bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wide-Field Plate Database: A Progress Report
Authors: Tsvetkov M.K. , Stavrev K.Y. , Tsvetkova K.P. , Mutafov A.S. 
Published: July 2016

AbstractThe current status of a database containing information on wide-field observations stored in plate archives all over the world is presented. The database will permit on-line access to information on nearly 2 · 106 wide-field (⪆ 1 degree) plates and films, obtained over more than a century with about 200 telescopes and cameras.
GCVS Problems with Flare Stars
Authors: Kazarovets Elena V. , Samus Nikolai N. 
Published: July 2016

The astrometric aspect of cataloguing variable stars becomes more and more important. During the past thirty years there has been approximately an three-fold increase of the number of known variables; now the rate of new discoveries becomes extremely high, and we may expect a new twofold increase in a couple of years due to discoveries made with space-borne instruments. To avoid confusion, we should continue our policy of naming new variables, and this is impossible without checking identifications with known variable stars, requiring good coordinates and/or finding charts. Operation of automatic telescopes also needs excellent coordinates just for pointing. For all these reasons, we are now working on improving considerably the accuracy standard of variable star coordinates, providing at least reasonably good coordinates for extragalactic variables (GCVS, 4th Edition, Vol. V, now in press, gives coordinates mainly to a second of arc) and variables in globular clusters, identifying variables, including those with rough published positions, with positional catalogues, etc.Flare stars are very important variables; potentially they are one of the most abundant types of variable stars. Their identification in minimum light may be rather complicated, especially for dense regions of star clusters and associations. Most regretfully, there are many cases of papers on flare stars introducing additional confusion connected with wrong designations, wrong coordinates, missing finding charts. Thus, there appear problems preventing us from incorporating some flare stars in the GCVS. Many definite variables remain in the status of “suspects”, being positionally close to known variables, and no finding chart being available either for the earlier known variable or for the new one. Sometimes we do include such a “pretender” into the GCVS, and years after a finding chart or good coordinates appear, and it turns out that we have two entries for the same star (see, for instance, numerous cases of duplicated names for flare stars in Taurus in the GCVS Vol. III).
Wide-field Cameras for GRB Observations in X-rays and EUV
Authors: Moskalenko Eugene 
Published: July 2016

Recent observations of the ASCA satellite resulted in the first identification of a GB source (Murakami et al. 1994). This success confirmed the importance of simultaneous observations in different wavelength bands for GB studies. Besides the ASCA results, there were several observations of GBs in X-ray band with the Ginga (Yoshida et al,.1989), V 78/1 (Laros et al. 1984) and other satellites. It became clear that GBs emit 4 - 8% of their energy in the 2 - 10 keV range. The main task now is to have an equipment which will be able to monitor the sky in X-rays in a mode similar to that of GRO observations, i.e. the telescope should have an all-sky field-of-view (FoV) and should work continuously.A telescope with these features but operating at soft X-ray energies may directly determine the GB distance scale, due to interstellar absorption of the photons with energies less than 2 keV, as was pointed out first by Schaefer (1993). Flaring sources similar to GBs in time scale may be found also in the EUV (hundreds of angstroms) with the help of very wide-field cameras. Of course each such device - in X-ray, soft X-ray and EUV bands - will discover many transient objects, flaring events, will study time variability of bright “stationary” sources etc. In this paper we describe several instrumental approaches in these fields.
Dissecting the EUV Spectrum of Capella
Authors: Brickhouse Nancy S. 
Published: July 2016

Extreme ultraviolet spectra of Capella, obtained at various orbital phases over the past two years by the EUVE satellite, show strong emission lines from a continuous distribution of temperatures (~ 105 − 107.3 K). In addition to the strong He II λ303.8, the spectra are dominated by emission lines of highly ionized iron. Strong lines of Fe IX, XV, XVI, and XVIII–XXIV are used to construct emission measure distributions for the individual pointings, which show several striking features, including a minimum near 106 K and a local maximum at 106.8 K. Furthermore, intensities of the highest temperature lines (Te > 107 K) show variations (factors of 2–3) at different orbital phases, while the lower temperature Fe lines show variations of about 30% or less. The low variability of most of the strong low temperature features motivates a detailed analysis of the summed spectrum. With ~ 280 ks of total exposure time, we have measured over 200 emission features with S/N ≥ 3.0 in the summed spectrum. We report here initial results from the analysis of this spectrum. We can now identify lines of Fe VIII and X–XIV, as well as a number of electron density and abundance diagnostic lines.We also report here the first direct measurement of the continuum flux around ~ 100 Å in a cool star atmosphere with EUVE. The continuum flux can be predicted from the emission measure model based on Fe line emission, and demonstrates that the Fe/H abundance ratio is close to the solar photospheric value.
Features of the Soft X-ray Background and Implications for the EUV Background
Authors: Barber C.R. , Warwick R.S. 
Published: July 2016

A series of eight overlapping ROSAT PSPC observations situated in the Lockman hole region have been analysed in the 0.1 – 0.4 keV band. The total exposure of ~ 137 ks and the ultra-low interstellar column density make the data extremely suitable for studies of the diffuse signal. After excluding the contribution of bright discrete sources the remaining signal was examined on a scale of 20′. As expected the 0.1 – 0.4 keV signal exhibits a strong anticorrelation with column density. However, there is also evidence for significant excess fluctuations superimposed on this anticorrelation which may be attributable to some form of cloud structures within the hot ISM.The diffuse signal expected in the ROSAT WFC all-sky survey for this region is predicted and shown to be far in excess of that observed. The origin of the fluctuations in the soft X-ray background and their possible relevance to the Extreme-Ultraviolet background are discussed.
Searching EUVE Data for Transient/Flaring Extreme Ultraviolet Sources
Authors: Lewis J. , Bowyer S. , Lampton M. , Wu X. , Mathioudakis M. 
Published: July 2016

The Extreme Ultraviolet Explorer (EUVE), because of its sky survey strategy, performed two observations of each point along a 180° by 1° strip of the ecliptic during the initial survey phase of the mission. One observation used the deep survey telescope, and another, 90 days earlier or later, used the all sky scanner telescopes, two of which have a nearly identical passband to that of the ecliptic deep survey. Since the completion of the initial sky survey, EUVE has been used to carry out deep, pointed observations of selected targets. Many areas of the sky have therefore been observed two or more times, allowing us to compare count rates for some objects over a long temporal baseline. Objects with significantly varying count rates for widely separated times are of particular astrophysical interest.With this technique, we have discovered one such object, which appears in the First EUVE Source Catalog as EUVE J2056-171. We present upper and lower limits on how frequently other highly-variable objects will be detected by EUVE in future observations.
Rapid Pulsations in Ap Stars
Authors: Martinez Peter , Kurtz D.W. 
Published: July 2016

AbstractThe rapidly oscillating Ap (roAp) stars are upper mainsequence stars that pulsate in non-radial p modes of high overtone. We present an observer’s overview of the roAp phenomenon and discuss significant developments since the last major observational reviews of Kurtz (1990a) and Matthews (1991).
Simulated Power Spectra of Solar-Type Oscillations Driven by an Elementary Excitation Source
Authors: Roxburgh I. W. , Vorontsov S. V. 
Published: July 2016

AbstractWe consider the synthetic power spectra of multi-mode solar-type acoustic oscillations in stars, computed within a general framework of the linear response of the dynamical system to an arbitrary excitation force which is decomposed in spherical harmonics in space and harmonic functions in time. We discuss possible signatures in the observational data which might be used as diagnostics of the excitation source.
Yellow Supergiants and R Coronae Borealis Stars
Authors: Cottrell P.L. 
Published: July 2016

AbstractThe study of luminous variable stars has important consequences both with respect to the scale of the Universe and for our understanding of the later stages of stellar evolution.This review will look at a number of groups of these stars, in particular the RV Tauri stars, the hydrogen-deficient Carbon (HdC) stars, including the R Coronae Borealis (RCB) stars and some aspects of Cepheid variables.Both photometric and spectroscopic observations will be presented to show the amount of progress that has been made in this area over the last several years. Links will be made to various models which are being used to understand the observational data.The most important conclusion is that there is still enormous scope for the acquisition and detailed analysis of data on the relatively bright members of these groups of stars. These can be used to provide further understanding of the more distant objects of each group and of the wider problems in astrophysics.
Pulsating Cool Stars and Galactic Structure
Authors: Whitelock Patricia 
Published: July 2016

AbstractThe review concerns the use of Miras and OH/IR stars as probes of Galactic structure and concentrates on groups of stars with both kinematic and luminosity data. The reliability of distance determinations for these stars is covered in some depth. Kinematic and scale height data for local Miras suggest that those with pulsation periods of around 200 day are members of the thick disk or inner halo. Longer-period stars are kinematically cooler and have smaller scale heights. Stars with moderate dust shells, which may be more evolved, seem to belong to the same population as thin-shelled sources with the same pulsation period. Our current knowledge of the structure of the Galactic Bulge is reviewed, as is our understanding of its rotation as derived from observations of SiO Masers from Mira variables. Infrared and radio surveys, in progress or planned, offer us the potential to extend the study of low-mass metal-rich stars well beyond the solar neighbourhood.
Pulsating Stars and the Distance Scale - I
Authors: Walker Alistair R. 
Published: July 2016

AbstractA summary is given of recent measurements, by various methods, of the absolute magnitudes for RR Lyrae stars. Calibrations within our galaxy, using the Baade-Wesselink method and by Statistical Parallaxes, give a result that is some 0.2–0.3 mag fainter than is obtained by all other methods considered. The resolution of this conundrum will be likely in the near future when new and improved datasets become available.
Pulsating Stars and the Distance Scale - II
Authors: Feast Michael 
Published: July 2016

AbstractThe current Cepheid zero-point is equivalent to an LMC distance modulus of 18.57 ± 0.10. The zero-point from corrected Baade-Wesselink data is probably not significantly different from this. A reexamination of the Baade-Wesselink data for RR Lyrae variables leads to an LMC modulus of 18.51, an age difference between β- and α-group galactic globular clusters of +1.46±0.70 Gyr, and an Mv - [Fe/H] slope in agreement with theory. Other questions discussed include; Avoiding bias in using the Cepheid PL relation; Metallicity spread amongst Cepheids; Cepheids and Ho.
Common Misconceptions about the Galactic Cluster Calibration of the Cepheid PLC Relation
Authors: Turner David G. 
Published: July 2016

Comments in the literature in recent years reveal a variety of misconceptions about the role and value of galactic clusters for calibrating the Cepheid period-luminosity-colour (PLC) relation. This paper attempts to clarify some of these points using personal experiences gained from studies of the sparse galactic clusters and groups in which some classical Cepheids are located.Reddening is often blamed for problems originating from other causes. Three features of reddening are sometimes overlooked: (i) no universal reddening law applies to all fields, (ii) mean reddening laws are not applicable to samples of dispersed objects, and (iii) patchy extinction is the norm.
Light Variability of 28 Aql
Authors: Wehlau William , Wehlau Amelia 
Published: July 2016

28 Aquilae (HR 7331, V1208 Aql) was first announced as a δ Scuti type variable by Breger in 1969 with a period of about 0.15 day. It was clear that the light variability could not be adequately represented as a sinusoidal variation with just one frequency. Since then several observers have provided additional light curves and new analyses of the light variation. In this paper we discuss observations which we have made and an analysis of the data available since 1966.Our objective was to find the frequencies of components which would represent the light variation of 28 Aql over the 28 years for which the star has been observed.Using the 30 cm reflector of the Hume Cronyn Memorial Observatory we observed 28 Aql in 1979, 1980, 1981, and 1993 in blue light. The light curves for JD 2444140 and 2449190 are shown below. Comparison stars were HD 180868 and HD 181383. Magnitude differences are referred to HD 181383. Nights on which the scatter in the observations, due to poor transparency, appeared to be excessive were discarded. Observations on 21 nights were retained for analysis.
The Variable Star Population in the Center of 47 Tuc as denned by HST Observations
Authors: Gilliland Ronald L. , Edmonds Peter D. , Petro Larry , Saha Abhijit , Shara Michael 
Published: July 2016

AbstractThe high stellar densities at the centre of some globular clusters provide prolific breeding grounds for exotic stars, e.g., the 11 msec pulsars in 47 Tuc and numerous blue stragglers. The same high density of stars as viewed on the sky makes ground-based photometry problematic for variable star detection. Even a very few tight binaries can be of fundamental importance for the dynamic evolution of the cluster core. We present results of a continuous 40-hour sequence of U-band CCD exposures acquired with WF/PC on HST. The high spatial resolution coupled with a stable PSF allows nearly Poisson limited time series on some 20,000 stars. The 1000 second sampling and long coverage provide excellent sensitivity to W UMa and δ Scuti variations. Light curves are shown for selected variables and the relative frequencies of binary and variable stars are discussed.
Estimating Cepheid Metallicities: a new approach
Authors: Zsoldos E. 
Published: July 2016

AbstractA relation between the Fourier decomposition parameters of Cepheid light curves and metallicities in the form [Fe/H]=f({Ri1, ρi1}) is presented. It gives [Fe/H] values with prediction errors 0.16−0.22 dex depending on the number of Fourier parameters used in the relation.
Comparison of the Galactic Cepheid Open Cluster and Surface Brightness Distance Scales
Authors: Gieren Wolfgang P. , Fouqué Pascal 
Published: July 2016

AbstractWe compare the best determined Baade-Wesselink (BW) period-luminosity (PL) relation for 100 galactic Cepheids to the PL relation derived for 32 open cluster and association Cepheids by the ZAMS-fitting method. Eighteen stars in common lead to the conclusion that BW and ZAMS-fitting distances can agree to better than 0.1 mag, after proper allowance of systematic effects in both methods.
The Long-term Variation in the RV Tauri Star U Mon
Authors: Pollard Karen R. , Cottrell P. L. 
Published: July 2016

The RV Tauri stars are semiregular pulsating variables located in the brightest part of the Cepheid II instability strip. They have a characteristic light curve of alternating deep and shallow minima. A subset of the RV Tauri stars (the RVb subclass) exhibit long-term (500 to 2600 day) light and radial velocity variations. Although it is well established that the short-term variations are due to pulsations, the long-term behaviour is not well understood.BVRI photometry and high-resolution spectra of U Mon (the brightest member of the RVb subclass) were obtained at the Mt John University Observatory (MJUO) between 1990 Aug and 1994 May. The light and colour curves obtained clearly show the long-term variation in U Mon (Fig. 1(a) and (b)). The reddest colours occur slightly later than the long-term minimum in the light curve. The short-term light and colour variations are ‘damped’ at the long-term minimum.
An Analytic Theory of Adiabatic p-modes in the Atmospheres of the Sun and Sun-like Stars
Authors: Dzhalilov Namig S. , Staude Jürgen 
Published: July 2016

AbstractAn analytic theory of resonant transmission has been used to study adiabatic, non-vertical oscillations in a realistic model of the solar or a stellar atmosphere and subphotosphere. Basic observed features of solar p-modes can be explained in this way.
On Expected Constraints on Stellar Transport Processes from Space Seismic Missions: EVRIS, COROT
Authors: Goupil M.J. , Michel E. , Cassisi S. , Dziembowski W.A. , Lebreton Y. , Baglin A. , Auvergne M. , Catala C. 
Published: July 2016

The first space seismological experiment, EVRIS (Baglin 1991) will be launched in 1996 and will observe ∼ 10 stars over ∼ 20 days each. A second one, COROT (Catala et al., 1994), should follow soon after (1999-2000), which should monitore ∼ 5 stars over ∼ 5 months each. The observed stars will be main sequence stars. For an optimum scientific outcome of EVRIS mission, one must select the best possible target stars. The first step of this selection is outlined. What would be further gained with COROT project is discussed.Specifications of both missions imply that among possible target stars,δScuti stars should present a large number of self excited modes, likely many more than presently observed from ground based networks.
Time Resolved Optical Spectroscopy of V795 Her
Authors: Dickinson R. J. , Prinja R. K. , Rosen S. R. , Horne K. 
Published: July 2016

AbstractWe present high resolution optical spectroscopy of the cataclysmic variable (CV) V795 Her. The time- and phase- dependent behaviour of the emission source is examined using two-dimensional image analysis and Doppler reconstruction techniques on the orbital profiles. A clear S-wave modulation of a weak emission feature in the Hβ and Hγ line wings (extending to ~1800 km s−1) is present, with complex asymmetric properties.
Slingshot Prominences During Dwarf Nova Outbursts?
Authors: Steeghs D. , Horne K. , Marsh T. R. 
Published: July 2016

AbstractWe present phase-resolved spectroscopy of two dwarf novae, IP Peg and SS Cyg, observed in outburst with the WHT/ISIS spectropolarimeter. Doppler tomograms of several emission lines show peculiar narrow, stationary emission components.
SPH Simulations of Tidally Unstable Accretion Disks
Authors: Murray James 
Published: July 2016

We use two dimensional Smoothed Particle Hydrodynamics simulations to investigate the the Tidal Resonance Instability (TRI) model for superhumps in SU UMa stars.In the TRI model, superhumps are the signature of an eccentric disk being periodically stressed by the binary system’s rotating tidal field. A slow prograde motion of the disk in the inertial frame is then responsible for the superhump period slightly exceeding the binary orbital period. The disk eccentricity is caused by a 3:1 resonance between orbits in the disk and the orbit of the binary itself. The development of the TRI model is due mainly to Whitehurst (1988), Hirose & Osaki (1990) and Lubow (1991a). Lubow in particular carried out a nonlinear mode analysis of a fluid disk’s response to a weak tidal field and identified the feedback mechanism responsible for disk eccentricity growth.
The Intermediate Polars
Authors: Hellier Coel 
Published: July 2016

AbstractRecently discovered intermediate polars extend the limits of known behaviour. They now fill the range between, and overlap with, nonmagnetic CVs and AM Hers. They have a wide range of asynchronism, a full range of field strengths, and several different accretion modes and pulsation mechanisms. I highlight (i) a puzzle over the symmetry between magnetic poles, (ii) the X-ray spectra, (iii) the similarity with polars, and (iv) the mass of EX Hya.
The Hard X-Ray Spectra of EF Eri and Other CVs
Authors: Done C. , Osborne J. P. , Beardmore A. P. 
Published: July 2016

AbstractReflection of the X-ray emission from the surface of the white dwarf should be present in all hard X-ray emitting CV systems. It is clearly identified in the Ginga 2… 20 keV spectra of the polars AM Her and EF Eri, and also in the quiescent spectra of the dwarf novae SS Cyg. The inclusion of the hard reflection spectrum lowers the derived continuum temperature, so resolving a long standing problem of the mismatch of the iron line and continuum properties, and, with more realistic multi-temperature continuua, the derived shock temperatures are close to those expected from theoretical models of a strong shock.
QQ Vul Revisited
Authors: Catalán M.S. , Davey S. D. , Smith R. C. , Jones D. H. P. 
Published: July 2016

AbstractWith simultaneous blue (λλ4200–5000 Å) and far-red (λλ7950–8380 Å) phase-resolved, high resolution spectrophotometry, we re-examine the magnetic CV QQ Vul. A thorough radial velocity and flux analysis of all the observable features is carried out. We derive a complete set of system parameters and classify the donor star to be a spectral type M4.5 V. In addition to the Balmer, He I and He II emission lines in the blue range, arising from the accretion regions, we detect various emission features which solely follow the movement of the secondary star. The lines, which we interpret as reprocessed light from the illuminated hemisphere of the donor star, are Mg II at λ4481 Å, He II at λ8236 Å and C I at λ8335 Å. Intensity maps based on the line flux and radial velocity variations of the Na I absorption near λ8190 Å and Mg II emission feature were also made. These show that the line distribution on the surface of the donor is consistent with being symmetric. As a result of our analysis the position of the real zero phase was found to be at ϕ = 0.42 of the linear polarisation ephemeris.
RX J1015.5+0904: A New Polar at the Lower Period Limit
Authors: Burwitz V. , Reinsch K. , Schwope A. D. , Beuermann K. , Mengel S. , Notni P. , Van Teeseling A. , Thomas H.-C. 
Published: July 2016

AbstractWe present X-ray and optical observations of the ROSAT discovered polar (AM Her binary) RX J1015.5+0904 and first results of our analysis of the X-ray and optical data. These results indicate a one-pole accretion geometry and an orbital period of P = 79.88 m for this V ~ 17 mag system.
Accretion Disk Winds in Cataclysmic Variables
Authors: Knigge Christian , Drew Janet E. , Mason Keith O. 
Published: July 2016

AbstractWe present preliminary results of a modelling campaign based on HST eclipse observations of the wind-formed C IV resonance line in the eclipsing nova-like variable UX UMa. Within the framework of a simple kinematic accretion disk wind model, we are currently able to reproduce the shapes (but not the strengths) of the observed line profiles away from and during eclipse, as well as the behaviour of the integrated line flux light curve. The most important aspect of our modelling is that it suggests the presence of a vertically extended, relatively dense and slow moving transition region between the disk photosphere and the fast wind.