bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photometry of CH Cygni During 1991-1994
Authors: Panov K.P. , Stegert J.S.W. , Hildebrandt G. 
Published: July 2016

CH Cygni has been observed since about one decade at the Bulgarian National Astronomical Observatory Rozhen. UBV photometry was obtained with the 60 cm telescope. The computer controlled photometer is equipped with an EMI 9789 QB multiplier, a set of u,b,v filters and a diaphragm of 28". The reduction includes corrections for dead-time and background, differential extinction and transformation to the standard UBV system.Observations between 1991 and 1994 are displayed in Fig. 1 and show the new outburst, which is still going on. The previous major outburst lasted until 1984, and CH Cyg declined slowly between 1985 and 1988. In 1988, it reached its minimum in brightness and activity. The cause for the activity is probably mass transfer from the M giant component onto the hot companion. In this model, only the M star is seen during activity minimum. In July 1988, the mean brightness was V = 8.50, B - V = 1.39 and U - B = 1.48. Since 1989, some erratic activities appeared, including a hot variable continuum, broad and variable emissions in the Balmer lines and rapid light variations (Leedjarv 1990, Tomov and Mikolajewski 1992, Kuczawska et al. 1992, Panov and Ivanova 1992). Since 1991, a trend of increasing activity is observed, which persisted also in 1994. The brightening of CH Cyg of about 5m in U in 1994 with respect to 1991 shows that it undergoes another major outburst. Moreover, it exhibits light variations with different other time scales, minutes (flickering), days and weeks, probably resulting from the mass-transfer. Fig. 2 showns an example of a short time variation on October 1, 1994. The flickering of CH Cyg was very pronounced in the U, B and V filters and the amplitudes reached several 0m.1 in about half an hour. More observations of this interesting system are planned.
The Origin of Flaring Activity in AE Aquarii
Authors: Ikhsanov Nazar 
Published: July 2016

AE Aqr is a close non-eclipsing binary system with an orbital period Porb ≈ 9.88 hr, eccentricity of the orbit e = 0.02 (Chincarini & Walker 1981) and a mass ratio q = 1.14 (Reinsch & Beuermann 1994), situated at the distance of ∼ 84 pc (Van Paradijs et al. 1989). The secondary is K3 red dwarf on or close to the main sequence (Bruch 1991). The primary cannot be observed directly. However, the stable photometric oscillations at a period of 33 s (and at half this period) in the optical (Patterson 1979), UV (Eracleous et al. 1994), X-rays (Patterson et al. 1980) and, probably, VHE γ-rays (Meintjes et al. 1992, Bowden et al. 1992) leave no doubt that the primary is a rapidly rotating magnetized compact object. The observed rate of deceleration of the primary rotation is Ṗ = 5.64 × 10−14 ss−1 (De Jager et al. 1994), and its mass is m1sin3i (0.56 ± 0.03) M⊙ (Reinsch & Beuermann 1994). The lack of eclipses allows to put a lower limit to the mass of the primary m1 ≥ 0.62M⊙.AE Aqr emits detectable radiation in all parts of the electromagnetic spectrum. In radio and γ-rays it is a powerful non-thermal source. However, in the optical, UV and X-rays the radiation is likely to be thermal and can be well explained by gas accretion onto a compact star (Patterson 1979, Patterson et al. 1980). The observed impulse profile of the pulsating component (Eracleous et al. 1994) looks similar to that of the accreting X-ray pulsars.
The Benefit of Archival Research in Investigating Dwarf Novae
Authors: la Dous C. 
Published: July 2016

Dwarf novae and nova-like stars are a sub-group of the class of cataclysmic variables. Most of these stars show high and low brightness states (maxima or outbursts and minima or quiescent states, respectively). They all are short-period interacting binaries consisting of a white dwarf primary, a late-type Roche-lobe filling secondary, and an accretion disk around the white dwarf. For details on observations of cataclysmic variables and their theoretical explanations and modelling, the interested reader is referred to recent reviews.The main problem when trying to understand these systems is the wealth of patterns presented by the whole group: no two objects are nearly identical and it is hard to say which the ‘typical’ features are. As a result of this, from an individual observation, or from observations of a few systems only, it is not possible to decide which of the observed features are characteristic of the entire class, and which are specific of individual members. The only way is to investigate many different members of the same class, arrange them according to their different physical parameters, and try to determine what the general characteristics are.
Eclipse Mapping the Flickering in HT Cas
Authors: Welsh William F. , Wood J.H. 
Published: July 2016

Flickering is a well-known, though poorly understood, signature of accretion in cataclysmic variables. HT Cas is an excellent system in which to study flickering because its well determined characteristics allow a calibration of the experimental system (see Horne et al. 1991).Patterson (1981) argues that the flickering in HT Cas originates from regions very near the white dwarf. In U Gem, the flickering appears to be associated with the bright spot (Warner & Nather 1971). In RW Tri, the flickering occurs throughout the disk but is centrally concentrated (Horne & Stiening 1985); the same holds true for V2051 Oph (Warner & Cropper 1983).HT Cas is a 16m.4 eclipsing dwarf nova with a binary period of 106 min and an inclination of ∼ 81°. The entire eclipse last about 15 min with the white dwarf totally eclipsed for ∼ 5 min. The mass ratio is 0.15 with the white dwarf having mass ∼ 0.6M⊙ (Horne et al. 1991).We obtained 20 eclipses of HT Cas between 1982 and 1991 in U, B and V at Mt. Palomar and also McDonald Observatory with 0.5 – 2 sec integrations. These data were folded on the ephemeris given by Horne et al. (1991) and corrected for the 30 sec drift in the phasing as noted by Wood et al. (1995).
Multiple Time Scales in Cataclysmic Variables: The Examples
Authors: Andronov Ivan L. 
Published: July 2016

AbstractDecades of patrol observations of cataclysmic variables (CVs) show variations of the accretion rate also at a time scale of a few years which may be explained by a solar-type activity of the secondary and/or by orientation changes of the magnetic axis of the white dwarf in polars. Secondary photometric periods seen in TT Ari and possibly some other CVs need theoretical explanation. Irregular variability of some objects is characterized by power-law power spectra with a power index depending on the luminosity state of the system.
Irregular X-ray Variation of LMC X-3
Authors: Pan H.C. , Skinner G.K. , Sunyaev R.A. , Alexandrovich N.L. 
Published: July 2016

LMC X-3 is an X-ray binary in the Large Magellanic Cloud. It was discovered by UHURU and observations with various satellites showed that the X-ray source was variable by a factor of up to 100 (e.g. Traves et al. 1988). Using the GINGA and HEAO-1 observations, Cowley et al. (1991) found a strong ∼ 198 (or possibly ∼ 99) day modulation in the X-ray luminosities of LMC X-3. They suggested that this modulation may be due to an accretion disc precession, or periodic variations in the mass transfer rate, or a combination of both.We observed LMC X-3 with the TTM in 1988-1990. The present paper gives some results from the analysis of the data obtained.The TTM is a coded mask telescope on board the MIR space station. It is capable of producing images in the energy range 2-30 keV with a spectral resolution of about 18% at 6 keV (Brinkman et al. 1985).
Observations of High-energy Gamma-ray Bursts with EGRET
Authors: Merck M. , Bertsch D.L. , Dingus B.L. , Fichtel C.E. , Hartman R.C. , Hunter S.D. , Kanbach G. , Kniffen D.A. , Lin Y.C. , Mayer-Hasselwander H.A. , Michelson P.F. , von Montignty C. , Mukherjee R. , Nolan P.L. , Pohl M. , Sreekumar P. , Schneid E.J. , Thompson D.J. 
Published: July 2016

Gamma Ray Bursts (GRBs) have puzzled astronomers since their discovery more than 20 years ago. As no counterparts at wavelengths other than X- and γ-rays have yet been found the identification of the sources is still missing. Theoretical explanations range from colliding comets (1993) and merging neutron stars (1982) to more exotic objects, such as superconducting cosmic strings (1988). Data accumulated until now still do not discriminate between these models, although results from the BATSE (Burst and Transient Source Experiment) instrument aboard the Compton Gamma Ray Observatory (CGRO) strongly favor extragalactic models.The Energetic Gamma Ray Experiment Telescope (EGRET) aboard CGRO has s ofar detected photons from 5 GRBs with its spark chamber. These are the highest energy γ-rays associated with GRBs to date. In this work we review previously published data and summarize the properties of these events. Elsewhere we present possible constraints from the data on the models proposed to explain GRBs.
ETC Observations of the Gamma-ray Burst GRB 941014
Authors: Vanderspek Roland , Richer George R. 
Published: July 2016

AbstractThe Explosive Transient Camera (ETC) is a dedicated wide-field sky monitor for short-duration optical transients. The ETC operates completely automatically, searching for transients in the night sky without the need for a human observer on site. Data products from the ETC include data from any transients detected, as well as CCD images of the fields-of-view observed. We report here the imaging by the ETC of the 2.5σ error region of GRB 941014 90 seconds after the end of the burst.
EUV Astrophysics with ALEXIS: The Wide View
Authors: Bloch Jeffrey 
Published: July 2016

The Array of Low Energy X-ray Imaging Sensors (ALEXIS) satellite is Los Alamos’ pathfinding small space mission achieving low cost and rapid development time for its technology demonstration and science goals. The ALEXIS satellite contains the ALEXIS telescope array, which consists of six EUV/ultrasoft X-ray telescopes utilizing normal incidence multilayer mirrors, microchannel plate detectors, and thin UV rejecting filters. Each telescope is tuned to a relatively narrow bandpass centered at either 130, 171, or 186 angstroms. Each telescope has a 33° field-of-view, and a resolution of ~ 0.25°. With each 50 s rotation of the satellite, the telescopes scan most of the anti-solar hemisphere of the sky. The spacecraft is controlled exclusively from a ground station located at Los Alamos.This paper discusses the characteristics and performance of the ALEXIS telescopes and the results from the mission in spite of the damage incurred to the spacecraft at launch.
RE J1255+266—Detection of an Extremely Bright EUV Transient
Authors: Dahlem Michael 
Published: July 2016

During a pointed ROSAT observation in the direction of the Coma cluster of galaxies an exceptionally bright EUV source, RE J1255+266, was detected serendipitously. The source is located close to the Galactic North pole, at bII ~ 89°. Its observed EUV flux (62-110 eV) at the time of the detection was of order 7 × 10−9 ergs s−1 cm−2, making RE J1255+266 temporarily one of the brightest EUV sources on the sky.The EUV flare of RE J1255+266 has a light curve with a decay time of about 0.86 days. With respect to earlier non-detections, the source brightened by a factor of > 7000. Such a behavior has not been observed before. Thus, it is unclear what type of source RE J1255+266 might be. The most likely optical counterpart is a faint (V ~ 18.5 mag) object with a blue spectrum (taken from an objective-prism Schmidt plate). For more details on the optical identification see the paper by J. Pye (this conference).Simultaneous observations with CGRO/BATSE resulted in non-detections of the source in the 8-50 keV energy range.
Astrophysical Applications of Delta Scuti Stars
Authors: Breger Michel 
Published: July 2016

AbstractThe δ Scuti stars pulsate with a large number of low-order radial and nonradial p-modes. There also exists some evidence for the presence of g-modes.The pulsational variability outside the classical δ Scuti star instability strip (A1V - F0V on the main sequence) is examined. New measurements do not confirm the short-period variability of the hot B9p star ET And. However, a number of cool, early-F stars shows variability around one day: the γ Dor variables. An explanation involving nonradial g modes appears the most promising.An examination of available information on the multi-periodicity of δ Scuti stars shows no systematic behaviour in which pulsation modes axe excited to an observable level with luminosity and temperature. The asteroseismological potential of δ Scuti vaxiables is briefly examined.So far, the period changes of five luminous Pop. I δ Scuti variables have been studied. While stellar evolution predicts period increases, decreases have been observed and reported for all five stars. The statistical significance of this result and alternative explanations axe briefly examined.
Helioseismology
Authors: Gilliland Ronald L. 
Published: July 2016

AbstractObservations of solar p-mode oscillations over the last two decades have provided a fundamentally new and unique means of probing the Sun’s interior structure. The history of understanding solar oscillations as trapped normal-mode pulsations will be briefly discussed. The large number of excited modes seen in the Sun have been used to constrain the solar core structure, determine the convection zone depth and to fix the variation of angular velocity with depth and latitude. Standard stellar structure and evolution theory does remarkably well in matching the helioseismic results. Further work promises to reveal the solar helium abundance. Upcoming network and space observations should provide the stability and resolution necessary to return detailed information on near-surface structures associated with solar activity.
Long Term Non Linear Thermal Effects in the Pulsation of Mira Variables
Authors: Yaari A. , Tuchman Y. 
Published: July 2016

The main conclusions that can be drawn from most of previous non-linear simulations of LPV (Keeley 1970, Rose & Smith 1972, Wood 1974, Tuchman et al. 1978, 1979) are the following:In all cases where the fundamental mode is predicted, by the linear analysis, to be the dominant, the pulsations are seen to diverge and lead to a rather violent mass-loss process (Wood 1974, Tuchman, Sack & Barkat 1979).A steady pulsation with (roughly) a limit cycle does set in only in those cases where the linear analysis predicts that the dominant mode (with the largest value of the growth rate) is the first overtone (or higher). In all these cases the actual limit cycle is found to be in a good agreement with the linear predictions, with regard to the pulsation mode and period (Wood 1974, Tuchman, Sack & Barkat 1979). However, it is important to note that periods, for these overtone pulsators, are always found to be smaller than 300 days (Wood 1974, Tuchman, Sack & Barkat 1979). Increasing the luminosity of these models, in order to increase their periods, results in a switch to the fundamental mode, followed by the violent relaxation oscillations, mentioned above.
Classical Cepheids and Galactic Structure
Authors: Fernie J.D. 
Published: July 2016

AbstractIn this review I consider recent results on the space distribution of classical Cepheids, first dealing with their Z-distribution normal to the galactic plane, and second considering their X,Y components in the plane. In doing so, use is made of a new database of 505 stars known to be or likely to be classical Cepheids which has recently been compiled by Fernie et al. (1995) and which is available electronically on the World Wide Web at the URL http://ddo.astro.utoronto.ca/cepheids.html, and by anonymous ftp at perseus.astro.utoronto.ca (128.100.77.18) in the directory pub/cepheids.Following the discussion of space distribution, a review of recent work on Cepheid kinematics and the resulting determination of the distance to the galactic centre will be given.
Theoretical Pulsations of Luminous Blue Variables
Authors: Cox Arthur N. , Guzik Joyce A. , Soukup Michael S. , Morgan Siobahn M. 
Published: July 2016

AbstractBoth radial and low degree and order g-mode nonradial pulsations are predicted for luminous blue variables that occur in the blue supergiant region of the Hertzsprung-Russell diagram. It is found that the radial strange modes have very large growth rates due to helium ionization in models at surface effective temperatures between 10,000 and 20,000 K.
Rotation Curve and Metallicity of the Outer Disc from Cepheids
Authors: Pont F. , Queloz D. , Mayor M. , Bratschi P. 
Published: July 2016

AbstractA group of faint, remote Cepheids in the outer disc of the Galaxy has been observed in spectroscopy and photometry. These Cepheids are used as tracers to measure the rotation curve of the disc beyond R=11 kpc, and to study the metallicity gradient in the outer disc.
Properties of the SX Phœnecis Stars in the Metal-Poor Globular Cluster NGC 5053, and Pulsation Modes of Three of the Newly-Discovered SX Phe Stars in 47 Tuc
Authors: Nemec James M. 
Published: July 2016

AbstractThe properties of variable blue stragglers (i.e., SX Phe stars) in the extremely metal-poor globular cluster NGC 5053 are reviewed. Pulsation modes are derived for three of the SX Phe stars recently discovered in the central regions of 47 Tuc by Gilliland et al. (1995a,b).
EROS: Short Period Cepheids in the Bar of the LMC
Authors: Beaulieu J.P. 
Published: July 2016

AbstractWe present Fourier analysis at 490 nm for 87 Cepheid light curves in the bar of the Large Magellanic Cloud. The photometry has been obtained through the EROS project whose main purpose is the search for baryonic dark matter in the Galactic halo. The very high quality of the photometry and the good phase coverage enable us to obtain accurate Fourier decomposition of the light curves. As a consequence we confirm that the so-called s-Cepheids are overtone pulsators and represent about 30 % of our sample, whereas the Classical Cepheids are fundamental pulsators. We have identified a number of features in plots of amplitude ratios and phase differences versus period. These features are usually related to resonances between different pulsation modes. If we accept that Fourier decomposition techniques applied to light curves yield positions for the centres of resonances, then it seems that resonances occur in LMC Cepheids at the same period as in Galactic Cepheids for fundamental pulsators, whereas they appear to be at shorter periods for overtone pulsators.
SUSI’s Potential for Cepheid Studies
Authors: Booth A.J. , Davis J. , Shobbrook R.R. 
Published: July 2016

AbstractThe Sydney University Stellar Interferometer (SUSI) is the first instrument with sufficient resolving power to measure the angular sizes of a large number of stars over the full range of spectral classes. It can also resolve the orbits of spectroscopic binaries, allowing masses and distances to be determined directly. One of the major programs envisaged for the instrument is a study of pulsating stars, in particular Cepheids.
Rapid Photometric and Spectroscopic Variability of the Be Star DX Eri
Authors: Štefl S. , Balona L. A. 
Published: July 2016

AbstractShort-period variations of high-resolution He I 667.8 nm line profiles obtained on 5 nights are analysed and compared to extensiveuvbyphotometry obtained during 1986 – 1993. The separation of short-period and medium-term light variations was done for 4 seasons. All prewhitened magnitudes can be phased with a single period of 1.2564 d. The radial velocity and the first moment of the He I 667.8 line follows the photometric period with a semi-amplitude of 42 km s−1. The large amplitude is very difficult to understand in terms of current models of non-radial pulsation or star spots.
Two Modes of Pulsation in the Rapidly Rotating O9.5 Dwarf, HD 93521
Authors: Reid A.H.N. , Bohlender D. , Bolton C.T. , Fullerton A.W. , Howarth I.D. , Manz C. , Smith K.C. , Townsend R.H.D. 
Published: July 2016

AbstractWe present preliminary results of a time-series analysis on the He II λ4541Å, Si III λλ4552, 4567, 4575Å and Hβ λ486lÅ lines of the late O-type dwarf, HD 93521. The spectra show line-profile variations (lpv) − ‘bumps’ and ‘dips’ − of amplitude ∼ 1% of the continuum, moving systematically redwards through the photospheric absorption lines. The analysis implies non-radial pulsation (NRP) as the origin for the lpv.
Asteroseismology in Open Clusters
Authors: Frandsen S. , Viskum M. , Hernandéz M.M. , Belmonte J.A. 
Published: July 2016

Within two groups or networks we are trying to build the observational fundamentals for better tests of stellar evolution. The first group is STACC (Small Telescope Array with CCD Cameras) and the second the EU HCM program ANTENA (involving institutes in Spain, France and Denmark).The first information needed is photometric data. Colour-Luminosity diagrams and time series photometry must be obtained. The time series require extensive campaigns in order to give the high quality data needed for asteroseismology. Ideally one should have time series of several quantities (see Balona & Stobie 1979, Mantegazza et al. 1994).The second type of observations is of spectroscopic nature. It is needed to ascertain membership of the stars in a given cluster and to check binarity. Also rotational velocities must be observed to help the attempt to identify the modes in 6 Scuti stars. Finally some information about metallicity and peculiarity is required.
Simultaneous Photometric and Spectroscopic Observations of the unusual Variable F-type stars HD 224638 and HD 224945.
Authors: Mantegazza L. , Poretti E. , Bossi M. , Zerbi F.M. 
Published: July 2016

The stars HD 224638 and HD 224945 belong to the new class of F0 V spectral type stars which show an unusual kind of variability for that region of the HR diagram (Mantegazza et al. 1993).The variability of these two stars has been discovered and studied by Mantegazza, Poretti & Zerbi (1994). They show small amplitude light variations with characteristic time scales of the order of one day. The light curves are not periodic and it is difficult to satisfactorily fit them even with several periodic terms.In order to explain our 1991 B colour observations we tentatively suggested that in both stars two close periodic terms were present with a characteristic frequency of about 0.8 c/d, and that these terms had a double wave shape for HD 224638 and a triple wave one for HD 224945.
The Cepheid Data Base
Authors: Berdnikov L. N. 
Published: July 2016

AbstractSince 1981, we have been regularly carrying out photoelectric observations of Cepheids. By now nearly 20450 observations in UBVRI have been acquired. These observations are the basis of our Cepheid data base; presently we have collected on magnetic media near 88000 photoelectric as well as near 18000 radial velocity measurements. We shall continue to append to this Cepheid data base our new observations as well as published data.
Models of the Double-mode Cepheids in the Large Magellanic Cloud
Authors: Petersen J. O. , Christensen-Dalsgaard J. 
Published: July 2016

AbstractVery recently the MACHO Collaboration published detailed data for 45 double-mode Cepheids in the Large Magellanic Cloud. Here we compare these data with new stellar pulsation models. We conclude that the new period ratios are in good agreement with a metal content Z = 0.005 – 0.01 in the Large Magellanic Cloud.
Uncertainties in the Galactic Cepheid Distance Scale
Authors: Barnes Thomas G. , Moffett Thomas J. 
Published: July 2016

AbstractWe have examined the uncertainties involved in using the visual surface brightness technique on Galactic Cepheid variables. The random error in a single Cepheid distance measurement is well determined to be ±8%. An upper limit to the systematic uncertainty is shown to be ±6% in distance. These combine for a single Cepheid to a typical uncertainty of ±10% and, for samples larger than ten Cepheids, to a typical uncertainty of less than ±6% in distance.