longitude belts for the spot activities on the primary star, for which the effect of tidal force seems dominant comparing with the one of common magnetic field of the binary system. We have investigated its chromospheric activities through the indicators including Hα, Hβ, CaII H&K, and HeI D3 lines covered by the low resolution spectroscopic observations. There are obvious spatial correlations between the magnetic activities in its photosphere and chromosphere. The EHα/EHβ values suggest that both plages and prominences led to the emissions seen in the Balmer lines at most phases. A prominence structure appeared around the phase of 0.8 on 2018 October 25 and evolved in November and December, 2018. The spectra demonstrate that there were frequent flare events in the system. Moreover, the decay part of a white-light flare event was hunted by the YNHK survey on 2021 October 26.

МОЖЛИВОСТІ АСТРОНОМІЧНИХ І ЕКОЛОГІЧНИХ ДОСЛІДЖЕНЬ ІЗ ГОРИЗОНТАЛЬНИМ СОНЯЧНИМ ТЕЛЕСКОПОМ АСТРОНОМІЧНОЇ ОБСЕРВАТОРІЇ КНУ – ОБ'ЄКТОМ НАЦІОНАЛЬНОГО НАДБАННЯ

B a c k g r o u n d . The appearance in recent years of large solar telescopes, which achieve a spatial resolution of up to 50 km on the Sun, exacerbates the question of the feasibility of using much smaller solar telescopes. The presented work argues the thesis that even medium and relatively small solar telescopes can provide important information that corresponds to the current level of science in the fields of astronomy and environmental research. This is due to the fact that for spectral-polarization studies of active processes on the Sun, not only direct spatial resolution is critically important, but also spectral resolution and the width of simultaneous spectrum registration. At the same time, high spectral resolution can to some extent compensate for insufficiently high spatial resolution. The purpose of the presented work was to highlight specific methodological approaches and results in the specified scientific directions using the example of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv (hereinafter – HST AO KNU), which recently received the status of an object of national heritage. M e t h o d s . The spectral-polarization method was mainly used for analysis of observational data in many spectral lines formed in the “photosphere-lower corona” height range. The local characteristics of the magnetic fields on the Sun were determined both by the direct method (for sunspots) and by analyzing subtle effects in the distant wings and the nearby spectral continuum of H-alpha and D3 helium lines (for solar flares). In the latter case, the local characteristics of the magnetic field and the velocity field were also estimated by simulation. R e s u l t s . According to the observations with the HST of AO KNU, a reliable circular polarization of the opposite sign was found in the far wings of H-alpha and D3 HeI lines in two powerful solar flares of X class, which most likely indicates magnetic fields of 105 G range. To justify this interpretation, theoretical features of the Paschen-Back effect in magnetic fields up to 100 kG were investigated by Ivan Yakovkin. It turned out that at such fields the spectral width of the splitting components of the D3 line is relatively small, 0.3 Å, while the width of the observed peaks is sometimes much larger, which may indicate a significant dispersion of the magnetic field intensities in the flares. On the basis of model calculations, it is shown that in some cases an alternative explanation of the observed data is possible, which includes much weaker magnetic fields (5.5-7.1 kG), but significant macroscopic velocities of different signs, at the level of 50-60 km s -1 . C o n c l u s i o n s . We conclude that spectral-polarization observations of active processes on the Sun using the HST of AO KNU have the greatest value when they are carried out in the monitoring mode and with the aim of recording extremely powerful manifestations of solar activity. It was shown that magnetic fields of 105 G range are possible in solar flares even in the lower solar corona till heights of 10-20 Mm, which is of considerable interest for the MHD theory of concentrated fields in the solar atmosphere

Character Testing Of New Superior Rice Line Through Participatory Plant Breeding Method

Among the superior varieties can be obtained through breeding. The low level of farmer adoption of improved varieties resulting from breeding is partly due to the different preferences of farmers with breeding. The development of specific varieties will be successful through a participatory breeding program that involves breeders, farmers and rice industry players in the selection process for prospective new varieties. The research objective was to analyze and select the quantitative and qualitative characters of 12 new rice lines to produce new superior rice varieties that were more suitable to farmers' tastes. The research in the field was compiled using a Randomized Completely Block Design (RCBD), as a treatment consisting of 12 lines of F11 generation, each treatment was repeated three times. Observations were made on the like and dislike statements of respondents consisting of 20 farmers on the phenotypic character of each line, as well as an assessment of the phenotype acceptance of each line as assessed by the breeders (4 breeders) before harvest following the guidelines (IRRI, 2002) . The results showed that the F3 line had the highest preference value, namely the value of 0.9, meaning that the farmers liked the most. The line with the lowest preference value is the D2 line with a value of -1 (minus one), meaning that it is the least preferred. Based on the phenotype acceptance value of the breeders for each line, three lines had a phenotypic value of 1 or very good value, namely the B4, H1, and H4 lines, while those with a value of 3 or good were eight lines, namely the B2, B3, B7, D2, D3, F3, F4, and L2 lines. One line has a bad phenotype value, namely the K.

Magnetic activities on two single-lined RS Canum Venaticorum binaries IM Pegasi and σ Geminorum

ABSTRACT We present the study on continuous high-resolution spectroscopic observations of two long-period single-lined RS Canum Venaticorum (RS CVn) binary stars IM Pegasi (IM Peg) and σ Geminorum (σ Gem), obtained with the Hertzsprung SONG telescope during the 2015–2016 season. Chromospheric activity indicators Hα, $\rm{Na\,\,{\small I}}$ D1, D2 doublet, $\rm{He\,\,{\small I}}$ D3, and Hβ lines have been analysed by using the spectral subtraction technique. The expected chromospheric emission features in the Hα, $\rm{Na\,\,{\small I}}$ D1, D2 doublet, and Hβ lines confirm that both of two stars are very active systems. In the spectra, the $\rm{He\,\,{\small I}}$ D3 line had been always detected in absorption feature. Although the behaviour of chromospheric activity indicators is very similar for both stars, the activity level of IM Peg is much stronger than that of σ Gem. Moreover, the equivalent width variations of the Hα, $\rm{He\,\,{\small I}}$ D3, and Hβ line subtractions correlate well and show different behaviour among different orbital cycles, which indicates the presence and evolution of activity longitudes over the surface of two stars. Furthermore, the subtracted Hα line profile is usually asymmetric. The red-shifted excess absorption features could be interpreted as a strong down-flow of cool absorbing material, while the blue-shifted emission component is probably caused by up-flow of hot materials through microflare events.

He i 10830 Å Dimming during Solar Flares. I. The Crucial Role of Nonthermal Collisional Ionizations

Abstract While solar flares are predominantly characterized by an intense broadband enhancement to the solar radiative output, certain spectral lines and continua will, in theory, exhibit flare-induced dimmings. Observations of transitions of orthohelium He i λ λ 10830 Å and the He i D3 lines have shown evidence of such dimming, usually followed by enhanced emission. It has been suggested that nonthermal collisional ionization of helium by an electron beam, followed by recombinations to orthohelium, is responsible for overpopulating those levels, leading to stronger absorption. However, it has not been possible observationally to preclude the possibility of overpopulating orthohelium via enhanced photoionization of He i by EUV irradiance from the flaring corona followed by recombinations. Here we present radiation hydrodynamics simulations of nonthermal electron-beam-driven flares where (1) both nonthermal collisional ionization of helium and coronal irradiance are included, and (2) only coronal irradiance is included. A grid of simulations covering a range of total energies deposited by the electron beam and a range of nonthermal electron-beam low-energy cutoff values were simulated. In order to obtain flare-induced dimming of the He i 10830 Å line, it was necessary for nonthermal collisional ionization to be present. The effect was more prominent in flares with larger low-energy cutoff values and longer lived in weaker flares and flares with a more gradual energy deposition timescale. These results demonstrate the usefulness of orthohelium line emission as a diagnostic of flare energy transport.

24 synoptic maps of average magnetic field in 296 prominences measured by the Hanle effect during the ascending phase of solar cycle 21

Aims. We present 24 synoptic maps of solar filaments, in which the average unambiguous magnetic field vectors of 296 prominences were determined with Pic-du-Midi observations between 1974 and 1982. This was the ascending phase of cycle 21. Methods. The magnetic field was determined by interpreting the Hanle effect, which is observed in the He I D3 line. Previous results for the prominence field polarity and prominence chirality were applied to solve the fundamental ambiguity. The measurements were averaged in each prominence for accuracy reasons. Results. The result is twofold. First, alternating field directions can be observed from one neutral line to the next. Second, a general field alignment is found along a solar north-south field that is distorted by the differential rotation effect.

Влияние деформации сжатия и растяжения на спектр дислокационной люминесценции в кремнии

Photoluminescence has been studied in silicon deformed by four-point bending at temperature of 600◦C. So-called dislocation-related luminescence lines D1, D2, D3 and D4 are observed from both the sides of the deformed samples. It is found that in the samples with the induced dislocation density ~10^7 cm^−2, a luminescence intensity of the D3 and D4 lines is the same on both the sample sides, and the intensity of the D1 and D2 lines from the tensile side is higher than that from the compressive side. Behavior of the intensity of the D1 and D2 lines is well correlated with a quantity of dislocation trails. Possible reasons of observed effect are discussed.

Imaging spectropolarimetry for magnetic field diagnostics in solar prominences

Context. Narrowband imaging spectropolarimetry is one of the most powerful tools available to infer information about the intensity and topology of the magnetic fields present in extended plasma structures in the solar atmosphere. Aims. We describe the instrumental set-up and the observing procedure that we have developed and optimized at the Istituto Ricerche Solari Locarno in order to perform imaging spectropolarimetry. A measurement that highlights the potential of the ensuing observations for magnetic field diagnostics in solar prominences is presented. Methods. Monochromatic images of solar prominences were obtained by combining a tunable narrowband filter, based on two Fabry-Perot etalons, with a Czerny-Turner spectrograph. Linear and circular polarization were measured at every pixel of the monochromatic image with the Zurich Imaging Polarimeter, ZIMPOL. A wavelength scan was performed across the profile of the considered spectral line. The HAZEL inversion code was applied to the observed Stokes profiles to infer a series of physical properties of the observed structure. Results. We carried out a spectropolarimetric observation of a prominence, consisting of a set of quasi-monochromatic images across the He I D3 line at 5876 Å in the four Stokes parameters. The map of observed Stokes profiles was inverted with HAZEL, finding magnetic fields with intensities between 15 and 30 G and directed along the spine of the prominence, which is in agreement with the results of previous works.

On the Possibility of Detecting Helium D3 Line Polarization with Metis

Abstract Metis, the space coronagraph on board the Solar Orbiter, offers us new capabilities for studying eruptive prominences and coronal mass ejections (CMEs). Its two spectral channels, hydrogen Lα and visible light (VL), will provide for the first time coaligned and cotemporal images to study dynamics and plasma properties of CMEs. Moreover, with the VL channel (580–640 nm) we find an exciting possibility to detect the helium D3 line (587.73 nm) and its linear polarization. The aim of this study is to predict the diagnostic potential of this line regarding the CME thermal and magnetic structure. For a grid of models we first compute the intensity of the D3 line together with VL continuum intensity due to Thomson scattering on core electrons. We show that the Metis VL channel will detect a mixture of both, with predominance of the helium emission at intermediate temperatures between 30 and 50,000 K. Then we use the code HAZEL to compute the degree of linear polarization detectable in the VL channel. This is a mixture of D3 scattering polarization and continuum polarization. The former one is lowered in the presence of a magnetic field and the polarization axis is rotated (Hanle effect). Metis has the capability of measuring Q/I and U/I polarization degrees and we show their dependence on temperature and magnetic field. At T = 30,000 K we find a significant lowering of Q/I which is due to strongly enhanced D3 line emission, while depolarization at 10 G amounts roughly to 10%.

Modelling and observations: Comparison of the magnetic field properties in a prominence

Context. Direct magnetic field measurements in solar prominences occur infrequently and are difficult to make and interpret. As a consequence, alternative methods are needed to derive the main properties of the magnetic field that supports the prominence mass. This is important for our understanding of solar prominences, but also for understanding how eruptive prominences may affect space weather. Aims. We present the first direct comparison of the magnetic field strength derived from spectro-polarimetric observations of a solar prominence, with corresponding results from a theoretical flux rope model constructed from on-disc normal component magnetograms. Methods. We first used spectro-polarimetric observations of a prominence obtained with the magnetograph THEMIS operating in the Canary Islands to derive the magnetic field of the observed prominence by inverting the Stokes parameters measured in the He D3 line. Next, we constructed two data-constrained non-linear force-free field (NLFFF) models of the same prominence. In one model we assumed a strongly twisted flux rope solution, and in the other a weakly twisted flux rope solution. Results. The physical extent of the prominence at the limb (height and length) is best reproduced with the strongly twisted flux rope solution. The line-of-sight average of the magnetic field for the strongly twisted solution results in a magnetic field that has a magnitude of within a factor of 1−2 of the observed magnetic field strength. For the peak field strength along the line of sight, an agreement to within 20% of the observations is obtained for the strongly twisted solution. The weakly twisted solution produces significantly lower magnetic field strengths and gives a poor agreement with the observations. Conclusions. The results of this first comparison are promising. We found that the flux rope insertion method of producing a NLFFF is able to deduce the overall properties of the magnetic field in an observed prominence.

Analysis of cobalt (Co) in the soil of Antang Landfill, Makassar City, South Sulawesi Province, Indonesia by use of ICP-OES

This study analyzed the content of cobalt (Co) heavy metal in the soil conducted around the Final Disposal Sites landfill of Antang Makassar, Indonesia. There were 12 sampling points such as points A1, A2, and A3 (line A); points B1, B2, and B3 (line B); points C1, C2, and C3 (line C); and points D1, D2, and D3 (line D). Every sampling points have a depth of 30 cm vertically, and the soil samples were divided into three layer (upper layer, middle layer, and lower layer) with a depth of 0-10 cm (upper layer), 10-20 cm (middle layer), and 20-30 cm (lower layer). The study used 36 samples all of which were analyzed using ICP-OES to measure the concentrations of heavy metals. The concentration of heavy metals in the soil around landfill of Antang had spread vertically and laterally. The analysis found that cobalt (Co) heavy metal concentrations in Line A, Line B, Line C and Line D for every depth exceeded the normal limit. However, on line B the B1 sampling point at a depth of 10-20 cm and 20-30 cm had a relatively normal concentration, which was 10 ppm. That value was the standard permitted by the General of Drug and Food Control as the level of pollution in the soil. Soil pH varies from 4.82 to 6 and is considered acidic. Soil pH significantly affects the solubility and mobility of metals, because most metals dissolve in acidic soils. Thus, remediation or appropriate precautions were needed to prevent risks to humans and the environment.

Chromospheric condensations and magnetic field in a C3.6-class flare studied via He I D3 spectro-polarimetry

Context. Magnetic reconnection during flares takes place in the corona, but a substantial part of flare energy is deposited in the chromosphere. However, high-resolution spectro-polarimetric chromospheric observations of flares are very rare. The most used observables are Ca II 8542 Å and He I 10830 Å. Aims. We aim to study the chromosphere during a C3.6 class flare via spectro-polarimetric observations of the He I D3 line. Methods. We present the first SST/CRISP spectro-polarimetric observations of He I D3. We analyzed the data using the inversion code HAZEL, and estimate the line-of-sight velocity and the magnetic field vector. Results. Strong He I D3 emission at the flare footpoints, as well as strong He I D3 absorption profiles tracing the flaring loops are observed during the flare. The He I D3 traveling emission kernels at the flare footpoints exhibit strong chromospheric condensations of up to ∼60 km s−1 at their leading edge. Our observations suggest that such condensations result in shocking the deep chromosphere, causing broad and modestly blueshifted He I D3 profiles indicating subsequent upflows. A strong and rather vertical magnetic field of up to ∼2500 G is measured in the flare footpoints, confirming that the He I D3 line is likely formed in the deep chromosphere at those locations. We provide chromospheric line-of-sight velocity and magnetic field maps obtained via He I D3 inversions. We propose a fan-spine configuration as the flare magnetic field topology. Conclusions. The He I D3 line is an excellent diagnostic to study the chromosphere during flares. The impact of strong condensations on the deep chromosphere has been observed. Detailed maps of the flare dynamics and the magnetic field are obtained.

The interaction of strigolactones with abscisic acid during the drought response in rice.

Both strigolactones (SLs) and abscisic acid (ABA) biosynthetically originate from carotenoids. Considering their common origin, the interaction of these two hormones at the biosynthetic and/or regulatory level may be anticipated. Here we show that, in rice, drought simultaneously induces SL production in the root, and ABA production and the expression of SL biosynthetic genes in the shoot. Under control conditions, the ABA concentration was higher in shoots of the SL biosynthetic rice mutants dwarf10 (d10) and d17 than in wild-type plants, while a similar trend was observed for the SL perception mutant d3. These differences were enhanced under drought. However, drought did not result in an increase in leaf ABA content in the rice mutant line d27, carrying a mutation in the gene encoding the first committed enzyme in SL biosynthesis, to the same extent as in the other SL mutants and the wild type. Accordingly, d10, d17, and d3 lines were more drought tolerant than wild-type plants, whereas d27 displayed decreased tolerance. Finally, overexpression of OsD27 in rice resulted in increased levels of ABA when compared with wild-type plants. We conclude that the SL and ABA pathways are connected with each other through D27, which plays a crucial role in determining ABA and SL content in rice.

Visibility of Prominences Using the He i D3 Line Filter on the PROBA-3/ASPIICS Coronagraph

We determine an optimal width and shape of the narrow-band filter centered around the He\,{\sc i} D$_{3}$ line for prominence and coronal mass ejection (CME) observations with the ASPIICS ({\it Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun}) coronagraph onboard the PROBA-3 ({\it Project for On-board Autonomy}) satellite, to be launched in 2020. We analyze He\,{\sc i} D$_{3}$ line intensities for three representative non-LTE prominence models at temperatures 8, 30 and 100~kK computed by the radiative transfer code and the prominence visible-light (VL) emission due to Thomson scattering on the prominence electrons. We compute various useful relations at prominence line-of-sight (LOS) velocities of 0, 100, and 300~km~s$^{-1}$ for 20~\AA~wide flat filter and three Gaussian filters with full width at half maximum (FWHM) equal to 5, 10, and 20~\AA~to show the relative brightness contribution of the He\,{\sc i} D$_{3}$ line and the prominence VL to the visibility in a given narrow-band filter. We also discuss possible signal contamination by Na\,{\sc i} D$_{1}$ and D$_{2}$ lines which otherwise may be useful to detect comets. Results mainly show: i) an optimal narrow-band filter should be flat or somewhere between flat and Gaussian with FWHM of 20~\AA~in order to detect fast moving prominence structures, ii) the maximum emission in the He\,{\sc i} D$_3$ line is at 30~kK and the minimal at 100~kK, and iii) the ratio of emission in the He\,{\sc i} D$_3$ line to the VL emission can provide a useful diagnostic for the temperature of prominence structures. This ratio is up to 10 for hot prominence structures, up to 100 for cool structures and up to 1000 for warm structures.