bluuebunny/crossref_metadata_2025 huggingface dataset:
7.1. NIR and mm mosaics of the central 100 pc
Authors: Zylka R. , Philipp S. , Duschl W.J. , Mezger P.G. , Herbst T. , Tuffs R.
Published: July 2016

The conditions within the nuclear bulge (NB, R ~ 300 pc) of our Galaxy are extreme: less than 0.1% of the volume of the galactic disc contains more than 10% of the total ISM and stars. There are indications that star formation in the NB is not a continuous process, but rather undergoes cyclic variations. Details of the current and past star formation processes and the stellar content of the central parsecs - especially the ratio of old to young population - are not very well known (Mezger et al., 1996).
7.3. Sgr A∗ in the mid-infrared reference frame: no evidence of an infrared counterpart, or interaction with nearby sources
Authors: Gezari Dan
Published: July 2016

We have determined the position of Sgr A∗ with respect to the mid-infrared (5-25 m) sources in the central parsec by direct correlation of our 12.4 m array image (Gezari et al. 1994) and the new 2-cm continuum VLA map (Yusef-Zadeh 1997; private communication), without a priori knowledge of any other position determinations. Menten et al. (1997) recently succeeded in registering the radio and near-infrared (2.2 m) reference frames with high precision (+0.03 arcsec) using VLA observations of Sgr A∗, SiO masers and H2O masers. Unfortunately, registering the mid-infrared and radio reference frames with comparable accuracy cannot be done by applying the 2.2 m calibration. Most near-infrared sources have no detectable mid-infrared counterparts, and it is not obvious which of those that do are coincident (if any), since near-infrared and mid-infrared emission generally does not arise from the same physical source component. Dramatic examples of shifts between the brightest near- and mid-infrared peaks can be seen in Orion BN/KL and the Ney-Allen Nebula (Gezari and Backman 1994; Gezari, Backman and Werner 1997) corresponding to 0.1 - 0.5 arcsec if they were located at 8.5 kpc. Further, several Sgr A West IRS sources are displaced significantly in the infrared and radio, suggesting they may actually be compact clusters of objects.
7.14. Gaseous accretion flows in the inner parsec of the Galaxy
Authors: Coker Robert , Melia Fulvio
Published: July 2016

Many characteristics of galactic nuclei may be associated with the accretion of ambient gas by a central concentration of mass. Using a 3D hydrodynamical code, we have been simulating this accretion process for Sgr A∗, the compact nonthermal source at the center of the Milky Way, in order to realistically model the gaseous flows in the inner parsec of our Galaxy. In the most recent simulations, we have taken into account the multi-point-like distribution of wind sources and we find that the structure of the flow can be significantly different from that due to a uniform medium. We here present our results concerning the mass and angular momentum accretion rates and discuss how these may be used to set constraints on our Galaxy's central engine.
8.6. Magnetic reconnection as the origin of superhot plasmas in the Galactic center
Authors: Yokoyama T. , Tanuma S. , Kudoh T. , Shibata K.
Published: July 2016

Recent X-ray astronomy satellite (e.g., Ginga, ASCA) has revealed that the center of our Galaxy is filled with a large amount of very hot plasmas (a few − 10 keV) on a scale of 100 pc, which are referred to as superhot plasmas. These plasmas are similar to the Galactic Ridge X-ray Emission (GRXE; cf Tanuma et al. 1997), but with larger gas pressure, and their formation mechanism has been a big puzzle. Here we propose a new model, magnetic reconnection model (Fig. 1), to explain the heating as well as the confinement of the Galactic center superhot plasmas, by performing MHD numerical simulations of magnetic reconnection in the situation suitable for the Galactic center. In our model, the magnetic field is amplified by the rotation of the Galactic gas disk (Fig. 2), and inflate from the disk to outside by the Parker instability. The inflating magnetic loop collides with ambient field lines, thus inducing the magnetic reconnection (the same process applied to the solar corona is shown in Yokoyama and Shibata 1995). In this model, energy release per single reconnection event is ΔE ≈ emVrec ≈ 2 × 1051 erg where em = P/β is the energy density of toroidal magnetic field, Vrec = λ2δ is the volume of the event, λ ≈ 60pc is the most unstable wavelength of the Parker instability, and δ ≈ 3pc is the thickness of the Galactic disk. The occurrence rate of this event is f ≈ N/Δτdep ≈ (3 × 104 yr)−1 where N = Vdisk/Vrec is the number of current sheets in the disk, Vdisk is the volume of the disk, and Δτdep is the time scale of energy deposit which is comparable with the time scale of the Galactic rotation. Then, the heating rate is h = fΔE = 2 × 1039 erg s−1 = 100L2–10keV.
8.9. MHD simulations of jets from accretion disks: nonsteady jets vs. steady jets
Authors: Kudoh T. , Shibata K. , Matsumoto R.
Published: July 2016

We present the results of 2.5-dimensional MHD simulations for jet formation from accretion disks in a situation such that not only ejection but also accretion of disk plasma are also included self-consistently. Although the jets in nonsteady MHD simulations (e.g., Uchida & Shibata 1985, Shibata & Uchida 1986, Matsumoto et al. 1996) have often been referred to as transient phenomena resulting from a special choice of initial conditions, we found that the characteristics of the nonsteady jets are very similar to those of steady jets: (1) The ejection point of the jet, which corresponds to slow magnetosonic point in steady MHD jet theory, is determined by the effective potential which results from the gravitational force and the centrifugal force along a field line (Blandford & Payne 1982). (2) The dependence of the velocity (vz) and mass outflow rate (Ṁω) on the initial magnetic field strength is about Ṁω ∝ B0 and vz ∝ (Ω2FB20/Ṁω)1/3, where B0 is an initial poloidal magnetic field strength, and ΩF is an ‘angular velocity of the field line’ which is nearly the same as the Keplerian angular velocity where the jet is ejected. These are consistent with those of 1D steady solution (Kudoh & Shibata 1997), although the explanation is a little complicated in the 2.5D case because of an avalanche-like accretion. We also confirm that the velocity of the jet is of order of the Keplerian velocity of the disk for a wide range of parameters. We conclude that the ejection mechanism of nonsteady jets found in the 2.5-dimensional simulations are understood with a previous theory which is studied on the assumption of steady state even when nonsteady avalanche-like accretions occur along the surface of disks.
8.11. Magnetic avalanche model of mass supply in active galactic nuclei
Authors: Kuwabara T. , Matsumoto R. , Shibata K.
Published: July 2016

We present the results of axisymmetric, two-dimentional magnetohydrodynamic (MHD) simulations of weakly ionized gas torus threaded by large scale vertical magnetic fields. The gas torus corresponds to the 100pc scale circumnuclear torus observed by HST in nearby AGNs (e.g. NGC4261) or 1010M⊙ circumnuclear gas found by CO observations in luminous IR galaxies and quasars (e.g. Scoville et al. 1991). The initial state of simulation is a constant angular momentum polytropic torus threaded by uniform vertical magnetic fields. The torus is assumed to be rotating in a static, spherical hot halo. The model parameters are Eth = vs02/(γvk02) = 5 ×10−3 and Eth = vA02/vK02 = 6.6×10−6 where γ is the adiabatic index and vs0 and va0 are the sound speed and the Alfvén speed at r = r0 respectively.
8.12. MHD accretion in a black hole magnetosphere
Authors: Takahashi M.
Published: July 2016

To explain the activity of active galactic nuclei or compact X-ray sources, I consider a black hole magnetosphere in the center of these objects. The considering black hole magnetosphere is composed of a massive black hole with surrounding fluids and magnetic fields, and rotates rapidly. Because of the strong gravitation and the rapid rotation, both an accretion and a wind/jet would be generated from plasma sources (e.g., an accretion disk and its corona). The outgoing flow carries the angular momentum from the plasma source effectively, and then the accretion would go on stationary, releasing its gravitational energy. I assume that the magnetosphere is stationary and axisymmetric, and that the ideal MHD approximation is available for the streaming fluid. I discuss the thermal effects on MHD flows, and then I argue that the trans-fast MHD accretion solution can be broken by highly thermal effects.
9.1. HST detections of massive black holes in the centers of galaxies
Authors: Ford H.C. , Tsvetanov Z.I. , Ferrarese L. , Jaffe W.
Published: July 2016

After correcting spherical aberration in the Hubble Space Telescope in 1993, the central masses of galaxies can be measured with a resolution 5 to 10 times better than can be achieved at the best terrestrial sites. This improvement in resolution is decisive for detecting the gravitational signature of massive black holes in galaxy nuclei. The discovery of small (r~ 100–200 pc) rotating gaseous and stellar disks in the centers of many early-type galaxies provides a new and efficient means for measuring the central potentials of galaxies. Concomitantly, VLBI observations of H2O masers in the nuclei of NGC 4258 and NGC 1068 revealed exquisite Keplerian rotation curves around massive black holes at radii as small as 0.1 pc. Recent terrestrialK-band measurements of the proper motions of stars in the cluster at the center of the galaxy provide irrefutable evidence for a black hole with a mass of 2.7 × 106M⊙. At the time of this symposium, the presence of central massive black holes has been established in 12 galaxies. The evidence suggests that there are massive black holes in the centers of all AGNs and in most, if not all, nucleated galaxies. The present data show at best a weak correlation between black hole mass and bulge luminosity.
9.5. The “double nucleus” of M31 in J, H, and K
Authors: Hinz P. , Hege K. , McCarthy D. , Lloyd-Hart M. , Melia F.
Published: July 2016

Hubble Space Telescope images of the nucleus of M31 show a double-peaked structure with the primary peak being offset from the center by approximately 0.5″. We observed the central 13″ of M31 in the J, H, and Ks passbands to determine the nuclear structure in the near-infrared. Observations were taken at the MMT Observatory, using a low-order adaptive optics system, FASTTRAC II (Gray et. al. 1995). The diffraction limit for the system is 0.25″ in K band. PSF images showed correction to 0.5″ FWHM. Uncorrected images showed the seeing to be about 1″. The images were deconvolved using several methods to check for consistency. We used Iterative-Blind Deconvolution, Richardson-Lucy, and Wiener filter algorithms, getting similar results for each. Measurements suggest the PSF in the deconvolved images is approximately 0.35″ FWHM.
9.11. Global VLBI observations of the central region in NGC 3079
Authors: Satoh Satoko , Inoue M. , Shibata K.M. , Kameno S. , Migenes V. , Nakai N. , Diamond P.J.
Published: July 2016

NGC 3079 has very luminous water megamaser from the nucleus, the peak of the spectrum being blueshifted by 180 km s−1 from the systemic velocity of the galaxy (Vsys = 1131 km s−1) (Henkel et al. 1984, Haschick & Baan 1985). Core-jet like continuum structure is also found in the nuclear region (Irwin & Seaquist 1988). No velocity drift for main features of water maser (VLSR = 941–975 km s−1) has been shown (Nakai et al. 1995). However, the drift was recently detected for the maser of 1190 km s−1 (Nakai 1997). HI and OH absorptions are detected in the nucleus (Haschick & Baan 1985, Irwin & Seaquist 1991). Thus this galaxy is very unique object to investigate water masers, continuum structure and absorption features all together with VLBI.
9.13. Story of the discovery of a massive black hole in NGC4258
Authors: Miyoshi M.
Published: July 2016

In the Autumn of 1991, Nakai et al.(1993) began monitoring observations of water mega masers including NGC4258 using Nobeyama 45 m telescope. The 45 m telescope was equipped with wide band cooled HEMT receiver (22 GHz) and wide band spectrometers (AOS). Nakai used 8 AOSs which covered 4480 km/sec in velocity. It was from the wide-band system that the high velocity maser components were detected unexpectedly which locate ±1000 km/sec from the known features of the NGC4258 (Claussen et al. 1984). The finding was in May 1992 when busy Nakai got time checking the data deeply, half year had passed since the beginning of the observations.
10.4. Multi-wavelength VLBA mapping of Sgr A∗
Authors: Shen Zhi-Qiang , Lo K. Y. , Zhao Jun-Hui , Ho Paul
Published: July 2016

Sgr A∗, the enigmatic compact nonthermal radio source located at the center of the Galaxy for many years has been considered as the signpost of a massive black hole (Rees 1982; Lo 1986; Falcke et al. 1997). Its properties are unique in the Galaxy, but it resembles other nuclear radio sources (Lo 1993). Efforts to delineate the source structure of Sgr A∗, in order to constraint the nature of the underlying energy source, have been ongoing since 1975 (Lo et al. 1975).
10.6. Evaporating stars at galactic centers?
Authors: Meynet G. , Mowlavi N. , Schaerer D. , Pindao M.
Published: July 2016

The Geneva group has computed a complete grid of stellar models from 0.8 to 60 M⊙ at a metallicity of Z=0.100 (i.e. 5 times solar, Mowlavi et al. 1997). These stellar models present interesting features such as the nearly complete evaporation of the most massive stars due to intense stellar winds. For instance, for Z >> 0.040, final stages of massive stars (M > 60 M⊙) might be white dwarfs rather than neutron stars or black holes.
11.7. Signature of accretion disks in active galactic nuclei
Authors: Koratkar Anuradha
Published: July 2016

One of the fundamental components of any theory of Active Galactic Nuclei (AGNs) is an accretion disk surrounding a supermassive blackhole. While most theories predict the formation of such a disk, fewer say anything about the observational consequences of the disk. Those studies which have addressed the observational signatures of accretion disks have found that the Lyman edge at 912Å is a powerful diagnostic feature for the physical characteristics of the disk. One of the important consequences of such disks is a feature at the Lyman edge (912Å). Spectroscopic investigations have found scant evidence for Lyman edge features arising in an accretion disk (Koratkar, Kinney and Bohlin 1992). Proving the existence of radiating disks in even a few AGNs would be a major step in our understanding of the phenomenon.
11.10. The propagation of fast magnetoacoustic waves near a rotating black hole
Authors: Abe Junya , Yokosawa Masayoshi
Published: July 2016

We belive that Active Galactic Nucleis(AGNs) have one or a few black holes in the center and get the activity from the binding energy of the matter falling into the black hole or(and) the rotational energy of the black hole. Since the sources of their energy exist near the black hole, the energy have to be carried from the vincity of black hole to a distance by some ways. As one of the way, we study the propagation of the waves (ex. The case of the light waves, Hanni 1977, and of sound wave, Takahashi et al. 1990). We investigated the propagation of fast magnetoacoustic wave. We belive the collimation of jet are caused by magnetic field. Further more, we think that the waves can extract the rotational energy of the black hole. This process is the version of wave of Penrose process(Penrose 1968), and is called the super radiant scattering.
Measurement and Implications of the Cosmic Microwave Background Spectrum
Authors: Mather John C.
Published: July 2016

The Cosmic Background Explorer (COBE) was developed by NASA Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe. It also measured emission from nearby sources such as the stars, dust, molecules, atoms, ions, and electrons in the Milky Way, and dust and comets in the Solar System. It was launched 18 November 1989 on a Delta rocket, carrying one microwave instrument and two cryogenically cooled infrared instruments. The Far Infrared Absolute Spectrophotometer (FIRAS) mapped the sky at wavelengths from 0.01 to 1 cm, and compared the CMBR to a precise blackbody. The spectrum of the CMBR differs from a blackbody by less than 0.03%. The Differential Microwave Radiometers (DMR) measured the fluctuations in the CMBR originating in the Big Bang, with a total amplitude of 11 parts per million on a 10° scale. These fluctuations are consistent with scale-invariant primordial fluctuations. The Diffuse Infrared Background Experiment (DIRBE) spanned the wavelength range from 1.2 to 240 μm and mapped the sky at a wide range of solar elongation angles to distinguish foreground sources from a possible extragalactic Cosmic Infrared Background Radiation (CIBR). In this paper we summarize the COBE mission and describe the results from the FIRAS instrument. The results from the DMR and DIRBE were described by Smoot and Hauser at this Symposium.
Status of the Relict-2 Mission and Our Future Plans
Authors: Strukov I. , Skulachev D. , Budilovich N. , Brjukhanov A. , Nemlikher Yu. , Korogod V. , Kosov A. , Rukavicin A. , Borovsky R. , Nechaev V.
Published: July 2016

We review the main results obtained in the first cosmic experiment for study of the large scale anisotropy of CBR at 8 mm RELICT-1 and compare them with data of COBE mission.
Temperature Fluctuations of the Microwave Background in Primeval Isocurvature Baryon Models
Authors: Dutta S. N. , Efstathiou G.
Published: July 2016

We calculate the temperature fluctuations in the microwave background in open primeval isocurvature baryon models (Peebles, 1987) with cosmological densities in the range 0.05 ≤ ω ≤ 0.2 We assume that the power spectrum of fluctuations is a power law with the index varying between – 1 ≤n≤ 0, as indicated by observations of large scale structure in the Universe. The Universe is assumed to be always fully ionized. The South Pole 13 field point experiment (Schusteret al., 1993) is compared to our theoretical predictions, and we find that the models predict larger temperature fluctuations than are observed. The observed temperature fluctuations on intermediate scales of ≲ 1°thus seem difficult to reconcile with the isocurvature baryon model.
Mapping Large-Scale Structure with Radio Sources
Authors: Wall J.V. , Benn C.R. , Loan A.J.
Published: July 2016

In regions away from the Galactic plane, formal tests indicate an isotropic, random and independent distribution of radio sources on the sky (e.g.[1], although there are strong indications of large-scale anomalies (e.g.[2], [3]). An accommodation of these results was suggested by Shaver and Pierre [4] and by Shaver [5] who showed that the large-scale deviations could be due to the supergalaxy, a possibility which had been noted by Pauliny-Tothet al.in 1978 [6]. As to the influence ofothersuperclusters, or indeed the cellular structure of the universe in which galaxies cluster on scales up to at least 100h−1Mpc (e.g.[7]), at what flux-density level does this large-scale structure become apparent? Conversely, what can be learnt about structure on the largest scales through the sky distribution of radio sources? Here we describe three investigations in various stages of completion which consider these issues.
A Hint to Possible Anisotropy in Radio Universe
Authors: Nan Rendong , Cai Zhengdong
Published: July 2016

This paper presents our investigations of statistical behavior of the small-scale jet orientations and the intrinsic polarization position angles. We found that the distribution of the milliarcsecond-scale jet orientations and intrinsic polarization position angles of extragalatic radio sources appears anisotropic with high significance levels in most cases.
Chance and Non-Chance Clustering in the Universe and Problem of High Redshift Galaxies in Compact Groups
Authors: Anosova Joanna , Kiseleva Ludmila
Published: July 2016

In previous work (Anosova, Kiseleva 1993) we have studied the statistical properties of Hickson's (1982) compact galaxy groups. We have shown that most of these groups are confident and probable physical systems of galaxies. Only about 13% of galaxies can be non-members of their groups due to the effects of projection.
Analysis of the CFA “Great Wall” Using the Minimal Spanning Tree
Authors: Bhavsar S.P. , Lauer D.A.
Published: July 2016

MST analysis shows the “Great Wall” as a statistically significant linear feature in the galaxy distribution. It is not as long as visual impressions may suggest. Another “Wall” extends radially, perpendicular to the GW. These two walls intersect at the Coma cluster.
Mutual Interference and Structural Properties of Object Images in the Vicinity of the Gravitational Lens CUSP Point
Authors: Mandzhos Av.
Published: July 2016

Gravitational lens system could form multiple images of the same radiating surface of a cosmic object. The radiation fluxes of these images interfere to one another (Refsdal, 1964). The practical importance of this effect is seems to be as follows: (i) it is the only direct test of microlensing (Schneider et al. 1985); (ii) this effect may say about fine structure of a lensed object; (iii) it must be allowed for simulations of microlensing process. The maximum effect is expected in the case when a cusp point of the microlensing caustic is projected on the lensed object. To investigate the interference effect in this case, the exact solution of the lens equation in the vicinity of the cusp point was obtained (Mandzhos, 1993):were ξ, η are dimensionless coordinates of a radiating element on the object plane; x, y are coordinates of the point at which the lens plane is intersected by light beam; furthermore:whereis the lens scalar potential.
Field Spectroscopy Observations of the Gravitational Lenses H1413+117 and Q2237+030. Preliminary Results
Authors: Afanasiev V.L. , Balayan S. , Dodonov S.N. , Khmil S.V. , Mandzhos A.V. , Spiridonova O.I. , Vlassiuk V.V. , Zhdanov V.I.
Published: July 2016

The long-term observational programme for investigation of quasar microlensing spectral effects was devised and now is implemented at the Special Astrophysics Observatory (Russia, N.Arkhys) and at the Astronomical Observatory of Kiev University (Ukraine, Kiev). The main goal of this programme is to study the fine quasar structure. For this purpose the observations of the gravitational lenses H1413+117 and Q2237+030 are carried out with the 6m SAO telescope in the integral field spectroscopy mode. The suitable equipment for such observations - the Multi-Pupil Field Spectrograph - was designed and built in SAO. From February 1993 several observations of each of these objects were performed. Here we present the preliminary results of the Clover Leaf observations on April 23/24, 1993. The quasar images are separated by angles nearly 1 arcsec. At seeing of the order of 1.5 arcsec the separation of the individual quasar image spectra was a problem. For this purpose a special procedure is developed. This procedure is based on the maximum likelihood hypothesis to restore a simple 4-point source picture plus the background. The effect of light scattering for a point source was simulated by means of observations of a reference star. Statistical properties of the radiation flux in question were studied by using the data of photon registration each 40 msec. The individual spectra of quasar images were obtained. The internal relative errors of the spectra separation procedure vary from 7 to 12% depending on wavelength. The spectra of quasar images 1, 2, 4 are not actually distorted. On the contrary, in the spectrum of the third image the profile of the emission line CIV differs considerably from the profile of the same line in the “undisturbed” quasar spectrum. Fig. 1a,b show the spectra of the 1st and the 3rd images.
Tauvex and the Nature of the Cosmological UV Background
Authors: Brosch Noah
Published: July 2016

TAUVEX is a three-telescope array intended to image wide sky areas in the UV. It is being constructed in Israel for flying on-board the Spectrum X-γ (SRG) international high-energy observatory. SRG will be orbited by Russia in early 1996 for a three-year+ mission. TAUVEX will operate in parallel with X-ray imaging telescopes on board SRG to provide time-resolved photometry and deep UV imaging.
Cosmological Models in AP-Spaces
Authors: Wanas M.I.
Published: July 2016

To solve some of the problems of standard cosmology, the Absolute Parallelism (AP) space is used to construct alternative field theories other than GR. Four different field theories are being reviewed. The consequences of their cosmological applications are being compared with those of GR. The results are promising and show that more investigations, concerning this space, are needed, especially generalization of the singularity theorems.
A New Class of Solar Oscillation Measurements
Authors: Schou J.
Published: July 2016

Over the past few years the quality and quantity of basic helioseismic data have increased dramatically as instruments such as MDI on the SOHO spacecraft and the GONG network have become operational. The data from these new instruments have led to a significant increase in our ability to make inferences about the solar interior, and resulted in a long series of often surprising and spectacular discoveries. In this review I describe some of the most recent results and what progress we may be able to make in the near future with improved analysis methods and with a better understanding of solar oscillations and the instruments used to observe them.
Interior Solar-Cycle Changes Detected by Helioseismology
Authors: Howe R. , Hill F. , Komm R. W. , Christensen-Dalsgaard J. , Munk Larsen R. , Schou J. , Thompson M. J. , Toomre J.
Published: July 2016

Helioseismic measurements with the MDI instrument aboard SOHO, and complementary measurements from the GONG network, are revealing changes deep within the Sun as the solar cycle progresses. We present results based on recent data from both experiments, including variations in the rotation rate deep inside the convection zone.
Recent Progress in Asteroseismology
Authors: Christensen-Dalsgaard J.
Published: July 2016

Asteroseismology, the study of stellar interiors on the basis of observations of multi-mode stellar oscillations, extends over a large part of the Hertzsprung-Russell diagram. The recently discovered EC14026 stars promise information about the properties of stars on the horizontal branch. Solar-like oscillations excited stochastically by convection have been tentatively identified in a few cases. Promising examples are giant stars, where the expected amplitudes may make ground-based observations of the oscillations relatively straightforward. Major advances can be expected from the upcoming asteroseismic space projects under development or study, including the Eddington mission adopted by ESA as a ‘reserve mission’ in the recent round of selections.
Asteroseismology of the Rapidly Oscillating Ap Stars
Authors: Bigot L.
Published: July 2016

The pulsation properties of the rapidly oscillating Ap (roAp) stars are briefly presented. The combined effect of a strong magnetic field and rotation on pulsations is also discussed.
New Insight in Sounding the Solar Interior
Authors: Godier S. , Rozelot J.-P.
Published: July 2016

The solar limb is potentially a sharp spatial reference with which we can detect the effects of solar oscillations (both pression and gravitation modes), the quadrupole moment -and higher moments if any-, the true shape of the helioid (the oblateness at the first order), and changes in the solar radius. It is shown in this paper, that the accurate determination of the successive differential gravitational moments are useful to probe the solar interior. We emphasize the main reasons, mainly the accurate determination of the planetary orbits and the adjustement of the Eddington-Robertson coefficient of the PPN gravitational theory. Moreover, both the shape and the radius measurements of the Sun help to determine the solar luminosity, as empirical models of total irradiance (solely based on magnetic effects) can not explain all aspects of irradiance changes. A complete theory is still pending. The space mission Picard, currently scheduled by the end of 2004 and currently under a manufacturing process, will lead to validate our differential theory.
Subsurface Flows with Advancing Solar Cycle Using Dense-Pack Ring-Diagram Analyses
Authors: Haber D. A. , Hindman B. W. , Toomre J. , Bogart R. S. , Hill F.
Published: July 2016

Ring-diagram analyses have become a powerful local helioseismic tool for studying large-scale flows in the upper solar convection zone. Using this technique on a dense-pack mosaic of many small regions extracted from the full-disk Doppler velocity data taken with the Michelson Doppler Imager (MDI) on SOHO, we study how the mean meridional and zonal flows vary with depth and latitude over the course of the advancing solar cycle from 1996 to 2000.
Flux Separation in Photospheric Magnetoconvection
Authors: Weiss N. O. , E. Proctor M. R.
Published: July 2016

Numerical experiments on three-dimensional magnetoconvection in a stratified compressible layer reveal a range of different patterns, depending on the strength of the imposed magnetic field. As the field is decreased there is a transition from small-scale plumes, in the magnetically dominated regime, to large-scale vigorous plumes when the field is dominated by the motion. In the intermediate regime magnetic flux separates from the motion, so that there are almost field-free regions, with clusters of vigorous plumes, surrounded by regions where the Lorentz force is strong enough to control the dynamics. There is a range of field strengths where either small-scale plumes or flux-separated solutions can persist, depending on initial conditions for the computation. These results can be related to magnetic features at the surface of the Sun.
Soft X-ray Flares and Magnetic Configuration in Solar Active regions
Authors: Zhang H.
Published: July 2016

In this paper, we analyze the soft X-ray flares and the relationship with photospheric vector magnetograms and current helicity in solar active regions.
Formation of Arching Flux Tubes at the Base of the Solar Convection Zone
Authors: Fan Y.
Published: July 2016

Solar active regions are believed to correspond to the topmost portions of Ω-shaped arching flux tubes that have risen buoyantly from the base of the solar convection zone, where strong toroidal magnetic fields are being generated by the dynamo process. The development of such emerging Ω-loops is likely a result of the buoyant instability associated with the submerged toroidal magnetic field. Using an anelastic MHD code, we simulate the formation of buoyant, arching flux tube structures as a result of the non-linear growth of the undular instability of a neutrally buoyant layer of horizontal, unidirectional magnetic field at the base of the solar convection zone.
Solar Flare Observations at Submm-waves
Authors: Kaufmann P. , Raulin J.-P. , Correia E. , Costa J. E. R. , Giménez de Castro C. G. , Silva A. V. R. , Levato H. , Rovira M. , Mandrini C. , Fernández-Borda R. , Bauer O.
Published: July 2016

First 405 GHz and 212 GHz solar flare observations were obtained during short campaigns while the new solar submillimeter-wave telescope (SST) was still undergoing adjustments at the CASLEO El Leoncito observatory in the Argentina Andes. We show here preliminary results for a large X1.1 class X-ray event occurred on 2000 March 22, which exhibited a small submm-w continuum response to the slow (minutes) bulk flare emission, and numerous subsecond spikes (100-300 ms), the brightest spikes reaching about 180 and 50 s.f.u. at 405 and 212 GHz, respectively.
Resonant Transmission of Magneto-atmospheric Waves in Sunspot Umbrae
Authors: Staude J. , Rendtel J. , Settele A.
Published: July 2016

We discuss intensity and velocity oscillations which were observed by SOHO in lines of C IV and Ne VIII formed in the EUV plume above a sunspot during a continuous time series of 4.3 hours. Applying a wavelet analysis, we find periods mainly around 3 mHz; the behavior in time is different for the different EUV lines and strongly intermittent, for the velocity oscillations in particular. Moreover, we discuss the observed oscillations within the frame of model calculations for the resonant transmission of magneto-atmospheric waves through realistic models of the sunspot atmosphere. The nonstationary behavior could hint at the appearance of blinkers in the umbral transition region.
Flare-CME Events Associated With a Superactive Region
Authors: Wang J. , Zhang J. , Wang T. , Zhang C. , Liu Y. , Nitta N. , Slater G. L.
Published: July 2016

In a few recent studies, 8 coronal mass ejections (CMEs) were identified to associate with a superactive region, AR 8100. They were all flare-CME events, It is found that the region is characterized by vigorous flux emergence and an imbalance of magnetic flux in two polarities. With the continuous flux emergence and its driven flux cancellation, the EUV dimming associated with flare activity increased in area. Whenever the dimming extended to an area of more than 50×50 square degrees on the solar surface, a flare in the region became CME-associated.
Solar Flares and Related Coronal Magnetic Field Structures in NOAA 8100
Authors: Yan Y.
Published: July 2016

In this paper we describe the available methods for the non-constant-α force-free field reconstruction and study the associations between reconstructed 3-d coronal fields by a new technique and the 2B/X2 flare process from observations in AR 8100 on 4 November 1997.
Looking for the FIP Effect in EUV Spectra
Authors: Dwivedi B. N. , Landi E. , Mohan A.
Published: July 2016

We present results from a study of extreme-ultraviolet (EUV) off-limb spectra obtained with the SUMER instrument on the spacecraft SOHO. Using EUV line intensities, we deduce plasma temperatures and densities in the off-limb solar plasma. We make use of this information to study the FIP effect in the solar corona. We have looked for FIP effect in EUV spectra obtained by SUMER in a considerable detail. In particular, we report K/Ar, Si/Ar and S/Ar relative element abundances and investigate the height dependence of the FIP bias in the solar corona. Also, we study the relative Mg/Ne abundance in an active region at the solar limb to investigate the correlation of the FIP bias with magnetic loop structures in the field of view.
Source Regions of Coronal Mass Ejections
Authors: Dere K. P. , Subramanian P.
Published: July 2016

Observations of the solar corona with the LASCO and EIT instruments on SOHO provide an unprecedented opportunity to study coronal mass ejections (CMEs) from their initiation through their evolution out to 30 R⊙. The objective of this study is to gain an understanding of the source regions from which the CMEs emanate. To this end, we have developed a list of 32 CMEs whose source regions are located on the solar disk and are well observed in EIT 195 Å data during the solar minimum phase of January 1996-May 1998. We compare the EIT source regions with photospheric magnetograms from the Michelson Doppler Imager (MDI) instrument on SOHO and the NSO/Kitt Peak Observatory and also with Hα data from various sources. The overall results of our study show that 59% of the CME related transients observed in EIT 195 Å images are associated with active regions without prominences, 22% are associated with eruptions of prominences embedded in active regions and 19% are associated with eruptions of quiescent prominences. We describe 3 especially well observed events, one from each of these 3 categories. These case studies suggest that active region CMEs are associated with active regions with lifetimes between 11-80 days. They are also often associated with small scale emerging or cancelling flux over timescales of 6-7 hours. CMEs associated with active region prominence eruptions, on the other hand, are typically associated with old active regions with lifetimes ~ 6-7 months.
Flare and CME Onset: UV Spectra Show Fast 3-D Flow
Authors: Innes D. E.
Published: July 2016

We present observations taken in the corona above a flare that occurred on the west limb of the Sun. SUMER spectra show large red (350 km s−1) and blue (650 km s−1) Dopplershifts in Fe XX (107 K), Cr XVI (5 × 106 K), Si IX (106 K) and O III (105 K) emission lines. These shifts are associated with a fast moving (400 km s−1) optical emission front detected in high cadence images, taken with the coronagraph MICA. SXT images show fast soft X-ray ejecta that can be extrapolated back to the position of pre-flare coronal arcade structure seen in EIT 195 images. The observations are interpreted as evidence of a blast wave propagating through the active region coronal loop structure very early in the flare evolution.
Computed vs. Observed Line Profiles of Metallic Atoms in Prominences
Authors: Cirigliano D. , Rovira M. , Mauas P. , Stenborg G.
Published: July 2016

By solving simultaneously the radiative transfer and statistical equilibrium equations we compute lines profiles for the Ca II H and K lines, Mg II h and k lines and He I at 584,3 Å for several prominence models given by the hydrogen atom. The computed profiles are compared with the observations in order to constrain the physical plasma parameters of solar prominences.
Solar Polar Rays Are Not Polar
Authors: Li J. , Jewitt D. , LaBonte B. , Acton L.
Published: July 2016

We discuss the nature of polar rays, based on limb synoptic images constructed from Yohkoh/SXT and SORafElT data. In the literature, polar rays and polar plumes are often mentioned interchangably. We find that polar rays are projection effects caused by hot plasma from equatorial active areas and are not physically associated with the coronal polar holes. Instead, the rise in number and strength of polar rays toward solar activity maximum may be responsible for hiding the polar holes and polar plumes.
A Comparison of Coordinated TRACE and EIT Observations
Authors: Zhang M.
Published: July 2016

Using coordinated TRACE and EIT observations, we discussed which pair of coronal abundances and ionization equilibrium assumption will give the least difference of temperature and emission maps. It is found that the combination meyer_coronal.abund and shull.ioneq gives the smallest difference between TRACE and EIT observations among the 42 pairs of combination, while the difference between each pair is not much. The difference between temperature or emission maps from coordinated TRACE and EIT observations may be regarded as an estimation of the accuracy of the temperature or emission maps using this kind of method. Under this assumption, the error for temperature diagnosis is estimated at Δ(log10T) = 0.01 and the error for emission diagnosis is estimated at Δ(log10EM) = 0.08 at largest.
Observations and Models of the Fast and Slow Solar Wind
Authors: Marsch E.
Published: July 2016

There are two major types of solar wind. The steady fast wind originating on open magnetic field lines in coronal holes, and the unsteady slow wind coming from the bulk or boundary layer of streamers, which are mostly magnetically closed but may open up temporarily. Many observations of the solar wind have in the past been made in situ and remotely. Key empirical constraints, which are imposed on the models by the Helios (near-Sun, in-ecliptic) and Ulysses (high-latitude) interplanetary measurements and by the Solar and Heliospheric Observatory (SOHO) plasma diagnostics, are discussed with respect to the fluid and kinetic properties of the wind. The majority of the models is concerned with the fast wind, essential properties of which can be reproduced by 1-D multi-fluid models involving broad-band waves. Owing to its time-variable nature, no robust understanding of the slow wind exists. Selected results from modelling and observations are discussed.
Stellar Coronae
Authors: Schmitt J. H. M. M.
Published: July 2016

The last two decades have seen the emergence of a new field in stellar astrophysics, the study of stellar coronae mostly in X-ray domain. With the advent of soft X-ray imagery X-ray emission was found from many thousands of solar-like stars. I will summarize the most important findings of X-ray surveys of late type stars and put the results in the context of the solar-stellar connection.
A Spectroscopic Study of the Solar Corona from Norikura and SOHO data
Authors: Raju K. P. , Sakurai T. , Ichimoto K.
Published: July 2016

We report the results from a spectroscopic study of the solar corona using both ground-based and space-based data. Some of the current topics in coronal physics, such as the plume-interplume differences in coronal holes and wave propagation in the corona have been examined. The distribution of emission line intensities, Doppler velocities and line widths were obtained from the spectroscopic observations from Norikura Solar Observatory of National Astronomical Observatory of Japan. The coronal images in Fe IX,X 171 Å and Fe XII 195 Å from SOHO EIT were used to get the temperature map of the corona. Combining both results, we have obtained the nonthermal velocities in the coronal hole region, without the usual assumption of a uniform ion temperature. It has been found that the histogram distributions of Doppler velocities and nonthermal velocities for coronal hole and quiet regions are markedly different. The nonthermal velocities have been found to be larger by about 27 %at the interplume regions as compared to plumes which supports the view that the interplume regions are the source regions of the fast solar wind. The analysis of the time sequence spectral data shows signatures of coronal oscillations at localized regions. Periods of the order of a few minutes have been found mainly in Doppler velocities.
Particle Acceleration on the Sun and in the Heliosphere
Authors: Roelof E. C.
Published: July 2016

Examples of the acceleration of energetic ions and electrons are given for the Sun, the middle heliosphere, and the outer heliosphere. The characteristics of the acceleration are revealed only after the effects of energetic particle propagation are understood.
Isotopic Fractionation in Slow and Coronal Hole Associated Solar Wind
Authors: Kucharek H. , Klecker B. , Ipavich F. M. , Kallenbach R. , Grünwaldt H. , Aellig M. R. , Bochsler P.
Published: July 2016

Data from the Mass and Charge Time-of-Flight spectrometers MTOF and CTOF on board SOHO have been accumulated for time periods in which coronal hole and non-coronal hole type plasma has been detected by using different methods in order to determine the abundance ratios of magnesium isotopes in these two different source regions of the solar wind. As indicators for the two different solar wind type plasma we have used several plasma parameters such as, the freeze-in temperatures, the Fe/O and the He/H ratio, which are known as reasonable indicators. For this study we have used the refractory element Mg which is an authentic whitness for matter in the solar nebula because temperatures of the Sun never have been high enough to change their isotopic composition by nuclear burning. In addition Mg has three isotopes with abundance ratios greater than about 10% and therefore they are easy to observe.
Shock Drift Electron Acceleration and Pitch Angle Scattering
Authors: Vandas M.
Published: July 2016

Spacecraft measurements of energetic electrons in the vicinity of the Earth's bow shock and interplanetary shocks are analyzed and compared with theoretical calculations. It is concluded that shock drift acceleration of electrons is very modified by an additional process, probably by strong pitch angle scattering. Calculations including this effect are presented.
Results of the SiO Maser Survey of the Galactic Bulge IRAS Sources
Authors: Deguchi S. , Ukita N. , Izumiura H. , Ono T. , Nakada Y. , Onaka T. , Yamamura I. , Hashimoto O.
Published: July 2016

Evidence for the bar structure in our Galaxy has been shown by Blitz and Spergel (1991b) based on the near-infrared maps of the bulge, by Nakada et al. (1991) based on IRAS point source catalogue, and more clearly by recent COBE maps. However, no clear “dynamical” signature of the bulge bar has been found yet. At optical wavelengths, stellar radial velocities of the bulge stars were observed only at the optical windows and were not observed for the entire region of the bulge because of the dust extinction in this direction.
The Radio Spectrum of Sgr A∗
Authors: Duschl Wolfgang J. , Lesch Harald
Published: July 2016

We discuss the radio spectrum of Sgr A∗ in the frequency range between ≈ 1 GHz and ≈ 1 000 GHz, show that it can be explained by optically thin synchrotron radiation of relativistic electrons, and point toward a possible correlation between the spectrum of Sgr A∗ and larger-scale (≲ 50 pc) radio emission from the Galactic Center region.
Mid-Infrared (4.8–12.4 and 20.0 μm) Imaging of the Galactic Center: Modeling the Dust Emission and Energetics of the Central Parsec
Authors: Gezari Dan , Dwek Eli , Varosi Frank
Published: July 2016

We have modeled the mid-infrared emission from the Galactic Center using our array camera images at eight wavelengths. The results suggest that the high infrared luminosity of the region is provided by a cluster of luminous stars. There is no direct indication in the new model results of a very luminous object or “central engine” near Sgr A∗.
The Hot Gas in the Galactic Bulge
Authors: Koyama K. , Maeda Y.
Published: July 2016

X-ray imaging spectroscopic observations near the Galactic center region were carried out with the ASCA satellite. We found two bright spots very close to the Galactic center (Sgr A∗); one is extended and has a soft spectrum associated with strong emission lines from highly ionized irons, while the other is a point-like object with a harder spectrum and a larger absorption. We also found extended emission with K-shell transition lines from highly ionized Si, S, Ar, Ca and Fe. Remarkable feature found with ASCA is an extended emission of 6.4 keV lines of low ionization irons. The 6.4 keV line fluxes are found to be well correlated to the region of cool clouds. We interpret that the 6.4 keV line is due to florescence from the cool clouds irradiated by strong (and obscured from our line of sight) X-ray beams.
Motions and Deformations of the Inner-Galaxy Neutral Gas Layer
Authors: Liszt H. S. , Burton W. B.
Published: July 2016

Neutral gas in the inner few kpc of the Milky Way is notable for showing strong non-circular motions, large excursions from the nominal galactic plane, and an overwhelming preponderance of molecular (rather than atomic) neutral gas. Here, we discuss the coherent nature of the kpc-scale tilts seen in H I and CO emission and demonstrate the congruence of the inner-Galaxy atomic and molecular gas distributions, out more than 1 kpc in radius and 300 pc vertically from the center. We point out that features in inner-Galaxy spectra can usually not be identified with discrete, underlying material entities, but instead arise solely as the result of kinematic projection effects.
Stellar Populations in the Galactic Bulge
Authors: Habing H.J.
Published: July 2016

In this review I discuss stars in the bulge of our Milky Way, but I exclude stars within a few parsec from Sgr A West; they are the subject of other reviews at this Symposium. We should, however, not forget that there may be an intimate connection between the central cluster and the bulge: bulge stars may eject matter that feeds the monster at the center and eruptions by this monster may have an important effect on the bulge.