A new method for the analysis of the solar photospheric spectrum

A new numerical method for the analysis of the high dispersion photospheric spectrum is described. In particular the method is applied to study the C₂(0, 0) d ³ Πg-a ^a Πu molecular band. From measurements of the equivalent widths of C₂ lines, a rotational temperature of 4450 ± 305 K is obtained, and the band intensity log W ₀ /S ₀ = ?0.051 ± 0.101 is found.     

Five-minute oscillations of solar equivalent widths

Equivalent widths of weak and moderately strong Fraunhofer lines observed in an area roughly 3500 × 10000 km in extent are found to show small variations of the order of 1 mÅ, on a time scale of minutes. The dependence of amplitude on line strength and excitation closely fits that predicted for a compressional disturbance associated with temperature variations that manifest themselves in the equivalent widths. The rms amplitude is about 20K near τ₅₀₀₀ = 10^-2. These equivalent width variations frequently exhibit a 5-min periodicity and are accompanied by prominent oscillations of velocity. Power spectra of both quantities closely resemble each other and demonstrate that most of the equivalent width variations in the range 200 to 500 s are due to the thermal response of the atmosphere to 5-min oscillations. A systematic phase lag between velocity and equivalent width is observed, in the sense that temperature leads velocity by an average angle of 120°. This deviates significantly from 90° valid for standing adiabatic waves, showing that in the line-forming layers, τ₅₀₀₀ ≈ 10^-2, the 5-min oscillations are markedly affected by radiative exchange. The observed phase lag implies a radiative decay time of ≈40 s, a value which agrees with modelatmosphere predictions for the line-forming layers. Since the observed wave trains frequently show constant amplitude over a much longer time, a continuous feed-back of energy seems to occur.     

High-resolution analysis of solar photospheric oscillations

The coherent 5-min photospheric pressure oscillations with spherical harmonic degrees in the range 100 <l< 1000 were directly imaged over the photosphere with the monochromatic solar telescope FPSS at Meudon Observatory. Movie films were obtained with images spatially filtered to select sizes of increasing wave numbers (or l). Areas with ephemeral concentrations of coherent waves evolve in shape and may move horizontally with velocities of several tenths of km s^–1. When a large number of waves are interacting, the maximum vertical velocity V _max of the pulsation reaches around 1000 m s^–1, irrespective of the size. Extrapolation to the ideal case of a single isolated wave gives V _max proportional to size. For the areas of the smallest scale measured (l = 1000), when about 100 waves are interacting, V _max is found to be 260 + 25 m s^–1 at an altitude of 210 km above the reference level ₅₀₀₀ = 1 and increases vertically with a scale height of 750 ± 400 km.     

A new method for the multitemperature analysis of solar X-ray line emission

Solar Physics - An application of nonlinear least squares methods for determining the temperature models of coronal active regions, based on the measured X-ray line intensities, is described. These...     

Determination of solar Doppler widths by Goldberg's method

The so-called Goldberg or profile intercomparison method of determining Doppler widths from spectral line profiles was used to analyze a group of high quality solar profiles which were observed with the McMath solar telescope at the Kitt Peak National Observatory. The observations consisted of profiles of eight lines of calcium and chromium, made at either four or five positions on the solar disk.A depth dependence of solar microturbulence could not be derived by applying the Goldberg method to a single pair of lines at a single disk position. When the depth dependence was determined from line pairs at different disk positions, a depth dependent turbulence model was obtained. The final model was anisotropic with radial and tangential components increasing with depth in the atmosphere.Now at Teledyne Brown Engineering, Huntsville, Alabama.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

A principal component analysis of the equivalent widths of spectral lines of star clusters

Using principal component analysis, we have studied the equivalent widths of optical spectral lines of 41 Galactic globular clusters and 22 young stellar clusters. We have discovered that some characteristic spectral lines, such as the CN, Ca IIK, Ca IIH and MgI+MgII lines, are rather sensitive to metallicity. We have also found some lines that may be used as indicators of age, e.g. Hδ, Hγ, Hβ and H. These lines can help us to disentangle the coupling effects of age and metallicity in the clusters.     

Quality analysis of Moore,Minnaert, and Houtgast's equivalent widths

A quality analysis of the equivalent widths (W) for solar lines tabulated in the Atlas of Moore et al. (1966) is undertaken by comparison with other modern sources. No significant correlation with is detected, and only a weak systematic dependence with W turned out which may be neglected for most practical purposes. An approximate trend for the internal dispersion as a function of W is also derived.Fellowship holder of CONICET, Buenos Aires, Argentina.     

A prediction method for ground-based stellar occultations by ellipsoidal solar system bodies and its application

A new programmable prediction method is developed to refine the occultation band by taking into consideration the triaxiality of an occulting body, as well as two more factors, namely, the barycenter offset of an occulting planet from the relevant planetary satellite system and the gravitational deflection of light rays due to an occulting planet. Although these factors can be neglected in most cases, it is shown that there are cases when these factors can cause a variation ranging from several tens to thousands of kilometers in the boundaries of occultation bands. Knowledge of analytic geometry simplifies the process of derivation and computation. This method is applied to long-term predictions of Jovian and Saturnian events.     

K emission-line widths and the solar chromosphere

Closely spaced microphotometer tracings parallel to the dispersion of one excellent frame of a K-line time sequence have been utilized for a study of the nature of the K_2v , K_2R intensities in the case of the solar chromosphere. The frequency of occurrence of the categories of intensity ratio are as follows: per cent; per cent; per cent; per cent; per cent. Two types of absorbing components are postulated to explain the pattern of observed K_2v , k_2R intensity ratios. One component with minor Doppler displacements acting on the normal K₂₃₂ profile, where K_2V >K_2R , produces the cases K_2v K_2R , K_2v = K_2R , K_2v <K_2R . The other component arises from dark condensations which are of size 3500 kms as seen in K_2R . They have principally large down flowing velocities in the range 5–8 km/sec and are seen on K₃ spectroheliograms with sizes of about 5000 kms, within the coarse network of emission. These dark condensations give rise to the situation K_2R = 0.K₂-line widths are measured for all tracings where K_2v , K_2R are measurable simultaneously. The distribution curve of these widths is extremely sharp. The K₂ emission source is identified with the bright fine mottles visible on the surface. Evidence for this interpretation comes from the study of auto-correlation functions of K₂ intensity variations and the spacing between the bright fine mottles from both spectrograms and spectroheliograms. The life time of the fine mottling is 200 sec.The supergranular boundaries which constitute the coarse network come in two intensity classes. A low intensity network has the fine mottles as its principal contributor to the K emission. When the network is bright, the enhancement is caused by increased K emission due to the accumulation of magnetic fields at the supergranule boundary. The K₂ widths of the low intensity supergranular boundary agree with the value found for the bright mottles. Those for the brighter network are lower than this value, similar to the K₂ widths as seen in the active regions.It is concluded that bright fine mottling is responsible for the relation, found by Wilson and Bappu, between K emission line widths and absolute magnitudes of the stars.The paper discusses the solar cycle equivalents that stellar chromospheres can demonstrate and indicates a possible line of approach for successful detection of cyclic activity in stellar chromospheres.     

A new method of magnetograph observation of the photospheric brightness,velocity, and magnetic fields

Several improvements have been made to the Mount Wilson Observatory solar magnetograph, including changes to the guider, the Doppler compensator, and the data-handling system. The improved magnetograph has been used for a new type of solar observation consisting of several hundred scans back and forth along a straight line of length 3/4 R ₀ perpendicular to central meridian. The data reduction, which is done entirely with a computer, eliminates those effects which have their origin in the earth-sun geometry. The spatial and temporal properties of the 5-min oscillations are discussed.     

A new search method for streams in meteor data bases and its application

A new search method for locating meteoroid streams within an orbit data base and obtaining their central core orbits is introduced. The method is based on the transformation of a data base of discrete orbits into a continuous density map. Artificial data bases are used to determine if a density is statistically unlikely to occur by random chance. A search is then run to identify all density peaks within the map that correspond to the central core of a meteoroid stream. Drummond D' criterion is used as a metric within the transformation and a D' acceptability limit, D _l, defines the length scale over which a discrete meteor orbit can have an influence on the density map. Examination of the search dependence on D _l for both real and artificial data sets indicates an appropriate standard value. A full search is run on 5280 meteor orbits from the IAU data base, detecting 16 known major and minor meteoroid streams. New central core orbits are presented for these. No major differences from the published orbits are detected, apart from possible multi-branched structure in the southern δ Aquarids.     

Computation of oscillator strengths by a semi-empirical method for some elements of the iron-group and their solar photospheric abundance

Oscillator strengths are calculated by the STF method for selected transitions of Mn i. The results, applied to the analysis of solar spectra, support the ‘high’ solar photospheric abundance of manganese recently obtained on the basis of experimental gf-values.     

Computation of oscillator strengths by a semi-empirical method for some elements of the iron-group and their solar photospheric abundance

Oscillator strengths calculated by the STF method for selected transitions of V i and Co i have permitted to deduce, from an LTE study of weak lines, photospheric abundances in agreement with those obtained from carbonaceous chondrites. A summary of results is also presented for all the iron-group elements.     

Structure of the solar photospheric convection on subgranulation scales

We investigate the structure of convective flows in the solar photosphere on subgranulation scales. The solar granulation pattern is reproduced by solving the inverse problem of nonequilibrium radiation transfer on the basis of the profiles of the neutral iron line λ 523.42 nm. The wave motions are excluded by the k-ω filtration. The line-of-sight velocity has an asymmetric distribution inside the convective flows in large granules (1.5″ and larger) in the lower photosphere and at the bottom of the middle photosphere. This asymmetry is weaker in the upper photosphere. For smaller flows the distribution is more symmetric at all heights. The asymmetry of the temperature distribution is less pronounced. Large convective flows were found to have a fine structure: they are fragmentized into several smaller flows. The fine structure of large flows and spatial smearing are responsible for the observed asymmetry of the convection velocity distribution inside flows.     

Center-to-limb analysis of the solar oxygen lines

Several lines of neutral oxygen observed at various positions on the solar disk were used to study the influence of (1) the temperature distribution, (2) the velocity field, and (3) the damping on the line profiles and the abundance of oxygen in the photosphere. Theoretical profiles were calculated on the basis of four different model atmospheres in LTE. It was found that the model proposed by Holweger (1967) best reproduced the center-to-limb observations of the lines studied. The weighted mean of the oxygen abundance turned out to be log _O = 8.83 on the basis of log _H = 12.00.     

A new method for determining the helium abundance in the solar atmosphere

Recent observations of a cut-off frequency in the acoustic modes of the Sun (Claverie et al., 1981b) should help determine the mean molecular weight and, thereby, the helium abundance in the visible layers of the solar atmosphere. A first preliminary result of Y = 0.42 ± 0.04 is obtained for an assumed minimum photospheric temperature of 4400 K ± 200 K.     

Computation of oscillator strengths by a semiempirical method for some elements of the iron group and their solar photospheric abundance

Absolute oscillator strengths are computed by the STF method for selected lines of Sci.The lifetimes deduced from these values are in satisfactory agreement with recent beam-foil measurements. From a study of 10 selected lines, a new value of the solar photospheric abundance is derived (logN _sc = 3.04) in agreement with the meteoritic value.     

The solar continuum from 900 to 130 000 Å and the photospheric temperature model

In order to obtain a better agreement between observed and computed values of the solar intensity, an improved temperature distribution is deduced for the range 0.02<0< 10. The intensity observations here considered refer to the wavelength region between 1980 and 129 500, and the center-limb variations generally go down to cos = 0.1. The improved model, given in Figure 4 and Table II, differs rather little from the Utrecht 1964 model, used here as a reference.It appears necessary to introduce an empirical correction function to be applied to the continuous absorption coefficient. This function was derived for the spectral region between 2000 and 130000 Å; it is shown in Figure 5.Furthermore, an extension of the model (1.10^–7<0< 2.10^–2) is deduced (see Table III and Figure 8), which reasonably well represents the observations of the ultraviolet solar flux ( 900–1700 Å).     

Two-dimensional spatial spectrum of the photospheric brightness field near to the solar disc center

From high-quality direct frames taken by the Soviet Stratospheric Solar Observatory, using coherent optical methods, the two-dimensional spatial spectrum of the photospheric brightness field was obtained (Figure 1). This spectrum is isotropic and continuous. Spectral densities P(k) and A(k) = 2k P(k), where k is the radial wavenumber, were estimated for the solar disc centre, and their statistical uncertainty calculated. P(k) has a maximum near k = 10^–3 km^–1 and then it tends to fall after that to zero frequency. The k dependence of A(k) cannot be satisfactorily approximated by a power law. For the highest frequencies studied, the spectrum falls as k ^–9. The measured statistical uncertainty of the spectra of individual domains for k 125 × 10^–4 km^–1 is in agreement with that calculated for a gaussian homogeneous field. But for a higher k the uncertainty may essentially exceed that of a gaussian homogeneous field. The true rms value for 4650 is equal to about 29%.