Solar atmospheric model including OH-continuum opacity

Flux-constant model has been constructed for solar atmosphere, including OH-bound-free opacity, but without any line opacity, atomic, ionic or molecular. A comparison between the theoretical and observed intensity and flux shows that OH-opacity can account for the missing solar opacity, except at those wavelengths where the intensity shows the presence of numerous absorption lines, provided the unknown oscillator strength of the transition is 0.3. The T – relation, however gives larger temperatures at smaller depths than those by the empirical model. This and the large theoretical flux in the spectral region with heavy line absorption indicate the importance of line opacity.On leave from Tata Institute of Fundamental Research, Bombay-400005, India.     

Empirical limb effect curves for the FeI lines λ5250 and λ5576

The center to limb variation of solar spectral line positions, or limb effect, has been measured for the two neutral iron lines at 5250.2 Å and 5576.1 Å. Both limb effect curves show a disk-center reversal of 40–60 ms^–1 and the 5576 data also exhibit a possible second reversal at the limb. The limb effect curves are best described by polynomial expressions rather than by traditional power law expressions.Visiting Student, Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

New calculations of interstellar dust (ID) contraction in a non-isothermal regime

We have calculated the opacity as resulting from different interstellar grain models, molecules, atoms, and ions. The resulting opacities have been applied to a numerical code used to follow the thermal evolution of a contracting cloud in one dimension. An exact analytical and computational developments of both Mie theory for isolated grains and Güttler's formulae for composite grain models have been used to calculate the extinction coefficients. We have studied two models of composite grain and three models of isolated grain. The opacity of interstellar grains has been calculated in the temperature range 10–1500 K. The molecular opacity is splitted into continuous and line opacities. The different sources of continuous opacity have been studied. The line opacity has also been included. The atomic opacities are also considered. The hydrodynamical equations are solved explicitly but the energy and Poisson equations are solved implicitly.It has been found that the thermal evolution during contraction of protostellar clouds is sensitive to both: the assumed grain models and the considered chemical composition. A cloud of an initial temperature of 10 K collapsed to a stage in which the temperature increases to 91 000 K and the density reached to 0.16 g cm^–3.     

Absolute spectroscopic determination of solar rotation

We have made absolute measurements at Kitt Peak of the dependence of solar rotation rate upon latitude during the period 17–20 June 1977. We observed the solar potassium line at 7699 Å using an atomic-beam resonance scattering apparatus. The measured sidereal equatorial rotation rate is 13.5±0.5 deg day^–1. Our results are in agreement with those of Howard and Harvey from 1966–68. We intend to use this technique in a long-term program at Oberlin to monitor the equatorial rotation rate.Visiting Astronomer, Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Transition-zone observations of rapid flare events as observed by OSO-8

The rapid dissipation of flare energy has been observed in the transition-zone line of C iv at 1548.2 Å using the University of Colorado spectrometer aboard OSO-8. Impulsive brightenings have been resolved with characteristic risetimes as low as 3.5 s. One event is analyzed in detail, in which it is inferred that the electron density is greater than 2 × 10¹¹ cm^–3 at T = 60 000 K, and that the flare energy is deposited at a rate of 2 ergs cm^–3 s^–1 or greater. The temporal behavior of the intensity at the center of the C iv line is consistent with a non-equilibrium ionization of C iii through C v. If this event is a result of the multiple tearing mode instability as the primary energy release mechanism, then the observations indicate a pre-flare magnetic field of about 175 G.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Investigation of the Mg XII 8.42 Å doublet in solar flare spectra

The intensity ratio of the components of the Mg xii 8.42 Å (1s ² S _1/2 – 2p ² P _{1/2, 3/2}) doublet in solar flare spectra has been investigated using observations recorded from the Intercosmos 7 satellite. The observed values of the ratio fall within the interval 0.38–0.66 and have been compared with recent theoretical predictions based on an optically thin collisional-radiative model. It has been found that for the flare plasma the low values of the ratio cannot be explained since they fall below the smallest theoretical value. The highest values on the other hand require that an unacceptably high electron density be postulated. It is suggested that both high and low values may be caused by the resonance line scattering of the Mg xii quanta in the flare volume, provided that the volume is elongated and not spherical.The intensity of the nearby satellite lines is also investigated. Good agreement between the theoretical and observed intensities is found.     

Line transfer in supernovae envelopes by Sobolev's treatment

We combine an accurate treatment of continuum transfer in supernovae envelopes with a line transfer treatment using Sobolev's approximation to analyze the influence of some physical parameters (the continuum opacity, the ratio of scattering over absorption and the temperature profile) on the emergent intensity of a resonant scattering line.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

On the problem of the formation of quasar emission lines by the Cherenkov mechanism

In a series of papers of You, Cheng, et al. (cf., for example, [2–4]) the Cherenkov mechanism of radiation was proposed as the explanation of the wide emission lines in the spectra of quasars. This mechanism acts because the refractive index of the plasma in a certain frequency range near a spectral line can exceed one. It has been found that the role of Cherenkov radiation becomes significant for an optically thick medium when the density of the packet of relativistic electrons ñ_e is 10⁴–10⁶ cm^–3. However, the question of the formation of a spectral line as the result of ordinary (recombination and collision) processes under the same physical conditions has not been considered, and hence no comparison has been made between the intensities of lines formed by different mechanisms. Moreover, a large number of effects that may have significant influence on the profile of a line (multiple scattering in the medium, redistribution of radiation over frequencies within a line, redistribution of energy between a line and the continuous spectrum) have remained unexamined by these authors.The present work aims at sharpening some of the formulas used in [2–4] and filling up some of these gaps. We pose the classical problem of formation of a spectral line taking account of the action of the Cherenkov radiation mechanism and give an exact solution of it. The computations are carried out for the line L. It is shown that under the values presently accepted for the electron temperature for an average quasar (T_e 1.5 · 10⁴ K) the influence of the Cherenkov mechanism becomes noticeable only for implausibly high densities of relativistic electrons (10¹¹ cm^–3, The geometric model proposed in [4] for quasar radiation in a line encounters insuperable difficulties involving the energy of the quasar and the sizes of the radiating regions.Translated fromAstrofizika, Vol. 37, No. 3, 1994.     

Ionospheric corrections via PIM and real-time data

We describe a method for removing ionospheric effects from single-frequency radio data a posteriori. This method is based on a theoretical climatological model developed by the USAF, which returns along the line of sight to the source. Together with a model of , ionospheric delay and Faraday rotation values ensue. If contemporaneous ionospheric data – GPS TEC observations or ionosonde profiles – exist, they can be incorporated to update the modeled n_e.     

Radiation transport in a cylinder. I. Resolvent of the fundamental integral equation

A new method is presented for calculating spectral line radiation transport in a homogeneous circular cylinder with infinitely long axis for isotropic scattering with complete frequency redistribution or no change in frequency. In addition to the cylinder, scattering in a layer symmetric about its midpoint and in a sphere are also studied. Equations are derived which are satisfied by the resolvent of the fundamental integral equation describing these cases of scattering. By applying a Hankel transform over a finite interval, the resolvent is expressed in terms of an auxiliary function. An equation is derived for this auxiliary function which is easily soluble by iteration, with the speed of its convergence increasing with growth in the radius of the scattering region.Translated from Astrofizika, Vol. 37, No. 1, pp. 111–127, January–March, 1994.This study was carried out with financial support from the Russian Fund for Fundamental Studies (project 93-02-2957).     

The H− equilibrium using coupled rate equations for H−, H,H+, H2, and H2 +

We formulate rate equations for the reaction network coupling H, H^–, H⁺, H₂, and H₂ ⁺. We attempt to systematize the notation, and to write the equations in a form suitable for modern computational methods of handling the coupled rate equations and radiative transfer equations, for both dynamical and static atmospheres. We have accounted for more processes than are generally considered in most current work; some of these may have an impact on the equilibrium of H^– (hence its opacity) and on charge conservation (hence the proton density) in the atmospheres of solar-type stars.Operated by the Association of Universities for Research in Astronomy, Inc. under Contract AST 78-17292 with the National Science Foundation.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The absorption spectrum of atmospheric water vapor in the vicinity of the He 10830 Å triplet

Wavelengths of clean atmospheric water lines, and some solar lines, in the wavelength interval 10750 Å to 10900 Å have been measured to an accuracy approaching ± 1 mÅ. Strengths and wavelengths have been measured for all atmospheric water lines with absorption coefficients > 5 × 10^–4 cm^–1 gm^–1 cm^–2 at 280K, that lie within 15 Å of the He I 10830 Å featur of the stronger He component is affected by a weak water line which reduces atmospheric transmission by nearly 1 % with 10 mm precipitable water in the line of sight.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Elemental abundance analyses with DAO spectrograms — XVIII. The double-lined spectroscopic binary 46 Draconis

Equipartition magnetic fields can dramatically affect the polarization of radiation emerging from accretion disc atmospheres in active galactic nuclei. We extend our previous work on this subject by exploring the interaction between Faraday rotation and absorption opacity in local, plane-parallel atmospheres with parameters appropriate for accretion discs. Faraday rotation in pure scattering atmospheres acts to depolarize the radiation field by rotating the polarization planes of photons after last scattering. Absorption opacity in an unmagnetized atmosphere can increase or decrease the polarization compared to the pure scattering case, depending on the thermal source function gradient. Combining both Faraday rotation and absorption opacity, we find the following results. If absorption opacity is much larger than scattering opacity throughout the atmosphere, then Faraday rotation generally has only a small effect on the emerging polarization because of the small electron column density along a photon mean free path. However, if the absorption opacity is not too large and it acts alone to increase the polarization, then the effects of Faraday rotation can be enhanced over those in a pure scattering atmosphere. Finally, while Faraday rotation often depolarizes the radiation field, it can in some cases increase the polarization when the thermal source function does not rise too steeply with optical depth. We confirm the correctness of the analytic calculation by Silant'ev of the high magnetic field limit of the pure scattering atmosphere, which we incorrectly disputed in our previous paper.     

Negative ions in comets

The primary negative ion sources in comets are shown to be: for the inner coma—both polar photodissociation of HCN, electron attachment of OH and collisions with alkalis; in the vicinity of the nucleus—plasma, excavated during interplanetary dust impacts on the nucleus; for both the contaminated solar wind region and sporadic discharges in the non-homogeneous inner coma plasma—dissociative electron attachment and charge inversion during keV positive ion scattering by cometary dust are also significant sources. Negative ion abundance for Halley's Comet has been estimated to be from 10^–6 to 10^–10 of electron densities. However, this ratio may be more due to the formation of clusters A^–(H₂O)_n. Some possible cometary plasma effects, caused by negative ions, have also been discussed.     

A possible interpretation of the optical spectrum for BL Lac-type objects

On the basis of Sobolev's method, the population of 30 levels of hydrogen atom is determined allowing for the radiative and collision processes of the heating and ionization of the medium with velocity gradient gradv=10^–9–10^–11s^–1, electron temperatureT _e=10⁴ K-2×10⁴ K and electron densityN _e=10¹⁰ cm^–3–10¹¹ cm^–3. The central source radiation is characterized by a power spectrum with spectral indices varying from 0 to 2. A region of possible physical conditions is found where the thermal diffuse radiation of the envelope exceeds the emission in the Balmer H line.     

On the minimum intensity of the Na D2-5890 Å line in sunspot umbra

The line-to-continuum intensity ratio for the center of the Na D₂ absorption line in a spot of area 20 × 10^–6 in the Rome Group 5847 was found to be 0.033±0.05 on 6–7/7/70 by two methods.Goethe Link Publication No. 139. This work was supported by the National Science Foundation and the National Aeronautics and Space Administration.     

A rare centimetric spike event on 10 March 2002

A group of centimetric spikes was detected during the burst of 10 March 2002 with the spectrometer of NAOC (National Astronomical Observatories of China). These centimetric spikes are resolved clearly in the time and frequency panels. A statistical analysis shows that these spikes have very short durations (5–10 ms), narrow bandwidths (20–40 MHz), very high polarization degrees (≥90%), and relatively weak flux densities (10–40 sfu). The simultaneous 2D image observations of NoRH (Nobeyama Radioheliograph) and SSRT (Siberian Solar Radio Telescope) imply that the spikes should come from a small source region, which was located in an area with a complex magnetic field. It is also found that the spikes are polarized in the X-mode. These observations suggest that the electron cyclotron maser (ECM) is the most likely mechanism of these centimetric spikes.     

Bursts of gravitational radiation from active galactic nuclei and globular clusters

The characteristics of gravitational bursts from active galactic nuclei, and globular clusters are obtained for three astrophysical situations:(i) scattering of stars by massive black holes residued at the centers of galaxies and globular clusters; (ii) the close encounters of stars in the nuclear regions of these objects; (iii) scattering of stars by black holes of stellar mass containing in the stellar population of galactic nuclei and clusters. The most effective source of gravitational bursts appears to be a scattering of stars by the massive central black holes which produces the bursts with dimensionless amplitudeh10^–19–10^–21 and frequencies from 10^–1 to 10^–5 Hz. The characteristics obtained correspond to the possiblities of a future gravitational-wave experiment with use of laser Doppler tracking of interplanetary spacecrafts.     

Disc structure around strongly magnetic accretors: a full disc solution with turbulent diffusivity

The problem of the effect of a strongly magnetic star on a surrounding accretion disc is considered. For stellar rotation periods greater than a critical value, a numerical solution is found for a steady disc with turbulent magnetic diffusion, including electron scattering opacity and radiation pressure. Inside the corotation radius, the extraction of disc angular momentum by magnetic coupling to the star becomes strong and this leads to enhanced viscous stress and dissipation. The resulting elevated temperature causes electron scattering opacity and radiation pressure to become significant further from the star than in the absence of its magnetic field. The disc ends as its height increases rapidly due to the large central pressure, its density decreases and magnetically induced viscous instability occurs.     

Limb darkening in the solar ultraviolet

New photoelectric limb-darkening data are given for 38 of the windows in the UV solar spectrum in which Houtgast has supplied absolute energy measurements. The region, 4000 Å to 3000 Å, is marked by unaccounted opacity. Results are given also for 13 longer wavelengths. The measurements are fully corrected for atmospheric seeing and scattering. The corrected drift curves exhibit a quasi-periodic character suggestive of the supergranulation.