bluuebunny/crossref_metadata_2025 huggingface dataset:
Brief summary of Kleť photographic search programme for minor planets
Authors: Tichá J. , Tichý M. , Moravec Z.
Published: July 2016

A long-term photographic search programme for minor planets was begun at the Kleť Observatory at the end of seventies using a 0.63-m Maksutov telescope, but with insufficient respect for long-arc follow-up astrometry. More than two thousand provisional designations were given to new Kleť discoveries. Since 1993 targeted follow-up astrometry of Kleť candidates has been performed with a 0.57-m reflector equipped with a CCD camera, and reliable orbits for many previous Kleť discoveries have been determined. The photographic programme results in more than 350 numbered minor planets credited to Kleť, one of the world's most prolific discovery sites. Nearly 50 per cent of them were numbered as a consequence of CCD follow-up observations since 1994.

This brief summary describes the results of this Kleť photographic minor planet survey between 1977 and 1996. The majority of the Kleť photographic discoveries are main belt asteroids, but two Amor type asteroids and one Trojan have been found.
On gas productivity of elongated cometary nucleus in rotation
Authors: Medvedev Yu.D.
Published: July 2016

Dynamics and distribution of dust and ice particles in the cometary head is investigated for the elongated nucleus in rotation. Three kinds of particles are considered: the dust particles, the ones with volatile fraction and the ice ones. The particles with volatile fraction and sublimated from larger particles are in the cometary head for rather a long time and some abundance of particles and gas can be observed in the region of the head facing the Sun.

To estimate the influence of dust density on the gas productivity a numerical simulation was done. The results show that the presence of grains in the coma causes the effects of damping and time delay for gas productivity of an elongated nucleus.
The structure of thermal infrared radiation of the inner coma of comet Hale-Bopp
Authors: Pittichová J. , Käufl H.U.
Published: July 2016

The distribution of the thermal infrared radiation from dust in the inner coma of comet Hale-Bopp (1995 O1), based on observations obtained at ESO, LaSilla, Chile, has been mapped in the 10-/μm atmospheric window on July 16, 1997. A preliminary analysis of the infrared data taken with a resolution of 0.498 arcsec per pixel shows a heterogeneous distribution of the infrared radiation in the inner coma. Three asymmetric brightness peaks (in addition to the nucleus) are apparent. Similar behaviour of the distribution of the infrared brightness was found on all observed spectral bands centered around 8.39 μm, 9.78 μm, 11.65 μm, and 12.56 μm. The spectral energy distribution is compared to black-body curves. The observed distribution of the infrared brightness close to the nucleus could be interpreted by multiple sources of ejected dust particles. Simulated aperture photometry shows only minor deviation from a simple spherically symmetric outflow model.
Numerical modelling of Kuiper belt objects’ dynamics – limitations
Authors: Gabryszewski R.
Published: July 2016

The investigation of KBOs’ dynamics is based on numerical orbital integrations on extremly long time scales due to orbital evolution of particles. The evolution of KBOs to JFCs needs a time-span of order of 109years. Such a long time of integration affects errors. So the question arises what is the boundary of an integration time to distinguish the physical solution from numerical noise and what it depends on. This paper presents numerical integrations of less than 150 massless test particles in the model of the Solar System which consists of 4 giant planets and the central mass. For each test particle computations were repeated at least twice on different computers and using two different methods of integration. The results show that an increase of errors in a solution depends on the eccentricity and the inclination of an orbit. The estimated maximum time-span of integration is of the order of 10 million years for highly elliptic orbits (e 0.6) and up to 125 million years for quasi-circular orbits (for particular model of the Solar System with orbits of massless objects outside Neptune's orbit). After long time-span of integration (120-130 Myrs) the solution can be completely chaotic. It cannot be stated unequivocally that this is one of the possible particle's paths or that this is just a numerical noise. So a different way of studying KBOs’ and SP comets’ dynamical evolution is needed. The integration of equations of motion between particular phases of objects which are considered as comets in different phases of their lives (KBOs − Centaurs − Comets − possibly extinct Comets) could be the new way of studying the dynamical evolution of SP comets.
A Solar Flare Observed with the Smm and Einstein Satellites
Authors: Schmitt J. H. M. M. , Lemen J. R. , Zarro D.
Published: July 2016

We present X-ray observations of the 21 July, 1980 flare which was observed both with the Einstein Observatory Imaging Proportional Counter (IPC) and the X-Ray Polychromator (XRP) and Gamma-Ray Spectrometer onboard the SMM satellite. The Einstein observations were obtained in scattered X-ray light, i.e., in X-rays scattered off the Earth's atmosphere. In this way it is possible to obtain spatially unresolved X-ray data of a solar flare with the same instrument that observed many X-ray flares on other stars. This paper juxtaposes the results and implications of the ‘stellar interpretation’ to those obtained from the far more detailed SMM observations. The result of this ‘calibration’ observation is that the basic properties of the flaring plasma can be reliably determined from the ‘stellar’ data, however, the basic physics issues can only be studied through models.
Stellar Flare Statistics - Physical Consequences
Authors: Shakhovskaya N. I.
Published: July 2016

The observational data permit us to establish clear statistical correlations between different parameters of stellar flare activity and the characteristics of quiet stars. These relations are:

(i)

between energies and frequencies of flares on stars of different luminosities;

(ii)

between total radiation energies of flares and quiet stars both in X-ray and Balmer emission lines;

(iii)

between flare decay rates just after the maxima and flare luminosities at maxima.
Rapid Photoelectric Spectrum Scanning Techniques
Authors: Hutchings J. B.
Published: July 2016

Photoelectric spectrophotometry has been pursued with increasing success in recent years. In studies of single line profiles, restricted spectral regions, or stellar continua at low resolution, the photomultiplier offers an increase in speed of up to 20 times over the photographic emulsion and an output directly proportional to light intensity over a wide range of intensity. Difficulties in slow scanners have been caused chiefly by fluctuations in light due to seeing, guiding and extinction changes, necessitating either wide slits and photometric weather or ratio circuits. The technique of rapid scanning and exact superposition of digital data from rapid scans offers a solution to these problems. The basic requirement for rapid scanning is therefore a multichannel analyser and a suitable triggering mechanism. I shall describe briefly the way this is being developed at the 48-inch telescope coudé of the Dominion Astrophysical Observatory, and other uses this instrument is being put to.
Design of an Automatized Iris Photometer
Authors: Behr A.
Published: July 2016

In cooperation between the European Southern Observatory and the Göttingen Observatory the design of an automatized iris photometer has been developed. The principal idea, based on the classical iris photometer as described by Haffner (Veröff. Göttingen, Nr. 106, 1953), may be described here. (Fig. 1).
An X-Y Programmed Microdensitometer for Star Spectra Analysis
Authors: Parks R. , Porteous R. L. , Brandie W.
Published: July 2016

The instrument described in this paper has been developed as the result of close collaboration over a number of years with the University of Utrecht.

It features a combination of advanced facilities which have not previously been available for such work.
Polarization of Variable Stars
Authors: Serkowski K.
Published: July 2016

The changes in stellar polarization with time were first discovered in 1958 by GRIGORYAN (1958) for the red supergiant µ Cephei. In subsequent year BEHR (1959) gave a hint in a footnote to his catalogue that the emission-line B-type star α Cas seems to have variable polarization. However, several years had to pass before these discoveries were confirmed and the changes in polarization with time for the red giants and supergiants and for the emission-line B-type stars were firmly established, first by the observations made by SHAKHOVSKOJ (1963, 1964) and then by COYNE, GEHRELS (1967) and the writer (SERKOWSKI 1966, 1968). The changes in polarization with time were also found for the RV Tauri and T Tauri stars, R Coronae Borealis stars, novae, Wolf-Rayet stars, and white dwarfs. The rapid changes in polarization with time indicate that the polarization is not produced in the interstellar medium but in the vicinity of a star; such polarization is called intrinsic.
A Report on Flare Stars on the Sproul Astrometric Program
Authors: Lippincott Sarah Lee
Published: July 2016

The long range program of the Sproul Observatory initiated in 1937 by P. VAN DE KAMP has been primarily devoted to a detailed astrometric study of the positions of nearby stars from photographs taken with the 24-inch refractor. By now there are 30 years of observations on most stars with parallaxes greater than + O″10 and brighter than the 12th magnitude which are observable at latitude +40°. It follows therefore that there are long series of photographic records of many red dwarf stars.
The Spectrum Variable a Centauri (HD 125 823)
Authors: Klinglesmith D. A. , Bernacca P. L. , Frey H.
Published: July 2016

High dispersion spectra in the blue violet region and OAO II spectral scans in the UV of the star a Centauri are presented. The variation of equivalent widths and radial velocity are presented. The appearance and disappearance of the forbidden lines of helium, the change in the wing structure of λ 4471 of He I, the strengthening of the UV resonance lines at phase 0.5 and the presence of the UV feature of λ 1720 indicate that the star’s atmosphere is experiencing drastic density changes.
A highly flattened Secondary Star in the Young Eclipsing Binary BM Orionis
Authors: Hall Douglas S.
Published: July 2016

A model is proposed for BM Ori to explain why DOREMUS saw only the early B star in the spectrum, whereas the light curve seemed to predict an equally bright cooler star which should have been seen alone at supposed totality. The cool star is assumed to be a disk-shaped object, similar in shape to that proposed by HUANG for ε Aur, seen nearly edge-on. By means of various restraints, it is estimated that the disk covers about 55% of the B star at primary eclipse. This leads to the relative luminosities (Lh = 0.74, 0.87 and 0.92 in V, B, and U), the color of the disk (the opposite side of the disk has the color of a G or F giant), the relative geometrical dimensions (rB = 0.09, rD = 0.25, and the height of the disk h≈0.1), and the orbital inclination (i ≈ 90°). The model with these parameters predicts a theoretical light curve which represents the observations as well as did the solution of HALL and GARRISON, which was based on spherical stars.
A Photoelectric Investigation of the Eclipsing Binary V 78 in Omega Centauri (NGC 5139)
Authors: Geyer Edward H.
Published: July 2016

The existence of eclipsing binaries, though extremely rare, in stellar systems like globular clusters, should attract the observers, because one could obtain fundamental data on highly evolved stars. The variable star V 78 in the globular cluster NGC 5139, which was found by BAILEY (1901), is one of these rare cases. MARTIN (1938) derived the period P = 1ḍ168118, and showed by means of an extensive photographic photometry that it is an Algol type eclipsing binary. Recently SISTERO et al. (1968, 1969) rediscussed the observations of MARTIN, and with additional measurements derived the following light elements:
A Model of Nova Delphini 1967 from its Nebular Spectrum
Authors: Seitter Waltraut Carola
Published: July 2016

Nova Delphini 1967 is outstanding among other recent novae since it belongs to the rare class of extremely slow objects. Another unusual characteristic is the pronounced pattern of the emission lines during the nebular stage.
Minimum-Light Phenomena in Nova-like Variables
Authors: Mumford George S.
Published: July 2016

Some characteristics of the small-amplitude, quasi-periodic light fluctuations common to novalike variables are described. There appears to be a weak correlation for the majority of the objects between the dispersion about the mean magnitude and the interval between outbursts such that systems with infrequent outbursts exhibit the largest dispersions.
Metal Line-Blanketing and Opacity in the UV of α2 CVn
Authors: Molnar Michael R.
Published: July 2016

Ultraviolet photometric observations by OAO-A2 were made of α2 CVn covering the entire 5ḍ5 period of this magnetic Ap variable. The light curves ranging from 1250A to 3330 A indicate the dominant role of rare-earth line-blanketing in redistributing flux. In a broad depression of the continuum covering 2300 A to 2600 A scanner observations identify strong lines of Eu III as major contributors to this feature. At maximum intensity of the rare-earth lines the ultraviolet continuum shortward of 2900 A is greatly diminished while the longer wavelength regions into the visual become brighter. Thus, the light variations in α2 CVn are: due to the variable strong line-blanketing by the abundant rare-earth elements.
Some Problems in the Study of Variable Stars in Globular Clusters
Authors: Kukarkin B. V.
Published: July 2016

Three quarters of a century separates us from the beginning of systematic observations of variable stars in globular clusters. During the last 45 yr the name of Mrs Prof. Dr H. B. Sawyer Hogg has always been in the astronomical literature. Her activity is closely connected with investigations of variable stars in globular clusters.

The complex dependences between the presence of variable stars of different types and the properties of the globular clusters were discovered long ago. For instance, the RR Lyr variables do not occur in clusters of high metallicity. Red variables on the contrary do not occur in clusters of very low metallicity. The presence and peculiarities of variable stars have been used for the classification of globular clusters (van Agt and Oosterhoff, 1959; Castellani et al., 1970).
An Abundance Analysis of Fehrenbach’s Star (HD 116745) in Omega Centauri
Authors: Dickens R.J. , Powell A. L. T.
Published: July 2016

HD 116745 is an eleventh magnitude early F-type giant occurring in the field of the globular cluster ω Cen. Membership in the cluster appears virtually certain since the star’s radial velocity differs insignificantly from the mean cluster velocity of +238 km s-1. HD 116745 lies nearly 4 mag. above the horizontal branch in the HR diagram and is presumably in a rapid, advanced stage of evolution. Spectrograms at 22.5 Å mm-1 and 155 Å mm-1 have been obtained by one of us (R.J.D.) at the Radcliffe Observatory in South Africa using a McGee spectracon image tube. The lower dispersion spectra have been used to measure Hy profiles and the Balmer discontinuity, and one high dispersion film has provided the basis for a differential curve-of-growth analysis with respect to the Sun in order to determine some heavy element abundances. Physical data derived for the star are Mv= –3.32, θe=0.77±0.02, logg = 1.0±0.3 and Results of the curve-of-growth analysis, in which a model atmosphere was used to determine the curve appropriate to the star, yield a logarithmic iron-to-hydrogen abundance ratio with respect to the Sun of [Fe/H]= —1.2 with a provisional estimated uncertainty of about +0.2. This result is based on 28 lines of Fe i. Ti may be marginally overabundant, with a value of [Ti/Fe] = + 0.4, based on 7 lines of Ti II. Other elements and ionization states identified are Mg I, Al I, Si I, Ca I, Sc II, VI, VII, Mn I, Sr II, Zr II (Eu II).
Determination of the masses of Jupiter and Saturn from the motion of Trojans
Authors: Scholl H.
Published: July 2016

The mass of a planet can be determined by the motion of its satellites or by perturbational effects on nearby bodies, such as comets, planets, minor planets. It is well known, for instance, that a body on a nearby orbit which is in close resonance with a planet is suitable for the determination of the planetary mass. In this case the orbital periods of the two bodies are equal or nearly equal to the ratio of small integers (i.e. 1: 1, 2: 1, 3:2).
On the fragmentation of asteroids
Authors: Levin B. J.
Published: July 2016

Members of each family or stream of asteroids represent fragments of a single collision of two parent asteroids. Therefore the mass distribution for family members is at the same time the distribution for such fragments. For 4 families with large numbers of known members the mass distribution can be approximated by an inverse power low withs≈ 1.7–2.0. The comparison of distributions for big and small members of these 4 families shows that the Palomar-Leiden Survey of faint asteroids contain about 1/60 of their true number which is thus of about 120000. About 1/3 of families contain from 1 to 4 big asteroids more than 10 times more massive than the remaining. Among 49 asteroids revealed to be of variable brightness, 18 are members of asteroid families and 17 of the latter are their biggest members.
Development of the theory of planetary perturbations in non-classical cases
Authors: Petrovskaya M. S. , Ivanova T. V. , Lobkova N. I.
Published: July 2016

Three expansions of the perturbation function R have been suggested which remain valid when planetary orbits have points equidistant from the Sun. In the first two cases the exterior summations are extended over the powers of the eccentricities, whereas the interior series is developed in functions of the ratio of the semi-major axes. At the same time, factors have been found which could be carried out of the sums and represent the poles of R in an asymptotic case (the circular intersecting orbits of the same radius). In this way the convergence of the series is increased considerably for large values of the semi-major axes ratio. The third expansion differs from the previous ones by having the exterior sum with respect to the functions of the ratio of the semimajor axes, the interior expansions being in powers of eccentricities. This development of R may be useful in situations where the eccentricities are rather large and the distance between orbits is not too small.
Perihelion longitudes and Jacobi constants of Jupiter group comets as indicators of their possible origin from the two equilateral Trojan clouds
Authors: Rabe Eugene
Published: July 2016

The perihelion longitudes of the Jupiter comets can be divided into two unequal groups, associated with (π4– 60°) and π4– 60°), respectively. This finding favors the authors earlier suggestion that many of these comets may have originated from the correspondingL5andL4Trojan clouds, which today are known to contain many hundreds of Trojans brighter than magnitude 20.9. The proposed origin of the Jupiter group comets is supported also by the finding that the preceding Lagrangian pointL5is associated not only with distinctly more Trojans but also with more comets thanL4, as well as by the association of the largest Trojans with the larger and denser cloud aroundL5. The larger size of theL5cloud is suggested by the association with it of a significant number of comets with smaller Jacobi constantsCthan those found in theL4cloud. All the observed distribution anomalies, of the Trojans as well as of the Jupiter group comets, would follow automatically from the assumption that both groups of bodies originated from two primordial clouds of matter associated with the equilateral regions. These two clouds would have been of unequal size and density, perhaps due to some initial by-chance irregularities in the uniformity of the relevant parts of the solar nebula. As to the long-range survival of volatile matter embedded in solids, certain observations encourage the assumption of such a possibility, while simplified theoretical considerations apparently do not suffice to produce any meaningful constraints.
Nongravitational effects on comets: a progress report
Authors: Marsden B. G.
Published: July 2016

New developments since 1970 are discussed, notably the identification of the comets exhibiting sudden anomalies in their motions with those comets whose nongravitational effects normally increase with time (resulting in the eventual complete dissolution of these comets, rather than conversion into asteroidal objects) and the introduction of a law for the variation of the nongravitational forces with heliocentric distance that is based on the theory of vaporization of ice.
The capture of comets
Authors: Rickman Hans
Published: July 2016

The expression: “Capture of a comet” may lead thoughts primarily to the single encounter mechanism, when a comet happens to pass very close to Jupiter and is at once “captured” into Jupiter’s family of comets, getting an aphelion just outside Jupiter’s orbit, but I would rather suggest that any evolution from a long-period orbit far from the Sun to a short-period orbit, making use of different kinds of perturbations, may be termed a “capture process”, and it is evident that single encounters must play a rather limited role in such evolutions.
The vaporization of the volatile fraction in comets
Authors: Delsemme Armand H.
Published: July 2016

Very large gas productions have been recently established for comets. They rule out desorption models of the cometary nucleus and strongly support the vaporization of an icy conglomerate. The vaporization theory of the cometary nucleus can also be used to predict, for different types of ice, the law of dependence of the non-gravitational force on heliocentric distance. The results are compared here with the empirical dependence that can be derived from Marsden’s recent work on comet Schwassmann-Wachmann II. The law, as deduced from this comet’s observations, rules out the vaporization of all gases with high vapor pressure, like CO, CH4, NH3etc., and even CO2, but coincides surprisingly well with a vaporization controlled by the latent heat and vaporization rate of water, as would be the case for pure water ice or for solid hydrates of gases. The fact that the gas molecules encaged in the cavities of the solid hydrates would simply be liberated in proportion by the vaporization of their water, seems therefore o be confirmed by the present results.
Flare Stars in a Field Near the North Galactic Pole: ROSAT and Optical Observations
Authors: Richter G.A. , Bräuer H.-J. , Greiner J.
Published: July 2016

In a field of 100 square degrees around 26 Com, 238 X-ray sources have been discovered by ROSAT during the All-Sky-Survey observations. These sources were identified using objective prism spectrograms taken with the Hamburg Schmidt telescope on Calar Alto (courtesy N. Bade) and including the positional accuracy of typically 30" and the X-ray to optical luminosity ratio. In an ongoing investigation of these X-ray sources on more than 400 plates of the Sonneberg astrographs 400/1600 mm and 400/2000 mm, a total of 5 of the M type counterparts were found to be flare stars. In Table 1 we give the ROSAT name (column 1), the new designation as a Sonneberg variable (2), the position of the optical counterpart (3), the magnitude range of the newly discovered flare stars (4), the ROSAT PSPC countrate during the All-Sky-Survey (5), the distance D between X-ray and optical position (6). All 5 objects had not been known to be flaring. The real amplitudes must be larger than those given in column 3 because the (unknown) duration of the flares is usually much shorter than the exposure time of the plates. The figures give APM finding charts of these new flare stars.
Photometric Research of Pre-flare and Extra-flare Activity of Flare Stars
Authors: Roizman G. , Pustil’nik L. , Pundak D.
Published: July 2016

Preliminary results of a photometric search for non-flare activity of the flare star EV Lac during June-August 1994 are presented. These observations are part of the long-term project entitled “Investigation of pre-flare processes on flare stars” being carried out at the Observatory of the Jordan Valley Regional College since July 1994. The project was motivated by reports of the existence of slow, low-amplitude non-periodic variability of both spectral lines and continuum outside/between flares (Rodono et al. 1979, Roizman et al. 1984).
Automated Search for Flare Stars Continued
Authors: Winterberg J. , Nolte M. , Seitter W.C. , Duerbeck H.W. , Tsvetkov M.K. , Tsvetkova K.P.
Published: July 2016

To date we obtained 511 blue plates with multiple exposures of nine young clusters and associations to be used for studying the flare activity-age relation. First attempts showed already that automatic search increases the number of discovered flares by 50% compared to visual inspection (Aniol et al. 1989). Improved algorithms have now been implemented and applied. Automated object identification in existing catalogues (FSDB, GCVS, SIMBAD) is also available.

All plates are digitized with the PDS 2020 GMplus microdensitometers at AIM and reduced with the AIM software. Steps following the reconstruction of images include the transformation of plate to sky coordinates and matching of the multiple exposure chains with the stars on the deep reference plate. All complete chains (generally six exposures) are used to derive average light curves for all objects. For each magnitude interval 10-11, 11-12, … 15-16 the mean deviation and standard error of an image from the overall mean value of the respective chains is determined. If any image in a chain differs by more than a preset multiple of the mean error it is considered a potential flare event and registered for visual inspection, together with the chains immediately preceding and following the suspected flare event, to obtain information on the total duration of the outburst. The candidates are filed and the data of all stars are stored for checks of long-term variability.
The Role of Flare Stars in Cosmic-ray Origin
Authors: Shapiro Maurice M.
Published: July 2016

Supernovae and their expanding shock fronts are evidently the main agents of cosmic-ray acceleration. The thermal gas in the interstellar medium has been regarded as the reservoir of seed particles destined to become cosmic-ray nuclei. This assumption is, however, at variance with the source composition of galactic cosmic iays. In an alternative hypothesis, the seed particles are injected into the interstellar material as suprathermal seed ions, and it has been surmised that flare stars provide the initial boost. We find that the dMe and dKe stars are probably the principal sources of cosmic-ray seed particles. Most stars in the Galaxy are red dwarfs and many of these flares much more powerfully and frequently than solar flares. Augmenting the optical data, recent X-ray and far-ultraviolet observations now permit a better estimate of the energy budget. Altogether, dMe and dKe stars seem to be the most promising class of cosmic-ray injectors.
Long-term Photometry of the Symbiotic Star AG Draconis
Authors: Luthardt R.
Published: July 2016

Photoelectric UBV-observations of the well known symbiotic star AG Draconis were obtained between 1982 and 1984 with the 60cm photoelectric reflector II of Sonneberg Observatory. The light curve shows two large optical outbursts: (at JD = 244 5000…5500 and JD = 9000…9500) and two smaller eruptions (at JD = 6200, 6600). The recent outburst is the largest one since 1952.

During the quiet stage a significant variability with an amplitude of about one magnitude is only visible in the U-band. L. Meinunger (1979) detected a period of 554 days and calculated the following ephemeris:

Umax = 243 8900 + 554 · E

All outbursts and smaller eruptions are correlated with the period of the U-maxima, the outburst maxima always coincide with U-maxima of the quiet stage, calculated by the above formula.
TTM Observations of X1755-338
Authors: Pan H.C. , Skinner G.K. , Sunyaev R.A. , Borozdin K.N.
Published: July 2016

X1755-338 is an X-ray binary source which displays X-ray dips with a 4.4 hour period (White et al. 1984). It was previously noted as an unusually soft X-ray source by Jones (1977) and was suggested later as a black-hole candidate (BHC) by White & Marshall (1984), and White et al. (1984), based on the similarity of its location in an X-ray colour-colour diagram to that of a group of BHCs.

The TTM is a coded-mask imaging spectrometer on board the KVANT module of the MIR space station. It is capable of producing images in the 2 – 30 keV band with an energy resolution of about 18% at 6 keV. The instrumental details are given in Brinkman et al. (1985).

We observed X1755-338 in 1989 March-September during the period of the TTM Galactic Centre Survey.
Temporal Behaviour of Sources in the ROSAT Extreme-Ultraviolet All-Sky Survey
Authors: McGale Paul , Pye J.P. , Barber C.R. , Page C.G.
Published: July 2016

From a total catalogue of 479 2RE sources, 31 have been found to be variable. All the variable sources are optically identified, with a breakdown by source type as follows: cataclysmic variables 9, late-type (F-M) stars 18, the high-mass X-ray binary Her X-1, the eclipsing binaries Algol and V471 Tau, and the active galaxy Mkn 478. The most highly variable objects in the EUV band are cataclysmic variables. The survey was sensitive to timescales from ~ 1.5 h to ~ 5 d, and observed variability ranges from flare-like events lasting < 1.5 h to irregular and periodic flux changes over ~ 0.5–2 d. With the exception of the cataclysmic variables, and possibly a few late-type dK-dMe stars with large flares, the observed variability levels should not substantially affect EUV luminosity functions
EUVE Observations of AR Lacertae: The Differential Emission Measure and Evidence for Extended Prominences
Authors: Walter Frederick M.
Published: July 2016

EUVE observed the eclipsing RS CVn system AR Lac in October 1993. The differential emission measure shows a double-peaked structure similar to the two-temperature distribution seen in X-rays. The best-fit Fe abundance is 0.4 solar. The DS light curve shows a deep primary eclipse. The slow egress from eclipse may be due the presence of spatially extended, optically-thick “prominences” in the equatorial plane of the K star.
EUVE Observations of BY Dra Systems
Authors: Stern R.A. , Drake J.J.
Published: July 2016

We have observed 3 nearby BY Dra systems, FK Aqr, BF Lyn, and DH Leo, with the EUVE spectrometers. All 3 show evidence of high-temperature (~ 107 K) plasma; FK Aqr and DH Leo show significant variability in their Deep Survey lightcurves. In FK Aqr, spectral differences between its “quiescent” and “active” states suggest possible differences in the plasma density. In DH Leo, the Deep Survey lightcurve, taken over nearly 8 days, shows a distinct period of ~ 1.05 days, consistent with the photometric period. The emission measure distributions of all three systems are rather similar in shape, and can be well-represented by a power law with slope ~ 1.5 from 6.2–7.0 in log T.
The Hot White Dwarf Population in the EUVE Survey
Authors: Vennes Stéphane
Published: July 2016

The processes leading to the formation of white dwarf stars are known only in their most general principles; post-asymptotic giant branch evolution, leading to the formation of C-O degenerate cores, is possibly the main formation channel of white dwarf stars. In contrast, observations of hot white dwarf stars and studies of their main population characteristics offer detailed insights into the origin and evolution of these objects. We examine some new facts uncovered in the study of the survey of hot white dwarf stars at extreme ultraviolet (EUV) wavelengths. We describe model atmosphere techniques required to interpret these observations and discuss some implications of our findings for stellar evolution theory.
The Unusual UV Spectra of EUV-Discovered AM Herculis Stars
Authors: Herzog Adrienne E. , Howell Steve B. , Mason Keith O.
Published: July 2016

International Ultraviolet Explorer observations of the ROSATWFC-discovered AM Hers RE2107–05, RE1938–46, RE1833–74, RE1149+28, and RE0751+14 reveal UV spectra (1200 – 2000 Å) which are unique when compared with previously studied systems. Specifically, the intensities of individual emission lines due to CIV, CII, N V, HeII, and Si IV, are 2 – 4 times stronger then typically seen. However, the equivalent width ratios of these same emission lines, (CII/CIV, N V/CIV, HeII/CIV, and Si IV/CIV), are similar to those in typical AM Hers. These results indicate that the EUV-discovered AM Hers must have larger UV emitting volumes. Using additional observations of these stars made by EUVE, we speculate on the cause of their larger UV line fluxes.
EUV Radiation from Hot Star Photospheres: Theory Versus Observations
Authors: Hubeny Ivan , Lanz Thierry
Published: July 2016

The only stars other than white dwarfs whose photospheric extreme ultraviolet radiation has been detected are ϵ and β CMa. It is therefore of considerable theoretical interest to compare the EUVE observations of these two giant B stars to predicted spectra. However, both LTE and non-LTE very sophisticated line blanketed model atmospheres fail to match the observed flux. This failure leaves the stellar photosphere theory, even for seemingly “simple” objects as normal B giants were believed to be, in a rather dubious position. This paper briefly summarizes possible reasons for the failure of existing models to describe the EUVE observations of hot stars. In particular, we discuss the effects of uncertainties in the line blanketing, and the effects of the photosphere-wind interaction.
Fe XIII Emission Lines Observed by EUVE and the S082A Instrument On-Board Skylab
Authors: Keenan F.P. , Drake J.J. , Foster V.J. , Greer C.J. , Tayal S.S. , Widing K.G.
Published: July 2016

Recent R-matrix calculations of electron impact excitation rates for Fe XIII are used to derive the theoretical electron density sensitive emission line ratios R1 = I(318.12 Å)/I(320.80 Å) and R2 = I(256.42 Å)/I(251.95 Å), which are found to be up to 50% different from earlier diagnostics. A comparison of the current line ratios with both solar flare and active region observations, obtained by the Naval Research Laboratory’s S082A spectrograph on board Skylab, reveals generally good agreement between densities deduced from Fe XIII and those estimated from diagnostic line ratios in species formed at similar temperatures. This provides experimental support for the accuracy of the line ratio calculations, and hence the atomic data adopted in their derivation. In Extreme Ultraviolet Explorer satellite (EUVE) spectra the Fe XIII emission lines are found to be severely blended. However, an analysis of these lines measured in the spectra of Procyon and α Cen demonstrates that they still allow very approximate values of the electron density to be inferred. Moreover, it should be possible to increase the accuracy of the measured line fluxes, and hence of the inferred densities, if longer exposures of the stars concerned can be obtained.
Skylab Observations of Temperature and Density Sensitive Emission Line Ratios in Ne VI
Authors: Greer C.J. , Foster V.J. , Keenan F.P. , Reid R.H.G. , Doyle J.G. , Zhang H.L. , Pradhan A.K.
Published: July 2016

Recent calculations of electron and proton impact excitation rates in Ne VI are used to derive the intensity ratios of lines in the ~402–1006 Å wavelength range as a function of electron temperature (Te) and density (Ne). These results are presented in the form of ratio-ratio diagrams, which should in principle allow both Ne and Te to be deduced for the Ne VI line emitting region of a plasma. Electron temperatures and densities derived from ratio-ratio diagrams involving the 562.7, 997.4, 999.6 and 1006.1 Å lines, in conjunction with observational data for a sunspot obtained with the Harvard S-0555 spectrometer on board Skylab, are found to be compatible, and in good agreement with plasma parameters determined using other methods. This provides some support for the diagnostic calculations presented in this paper, and hence the atomic data used in their derivation. However agreement between theory and observation is very poor for other Ne VI lines in the sunspot spectrum, and for most transitions observed in S-0555 active region and flare data, which is probably due to blending with lines from N III, Mg VI and Mg VII. The application of the calculations to non-solar EUV sources is discussed.
Plasma Emission Codes: Comparisons and Critiques
Authors: Mason Helen E.
Published: July 2016

A great deal of effort in recent years has gone into the development of spectroscopic techniques to probe the physical parameters of solar, stellar and other astrophysical plasmas. One aspect of this work is the calculation of plasma emission codes which are used to study EUV spectral lines. These codes require the input of a large amount of atomic data. In this paper, we present an overview of the atomic processes involved and an assessment of the accuracy of the parameters which are incorporated into different emission codes.
The Opacity Project and the Iron Project
Authors: Pradhan Anil K.
Published: July 2016

Systematic and large-scale calculation of accurate plasma opacities and atomic data by the Opacity Project and the Iron Project has applications in many areas of astrophysics. Analysis of EUVE observations using monochromatic opacities of elements calculated by the Opacity Project is described. Theoretical methods and atomic calculations are discussed briefly. Recent work related to ionization balance, photoionization and recombination, and the modeling of plasmas in local thermodynamic equilibrium (LTE) and non-LTE are discussed. New calculations for the important iron ions, under the Iron Project, are also described and their relevance to the more extensive non-LTE calculations is pointed out. The comprehensive radiative and collisional data sets from the Opacity and the Iron Projects should be applicable to a large number of sources in the EUV and other wavelength regions.
Diagnostics of EUV Spectral Emission from Boron-like Ions
Authors: Peng Jianfang , Pradhan Anil K.
Published: July 2016

Recent developments of EUV diagnostics from transitions in Boron-like ions, C II, N III, O IV, Ne VI, Mg VIII, Al IX, Si X, and S XII, are discussed based on new atomic data (Zhang, Graziani & Pradhan (1994)) and systematic theoretical calculations of line intensity ratios (Peng & Pradhan 1995). The available EUV and UV lines which are good temperature and density diagnostics are summarized. Possible applications of these lines to the investigation of the physical conditions in astrophysical objects are proposed.
Line Ratio Diagnostics Applicable to Astronomical Spectra in the 50–3000 Å Wavelength Region
Authors: Keenan F.P.
Published: July 2016

A bibliography has been produced of the most reliable emission and absorption line ratio diagnostic calculations currently available for application to the spectra of astrophysical sources in the UV and EUV wavelength region (50-3000 Å). References are listed containing diagnostics for species in the Li through P isoelectronic sequences, as well as the iron ions Fe II-Fe XXIII and nickel ions Ni XVII-Ni XXV. Also given is the wavelength range for which diagnostic calculations are presented in each reference, along with the type of diagnostic considered. These include, for example, emission line ratios for determining electron temperatures and densities, and absorption line diagnostics for evaluating hydrogen densities.
The Extreme Ultraviolet Explorer Public Right Angle Program
Authors: McDonald K. , Craig N. , Olson E. , Christian C.A.
Published: July 2016

The new Extreme Ultraviolet Explorer (EUVE) Public Right Angle Program (RAP) offers the opportunity for researchers to obtain observations with the EUVE imaging telescopes, oriented at right angles to the EUVE spectrometer used for the NASA Guest Observer Program. Scientists may submit proposals electronically through the World Wide Web or e-mail using a template form to list specific targets and present the scientific motivation for the work. The RAP electronic proposal process is streamlined from proposal submission through data delivery and is a prototype for a system to be used for all guest observers during the EUVE extended mission starting in February, 1996.
Oblique Pulsator Model for the Blazhko Effect of RR Lyrae Stars
Authors: Shibahashi Hiromoto , Takata Masao
Published: July 2016

By assuming that the RR Lyrae stars have fairly strong dipole magnetic fields with the symmetry axis oblique to the rotation axis of the star, we show that the oscillation mode which would be a pure radial oscillation in absence of the magnetic field has a quadrupole component, which is axisymmetric with respect to the magnetic axis. The aspect angle of the quadrupole component changes due to the stellar rotation, and this apparent variation is interpreted as the Blazhko effect in RR Lyrae stars.
New Results on Pulsating OB Stars
Authors: Moskalik Paweł
Published: July 2016

Until very recently the physical mechanism driving oscillations in β Cep and other early type stars has been a mystery. The breakthrough came with the publication of new OPAL and OP opacity data. Model calculations with the new opacities have demonstrated that the pulsations are driven by the familiar K-mechanism, acting in the metal opacity bump at T ≈ 2 × 105K. The mechanism excites the low order p- and g-modes in the upper part of the instability strip and the high order g-modes in the lower part of the strip. The theoretical instability domains agree well with the observed domains of the β Cep and the SPB stars. In this review I present these recent theoretical results and discuss their consequences for our understanding of B stars pulsations.
Variable Stars in the MACHO Collaboration Database
Authors: Cook Kem H. , Alcock C. , Allsman R.A. , Axelrod T.S. , Freeman K.C. , Peterson B.A. , Quinn P.J. , Rodgers A.W. , Bennett D.P. , Reimann J. , Griest K. , Marshall S.L. , Pratt M.R. , Stubbs C.W. , Sutherland W. , Welch D.
Published: July 2016

The MACHO Collaboration’s search for baryonic dark matter via its gravitational microlensing signature has generated a massive database of time ordered photometry of millions of stars in the LMC and the bulge of the Milky Way. The search’s experimental design and capabilities are reviewed and the dark matter results are briefly noted. Preliminary analysis of the ~ 39,000 variable stars discovered in the LMC database is presented and examples of periodic variables are shown. A class of a periodically variable Be star is described which is the closest background to microlensing which has been found. Plans for future work on variable stars using the MACHO data are described.
HIPPARCOS Data on Pulsating Stars
Authors: Turon Catherine , van Leeuwen Floor
Published: July 2016

The preliminary astrometric and photometric results obtained from the first 30 months of HIPPARCOS data are presented. Examples of the results obtained for the various categories of pulsating variables included in the HIPPARCOS programme are given. The perspectives opened by GAIA (Global Astrometric Interferometer for Astrophysics), the concept for an astrometric interferometer submitted in September 1994 to the ESA Horizon 2000+ survey committee, are briefly exposed.
Search for Pulsational Instability among h Persei Stars
Authors: Krzesinski J.
Published: July 2016

The northern-hemisphere double cluster h and χ Persei is one of the richest young open clusters. At least half of the brightest stars in the cluster appear to be variables and most of them axe Be stars. Till now there was no evidence for the presence of β Cephei stars in the cluster. It is remarkable that the similar age southern cluster NGC 3293 and other clusters belonging to the same age group are documented as clusters in which β Cephei stars have been observed. In this work we report finding one suspected β Cephei-like object, basing on our own observations.
The Evolutionary Status of λ Boo Stars
Authors: Paunzen E. , Gelbmann M. , Heiter U. , Kupka F. , Kuschnig R. , Weiss W. W.
Published: July 2016

We summarise the history of the λ Boo criterion and our strategy to determine the evolutionary status of this group of stars.
Formation Depths of Spectral Lines in Cepheids
Authors: Albrow Michael D. , Cottrell P. L.
Published: July 2016

There has been a number of observational programmes that have endeavoured to investigate the atmospheric velocity fields in Cepheids (e.g., Sanford 1956, Wallerstein et al. 1992, Butler 1993). These studies measured the radial velocities of lines of different strength, excitation and ionisation potential as these provide an indication of line formation at different levels in the atmosphere. From these measurements, the presence of velocity gradients can be inferred, but determination of the magnitude of such gradients requires knowledge of the spectral line depth of formation. Through dynamical modelling we are endeavouring to ascertain what is actually being measured in the above observational programmes.
A Century in Period Changes of the Variables in M15
Authors: Barlai Katalin , Szeidl B.
Published: July 2016

Period behaviour of 62 RR Lyrae stars in the M15 globular cluster has been investigated. About one half of the sample (30 stars) exhibited linear period change. The remaining 32 variables can be characterized by abrupt or erratic changes in their periods.
Pulsation & Long-Periods in Three Nearby M Supergiants
Authors: Smith M. A. , Teays T. J. , Taylor L. L. , Wasatonic R. , Guinan E. F. , Baliunas S.
Published: July 2016

We report on pulsational variability found in our decade-long study of UV and optical RV, light, K-line data sets for α Ori, α Sco A, and α Her A. As summarized by Smith et al. (1990), our radial velocities are derived from McMath observations of five metallic lines near Hα plus Hα itself. Optical light curves were obtained by small photometric telescopes, and K-line emissions from the Mt. Wilson K-line project. UV continua at 3000Å and k/h emission indices were obtained with the IUE LWP camera.
Long-term Photometric Monitoring of Cool Hydrogen-deficient Carbon Stars
Authors: Cottrell P.L. , Gilmore A.C. , Kilmartin P.M. , Lawson W.A.
Published: July 2016

Interest in the hydrogen-deficient carbon (HdC) stars, and the R Coronae Borealis (RCB) stars in particular, has been rekindled by the realisation that these stars provide the potential for testing models in a number of areas. These include: pulsation theory; grain formation; grain evolution; stellar nucleosynthesis and extended stellar atmospheres.

Observational work on these objects has increased dramatically over the last 10 years. This has included both spectroscopic and photometric projects, see Lambert & Rao (1994) and Lawson et al. (1990).

We have continued to observe a number of the cool HdC stars in the Galaxy and the LMC and now have light curves exceeding 2000 days in duration for many of these objects. In particular, we are observing the RCB stars to investigate both the low amplitude, pulsation-related variations present at maximum light and the photometric behaviour during the large amplitude declines.