bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical Fine Structure of Filaments and Prominences
Authors: Mein N. , Mein P. , Wiik J.E.
Published: July 2016

We observed a quiescent prominence on the east limb of the Sun, on June 7, 1988 (Mein P. et al 1990) and a quiescent filament (N 5, W 5) on June 17, 1986 (Schmieder et al 1991). These two observations are made with the Multichannel Subtractive Double Pass spectrograph of the turret dome refractor of the Pic du Midi Observatory, providing simultaneous 2D pictures in 9 channels for Hα.
The Spontaneous Reconnection of Force Free Magnetic Field
Authors: Xing Li , Hu Y.Q.
Published: July 2016

Two dimensional, three components compressible MHD equations are solved with multistep implicit scheme. The spontaneous reconnection of current sheets with force free field background is simulated. In comparison with the case where the background is potential field, a great difference is found. Our conclusion is that the force free magnetic field can accelerate reconnection. It may have important scientific significance to solar physics, for force free field is widely present in solar atmosphere.
Electric Conductivity of Lower Solar Atmosphere
Authors: Wang Jingxiu
Published: July 2016

Electric conductivity tensor of partly-ionized plasma is deduced. Four atmospheric models are used then to estimate the conductivity in the lower atmosphere. The parallel conductivity reaches its minimum value in the temperature minimum zone, which is 1 to 2 orders smaller than the conductivity of fully-ionized plasmas of the same condition; the effective perpendicular conductivity, or Cowling conductivity, becomes 5 to 6 orders smaller than the fully-ionized value in the lower chromosphere.
Flux Emergence and the Evolution of Large-Scale Photospheric Field Patterns
Authors: Wang Y.-M. , Sheeley N. R.
Published: July 2016

Stackplot displays of the photospheric magnetic field show long-lived patterns that often rotate at rates differing from the intrinsic photospheric rate. These complex patterns are produced naturally by the flux-transport model, in which magnetic flux emerging in the form of active regions is dispersed over the solar surface by differential rotation, supergranular diffusion, and a poleward meridional flow. Numerical simulations show that long-lived patterns with slopes similar to the observed ones arise even when the longitudes of the erupting flux are randomized, suggesting that a deep-seated longitudinal organization is not required to explain the qualitative nature of the patterns. Both autocorrelation analysis and visual comparison between the slopes of the observed and simulated patterns indicate that the equatorial rotation period of the Sun is close to 26.75 days, significantly shorter than the traditional 26.9 day value of Snodgrass and Newton & Nunn but in agreement with the recent measurements of Komm, Howard, & Harvey. A complete discussion of these results may be found in Sheeley, Wang, & Nash, ApJ, 401, 378 (1992).
Oscillations of the Magnetic Network
Authors: Lites Bruce W. , Rutten Robert J. , Kalkofen Wolfgang
Published: July 2016

We present high-quality power spectra of oscillations in the quiet solar chromosphere measured from the Ca II H line. They show unambiguously that the network does not participate in chromospheric three-minute oscillations, but that instead it oscillates in slow wave motions which are neither present in the surrounding non-magnetic chromosphere, nor in the underlying photosphere.
Fractal MHD Waves in the Solar Atmosphere
Authors: Nocera Luigi
Published: July 2016

Nonlinear MHD waves forced into a bounded cavity exhibit structural instability of their equilibria and periodic orbits as the forcing varies. For some values of the forcing the computed Poincaré maps, Lyapunov exponents and phase-space correlation reveal that the waves become chaotic; the Haussdorff dimension of the waves’ attracting set lies between its correlation dimension (≈ 2.2) and its information dimension (≈ 2.25).
MHD Simulations of Solar and Interplanetary Phenomena
Authors: Dryer M.
Published: July 2016

Workers in the field of magnetohydrodynamics (MHD) have been interested in the hypothesis that observed solar activities can be utilized in a deterministic way to predict the bulk flow consequences of these activities in the three-dimensional heliosphere. Exploration of this hypothesis, using the conventional/classic initial boundary value approach, will be reviewed against the background of basic, ideal (except for shocks) one-fluid approximations. This work has been divided into two parts: near-Sun simulations in two dimensions of coronal mass ejections (CMEs) as well as interplanetary simulations in 2D and 3D of propagating shocks. In the latter case, the flows behind the shocks should be thought of as interplanetary “ICMEs”, i.e., the interplanetary, evolutionary consequences of the near-Sun simulations.

Initialization of these simulations has been based on observations (optical, soft X-ray, radio) from both ground- and space-based instruments. Simulation outputs have been compared within situplasma and field observations and interplanetary scintillations (IPS). Improvements in the initialization procedures - spatial/temporal variations of solar plasma and field parameters at the coronal base - are expected from YOHKOH, SOHO, CORONAS-I, and TRACE experiments. “Ground truth” observations from WIND, SOHO, ACE, and INTERBALL experiments should then be compared with three-dimensional MHD outputs in tests of the fluid hypothesis noted above.
MHD Compressive Turbulence in the Solar Wind and the Nearly Incompressible Approach
Authors: Bavassano B. , Bruno R. , Rosenbauer H.
Published: July 2016

At MHD scales density fluctuations in the solar wind generally have a relative amplitude less than 0.1. The nearly incompressible MHD theory would seem then appropriate to describe a major part of the compressive turbulence at these scales. As a test of the theory, we focus on the scaling properties of density fluctuations with turbulent Mach numbers and on the level of correlation between density and temperature fluctuations. Our findings do not appear in favour of an extended applicability of the nearly incompressible theory to MHD compressive turbulence in the solar wind.
Interplanetary Consequences of Transient Coronal Events Observed with YOHKOH SXT: A Case Study of Polar Coronal Transient on 15 May 1992
Authors: Watanabe T. , Nakagawa Y. , Kojima M.
Published: July 2016

A large area (5 × 1010km2) of a coronal hole disappeared in concert with a transient brightening of a nearby high-latitude coronal arcade in the northern hemisphere on 15 May 1992. This coronal-hole disappearance took place in a time scale of half a day. It is suggested that the large-scale and quick change in coronal-hole geometry induced the eruption of originally closed coronal magnetic structure of the high-latitude arcade. An associated solar wind disturbance with the plasma speed of > 700 km/sec was observed by IPS, and geomagnetic sudden commencement was reported on 18 May 1992.
The IPS Work in Beijing Astronomical Observatory
Authors: Yuhai Qiu
Published: July 2016

This article describes the IPS work in the Beijing astronomical observatory including the hardware and software of the instrument and some theoretical research.
Luminosity Function and Evolution of Optically Selected QSOs
Authors: Wisotzki Lutz
Published: July 2016

I summarise a few recent results on the evolution of optically selected QSOs, with special emphasis on the notoriously difficult but physically important extremes at low and high luminosities and redshifts. It seems that quasar evolution is a more complex phenomenon than has often been assumed, and the new generation of surveys is just about to make this visible.
The Byurakan-IRAS Galaxy (BIG) Sample: The Redshift Survey
Authors: Mickaelian A.M. , Balayan S.K. , Hakopian S.A.
Published: July 2016

The Byurakan-IRAS Galaxy (BIG) sample (1967 galaxies) is based on optical identifications of IRAS PSC sources at δ>+61° and |b| >15° (FBS area). A redshift survey for brighter objects (B<18m) is being carried out with the Byurakan Observatory 2.6m, Special Observatory 6m, and Observatoire de Haute-Provence 1.93m telescopes. 213 objects have been observed, and redshifts in the range 0.008-0.173 have been measured. For this subsample, 15% of the objects are AGNs, and 15% are LIGs and ULIGs.
AGN Populations from Optical Identification of ASCA Surveys
Authors: Akiyama Masayuki , Ueda Yoshihiro , Ohta Kouji
Published: July 2016

To understand luminous AGNs in the z < 1 universe, the ASCA AGN samples are the best at present. Combining the identified sample of AGNs from the ASCA Large Sky Survey and Medium Sensitivity Survey, the sample of hard X-ray selected AGNs has been expanded up to 108 AGNs above a flux limit of 10-13 erg s-1 cm-2 in the 2-10 keV hard X-ray band. We discuss the fraction of absorbed AGNs in the hard X-ray selected AGN sample, and the nature of absorbed luminous AGNs.
Surveys of High-Redshift QSO Hosts
Authors: Hutchings J.B.
Published: July 2016

Recent investigations of high-redshift QSO morphology are reviewed and compared. The PSF-removal is difficult and results are given in several different forms. The reliability of results from HST and ground-based AO are compared, and several caveats to conventional wisdom are given.
AGN and the Demographics of Supermassive Black Holes
Authors: Green Richard F.
Published: July 2016

High angular resolution observations from WFPC and STIS now allow well-constrained dynamical measurement of the masses of supermassive black holes (SMBH) in nearby galaxies. An initial statistical analysis by Magorrian et al. showed that 97% of bulges host SMBH. Black hole mass is correlated moderately with bulge luminosity and strongly with the velocity dispersion of the whole bulge, suggesting that black hole formation may be an intrinsic aspect of bulge formation. Black hole masses for AGN determined from reverberation mapping fall on the same relationship with bulge velocity dispersion as those determined from stellar dynamical measurements. The prospect is therefore that the large-scale distribution of black hole masses in distant quasars may be determined through relatively straightforward measurement. Integral constraints show consistency between the total AGN luminosity density and the total volume density in SMBH contained in galaxy bulges. The strong peak of the high-luminosity quasar luminosity function at early cosmic time is consistent with the association of the build-up of SMBH through accretion and bulge formation. Alternate scenarios requiring substantial build-up of the most massive black holes at later cosmic times are more difficult to reconcile with the evolution of the LF.
The orbital evolution of some near-Earth asteroids
Authors: Timoshkova E.I.
Published: July 2016

The orbital evolution of the selected Near-Earth asteroids is studied by the numerical integration of the differential equations taking into account the perturbations due to all major planets for a time interval representing approximately 2000 revolutions of Jupiter. The new accurate DINCH integration procedure was used. Together with the orbital elements the Tisserand invariant is selected as a parameter to be investigated.
Spectral observations of comets with simple instruments
Authors: Avila G. , Guirao C. , Rodríguez J. , Alcalá J.M. , Pittichová J.
Published: July 2016

Low resolution optical spectra of comet Hale-Bopp 1995 O1 taken with a simple equipment are presented. A small fiber feed spectrograph was used linked first to a telescope of 0.1 m aperture and then to another one of 0.25 m aperture. The qualitative survey of the evolution of the Na (λ5893) doublet in comet Hale-Bopp is reported.
Cometary dust trails and ejection velocities
Authors: Gajdošík M. , Klačka J.
Published: July 2016

Some physical quantities are recalculated on the basis of the data for cometary dust trails presented in Sykes and Walker (1992). The final results for ejection velocities of meteoroids ejected from comets, trail ages and cometary mass loss rates are different from those presented in Sykes and Walker (1992). As a consequence, cometary mass loss rates may be higher than generally considered.
From the Solar system comet cloud to near-Earth space
Authors: Emel'yanenko V.V.
Published: July 2016

The dynamical evolution of objects from different zones of the solar system comet cloud to near-Earth space has been investigated. The steady-state number of objects with perihelion distancesq< 1.5 AU and periodsP <20 yr, arising from the near-parabolic flux of comets with absolute magnitudes brighter thanH10= 7 is ∼ 200 − 1000. The corresponding number for Halley-type comets is hundreds of times larger than the number of known Halley-type comets. The flux of objects in the Centaurs zone, captured from the near-parabolic flux is 300 times as large as the flux of new comets. The total number of cometary objects with semi-major axesain the range 50 <a< 500 AU andq∼ 1 AU is ∼ 10 times as large as the number of active comets. The probability of the transfer of objects from the trans-Neptunian orbits with 35 <q< 50 AU anda∼ 600 AU into the Jupiter family is ∼ 0.0001. The calculations show that trans-Neptunian objects on high-eccentricity orbits can be a significant continuous source for both the replenishment of the Oort cloud and the capture to short-period orbits.
Particle Acceleration in Solar Flares
Authors: Vlahos Loukas
Published: July 2016

Particle acceleration during solar flares is a complex process where the main ‘actors’ (Direct (D.C.) or turbulent electric fields) are hidden from us. It is easy to construct a successful particle accelertion model if we are allowed to impose on the flaring region arbitrary conditions (e.g., strength and scale length of the D.C. or turbulent electric fields), but then we have not solved the acceleration problem; we have simply re-defined it. We outline in this review three recent observations which indicate that the following physical processes may happen during solar flares : (1) Release of energy in a large number of microflares ; (2) short time-scales; (3) small length scales; and (4) coherent radiation and acceleration sources. We propose that these new findings force us to reformulate the acceleration process inside a flaring active region assuming that a large number of reconnection sites will burst almost simultaneously. All the well-known acceleration mechanisms (electric fields, turbulent fields, shock waves, etc.) reviewed briefly here, can be used in a statistical model where each particle is gaining energy through its interaction with many small reconnection sites.
On-line Computing Facilities at Jodrell Bank
Authors: Davies J. G.
Published: July 2016

An on-line computer has been in use at Jodrell Bank since 1964, both controlling the Mk II radio telescope and performing data processing functions in connection with it. However this system is now being superseded, and the following describes the present state of development, including some facilities that are only now being constructed.

An Argus 400 computer is associated with each of the two main telescopes. Each has 12 000 words of core store, the word length being 24-bits, and the time for obeying most functions is 12 μs. The 24-bit word length is well suited to the application since more than 16-bit accuracy is required in the coordinate transformation. This fact, and the very versatile organization of the Argus computer, makes the effective speed relatively higher when compared with faster machines of smaller word size. In addition a drum store of about 50,000 words capacity will be fitted to each machine, and CRT and graphical output devices are available. Each machine operates a permanent program, which performs a number of functions, including in the case of the Mk II telescope the control of the instrument itself. In addition, up to three “user” programs may be operated simultaneously; these may be on-line data collection, with links to the telescope control sections, or completely off-line background jobs. A wide selection of library routine, available to all programs, is permanently in the core store, and this makes the writing of programs a relatively simple matter.
Experimental Measurement of Variable Star Brightness by On-line Electronic Computer
Authors: Luud L. , Koppel R. , Maasik M.
Published: July 2016

After having introduced the electronic computer at the W. Struve Tartu Astrophysical Observatory, an opportunity to put into practice some measuring and data handhng systems presented itself. The simplest measuring of variable star brightnesses by the on-line computer was chosen for the beginning, and for today the first stage has passed with certain success. In the present paper we give a brief report about the work done.
Real-time System for Solar Spectrophotometry
Authors: Biase G. A. De , Gregorio G. De
Published: July 2016

A system is being developed at the Rome Astronomical Observatory for real-time detection of solar spectral information. The scheme and the philosophy of the system are here described. Finally, the first program to which it will be applied is presented.
Photometry of R Coronae Borealis
Authors: Fernie J. D. , Sherwood Vicki , DuPuy David L.
Published: July 2016

Photoelectric photometry of R CrB was obtained during the years 1966–71. During this time the star emerged from a prolonged minimum, showing a change in colour indices which was very like those of the supergiant sequence between G 8 and F 8 if allowance is made for an ultraviolet excess and some interstellar reddening. Superimposed on this rise towards maximum was a sharp minimum, during which the V magnitude was observed to decline through more than 3 magnitudes without any corresponding reddening in the colour indices. Throughout the emergence from the extended minimum the star showed irregular fluctuations of up to 0.2 mag. on a timescale of weeks.
V1016 Cygni, Spectral Observations 1968—1971
Authors: Fitzgerald M. Pim
Published: July 2016

Identification of approximately 230 emission lines between 3120 Å and 5045 Å have been made on twelve plates taken between 1968 and 1971. The line intensities and ratios fail to give a consistent detailed picture of the nebula, but indicate that on average the electron pressure and density have changed little. The Balmer decrement has become less steep since 1968, indicating higher optical depth. However, the permitted iron lines have completely gone, indicating lower density. Excitation is increasing in some parts of the nebula, as indicated by the increased strength of the [Fe V] lines, and the recent appearance of strong lines of [Ne Y]. The continuum remains weak, though it is easily seen on plates taken on April 8, 1969, and on those taken in June 1971. The radial velocity of the object fluctuates between —50 and — 70 km/sec, and the line widths remain about 120 km/sec. The wing to the violet of the emission lines is still present. The continued brightness of this object, and the relative lack of change in the spectrum over several years, indicate even more strongly that V 1016 Cygni is likely to be a planetary nebula in the stages of formation.
Techniques and Results of Observations of Rapid and Ultrarapid Variable Stars
Authors: Warner Brian
Published: July 2016

The inception of the present era of interest in rapidly varying stars may be identified with M. F. WALKER’s discovery in 1954 (WALKER 1954) of changes in the brightness of the blue object MacRae+43° 1 (now known as MVLyr), on a time scale of a few minutes. Outside of flare stars, few other stellar objects were suspected to vary on such a short time scale. GREENSTEIN’s (1954) spectra showed that MV Lyr resembles an old nova, which stimulated WALKER to look for light fluctuations in old, recurrent, and dwarf novae and related stars. His observational evidence that all members of these classes show variations of various amplitudes and time scales is summarized in the IAU Colloquium on non-stable stars (WALKER 1957). Most spectacular of his discoveries was the existence of 71 sec periodic variations in the light from the remnant of Nova Herculis 1934 (DQ Her) (WALKER 1956).
OAO-2 Observations of Beta Lyrae and a Provisional Interpretation
Authors: Kondo Yoji , McCluskey George E. , Houck Ted E.
Published: July 2016

Six-color ultraviolet photoelectric observations of Beta Lyrae obtained with OAO-2 are presented. These observations, made at 1380 Ǡ, 1500 Ǡ, 1920 Ǡ, 2460 Ǡ, 2980 Ǡ, and 3330 Ǡ, represent the first truly continual coverage of the light changes of Beta Lyrae during one orbital revolution and were obtained in November 1970. The photometric data are supplemented by spectral scans in the wavelength intervals 3800 Ǡ to 1800 Ǡ and 2000 Ǡ to 1050 Ǡ; the latter interval was scanned at 10 Ǡ resolution once during every OAO-2 orbit, i. e., about 100 minutes. Anomalous features, such as asymmetries and short and long term variations, are present in the light curves. A tentative discussion of solutions of the light curves is given. The problems of combining the photometric and spectroscopic information to arrive at a model of the system are also discussed.
Two-Color Observations of RR Lyrae Stars in M14
Authors: Wehlau Amelia , Potts Nicholas
Published: July 2016

Two-color photographic photometry has been carried out on RR Lyrae variables in M14. The position of these variables in the color-magnitude diagram is shown, and it is noted that there is a lack of horizontal branch stars to the red of the variable star gap. Color-amplitude, period-amplitude and color-period relations for the RR Lyrae variables measured are shown.
Red Variable Stars in Metal Rich Globular Clusters
Authors: Lloyd Evans T. , Menzies J. W.
Published: July 2016

The globular clusters contain sufficiently large numbers of stars to permit a systematic study of the intrinsically rare variable stars which lie near the tip of the red giant branch. The position of the smaller amplitude stars in the colour magnitude diagram is of particular interest. Eggen (1972) has published photoelectric observations of such stars in several globular clusters, most of intermediate or low metal abundance. The mean colour of 14 stars in 5 clusters is (V-IK) = 1.40, with a spread from 1.60 to 1.12 (or 0.75 if V8 in M22 is of this type) which Eggen regards as indicating a range of temperature. The red variable stars in the metal rich globular cluster 47 Tucanae are much redder and show a considerable range of colour.
The system of short period meteor streams
Authors: Lindblad B. A.
Published: July 2016

The orbital characteristics of precisely reduced photographic meteors were studied. Most photographic meteors move in short period, direct orbits with orbital periods inbetween those of Jupiter and Mars. Practically no meteors have (Orbital periods coincident with those of the planets Jupiter, Mars and Earth.

A search among all precisely reduced, photographic meteors revealed a number of new – or previously not well studied – meteor streams. For 18 short period meteor streams the scatter in the orbital elements 1/a,πand Ω was studied. An almost linear relation was found between the mean orbital energy of a meteor stream (– 1/a) and the standard deviation σ(1/a), indicating a progressive increase in the orbital scatter with decreasing mean distance to the sun. An index of mean meteoroid density was computed for 11 of the short period streams. The mean density increases with decreasing semi-major axis.

The results are interpreted as indicating that the short period meteor streams are initially formed in orbits with periods slightly shorter than Jupiter’s. As the streams gradually drift inwards towards the sun under the influence of various drag forces the individual stream members spread out and only the high density, resistant meteors still remain, or can be recognized, as stream members.
Kinematics and Ages of UV Ceti Stars
Authors: Poveda A. , Allen C. , Herrera M.A.
Published: July 2016

The kinematic properties of 93 UV Ceti stars of the solar neighborhood are studied, based on a list of flares within 25 pc of the Sun (π ≥ 0".04). With updated values for their distances, proper motions and radial velocities (Gliese & Jahreiss 1991) space velocity dispersions are calculated for these stars. It is found that the total velocity dispersion of the flare stars (σ=30±3 km s−1) is similar to that of the F5 V stars from the same catalogue, for which the conventionally estimated mean age is about 3 · 109 years. A number of flare stars are identified as members of the Hyades, Sirius or Pleiades groups. The velocity dispersions found for the nearby flare stars, as well as their scale height and the membership of some of them to young kinematic groups, indicate that they belong to the young disk population. A small number (7) of UV Ceti stars have kinematics corresponding to the thick disk or halo population. Their long-lived chromospheric activity is interpreted as due to coalescence of old contact binaries. The question of the age of Proxima Centauri is examined in the context of our results, and found to be compatible with the ages of a Centauri A and B.
Young and Old Subsystems of Flare Stars
Authors: Mirzoyan L.V. , Hambarian V.V.
Published: July 2016

Photographic observations with wide-field telescopes of flare stars in the Orion association and the Pleiades cluster have been carried out since 40 years. About 500 flare stars were found in each of these systems. The ages of these stellar systems differ by one or two orders of magnitude (Mirzoyan 1991). This fact allows us to compare them, in order to show that they fit into the concept, suggested first by Haro (1957), that the evolutionary status of flare stars is a stage of red dwarf star evolution which follows that of the T Tau stars (Haro 1976, Ambartsumian & Mirzoyan 1970).

The basic difference between the Orion and Pleiades subsystems of flare stars has been known for a long time: the coexistence of flare stars and T Tau stars in the Orion association, and the absence of the latter group in the Pleiades. Some of the T Tau stars show flare activity (Haro 1964). This fact and the existence of multiple systems of trapezium type, which are dynamically unstable, in the Orion association, are arguments in favour of an evolutionary connection between these two types of stars.
Flare Star Observations with a Single-Photon Counting Imaging Detector
Authors: Casperson Donald E. , Priedhorsky William C. , Baron Miles H. , Ho Cheng
Published: July 2016

At Los Alamos National Laboratory we are developing a new imaging sensor which combines high spatial and high temporal resolution over a large area format, while maintaining single-photon counting sensitivity and sustaining a high count rate. The detector is called a microchannel plate with crossed delay line readout, or MCP/CDL. This detector is ideally suited to the observation of weak transient events, such as stellar flares from red dwarf flare stars in our Galaxy. At present we are initiating an experiment with the MCP/CDL detector which will utilize a 30-cm aperture f/7 telescope to characterize U-band, B-band, and V-band emission from such low-luminosity flare stars, and to search for weak optical transients associated with other astrophysical sources.
PU Vul: 15 Years of Studies, Important Findings and Remaining Mysteries
Authors: Gershberg R.E.
Published: July 2016

In autumn 1979, the young W. Wenzel - at this time he was only 50 years old - came to the Byurakan meeting on flare stars and informed the participants about a recently discovered flaring object: the Kuwano-Honda object = PU Vul. During that time, FU Ori and related stars were the most intriguing variable objects, and PU Vul had shown some similar features such as the rate of brightening and the spectrum at maximum. It turned out to be an extremely interesting object, and the Crimean team has studied it for the last 15 years. Over this time, this team included T.S. Belyakina, N.I. Bondar, K.K. Chuvaev, Yu.S. Efimov, R.E. Gershberg, V.I. Krasnobabtsev, E.P. Pavlenko, P.P. Petrov, I.S. Savanov, N.I. Shakhovskaya, N.M. Shakhovskoy, A.G. Shcherbakov and V.A. Shcherbakov, and we collaborated with V.I. Shenavrin from Russia, with D. Chochol, J. Grygar and L. Hric from former Czechoslovakia and with V. Piirola, I. Tuominen, M. Poutanen and J. Huovelin from Finland.

Now the number of publications on PU Vul approaches one hundred. It was established that PU Vul is a symbiotic nova, the object among the known variables of this type, whose explosion became observable most recently (with the possible exception of Wakuda’s object in Sgr, Grebel et al. 1994), and many details have been observed from the very beginning of the flare. I intend to list the most interesting findings and the most intriguing remaining mysteries of PU Vul.
UBVRI Photometry of AE Aquarii in July-August 1994
Authors: Beskrovnaya Nina , Ikhsanov Nazar , Bruch Albert , Shakhovskoy Nikolaj
Published: July 2016

The most striking feature of the close binary system AE Aqr is its unique photometric behaviour - irregular alternations of quiet and active phases without noticeable transition periods. Although extensive photometric observations of AE Aqr have been carried out for more than forty years (see Bruch 1991 and references therein), the mechanism of its flaring activity is still poorly understood and the star - although generally classified as a cataclysmic variable - does not fit well into any of the subclasses.

According to us, much insight into this peculiar object can be gained by an investigation of the connections between the flaring activity of AE Aqr and the strictly periodic oscillations at 33s, identified as the spin period of the primary. The latter have been seen in optical (Patterson 1979) and UV light (Eracleous et al. 1994), in X-rays (Patterson et al. 1980) and in TeV γ rays (Meintjes et al. 1992). There are contradictory reports about the relation between their amplitude and the flaring activity in AE Aqr: Patterson (1979) noted that the amplitude of the pulsations increases during active phases, while Eracleous et al. (1994) observed that their characteristics are not strongly affected by the flares.
Resolved Shot Noise in the AM Her System V834 Cen
Authors: Larsson Stefan , Larsson Bengt
Published: July 2016

Cataclysmic variables of the AM Her type are close binary systems with accretion onto a highly magnetic (a few times 107 G) white dwarf. In these systems the magnetic field is strong enough to prevent the formation of an accretion disc. The accretion flow is instead funneled directly onto the polar caps where the plasma is shocked and radiates intense optical cyclotron radiation as well as bremsstrahlung at X-ray energies. The cyclotron radiation component, which dominates in the optical, is highly polarized (5-35%). The cyclotron emission exhibits intensity variations on a large range of time scales. This include quasi-periodic oscillations, flickering and long term changes between brightness states. The observed source intensity is also modulated by the white dwarf rotation which is synchronized with the orbital period (101 min for V834 Cen). The flickering is believed to be due to inhomogeneities in the accretion flow. These could either be density variations in a continous flow or it could be in the form of independent blobs accreting over the polar cap region. As blobs hit the white dwarf surface and radiate their accretion energy they should be seen as shot noise. For a theoretical discussion of the fate of such blobs see Frank et al. (1988). A modeling of the optical variability in AM Herculis, in terms of a shot noise process was made already by Panek (1980). It was found that a consistent model could be constructed by randomly occurring 708 – 908 rectangular shots, with on the average a few overlapping shots. The power spectrum had a v−2 shape above 0.02 Hz as expected, although it is not clear whether a break in the slope of the power spectrum was actually seen around 0.01 Hz. The shot overlap meant that individual shots could not be resolved directly in the light curve. This limits the precision and uniqueness by which shot parameters can be determined. However, in our observational data of AM Her objects we have found occasions when the character of the flickering has changed to become much more “flarelike”, suggesting that individual shots might be seen in these cases. This change is also associated with a change in the shape of the power spectrum, in particular a higher power level and a steepening at the high frequency end. Most importantly, there is a distinct break in the power spectra around 0.03 Hz, indicative of a characteristic time scale in the flickering noise. In addition to a power spectrum analysis we have also made a direct modeling of individual flares in the light curve. The distribution and correlations of the fitted pulse parameters were studied and compared with simulated data. The primary aim was to investigate whether the flares are really individual shots or produced by a random superposition of more frequent smaller amplitude shots.
Gamma-ray Bursts: Observational Overview, Searches for Counterparts, and BACODINE
Authors: Fishman G.J. , Barthelmy S.
Published: July 2016

The basic pioperties of γ-ray bursts are reviewed. Many of these properties have been known for over two decades, although new and more detailed observations have been made by Compton Observatory in the past three years. The new observation with the greatest impact has been the observed isotropic distribution of bursts along with a deficiency of weak bursts. This is not compatible with any known Galactic population of objects.

The observation of a γ-ray burst counterpart in another wavelength region has yet to be made, even though there have been substantial efforts in this pursuit from a wide variety of observations in many wavelength regions. Perhaps the greatest chance for a simultaneous or rapid observation of a γ-ray burst counterpart lies with the newly-developed BAtse Coordinates Distribution NEtwork (BACODINE) system. The objectives and characteristics of this system are described.
Optical Transients
Authors: Hudec René
Published: July 2016

We outline and discuss the recent results of optical searches for counterparts to gamma-ray burst sources as well as related problems.
EUVE Spectra of Coronae and Flares
Authors: Jordan Carole
Published: July 2016

Following a summary of early solar EUV spectroscopy the spectra of some late-type stars obtained with the Extreme Ultraviolet Explorer (EUVE) are briefly surveyed. Some transitions which are not included in current emissivity codes but could lead to numerous weak lines, and an apparent continuum in the EUVE short wavelength region, are discussed. The importance of the geometry adopted when interpreting the emission measure distribution is stressed, since radial factors can lead to an apparent emission measure distribution gradient that is steeper than the value of 3/2 expected in plane parallel geometry.
Spectroscopic EUVE Observations of the Active Star AB Doradus
Authors: Rucinski Slavek M. , Mewe Rolf , Kaastra Jelle S. , Vilhu Osmi , White Stephen M.
Published: July 2016

We present observations of the pre-Main Sequence, rapidly-rotating (0.515 day) late-type star, AB Doradus (HD 36705), made by the Extreme Ultraviolet Explorer (EUVE) satellite. A high-quality spectrum was accumulated between November 4-11, 1993, with an effective exposure time of about 40 hours. The data constrain the coronal temperature structure between several 104 K up to roughly 2 × 107 K through a differential emission measure analysis using an optically-thin plasma model. The resulting differential emission measure (DEM) distribution shows: a) dominant emission from plasma between about 2 × 106 K and 2 × 107 K, b) very little emission from plasma between 105 K and 2 × 106 K, and c) emission from plasma below about 105 K. If solar photospheric abundances are assumed, then the formal DEM solution also requires the presence of a strong high-temperature component (above about 3 × 107 K) in order to fit the strong continuum emission below about 150 Å; however, we believe that this component of the solution is not physical. The DEM analysis gives a best-fit value for the interstellar hydrogen column density of NH = (2.4 ± 0.5) × 1018 cm−2.
Detection of Heavy Elements in the EUVE Spectrum of a Hot White Dwarf
Authors: Jordan S. , Koester D. , Finley D.
Published: July 2016

Observations with the ROSAT satellite have already indicated that metal absorbers must be present in the atmosphere of the hot DA white dwarf PG 1234+482. This is now confirmed by strong absorption features found in the short and medium wavelength EUVE spectrum of the star. With fully blanked model atmospheres, taking into account several million lines of heavy elements, we could attribute the strongest features to absorption by FeVI and FeVII. Since the spectrum has not been dithered during the observation other elements could not be identified with the same level of confidence, but upper limits could be determined. These are in general lower than predicted by models, which attempt to explain the presence of the metals by theoretical calculations of radiative forces in hot DA white dwarf atmospheres.
A Search for the Signature of the Diffuse Soft X-ray Background in the ROSAT Wide-Field Camera All-Sky Survey
Authors: West R.G. , Willingale R. , Pye J.P. , Sumner T.J.
Published: July 2016

We present the results of an attempt to locate the signature of the diffuse soft X-ray background in the ROSAT Wide-Field Camera (WFC) all-sky survey. After removal of non-cosmic background sources (eg. energetic charged particles), the field-of-view integrated count rate in the WFC S1a filter (90–185 eV) shows no consistent variation with Galactic latitude or longitude. We place limits on the signal from the soft X-ray background (SXRB) in the WFC, and show that these limits conflict with the observations of the Wisconsin Sky Survey if the SXRB in this energy range is assumed to be produced by a thermal plasma of cosmic abundance and a temperature T ~ 106 K within d ~ 100 pc of the Sun.
The EUV Excess in Magnetic Cataclysmic Variables
Authors: Warren John K. , Mukai Koji
Published: July 2016

We present preliminary analysis of EUVE pointed data of 8 magnetic cataclysmic variables. Blackbody temperatures, luminosities, and interstellar columns have been better constrained. Using these luminosities we look for correlations between the EUV excess (over optical and hard X-rays) and various system parameters. While it appears there is no correlation between the EUV excess and the system inclination and orbital period, correlations are suggested between the EUV excess and the longitude of the accretion spot, the colatitude of the accretion spot, the white dwarf magnetic field, and the magnetic capture radius.
Non-Magnetic Cataclysmic Variables in the ROSAT WFC Survey
Authors: Wheatley Peter J.
Published: July 2016

Six non-magnetic cataclysmic variables were detected during the ROSAT WFC survey; four dwarf novae and two nova-like variables. In two dwarf novae (VW Hyi & SS Cyg) the flux evolution through outburst was followed across a broad wavelength range. The two other detections (Z Cam & RX J0640−24) also suggest the presence of distinct luminous EUV emission components; supporting the view that such components are a ubiquitous feature of dwarf nova outbursts. Two bright nova-like variables were detected, but these detections are found to be consistent with the soft tail of the X-ray emission.
The X-ray and EUV Turnoff of GQ Mus and V1974 Cyg
Authors: Starrfield S. , Krautter J. , N. Shore S. , Idan I. , Shaviv G. , Sonneborn G.
Published: July 2016

Both GQ Mus and V1974 Cyg were observed to turnoff in X-rays by ROSAT. The turnoff of V1974 Cyg was also observed with EUVE. GQ Mus was observed near the beginning of its outburst withEXOSATand then 7 years later byROSAT inthe all-sky survey. LaterROSATPSPC observations showed that its X-ray intensity was slowly declining with time and it was not detected in the last pointing that occurred in August 1993. We observed GQ Mus withIUEover the entire active phase of its outburst and found a change in the slope of the UV continuum around the time that the X-rays turned off. V1974 Cyg was observed byROSATthroughout its entire active phase in X-rays which lasted about 18 months. V1974 Cyg was detected in theEUVEall-sky survey, but not in pointed observations that occurred in August 1993 (and June and November 1994). We use the measured times of the active phases to determine important properties of these two novae. For example, for V1974 Cyg we predict that more than 10−5M⊙of helium rich material was left on the white dwarf when it returned to quiescence. For GQ Mus, ~ 10−4M⊙was left on the white dwarf. These results imply that a significant amount of the helium seen in nova ejecta was produced in outbursts prior to the one that was just observed. They also imply that the mechanism which mixes core material into the ejecta must be efficient.
Extreme Ultraviolet Emission from Neutron Stars
Authors: Foster R.S. , Edelstein J. , Bowyer S.
Published: July 2016

We summarize the detections of extreme ultraviolet (EUV) emission from neutron stars. Three firm detections have been made of spin-powered pulsars: the aged millisecond pulsar PSR J0437−4715, the middle-aged X-ray pulsar Geminga, and the radio pulsar PSR B0656+14. These observations allow us to evaluate both power-law and thermal-law emission models as the source of the EUV flux. For the case of PSR B0656+14 the lack of flux modulation with pulse period argues that the EUV radiation originates from the cooling neutron star surface rather than from a hot polar cap. If the emission is from a thermalized neutron star surface, then limits can be placed on the surface temperature. For the case of Geminga we can explain the observed EUV flux using thermal models that are consistent with standard neutron cooling scenarios. We also have a weak indication that the EUV emission from Geminga is pulsed in a manner consistent with the lowest energy channel observed with Rosat. For the case of the millisecond pulsar PSR J0437−4715 standard neutron star cooling models require surface re-heating. We compare different heating models to the data on this object. We rule out re-heating by crust-core friction, and find that models for the accretion from the interstellar medium, accretion from the white dwarf companion and a particle-wind nebula do not account for the EUV luminosity. Models of pulsar re-heating by magnetic monopole catalysis of nucleon decay are used to establish new limits to the flux of monopoles in the Galaxy. A single power-law source with properties derived from X-ray data cannot explain the EUV flux from PSR J0437−4715. The strongest model for explaining the EUV emission consists of a large ~ 3 km2 polar cap heated from particle production in the pulsar magnetic field. We consider the prospects for detecting other neutron stars in the extreme ultraviolet.
Three-Dimensional Modelling ofEUVEObservations of the Io Plasma Torus
Authors: Thomas N. , Innes D.E. , Lieu R.
Published: July 2016

First results from a 3-D model ofEUVEobservations of the Io Plasma Torus are reported. The semi-empirical model calculations follow a method previously used to describe visible and near-UV emissions. The extension to EUV wavelengths is described. Several EUV emissions have been successfully modelled although some discrepancies remain at this stage. Most EUV emissions peak at a jovicentric distance of ≈ 5.8RJ. The observed dawn-dusk asymmetry of the torus was well fitted with a shift parameter (ϵ) of 0.03. The modelling also indicates that optical depth effects need to be considered for several EUV emission lines.
Pulsation and Evolution. An observer’s viewpoint
Authors: Waelkens C.
Published: July 2016

We review observational evidence on the interaction between stellar pulsation and evolution. We discuss to what extent observations of pulsating stars with variable amplitudes and pulsation periods have implications on our understanding of stellar structure and evolution. The probable link between mass loss and pulsation in AGB stars and in hot luminous stars appears to be the strongest way in which pulsations affect evolution. We point out the possibility that forced oscillations in the components of binaries may have important consequences on evolution, that could offer an explanation for some classes of peculiar evolved objects.
Seismological Properties of Evolutionary Delta Scuti Models Using OPAL Opacities
Authors: Guzik Joyce A. , Bradley Paul A.
Published: July 2016

We present the first results of our project of calculating the evolutionary and seismological properties of δ Scuti models using Livermore OPAL opacities. We calculate the radial and low-degree nonradial nonadiabatic pulsation frequencies for a 1.8 and 2.0M⊙ model. Our radial first overtone/fundamental mode period ratios are × 0.772, which agree well with observed period ratios. We find a dense spectrum of unstable nonradial modes including both low order g-type modes and low to intermediate order p—type modes, confirming that we need a selection mechanism allowing only some modes to grow to observable amplitudes.
Mira Variables: Theory versus Observation
Authors: Wood P.R.
Published: July 2016

The identification of the mode of pulsation of Mira variables remains a major problem. Recent angular diameter measurements of solar neighbourhood Miras suggest large radii consistent with first overtone pulsation. On the other hand, the pulsation velocity amplitudes of Mira variables point to fundamental mode pulsation. There is some marginal evidence from multiple modes in Miras that the prime pulsation mode is the first overtone, while distinct (K,logP) sequences in the Magellanic Clouds point to the Miras being fundamental mode pulsators. The above confusing evidence is presented and discussed. Finally, the (K,logP) relations in the SMC and LMC are compared in order to determine if there is any metallicity dependence.
A Period Analysis of the Optical Line Variability of β Cephei
Authors: Telting J. , Aerts C. , Mathias P.
Published: July 2016

Recently Aerts et al. (1994, Paper I) discovered multi-periodicity in the variations of optical lines of β Cephei. They identified the frequency of the radial pulsation (f1 = 5.25cycles/day), and additionally found 2 frequencies (f2 = 5.38 c/d, f3 = 4.92 c/d) close to the main frequency. The amplitude of these variations was found to be much smaller than that of the radial pulsation. Aerts et al. (1994) attributed these small variations at the newly found frequencies to non-radial pulsation modes of the star, but labelled the mode-identifications as uncertain.
Cepheids and LPVs in and around Magellanic Cloud Clusters
Authors: Sebo K.M. , Wood P.R.
Published: July 2016

V and I band CCD photometry of the young clusters NGC 330 (SMC), NGC 1850, NGC 2058 and NGC 2065 (LMC) has been used to find variable stars in and around the clusters. The variables detected are mostly Cepheids and long-period variables (LPVs). Here we outline some results of these studies.
HST UV Observations of the Disk and Wind of V795 Her
Authors: Rosen S. R. , Prinja R. K. , Drew J. E. , Mason K. O. , Howell S. B.
Published: July 2016

HST UV observations of V795 Her reveal a strong 2.6-h orbital variation in the prominent UV lines, in contrast to earlier (IUE) evidence of a 4.8-h period. Only the C IV line contains a strong blue-shifted, wind formed absorption component. Several lines exhibit a ‘narrow’ absorption feature near rest velocity which may originate in the disk, and a blue-shifted emission feature which accounts for most of the line profile variability.
Line Formation in U Gem and T Leo
Authors: Hummel W. , Horne K. , Marsh T.R. , Wood Janet H.
Published: July 2016

We present 3-D LTE radiative transfer calculations [1] for H, He and Ca in accretion disks (AD) of dwarf novae in quiescence. The model disk is assumed to be in hydrostatic equilibrium vertically, and to rotate with Keplerian velocities. Calculated emission lines are fitted to phase-averaged, continuum-subtracted spectra of U Gem (Fig. 1) and T Leo (Fig. 2). Up to four parameters of the AD have been fitted: distance D, baryonic number density N, isotropic turbulence Vtu and disk temperature T; the latter two are assumed to be constant throughout the disk. Geometrical parameters are from [2] and [3].