bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Optical Polarization in Flat-Spectrum Radio Sources
Authors: Wills D. , Wills Beverley J. , Antonucci R.R.J. , Barvainis Richard , Breger Michel , Bailey J. A. , Hough J. H. , Ballard K. 
Published: June 2019

We have made a polarimetric survey of 84 quasi-stellar objects, to supplement published polarization measurements for two samples of quasars identified with flat-spectrum (core-dominant) radio sources in 5 GHz surveys made at Bonn (Kühr 1980) and at the VLA (Perley 1982). The observations were made using the McDonald 2.1m Struve reflector and the polarimeter described by Breger (1979); the typical accuracy is 0.5% for an 18 mag object after half an hour. Earlier surveys, such as those by Stockman, Moore and Angel (1984), included objects of various radio spectral types, and only a small fraction of the objects showed high polarization (> 3%), but our sample of flat-spectrum quasars reveals many more (about half) of the objects to be highly polarized. Some of them are, expectedly, of the BL Lac class, but many of them have strong broad emission lines. There are two striking correlations among the results:
(1)The degree of polarization is strongly correlated with the dominance of the radio core - specifically, with the ratio, R, of core to lobe luminosity (Fig. 1). For example, about 75% of the objects with log R > 1.25 and redshift z < 1 have p > 3%. This relation implies that if the radio core radiation is beamed, as seems likely, then so is the optical synchrotron component.(2)The fraction of objects with p > 3% is inversely correlated with redshift (e.g. Fig. 2). The most likely interpretation of this result is that quasars' degree of polarization decreases with decreasing rest wavelength, and the shorter wavelengths are shifted into our wide observational passband at higher redshifts.
Lyman α Emission from Disk Absorption Systems in QSOs: Star Formation in Young Galaxy Disks
Authors: Smith Harding E. , Cohen Ross D. , Burns Joseph E. , Moore David J. , Uchida Barbara 
Published: June 2019

The strong self-damped Lyman α absorption systems present in the spectra of high redshift QSOs represent a unique population of absorber which has recently been associated with the precursors of current disk galaxies. In a low resolution survey for what we have come to call “Lyman α disk systems” performed at Lick Observatory (Wolfe, et al. 1986, Ap. J. Suppl. 61, 249) approximately 18 systems with confirmed damped Lyman α profiles and rest frame equivalent widths greater than 5 Å were detected in a sample of 68 high redshift QSOs (Smith, Cohen and Bradley 1986, Ap. J. 310, 583). Subsequent higher resolution study has shown these systems to have the following properties (Turnshek, et al. 1988, Ap. J., in press):
1.Neutral hydrogen column densities, 2 × 1020 ≤ NHI ≤ 8 × 1021 cm−2.2.Low-mixed ionization state. Typically the low ionization states dominate the high ionization states (e.g. CII ≫ CIV). Some enrichment has occurred, −2≲[X/H]⊙ ≲0.3.Gas density, n ≲ 1 cm−3.4.The gas shows two components, a quiescent (disk) component, σν ≲ 10 km s−1, and a turbulent (halo) component, σν ≲ 20 km s−1. Some systems show only the low velocity dispersion component.5.At least one system intervening toward a radio QSO (Pks 0458-020) shows 21-cm absorption. The system shows multiple cloud structure with σν ≈ 6 km s−1, Ts ≈ 100 K, and structure extended over several kpc on the sky.6.There is evidence that these systems may be self gravitating with scale height of the order of 300 pc.7.These systems represent a unique population of absorber (distinct from the ‘Lyman a forest’ and heavy element systems) covering approximately 20% of the sky to z ≈ 3 and accounting for all of the baryonic matter at that redshift.
Assisting Extrasolar Planetary Detection Through the Determination of Stellar Space Orientations
Authors: Doyle Laurance R. 
Published: June 2019

Various methods outlined for indirect planetary detection would greatly benefit (in some cases require) the determination of the planetary orbital plane, which is theoretically equivalent to the stellar equatorial plane. Determining the stellar space orientation, therefore, would greatly benefit extrasolar planetary detection.We utilize stellar rotation periods determined from short-term variations in Call H&K sunspot emission combined with both stellar radii measurements and Doppler broadened spectral line profiles to get the stellar inclination to the line of sight.The clocklike, on the plane-of-the-sky component determination utilizes the concentration of sunspot associated plage areas at central stellar latitudes when viewed in Call H or K emission. One can perform Call H&K emission speckle interferometry to measure the clocklike angle of this stellar Call H&K emission band, modeling it as an elliptical intensity distribution. Both components should be determinable to within ten degrees for at least resolvable fifth magnitude stars.
The Structure and Internal Kinematics of Open Clusters
Authors: Mathieu Robert D. 
Published: June 2019

Open clusters provide an opportunity for observational study of several important facets of stellar dynamics which cannot easily be addressed in globular clusters for either fundamental or practical reasons. In particular, open clusters are case studies for:
1)The dynamics of small-N stellar systems. This aspect of open clusters has been excellently reviewed by King (1980), to which the reader is referred. The work of Retterer (1979) and Goodman (this volume) suggests that any differences in the velocity distributions of small-N systems as compared to large-N systems due to the increased importance of close stellar encounters will appear primarily in the high-energy tails of the distributions. This will be reflected in the structure of the cluster halos, where quality data are difficult to obtain. In order to guide observational study, more theoretical work is needed regarding the expected nature and magnitude of any observable deviations from large-N theory.2)The effects of a large stellar-mass spectrum. While globular clusters probably also have a spectrum of masses spanning an order of magnitude or more, the extension of the mass spectrum to higher masses in open clusters permits the dynamical consequences of a mass spectrum to be more easily studied. In addition, many studies have pointed out the significance of stellar mass lośs in massive stars for the evolution of clusters (e.g., Terlevich 1983). However, as yet the theory regarding the effects of such mass loss has not provided unique observational predictions which might act as critical tests, so this important issue will not be discussed further here.3)A spectrum of cluster ages. Open clusters span the complete spectrum of age from birth to dissolution. Except for the classic work of Wielen (1971 and this volume) in which he analyses the observed distribution of cluster ages, this feature of open clusters has been little exploited. Yet by mapping appropriate diagnostics with cluster age open clusters have the potential to provide empirical measures of the fundamental dynamical time-scales, e.g. the relaxation time, equipartition time and mixing time. Also, study of the very youngest clusters provides appropriate initial conditions for evolutionary models as well as insight into star- and cluster-formation processes.4)The effect of the external environment. Open cluster halos are molded by the galactic tidal field. In addition, open clusters are subject to Impulsive encounters with clouds in the interstellar medium. The effects of these environmental influences can be examined in numerous ways, including detailed analyses of the structure of cluster halos and observations of the variation with radius of anisotropy in the cluster velocity distributions.
Space astrometry prospects and limitations
Authors: Kovalevsky J. , Mignard F. , Froeschlé M. 
Published: June 2019

Among the few parameters that describe the generalized space time metrics, astrometric techniques are essentially sensitive to the displacement of the apparent positions of celestial bodies. This includes the relativistic light deflection and aberration. The possibilities of small field and wide field astrometry in measuring these effects are described. The case of the second order aberration terms is considered with some detail from the theoretical point of view, both for stellar and planetary aberration. New results are presented in the latter case.A section is devoted to a description of the existing space astrometry projects among which Space Telescope and HIPPARCOS are approved but will not contribute significantly to relativistic studies. Several “second generation” projects exist that aim at 2 or 3 orders of magnitude improvement in precision. They would yield results on second order relativistic effects and may be used to determine masses of some single stars. However, the present state of engineering of space astrometric missions has permitted to identify several limitations of the present and future missions. They will not all be readily suppressed and one should be very careful in assessing now their potentialities. It seems however that interferometric techniques have more chance to reach the 10−4and 10−5arc second precision than the imaging methods.
Evolution of PN Morphologies: Concepts, Models and Observations
Authors: Balick Bruce 
Published: June 2019

The shapes of planetary nebulae (PNs) provide paleontological clues about the origin and evolution of the gas expelled in the late phases of stellar evolution. The morphological classes of planetaries and various structural components of the nebulae are interpreted as hydrodynamic interactions of episodes of relatively brief, axisymmetric wind driven mass-loss events. Theoretical studies of the past five years are compared with extant data to show that astrophysical hydro models are achieving a very high level of success as explanations for the shapes of most PNs.The most successful models are those for which the star is assumed to expel much or most of its mass in an equatorial wasteband. In stark contrast are dense ansae, dense and low-ionization knots of fast-moving gas, for which the mass distribution is decidedly polar. The origins of both the equatorial wastebands and polar knots remain decidedly enigmatic.
Perturbation of the Non-Radial Oscillations of a Gaseous Star by an Axial Rotation, a Tidal Action or a Magnetic Field
Authors: Smeyers P. 
Published: June 2019

The study of the linear and adiabatic oscillations of a gaseous star gives rise to an eigenvalue problem for the pulsation σ, if perturbations proportional to eiσt are considered. In the presence of a rotation, a tidal action or a magnetic field, the equations are not separable in spherical coordinates. To get approximate expressions for the influence of these factors on the non-radial oscillations of a star, the author and his collaborators J. Denis and M. Goossens have used a perturbation method (Smeyers and Denis, 1971; Denis, 1972; Goossens, 1972; Denis, 1973). Their procedure corresponds to a generalization of the method proposed by Simon (1969) to study the second order rotational perturbation of the radial oscillations of a star.Two types of perturbations are taken into account: volume perturbations due to the local variations of the equilibrium quantities and to the presence of a supplementary force in the equation of motion (Coriolis force, Lorentz force); surface perturbations related to the distortion of the equilibrium configuration and to the change of the condition at the surface in the presence of a magnetic field. The resulting expressions are accurate up to the second order in the angular velocity in the case of a rotational perturbation, to the third order in the ratio of the mean radius of the primary to the distance of the secondary in the case of a tidal perturbation, and to the second order in the magnetic field in the case of a perturbing magnetic field. These expressions can in principle be applied to any mode.Numerical results have been obtained for a homogeneous model and for a polytropic model n = 3. In particular, the splitting of the frequencies of the fundamental radial mode and of the f-mode belonging to l = 2 and m = 0 has been studied for the critical value of y, in the case of a component of a synchronously rotating binary system.
The Art of Fitting P-Mode Spectra
Authors: Appourchaux T. , Gizon L. 
Published: June 2019

For deriving p-mode parameters from m, v diagrammes, one has to treat correctly the statistics of the observation. The correct statistical treatment of these diagrammes was first achieved by Schou (1992) (PhD thesis, Aarhus University). Fitting p-mode spectra requires 4 major steps:
1.Compute the mode leakage matrices2.Compute mode covariance matrices from the previous matrices3.Compute the noise covariance matrices4.Compute and maximize the likelihood of the observation
Solar Internal Rotation
Authors: Schou Jesper ,   The SOI Internal Rotation team
Published: June 2019

With the flood of high quality helioseismic data from the instruments on the SOHO spacecraft (MDI/VIRGO/GOLF) and ground based instruments (e.g. GONG, LOWL, BiSON, IRIS, MWO-CrAO and TON) we have been able to get increasingly detailed information on the rotation and other large scale flows in the solar interior.Here we will discuss some of the highlights of what we have learned so far and what we may expect to learn in the near future. Among the recent advances have been tighter constraints on the tachocline at the bottom of the convection zone and detection of details in the surface rotation rate similar to the torsional oscillations found in the surface Doppler shift.
The Galactic Nucleus
Authors: Oort J. H. 
Published: June 2019

The ionized gas within 2 parsec from the centre region is distributed in spiral-like features which appear to emanate from a nucleus. This nucleus is close to the ultra-compact radio source and the infrared source IRS 16, but does not exactly coincide with either. The spiral is strongly inclined to the galactic plane. The arms are clumpy. The spiral appears to rotate, but there appear to be also large radial motions.The phenomena show some resemblance to what is observed on a very much larger scale in the nuclei of radio galaxies and quasars.An exceptionally powerful, variable source of hard X- and gamma-rays, GCX, has been found in the direction of the centre. This may be the true galactic nucleus. Strong, variable emission of the 511-keV electron-positron annihilation line has also been observed to come from the central region.The evidence for a central black hole is discussed. It is not compelling. The energy required for the strong infrared radiation emitted by the central few parsecs is probably coming from a large number of luminous stars, and due to a recent burst of star formation. The observed state of ionization indicates the burst to have occurred about one million years ago.The distribution of the dense molecular clouds within 300 pc from the centre is very asymmetric: practically all lie at positive longitudes. Their motions differ radically from circular motions. The layer of clouds is tilted relative to the galactic plane. The so-called “+40-km/s cloud” lies in front of the nuclear spiral, and is therefore moving towards the centre. Different interpretations of the systematic motions are considered. The outspoken asymmetry excludes a static condition. If the “molecular ring” at R ~ 150 parsec is actually an expanding feature, its origin might be sought in the same burst of star formation proposed to explain the state of ionization and the infrared radiation of the nuclear region.
I/ Geography of the Mogollon Area
Authors: Wheat Joe Ben 
Published: June 2019

In cultural terms, the Southwest has never been satisfactorily defined. This is particularly true of the southern boundaries. Archeologists usually include the territory occupied by the groups we term Anasazi, Hohokam, Mogollon, and Patayan; it is this area that will be considered here.Physiographically (Atwood 191+0; Darton 1925; Fenneman 1931), the northern and eastern parts of this area belong primarily to the Colorado Plateaus Province; the southern and western parts comprise a portion of the Basin and Range Province. Physiographers subdivide these major provinces into lesser units having more significance for the archeologist. The Colorado Plateaus Province is marked primarily by high mesas and plateaus underlain by nearly horizontal strata of strong, cliff-producing rocks locally covered by volcanic features or domed by igneous intrusions. This extensive area is drained largely by the Colorado River and its tributaries. Among the distinguishing features are the hundreds of deeply entrenched canyons and great retreating cliffs or escarpments.
Astrophysics in the 1890s – The Dawn of a New Age in Astronomy
Authors: Hearnshaw J. B. 
Published: June 2019

AbstractThe Konkoly Observatory was established as a public institution in Hungary in 1899, when Nicholas von Konkoly Thege (1842–1916) bequethed his private observatory at Ógyalla to the state. Konkoly himself was one of the pioneers in the new science of astrophysics, and he was an expert in astronomical instruments used for photometry and spectroscopy.In this paper I review, from a global perspective, the 1890s decade as ten years of prodigious achievements in stellar astronomy, with many huge programmes being launched and undertaken in spectral classification, radial velocities, photometry and astrometry. New astrophysical observatories were founded in America and Europe and new large telescopes designed and built, and the first international conferences were held in astronomy.Astrophysics was still a largely qualitative science in the 1890s, but this was soon to change in the early years of the present century. I review the development of astrophysics in the 1890s, its interaction with new discoveries in physics, and comment on some of the large projects in stellar photometry, spectroscopy and astrometry and especially the influence of photography on observational astrophysics. The place of Nicholas von Konkoly in this overall endeavour is discussed and I pay tribute to his considerable influence and to the observatory he founded. A century of state-funded astronomy in Hungary has been the result.
Impact of the Sloan Digital Sky Survey on Variable Star Research
Authors: Ivezić Željko , Goldston Josh , Finlator Kristian , Knapp Jill , Yanny Brian ,   the SDSS Collaboration
Published: June 2019

AbstractWe present the results of a preliminary search for variable objects in about 100 deg2 of SDSS commissioning data surveyed twice with Δt=1.99462 days. In particular, we find that the density of RR Lyrae star candidates abruptly ends at a galactocentric radius of 50–60 kpc.
Red Variables from the MOA Database
Authors: Takeuti Mine , Noda Sachiyo , Bond I. A. , Rattenbury N. J. , Abe F. , Carter B. S. , Dodd R. J. , Hearnshaw J. B. , Honda M. , Jugaku J. , Kabe S. , Kilmartin P. M. , Masuda K. , Matsubara Y. , Muraki Y. , Nakamura T. , Reid M. , Rumsey N. J. , Saito To. , Sato H. , Sekiguchi M. , Sullivan D. J. , Sumi T. , Watase Y. , Yanagisawa T. , Yock P. C. M. , Yoshizawa M. 
Published: June 2019

AbstractThe red variables whose amplitude is larger than 1.3 mag in the MOA database are studied for the LMC. Among 3 196 such stars, 532 stars are likely to be Miras or red semiregular variables. The period–colour relation of these stars is shown.
Pulsation of the AGB Variable in the Symbiotic Nova PU Vulpeculae
Authors: Chochol D. , Pribulla T. 
Published: June 2019

AbstractAnalysis of the 1993–4 eclipse in the slow symbiotic nova PU Vul (4900-d binary orbital period) and 1995-9 photoelectric observations in V and R bandpasses show that the cool component of this object is pulsating AGB variable with a 215-d pulsation period. Basic properties of the components of the system are discussed.
Optical and Radio Monitoring of a Sample of Late-Type Variables
Authors: Esipov V. F. , Lekht E. E. , Pashchenko M. I. , Rudnitskij G. M. 
Published: June 2019

AbstractResults of regular observations of about 20 Miras and semiregular variables (∘ Cet, R Leo, R Aql, U Her, χ Cyg, R Tri, and others) in 1994–1999 are presented. The monitoring includes optical spectroscopy, optical (UBV) and infrared (JHKLM) photometry, high-resolution radio spectroscopy in the 1.35-cm water-vapour maser line (on the 22-m radio telescope in Pushchino). Optical spectroscopy shows that the appearance of strong Balmer emission lines in Miras may be a rare event, and the presumed shock waves are thus weak. The H2O maser flux generally correlates with visual light curves of the stars with some delay Δφ = 0.1 – 0.4P (P is the variability period). For R Leo, R Cas, and U Aur strong flares in the Hφ line, observed in 1997–1998, were followed by corresponding outbursts of the H2O maser emission about 2P later. This sequence of events is probably caused by a shock wave propagating outward in the stellar atmosphere and consecutively initiating the Hα emission and, later, the maser flare at a larger distance from the stellar surface.
Cepheids in the Nearby Galaxy IC 1613
Authors: Antonello E. , Mantegazza L. , Fugazza D. , Bossi M. , Covino S. 
Published: June 2019

AbstractA summary of the first results of a search for Cepheids in IC 1613 is reported along with a short discussion of the adopted technique, a comparison of the characteristics of Cepheid light curves in the Galaxy, Magellanic Clouds and IC 1613, and a possible application for a P–L relation derivation. First overtone Cepheids have been identified for the first time in a galaxy farther than the Magellanic Clouds.
Accurate Fourier Decomposition of Cepheid Radial Velocity Curves
Authors: Moskalik P. , Krzyt T. , Gorynya N. A. , Samus N. N. 
Published: June 2019

AbstractThe shapes of light curves and of radial velocity curves are two main predictions of the hydrodynamical models of Cepheids. Of the two, the velocity curves are more robust numerically and therefore, more suitable for comparison with the observations. In this report, we present accurate Fourier parameters for an extensive set of classical Cepheid velocity curves. Published radiative models reproduce the observations very well, with only small discrepancies present. We estimate the center of the ω2 = 2ω0 resonance to occur at Pr = 9.947 ± 0.051 day
Structural Properties of s-Cepheid Velocity Curves: Constraining the Location of the ω4 = 2ω1 Resonance
Authors: Kienzle F. , Pont F. , Moskalik P. , Bersier D. 
Published: June 2019

AbstractThe light curves of the first overtone Pop I Cepheids (s-Cepheids) show a discontinuity in their ϕ21 vs. P diagram, near P = 3.2 d. This feature, commonly attributed to the 2:1 resonance between the first and the fourth overtones (ω4 ≈ 2ω1), is not reproduced by the hydrodynamical models (Antonello & Aikawa 1995). With the goal of reexamining the resonance hypothesis, we have obtained new CORAVEL and CORALIE radial velocity curves for 17 overtone Cepheids. Together with 10 objects from Krzyt et al. (2000), the combined sample covers the whole range of overtone Cepheid periods. The velocity Fourier parameters display a strong characteristic resonant behavior. In striking contrast to photometric ones, they vary smoothly with the pulsation period and show no jump at 3.2 d. The existing radiative hydrodynamical models match very well the velocity parameters. The center of the ω4 = 2ω1 resonance is estimated to occur at Pr = 4.58 ± 0.04 d, i.e. at a period considerably longer than previously assumed (3.2 d). Five new s-Cepheids, with periods above 5 d, have been identified from the radial velocity curves morphology: V419 Cen, V659 Cen, MY Pup, GH Car and V440 Per. The data and the discussion can be found in Kienzle et al. (1999). Preprints and the data are available at: http://obswww.unige.ch/˜kienzle.
The RR Lyrae Period–Amplitude Relation
Authors: Clement Christine M. 
Published: June 2019

AbstractA study of the period–amplitude relation for RR Lyrae variables in the globular clusters 47 Tucanae, NGC 6441 and M55 confirms a recent finding that the period–amplitude relation for RRab stars with ‘normal’ light curves is not a function of metal abundance. Evolutionary effects are more important.