bluuebunny/crossref_metadata_2025 huggingface dataset:
Photospheric Flow Fields and Properties of Embedded Small-scale Magnetic Flux Concentrations
Authors: Rajaguru S. P. , Srikanth R. , Hasan S. S.
Published: July 2016

The association between the different scales of convection on the solar photosphere and the field strengths/flux content of discrete magnetic flux concentrations is analyzed using simultaneously recorded SOHO/MDI high resolution filtergrams and magnetograms. The convective flow field is derived using the Local Correlation Tracking (LCT) technique. The locations and strengths of the flux elements with respect to the flow cells are analyzed to obtain information about different scales of convection.
Fractional Frequency Shifts of Local Helioseismic Modes With Magnetic Activity Using Ring-Diagram Analysis
Authors: Hindman B. , Haber D. , Toomre J. , Bogart R. S.
Published: July 2016

Using full-disk Doppler velocity data from MDI on SOHO, we have determined the central frequencies of high-degree p modes and f modes over a dense mosaic of localized regions on the sun using ring-diagram analyses (Haber et al. 2000). The motion of active regions as they rotate across the solar disk is well traced by changes in the central frequencies of the acoustic wave modes. Active regions appear as locations of large positive frequency shifts.
The Emergence of Magnetic Flux in Active Regions
Authors: Abbett W. P. , Fisher G. H. , Fan Y.
Published: July 2016

Over the past decade, “thin flux tube” models have proven successful in explaining many properties of active regions in terms of magnetic flux tube dynamics in the solar interior. On the other hand, recent 2-D MHD simulations of the emergence of magnetic flux have shown that many of the assumptions adopted in the thin flux tube approximation are invalid. For example, unless the flux tubes exhibit a large degree of initial field line twist — and observations of emerging active regions suggest they do not — they will fragment (break apart) before they are able to emerge through the surface. We attempt to resolve this paradox using a number of 3-D MHD simulations (in the anelastic approximation) that describe the rise and fragmentation of twisted magnetic flux tubes. We find that the degree of fragmentation of an evolving Ω-loop depends strongly on the 3-D geometry of the loop, and that the Coriolis force plays a dynamically important role in the evolution and emergence of magnetic flux.
Active Longitudinal Structures of the Sun from MDI and EIT Observations
Authors: Benevolenskaya E. E. , Kosovichev A. G. , Scherrer P. H.
Published: July 2016

We present results of investigation of the large-scale structure of the solar corona during the transition period between solar cycles 22 and 23 and at the beginning of the current cycle 23 using the SOHO/EIT EUV data obtained in 171 Å, 195 Å, 284 Å and 304 Å lines. For this analysis the data were transformed into synoptic maps for each of the spectral lines, and for the 195/171 line ratio which is an index of the coronal temperature. The synoptic maps reveal stable longitudinal structures in the coronal intensities and temperature, which are related to large-scale magnetic field structures. We discuss the relation between the coronal and photospheric magnetic structures obtained from the SOHO/MDI data, and compare the rotation rates of these structures with the rotation profile of the solar interior in order to determine the possible origin of the coronal structures.
Magnetic Shear and Nonpotential Energy Evolution of Solar Minimum and the Onset of Solar Cycle 23
Authors: Dun J. , Zhang H. , Zhang B. , Li R.
Published: July 2016

Using a 1995-1998 data set of vector magnetograms, the magnetic field flux, shear angle of the transverse field and nonpotential energy of active regions were calculated. The evolution of these parameters were analyzed together with time series of the solar monthly sunspot relative number and area to study their relationships in the ascending phase of solar cycle 23. We find the magnetic flux and nonpotential energy have a good correlation with sunspot relative number and area. But the magnetic shear angle does not develop as above indices.
EUV Line Intensities and the Magnetic Field in Solar Active Regions
Authors: Ireland J. , Fludra A.
Published: July 2016

The Coronal Diagnostic Spectrometer (CDS) on SOHO carries out daily synoptic observations of the Sun in four EUV (extreme ultraviolet) spectra: He I 584 Å, O V 630 Å, Mg IX 368 Å and Fe XVI 360 Å, over a 4 arcmin-wide strip along the solar central meridian. Using 53 active regions observed in this data set along with co-temporally observed SOHO-MDI (Michelson Doppler Imager) magnetograms we study the correlation of the chromospheric, transition region and coronal emission with the photospheric magnetic field for meridional active regions, probing the relation between the radiative output and magnetic observables. We also establish empirical, quantitative relations among intensities of different lines, and between intensities and the magnetic field flux.
SUMER/SOHO Observations of Long Period Oscillations in an Active Region Filament
Authors: Régnier S. , Solomon J. , Vial J. C.
Published: July 2016

During the MEDOC campaign #4 (October 1999), we observed an active region filament with the SUMER/SoHO spectrometer using the 584.33 Å HeI line. After a description of the HeI line profile in the filament, we present a Fourier analysis of SUMER long time observations. This analysis allows to detect oscillations in several ranges of periodicities: 6–20 min, 40–90 min. We discuss these periodicities in terms of Alfvén and magnetoacoustic waves obtained with a filament model developed by Joarder & Roberts (1993).
Magnetic Field Reconstruction in a Solar Active Region
Authors: Wang H. , Yan Y. , Sakurai T.
Published: July 2016

Supposing coronal magnetic fields are in a force-free state from the chromosphere to the height of two solar radii, we reconstruct 3D force-free magnetic fields by making use of a new numerical technique, in which the fields are represented by a boundary integral equation based on a specific Green's function. Vector magnetic fields observed on the photospheric surface can be taken as the boundary conditions of this equation. Magnetic fields in AR8270 on 14 July 1998 were employed as an example to exhibit the capability of this numerical technique.
Evolution of the Filament and the Eruption of the Two-Ribbon Flare on MAY 13, 1981
Authors: Xu A. A. , Wu G. P. , Tang Y. H.
Published: July 2016

Using the observational Hα, radio and X-ray data, we measure the ascending movement of the filament in the active region, and derive the current intensity and the current distribution inside the filament. The comparison between the ascending filament and the position of the hard X-ray image shows that they are co-spacial. These results suggest that the physical process in the thermal and non-thermal phases of the flare could be explained respectively by the tearing instability occurred inside the filament and the revised Alfvén-Carlqvist current interruption theory. The theoretical calculations are basically consistent with the observations.
Transition Region Blinkers
Authors: Parnell C. E. , Bewsher D. , Harrison R. A. , Hood A. W.
Published: July 2016

To allow an objective study of transition region blinkers an automated identification program has been developed to analyse the CDS/SoHO data. The general properties of blinkers identified by this method confirmed the properties of those identified by eye in previous studies. Blinkers have typical lifetimes of about 20 minutes, areas of about 2.8 × 107 km2 and intensity enhancement factors of about 2. For the first time, blinkers have been identified in active regions. These blinkers have the same general properties as quiet-region blinkers. The automated approach found many more blinkers than previously had been found giving a global birth rates of about 9 s−1 for quiet-region blinkers and 16 s−1 for active-region blinkers. Most blinkers, active or quiet region, are red shifted with typical velocities of about 13 km s−1. Finally, we can confirm that blinkers are not enhancements in temperature, but either enhancements in density or increases in the filling factor.
An Analysis of the Solar Rotation Velocity by Tracing Coronal Features
Authors: Brajša R. , Vršnak B. , Ruždjak V. , Roša D. , Hržina D. , Wöhl H. , Clette F. , Hochedez J.-F.
Published: July 2016

The solar rotation is determined tracing coronal EUV and soft X-ray bright points, active regions, parts of coronal holes and foot points of coronal loops. Full-disc solar images in the EUV part of the spectrum from the SOHO spacecraft (EIT, Fe XV, 28.4 nm) and from the Yohkoh satellite (SXT, 2 nm) are used.
Cyclic Variation in the Solar Lower Atmosphere
Authors: Fang C. , Zhang Y. X. , Ding M. D. , Livingston W. C.
Published: July 2016

CaII K line has been measured regularly nearly every month since 1974 at Kitt Peak. Our study on the data of CaII K profiles over two solar cycles indicates that in center disc spectra, the distance of the K1 component of the CaII K line from the line center and its intensity show periodical variations, but has a time delay of 1.2 years with respect to the sunspot number. Non-LTE computation implies a cyclic temperature variation of about 17 K of the temperature minimum region (TMR) in the quiet-Sun atmosphere and a cyclic variation of about 15-20 km of the position of the TMR.
Anomalous Line Shifts on the SOHO/CDS NIS Detector
Authors: Haugan S. V. H.
Published: July 2016

Observations with the SORO/CDS NIS detector prior to the recovery of SOHO showed strong correlations between line shifts and local intensity gradients along the slit, probably caused by an elliptical, tilted point spread function. This must be taken into account when interpreting NIS observations with strong intensity gradients. An initial analysis of post-recovery data does not display the same pattern, indicating that this particular problem was eliminated by changes in the optics during SOHO's “vacation”.
Statistical Study of Solar Eruptive Events Observed with Nobeyama Radioheliograph at 17 GHz
Authors: Hori K.
Published: July 2016

We report statistical features of 49 eruptive prominences observed near solar maximum (1999-2000) with Nobeyama Radiohelograph. Here we focus on the location and related phenomena of the prominence activity. By using white light synoptic maps from LASCO C2 coronagraph, we found that most of the events are associated with some heating process taking place around the prominence site, and occur along pre-existing streamers associated with CMEs as well as small mass ejections. These features suggest that streamers connect the activity on the solar surface toward the outer corona.
Electron Density Enhancement During an UV Explosive Event
Authors: Madjarska M. S. , Doyle J. G. , Teriaca L.
Published: July 2016

High resolution temporal observations performed with the SUMER spectrometer on SoHO provide us the opportunity to investigate the electron density variations in the solar mid-transition region due to explosive event-like phenomena. The O IV 1401.16/1404.81 density sensitive line intensity ratio shows a clear increase during a strong explosive event, corresponding to an electron density enhancement of a factor of ~ 3 with respect to pre-event values. This is consistent with recent MHD simulations (2.5 D).
Plasma Parameters of a Prominence Observed on October 16/17 1999 by SUMER and CDS/SOHO
Authors: Madjarska M. S. , Vial J.-C. , Bocchialini K. , Dermendjiev V. N.
Published: July 2016

The aim of the present study is to confirm and enrich the results obtained so far on dynamics and diagnostics of solar prominences. A prominence observed on October 16/17, 1999 in the frame of the updated JOP09 was studied. A density diagnostics was made on the basis of the line intensity ratio O IV 1401/1404. The Doppler velocities were derived using SUMER Si IV, O IV and CDS O V 629.73 Å lines.
Statistical Features of the Quiet Sun in EUV
Authors: Pauluhn A. , Solanki S. K. , Rüedi I. , Landi E. , Schühle U.
Published: July 2016

Frequency distributions of the intensities of EUV emission lines in the quiet Sun have in the past usually been modelled using two Gaussians. Here we test this and other distribution functions against observed distributions with exceptional statistics. The data were obtained in a number of spectral lines observed with CDS and SUMER. We show that the frequency distribution of the radiance is best modelled by a lognormal distribution. The fact that the radiance distribution of the quiet Sun including the network and the intranetwork is better reproduced by a single lognormal distribution function than by two Gaussians suggests that the same heating processes are acting in both types of features.
Oscillations Observed in Intensity and Velocity for a Quiescent Prominence
Authors: Bocchialini K. , Costa A. , Domenech G. , Rovira M. , Vial J.-C.
Published: July 2016

We present the results obtained from analyzing SUMER/SOHO observation data of a quiescent solar prominence. From the 1 hour data set, we derive via a wavelet transform, characteristic frequencies in terms of intensity and velocity oscillations, as measured in 4 transition region lines.
SUMER Observations of the Solar Transition Region: Spatial and Temporal Behaviour
Authors: Teriaca L. , Doyle J. G. , Banerjee D.
Published: July 2016

We examine the spatial and temporal behaviour of the quiet Sun transition region (TR) using high resolution SUMER observations in O VI 1032 Å. A detailed study of raster images allows us to differentiate the network and internetwork through Doppler shift and line width measurements. The oscillatory nature of the TR is investigated using wavelet analysis over a series of spectra obtained with high temporal cadence.
TRACE Emission Heights Estimated from TRACE Limb Observations
Authors: Zhang M.
Published: July 2016

While TRACE data have provided us much information of transition region and coronal structures, many TRACE data users would like to have a knowledge of emission heights of TRACE bands. By analyzing TRACE limb observations, we give an average estimation of emission heights of TRACE 171, 195 and 1216 bands for different features like quiet Sun regions, active regions and coronal holes. Average emission heights over the limb are also discussed. Previous equator-to-pole height variation is further confirmed by TRACE data when averaging on quiet Sun regions. If averaging for all fluxes, a reverse equator-to-pole height variation is shown.
Helical Magnetic Structure of White Light Polar Plumes
Authors: Zhukov A. N. , Veselovsky I. S. , Koutchmy S. , Llebaria A.
Published: July 2016

We describe the fine structure of white light polar plumes observed using SOHO/LASCO C2 coronagraph. The evolving helical structures of different scales are clearly seen on processed images (the processing is made to reveal the faint contrast objects). The observed structures trace the magnetic field lines, so the electric currents flow along the axes of plumes. An MHD model of a plume which takes into account field-aligned electric currents is developed. The model permits to understand the existence of high-density plasma inside the plume due to the balance between the magnetic forces and the transverse pressure gradient.
Reconstruction of the Coronal Magnetic Field for Active Region NOAA 8151
Authors: Régnier S. , Amari T.
Published: July 2016

The active region NOAA 8151 observed between February 11–13, 1998 exhibits a filament eruption linked to the disappearance of a sigmoidal structure. Using vector magnetograms from IVM (Mees Observatory, Hawaii), we perform a non linear force-free reconstruction of the coronal magnetic field above this active region. This reconstruction allows to determine the distribution of electric currents, the magnetic energy and the relative magnetic helicity. The reconstructed magnetic field lines are compared to the soft X-rays (SXT, Yohkoh) observations.
Observations and Models of Coronal Heating
Authors: Malara F. , Velli M.
Published: July 2016

Energy release in the solar Corona is characterized by a sequence of space and time localized events, whose intensity follows power-law distributions. In quiet Sun regions, small energy events, possibly under the detection threshold, dominate, thus supporting the “nanoflare” scenario of coronal heating. Two complementar models of heating are discussed, in connection with the above observational features. The first model is based on Alfvénic wavepackets dissipation in 3D force-free magnetic fields; the presence of regions of chaoticity of magnetic lines allows for a fast wave dissipation, within a fraction of a solar radius. The second model describes a MHD turbulence in low-β plasma, in which magnetic energy is continuously furnished by slow photospheric motions. Energy release events corresponds dissipation of current sheets, often associated with magnetic reconnection. The resulting distribution of dissipated power follows a power law, similar to observations.
Nonlinear Evolution of Phase-mixed Alfvén Waves Towards Short Length Scales
Authors: Goossens M. , Voitenko Y.
Published: July 2016

We study two nonlinear processes that are efficient in the spectral redistribution of Alfvén wave energy - second harmonic generation, and scalar decay. Both processes transport the energy of AWs towards smaller scales and/or higher frequencies, and can accelerate the energization of space plasmas implied by recent SOHO observations.
Mechanisms for Coronal Mass Supply by Evaporative Micro-Events
Authors: Brown J. C. , Krucker S. , Güdel M. , Benz A. O.
Published: July 2016

There is extensive evidence from SoHO and other data that “micro-events” play an important role in sustaining at least some components of the solar corona. These are often termed coronal micro-” heating events” though a major part of their role is feeding coronal loops through chromospheric evaporation. We consider what can be learnt from these data concerning the energy release and transport mechanisms driving the evaporation, including thermal conduction and fast particles. We conclude, from one large event and the statistics of many small ones, that conductive evaporation alone does not fit observations and that fast particles or some other nonthermal driver must be involved.
The Temperature of the Extended Solar Corona
Authors: Foley C. R. , Culhane J. L. , MacKay D.
Published: July 2016

We use the Coronal Diagnostic Spectrometer instrument on board the Solar and Heliospheric Observatory to analyse coronal helmet streamer structures observed close to the solar minimum / maximum on the 1996 July 8 / 1999 August 4-5th. The radial variation of peak electron temperature is extracted out to 2 solar radii. These are found to agree well with Yohkoh observations close to the solar maximum, but are found to be reduced by around half a million close to the solar minimum.
Parametric Instability of a Broad-band Alfvén Wave: Nonlinear Evolution and Saturation
Authors: Malara F. , Primavera L. , Veltri P.
Published: July 2016

The nonlinear evolution of parametric instability of a non-monocrhomatic Alfvén wave is studied using numerical simulations. After a linear stage the instability saturates. For β ~ 1 the initial mode remains dominant, except at large scales, where an inverse cascade of backscattered Alfvénic modes is present. A comparison with solar wind data gives a qualitative agreement, indicating that parametric instability could play an important role in the evolution of solar wind turbulence.
An Observational Test for Solar Atmospheric Heating
Authors: van Driel-Gesztelyi L. , Démoulin P. , Ireland J. , Thompson B. , Fludra A. , Oláh K. , Kővári Zs. , Harra L. K. , Mandrini C. H. , Bocchialini K. , Orlando S.
Published: July 2016

We study the evolution of the emissivity correlated with magnetic flux density of an active region from its birth until its decay throughout all atmospheric layers. We analyse multi-wavelength data obtained from SOHO, Yohkoh, GOES, SOLSTICE and 10.7 cm radio data from DRAO, Canada. We utilise our results to understand the scaling laws in different atmospheric layers. We confirm that the relationship between the emitted excess flux (flux - basal flux) and photospheric magnetic flux density ΔF(< f B >) follow power laws, and the powers depend on the formation temperature of the line(s) involved.
Solar Wind and Heliospheric Compositional Variations
Authors: Galvin A. B.
Published: July 2016

Recent in-situ measurements of the composition of the solar wind and heliospheric particles from SOHO, ACE, Wind and Ulysses are providing valuable and often unique new information on origins and acceleration processes in the Sun and heliosphere. This paper reviews some of the more interesting recent findings and their implications.
Particle Acceleration in Collisionless Magnetic Reconnection
Authors: Browning P. K. , Vekstein G. E.
Published: July 2016

We investigate the acceleration of charged particles in the framework of collisionless reconnection. A steady reconnection scenario is considered, with a two dimensional X-point magnetic field geometry having also a uniform field component transverse to the plane of the X-point field, and an inductive electric field generating an inflow of particles. Test particle trajectories are studied, and the energy spectra of the accelerated particles are determined.
Solar Orbiter, a High-Resolution Mission to the Sun and Inner Heliosphere
Authors: Marsch E. , Antonucci E. , Bochsler P. , Bougeret J.-L. , Fleck B. , Harrison R. , Marsden R. , Schwenn R. , Vial J.-C.
Published: July 2016

Solar Orbiter will provide, at very high spatial (35 km pixel size) and temporal resolution, novel observations of the solar atmosphere and unexplored inner heliosphere, which will be made in the heliosynchronous segments of the orbits at heliocentric distances near 45 solar radii and out of the ecliptic plane at high heliographic latitudes up to 38°. The Solar Orbiter will achieve its wide-ranging scientific aims with a suite of sophisticated instruments through an innovative orbit design.
IPS Observations at Miyun Station, BAO
Authors: Zhang X.Z. , Wu J.H.
Published: July 2016

IPS observations have recently begun at Miyun Station, Beijing Astronomical Observatory. This paper briefly describes the radio telescope at Miyun Station, discusses the observation and the data reduction procedures and presents the preliminary results of observations on IPS source 3C48.
The Shape of the Disk: Clues from the Kinematics of Disk Stars
Authors: Weinberg Martin D.
Published: July 2016

It is a tall task to determine the structural parameters of one's own galaxy much less any deviations from axisymmetry. Nonetheless, after hard work, the existence of asymmetries has been reported and discussed in the literature from a wide variety of sources (most recently, Nakai & Nishiyana 1994). Now, in order to understand Milky Way evolutionary history, it is our job to determine the origin and intrinsic structure of these asymmetries.
A Survey of Surveys
Authors: Kent S. M.
Published: July 2016

A new era for the field of Galactic structure is about to be opened with the advent of wide-area digital sky surveys. In this article, I will review the status and prospects for research for 3 new ground-based surveys: the Sloan Digital Sky Survey (SDSS), the Deep Near-Infrared Survey of the Southern Sky (DENIS) and the Two Micron All Sky Survey (2MASS). These surveys will permit detailed studies of Galactic structure and stellar populations in the Galaxy with unprecedented detail. Extracting the information, however, will be challenging.
Ellipticity of Outer Regions of Galactic Disks
Authors: Haud Urmas
Published: July 2016

In hierarchical cosmologies, dark matter coronas arise from the gravitational collapse of density peaks in a random perturbation field. The result is a triaxial, slowly rotating, centrally concentrated dark corona (Dubinski and Carlberg, 1991; Dubinski, 1992). Binney (1978) was the first to consider the effects of triaxial coronas around disk galaxies, showing that they might explain the observed warps and apparent twists seen in many disks. In external galaxies these deformations of density and velocity fields are modeled with a system of circular annuli, each of which has its own inclination and line of nodes (LON). By examining warped systems in a variety of reference frames, Briggs (1990) has mentioned that galaxy kinematics uniquely specifies a new reference frame in which there is a common LON for orbits within the transition radius and also a differently oriented straight LON for the gas outside the transition radius, which is approximately equal to the Holmberg radius of the galaxy.
Near Infrared Star Counts as a Probe of Asymmetries in the Galaxy's Disk
Authors: Rhoads James E.
Published: July 2016

I have recently started an observing program to study the distribution of dynamically old giant stars in the disk, looking for (i) large amplitude spiral arms and (ii) small amplitude corrugations.

(i)

Theoretical studies of spiral density waves usually assume that the mass density contrast is weak and the waves linear. Recent observations in red and near-IR light (e.g., Elmegreen and Elmegreen 1984; Rix and Zaritsky 1994), coupled with stellar population models, suggest otherwise. In the Galaxy, we can compare observations of diffuse NIR light and of individual stars, eliminating the need for population modeling. Moreover, we can estimate distances to stars to learn about 3D structure.

(ii)

Recent work by Malhotra (1994a; 1994b) has shown that the midplane of the molecular and atomic gas differs from the nominal (Galactic latitude b = 0°) plane by up to 50 pc in the inner Galaxy. Various observations (Djorgovski & Sosin 1989, Freudenreich et al 1994, Carney & Seltzer 1993) show that the stellar distribution also deviates from b = 0. We will choose fields to test the possibility that the stars behave like the gas. This constrains theories of the corrugations; e.g., if old stars participate then magnetic fields aren't the cause.
Morphology of the Galactic Bulge from COBE DIRBE Observations
Authors: Dwek E.
Published: July 2016

The Diffuse Infrared Background Experiment (DIRBE) on-board the Cosmic Background Explorer (COBE) satellite has provided striking new images of the Galactic bulge at effective wavelengths of 1.25, 2.2, 3.5, and 4.9μ (Hauser 1993, plate 3; Arendt et al. 1994; Weiland et al. 1994). The bulge, defined here as the spheroid within the |l| < 20° and |b| < 10° region around the Galactic center, and its stellar content have been subjects of considerable interest since they contain important clues about the dynamical and star-formation history of our Galaxy. The morphology of the Galactic bulge is much harder to ascertain than that of bulges in many external galaxies, because of our location in the Galactic plane amid the obscuration by interstellar dust. In spite of this difficulty, there has recently been an accumulating body of evidence that the stellar distribution in the bulge is bar shaped, i.e. that the bulge is not rotationally symmetric in the plane of the disk (see Blitz 1993 for a review of the subject). The existence of a bar in our Galaxy would have important implications for the dynamics of the Galaxy. A bar would provide a mechanism for sweeping gas from the disk into the Galactic center “feeding” a central black hole (e.g. Shlosman, Frank, & Begelman 1989). It would also provide a mechanism for generating spiral arms, and a basis for estimating the mass of the halo relative to that of the disk (e.g. Combes & Sanders 1981 and references therein).
Dynamics of the Bar at the Galactic Centre
Authors: Gerhard Ortwin E.
Published: July 2016

There is now substantial evidence for a rotating bar in the inner Galaxy. This is an important change in our perception of the Galaxy because it changes the ways in which we have to think about its evolutionary history.
Results from the Optical Gravitational Lensing Experiment (OGLE)
Authors: Paczyński B. , Stanek K. Z. , Udalski A. , Szymański M. , Kałużny J. , Kubiak M. , Mateo M. , Krzemiński W. , Preston G. W.
Published: July 2016

The analysis of the first three years of the OGLE data revealed 12 microlensing events of the Galactic bulge stars, with the characteristic time scales in the range 8.6 < t0 < 80 days, where t0 = RE/V. A complete sample of nine events gave the optical depth to gravitational microlensing larger than (3.3 ± 1.2) × 10–6, in excess of current theoretical estimates, indicating a much higher efficiency for microlensing by either bulge or disk lenses. The lenses are likely to be ordinary stars in the Galactic bar, which has its long axis elongated towards us. At this time we have no evidence that the OGLE events are related to dark matter. The OGLE color magnitude diagrams reveal the presence of the Galactic bar and a low density inner disk region ∼ 4 kpc in radius. A catalogue of a few thousand variable stars is in preparation.
3D N-Body Simulations of the Milky Way
Authors: Fux R. , Martinet L. , Pfenniger D.
Published: July 2016

While the existence of a central bar in our Galaxy now seems to be well established, its parameters (such as position angle, extension, axis ratio, angular speed etc…) still remain controversial. The large amount of photometrical and stellar kinematical data becoming now available within ∼ 30° of the Galactic Centre should provide potentially new constraints on these parameters. Unfortunately, a detailed barred model of the Milky Way, which would offer a powerful work frame to interpret such observations, does not exist yet. We therefore report here on a first attempt at constructing a 3D dynamically self-consistent barred model of the Galaxy. The idea is to follow the time evolution of a set of 400,000 particles initially distributed according to a plausible axisymmetric mass model of the Milky Way and in virial equilibrium, hoping that a bar will form spontaneously. Gas is not included so far, but will be introduced as a next step in this ongoing work. Some results presented at this meeting will be only quickly summarised here and explained in some more details elsewhere (Fux et al. 1995 and A&A paper in preparation).
Comparison with External Galaxies Dynamics
Authors: Combes F.
Published: July 2016

Many features of the Milky Way appear weird or unique, because of the peculiar point of view. However the same features are observed more easily and clearly in nearby galaxies. The Milky Way appears to cumulate many dynamical features, such as a bar, a nuclear disk, a perpendicular nuclear bar (?), lopsidedness, an inner ring (molecular ring at 5kpc), a peanut-shape bulge, a warp, and a polar ring. By comparison with external galaxies, and also results from N-body simulations, we can infer the most probable bar angular velocity and length, and interpret the ring features.
Recurrent Starbursts or Intermittent Starburst/AGN Phenomena at the Galactic Center?
Authors: Ozernoy Leonid M.
Published: July 2016

Recently, I summarized arguments, both old and new, that the Galactic center has experienced a starburst in a recent past (Ozernoy 1994a). Here I propose a likely mechanism – collisions between giant molecular clouds – that might induce (recurrent) starbursts. Taken together, these two approaches seem to indicate that the history of the central part of our Galaxy can be described as recurrent starbursts or intermittent Seyfert activities/starbursts.
Evolution in the Nucleus
Authors: Burton M.G.
Published: July 2016

A personal reflection is presented of David Allen's research into the content of our Galactic nucleus.
Dynamical Evolution of Galactic Center Star Cluster and Importance of Stellar Collisions
Authors: Mok Lee Hyung
Published: July 2016

The Galactic Center (GC) star cluster is a compact stellar system. The surface brightness distribution at infrared has core radius of about 0.8 pc (Rieke & Lebovsky 1987) when the contribution from bright stars are removed. On the other hand number counts of infrared sources in the high resolution speckle image by Eckart et al. (1993) at 2.2 μm gives 0.15 pc for the core radius of the surface density distribution. At present it is not clear which is more appropriate for the mass distribution.
A Comparison of Near Infrared Spectra of the Galactic Center He I Emission Line Sources and Early Type Mass Losing Stars
Authors: Blum R. D. , Depoy D. L. , Sellgren K.
Published: July 2016

We have obtained R ≈ 570 resolution K band spectra of eight sources in the Galactic Center, including four sources within the IRS 16 cluster, IRS 13, IRS 1W, and the compact He I emission line sources AF (also known as AHH) and AHH NW. We have also obtained R ≈ 570 H and K band spectra of nine galactic and LMC early–type mass–losing stars, including Ofpe/WN9 and WN stars. The spectra of both the Galactic Center sources and the comparison stars show a wide range of behavior in the He I (1.70 μm, 2.06 μm, 2.11 μm) and H I (Brackett series) lines. We find significantly larger He I equivalent widths in the AF source and two galactic early type mass losing stars than in any of the LMC stars. Several of the Galactic Center He I sources are found to have higher He I velocity widths than any of the galactic or LMC early type mass losing stars. At least one source, IRS 13, shows a strong red wing to the He I 2.06 μm emission.
Mini-Spiral at the Galactic Center: A Link between its Structure and the Value of a Central Point Mass
Authors: Fridman A.M. , Khoruzhii O.V. , Lyakhovich V.V. , Ozernoy L. , Blitz L.
Published: July 2016

The innermost 2 pc contain a rotating ring (“circumnuclear disk”) of molecular gas, neutral hydrogen, and dust with an embedded H II region called Sgr A West; a dense stellar cluster; and a compact nonthermal radio source Sgr A∗ (for a recent review, see Blitz et al. 1993). The clumped, spiral-shaped morphology of Sgr A West, sometimes called lthe mini-spiral”, has been a subject of numerous speculations concerning its origin (for a review, see Genzel & Townes 1987). Lacy et al. (1991) demonstrated that both the kinematics and shape of a part of Sgr A West can be fairly well approximated using an one-armed density-wave model.
C18O and HNCO in the Galactic Centre
Authors: Lindqvist M. , Sandqvist Aa. , Winnberg A. , Nyman L.-Å. , Combes F. , Genzel R. , Gerin M. , Mezger P.G.
Published: July 2016

Using the SEST, we have observed 554 positions with a spacing of 45″ in the C18O(J = 1 → 0) and HNCO(Jkk′ = 505 → 404) lines. The data covers most of the Sgr A region including the Arc. Many of the dominant clouds in the GC region (see e.g. Güsten et al. 1981, A&A 103, 197; Bally et al. 1987, ApJS, 65, 13) are readily identified in the total integrated C18O and HNCO maps (Fig. 1). The results will be published in A&AS and will include intensity maps with 5 km s–1 velocity resolutions, as well as galactic longitude-velocity and galactic latitude-velocity maps. J = 2 → 1 C18O observations are planned for selected regions. The objectives of the project are twofold: 1. Geometrical, morphological, and dynamical relationships between the molecular regions and the radio continuum sources. 2. Heating mechanisms in GC molecular clouds.
Possible Evidence for a Binary Massive Black Hole in the Galactic Nucleus
Authors: Meurs E.J.A.
Published: July 2016

The Galactic Centre candidate Sgr A∗ may exhibit a 40 km/s radial velocity component, which is not observed for OH/IR stars around the centre. This could be interpreted as orbital motion of one member of a binary massive black hole. In other galaxies such pairs may be inferred from radio jet precession and emission line profiles.
Chemical and Dynamical History of the Milky Way
Authors: Bikmaev I.F. , Mashonkina L.I. , Sakhibullin N.A. , Shimanskij V.V. , Shimanskaya N.
Published: July 2016

F-G dwarf stars of different metallicity are used as tracers of chemical and dynamical history of the Galaxy. Observed ratios of element abundances “[X/Fe] versus [Fe/H]” (where “X” is a some of chemical element) are compared with theoretical ones and allow us to make the choice between models (or parameters of theoretical models) of the Galaxy chemical evolution, nucleosynthesis and processes of star formation. Our experience has shown (Bikmaev, 1991, 1994a,b; Bikmaev et al., 1990) that in some cases classical approaches in abundance determination are affected by methodical uncertainties and the spread in [X/Fe] ratios may be large even if high quality spectra used.
The Velocity Dispersion in the Cold Collapse
Authors: Kan-ya Y. , Sasaki M. , Tsuchiya T. , Gouda N.
Published: July 2016

We investigate the growth of the velocity dispersion in the initial stage of the cold dissipationless collapse of spherical collisionless systems by a perturbation theory. We show that the tangential velocity dispersion grows faster than the radial one for the system with centrally condensed initial density profile.
The Formation of the Galactic Bulge
Authors: Samland M. , Hensler G.
Published: July 2016

The question is adressed whether the problem of the stellar metallicity distribution and the dynamics of the stellar components in the bulge as found out by refined observations during recent years can be understood within the context of the evolution of the whole Galaxy. A selfconsistent galaxy model has to explain the apparent differences in the effective yields of the enrichment of bulge, disk and halo. Moreover, it has to account for the observed age-metallicity distribution of the stellar components. It appears that chemo-dynamical infall models provide a consistent description of the bulge, in particular the metallicity distribution of the K giants. It should be emphasized that simple closed-box models are not appropriate, because during the bulge formation there is infall of cloudy medium (CM), as well as outflow of hot, ionized gas ejected by supernovae type II (SNII). Therefore dynamical processes have to be taken into account. For details of the chemo-dynamical description we refer to Samland & Hensler (1994) and references therein.
The Scatter of Metallicities of Stars in the Solar Neighbourhood
Authors: Fuchs B. , Dettbarn C. , Wielen R.
Published: July 2016

It is well known that the velocity dispersions of the stars in the solar neighbourhood increase with their ages (Wielen 1977). In Fig.1 we show |W| weighted velocity dispersions (cf. Wielen 1977) of the stars in the Third Catalog of Nearby Stars (Gliese and Jahreiß 1994). Open symbols indicate main sequence stars and crosses indicate McCormick stars, a kinematically unbiased subset of the CNS3, respectively, whereas the filled symbols are the Edvardsson et al. (1993) data. Stars older than 14 Gyr are not shown because they are probably thick disk stars (Freeman 1991). We have assumed a maximum age of the old thin disk stars of 12 Gyr as suggested by the Edvardsson et al. data. As can be seen from Fig.1 both data sets fit ideally together. The solid line indicates a σ ∝ τ1/2 law.
How Important is Neutral Carbon to an Understanding of the Dense Interstellar Medium?
Authors: Jaffe D.T.
Published: July 2016

In virtually all of the dense interstellar medium, H2 is the most abundant form of hydrogen, but it is not directly observable in the bulk of the gas. As a result, we are forced to use trace constituents of the gas as surrogates when we want to know the distribution of material in the dense ISM. Most commonly, we employ the lowest few rotational transitions of CO and its isotopes as the trace species. One of the most hotly debated issues in the study of the molecular ISM is the extent to which one can trust CO or isotopic CO lines to reflect reliably the underlying H2 distribution (see Shier, Rieke, & Rieke (1994), Sodroski et al. (1995) for recent comments on the I(12CO)/N(H2) ratio and Lada et al. (1994) for a recent analysis of the relationship between isotopic CO and total cloud column densities). CO becomes increasingly unreliable as a tracer of H2 as the average column density between cloud surfaces exposed to ultraviolet photons and the shielded centers of clouds becomes smaller. Young stars in the galactic plane perfuse atomic and molecular clouds with far–UV (λ > 91 nm) radiation. This radiation tends to dissociate CO more readily than it dissociates H2 (Van Dishoeck & Black 1988). The differences in susceptibility of H2 and CO to photodissociation may lead to the existence of significant portions of the molecular medium where the usual trace species are underabundant or even absent. In addition, there is dense H I at the cloud boundaries, immediately outside the molecular material. In the UV–illuminated cloud surfaces, the gas-phase carbon is in the form of C I or C II. It is important, therefore, to determine the amount and location of large-scale C I emission if one hopes to know how much molecular and dense atomic gas is missing from studies using CO as a tracer and to what extent photodissociation is responsible for the absence of this CO. We discuss here some of the relevant theoretical and observational work on the relationship between C II, C I, CO and H2. Our principal aim is to see if and how observations of C I might help us to improve our knowledge of the distribution of dense neutral gas in the Milky Way.
The Z Velocity Dispersion of Outer H I Disks
Authors: Dickey John M.
Published: July 2016

The velocity dispersion of the interstellar gas measured perpendicular to the disk in face-on spiral galaxies shows a remarkable consistency. Typically the width of the velocity distribution decreases monotonically with increasing galactic radius through the luminous, stellar disk; but in the outer disk where there is gas but no stars the velocity dispersion is συ ≃ 7 km s−1 with a scatter of 2 km s–1 at most from one position to another and from one galaxy to another. Trying to understand this number raises questions about the thermal state of the H I in outer, gaseous disks. The most important issue is to understand the dominant heating and cooling processes for the atomic gas.
Physical Conditions of Molecular Gas in the Galaxy
Authors: Sakamoto S. , Hasegawa T. , Handa T. , Oka T. , Hayashi M.
Published: July 2016

Physical conditions of molecular gas are key parameters to the formation rate and initial mass function of stars formed in molecular clouds. The ongoing Tokyo-NRO survey has been observing the Galactic CO (J=2–1) emission with a beamsize matched to the Columbia CO (J=1–0) survey. Intensities of the two lines should reflect physical conditions of the CO-emitting gas. An out-of-plane survey of the inner Galaxy which covers from 20° to 60° in galactic longitude and from −1° to +1° in galactic latitude with grid spacings of 0.25° has already been made (Sakamoto et al. 1994). Its coverage is large enough to draw conclusions on global properties of molecular gas in the inner Galaxy.
Does a Rotation Velocity Jump Generate the Outer Spiral Structure?
Authors: Fridman A.M. , Khoruzhii O.V. , Lyakhovich V.V.
Published: July 2016

We investigate a stability of the gaseous disk in the Milky Way. The rotation curve with smooth two kinks in the Solar vicinity (Fig.1) was adopted in accordance with the observations (Fridman et al., 1994a). Such a gaseous disk is unstable. The instability can generate the four-armed spiral (Fig.2) and four-vortex structure (Fig.3). The method of the analysis is described by Fridman et al., 1994b. The generation mechanism is similar to that described by Glatsel, 1987.
Stability of a Collisionless Stellar Disk
Authors: Griv E.
Published: July 2016

The study of stability of the stellar disks of flat galaxies is the first step towards an understanding of the phenomena of spiral structure. To explain the spiral pattern, Lin and Shu (1964) further developed the Lindblad's idea of density waves by considering the spiral structure as the collective effect in a self-gravitating system. As an extension to the original Lin-Shu theory, unstable spiral modes have been obtained from an asymptotic analysis (e.g., Bertin [1980]). In such “modal theory”, the Jeans-type instability (even weak) is important to the maintenance of spiral structure.
Galactic Orbits of Different Galactic Population Objects
Authors: Ossipkov L. P. , Kutuzov S. A.
Published: July 2016

It is evident that the knowledge of not only positions and velocities of objects belonging to different populations but also their osculating galactic orbits can clarify the structure and history of our Galaxy. Action variables being adiabatic invariants are especially useful for these purposes (Binney, May 1986). One of them is a usual area integral (and it can be found without any orbit calculation). The second action variable is connected with an energy integral but for 3–D orbits and arbitrary potentials it cannot be found analitically. Eccentricities resulting from orbit calculations can be used here (Lynden-Bell 1963). Comparison of eccentricities defined with different ways shown that differences between them are practically negligible (Kutuzov 1985, 1987). As for the third action variable and the corresponding third isolating integral orbit calculations can confirm its existence and control the validity of various approximations. Numerical technique allowing to find it and working at any potential is now in progress (Binney, Kumar 1993).
What do we really know about Cloud Formation?
Authors: Elmegreen Bruce G.
Published: July 2016

Four processes of molecular cloud formation are discussed: formation in swept-up shells, coagulation of smaller clouds, condensation in larger clouds, and compression in a supersonically turbulent medium. Examples and constraints for each process are given.
Far-Infrared Spectral Observations of the Galaxy by the Far-Infrared Absolute Spectrophotometer
Authors: Reach William T.
Published: July 2016

The Galactic continuum spectrum from 5–96 cm−1 is derived from COBE/FIRAS observations. The spectra are dominated by warm dust emission, which may be fit with a single temperature along each line of sight in the range 16–21 K. A widespread, very cold component (4–7 K) with optical depth that is spatially correlated with the warm component is also detected. The nature of the cold component and its implications for the amount of very cold material in the Milky Way are discussed.
Outer Disc Rotation from Cepheid Variables
Authors: Pont Frederic , Queloz Didier , Mayor Michel , Bratschi Pierre
Published: July 2016

We have measured radial velocities for a large number of classical cepheids of the Galaxy, particularly in the outer disc. We determine the rotation curve up to a galactocentric radius of 16 kpc. The results are then compared to similar studies using HII regions. We also consider some possible complications.
The Structural Parameters of the Milky Way
Authors: Buser Roland , Rong Jianxiang
Published: July 2016

A new homogeneous catalog of photographic RGU star count and three-color data in seven high-galactic latitude fields has been used to determine the structural parameter values from a large number of multi-component population models of the Galaxy. The data provide strong evidence of a prominent thick disk component coexisting with a canonical thin disk and a low-density spheroidal halo.
A System of Galactic Constants Based on Stellar Dynamics
Authors: Ninković S.
Published: July 2016

A system of galactic constants is proposed. Due to the intention of basing it on stellar dynamics, the working hypothesis is the assumption that the Galaxy is in a steady state characterized with axial symmetry. Then, as easy to see, one reaches a system containing seven independent constants typical for the present assumption. The current knowledge concerning the amounts of these constants is discussed.
Estimation of Galactic Model Parameters by Interval Method
Authors: Kutuzov S. A.
Published: July 2016

The interval method of estimating model parameters (MPs) for the Galaxy was suggested earlier (Kutuzov 1988). Intervals are proposed to be used both for observational estimates of galactic parameters (GPs) and for the values of MPs. In this work we consider a model as a tool for studying mutual interaction of GPs. Two-component model is considered (Kutuzov, Ossipkov 1989). We have to estimate the array P of eight MPs.