bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation of the Profiles of Absorption Lines in the Inhomogeneous Medium
Authors: Kostik R.I. 
Published: July 2016

AbstractThe shapes of weak fraunhofer lines, including their asymmetry, are explained by the influence of acoustic waves and granular motions. The following pattern of granula is adopted: the ascending (granular) and descending (intergranular) velocities V1 and V2 as well as the relevant temperatures T1 and T2 are maximum (minimum) at the center of granula (intergranula) and decrease (increase) sinusoidally outwards. There is also tangential outflow of the matter from the center of granula with the velocity V3 = const. and temperature T3 equal to the temperature of the photospheric model T0. The areas occupied by ascending, descending, and tangential motions are S1, S2, S3 respectively.The inhomogeneities caused by granulation are perturbed by the acoustic waves with the velocity amplitude V0 = 0.4 km/s and with the period T = 300 sec. The formula for the absorption line coefficient was derived, and the center-to-limb profiles of 11 weak fraunhofer lines were calculated. The comparison of calculated and observed line profiles have resulted in determining “best fit” values of V1, V2, V3, S1, S2, S3 and ΔT = T1 - T2. Tangential motions occupy the larger part of the solar surfaces S3 = 0.7, V3 ≈ 2.7 km/s, V ≈ 1.0 km/s, ΔT ranges between 270° - 400°.
Turbulence in the Atmospheres of Eclipsing Binary Stars
Authors: Wright K.O. 
Published: July 2016

Abstract:A review of the orbits and dimensions of the ζ Aurigae systems is given, based on photometric and spectrographic observations. The Ca II K-line has been studied intensively to determine the extent and uneven structure of the chromospheres of these stars; the multiple structure of this line observed at several eclipses confirms the presence of large-scale clouds in the atmospheres. Measurements of line profiles and equivalent widths show that macroturbulent velocities up to 10 km/sec in the upper chromosphere, and up to 20 km/sec. in the lower chromosphere are present. Microturbulent velocities in the lower chromosphere are about 10 km/sec. Recent ultraviolet observations indicate that the B star in the 32 Cygni system may be within the outer chromosphere of the giant component and its radiation may affect the chromospheric structure more than had previously been suggested.
Time Dependence of Balmer Progression in the Spectrum of HD 92207
Authors: Groth H.G. 
Published: July 2016

AbstractThe radial velocities measured in the spectrum of HD 92207 (AO Ia+) show a Balmer progression, which varies considerably within one week and reverses within one month (or less). These observations give strong evidence, that at least in some parts of the atmosphere the velocity field reverses with time. (To be published in Astronomy and Astrophysics).
Microturbulence: Age Dependences
Authors: Foy R. 
Published: July 2016

The study of microturbulence in stars for itself, and not as a byproduct of abundance determinations, is relatively recent. The first comprehensive study on this topic was carried out in 1966, by Bonsak and Culver. They found general trends of the behaviour of microturbulence in the HR diagram. A decisive advance occured when ttarz and Kock (1969) revised the scale of oscillator strengths of iron and, as a consequence, the value of the microturbulent velocity in the solar photosphere. The use of microturbulent velocities determined before 1969 should be avoided.Before describing what we know about the behaviour of microturbulence with stellar age, I shall make some statements, and describe how the microturbulent velocity is found, from observations, to depend on the atmospheric parameters.
Effects of Acoustic Waves on Spectral Line Profiles
Authors: Cram Lawrence E. 
Published: July 2016

AbstractAlmost all studies of spectral line formation in the presence of non-thermal velocity fields have been made assuming that the only effect of the velocity field is to produce a Doppler shift of the absorption and emission coefficients. However, a non-thermal velocity field will entail velocity-correlated fluctuations in temperature, pressure, level populations, and other parameters of the line formation problem. Using a time-dependent dynamical calculation describing the propagation of non-linear, radiatively-damped short period (P = 30s) acoustic waves in the solar photosphere, Cram, Keil and Ulmschneider (1980) have shown that velocity-correlated fluctuations in state variables (particularly the temperature) may lead to important effects in line broadening, line shifts and asymmetries, and in line-shift oscillations. Upwardly propagating waves generally produce significant redshifts in the cores of medium-strong Fe I lines, and the increased ratio of observed line shift to wave velocity amplitude would significantly modify the results of kinematic studies of high frequency line shifts such as those of Deubner (1976) and Keil (1980).Cram (1980) has further explored dynamical effects in the formation of Fe I and Fe II lines by using the “microturbulence” limit, wherein an average is made over the phase of the wave before the transfer equation is solved. Except for weak, high EP Fe II lines, the predicted solar lines are redshifted and show a “red” asymmetry. For a model of Arcturus the lines are often shifted to the blue, but it does not appear that this model can account for the observed differences between solar and Arcturan line asymmetries (Gray 1980).
Observations of the Outer Atmospheric Regions of α Orionis
Authors: Bernat A.P. , Goldberg L. 
Published: July 2016

AbstractWe present three separate observational studies of mass flows above the photosphere of α Ori (M2 Ia-Ib). The Ca II infrared triplet lines and Hα are asymmetric showing a systematic blue shift with decreasing residual intensity. These lines remain fixed in wavelength although the weak photospheric lines vary by ±4 km/sec. Observations of the 4.6μ vibration-rotation spectrum of CO show two sharp, cold components expanding at velocities of 10 and 17 km/sec relative to the centre of mass. Direct photographs of the shell in the light of KI λ7699 show that the cold shell is asymmetric and extends outward to at least 50”.Details of these studies are either in press or will be submitted to “The Astrophysical Journal”.
Stellar Winds and Coronae in Cool Stars
Authors: Dupree A.K. , Hartmann L. 
Published: July 2016

AbstractRecent observational and theoretical results are reviewed that pertain to the presence and characteristics of stellar coronae and winds in late-type stars. It is found that stars - principally dwarfs - exist with “hot” coronae similar to the Sun with thermally driven winds. For stars, at the lowest effective temperatures, and gravities characteristic of supergiant and giant stars, high temperature (~105K) atmospheres are absent (or if present are substantially weaker than in the dwarf stars), and massive winds are present. There also exist “hybrid” examples - luminous stars possessing both a “hot” corona and a supersonic stellar wind. Constraints for theoretical models are discussed.
Relationship between Envelope Structure and Energy Source of Non-Thermal Motions
Authors: Ando Hiroyasu 
Published: July 2016

AbstractThe ionization zone in the envelope of the late type stars is reasonably considered as a heat engine to transform some of the radiative energy into mechanical energy. This idea is suggestive for explaining Linsky and Haisch’s (1979) observation, which shows the sharp division into solar-type and non-solar type stars in the outer atmosphere. Also non-thermal velocity fields in “microturbulence” and in Wilson-Bappu effect are proposed to be formed essentially from this engine. Therefore, their envelope structure dependence observationally obtained is possibly explained by the envelope parameters (g, Te) dependence of the generated mechanical energy flux in this layer. If “microturbulence” is not contaminated by the other surface activities, it is expected to show a clear relation with envelope parameters (g, Te) similar to Wilson-Bappu effect.
An Analysis of Microturbulence in the Atmosphere of the F-Type Supergiant Gamma CYGNI
Authors: Boyarchuk A.A. , Lyubimkov L.S. 
Published: July 2016

AbstractWe have analysed high dispersion spectra of the supergiant γ Cyg (F8 Ib). On the basis of the curve of growth method it has been shown that there is no dependence of microturbulent velocity ξt on excitation potentials of spectral lines. Using model atmospheres we considered about 100 Fe I lines and found that no constant value ξt makes possible to remove the systematic discrepancy in iron abundance between groups of lines with different equivalent widths. The depth dependence of microturbulence in the atmosphere is investigated. It is shown that parameter ξt increases outwards from about 0-1 km/s at the optical depth τ5000 = 0.2 to 10 km/s at the depth τ5000 = 10-3. Deducted function ξt (τ5000) gives the same iron abundance log ε(Fe) = T = 7.45 ± 0.05 for all groups of Fe I lines. The detailed analysis will be published in Izv. Crimean Astrophys. Obs.
The Energy Distribution of Sirius B
Authors: Böhm-Vitense E. 
Published: July 2016

The DA white dwarf Sirius B has gained special interest because of the unexplained observed X-rays (Mewe et al. 1975). Coronal emission, accretion and normal photospheric radiation have been discussed as sources.A DA white dwarf with Teff ∽ 28000K (Savedoff et al. 1976, 1978, Koester 1979) should not have a corona (Böhm and Cassinelli 1971, Fontaine 1973). For accretion we do not see where the accreted mass should come from. Normal photospheric radiation requires an effective temperature around 32000K or higher (Shipman 1976). All possibilities to explain the X-rays therefore encounter severe problems.
On the Spectrum of Feige 7
Authors: Wickramasinghe D.T. , Martin Brian 
Published: July 2016

AbstractThe Zeeman theory of hydrogen and neutral helium lines is used to analyse the spectrum of the magnetic DBA white dwarf Feige 7. On the assumption of a centered dipole field distribution and a uniform chemical composition, the atmospheric helium to hydrogen ratio by number, , is found to be ~ 102. However, it is argued that either one, or both of these assumptions are likely to be in error.
What Determines the Speed Cuss of a Nova?
Authors: Shara M.M. , Prialnik D. , Shaviv G. 
Published: July 2016

Recent theoretical hydrodynamic models show that novae of different speed class can be obtained by varying the CNO enrichment and envelope mass. Recent observations of old nova shells, uncontaminated by disc or stellar emission, indicate that various degrees of CNO enrichment are found in slow novae. Using Prialnik et al’s (1978) finding that the “shut-off” mechanism of novae is fuel exhaustion, i.e. expulsion of most of the hydrogen-rich envelope by means of an optically thick wind, we propose the following unified picture for novae:
1) CNO enrichment and envelope mass Menvel together determine the speed class of a nova.2) is determined by the accretion mechanism and convective efficiency on the white dwarf surface.3) Menvel is determined by the nature of the binary system and by envel the accretion rate ṁ.4) Fast novae tend to have larger and smaller Menvel than slow novae, but CNO-rich slow novae and CNO-poor fast novae are permitted with certain envelope masses. We present below a qualitative diagram of the Menvel, - plane.
X-Ray Astronomy Satellite Ginga
Authors: Makino F. 
Published: July 2016

AbstractThe X-ray astronomy satellite Ginga carries three scientific instruments, the Large Area proportional Counters (LAC), All Sky X-ray Monitor (ASM) and Gamma-ray Burst Detector (GBD). The LAC is the main instrument with an effective area of 4000 cm2 giving it the highest sensitivity to hard X-rays so far achieved. Ginga observed about 250 targets up to the end of 1989.
The Joint European Telescope for X-Ray Astronomy (JET-X)
Authors: Pounds K. A. 
Published: July 2016

AbstractJET-X is one of the main payload elements in the Soviet Spectrum-X Gamma mission scheduled for launch in 1993. It consists of two Wolter I X-ray telescopes feeding cooled arrays of CCD’s. The combination of good angular resolution and long exposures during the four day orbit of Spectrum-X Gamma, will allow the JET-X telescopes to reach a sensitivity level ten times fainter than that of the Einstein Observatory deep survey. The CCD’s will provide good spectral data for many thousands of brighter sources over an energy band ~0.3–10 keV. The JET-X project is an international collaboration involving groups in the United Kingdom, Italy, West Germany and the Soviet Union together with an input from the Space Science Department at ESTEC. A brief description is given of the design and anticipated performance of JET-X together with illustrations of the anticipated scientific results.
ESA’s X-Ray Astronomy Mission, XMM
Authors: Taylor B.G. , Peacock A. 
Published: July 2016

AbstractESA’s X-ray Astronomy Mission, XMM, scheduled for launch in 1998, is the second of four cornerstones of ESA’s long term science program Horizon 2000. Covering the range from about 0.1 to 10 keV, it will provide a high throughput of 5000 cm2 at 7 keV with three independant telescopes, and have a spatial resolution better than 30 arcsec. Broadband spectrophotometry is provided by CCD cameras while reflection gratings provide medium resolution spectroscopy (resolving power of about 400) in the range 0.3–3 keV. Long uninterrupted observations will be made from the 24 hr period, highly eccentric orbit, reaching a sensitivity approaching 10−15 erg cm−2 s−1 in one orbit. A 30 cm UV/optical telescope is bore-sighted with the x-ray telescopes to provide simultaneous optical counterparts to the numerous serendipitous X-ray sources which will be detected during every observation.
Lyman the far Ultraviolet Spectroscopic Explorer
Authors: Moos Warren 
Published: July 2016

AbstractThe Lyman Far Ultraviolet Spectroscopic Explorer mission will obtain high resolution spectra (R 30,000) in the 912–1200 Å region with sufficient sensitivity to study faint sources throughout the galaxy and at large extragalactic distances. This spectral region provides unique tools for solving problems in cosmology (e.g. deuterium), galactic structure and evolution (e.g. O VI and H2), stellar evolution (e.g. O VI) and planetary science (e.g. H2). Recent advances in optical and detector technology, which make this goal possible with a moderate size experimental package, also enable the spectral coverage to extend down to 100 Å with good sensitivity and only a minimal increase in complexity. Thus a secondary goal is to cover the 100–912 Å region with moderate spectral resolution. In 1989, following a Phase A study of the mission concept, NASA selected the mission for Phase A study in 1989. Both Canada and the United Kingdom are participating in the definition and development of the mission.
Ultraviolet Polarimetry
Authors: Code A.D. , Nordsieck K.H. , Anderson C.M. 
Published: July 2016

AbstractInterstellar polarization and polarization of the sky background is predicted to be significantly smaller in the ultraviolet than in the optical region of the spectrum; while intrinsic polarization is expected to be greater. For these reasons alone ultraviolet polarimetry should provide a powerful diagnostic tool. To date such polarization measurements have not been undertaken. The Wisconsin Ultraviolet Photopolarimeter Experiment (WUPPE) will be the first to carry out a program of UV spectropolarimetry. WUPPE is one of the four ASTRO-1 payloads. It consists of a half meter aperture Cassegrain telescope feeding a spectropolarimeter capable of measuring spectral energy distribution and linear and circular polarization in the spectral region from about 3300 Å to 1400 Åwith spectral resolutions from about 4 Å to 40 Å, depending upon the mode of observation and nature of the source. The effective area of WUPPE is approximately 100 cm2 at 2000 Å and the faint stellar limit for measurement of all four Stokes parameters is about 16 magnitude. The design provides for a large dynamic range and the high precision required for accurate polarimetry. Launch of the first ASTRO Mission is expected in May of 1990.The science goals for WUPPE include studies of ultraviolet interstellar polarization, intrinsic polarization of a wide variety of stellar types and measurements of polarization of selected extragalactic objects. A description of WUPPE and simulations of expected data will be presented. The paper will also discuss a wide field imaging survey polarimeter (WISP) now undergoing development for a sounding rocket payload at the University of Wisconsin. (This work is supported by NASA contract NAS5-26777).
The Hopkins Ultraviolet Telescope
Authors: Davidsen A. 
Published: July 2016

AbstractThe Hopkins Ultraviolet Telescope (HUT) will make pioneering observations in the far ultraviolet (912–1850 Å) and extreme ultraviolet (420–912 Å) bands during its upcoming flight aboard the Astro-1 shuttle mission, currently scheduled for launch on May 9, 1990. HUT employs an iridium-coated 0.9-meter f/2 primary mirror, an osmium-coated grating, and a CsI-coated microchannel plate intensifer to achieve a resolution of about 3 A in first order, with a peak effective area of 15 cm2 at 1100 Å, and time resolution of 2 milliseconds, HUT’s EUV response is obtained in second order, with a peak effective area of 10 cm2 at 600 Å.HUT is expected to obtain several hundred spectra during its upcoming mission, ranging from Comet Austin to the quasar HS 1700+64 at a redshift of 2.7. The design and operation of the instrument are described, and simulated spectra are used to illustrate a sample of the problems that will be addressed during the Astro-1 mission. In order for HUT to be exploited fully, however, it would be desirable to convert it to a free-flying satellite mode
Humanity or Robotics in Space?
Authors: Oda Minoru 
Published: July 2016

The diagram (Fig. 1) qualitatively exhibits how several important observations will have to be undertaken. Here, I would like to, at least, raise the question or discuss the problem referring to “Man in Space”.My question is as follows: How the man in space, like the Space Shuttle, and the robotics, like Voyager, precede the man in space “and/or” the robotics in the 21st century? I think, the answer is not obvious and we have to be cautious to make decisions. Once we make the decision, we may not be able to go backwards because the investments will be enormous and the impact to all humans will be very deep.
New Methods of Determining Spacecraft Attitude
Authors: Pitts R. , Jackson T. , R. Gilmozzi 
Published: July 2016

AbstractThe IUE spacecraft was launched with prime and redundant mechanical Panoramic Attitude Sensors (PAS) to determine coarse spacecraft pointing. Attitude determination typically took at least 24 hours. After launch both systems failed. A new method was developed which required pointing the spacecraft at the antisolar position. After the failure of the 4th IUE gyro, it was no longer possible to point in the antisolar direction. A second method was developed which utilizes IUE’s ability to track the sun with a solid state two-dimensional sun sensor. Attitude determination can now be completed in several hours. An hour is required for coarse position measurement and several more hours are needed, using a small 15 arc minute square finder camera, for final attitude confirmation. These methods should be of use for other spacecraft where weight is critical or there is a desire to avoid mechanical devices.
Knowledge Based Automated Scheduling and Planning Tools for IUE
Authors: Shrader Chris R. 
Published: July 2016

AbstractThe International Ultraviolet Explorer has been successfully operated as a real time user-interactive space observatory for twelve years. It is expected to continue operation for up to five additional years, but under increasing constraints. The option to operate IUE in a more automated, non user-interactive mode is under consideration. A sophisticated software system to support such an operation is a clear requirement. The conceptual framework of such a system is described. Results of a preliminary tests are presented for which a hypothetical four day schedule of space-craft activities at a time resolutions as low as ten minutes was generated.
Earth Observation System Plans of India
Authors: Chandrashekar M.G. , Jayaramn V. , Dutt C.B.S. , Manikiam B. 
Published: July 2016

AbstractOperational methodologies are available to retrieve several parameters related to the land, air and oceans from satellite data which is capable of providing well calibrated data/observations over large areas giving a synoptic view on a repetitive and reliable basis. The capability of satellites to provide data in various spectral, spatial and temporal scales is of great advantage in studying the dynamic aspects of earth atmosphere system. The present day capabilities of satellites include spatial resolutions ranging from 10 m and above and repetition of a few hours (geosynchronous Satellite) to few days. Higher spatial resolutions and all weather capabilities (through microwave sensing) are becoming available in the immediate future. Towards utilising the potentials of space based systems, India has been operating INSAT series of satellite for weather monitoring and 1RS series of satellites for natural resources monitoring/management. The INSAT is a series of geostationary satellites stationed over Indian region to provide meteorological observations on a continuous basis in visible and thermal regions in addition to providing services for disaster warning related to Cyclones and remote location data collection platforms. The space based observations on meteorology over the past 5 years is proving to be a valuable data base for studies related to monsoon dynamics and tropical cyclones.
Electron Acceleration at Quasi-Parallel Shocks in The Solar Corona and Its Signature in Solar Type II Radio Bursts
Authors: Mann G. , Lühr H. 
Published: July 2016

AbstractRecently, strong large amplitude magnetic field structures (SLAMS) have been observed as a common phenomenon in the vicinity of the quasi-parallel region of Earth’s bow shock. A quasi-parallel shock transition can be considered as a patchwork of SLAMS. Using the data of the AMPTE/IRM magnetometer the properties of SLAMS are studied. Within SLAMS the magnetic field is strongly deformed and, thus, the magnetic field geometry is locally swung into a quasi-perpendicular regime. Therefore, electrons can locally be accelerated to high energies within SLAMS. Assuming that SLAMS also exist in the vicinity of supercritical, quasi-parallel shocks in the solar corona, they are able to generate radio radiation via the enhanced Langmuir turbulence excited by the accelerated electrons. Since SLAMS are connected with strong density enhancements, the aforementioned mechanism can explain the multiple-lane structure often occurred in solar Type II radio bursts.Subject headings: acceleration of particles — Earth — shock waves — Sun: corona — Sun: radio radiation
Turbulent Acceleration in Solar Flares
Authors: Melrose D. B. 
Published: July 2016

AbstractTurbulent acceleration in the impulsive phase of solar flares is reviewed, with the emphasis on bulk energization of nonrelativistic electrons and prompt acceleration of the gamma-ray emitting nonrelativistic ions and relativistic electrons. The primary energy release in a flare cannot be due to collisional dissipation. Anomalous resistivity requires that the current flows in many narrow channels with the current density above threshold for current instability. The bulk energization of the electrons is due to the damping of low-frequency electrostatic turbulence generated by the current instability. This turbulence also limits the rate a nonthermal electron tail forms due to runaway acceleration. Stochastic and gyroresonant acceleration by MHD turbulence are discussed briefly, emphasizing the need for preacceleration. Stochastic acceleration is favorable for the gamma-ray emitting particles only if an adequated source of the MHD turbulence can be identified.Subject headings: acceleration of particles — MHD — Sun: flares — turbulence