bluuebunny/crossref_metadata_2025 huggingface dataset:
7.8. Particle cascades in Sgr A∗: the possibility of observing their γ-ray signature
Authors: Markoff Sera , Melia Fulvio , Sarcevic Ina
Published: July 2016

The recent detection of a γ-ray flux from the direction of the Galactic center by EGRET on the Compton GRO raises the question of whether this is a point source (possibly coincident with the massive black hole candidate Sgr A∗) or a diffuse emitter. Using the latest experimental particle physics data and theoretical models, we have examined in detail the γ-ray spectrum produced by synchrotron, inverse Compton scattering and mesonic decay resulting from the interaction of relativistic protons with hydrogen accreting onto a point-like object. Such a distribution of high-energy baryons may be expected to form within an accretion shock as the inflowing gas becomes supersonic. This scenario is motivated by hydrodynamic studies of Bondi-Hoyle accretion onto Sgr A∗, which indicate that many of its radiative characteristics may ultimately be associated with energy liberated as this plasma descends down into the deep potential well. Earlier attempts at analyzing this process concluded that the EGRET data are inconsistent with a massive point-like object (Mastichiadis & Ozernoy, 1994). Our results demonstrate that a more careful treatment of the physics of p-p scattering suggests that a ~ 106M⊙ black hole may be contributing to this high-energy emission.
7.15. The Fourier analysis of the observed velocity field of gas in the inner 1.5 pc of the Galaxy
Authors: Fridman A.M. , Lyakhovich V.V. , Khoruzhii O.V. , Silchenko O.K.
Published: July 2016

The Fourier analysis of the observed velocity field of ionized gas in the inner 1.5 pc of the Galactic Center (obtained by Roberts and Goss, 1993) is made. As follows from the analysis, the observed field of residual velocities is dominated by the second Fourier harmonic. This fact can be treated as a consequence of the presence of an one-armed density wave with the density maximum along the Northern Arm plus the Western Arc structure. The wave nature of this structure is proved on the base of the behaviour of the phase of the second harmonic of line-of-sight velocity field in the whole region. The Fourier analysis shows also the presence of systematic radial velocity. We consider this flow as a quasi-stationary radial drift caused by one-armed nonlinear density wave (‘mini-spiral’).
7.17. A possibility of measurement of distance and proper motion of galactic sources by using a differential VLBI method of VERA
Authors: Kameya O. , Sasao T. , Miyoshi M.
Published: July 2016

National Astronomical Observatory, Japan has a plan to construct a new VLBI system named VERA (VLBI Exploration of Radio Astrometry). The system can measure precise positions of Galactic radio sources (H2O masers and SiO masers) referring to adjacent radio sources (QSO etc.) by using a differential VLBI method (Sasao and Morimoto, 1991).
8.5. Radio polarimetric study of the Galactic center threads
Authors: Lang Cornelia C. , Morris Mark
Published: July 2016

The Very Large Array (VLA) has been used to carry out a high resolution, polarimetric study of the isolated non-thermal radio filaments, G0.08+0.15, and G359.96+0.09, also known as the Northern and Southern Threads, found near the Galactic Center (GC).
8.7. Magnetospheric structure filled by relativistic plasma jets/winds
Authors: Nitta Shin-Ya
Published: July 2016

Recent observations revealed that many kinds of astrophysical outflows have very similar structure, i.e. bipolar jets are surrounded by an equatorial (disk-shaped) wind or an expanded wind as in the outflows from YSO's, post AGB stars, pulsars or AGN's. One might think that this is very queer because the species of the central objects and the spatial scales are quite different among these objects. However this similarity is a result of self-organized magnetospheric equilibrium. In these systems, the rotating magnetic field plays an important role for the structure formation. In such systems, two components of the Lorentz force (the electrostatic force and the magnetic force arising from the toroidal component) dominate other forces in the region far distant from the rotation axis in spite of the difference of the acceleration mechanism of the flows. We can understand that such similarity of the structures is a nature of the plasma outflows itself.

We suppose relativistic, pressure-free, inviscid, resistive-less, stationary and axisymmetric MHD flows. In this case, MHD equations reduce to well known basic equations: the Bernoulli equation and the Grad-Shafranov equation. We should note that the special relativistic treatment is necessary to discuss the structure far beyond the light cylinder, even if the flow speed is not close to the light velocity.
8.8. On collimation of the outflows in force-free magnetospheres
Authors: Okamoto I.
Published: July 2016

The “force-free” (FF) approximation has often been evoked as a convenient means of treating electromagnetic processes of extracting rotational energy from pulsars and black holes through their magnetospheres, to energize a variety of activities in the environments. In order to produce relativistic jets with cylindrical topology like those associated with AGNs, some people further use this approximation for collimating relativistic outflows in the asymptotic domains from central sources. It is argued here that one can not collimate outflows by the FF magnetic field only, that is, the flow-field structure must asymptotically be conical far out from the light cylinder.
9.9. Extended UV emission in NGC6251
Authors: Crane Philippe , Vernet Joel
Published: July 2016

NGC 6251 is an optically normal elliptical galaxy that hosts one of the most spectacular radio jets(Perley, Bridle, and Willis, 1984). This jet extends about 1 Mpc and its axis is roughly perpendicular to the central dust ring. NGC6251 was originally observed with HST in a survey of elliptical galaxies(Crane et al., 1993) and revealed an anamoly which was pursued in the investigation reported here.
9.15. Theoretical method for treating force-free black hole magnetosphere in non-stationary and non-axisymmetric state
Authors: Uchida T.
Published: July 2016

The force-free approximation is a very useful method in studies of the global electromagnetic structure of the magnetospheres around the relativistic astronomical bodies. However, its application has almost been restricted to the stationary and axisymmetric configuration. In this work, we remove this restriction and construct a general method for treating the force-free electromagnetic field.
9.18. Galactic winds in active galaxies
Authors: Veilleux S. , Bland-Hawthorn J. , Cecil G. , Shopbell P.
Published: July 2016

The effects of large-scale galactic winds in active galaxies may be far-reaching. It has been suggested that the Hubble sequence can be understood in terms of a galaxy's greater ability to sustain winds with increasing bulge-to-disk ratio. The large-scale circulation of gas associated with these galactic winds might help explain the mass-metallicity relation between galaxies and the metallicity-radius relation within galaxies. Galactic winds probably contribute non-negligibly to the cosmic X-ray background and may be involved in the quasar absorption-line phenomenon. The cosmological implications of the wind phenomenon have been widely explored in the context of proto-galaxies and quasars. The extremely energetic galactic winds that were likely associated with galaxy formation almost certainly played a key role in heating and ionizing the intergalactic medium at high redshifts and may have created the seeds for the large-scale structure we see today.
10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole
Authors: Ghez A. M. , Klein B. L. , McCabe C. , Morris M. , Becklin E. E.
Published: July 2016

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.
10.3. Progress toward a trigonometric parallax of Sgr A∗
Authors: Reid M. J. , Readhead A. C. S. , Vermeulen R. , Treuhaft R.
Published: July 2016

In 1918, Harlow Shapley first noted that globular clusters were concentrated toward the constellation of Sagittarius, and hence the Sun was not near the center of the Milky Way. Since that time astronomers have expended considerable effort to determine the distance to the center of the Milky Way, because any change in the value of this distance, R0, has a widespread impact on astronomy and astrophysics. Beginning in 1991, we have conducted observations with the VLBA designed to make possible a program to measure the distance to the Galactic Center via a trigonometric parallax. This could be accomplished with the VLBA using Sgr A∗ as a phase reference for one or more (weaker) compact extragalactic sources. A time series of measurements of the position of Sgr A∗ relative to an extragalactic source should show the effects of the annual ≈ ±0.12 mas signature of the Earth's orbit around the Sun (trigonometric parallax), as well as the ≈ 6 mas yr−1 secular motion caused by the Sun's orbit around the Galactic Center.
10.8. A massive black hole in the active galaxy NGC6251
Authors: Ferrarese Laura , Ford Holland C. , Jaffe Walter
Published: July 2016

NGC 6251 is an E2 galaxy with mB = 13.6 mag (RC3) and heliocentric velocity 7400 km s−1(=106 Mpc for H0 = 70 km s−1Mpc−1). It is the host galaxy of one of the largest known radio sources in the sky: the radio lobes extend for 1°.2 (over 2 Mpc, Waggett et al. 1977, Readhead et al. 1978, Cohen and Readhead 1979, Jones et al. 1986, Jones and Wehrle 1994).
10.9. Dynamical constraints on alternatives to massive black holes in galactic nuclei
Authors: Maoz Eyal
Published: July 2016

There is now compelling evidence for massive dark objects at the centers of severals galaxies. The possibility that these are black holes (BHs) fits well into the picture where quasars and AGNs are powered by accretion onto a massive BH, so that dead quasar engines should be hiding in many nearby galaxies.
11.1. Black holes and galaxy centers
Authors: Richstone Douglas
Published: July 2016

The study of supermassive galactic black holes (BH) has moved beyond discovery to maturity. The are now ∼ 15 reliable detections. The mass of a central black hole apparently correlates with the mass of the hot component of its galactic host. It may be that every normal galaxy has a supermassive black hole carrying about 10−3 of its bulge mass, with important consequences for the structure and evolution of the core of the galaxy. The most recent major review is by Kormendy & Richstone (1995, KR).
11.4. Demographics of nuclear activity in nearby galaxies
Authors: Ho Luis C. , Filippenko Alexei V. , Sargent Wallace L. W.
Published: July 2016

Between 1984 and 1990 we conducted a survey at Palomar Observatory (Filippenko and Sargent 1985) to quantify the luminosity function of nearby active galactic nuclei (AGNs). The Hale 5 m telescope was used to obtain high-quality, moderate-resolution optical spectra of a nearly statistically complete sample of about 500 bright (BT ≤ 12.5 mag), northern (δ > 0°) galaxies (see Ho et al. 1995 for details). The survey has now been completed, and the first scientific results are reported in a series of papers by Ho et al. (1997a, b, c).
11.6. Spectral monitoring of AGN at the 6 meter telescope
Authors: Bochkarev N.G. , Shapovalova A.I. , Burenkov A.N. , Vlasyuk V.V.
Published: July 2016

To study broad line region (BLR) size and kinematics spectral monitoring of NGC 3516, NGC 4151, NGC 5548, NGC 7469 and 3C390.3 has been performed with the 6 m telescope of the Special Astrophysical Observatory (N. Arkhyz- North Caucasus) in 1986–1996. The spectra are obtained in the Nasmyth focus using the TV scanner with a resolution of 3–4Å and S/N= 10–25 within 4000–5200ÅÅ (1986–94, 500 spectra), and in the prime focus with the spectrograph UAGS (a long-slit mode) + CCD (resolution 5–10Å) or multi-pupil field spectrograph (MPFS) + CCD (resolution 4Å) within 4000–7000ÅÅ and S/N=50–100 (1995–96, 270 spectra).
11.17. Radio emission from low-luminosity active galactic nuclei
Authors: Van Dyk Schuyler D. , Ho Luis C.
Published: July 2016

“Low-luminosity” active galactic nuclei (LLAGNs) typically have ≳ mag, as opposed to −18 to −30 mag for luminous Seyfert 1 nuclei and QSOs. The physical origin of the class of emission-line nuclei known as low-ionization nuclear emission-line regions (LINERs; Heckman 1980) remains controversial. Based on the close resemblance of some LINERs to Seyfert nuclei, LINERs can arguably be considered another manifestation of the AGN phenomenon. An alternative view is that stellar processes account for LINER energy. The energetics alone do not provide a useful discrimator between the two possible mechanisms.
Galaxy Motions in the Nearby Universe
Authors: Huchra John P.
Published: July 2016

In this paper we review the history of the search for and study of the motions of nearby galaxies with respect to the Hubble Flow. The current status of the field is that (1) convincing infall has been detected into dense clusters, especially the Virgo cluster, (2) the microwave background direction is moderately well aligned with the measured flow nearby but not apparently on larger scales, and (3) there is good but not perfect consistency between the nearby density fields and velocity fields. Particular problems exist in the different Ω's required to fit the density field derived from optically selected and IRAS (60μ) selected galaxy samples.
The Sources of the Hard X-Ray Background
Authors: Setti Giancarlo , Comastri Andrea
Published: July 2016

The hard component (3 keV – ~ MeV) of the X-ray background (XRB) comprises the largest portion, ~ 90%, of the overall XRB intensity. The observed isotropy (the entire Galaxy is transparent above 3 keV) provides aprima facieevidence of its prevailing extragalactic nature. A large fraction (~ 75%) of the energy flux falls in the 3 – 100 keV band, the corresponding energy density being ≃ 5×10−5eV cm−3, of which 50% is confined to the narrower 3 – 20 keV band. Although the energy flux carried by the XRB is relatively small compared to other extragalactic backgrounds, it was soon realized that it cannot be accounted for in terms of sources and processes confined to the present epoch. An analysis of the combined observed spectra (Gruber 1992) concludes that, while a thermal bremsstrahlung with an e-folding energy = 41.13 keV accurately fits the data up to 60 keV, above this energy the sum of two power laws is required with normalizations such that at 60 keV the spectral index is ~ 1.6, gradually flattening to ~ 0.7 at MeV energies. It should also be noted that below 10 keV the XRB energy spectrum is well represented by a power law of index α = 0.4 (I∝E−α).
Diffuse Gamma Rays of Galactic and Extragalactic Origin: Preliminary Results from EGRET
Authors: Sreekumar P. , Kniffen D.A.
Published: July 2016

The all-sky survey in high energy gamma rays (E>30 MeV) carried out by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory provides for the first time an opportunity to examine in detail diffuse gamma-ray emission of extra-galactic origin. The observed diffuse emission at high galactic latitudes is generally assumed to have a galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, in addition to an isotropic component presumably of extragalactic origin. The galactic component can be estimated from a model of the interstellar medium and cosmic-ray distribution. Since the derived extragalactic spectrum depends very much on the success of our galactic model, the consistency of the galactic diffuse emission model is examined both spectrally and spatially with existing EGRET observations. In conjunction with this model, EGRET observations of the high latitude emission are used to examine the flux and spectrum of the residual extragalactic emission. This residual emission could be either truly diffuse in origin or could arise from accumulated emission from unresolved sources particularly in the light of EGRET observations showing the presence of numerous gamma-ray bright active galactic nuclei.
The Hot Big Bang and Beyond
Authors: Turner Michael S.
Published: July 2016

The hot big-bang cosmology provides a reliable accounting of the Universe from about 10−2sec after the bang until the present, as well as a robust framework for speculating back to times as early as 10−43sec. Cosmology faces a number of important challenges; foremost among them are determining the quantity and composition of matter in the Universe and developing a detailed and coherent picture of how structure (galaxies, clusters of galaxies, superclusters, voids, great walls, and so on) developed. At present there is a working hypothesis—cold dark matter—which is based upon inflation and which, if correct, would extend the big bang model back to 10−32sec and cast important light on the unification of the forces. Many experiments and observations, from CBR anisotropy experiments to Hubble Space Telescope observations to experiments at Fermilab and CERN, are now putting the cold dark matter theory to the test. At present it appears that the theory is viable only if the Hubble constant is smaller than current measurements indicate (around 30 km s−1Mpc−1), or if the theory is modified slightly, e.g., by the addition of a cosmological constant, a small admixture of hot dark matter (5 eV “worth of neutrinos”), more relativistic particles, or a tilted spectrum of density perturbations.
The Present Status of the Decaying Neutrino Theory
Authors: Sciama D.W.
Published: July 2016

A discussion is given of recent observations relevant to the decaying neutrino theory. The HST spectrum of the halo star HD 93521 obtained and analysed by Spitzer and Fitzpatrick supports our predictions that warm opaque clouds in the Galaxy should possess substantial partial ionisation, and that the electron density in such clouds near the sun should be constant.
Three Cosmolgical Remarks
Authors: Morrison Philip
Published: July 2016

In traditional societies the remarks of seniors were prized, for their memories often spanned events rare enough to have remained unseen by most yet frequent enough to offer eventual challenges to all. Even here among friends who are self-styled cosmological “old radicals”, I think I am the senior.
Knowledge Limits in Cosmology
Authors: Kafatos Menas
Published: July 2016

In cosmology one faces the observational challenge that knowledge about distant regions of the universe is dependent on assumptions one makes about these regions which are themselves coupled to the observations. Within the framework of the Friedmann-Robertson-Walker big bang models the universe becomes opaque to its own radiation at z ≈ 1,000 and the earlier, and more distant, regions of the universe are not directly accessible through observations. Other challenges exist such as possible merging of extended distant sources and confusion of spectra from distant galaxies. One, therefore, encounters horizons in our understanding of the universe. Such horizons exist in any mode of description. To use the quantum analogy, the observer is always part of the system under study, the universe, and a description of the universe entails including the observer and observing apparatus. Since the early universe should be described in quantum terms, it follows that non-locality in the universe is not an a-priori requirement but the outcome of the observing process itself. As such, the flatness and horizon problems may not be preconditions on theoretical models.
Planning Future Space Measurements of the CMB
Authors: Puget J.L. , Aghanim N. , Gispert R. , Bouchet F.R. , Hivon E.
Published: July 2016

A central problem in cosmology is the building and testing of a full and detailed theory for the formation of (large-scale) structures in the Universe. It is widely believed that the observed structures today grew by gravitational instability out of very small density perturbations. Such perturbations should have left imprints as small temperature anisotropies in the cosmic microwave background (CMB) radiation.
The Rhodes/Hartrao 2300 Mhz Horn Telescope
Authors: Jonas J.L.
Published: July 2016

The recently completed Rhodes/HartRAO 2300 MHz radio continuum survey is the highest resolution and highest frequency survey of the entire southern sky. This makes it useful for those wishing to model the Galactic foreground in order to study cosmic background emission. Unfortunately there are low-amplitude, large-scale gradients in the survey data which make it difficult to interpret the very high latitude Galactic emission. We describe a small, low-cost horn telescope which we hope to use to correct the gradients in the survey data.
Upper Limits on the LYα Emission at Z = 3.4
Authors: Martinez-Gonzalez E. , Gonzalez-Serrano J.I. , Sanz J.L. , Martin-Mirones J.M. , Cayon L.
Published: July 2016

Many searches have been carried out to detect emission from massive primeval hydrogen clouds at high redshift. By observing the 21 cm line it has been possible to impose strong upper limits on the mass and number of protoclusters at high redshift (Wieringa, et al. 1992). Since strong Lyα emission is expected from primeval galaxies undergoing their first burst of star formation, many attempts to detect this emission have been made, but no positive detection has been reported, imposing strong constraints on models of galaxy formation (see Djorgovski et al. 1993 for a review).
Foreground Galaxies around Luminous Quasars
Authors: Von Linde J. , Borgeest U. , Refsdal S. , Schramm K.-J. , Van Drom E.
Published: July 2016

We compare galaxy counts in deep R-band exposures of the fields of 36 highly luminous, high redshift QSOs to those in control fields at a distance of 1 deg. We find indication for a weak overdensity of galaxies in the foreground of QSOs on scales of arcminutes on a low significance level. Counts inside rings around the quasars, stars in the quasar fields and stars in the control fields show evidence for an excess of galaxies on scales of several arcseconds around the quasars as well as for a stronger clustering of galaxies in the QSO fields than in the control fields. We interpret this in terms of an amplification bias by gravitational lensing.
Typical Characteristics of Chance and Non-Chance Compact Groups of Galaxies
Authors: Kiseleva Ludmila , Anosova Joanna
Published: July 2016

In our previous works (Anosova 1987, Anosova and Kiseleva 1993) we developed a new objective statistical method for an identification of members of star and galaxy clusters as chance or non-chance ones. In the case of galaxies this method uses simultaneously their radial velocitiesVand angular separationsρ.
Accurate Measurements of the Local Deuterium Abundance from HST Spectra
Authors: Linsky Jeffrey L.
Published: July 2016

An accurate measurement of the primordial value of D/H would provide a critical test of nucleosynthesis models for the early universe and the baryon density. I briefly summarize the ongoing HST observations of the interstellar H and D Lyman-α absorption for lines of sight to nearby stars and comment on recent reports of extragalactic D/H measurements.
Halo/Thick Disk CVS and the Cosmic X-Ray Background
Authors: Grindlay Jonathan E. , Maoz Eyal
Published: July 2016

In a recent study (Maoz and Grindlay 1995) we have found that a number of previously recognized anomalies in the diffuse x-ray background at soft energies (~0.5-2 keV) can be understood if about 20-30% of the diffuse flux arises from a population of low luminosity sources in a thick disk or flattened halo distribution in the Galaxy. Here we summarize our results and review the arguements that these objects are not accreting neutron stars or black holes but rather white dwarfs (i.e. CVs) which may have been produced in a primordial population of disrupted globular clusters.
Phase Transition at the Metric Elastic Universe
Authors: Gusev Alexander
Published: July 2016

At the last time the concept of the curved space-time as the some medium with stress tensor σαβon the right part of Einstein equation is extensively studied in the frame of the Sakharov - Wheeler metric elasticity(Sakharov (1967), Wheeler (1970)). The physical cosmology pre- dicts a different phase transitions (Linde (1990), Guth (1991)). In the frame of Relativistic Theory of Finite Deformations (RTFD) (Gusev (1986)) the transition from the initial stateof the Universe (Minkowskian's vacuum, quasi-vacuum(Gliner (1965), Zel'dovich (1968)) to the final stateof the Universe(Friedmann space, de Sitter space) has the form of phase transition(Gusev (1989) which is connected with different space-time symmetry of the initial and final states of Universe(from the point of view of isometric groupGnof space). In the RTFD (Gusev (1983), Gusev (1989)) the space-time is described by deformation tensorof the three-dimensional surfaces, and the Einstein's equations are viewed as the constitutive relations between the deformations ∊αβand stresses σαβ. The vacuum state of Universe have the visible zero physical characteristics and one is unsteady relatively quantum and topological deformations (Gunzig & Nardone (1989), Guth (1991)). Deformations of vacuum state, identifying with empty Mikowskian's space are described the deformations tensor ∊αβ, wherethe metrical tensor of deformation state of 3-geometry on the hypersurface, which is ortogonaled to the four-velocityis the 3 -geometry of initial state,is a projection tensor.
Recent Progress in Solar or Stellar Interior Modelling
Authors: Turck-Chièze S.
Published: July 2016

Acoustic modes are well-suited probes to check the internal stellar structure and bring interesting constraints on turbulence regions, mixing in stellar interiors and magnetic fields. The SOHO satellite, through the helioseismic instruments GOLF, MDI and VIRGO, has significantly improved the knowledge of these modes owing to an excellent duty cycle (greater than 90%) and the capability to detect very low amplitude modes, down to 3 mm/s. Five years of the SOHO misson guarantee an accurate view of the solar interior, weakly dependent on the turbulent surface, from the energy-generating core to the surface.

The recent results allow us to verify some of the theoretical assumptions of stellar modelling. The tachocline layers, located in a narrow region at the base of the convection zone, support an hydro (or magnetohydro) dynamical instability which induces mixing and results in 7Li depletion in accordance with photospheric observations. On the contrary, central mixing is not favoured by the present observations. Nuclear reaction rates of the pp chain are now constrained by the behaviour of the sound speed and density. Döppler velocity measurements appear as an excellent technique to follow in real time the temporal evolution of the luminosity produced in the core. Some puzzling questions about dynamical effects in stellar plasmas can now start to be addressed for the first time. The theoretical neutrino emissions can be now directly deduced from our helioseismic vision of the energy-generating core.

Nowadays, helioseismology provides a dynamical vision of the external half of the Sun (20% in mass), as a result of the extraction of the sound speed, density, rotation profiles and of the time evolution of velocity measurements. Below, the classical static vision of the nuclear region persists because of the poor spatial resolution offered by acoustic modes (±6% in radius, 10% in mass) and the long integration time (several years). Gravity modes will be extremely useful to improve the spatial resolution in the radiative region. The extended observations with the SOHO satellite may be extremely useful to detect some of these modes.
Solar Metal Abundance Inferred from Helioseismology
Authors: Takata M. , Shibahashi H.
Published: July 2016

In our previous work (Takata & Shibahashi 1998), we constructed a solar model called the seismic solar model, which has the consistent profile of sound speed as well as the consistent depth of the convection zone with helioseismology. The profile of the heavy element abundance, however, had to be assumed to be constant for feasibility. Here we try to constrain the distribution of the heavy element abundance as well by the solar oscillation frequencies, adopting all of the basic equations which govern the solar structure.
Turbulent Convection and Subtleties of Differential Rotation Within the Sun
Authors: Toomre J. , Brun A. S. , DeRosa M. , Elliott J. R. , Miesch M. S.
Published: July 2016

The solar convection zone exhibits a differential rotation with radius and latitude that poses major theoretical challenges. Helioseismology has revealed that a smoothly varying pattern of decreasing angular velocity Ω with latitude long evident at the surface largely prints through much of the convection zone, encountering a region of strong shear called the tachocline at its base, below which the radiative interior is nearly in uniform solid body rotation. Helioseismic observations with MDI on SOHO and with GONG have also led to the detection of significant variations in Ω with 1.3 yr period in the vicinity of the tachocline. There is another shearing layer just below the solar surface, and that region exhibits propagating bands of zonal flow. Such rich dynamical behavior requires theoretical explanations, some of which are beginning to emerge from detailed 3-D simulations of turbulent convection in rotating spherical shells. We discuss some of the properties exhibited by such numerical models. Although these simulations are highly simplified representations of much of the complex physics occurring within the convection zone, they are providing a very promising path for understanding the solar differential rotation and its temporal variations.
The Solar Dynamo: Old, Recent, and New Problems
Authors: Brandenburg A.
Published: July 2016

A number of problems of solar and stellar dynamo theory are briefly reviewed and the current status of possible solutions is discussed. Results of direct numerical simulations are described in view of mean-field dynamo theory and the relation between the α-effect and the inverse cascade of magnetic helicity is highlighted. The possibility of ‘catastrophic’ quenching of the α-effect is explained in terms of the constraint placed by the conservation of magnetic helicity.
Vorticity, Current Helicity and Alpha-effect for Magnetic-driven Turbulence in the Solar Convection Zone
Authors: Rüdiger G.
Published: July 2016

The turbulent electromotive force as well as the kinetic and current helicities have been computed for a turbulence subject to magnetic buoyancy and global rotation. The dynamo-alpha is found as positive in the northern hemisphere and negative in the southern hemisphere and the kinetic helicity has just the same signs.

In agreement with the observations the current helicity is negative in the northern hemisphere and positive in the southern hemisphere. Our current helicities and alpha-effects are thus always out of phase. The signs of alpha-effect and both helicities exactly correspond to a numerical simulation by Brandenburg & Schmitt (1998).
New Developments in Local Area Helioseismology
Authors: Duvall T. L. , Kosovichev A. G.
Published: July 2016

Several techniques are used to study local areas in helioseismology, including time-distance helioseismology, acoustic imaging/holography, and ring diagram analysis. These techniques can be used to study flows, magnetic fields, and temperature inhomogeneities. The “local” area studied can be as small as a supergranule, or as large as the entire convection zone in the case of meridional circulation as studied by Giles and colleagues. Active regions have been studied with some interesting results, with complicated flow patterns below sunspots and detectable sound speed inhomogeneities in the 10 Mm below the spots. Another interesting result is the detection of sunspots on the back side of the Sun by Lindsey and Braun using the holography technique. A confirmation of their result using the time-distance technique is presented.
Seismic Holography of the Solar Interior and Far Side
Authors: Braun D. C. , Lindsey C.
Published: July 2016

The development of solar acoustic holography over the past decade has opened a major new diagnostic avenue in local helioseismology (Lindsey & Braun 1990; 1997; 2000b). Its application to SOI-MDI data from SOHO has revealed “acoustic moats” surrounding sunspots, “acoustic glories” surrounding complex activeregions, and “acoustic condensations” suggesting the existence of significant seismic anomalies up to 20 Mm beneath active-region photospheres. It has given us the first seismic images of a solar flare, and has uncovered a remarkable anomaly in the statistical distribution of seismic emission from acoustic glories. A review of these and other accomplishments is given by Braun & Lindsey (2000a).
Generation of the Solar Subsurface Shear
Authors: Chan K. L.
Published: July 2016

It is well known that a thin layer of angular velocity shear exists just below the solar surface. We propose that this layer is primarily generated by the radial-meridional component of the Reynolds stress. This Reynolds stress component is created by a characteristic upward-equatorward (or equivalently, downward-poleward) correlation of the turbulence velocity over a region in which the shear layer is embedded. Using 2D and 3D numerical experiments, we illustrate that this correlation is caused by vortices that get sucked down from the surface and turn aligned with the rotation vector (a la Taylor columns).
Nonlinear Modeling of the Solar Tachocline
Authors: Miesch M. S.
Published: July 2016

As a first step toward a more realistic model of the solar tachocline, we report simulations of rotating, stably-stratified turbulence in a thin spherical shell.
Effect of a Steady Flow and an Atmospheric Magnetic Field on the Solar p- and f-Modes
Authors: Erdélyi R. , Taroyan Y.
Published: July 2016

The combined effect of a subsurface steady homogeneous flow and a chromospheric uniform magnetic field on the solar p- and f-modes is evaluated theoretically for a simple model of the Sun. The derived dispersion relation is solved analytically in limit of the long wavelength approximation and is evaluated numerically for arbitrary wavelengths. The influence of an equilibrium flow is more dominant in limit of small wavenumbers. For arbitrary wavelengths the effect of a magnetic field might be stronger than frequency shifts caused by a steady homogeneous flow.
Long Period Oscillations in Polar Plumes as Observed by CDS on SoHO
Authors: Banerjee D. , O'shea E. , Doyle J. G. , Goossens M.
Published: July 2016

We examine time series of the transition region spectral line O v 629 Å, observed with the Coronal Diagnostic Spectrometer (CDS) onboard the SoHO spacecraft. Primarily we were looking for intensity and velocity oscillations in polar plumes, however by chance we detected a giant macro-spicule at the limb and were able to follow its dynamical structure. We have reported the dynamics of the giant macro-spicule in Banerjee et al. (2000a) and have also reported the existence of long period oscillations in the polar plumes as observed in the O v 629 Å line in Banerjee et al. (2000a,b). In this short contribution we revisit one of these dataset, namely s16834r01 to test the reliability of the observed periods. The statistical significance of the oscillations is estimated by using a randomisation method. Our analysis re-confirms the presence of compressional waves with periods of 20-25 minutes.
Magnetic Splitting of Molecular Lines in Sunspots
Authors: Berdyugina S. V. , Frutiger C. , Solanki S. K.
Published: July 2016

We investigate the magnetic sensitivity of molecular lines observed in sunspot umbrae and briefly discuss their major differences compared to atomic lines.
Spectroscopic Signatures of a Flare Observed by SUMER Onboard SOHO
Authors: Dammasch I. E. , Curdt W. , Kliem B. , Dwivedi B. N. , Wilhelm K.
Published: July 2016

We report on EUV observations of a solar limb flare obtained by the SUMER spectrometer. A time series was taken with fixed slit position and several spectral windows that covered a wide temperature range (104-107 K), preceded and followed by contextual raster scans in a He I line. During the time series, a C4.6 flare occurred in the region, also imaged in the EUV by SOHO/EIT and in soft X rays by YOHKOH/SXT. The temporal evolution seen in the SUMER spectra reveals a close spatial relationship and a correlated dynamical behaviour of the hot (T ≈ 107 K) and cool (T ≈ 104 K) material, which are difficult to reconcile with the notion (based on the Kopp-Pneuman flare model) that cool loops form at a lower height than the hot flare loops.
A Cylindrical Formulation of Force Free Magnetic Fields
Authors: Evangelidis E. A. , J. Botha G. J.
Published: July 2016

A new solution of the force free field equation is presented in cylindrical coordinates.
Active Region Evolution and Flare Activities: From the Photosphere to the Corona
Authors: Ishii T. T. , Kurokawa H. , Takeuchi T. T.
Published: July 2016

We studied the evolution of an active region and its relation with flare activities in order to solve the physical mechanism of solar flare occurrence. We investigated the evolutionary characteristics of the active region NOAA 8948 (April 2000) and found that the newly flux emergence caused the flares in this active region.
Oscillations in the Regions of Evershed Flows
Authors: Makarchik D. V. , Kobanov N. I.
Published: July 2016

Authors have investigated the line-of-sight velocity difference in the radial direction of sunspot penumbrae simultaneously at two height levels, NiI 4857 and Hβ by the differential method. Power spectra of time series exhibit in the range under consideration three groups of periods: 30-40, 12-15, and 8-10 minutes. Particular emphasis has been placed on the low-frequency portion of the spectrum (0.5-2 mHz). In addition to the 12-minute oscillations as detected by Rimmele the line-of-sight velocity component that is caused by Evershed motion is responsible for oscillations with periods of 15-35 minutes, which occur concurrently at the two height levels.
Three Dimensional image Reconstruction of an Hα Flare
Authors: Qu Z. Q. , Jiang Y. C. , Luan T. , Xu Z.
Published: July 2016

The three-dimensional (3D) image of an Hα flare is reconstructed from its line-center and seriary off-center filtergrams. The reconstruction is based on the principle of the line formation theory that the contribution function (CF) of emergent specific line intensity describes the escape photon distribution from stellar atmospheric layers. Thus the reconstruction depends on the model atmosphere accepted which determines the CF. An Hα flare taking place on April 22, 1992 is utilized to illustrate the process.
Origin of Universal Correlation between Temperature and Emision Measure for Solar/Stellar Flares
Authors: Shibata K. , Yokoyama T.
Published: July 2016

We study the reconnection and the chromospheric evaporation in flares using the numerical code including nonlinear anisotropic heat conduction effect (Yokoyama & Shibata 1998; 2001). The two-dimensional, nonlinear, timedependent, resistive, compressible MHD equations are solved. The evolution from the rise phase to (the early part of) the decay phase of a solar flare is qualitatively reproduced in this simulation. Based on the results, we obtained a relationship between the flare temperature and the coronal magnetic field strength. If we assume that the input of energy to a loop balances with the conduction cooling rate, the temperature at the loop apex is TA ≈ (2QL2/κ0)2/7 where Q is the volumetric heating rate, L is the half-length of the loop, and κ0 = 10−6 eGS is the Spitzer's thermal conductivity constant. In our simulations, the heating mechanism is magnetic reconnection so that the heating rate is described as Q = B2/(4π) · Vin/L · 1/sin θ, where B is the coronal magnetic field strength, Vin is the inflow velocity (≈ 0.1VA from our result and also from Petschek's theory), and θ is the angle between the slow-mode MHD shock and the loop and is approximately given by sin θ ≈ Vin/VA. By manipulating the equations, we find

where ρ is the mass density of the corona. The simulation results show very good agreement with this scaling law.
Observation of Reconnection Inflow of a Solar Flare
Authors: Yokoyama T. , Akita K. , Morimoto T. , Inoue K. , Newmark J.
Published: July 2016

We find an important piece of evidence for magnetic reconnection inflow in a flare on March 18, 1999. The flare occurred on the north-east limb, displaying a nice cusp-shaped soft X-ray loop and a plasmoid ejection typical for the long-duration-events. As the plasmoid is ejected, magnetic reconnection occurs at the disconnecting point. A clear ingoing pattern toward the magnetic X-point is seen. The velocity of this apparent motion is about 5 km sec−1, which is an upper limit on reconnection inflow speed. Based on this observation, we derive the reconnection rate as MA = 0.001 − 0.03, where MA is a Alfvén Mach number of the inflow.
The Opening of EUV Loops
Authors: Zhang J. , Wang J.
Published: July 2016

We analyzed simultaneous data from Huairou Solar Observing Station (HSOS) and the Transition Region and Coronal Explorer (TRACE) of November 4, 1998 in the active region NOAA 8375. The magnetic fields in this region had the following properties: a main positive polarity line-of-sight field was surrounded by relatively weak negative polarity fields; many moving magnetic features emerged from the positive magnetic field, and cancelled (merged) with the opposite (the same) polarity fields. There was a filament on the neutral line between the main positive polarity field and its surrounding negative polarity fields. The filament was cut off at a magnetic cancellation site and separated into two segments. One segment erupted and disappeared; the other segment rose from one end, but another end was fixed at an interface of a pair of opposite magnetic polarities, finally the morphology of this segment appeared as an Hα surge. Comparing Hα filtergrams with EUV images, we noticed that the Hα surge was co-spatial with an EUV surge. The EUV surge was whiplike in shape, then sidewards moved. We suggest that the evolution of the EUV surge represent the process of EUV loop opening.
DEM Study of Selected Quiet Sun Regions
Authors: Gontikakis C. , Landi E. , Dara H. C. , Alissandrakis C. E. , Vial J.-C.
Published: July 2016

In the present work EUV spectra of quiet Sun regions, observed with the Coronal Diagnostic Spectrometer (CDS) on SOHO, are analysed in order to determine the Differential Emission Measure (DEM) of selected areas of the field of view. The purpose of the present work is to study the differences between the DEM curves of the quiet Sun cell centers areas, intermediate areas and network boundaries.
Properties of Different Coronal Streamers
Authors: Parenti S. , I. Bromage B. J. , Poletto G. , Noci G. , Raymond J. C. , Bromage G. E.
Published: July 2016

In this paper a summary of results from coordinated observations of streamers acquired by the SOHO Coronal Diagnostic Spectrometer (CDS) and Ultra Violet Coronograph Spectrometer (UVCS) experiments is presented (Parenti et al. 2000). Data from different altitudes within the solar corona were taken, with the purpose of determining their physical parameters – densities, electron temperatures and element abundances – and their changes over the altitude range between 1.02 and 1.6 R⊙. Further UVCS streamer data, taken about two months later are used to compare with the behaviour seen in two different streamers. The streamers resulted to have a different behaviour in temperature and density. The low corona, covered by CDS data, shows little evidence of abundance variation with respect to photospheric values, while, at UVCS altitudes, a depletion of all element abundances is clearly evident.
Possible Magnetic Activity Cycles of Four Chromospherically Active Binaries: ER Vul, UV Psc, AR Lac and BH Vir
Authors: Qian S. B.
Published: July 2016

The study of a possible connection between magnetic activity and orbital period variation in close binaries is a very interesting work. Recently, the orbital periods of four chromospherically active binaries, ER Vul, UV Psc, AR Lac and BH Vir, are analyzed. It is discovered that the orbital periods of UV Psc and BH Vir oscillate with periods of 61 and 9.12 years, and the orbital periods of ER Vul and AR Lac show periodic variations with periods of 31 and 47 years respectively while they undergo secular decrease. The mechanisms that could explain the changes in the orbital periods of the four systems have been studied. The period variation of UV Psc may be caused by the cyclical magnetic activity in the primary component, and the magnetic activity in secondary component of AR Lac can explain its periodic component in the orbital period changes. For the other two systems, BH Vir and ER Vul, the cyclical magnetic activity in one or both of the components can explain the cyclical orbital period changes of BH Vir and the periodic component in the changes of the orbital period of ER Vul. These results suggest that the periods of the orbital period oscillations in the four systems may be the magnetic activity cycles.
Non-ideal MHD Properties of Photospheric Flux Tubes
Authors: Kleimann J. , Hornig G.
Published: July 2016

Magnetic flux tubes reaching from the solar convection zone into the chromosphere have to pass through the relatively cool, and therefore highly non-ideal (i.e. resistive) photospheric plasma. It is shown that stationary MHD equilibria of magnetic flux tubes which pass through this region require an inflow of plasma into the tube and a deviation from isorotation along the tube axis. Although for characteristic parameters of thick flux tubes the effect is negligible, a scaling law indicates its importance for small-scale structures. The relevance of this inflow for the expansion of flux tubes above the photosphere is discussed.
Nonlinear Damping of Fast Waves and Plasma Heating in the Solar Corona
Authors: Voitenko Y. , Goossens M.
Published: July 2016

A nonlinear mechanism for the damping of fast magnetoacoustic wave in the solar corona is studied. It is shown that the nonlinear coupling of finite-amplitude fast waves to small-scale Alfven waves can be much faster than damping mechanisms involving classic transport coefficients.
Magnetic Cloud as a Dual-Polarity Flux Rope
Authors: Vandas M. , Geranios A.
Published: July 2016

The magnetic cloud of November 17-18, 1975 is analyzed and it is shown that measurements of magnetic field and solar wind plasma are consistent with the interpretation that this magnetic cloud is a dual-polarity flux rope which consists of a core and an annular region. The core has a strong magnetic field; the annular region has a higher plasma density and opposite magnetic polarity.