Remarks concerning Ward's ‘the latitudinal motion of sunspots and solar meridional circulations’

Oscillator strengths are calculated for 259 lines of Ti i by taking configuration interaction into account in a somewhat simplified treatment. Radial integrals are obtained by an adaptation of the scaled Thomas-Fermi method. The great majority of selected lines originate from slightly perturbed terms. From a satisfactory comparison of our g \({\text{f}}\) -values with recent experimental data and with solar results in the visible region, we have been able to extend the work for some infrared lines. Very few transition probabilities were known for Ti i in that spectral range. On the basis of our oscillator strengths, a mean value logN _ti = 4.88 ± 0.12 (in the usual scale), is proposed for the solar photospheric abundance, in agreement with the meteoritic value.     

The solar photospheric abundance of iron

A new value of the solar photospheric abundance of iron, independent of line-shape parameters, is derived. Our analysis is based on a study of 40 weak infrared lines (0.85<λ<2.5 μ) for which theoretical oscillator strengths (calculated with configuration interactions taken into account) have recently been computed by Kurucz (1974). The abundance obtained, A _Fe = 7.57±0.11 (in the usual scale where log N _H = 12.00) is in agreement with the ‘high’ solar values recently reported in the literature and with the meteoritic abundance.     

Spectrum of the star BM Ori at minimum light

Two spectra of the star BM Ori were obtained with the 2.6-m Crimean Astrophysical Observatory telescope near its maximum eclipse phase. The light detector was a CCD array. The wavelength range 5305–5373 Å was chosen in such a way that it contained no strong primary lines. Optimum filtration of the spectra yielded a signal-to-noise ratio of ～300. Eighteen secondary lines are seen in the spectrum. Atmospheric parameters of the secondary star were determined: T _eff=5740 K and logg=3.0; the secondary was classified by these parameters as being of spectral type G2 III. The best agreement between observed and synthetic spectra is achieved for metallicity [M/H]=?0.5 and microturbulence ξ_t=0 km s^?1. The projected rotational velocity is Vsini=60 km s^?, in agreement with the synchronous velocity in the hypothesis that assumes a total eclipse by the secondary star. Atmospheric elemental abundances in the secondary are estimated. Nickel, chromium, and iron exhibit an underabundance of ～1 dex.     

Network to cell contrast at microwaves

Using different models deduced from EUV lines for the cell and for various network components, the corresponding radio brightness temperature in the millimetric and centimetric range of wavelengths are computed. The contrast C = [T _b (network)]/[T _b (cell)] and the difference ΔT = T _b (network) - T _b (cell) are compared with the few available observations of the quiet Sun inhomogeneities performed with sufficient angular resolution. The comparison shows a satisfactory agreement with most of the observations.     

Influence of departures from LTE on oxygen abundance determination in the atmospheres of A-K stars

We have performed non-LTE calculations for O I with a multilevel model atom using currently available atomic data for a set of parameters corresponding to stars of spectral types from A to K. Departures from LTE lead to a strengthening of O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The non-LTE correction does not exceed 0.05 dex in absolute value for visible O I lines for main-sequence stars in the entire temperature range. For the infrared O I 7771 Å line, the non-LTE correction can reach ?1.9 dex. The departures from LTE are enhanced with increasing temperature and decreasing surface gravity. We have derived the oxygen abundance for three A-type mainsequence stars with reliably determined parameters (Vega, Sirius, HD 32115). For each of the stars, allowance for the departures from LTE leads to a decrease in the difference between the abundances from infrared and visible lines, for example, for Vega from 1.17 dex in LTE to 0.14 dex when abandoning LTE. In the case of Procyon and the Sun, inelastic collisions with HI affect the statistical equilibrium of OI, and agreement between the abundances from different lines is achieved when using Drawin’s classical formalism. Based on the O I 6300, 6158, 7771-5, and 8446 Å lines of the solar spectrum, we have derived the mean oxygen abundance log ? = 8.74 ± 0.05 using a classical plane-parallel model solar atmosphere and log ? _+3D = 8.78 ± 0.03 by applying the 3D corrections taken from the literature.     

Time-dependent configuration changes of the magnetotail and plasma sheet thinning

The configuration of the magnetotail magnetic field has been calculated for a situation where a disruption of a portion of the tail current system develops. The decrease of the current in a localized region of the magnetotail leads to a collapse of the magnetic field in that vicinity. The calculated configuration of the field resembles what is predicted by reconnection models with the field lines moving toward the neutral sheet and then connecting and either moving toward or away from the earth. Associated with this changing magnetic field there is an induced electric field which will then influence the motion of the plasma in the magnetotail via E × B drifts.When the current from X_sm = ?20 to ?40 R_E in the tail is decreasing with a tune-constant of 0.5 h the electric field produced, which is primarily westward, has a maximum value of 0.83 mV m^?1 and produces plasma sheet thinning velocities of 0.3 km s^?1. Higher velocities result for more rapid rates of current decrease, and they agree well with experimental observations. The plasma flows in the sunward direction are, however, much smaller than what has been observed. This is due in part to the inability of the magnetic field model to adequately represent the magnetic field in the immediate vicinity of the neutral sheet. Use of an improved model would give better agreement with the observations.The calculations show that the induced electric field of a time-dependent magnetic field is able to explain certain observed features of the plasma sheet motions. Also, this agreement suggests that the assumption that there is no charge separation contribution to the electric field may be reasonable during situations of large scale and rapid current disruptions in the magnetotail.     

Torsional Alfvén waves and the period ratio P 1/P 2 in spicules

The effects of both density stratification and magnetic field expansion on torsional Alfvén waves in solar spicules are studied. Also, their eigenfrequencies, eigenfunctions, and the period ratio P ₁/P ₂ are obtained with a novel mathematical method. We showed that under some circumstances this ratio can approach its observational value even though it departs from its canonical value of 2. Moreover, Eigenfunction height variations show that the oscillations amplitude are increasing towards higher heights which is in agreement with the observations. This means that with a little increase in height, amplitude of oscillations expands due to the significant decrease in the density.     

Massive stellar populations in Wolf-Rayet galaxies

The analysis of the long-slit spectral observations of 40 Wolf-Rayet (WR) galaxies with heavy element mass fraction ranging over two orders of magnitudes from Z_⊙/50 to 2Z_⊙ are presented. We derive the number of O stars from the luminosity of the Hβ emission line, the number of early carbon Wolf-Rayet stars (WCE) from the luminosity of the red bump (broad CIV λ5808 emission) and the number of late nitrogen Wolf-Rayet stars (WNL) from the luminosity of the blue bump (broad emission near λ4650). We identified some of weak WR emission lines, most often the N III λ4512 and Si III λ4565 lines, which have very rarely or never been seen and discussed before in WR galaxies. A new technique for deriving the number of WNL stars (WN7–WN8) from the N III λ4512 and the number of WN9–WN11 from Si III λ4565 emission lines has been proposed. This technique is potentially more precise than the blue bump method because it does not suffer from contamination of WCE and early WN (WNE) stars and nebular gaseous emission. We find that the fraction of WR stars relative to all massive stars increases with increasing metallicity, in agreement with predictions of evolutionary synthesis models. The relative number ratios N(WC)/N(WN) and the equivalent widths of the blue and red bumps derived from observations are also in satisfactory agreement with theoretical predictions, except for the most metal-deficient WR galaxies. A possible source of disagreement is too low a line emission luminosity adopted for a single WCE star in low-metallicity models.     

NLTE formation of the solar spectrum of silicon: Abundance of silicon in a three-dimensional model of the solar atmosphere

We investigated the NLTE formation of the solar spectrum of neutral silicon using 3D hydrodynamic model of the solar atmosphere and realistic atomic model. We show that, within the intergranular region, combined action of the deficit in the source function and excess in opacity due to the overpopulation of the lower Si I levels leads to a considerably higher increase in the central depth D and equivalent width W of these lines as compared to the granules. We have fitted silicon abundances A _W and A _D from the equivalent widths W and central depths D for 65 Si I lines using a 3D model. We show that a total error in the calculated silicon abundance due to neglecting NLTE and 3D effects, as well as the uncertainty in the van der Waals broadening constant γ₆, turns out to be ?0.1 dex. Using a semiclassical theory by Anstee, Barklem, and O’Mara in calculating γ₆ yields a fair coincidence between the values of A _W and A _D , because the average difference A _W — A _D does not exceed 0.01 dex for both NLTE and LTE. When applying the Unsold’s approximation in calculating γ₆ with an enhancement factor E = 1.5, the abundances A _W and A _D proved to be in disagreement with one another. We analyzed the “solar” oscillator strength scale by Gurtovenko and Kostik, as well as the experimental one by Garz and Becker et al. We show that using “solar” oscillator strengths log gfw leads to a minimum trend with the equivalent widths for NLTE abundances A _W , A _D , their difference A _W — A _D , and standard deviations. The NLTE abundance of silicon obtained using solar oscillator strength scale by Gurtovenko and Kostik is A _W ^NTLE = 7.549 ± 0.016. This value is in good agreement with the value of silicon abundance recommended by Grevesse and Sauval for the CI chondrite meteorites.     

On the behaviour of the hydrogen Lyman series in flares

The Lyman spectrum of hydrogen has been computed for a number of flare models, characterized by the column density of hydrogen atoms in the ground state (N ₁), the electron density (n _e) and the electron temperature (T _e). Broadening by the thermal Doppler effect and by Stark effect has been accounted for. The source functions for the individual lines of the series have been derived from non-LTE calculations of the excitation in hydrogen flares. The aim of the investigation is to evaluate the use of the intensities in between two successive Lyman lines for a determination of the value for N ₁, which is a physical parameter of the flare for which only indirect determinations are available. Whilst in principle this method could give reliable results, its practical application meets with difficulties which hardly can be overcome. Therefore, one probably has to base the N ₁ determination on the highest line resolvable in the spectrum.     

A laboratory atlas of the 5ν1 NH3 absorption band at 6475 Å with applications to Jupiter and Saturn

The 5ν₁ absorption band of NH₃ is displayed from 6418 to 6550 Å. The total band intensity has been measured: S_B = 0.66 cm^?1m^?1amagat^?1. Line intensities and self-broadening coefficients have been measured for some of the prominent lines. Our line intensities are in good agreement with those of Rank et al. (1966), but are about 2 times greater than those of Mason (1970). The spectrum displayed was obtained photoelectrically at a pressure of 0.061 atm, and shows many more lines than the spectrum obtained by McBride and Nicholls (1972a) at a pressure of 0.39 atm. Therefore, our new measurements can provide the basis for making a more complete rotational analysis than those of McBride and Nicholls (1972a).Since the total band absorption has previously been measured by others on moderate resolution photoelectric scans of the spectra of Jupiter and Saturn, we can use the band intensity to derive the NH₃ abundance in the atmospheres of these two planets. The NH₃ abundances in a single vertical path obtained by this method are about 10m amagat for Jupiter and 2m amagat for Saturn. These results are in agreement with previous results obtained from higher resolution photographic spectra.     

On the thermal structure of Uranus

Uranus has an effective temperature close to the solar equilibrium value and undoubtedly a thermal inversion of at least 140 K at a pressure of ～3 dyncm^?2. With the inversion and the thermal opacity provided by a HeH₂ mixture in a ratio close to solar abundance, acceptable agreement can be achieved with the available infrared observations. The cause of the inversion is, however, uncertain. The use of the HeH₂ opacity for Uranus is justified by the excellent agreement of the frequency variation of that opacity with the thermal spectrum of Jupiter.     

Revisiting the Amati and Yonetoku correlations with Swift GRBs

We use a sample of Swift gamma-ray bursts (GRBs) to analyze the Amati and Yonetoku correlations. The first relation is between E _p,i , the intrinsic peak energy of the prompt GRB emission, and E _iso , the equivalent isotropic energy. The second relation is between E _p,i and L _iso , the isotropic peak luminosity. We select a sample of 71 Swift GRBs that have a measured redshift and whose observed $E^{obs}_{p}$ is within the interval of energy 15–150 keV with a relative uncertainty of less than 70 %. We seek to find correlation relations for long-duration GRBs (LGRBs) with a peak photon flux P _ph ≥2.6 ph/cm²/s. Uncertainties (error bars) on the values of the calculated energy flux P, the energy E _iso , and the peak isotropic luminosity L _iso are estimated using a Monte Carlo approach. We find 27 Swift LGRBs that satisfy all our constraints. Results of our analyses of the sample of 71 GRBs and the selected subsample (27 GRBs) are in good agreement with published results. The plots of the two relations for all bursts show a large dispersion around the best straight lines in the sample of 71 LGRBs but not so much in the subsample of 27 GRBs.     

Relationship between intensities of strong emission lines in the spectra of H II regions and their chemical compositions

The method of determination of heavy element abundances in H II regions (the strong-line method) uses the assumption that some combinations of strong emission line intensities in spectra of H II regions can serve as indicators of metallicities and electron temperatures in nebulosities. Three sets of strong lines are considered, namely, A (R ₃, R ₂, N ₂, S ₂ lines), B (R ₃, R ₂, N ₂ lines), and C (R ₃, N ₂, S ₂ lines). Strong line intensities are normalized to the H _?? intensity). We searched for an unambiguous relationship between strong emission line intensities of these line sets in spectra of H II regions and their compositions. The extensive model grid for H II regions is computed. Chemical compositions of nebulosities and intensities of A and C lines are shown to be related unambiguously. For the B line set, 5% of model H II regions do not have any unambiguous relationship, namely, the models with appreciably different oxygen and nitrogen abundances in H II regions can have similar intensities of the B set lines. The versions of strong-line method (calibrations) using the A and C lines are more reliable than those based on the B lines.     

The solar niobium abundance

The solar Nb abundance is derived from five Nb i and ten Nb ii lines in the photospheric spectrum. Equivalent widths are obtained from measurements on spectra recorded at Kitt Peak National Observatory. Synthetic spectrum calculations gave abundances of 2.23 and 2.08 from neutral and ionized lines respectively in the logarithmic A _H = 12.00 scale. This gives an average abundance value of A _Nb = 2.13 ± 0.10.     

The analysis of a high resolution X-ray spectrum of a solar active region

Absolute intensities and wavelengths for 98 X-ray emission lines between 9 and 22.5 Å are reported. The active region spectra were obtained with three rocket-borne crystal spectrometers. Identifications are proposed for 62 of the lines and a model of the emitting plasma is constructed from the intensities of the strongest lines. The emission measure (N _e ² V) of the model peaks at 3 × 10⁶ K with a value of 1.5 × 10⁴⁷ cm^?3 and decreases to 10⁴⁶ cm^?3 at 5 × 10⁶ K. Effective oscill and collision strengths are calculated for the other transitions that are observed. The relative intensities of O viii and Ne ix give an oxygen : neon abundance ratio of 8 ∶ 1. The intensities of the satellite lines to helium-like lines are investigated and it is shown that these lines can be used with confidence in constructing active region models.     

Spectroscopic studies of four planetary nebulae with emission-line nuclei

Spectroscopic observations of four planetary nebulae (PNe) with emission-line central stars of different spectral types are presented: Cn 1-5, Pe 1-1, NGC 5873, and M1-19. The interstellar extinction, physical conditions (n _e , T _e ), and abundances of several elements (He, N, O, Ne, S, Ar, Cl) have been determined for all nebulae. The nebula Cn 1–5 with fairly high abundances of helium and nitrogen is shown to belong to type I PNe. Possible variability of the intensities of low-excitation emission lines in NGC 5873 has been found; it can be related to variations of the stellar wind from the central star. The measured α-element abundance ratios (S/O, Ne/O, Ar/O, Cl/O) are in good agreement with those typical of HII regions.     

Spectrographic observations of the suspected delta scuti variable beta ari

Three sets of spectra (in all 85 spectra) of the well-known standard and high eccentricity spectroscopic binary star Beta Ari were taken with the Boller and Chivens grating spectrography (29 and 35 Å mm^?1) applied to the 137 cm reflector of the Merate Astronomical Observatory. These sets were takenduring the periastron passage of 14–15 November 1976,after the periastron passage of 2–3 October 1977 and before the apastron passage of 23 November 1977. The analysis of the radial velocitiesRV and equivalent widthsW _λ of hydrogen and metal lines show periodic variations similar to those of some classical Delta Scuti stars. The variations of the asymmetries of the profiles of H and Caii K lines, linked to the variations of theRV seem to recall the Schuster effect observed in classical Cepheids. A periastron effect appears from: (a) increased amplitudes of theRV curves, (b) remarkable variations of the averagedW _λ curves, (c) strong positive asymmetry (blue wing larger than red wing) in the Hγ and Caii K lines. A faint ‘bump’ inRV andW _λ curves of Caii K line is singled out and could be in agreement with some theoretical forecasts of Aleshin (1964).     

The possible presence of C2 lines in sunspot spectra

Indirect evidence against the presence of C₂ lines in umbral spectra is discussed. The dominant role of CO in the molecular equilibrium of C at umbral temperatures ensures that CN, CH and C₂ lines are formed in the same atmospheric regions. Observations of CN and CH umbral lines are in good accord with predictions based on accepted umbral model atmospheres. This implies that C₂ must follow the predictions and that it is too weak to contribute to the umbral spectrum. C₂ lines in the photosphere and penumbrae are in excellent quantitative agreement with predictions. Additional tests are proposed.     

Analysis of HST ultraviolet spectra for T Tauri stars: RU Lup

The ultraviolet spectra of the star RU Lup obtained with the Hubble Space Telescope are analyzed. Emission lines are identified. The presence of absorption components with a nearly zero residual intensity in the Mg II resonance doublet lines is indicative of mass outflow with a velocity V _∞?300 km s^?1. These lines also exhibit a broad (?1400 km s^?1 at the base) component originating in the star itself. The profiles of the (optically thin) Si II] and Si III]1892 Å lines for the first time unequivocally prove that these lines originate in an accretion shock wave rather than in the chromosphere, with the gas infall velocity being V ₀?400 km s^?1. The intensity ratio of the C IV 1550 Å and Si IV 1400 Å resonance doublet components was found to be close to unity, suggesting a high accreted-gas density, logN ₀>12.5. Molecular H₂ Lyman lines formed in the stellar wind were detected. The H I Lα luminosity of RU Lup was found from their intensities to exceed 10% of L _bol. Radiation pressure in the Lα line on atomic hydrogen may play a significant role in the initial acceleration of stellar-wind matter, but the effect of Lα emission on the dynamics of molecular gas is negligible.