The Zeeman broadening of high n solar recombination lines

The Zeeman broadening of high n lines is derived. While in areas of the quiet Sun with field strengths of 1 G the upper boundary of the observable frequency region of recombination lines is defined by electron impact broadening, in active regions with field strengths 25 G the Zeeman broadening will shift this boundary to higher frequencies. The frequency region most favourable for observations is derived and the corresponding Doppler, electron impact and Zeeman broadening are discussed. The strengths of the recombination lines obtained in earlier calculations is reduced when one considers besides the Doppler broadening the electron impact and Zeeman broadening also. The frequency region favourable for observations is compared with the atmospheric transparency of the microwave region; it is found that observations require at least high altitude stations or space-based platforms. Details of using the Zeeman broadening of high n recombination lines for mapping (coronal) magnetic fields are given.     

Stark Broadening Parameters for Neutral Oxygen Spectral Lines

Stark broadening parameters for nine neutral oxygen (O I) lines have been determined within the impact approximation and the semiclassical perturbation method. The atomic data have been taken from the TOPbase and NIST atomic databases. The electron and proton Stark widths and shifts and ion broadening parameter values for these O I lines have been calculated for electron density of 10 ¹⁶ cm ^?3 and for 4 different electron temperatures in the range of 5000 K to 40000 K. These Stark broadening parameters are compared with our previous results (Ben Nessib, N. et al. 1996, Physica Scripta, 54, 603–613), where we calculated Stark broadening parameters for only four O I spectral lines and where Stark widths and shifts were compared with experimental and theoretical data available in the literature. In the present paper, we have also compared our results with the Griem’s book (Griem, H. R. 1974, Spectral line broadening by plasmas) and VALD (Ryabchikova, T. et al. 2015, Physica Scripta, 90, 054005) values.     

The Kα complex of He-like iron with dielectronic satellites

It is shown that the dielectronic satellites (DES) dominate X-ray spectral formation in the 6.7-keV K α complex of Fe  xxv at temperatures below that of maximum abundance in collisional ionization equilibrium T _m. Owing to their extreme temperature sensitivity, the DES are excellent spectral diagnostics for     in photoionized, collisional or hybrid plasmas; whereas the forbidden, intercombination and resonance lines of Fe  xxv are not. A diagnostic line ratio GD ( T ) is defined including the DES and the lines, with parameters from new relativistic atomic calculations. The DES absorption resonance strengths may be obtained from differential oscillator strengths, possibly to yield the     column densities. The DES contribution to highly ionized Fe should be of interest for models of redward broadening of K α features, ionized accretion discs, accretion flows and K α temporal-temperature variability in AGN.     

The influence of molecular blends and non-thermal line broadening on the profile of the Zeeman triplet λ5250.22 in sunspots

Calculations of the umbral profile of the Zeeman triplet 5250.22 are presented. We have taken into account the effect of a molecular blend from TiO at 5250.24 causing an apparent -component even for longitudinal magnetic fields. Also included is the depression of the spot continuum due to line wings and veiled weak lines in the umbra spectrum. The effect of different amounts of non-thermal broadening is investigated.The results point to the need of a better theoretical treatment of molecular and atomic blends and to the importance of more reliable values for the non-thermal broadening in sunspots. Furthermore, the importance of a proper stray light correction is noted, particularly including the stray light from the penumbra.     

High n solar radio recombination lines

For a representative set of atmospheric and atomic parameters we determine the strengths of solar dielectronic recombination lines originating in ions with Z 6 at frequencies of 70 GHz. We compare the line strengths derived here with those calculated by Berger and Simon (1972) and find that our values for representative ions with Z3 are lower by a factor 10²–10³, being mainly the result of the inclusion of the electronic pressure broadening. We outline the requirements for the detection of lines, which must establish an upper limit of at least 10^-5 for the line to continuum ratio.     

Accurate Determination of Electron Densities in Active and Quiescent Prominences: the Mid-Infrared Advantage

We have analyzed all lines in the MIR (8 to 20 micron) spectra of a quiescent and two time-frames of an active prominence. In the quiescent prominence, in addition to those lines found by Zirker (1985), we have identified a higher excitation hydrogen line and two helium recombination lines. Accounting for instrumental broadening, we can further separate out the Doppler and the Stark contributions to the line width. The former yields maximum temperatures of 6200 K, 34000 K and 12000 K and the latter electric field strengths of 7, 17, and 10 V cm^-1 for the above prominences, respectively. We show that these electric fields when divided by 2.2 are equal to the normal electric field in Holtsmark's quasi-static Stark broadening theory. Hence, we obtain electron densities of N₃=2.4(0.3), 9.1(1.2), and 5.5(0.6) in units of 10¹⁰ cm^-3 respectively. Using the same assumptions as made by Zirker, namely, (1) the strongest line (7-6) is optically thin, (2) the population of the lower level (n=6) is determined by direct radiative recombination and photo-ionization, (3) the equality of proton and electron densities, and (4) the thickness of the prominence is at least 10⁸ cm, we derive a new inequality, N_e 1.83 × 10⁸ T^0.75 e^-2195/T. Substituting our maximum temperatures into the right-hand side, we find upper bound N_e values of 9, 43, and 30 in the same units as above. These upper bound values are comfortably higher than our measurement, unlike those of Zirker's derived from the same set of assumptions. We have also observed the helium recombination spectrum which has been postulated by Tandberg-Hanssen as one of three possible ways of equilibrating the triplet/singlet ratio. Surprisingly, it is present in the quiescent as well as in the active prominence. We show that no meaningful values can be found for the turbulent velocities by combining the helium with the hydrogen line widths.     

Ultraviolet brightenings in active regions as observed from OSO-8

Repeated raster images of solar active regions taken at the line centers of the Si iv and C iv resonance lines using the University of Colorado (CU) ultraviolet spectrometer aboard OSO-8 reveal dramatic transient brightenings of up to factors of 10. These brightenings last several minutes and frequently show a repetitive character. Inspection of simultaneous H flare patrol records show that these transition zone events are often associated with subflare-like brightenings in the chromosphere. These observations indicate that direct excitation or heating of material already at transition zone temperatures caused by non-thermal particle streams is inadequate to explain the degree of brightening of these lines. The measurements suggest that some process that enhances density of material at 10⁵ K is occurring during these events.     

ON BROADENING MECHANISMS OF THE Ca XIX RESONANCE LINE IN SOLAR FLARES

There are two explanations for the broadening mechanisms of the Caxix resonance line in the rising phase of a solar flare. One is due to the velocity dispersion of the chromospheric evaporation along the loop; the other is due to the non-thermal turbulence resulting from the flare energy release. In this paper we distinguish between these two possibilities by studying the influence of the loop orientation on the broadening of the Caxix resonance line, based on the data observed with SXT and BCS on Yohkoh. The results seem to support that the broadening of the Caxix resonance line is caused by non-thermal turbulence, rather than by the velocity dispersion.     

OSO-8 observations of CaII H and K,MgII h and k,Lα and Lβ above a sunspot

Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of L above the umbra an electron density of 4.3 × 10¹⁰ cm^-3 n _e ^* 2.3 × 10¹¹ cm^-3 at 20 000 K is estimated.Mitteilungen aus dem Kiepenheuer-Institut Nr. 186.Stockholm Observatorium, S-13300 Saltsjöbaden, Sweden.Laboratoire de Physique Stellaire et Planétaire, CNRS, P.O. Box 10, F-91370 Verrières-le-Buisson, France.     

The Violet Opacity in the Red Peculiar Stars – III. Spectral analysis of the SC star GP Ori

Medium-resolution (1.5-2.5 Å) spectrum has been obtained for SC star GP Ori in a wide range of wavelengths from 3730 to 6250 Å. It is characterised mainly by strong atomic lines, as well as moderately strong bands of the CN violet system and CH (0,0) and (0,1) bands at 4315 and 4890 Å. Weak bands of C₂, C₃, and ZrO molecules are observed, however, no evidence is found for the presence of either SiC₂ (Merrill-Sanford bands) or YO. The most prominent atomic lines along with the NaID12 are those of CaII (K,H), CaI at 4227 Å, SrI at 4607 Å, SrII at 4077 and 4215 Å, and BaII at 4554 Å. H seems to be in emission.     

The interpretation of hydrogen radio recombination lines

Computations of the high level populations of hydrogen in gaseous nebulae are used to compare observations of radio recombination lines with theoretical predictions based on possible line enhancement. Attempts to confirm the existence of maser action from electron temperatures derived on the assumption of thermodynamic equilibrium are inconclusive. There is evidence that most of the low (5000 K) derived temperatures can be increased by at most a few percent by allowing for line enhancement. Measured ratios of the peak temperatures of lines of the same frequencies originating from different upper quantum levels, indicate maser action if Stark broadening is not taken into account. The inclusion of Stark broadening allows confirmation of maser action only in the central regions of the Orion Nebula in the case of the 137/109 ratio, and in Orion, and, possibly, IC 1795 and M17, in the case of the 197/156 ratio.     

Lα, Lβ (of Hi), k and h (of Mgii), K and H (of Ca ii) observations in a quiescent prominence with the OSO-8 LPSP instrument

A sequence of images taken at different positions in the resonance lines of Ca ii, Mg ii, and H i was obtained over a quiescent prominence with the LPSP instrument on OSO-8. Ca ii K (and H) profiles are reconstructed at different locations in the prominence with a (10 × 5) arc sec² resolution. Significant variations of FWHM and line shifts are found: FWHM range from 0.14 Å to 0.5 Å; blue shifts reach about 14 km s^-1. The ratio of K to H absolute intensities shows a large spread around the average value of 1.2. The same ratio for the Mg ii lines in the whole prominence is higher (1.7), a fact already noticed at the edge of an active prominence (Vial et al., 1979). The ionization degree, as measured by the L/Ca K ratio, shows noticeable variations within the prominence. The L intensity is about 0.3 times the intensity measured in the quiet Sun, and the L/L ratio is less than one half the disk value. These results indicate important variations of the thermal conditions inside the prominence.DASOP, Observatoire de Paris, 92190 Meudon, France.     

Solar flare X-ray spectra

Results are presented of an investigation of solar flare X-ray spectra in the region 1.70–1.95 Å, obtained aboard the Intercosmos-4 satellite during the maximum of solar activity (October–November, 1970). With the use of 6 high resolution spectra in the region 1.85–1.87 Å the identification of lines due to 18 transitions of 2p 1s type, consisting of the resonance, intercombination and forbidden Fe xxv ion lines and the satellite Fe xxiv lines has been performed. With the use of the recent laboratory data the averaged wavelengths of the lines were obtained confirming the theoretically calculated ones with an accuracy about ± 0.0004 Å. A variable Doppler shift of the Fe xxv resonance lines was observed for the flare of November 16, 1970, which points to hot plasma motions with velocities up to 400 km s^-1.     

O VI (λ = 1032 Å) profiles in and above an active region prominence,compared to quiet Sun center and limb profiles

O vi ( = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H i, Mg ii, Ca ii resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb.Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3); at the top of the prominence (15 above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s^–1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s^–1) is lower than in Ca ii lines.The O vi profile recorded 30 above the limb outside the filament is wider (FWHM = 0.33 Å). It can be interpreted as a coronal emission of O vi ions with a temperature of about 10⁶ K, and a non-thermal velocity (NTV) of 49 km s^–1. This NTV is twice the NTV of quiet Sun center O vi profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of euv lines.     

A study of weak molecular and atomic lines in the photospheric spectrum

An attempt is made to detect the lines of Mg²⁵H and Mg²⁶H in the photospheric spectrum, using calculated isotope shifts. From comparisons with the Mg²⁴H lines of the ² –² transition in the (0, 0) band the ratios Mg²⁵/Mg²⁴ = 0.12 ± 0.04 and Mg²⁶/Mg²⁴ = 0.12 ± 0.02 are derived. These are essentially the same as the terrestrial ratios. The profile of one line of Mgi confirms these values.The wavelengths of MgH and C₂ lines, when corrected for the gravitational red shift, indicate that macroturbulent (or streaming) velocities die out near log ₀ = – 1.0. From the equivalent widths of the MgH lines a rotational temperature of 5132 ± 200 K is obtained and compared to predictions from various model atmospheres. The band oscillator strength is found to be 0.024 ± 0.002, in serious disagreement with the single laboratory determination.The profiles of MgH, C₂, CN and some weak atomic lines are used to derive the variation of the radial component of microturbulence with optical depth, on the assumption of streaming velocities of 2.5–3.0 km/sec. A slow increase with increasing height in the photosphere is found, over the range –1.5 < log₀< 0.2.The center-limb variation of the equivalent widths of MgH and C₂ lines for a wholly inhomogeneous model is found to be the same as for a model which is homogeneous above log ₀ = - 1.0. With such a model as the latter, the center-limb variation of the profiles of the selected molecular and atomic lines is moderately-well reproduced by an anisotropic microturbulent velocity with a tangential component of 3 km/sec which seems to be constant with height over the range considered.     

The quadratic Zeeman effect in the Caii H and K lines

The effects of a large magnetic field on the H and K lines of Caii are investigated incorporating both the linear and quadratic Zeeman effects for fields in the range 10⁶–10⁸ G. For these fields the linear term is the dominant one, resulting in a Paschen-Back effect with a smaller quadratic Zeeman shift superimposed on all components. Due to the partial cancellation of the quadratic effect between the upper and lower states of the lines, a much smaller quadratic Zeeman shift occurs than in the lines of other atoms previously studied at similar fields.     

Spectroscopy of Solar Prominences Simultaneously From Space and Ground

We present a comprehensive set of spectral data from two quiescent solar prominences observed in parallel from space and ground: with the VTT, simultaneous two-dimensional imaging of H4862 Å and Caii 8542 Å yields a constant ratio, indicating small spatial pressure variations over the prominence. With the Gregory, simultaneous spectra of Caii 8542 Å and Hei 10830 Å were taken, their widths yielding 8000 K <T _kin<9000 K and 3<v _nth<8 km s^–1. The integrated line intensities show a distinct relation E(Hei) versus E(Caii) for each prominence (`branching'). The intensity ratio of the helium triplet components is used for a simple estimate of the optical thickness, which is <1.0 for the fainter prominence but reaches up to =2.0 for the brighter one. The <sub>0</sub> values allow us to deduce the source function from the central line intensities and thus a mean excitation temperature T<sub>ex</sub> <sup>mean</sup>=3750 K, which determines the relative populations of the helium <sup>3</sup> S and <sup>3</sup> P levels. With SUMER, we sequentially observed six spectral windows containing higher Lyman lines, `cool' emission lines from neutrals and singly charged atoms, as well as `hot' emission lines from ions like Oiv, Sv, Nv, Ov, and Svi. The spatial variation of the EUV lines along the SUMER slit shows a pronounced maximum at the main prominence body and `side-regions' where the `hot' lines are significantly enhanced with respect to the `cool' lines from neutral and singly-ionized atoms. These selected locations were averaged over 7 and the resulting mean EUV lines were fitted by Gaussians yielding realistic widths and integrated line intensities. The intensities of `hot' lines blue-wards of the Lyman series limit appear reduced in the main prominence body but enhanced in the `side-regions'. This absorption is also visible in TRACE images of Feix/x171 Å as fine dark structure which covers only parts of the main (`cool') prominence body. The Lyman lines show a smooth decrease of both line widths and integrated emission, with increasing upper level k=5 to k=19; the widths are smaller for the prominence that yields lower T <sub>kin</sub> from the ground-based spectra. The level populations along the line of sight follow for 5 lek le a smooth Boltzmann distribution with T <sub>ex</sub>>6×10<sup>4</sup> K, the levels k>8 appearing more and more overpopulated. The larger widths of the Lyman lines require high non-thermal broadening close to that of `hot' EUV lines. In contrast, the Heii emission is more related to the `cool' lines.     

On the branching in the emission relations of Ca+ in prominences

Spatially well resolved prominence spectra of the three lines Ca⁺ K, H, and Ca⁺ 8542 are analysed. It is confirmed that the branching in the emission relations of Ca⁺ versus H correlates with the magnitude of non-thermal (turbulent) broadening.     

The photospheric barium spectrum: Solar abundance and collision broadening of Baii lines by hydrogen

A study of the solar Ba ii spectrum leads to a solar abundance of barium of log ba = = 2.11±0.12, on the scale log h = 12. The observed asymmetry of the resonance line 4554 is consistent with an isotopic abundance ratio equal to the terrestrial one. The meteoritic Ba/Si abundance ratio found in carbonaceous chondrites appears to exceed the solar ratio by 0.1 to 0.2 dex (Section 5).The broadening by collisions with hydrogen atoms is determined from the solar spectrum (Section 4). Damping half-widths, h, of the three stronger Ba ii lines turn out to be larger by a factor of about 3.0 than predicted from pure van der Waals interaction of dipoles. Departures from LTE appear to be present in the cores of the resonance lines and of the lines arising from the metastable 5D levels (Section 6). The equivalent widths, however, remain practically unaffected.Equivalent widths of neutral barium lines are predicted and some new identifications of photospheric Ba i lines are suggested (Section 7).     

Directional radiation and photodissociation regions in molecular hydrogen clouds

Some astrophysical observations of molecular hydrogen point to a broadening of the velocity distribution for molecules at excited rotational levels. This effect is observed in both Galactic and high-redshift clouds. Analysis of H₂, HD, and CI absorption lines has revealed the broadening effect in the absorption system of QSO 1232+082 (z _abs = 2.33771). We analyze line broadening mechanisms by considering in detail the transfer of ultraviolet radiation (in the resonance lines of the Lyman and Werner H₂ molecular bands) for various velocity distributions at excited rotational levels. The mechanism we suggest includes the saturation of the lines that populate excited rotational levels (radiative pumping) and manifests itself most clearly in the case of directional radiation in the medium. Based on the calculated structure of a molecular hydrogen cloud in rotational level populations, we have considered an additional mechanism that takes into account the presence of a photodissociation region. Note that disregarding the broadening effects we investigated can lead to a significant systematic error when the data are processed.