bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of the Profiles of Absorption Lines in the Inhomogeneous Medium
Authors: Kostik R.I.
Published: July 2016

The 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

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

The 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

Almost 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

We 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

Recent 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

The 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

We 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.
Evolution of White Dwarfs and their Physics
Authors: Shaviv Giora
Published: July 2016

White Dwarfs (WD) are one of the fields in stellar structure in which the so-called “input physics” is not yet completely clear today. In particular the equation of state (EOS) of WD affects directly one of the eminent problems in present day research of WD, namely is the “paucity” of low luminosity WD real? The reply depends in a sensitive way on the physical properties of the dense matter. For this reason we go in some detail into the physical problems of the “input physics”. We distinguish between the problem of the interior-fully ionized matter and the envelope-partially ionized matter. Unfortunately space-time is not sufficient to cover in any detail the EOS of the envelope although this problem is extremely important to the evolution.
Gravity Indicators in DB White Dwarfs
Authors: Wickramasinghe D.T.
Published: July 2016

Theoretical helium line spectra in the wavelength region λλ 3000-6000Å are presented and possible spectroscopic gravity indicators are discussed. The feasibility of using spectrum synthesis techniques for the analysis of DB white dwarfs is investigated.
Masses of DB Degenerate Dwarfs
Authors: Trimble Virginia
Published: July 2016

Alcock (1979a,b) has suggested that DB degenerate dwarfs can only be kept observably free of accreted interstellar hydrogen if their masses are not more than about 0.3 M⊙. This is distressing because (a) photometrically determined DB radii (hence masses) are not statistically different from those of DA’s (Shipman 1979), and (b) no one quite knows how to make a degenerate dwarf with this low a mass in the age of the galaxy. Several authors (Vauclair et al. 1979; Michaud and Fontaine 1979) have suggested that accretion is inhibited by effects of coronae and/or magnetic fields. I address here the possibility that the DB’s are a somewhat higher velocity population than the general run of degenerate dwarfs. Although, as we shall see, this may imply somewhat lower than average masses for them, the dominant effect will be reduced accretion due to the high speed of the stars through the interstellar gas.
Extreme Ultraviolet Observations of Hot White Dwarfs
Authors: Bowyer Stuart
Published: July 2016

The term extreme ultraviolet (EUV or XUV) is employed in upper atmosphere physics and in solar work where it usually denotes the wavelength band between 100 and 1000 Å. Since thermal emission with 30,000 ≲ T ≲ 300,000 K peaks in this band, it might be expected that studies at these wavelengths would be especially useful for objects with effective temperatures in this range. In fact9 few such studies have been carried out. The reason for this anomaly is that very few EUV studies have been made at all, particularly because of unreasonably pessimistic estimates of the opacity of the interstellar medium and partially because of instrumental difficulties encountered at these wavelengths. The first search for extreme ultraviolet emitting objects was carried out in 1975 with instrumentation on the Apollo spacecraft in the Apollo-Soyuz mission. Four of approximately thirty preselected objects were detected with this instrumentation. The objects detected unquestionably are more a reflection of the prejudices of the investigators than they are a sampling of the contents of the universe. Nonetheless, two of the four objects detected were hot white dwarfs: HZ 43 and Feige 24. In addition, upper limits which turned out to be extremely useful were obtained on the Sirius A/B system. These results, plus more recent results obtained on hot white dwarfs will be discussed in this review.
Middle- and Far-Ultraviolet Observations of Hot White Dwarfs
Authors: Parsons S. B. , Wray J. D. , Henize K. G.
Published: July 2016

Several hot subluminous stars were first recognized as such from low-resolution spectra obtained with the ultraviolet objective-prism survey from Skylab, Experiment S-019. About 9 percent of the sky was photographed, 3 percent with unwidened spectra. Two hot subdwarf stars have been reported previously, HDE 283048 (Laget et al. 1978) and the companion to HR 3080 (Parsons et al. 1976a). Papers on two other subdwarfs are in preparation. One previously unrecognized white dwarf star was found, HD 149499 B, and new observations (Wray, Parsons and Henize 1979) show it to be probably the hottest white dwarf known.
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.
Spectrophotometry of Hot White Dwarfs from the Palomar-Green Survey
Authors: Green Richard F. , Liebert James W.
Published: July 2016

The Palomar-Green Survey (1977) contains a list of some 3000 spectroscopically classified stellar objects, chosen on the basis of ultraviolet excess. The survey covers 10,000 square degrees of the sky above |b|=30° with δ≥10° down to an average limiting B=16.2. A significant subset of this sample is a new catalogue of over 700 newly discovered hot degenerates (Green 1979). The combination of selection by color only without regard to motion and the large area covered resulted in the discovery of some rare, luminous degenerates and pre-degenerate objects. We report here on the first observations in a program of more detailed spectroscopic study of these objects, and display representative groups of common spectral or physical properties. These scans at 1.5-2.5 Å resolution were obtained with either the KPNO 2.1-m and intensified image dissector scanner or the Palomar 1.5-m with SIT spectrograph.
Hard X-Ray Properties of Cataclysmic Variables
Authors: Swank J.H.
Published: July 2016

The production of hard X-rays in accretion onto degenerate dwarfs appears manifested by such sources as the magnetic variables AM Herculis and 3U0311-227 and the dwarf novae SS Cygni, EX Hydrae and U Geminorum. Upper limits on flux above 2 keV from Ariel 5 (Watson, Sherrington and Jameson 1978) and from the high energy detectors of the HEAO A2 experiment show that only a few others usually exhibit more than ~10-11 ergs cm-2s-1 or ~ 1031 ergs s-1. However, while there are only a few sources that these experiments could study, their behavior is complex (Swank et al. 1977a; Ricketts, King and Raine 1979; Swank et al. 1978; Mason, Cordova and Swank 1979). This paper is a brief summary of results for AM Her, EX Hya, SS Cyg and U Gem obtained with the high energy detectors of the HEAO A2 experiment from 2-60 keV and the Solid State Spectrometer Experiment (SSS) with the Monitor Proportional Counter (MPC) on the Einstein Observatory.
The Spectra and Colors of Cool White Dwarfs
Authors: Bessell M. S. , Wickramasinghe D. T. , Cottrell P. L.
Published: July 2016

White dwarfs fall in two main categories (1) the group with H-rich atmospheres (DA) the most numerous, and (2) the group with He-rich atmospheres (DB, DC, DF, DG, λ4670). Calculations of element separation (via gravitational settling) and convective mixing in white dwarf models have been made by Koester (1976) and Vauclair and Reisse (1977) in order to understand the existence and maintenance of these distinct groups and to predict at what stage during the cooling of the white dwarf some connection may occur between the two groups. Over the last few years, Wickramasinghe, Bessell and Cottrell (Wickramasinghe et al., 1977; Cottrell et al., 1977; Bessell and Wickramasinghe, 1979; Bessell, 1978 and Wickramasinghe and Bessell, 1979) have investigated the properties of cool (T < 6000K white dwarfs observationally and theoretically. We have attempted to establish at what temperature mixing does occur in DA white dwarfs, whether cool white dwarfs could be confused with G, K and M dwarfs, and if one can discriminate spectroscopically cool He and H-rich white dwarfs. In this paper we will discuss the spectra and colors of the coolest (Te < 5000K white dwarfs and compare them with model atmosphere calculations.
Diffusion Coefficients in Dense Plasmas
Authors: Fontaine G. , Michaud G.
Published: July 2016

It has been known for some time (Schatzman 1958) that diffusion could play an important role in the spectral evolution of white dwarfs. However, it is only recently that quantitative estimates have become available, making use of detailed envelope models (Fontaine and Michaud 1979, hereafter referred to as FM; Vauclair, Vauclair, and Greenstein 1979; Alcock and Illarionov 1979). These studies suggest that the observed monoelemental character of white dwarf spectra can qualitatively be explained in terms of the diffusion model. Moreover, it appears that the diffusion time scales are so short compared to evolutionary times that competing mechanisms, such as accretion, must be invoked to explain the small but measurable abundances of heavy elements in the spectra of cooler white dwarfs.
Close Binary (and Pulsating) Nuclei of Planetary Nebulae
Authors: Bond Howard E.
Published: July 2016

Close-binary central stars of planetary nebulae are of interest to participants in this Colloquium because of recent suggestions that the cataclysmic binaries, containing a white dwarf and a lower-main-sequence star, may be descended from such objects (e.g. Paczynski 1976; Ritter 1976; Webbink 1978; Meyer and Meyer-Hofmeister 1978; Livio, Salzman, and Shaviv 1979). The proposed scenario is. that a binary system of initially large separation (P.= 1-10 yr) forms a “common-envelope” binary after the primary has evolved to the red-giant stage and developed a degenerate core. The secondary star spirals inward inside the red-giant envelope, eventually transferring enough angular momentum to the envelope to eject it. The result is a close binary containing the hot degenerate core of the red giant and a cool main-sequence companion, surrounded by the ejected envelope, which is ionized by the hotter star. Much later, when the cool companion begins to evolve, it will start to transfer matter to the hot star (by now a white dwarf), and cataclysmic activity ensues.
General Theory for Shell Flash and nova Explosion of Accreting White Dwarfs
Authors: Sugimoto D. , Fujimoto M. Y. , Nariai K. , Nomoto K.
Published: July 2016

It is now well known that an accreting white dwarf experiences a shell flash near its suface. Such phenomena are related with rekindling of white dwarfs, slow and fast nova explosions etc. depending on its strength. Though many authors computed evolution through such shell flashes, they treated them only under specific conditions.
Helium Shell-Flashes in Accreting White Dwarfs
Authors: Fujimoto M. Y. , Sugimoto D.
Published: July 2016

When gas is accreted onto a carbon-oxygen white dwarf, a hydrogen shell-flash is triggered. Recently such phenomena are studied by many authors in relation to nova explosions and rekindling of white dwarfs. Unless all of the accreted gas is ejected by the process of the nova, a helium zone is formed as a result of hydrogen shell-burning. As the hydrogen shell-flashes recur many times, the helium zone grows gradually in mass. Then the helium shell-flash will be ignited as in the deep interior of ordinary red giant stars. We have investigated such process, simulating it by helium accretion at a constant rate. In the present paper we show that the helium shell-flashes result in a variety of strengths depending upon situations.
On the Spectrum of Feige 7
Authors: Wickramasinghe D.T. , Martin Brian
Published: July 2016

The 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.
Spectra of Variable White Dwarfs
Authors: Greenstein Jesse L.
Published: July 2016

Spectra of seven ZZ Ceti DA variables have been obtained with the multichannel spectrophotometer, several also with 7 Å resolution with the SIT digital spectrophotometer, one with the IUE. The colors fit hydrogen model atmospheres well; the combined IUE and MCSP energy distribution of G29-38 show no peculiarity from 10,000 to 2000 Å. Hydrogen model atmospheres yield  = 4.073±0.008; the dispersion is σ = ±0.02, quite near the total observational and model-fitting error. Using an estimate of the intrinsic 2σ as a half-width the instability strip for hydrogen degenerates lies at 11,800±600 K (for log g = 8). This applies, of course, only to the northern ZZ Ceti stars observed. Another measure of how normal these variables appear is the equivalent width of Balmer lines, which are normal for that T, and are at the line-strength maximum (estimated for log g = 8.2). Possibly the mean Hα is slightly strong; since the Balmer jump is also at maximum strength, a slightly anomalous low boundary temperature might be present. This is also suggested by marginally more positive U-B color for their G-R (or larger log g). I have counts from MCSP data giving the frequency of 162 DA effective temperatures. The ZZ Ceti stars represent 7 of 27 stars in the bin ±0.05 wide in log T centered on 4.05. They are a substantial fraction, but not necessarily all, stars at that temperature. An attempt to observe Ha emission with the Boksenberg IPCS at the Palomar coudé failed for lack of photons.
PG1159-035: A New, Hot, Non-DA Pulsating Degenerate
Authors: McGraw J. T. , Starrfield S. G. , Liebert J. , Green R.
Published: July 2016

PG1159-035 was originally detected as a 14.5 mag. blue object in a survey for QSO candidates (Green 1977), An SIT spectrogram obtained at the Hale 5m telescope at 6Å resolution showed this star to have a very blue continuum with absorption features near λ4686 and λ4650 which were tentatively attributed to Hell and the CIII/CIV complex, respectively. Possible narrow emission components to these lines appear in Figure 1 which shows confirming spectra obtained with the IIDS (at 2.5Å resolution) on the Kitt Peak 2.1m telescope. The blue continuum and possible presence of Hell in emission suggested that this star was perhaps similar to the helium mass-transfer binary AM CVn (HZ 29). For this reason, we put PG1159-035 on our program of high-speed photometry, expecting the star to show “flickering” associated with mass transfer into an accretion disk and possible orbital modulation or eclipses in the period range 10-20 minutes—photometric characteristics similar to those observed in AM CVn.
Instability of g-Mode Oscillations in White Dwarf Stars
Authors: Keeley Douglas A.
Published: July 2016

A white dwarf model with M=.6 M⊙, Te=12000K, and L=1.2×1031 erg sec-1 provided by A.N. Cox has been tested for linear stability of radial oscillations. The radial mode instability first reported for this model by Cox, et. al (1979) has been confirmed. The growth rates obtained are comparable to the rates found by Cox. A sequence of ℓ=2 g-modes has also been found to be unstable. The e-folding times range from around 1011 periods for a 137 second mode (1 radial node) to less than 100 periods for a 629 second mode (17 nodes). It is likely that the latter rate is too high because the eigenfunction has been forced to vanish at the non-zero inner radius of the model, at which the Brunt-Väisäla frequency is barely less than the mode frequency.
The Accretion Disk in DQ Her
Authors: Petterson J. A.
Published: July 2016

DQ Her is one of the best studied Cataclysmic Variables. It is a classical nova which erupted in 1934 (Nova Herculis). Its optical lightcurve does not repeat accurately from one binary cycle to the next, but usually looks roughly like it does in Fig. 1. The small hump and small eclipse-asymmetry are probably both caused by the hot spot at the outer rim of the disk. The eclipse depth of ~90% argues for an inclination angle near 90°.
CH Cygni – A White Dwarf and M-Giant Binary with Transient Accretion Disk
Authors: Luud L.
Published: July 2016

The unusual variable star CH Cygni was an object of numerous investigations over past ten years. The aim of the present paper is to give a summary of the most important observational data and to discuss briefly a double star model of CH Cygni which is in general accordance with observational facts.
Radiative Transfer in Nova Envelopes
Authors: Harkness R.P.
Published: July 2016

This paper presents some preliminary results of work aimed at producing model atmospheres for the steady-state, constant luminosity continuous ejection model of classical novae. The results are generally, applicable to any object with an outflowing atmosphere driven predominantly by radiation pressure in an optically thick continuum. In particular it is aimed at removing the limitations of assuming blackbody photospheric boundary conditions and strict LTE and the problems associated with their definition.
Radial Velocities of SS Cygni
Authors: Stover R. J.
Published: July 2016

SS Cygni was found by Joy (1956) to be a spectroscopic binary with an orbital period of about 6-1/2 hours. At minimum light it has mv=12 and is the brightest member of the dwarf nova class of variables. The minimum light spectrum reveals faint, narrow absorption lines of a G- or K-type star along with strong, broad emission lines of hydrogen, helium, and calcium which are produced by an accretion disk surrounding a white dwarf star. Joy’s radial velocities were not very accurate. Nevertheless, he was able to estimate the orbital elements, finding 115 km/s for the absorption line K-velocity and 122 km/s for the emission line K-velocity. In addition, he derived an orbital period of 0276244. Later minimum light observations by Walker and Chincarini (1968) were too few to be able to improve the orbital elements. Kiplinger (1979) refined the emission line radial velocities but was not able to remeasure the faint absorption line spectrum. This paper presents new radial velocity measurements of both the emission and absorption line spectra of SS Cygni at minimum light, and is the first thorough investigation of this star’s radial velocity variations in more than 20 years. The accuracy of the radial velocity curves has been greatly improved. We also find that Joy’s orbital period is in error by nearly two minutes.
Polarization of Dwarf Novae and Novalike Variables
Authors: Szkody P. , Michalsky J. , Stokes G.
Published: July 2016

Linear polarization observations have been made over the past several years on several bright dwarf novae (DN) and related objects (NL). The purpose was to investigate any possible variation that could be related to outburst state (changes in the asymmetry of the disk from max to min), short time scale variability (related to flickering) and variability over the orbital cycle (related to the view of the hot spot or to cyclotron emission as in the AM Her variables). The measurements were made at Kitt Peak (KP), Lowell (L), or Battelle Obs. (B) with either the Dyck (D), Hall/Bowell (HB) or Battelle (B) polarimeters and the system was calibrated in each case by taking 30-40 measurements of the nonpolarized and known polarized standards of Serkowski. The data is summarized in the following table. AE Aqr shows the only variation in mean p between runs while the largest variations on flickering timescales are evident in V Sge, RX And and V426 Oph. VSge and RX And show orbital phase dependent variability. SS Cyg does not show any changes in mean polarization over the outburst cycle although the wavelength dependence of the polarization (U-+R) reverses from max to min.
Minimum Orbital Period of Cataclysmic Variables
Authors: Paczynski B. , Krzeminski W.
Published: July 2016

The shortest known orbital period of a cataclysmic binary with a hydrogen dwarf secondary filling its Roche lobe is about 80 minutes. Theoretically the shortest possible orbital period for such a system is less than 60 minutes. We tried to explain why the periods shorter than 80 minutes are not observed. We estimated the time scale of angular momentum loss of a cataclysmic binary and the resulting mass transfer rate. The minimum orbital period for a given Ṁ is obtained during the transition of the secondary from the Main Sequence onto the Degenerate Dwarf Sequence. Pmin ∝ Ṁ½ Therefore, only those systems can reach low P for which Ṁ is small. This explains why among the shortest period cataclysmic variables there are no novae: presumably their mass transfer rates are too large. It also indicates that “polars” (AM Her-type stars) and SU UMa-type stars should have low Ṁ.
X-Ray Emission from Cataclysmic Variables
Authors: Lamb D. Q.
Published: July 2016

Many cataclysmic variables have been found to be hard, as well as soft, X-ray sources. Emission from the boundary layer of an optically thick accretion disk extending down to the stellar surface can, at outburst, produce soft X-rays, but the production of hard X-rays from such a disk is difficult to understand. We therefore conjecture that the sources which emit hard X-rays have magnetic fields and are, in general, rotating. We then propose a classification scheme for cataclysmic variables based on the size of the Alfven radius rA relative to the stellar radius R of the degenerate dwarf and the separation α of the binary system. We show that many of the varied characteristics displayed by the cataclysmic variable X-ray sources can be understood in terms of this ordering. We suggest that the AM Her Class (AM Her, AN UMa, W Pup, and 2A0311-23) have R ≪ α ≪ rA , the DQ Her Class (DQ Her, V533 Her, and AE Aqr) have R ≪ rA ≪ α, while the SS Cyg Class (SS Cyg, U Gem, EX Hya, and GK Per) have rA ≲ R ≪ α. Although rA depends on both the magnetic field strength of the degenerate dwarf ana the accretion rate, for comparable rates of accretion the ordering that we propose is essentially one of decreasing magnetic field strength.
A Possible Identification of the Quasi-Periodic Oscillations in Dwarf Novae
Authors: Winget D.E. , Wesemael F. , Van Horn H.M.
Published: July 2016

Quasi-periodic oscillations on timescales from ~30 sec to 150s have been observed in several dwarf novae during outburst. These oscillations have been qualitatively interpreted as pulsations of the accretion disks in these systems. We explore this suggestion quantitatively by examining the non-radial pulsation properties of viscous accretion disks in the linear, quasi-adiabatic approximation. The weak coupling of the pulsation modes in the radial direction is consistent with the interpretation of these modes as arising in individual disk annuli with periods and eigenfunctions characteristic of the properties of the annulus. The periods of the oscillations, which are periodic in ϕ, z, and t, are shown to be directly proportional to the Keplerian period of the annulus. The existence of a luminosity maximum at some radial position in the disk suggests that the annuli near this position will be the dominant contributors to the observed oscillations. For parameters typical of dwarf novae, the corresponding oscillation periods are ~ 20s, with a range from ~10s to ~ 150s. We suggest that these modes correspond to the observed quasi-periodic oscillations.
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

The 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

JET-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

ESA’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

The 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

Interstellar 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

The 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

The 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

The 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

Operational 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

Recently, 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

Turbulent 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
Pulsed Acceleration in Solar Flares
Authors: Aschwanden Markus J. , Benz Arnold O. , Dennis Brian R. , Kundu Mukul R.
Published: July 2016

We study the nonlinear dynamics of particle acceleration in solar flares by analyzing the time series of various quasi-periodic radio signatures during flares. In particular we present the radio and hard X-ray data of three flares which support the following tentative conclusions:

1.

Particle acceleration and injection into magnetic structures occurs intrinsically in a pulsed mode (with a typical period of 1-2 s), produced by a single, spatially coherent, nonlinear system, rather than by a stochastic system with many spatially independent components (“statistical flare” produced by a fragmented primary energy release).

2.

The nonlinear (quasi-periodic) mode of pulsed particle acceleration and injection into a coronal loop can be stabilized by phase locking with an MHD wave (oscillation) mode, if both periods are close to each other.

3.

Pulsed injection of electron beams into a coronal loop may trigger nonlinear relaxational oscillations of wave-particle interactions. This is particularly likely when the limit cycles of both systems are similar.

Subject headings: acceleration of particles— Sun: corona — Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays