bluuebunny/crossref_metadata_2025_split huggingface dataset:
The star formation histories of Low Surface Brightness galaxies
Authors: Bell E.F. , Bower R.G. , de Jong R.S. , Rauscher B.J. , Barnaby D. , Harper D.A. , Herald M. , Loewenstein R.F. 
Published: July 2016

AbstractNear-infrared images of a sample of red, blue and giant low surface brightness disk galaxies (LSBGs) were combined with optical data with the aim of constraining their star formation histories. Most LSBGs have strong colour gradients consistent with mean stellar age gradients. We find that LSBGs have a large range of ages and metallicities, spanning those observed in normal disk galaxies. In particular, red and blue LSBGs have very different star formation histories and represent two independent routes to low B band surface brightness. Blue LSBGs are well described by models with low, roughly constant star formation rates, whereas red LSBGs are better described by a ‘faded disk’ scenario.
A new catalogue of multiple galaxies in the Local Supercluster
Authors: Makarov D. I. , Karachentsev I. D. 
Published: July 2016

AbstractA new approach is suggested which makes use of the individual properties of galaxies, for the identification of small galaxy groups in the Local Supercluster. The criterion is based on the assumption of closed orbits of the companions around the dominating group member within a zero velocity sphere.The criterion is applied to a sample of 6321 nearby galaxies with radial velocities V0 ≤ 3000 km s−1. These 3472 galaxies have been assigned to 839 groups that include 55% of the sample considered. For the groups identified by the new algorithm (with k ≥ 5 members) the median velocity dispersion is 86 km s−1, the median harmonic radius is 247 kpc, the median crossing time is 0.08(1/H), and the median virial-mass-to-light ratio is 56 M⊙/L⊙.
Dark Matter in Groups and Clusters of Galaxies
Authors: Einasto Jaan , Einasto Maret 
Published: July 2016

AbstractWe compare the characteristics of stellar populations with those of dark halos. Dark matter around galaxies, and in groups, clusters and voids is discussed. Modern data suggest that the overall density of matter in the Universe is ΩM = 0.3 ± 0.1, about 80 % of this matter is nonbaryonic dark matter, and about 20 % is baryonic, mostly in the form of hot intra-cluster and intragroup gas, the rest in stellar populations of galaxies. All bright galaxies are surrounded by dark matter halos of external radii 200 − 300 kpc; halos consist mostly of non-baryonic matter with some mixture of hot gas. The Universe is dominated by dark energy (cosmological constant) term. Dark matter dominates in the dynamical evolution of galaxies in groups and clusters.
Mass Distribution in Compact Groups
Authors: Perea J. , del Olmo A. , Verdes-Montenegro L. , Yun M. S. , Huchtmeier W.K. , Williams B. A. 
Published: July 2016

AbstractNew redshift surveys of galaxies in the field of compact groups have discovered a population of faint galaxies which act as satellites orbiting in the potential well of the bright group. Here we analyze the mass distribution of the groups by comparing the mass derived from the bright members and the mass obtained from the satellite galaxies. Our analysis indicates the presence of a dark halo around the main group with a mass roughly four times that measured for the dominant galaxies of the compact group.We found that heavier halos are ruled out by the observations when comparing the distribution of positions and redshifts of the satellite galaxies with the distribution of satellites of isolated spiral galaxies. The results agree with a picture where compact groups may form a stable system with galaxies moving in a common dark halo.
Small Satellite Probes of Spiral Galaxies
Authors: Erickson Lance , Gottesman Steve , Hunter James 
Published: July 2016

AbstractSmall, bound satellites of larger spiral galaxies are employed in the determination of the statistical presence of mass beyond the rotation disk of the largest (primary) galaxy. Optical and neutral hydrogen data are combined to develop mass estimates using the small bound groups. The resulting distribution of the internal/external mass ratios provides limits on halo mass models, and a glimpse at this mass estimation technique.
The evolution of groups and clusters
Authors: Gottlöber S. , Klypin A. , Kravtsov A. V. , Turchaninov V. 
Published: July 2016

AbstractUsing high resolution N-body simulations we study the formation and evolution of clusters and groups in a ΛCDM cosmological model. Groups of galaxies already form before z = 4. Merging of groups and accretion leads to cluster formation at z ≲ 2. Some of the groups merge into large isolated halos.
The Visual Absolute Magnitude of the Central Objects in Be Stars
Authors: Moujtahid A. , Zorec J. 
Published: July 2016

AbstractUsing the circumstellar envelope parameters (mean temperature, extent and opacity) derived by fitting theoretical energy distributions to those observed in a sample of 20 Be stars, we estimate the respective magnitude difference ΔV = V – V* of the continuum flux excess produced by their circumstellar envelopes. Using then the HIPPARCOS parallaxes of these stars and the ISM E(B-V) colour excesses derived with the surrounding normal B stars, we estimate the visual absolute magnitude of the central objects in the program Be stars. In most cases the results obtained are in good agreement with the absolute magnitudes obtained from the photospheric (λ1, D) components derived in the BCD spectrophotometric system. There are, however, strong discrepancies in 4 program stars which deserve further studies. The magnitude excess seems to be ΔV ≲ 0 for the higher effective temperatures only. There is no correlation between ΔV and Vsin i, as would be expected if the circumstellar envelopes were strongly flattened.
X-ray Emission from Isolated Be Stars
Authors: Cohen David H. 
Published: July 2016

AbstractI discuss the X-ray observations of Be stars, and how their properties compare to non-emission B stars. I focus on several specific stars that show high flux levels and variability but also report on several interesting survey results. The Be X-ray properties are discussed in the context of wind-shock X-ray emission from normal OB stars as well as in the context of general mechanisms that have been proposed to explain the Be phenomenon. Finally, I conclude with a discussion of the spectral diagnostics that will be available from the new generation of X-ray telescopes.
Watching Binary Systems with Be Components with the GI2T-REGAIN Spectro-Interferometer
Authors: Thureau N. , Bonneau D. , Mourard D. , Stee P. , Vakili F. , Harmanec P. 
Published: July 2016

AbstractOur program aims at observing selected bright multiple Be stars using the technique of long-baseline optical spectro-interferometry with the GI2T-REGAIN interferometer. These observations - combined with spectral and photometric observations and with appropriate modelling - will bring new constraints on the nature and evolutionary stage of multiple Be stars through an accurate determination of their basic physical properties.
Multimode Detections from Surveys
Authors: Aerts C. 
Published: July 2016

AbstractIn this study we present an overview of the search for multiple frequencies in variable Be stars from surveys. We review the recent ground-based photometric surveys and conclude from them that multiperiodicity is not detected. The photometric experiment on board Hipparcos, on the other hand, does allow us to derive multiple periods for a few Be stars. We present the results of our frequency searches in the Hipparcos data for 50 λ Eri stars.Further we review the recent spectroscopic campaigns dedicated to some stars. It seems that all of these campaigns point to multiperiodic phenomena, although for most of them the time base is insufficient to derive the periods with high accuracy. Moreover, the spectroscopic periods are often not the same as those found from the photometry. This clearly demonstrates the necessity of long-term simultaneous photometric and spectroscopic campaigns. We present the preliminary results of such a campaign for the λ Eri star HD 105382.We close with reflections on the cause of the variability observed in the λ Eri stars and on the best viewpoint for further research in this area.
Fundamental Parameters of Be Stars Derived from Near-Infrared Spectra
Authors: Houziaux L. , Frémat Y. 
Published: July 2016

AbstractBecause of their spectral peculiarities, stellar parameters of objects undergoing the Be phenomenon cannot be determined in the same way as for normal B stars. In particular, the use of the first lines of the Hydrogen series is hampered by the presence of emission components. On the other end, the recently generalized use of CCD detectors, well adapted to the deep red spectral region, provides a large amount of quantitative and well calibrated flux measurements with spectral resolutions around 0.1 nm. We propose to use the shape of the continuum and line flux distribution in the range of the higher Paschen lines of Hydrogen to determine first the effective temperature and superficial gravity of Be stars where, in most cases, the photospheric spectrum is not disturbed by line or continuum emission.
Influence of the Plasma Opacity in the Calculations of IR Emission Due to Dielectronic Recombination of Mg II
Authors: Cruzado Alicia , Ringuelet Adela E. 
Published: July 2016

AbstractIn an earlier work (Cruzado, Di Rocco & Ringuelet, 1998), we showed that the dielectronic recombination of Mg II atoms contributes strongly to the infrared flux. In the present paper we aim at investigating whether the approximations made before could have biased our conclusions.
Continuum Flux Excess in Be Stars Determined from Spectral Lines
Authors: Zorec J. , Ballereau D. , Chauville J. 
Published: July 2016

AbstractWe study the continuum flux excess at λ4471 by comparing the observed He I λ4471 line profiles with non-LTE model line profiles. Assuming that emission of the Hγ line is formed nearly in the same regions of the circumstellar envelope as those where the visible continuum flux excess rises, we estimate the continuum opacity needed to account for the veiling of the He I λ4471 line. The flux excess so derived is then studied as a function of the stellar aspect angle in an attempt to determine the degree of incidence of the envelope geometry near the central star on the continuum flux of Be stars.
Discrete Structures in the CS Envelope of the Be star ζ Tau
Authors: Ballereau D. , Chauville J. , Cao H. , Floquet M. , Hubert A.M. , Zorec J. 
Published: July 2016

AbstractThe recent cycle of the V/R ratio and RV variations in ζ Tau has been found similar to that reported by Delplace (1970). As a rule, in both cycles, singly-ionized metallic shell lines display discrete components when the descending branch of RV curve of Balmer lines crosses the stellar RV value; a narrow sharp feature is mainly superimposed on a broad and bluer one, both being slowly varying over some months; very weak additional components are suspected on stronger Fe II lines. On another hand, in the ascending branch of RV curve (RV ≥ RVstar), secondary shell components varying in intensity are conspicuous on V and R emissions of the first Balmer lines.
Global One-armed Oscillations in the Be/X-ray Binary LS I +61° 235/RX J0146.9+6121
Authors: Reig P. , Negueruela I. , Coe M.J. , Fabregat J. , Tarasov A.E. 
Published: July 2016

AbstractWe present results of our long-term monitoring of LS I +61° 235 in the optical and infrared bands. This Be/X-ray binary exhibits V/R variability in the Hα line, which can be explained in the framework of the Global One-armed Oscillation model: a high density perturbation moves around inside the circumstellar disc of the Be star. The V>R and V<R peaks occur when the perturbation moves towards and away from the observer, respectively. In this work we show that the perturbation also affects the He I λ6678Å and Paschen lines. We also report on a correlation between the infrared emission and the V/R variability.
Confirmation of a Moving Component in the Hα Emission Line of LS I+61°303
Authors: Zamanov Radoslav K. , Martí Josep 
Published: July 2016

AbstractWe report our attempts to detect and confirm a narrow moving component in the Hα emission line of LS I+61°303. The existence of this spectral feature was already suspected in the past. As a result, we find that this component does exist and that its radial velocity varies in agreement with the radio period of the system. We interpret it tentatively as due to a denser region, or bulge, orbiting near the outer edge of the Hα emitting disk.
Pulsar Timing at Urumqi Astronomical Observatory
Authors: Wang Na , Wu XinJi , Zhang Jin , Manchester R. N. , Yusup Aili , Cheng K. S. 
Published: July 2016

AbstractA pulsar timing system has been set up using the 25-m Nanshan telescope of the Urumqi Astronomical Observatory. It uses a dual polarization receiver operating at 18 cm and a filterbank receiver. The data acquisition system is based on a PC using the Windows NT operating system. Timing properties of about 100 pulsars will be monitored with this system.
Detection of new emission components in PSR B0329+54
Authors: Gangadhara R. T. , Gupta Y. , Lorimer D. R. 
Published: July 2016

AbstractTo study the structure of emission beam, we have analysed the single pulse data of PSR B0329+54 at 325 and 606 MHz. In order to unambiguously detect the weak emission components, we have developed a new data analysis technique, which we term “window-thresholding”. By applying this technique to the data, we have detected three new emission components, and also confirmed the presence of a component which was proposed earlier. Hence our analysis indicates that PSR B0329+54 has nine components, which is among the highest of all the known pulsars. The symmetric distribution of pulse components about the pulse centre, indicates that the emission beam is conal.
Fine Phase Resolved X-ray Spectroscopy of the Crab Pulsar with BeppoSAX
Authors: Massaro E. , Litterio M. , Cusumano G. , Mineo T. 
Published: July 2016

AbstractWe present the results of a phase resolved spectroscopy of the Crab pulsar in the band 0.1 - 200 keV based on many observations performed with BeppoSAX. The spectrum was found soft in the main peak and significantly harder in the Interpeak region. This behaviour is explained by means of a two component model.
Coherent Mechanisms of Pulsar Radio Emission
Authors: Lyutikov Maxim , Blandford Roger , Machabeli George 
Published: July 2016

AbstractRelativistic plasma masers operating on the anomalous cyclotron-Cherenkov resonanceω−k||υ||+ωB/ϒres= 0 and the Cherenkov-drift resonanceω−k||υ||−kx/ud= 0, are capable of explaining the main observational characteristics of pulsar radio emission. Both electromagnetic instabilities are due to the interaction of the fast particles from the primary beam and from the tail of the secondary pairs distribution with the normal modes of a strongly magnetized one-dimensional electron-positron plasma. In a typical pulsar both resonances occur in the outer parts of magnetosphere atrres≈ 109cm.
Radiating Regions in Pulsar Magnetospheres: From Theory to Observations and Back
Authors: Usov Vladimir V. 
Published: July 2016

AbstractWe discuss plausible locations of radiating regions in the magnetospheres of pulsars and argue that the mechanisms of pulsar radiation at different frequencies are closely connected with the locations of the radiating regions, especially in the radio range. If the region that is responsible for the bulk of the non-thermal radiation at some frequency is localized in the pulsar magnetosphere then the nature of this radiation will be either determined or, at least, restricted significantly.
Some Peculiaritiers of the Relativistic Electron-Positron Plasma Dynamics in the Pulsar Magnetosphere
Authors: Nanobashvili Irakli S. 
Published: July 2016

AbstractSome aspects of relativistic electron-positron plasma dynamics in the pulsar magnetosphere are discussed. Namely it is shown that if we take into account the influence of centrifugal force, this gives rise to the new dynamical effect of plasma particle radial braking in the pulsar magnetosphere. Also the possibility of aperiodic instability development in the pulsar magnetosphere is demonstrated. The mechanism for the toroidal magnetic field generation is proposed. Besides, the possible changes of the pulsar magnetosphere structure caused by above mentioned processes is considered.
Kitab as One of the Five Stations of the ILS: History and Present
Authors: Ehgamberdiev Sh.A. , Eshonkulov S.K. , Litvinenko E.A. 
Published: July 2016

AbstractThe Tashkent Astronomical Observatory (Ulugh Beg Astronomical Institute of the Uzbek Academy of Sciences since 1966) was involved to the International Latitude Service (ILS) in September 1899, when the regular latitude measurements were started at Tschardjui (ϕ = +39°08′11″,λ = −63°29′). Because of the Civil War in Central Asia, the latitude observations were ended at Tschardjui in May, 1919. A new latitude station was established at Kitab (Uzbekistan) at latitude ϕ = +39°08′40″ and longitude λ= −66°53′, in November 1930. The Kitab Latitude Station was equipped with two visual zenith telescopes (1929, 1957) and the photographic zenith tube removed from the Pulkovo observatory in 1978. The Kitab station provided the ILS with more than 250000 instantaneous latitude measurements. Since the early 90s Kitab has hosted the ground-based beacons of GPS, PRARE and DORIS satellite tracking systems, providing the IERS data center with precise coordinates at sub daily frequency.
Time and Polar Motion in Early NASA Spacecraft Navigation
Authors: Muller Paul M. 
Published: July 2016

AbstractInclusion of Polar Motion and UT1 data (corrections) is essential to achieving the full accuracy in NASA (and other) spacecraft navigation. Tracking station locations are routinely determined to the meter-level and must be available inertially (on the rotating Earth) to equal accuracy a priori in real-time. This implies knowledge of UT1 to 2.5ms and polar motion to lm (and for practical use for the first time accurately predicted and disseminated to the navigation computer programs). This was essential from 1965 onward as we prepared for Apollo, for Apollo itself, and all subsequent missions. This paper presents the history behind the author’s “discovery” circa 1965 at JPL that UT1 and polar motion were not then included in NASA’s Orbit Determination models and programs; how this omission was being “observed” in station location determinations (and errors) from spacecraft radio tracking data; how it was rectified; the essential nature of these data in precision spacecraft navigation including Apollo; and how this became undoubtedly the highest and most critical application of these data in history. There followed widespread recognition of the many observers present and past who tirelessly and often with little visibility outside of professional astronomy made the necessary observations and calculations. As an historical paper, there is room for a few interesting anecdotes and personalities in NASA, as well as the late and much missed Dr. Markowitz then head of the USNO time service, and his successor Dr. Klock, with both of whom the author had the honor, professional benefit, and great personal pleasure of working during this time.
Nature and Properties of the Chandler Motion and Mechanism of its Damping and Excitation
Authors: Ferrándiz J.M. , Barkin Yu. V. 
Published: July 2016

AbstractThe analytical studies of the Chandler motion of the Earth’s pole on the basis of the special approach to the problem, using the canonical and noncanonical equations in the Andoyer elastic variables (Barkin, et al. 1995; Barkin, 1996; in press) have been fulfilled. The Earth is considered as an isolated celestial body with the anelastic (in general case) external envelope (the mantle) and an invariant central part (the core).The interpretation of the Chandler motion of the body, deformed by its own rotation, was given in the case of an elastic envelope. It was shown that the body rotates as a fictitious rigid body with different moments of inertia. The analytical solution of the problem let us explain the next properties of the motion of the deformable bodies: 1) observed period of the Earth’s polar motion; 2) ellipticity of the pole trajectory and difference of the eccentricities of the Chandler and Euler motions; 3) nonuniform velocity of the counter-clockwise polar motion along the Chandler ellipse; 4) orientation of this ellipse (its minor axis is located in the meridian plane, at 14.5 W degrees).The influence of the dissipation on the damping of the Chandler polar motion was studied. The analytical solution of the problem was obtained for the simplest treatment of the delay of the tides caused by the Earth’s rotation (Getino & Ferrándiz 1991; Kubo, 1991). This model explains the characteristic behaviour of the amplitude of the Chandler motion in the periods 1905–1920, 1943–1960 (Vondrák, & Cyril, 1966). The excitation of the Chandler motion can be explained by the upper and lower envelope displacements (Barkin, 1999) with Moon-Sun forced attraction with a period of 412 days, close to the Chandler period.
The Oscillation of a System Earth – Moon
Authors: Kurbasova G. , Rykhlova L. 
Published: July 2016

Internal links in the Earth-Moon system are determined by gravitational interaction. According to the least compulsion principle of Gauss, the deviation of “free motion” of heliocentric orbits of two material points with Earth and Moon masses is determined by the sum of the products of each material points’ deviation from its free motion and its mass.By solving the minimization problem using the Lagrange multiplier method, Lagrange equations of the first kind were obtained in vector form. With acceptable assumptions (introduction of non-dimensional time τ = nt, where n is the sidereal rotation of the Moon, and the lunar orbit is considered to be circular) the linkage coefficient (Lagrange multiplier) is:where v1and v2 are proper frequencies of the Earth and the Moon and μ is the Moon/Earth mass ratio.
The Quality of Sub-daily Polar Motion Estimates based on GPS Observations
Authors: Weber R. , Rothacher M. 
Published: July 2016

AbstractSince June 1992 the International GPS Service (IGS) has provided time series of its products comprising, among others, very accurate polar motion estimates. While the products of the pilot phase were based on data from about 30 permanent stations, the network now consists of about 140 globally distributed tracking sites (Neilan, 1998).Several efforts have been undertaken at the CODE Analysis Center of the IGS aiming at the optimization of the global processing strategy, including satellite orbit and troposphere modeling. In addition, the time resolution of the ERP series has been increased to two hours or even one hour. This paper deals with sub-daily polar motion and LOD series of four months in late 1996, which have been calculated in a reprocessing step very recently. The investigations performed allow for comparisons of the new series with results stemming from intensive VLBI tracking campaigns and for the detailed study of the influence of the processing strategy and parametrization on the ERP series.
Multiperiodicity In RRs and & Scuti Stars: An Observational View
Authors: Fitch W.S. 
Published: July 2016

On reviewing the observational literature of the recent past on RRs (or dwarf Cepheid or AI Velorum) and δ Scuti stars, it appeared that most present controversy is centered on three specific questions:(1) Are δ Scuti stars really periodic, or only quasi-periodic?(2) Are tidal modulations responsible for the slow cyclic variations observed in many of these stars, or not?(3) Are there any real physical differences between the members of these two groups, or are they actually the same kind of object?I would like to restrict this review primarily to these questions; and since some of our recent observational results bear directly on questions CI) and (2), and indirectly on question (3), I hope I will be forgiven for describing briefly here some of our current relevant findings.