bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemically Peculiar Stars Among Spectroscopic Binaries – Revisited
Authors: Seggewiss Wilhelm 
Published: July 2016

AbstractThis paper presents a new statistical investigation of peculiar A-type stars (Am, Ap, Hg-Mn) among spectroscopic binary (SB) stars. The relative frequency of Am (CP 1) stars is 55% in the spectral range A1 to A6 of main-sequence stars. The Ap (CP 2) stars amount to 15% in the range B9 to A2. The Hg-Mn stars are concentrated to the spectral types B8 to AO and reach a relative frequency of 23%. The Am SB stars have the shortest orbital periods and the smallest eccentricities (30% circular) whereas the Ap SB stars show a strong tendency to long periods and highly eccentric orbits (only 10% circular). The masses of the Am stars agree with the masses of non-peculiar SB stars of corresponding spectral type.
Magnetic Fields: Observations and Topology
Authors: Landstreet J. D. 
Published: July 2016

AbstractTo understand the complex physical processes revealed by the wide variety of surface chemical abundances and the inhomogeneous distributions of various elements over the surfaces of magnetic Ap and Bp stars, it is important to be able to describe the surface magnetic field structure. For most magnetic stars, the available observations are far from sufficient to define the surface magnetic structure even with low resolution, but more extensive and constraining observations are gradually becoming available for a small set of stars. This paper discusses the extent to which the surface field structure can be defined for stars for which only the usual measurements (essentially the variation of the mean longitudinal field strength Bɩ with rotational phase) are available, and how further information (variation of mean field modulus Bs with phase, line profile observations, and circular and linear spectropolarimetry of absorption lines or broad-band radiation) can be used to obtain a much more detailed picture of the magnetic field structure.
Broadband Measurements of the Transverse Magnetic Field of Cool Ap Stars
Authors: Leroy J.-L. , Landstreet J.D. , degl’Innocenti E. Landi , Landolfi M. 
Published: July 2016

AbstractObservations of variable broadband linear polarization in magnetic Ap stars (due to the transverse Zeeman effect), when combined with measurements of the mean longitudinal field Bɩ can in some cases allow one to determine the angles i and β (which describe the inclination of the stellar axis of rotation and the obliquity of the magnetic axis to the rotation axis) much more accurately than these angles can be determined from observations of Bɩ alone. Such variable intrinsic linear polarization has been observed for a number of stars; the effect is generally detectable only in cool Ap stars of unusually large field strength. We discuss the data and simple modelling for the stars HD 24712 = HR 1217, HD 137909 = β CrB, and HD 62140 = 49 Cam.
Broadband Linear Polarization in Ap Stars
Authors: Landolfi Marco , Degl’Innocenti Egidio Landi , Degl’Innocenti Maurizio Landi , Leroy Jean-Louis , Bagnulo Stefano 
Published: July 2016

AbstractBroadband linear polarization in the spectra of Ap stars is believed to be due to differential saturation between σ and π Zeeman components in spectral lines. This mechanism has been known for a long time to be the main agent of a similar phenomenon observed in sunspots. Since this phenomenon has been carefully calibrated in the solar case, it can be confidently used to deduce the magnetic field of Ap stars.Given the magnetic configuration of a rotating star, it is possible to deduce the broadband polarization at any phase. Calculations performed for the oblique dipole model show that the resulting polarization diagrams are very sensitive to the values of i (the angle between the rotation axis and the line of sight) and β (the angle between the rotation and magnetic axes). The dependence on i and β is such that the four-fold ambiguity typical of the circular polarization observations ((i,β), (β,i), (π-i,π-β), (π-β,π-i)) can be removed.
Variations of Ultra-Violet Lines for C, N, and O in the Ap Stars HD 18296 and HD 25823
Authors: Gonzalez Jean-François , Artru Marie-Christine 
Published: July 2016

AbstractFrom the rotational variation of UV resonance lines of carbon, nitrogen, and oxygen, we study the irregular distribution of these elements upon the surface of two magnetic Ap stars: HD 18296 (21 Per) and HD 25823 (41 Tau).
Search for λ Bootis Stars in Open Clusters
Authors: Pavlovski K. , Schnell A. , Maitzen H.M. 
Published: July 2016

AbstractIt was shown by Maitzen & Pavlovski (1989) that a majority of λ Bootis stars stand out by negative Δα indices. Using this as detection tool, three candidate stars with λ Bootis characteristics are picked up in open cluster Praesepe.
Determination of Luminosity, Atmospheric Structure, and Magnetic Geometry from Studies of the Pulsation in roAp Stars
Authors: Kurtz D. W. , Martinez Peter 
Published: July 2016

AbstractFor several of the rapidly oscillating Ap stars the best luminosity estimates available come from the asteroseismological interpretation of their pulsational frequency spectra. We give a list of the 23 currently known roAp stars along with their Strömgren photometric indices, Teffestimated from the Hβindex, and luminosity estimated asteroseismologically. In one case,ϒEqu, we have an asteroseismological luminosity and a parallax luminosity which are in good agreement. Some of the roAp stars pulsate with frequencies greater than the critical frequency calculated for standard A-star models. This plus multi-colour high-speed photometry of HR 3831 indicate that the temperature gradients in the atmospheres of these stars are substantially steeper than in standard A-star models. We advocate a fine analysis of HR 3831 to see if there is consistency with the pulsational conclusions about T-τin this star. Further fine analyses and multi-colour pulsational analyses on other roAp stars are then called for. The pulsation mode in HR 3831 can be decomposed into primarily an axisymmetric dipole mode with small radial, quadrupole and octupole perturbations. If the magnetic field is governing the distortion of this mode from a purely dipole mode, then the pulsation can be used to infer the magnetic field geometry. Comments on our current knowledge of all 23 roAp stars are made.
Wide-field Astronomy with Tech Pan Film - A Positive Outlook for Schmidt Photography
Authors: Parker Quentin A , Phillipps Steven , Morgan David 
Published: July 2016

AbstractThe introduction of film-based Kodak Technical Pan emulsion at the UKST has led to a new lease of life for deep, wide-field astrophotography. This is because the excellent imaging, resolution and low noise characteristics of Tech Pan typically yield a one magnitude depth gain over equivalent IIIa-F plates. Many new projects are underway to take advantage of the significant information gains. The cheap cost of film and ease of transportation gives direct economic benefits too. Tech Pan could also offer a medium term, competitive alternative to CCD mosaics for providing new, deep, wide-field surveys via stacking of several digitised exposures of the same field. A one magnitude gain could result from the stacking of just 6 Tech Pan films to yield an R ∼ 23.5–24. Even without digital co-addition the largest current CCDs cannot hope to match Tech Pan’s inherent ∼ 3 µm resolution and the 40 square degree area coverage of the UKST.
Faint Features of Galaxies revealed by the Digital Co-addition of Schmidt Plates
Authors: Kemp S. N. , Meaburn J. 
Published: July 2016

AbstractWe have digitally co-added eight IIIa-J/GG395 UKST plates centred on the IC 4296 cluster of galaxies. The factor of increase in S/N in the co-added array enables galaxy profiles to be followed, and filamentary and diffuse features to be detected, down to bj surface brightnesses of 28 mag arcsec−2. Examples of warped disks, shells, trails, diffuse IGM and extended haloes revealed by this technique are discussed and illustrated.
An Infrared Colour Discriminator for Giant and Supergiant Optical M Stars
Authors: Raharto Moedji 
Published: July 2016

AbstractAn infrared colour - MK spectral type diagram of optical M giants, M Miras and M supergiants is presented. The area in the diagram with m12 − m25 > 0.70 and MK spectral type earlier than M4 is occupied by early type optical M supergiants. The region of spectral type later than M4 is occupied by optical late M giants (Mira variables) and late M supergiants. The area in the diagram with a colour range of 0.15 < m12 − m25 < 0.70 is occupied by optical giants (Mira Variables) and supergiants (M supergiants with blue companions and probably some M supergiants in the evolutionary stage pre or post M supergiants with large infrared excesses). Finally, the area in the diagram with m12 − m25 < 0.15 is clearly occupied by M giants without circumstellar dust shells. The colour distribution of the M giants, M supergiants and M Miras in the colour - spectral type diagram suggests that we can use the colour properties as search criteria for (i) early M supergiants with colours of m12 − m25 > 0.70, (ii) late M supergiants with colours of m12 − m25 > 0.70, (iii) M giants with m12 − m25 < 0.15, (iv) Mira candidates using IRAS point sources which are also identified as optical M stars.
Nature of Emission-Line Stars in the Outer Orion Region
Authors: Nakano Makoto , McGregor Peter J. 
Published: July 2016

AbstractNear-infrared photometry is reported for 76 emission-line stars in outer regions of the Orion molecular cloud complex. Most of our program stars are selected from the Hα emission-line star catalog of the large-scale Kiso Schmidt survey of the Orion region. We confirm that most of the emission-line stars with strong emission detected in the Kiso survey are typical T Tauri stars with masses in the range 0.5 to 2 M⊙. Low mass stars have therefore continued to form in the outer parts of the Orion region, away from present day massive molecular clouds, until at least as recently as a few million year ago.
CCD Observations of Gravitational Lenses and Extragalactic Supernovae with the Brorfelde Schmidt Telescope
Authors: Florentin-Nielsen Ralph , Joergensen Henning E. 
Published: July 2016

AbstractThe Brorfelde Schmidt telescope has been modified to use a 1024 × 1024 12 micron pixels CCD camera. The field is 27 × 27 arcmin. When required, the spatial sampling is improved by co-adding multiple exposures with small offsets. The telescope is operated in service mode, with one observer carrying out several different observing programmes in parallel. The telescope is particularly well suited for long term monitoring programmes, most notably photometric monitoring of gravitationally lensed QSOs and searches for extragalactic supernovae.
Quasar Spectroscopy with FLAIR
Authors: Parker Quentin A. , Clowes R.G. , Watson F.G. 
Published: July 2016

AbstractWe demonstrate that the multi-object fibre-spectroscopy system ‘FLAIR’ on the UKST can be used to observe efficiently and effectively the brighter (B < 18.5) high-grade quasar candidates identified from UKST low-dispersion objective-prism plates. The quasar candidates were selected objectively by the application of AQD (automatic quasar detection) to prism plates that have been digitised using the COSMOS measuring machine. Thirteen high-grade quasar candidates with B ≤ 18.5 from a prism plate of ESO/SERC survey field 296 were observed with a 35-fibre version of FLAIR. From a total observing time of only 3 hours at a resolution of 8.4 Å/pixel six candidates were confirmed as quasars and four were identified as stars. The planned upgrade to a thinned, back-illuminated CCD in 1994 should yield a 3-fold increase in sensitivity and further enhance the capabilities of FLAIR for performing useful spectroscopic observations of quasars of moderate faintness over large areas of sky.
Basic principles in spectro-imaging Foreword on Marseilles Observatory - 3D spectroscopic methods
Authors: Courtès G. 
Published: July 2016

AbstractFocal reducers provide efficient solutions to the drawbacks introduced by the large focal length of direct foci on large modern telescopes. They house a variety of spectroscopic devices, and lead to various families of spectroimagers. Rational filterings, BPM irmltisimultaneous bandwidths, extreme spectral resolution of the field scanner interferometers (Tully’s first design, Taurus, Cigale) and their image reconstruction, as well as the possibility to obtain the spectra of all image elements of the field owing to the new (Tiger and Silfid) integral field spectrographs sometimes combined with Fabry Perot Interferometers (Pytheas) are now within reach. In classical spectrography the focal reducer leads to the optimized size Baranne’s white pupil spectrograph.
A New Technique for Characterising Planetary Nebulae in External Galaxies
Authors: Taylor K. , Douglas N.G. 
Published: July 2016

AbstractPlanetary Nebulae are proving to be powerful tertiary distance indicators as well as sensitive probes of a galaxy’s velocity field and mass distribution. We present a new technique for determining the positions, luminosities and radial velocities of the PNe in an external galaxy which may enable a one-step measurement of all these parameters.
Fabry-Perot Imaging of the Seyfert 2 Galaxy NGC 2273: Preliminary Report
Authors: Golev V. , Bonev T. , Jockers K. , Yankulova I. 
Published: July 2016

AbstractNarrow-band images of the ringed Seyfert 2 galaxy NGC 2273 = Mark 620 taken with tunable Fabry-Perot interferometer are presented. Some preliminary contusions are outlined.
Area Spectroscopy of the Extended Emission Line Region in the Seyfert Galaxy NGC 3516
Authors: Aoki K. , Ohtani H. , Kosugi G. , Yoshida M. 
Published: July 2016

The researches into extended emission line region (EELR) give us the valuable informations about the nucleus. A recent study of the EELR in the Seyfert 1 galaxy NGC 4151 by Yoshida and Ohtani (1993) have revealed that a strongly asymmetric radiation field in this typical Seyfert 1. They have suggested the anisotropy may be caused inside the BLR. It is important to examine if any other Seyfert 1 galaxy has an anisotropic nuclear radiation.The famous Seyfert 1 galaxy NGC 3516 has EELR which extends ∼ 10” on either side of the nucleus. The morphology of the EELR is Z-shape. This nearby (D=38.9Mpc) galaxy is of type SBO for which the object is expected to be free from contamination by HII regions and dust clouds.
Bidimensional Spectroscopy with the 6-meter Telescope in Time Resolving Mode
Authors: Afanasiev V. L. , Dodonov S. N. , Drabek S. V. , Vlasiouk V. V. 
Published: July 2016

Degradation of images of astronomical objects during observations with large optical telescope may be described as combination of atmosphere turbulence on a time scale shorter than some tenths of a second and random fluctuation of object’s position due to telescope and observer’s guiding errors, bending of construction under external factors (wind, etc.). Special investigations on the 6-meter telescope (Balega, 1989) showed, that the peak frequency of such low-frequency fluctuations is located near 1 Hz.The method of Time Resolving Image Mode, developed by J.-L.Nieto et al (1987) for post-detection improvement of angular resolution at CFHT, showed that, even in places with excellent quality of atmosphere, the resolution of large telescope may be increased by 20-30% only, although powerful methods of image recentering and frames selection were performed. Moreover, such method of data processing may be applied to relatively bright objects only. For 6-meter telescope, resolution improvement would be useless at all due to smaller Fried parameter and larger main mirror.
Reduction of 3D Spectral Data, Obtained with the 6-meter Telescope
Authors: Vlasiouk V. V. 
Published: July 2016

Development of 3D spectral methods on the 6-meter telescope prompted the necessity of creating specialized software for data reduction, adapted to personal computers IBM AT/386/486 class. We had to concentrate our efforts on preparing the software for bidimensional spectral data produced by Multi-Pupil Integral Field Spectrograph of the 6-meter telescope (MPFS) and analog of panoramic spectrophotometer with spectral channeling, using scanning Fabry-Perot interferometer (PYTHEAS-6).MPFS - analog of spectrograph TIGER (Courtes et al., 1988), developed for the 6-meter telescope, provides bidimensional spectroscopy of extended sources, allowing the simultaneous detection of 99 individual spectra, produced by a lens raster from 9 by 11 microlenses. The main features of this instrument are described in (Afanasiev et al, 1994).
Expansion of HII Regions in Density Gradients
Authors: Franco José , Tenorio-Tagle Guillermo , Bodenheimer Peter 
Published: July 2016

AbstractThe main features of HII regions expanding in spherical and disk-like clouds with density gradients are reviewed. The spherical cases assume power-law density stratifications, r~w, and the disk-like cases include exponential, gaussian, and sech2 distributions. For power-law profiles, there is a critical exponent, wcrit = 3/2, above which the ionization front cannot be “trapped” and the cloud becomes fully ionized. For clouds with w < 3/2, the radius of the ionized region grows as t4/(7-2w) and drives a shock front into the ambient neutral medium. For w = wcrit = 3/2 the shock wave cannot detach from the ionization front and the two move together with a constant speed equal to about 2ci, where ci is the sound speed in the ionized gas. For w > 3/2 the expansion corresponds to the “champagne phase”, and two regimes, fast and slow, are apparent: between 3/2 < w ≤ 3, the slow regime, the inner region drives a weak shock moving with almost constant velocity through the cloud, and for w > 3, the fast regime, the shock becomes strong and accelerates with time.For the case of disk-like clouds, which are assumed cylindrically symmetric, the dimensions of the initial HII regions along each azimuthal angle, θ, are described in terms of the Strömgren radius for the midplane density, Ro, and the disk scale height, H. For yo = Rosin(θ)/H ≤ α (where α is a constant dependent on the assumed density distribution) the whole HII region is contained within the disk, and for yo > α a conical section of the disk becomes totally ionized. The critical azimuthal angle above which the HII region becomes unbounded is defined by θcrit =sin-1(αH/Ro). The expansion of initially unbounded HII regions (i.e. with yo > α) proceeds along the z-axis and, if the disk column density remains constant during the evolution, the ionization front eventually recedes from infinity to become trapped within the expanding disk. For clouds threaded by a B-field oriented parallel to the symmetry axis, as expected in magnetically dominated clouds, this effect can be very prominent. The expanding gas overtaken by the receding ionization front maintains its linear momentum after recombination and is transformed into a high-velocity neutral outflow. In the absence of magnetic fields, the trapping has only a short duration.
Observations of the Progenitor Wind of SN 1987A
Authors: Wampler E.J. , Richichi A. , Baade D. 
Published: July 2016

AbstractAs part of a general ESO program to monitor the spectrum of SN 1987A, we are collecting intermediate high resolution (R = λ/Δλ ≈ 2x104) spectra of the supernova. By the end of the year 1987 it was possible to see narrow emission features due to [OIII] and hydrogen in spectra taken with the ESO Cassegrain echelle spectrograph (CASPEC) (Wampler and Richichi 1988, 1989). At that time, the velocities of these lines were about 286 km/sec and their widths were about 14 km/sec (FWHM). It is almost certain that these lines arise from a cloud of highly ionized gas that was first detected in ultraviolet spectra obtained by IUE in May 1987 (Fransson et al. 1989). This cloud is presumably a circumstellar shell that surrounded the progenitor of SN 1987A and was ionized by the initial UV flash from the supernova explosion. In the ideal case of an expanding spherical shell that is large enough for light travel times to be important, one would expect the intensity of an emission line to increase and then decrease again as the light from the front of the shell fades. At the same time the velocity of the line would increase as the integrated light became dominated by light from the back (receding) hemisphere. The IUE light curve (Fransson et al. 1989) for the ultraviolet [NV] line was consistent with the photometric behavior expected from a nebula about 400 light days in diameter. At the distance of the LMC, one light year is equal to a span of one arc-second, and the photometric behavior of [NV] is consistent with the extent of the nebula measured by Wampler and Richichi (1989).
The Trapezium Radio Cluster of the Orion Nebula
Authors: Garay Guido 
Published: July 2016

Abstract.We review the characteristics and discuss the nature of a dense group of compact radio sources found projected toward the Trapezium cluster of the Orion nebula. There are twenty-six radio sources, with flux densities greater than 2 mJy, clustered within a region of 35” radius around θ1C Orionis, the most luminous star of the Trapezium. The density of radio objects, of 1.4×104 pc-3, is extraordinarily high, about a thousand times greater than the density of stars in typical galactic clusters.
Numerical Simulation of CME Propagation in a Helmet Streamer: Emerging Magnetic Flux Mechanism
Authors: Zhang J. H. , Wu S. T. , Dryer M. , Wei F. S. 
Published: July 2016

AbstractWe examine a limited parametric study of time-dependent, numerical MHD simulations of coronal mass ejectsion (CMEs). The physical initiating mechanims (at the base of a helmet-streamer magnetic configuration) is assumed to be magnetic flux that emerges from below the photosphere. The peak flux is taken to be viariable in both magnitude and polarity as well as with/without additional physical mechanisms that include emerging mass and momentum flux. We find that magnetic flux of sufficient magnitude and with polarity opposite to that of the overlying helmet’s magnetic field can be a distinct, physically- viable mechanism. We also find: (i) with an appropriate magnetic driver, it is not necesssary to add an arbitrary heating function to a pre-event helmet-streamer, as suggested by Steinolfson and Hundhausen (1988) to produce observed CME features; nor (ii) is it necessary to introduce anad hocaccelerating mechanism to a plasmoid as sugested by Linkeret al. (1990). However, we agree with the latter workers that the CME driving mechanism has the same importance as the configuration of the initial ambient corona in the determination of the mass ejection’s evolution as detected by coronagraphs.
The Free Energies of Partially Open Magnetic Fields and Coronal Mass Ejections
Authors: Smith D. F. , Low B. C. 
Published: July 2016

AbstractThe results of Low and Smith (1993) on how to circumvent Aly’s limitation on the energy of force-free magnetic fields are briefly reviewed. Two non-force-free configurations with energies in excess of the energy of the corresponding completely open field are discussed: 1. A magnetic bubble configuration with completely detached field lines. 2. A combined configuration consisting of closed field lines with plasma compressed against the star and a superimposed helmet streamer with all field lines tied to the surface. The results of Low and Smith are extended by considering the stability of these two-dimensional equilibria. It is shown that the bubble configuration is unstable. The stability of the combined configuration can only be answered by a numerical analysis because of the stabilizing effect of line-tying.