bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionized Gas in Elliptical Galaxies
Authors: Sadler Elaine M.
Published: June 2019

More than half of all nearby elliptical galaxies contain modest amounts (103 − 105 M⊙) of ionized gas. In bright elliptical galaxies this gas appears to lie in a rotating, kiloparsec-scale central disk, with a spectrum characteristic of non-thermal ionization. Low-luminosity ellipticals have a clumpy gas distribution and the gas in these galaxies is photoionized by young stars.
Dynamics in the Centres of Triaxial Elliptical Galaxies
Authors: Gerhard Ortwin E.
Published: June 2019

Orbits in the inner kpc of a triaxial galaxy are discussed, taking into account the effect of a central density concentration like a massive black hole, a dense stellar nucleus, or a de Vaucouleurs-type cusp. Since the box orbits that form the backbone of a triaxial galaxy pass arbitrarily close to the centre after long enough time, they will eventually be subjected to large-angle deflections by a central point mass, and the triaxiality of the inner part of the system will thereby be destroyed. A 108 M⊙ black hole is estimated to affect box orbits out to 1kpc in a Hubble time, while a similar influence of the observed (extended) nucleus in M31 reaches out to 500pc in the bulge. Regular box orbits persist, however, in systems with singular central density profiles such as implied by carrying the r1/4 law all the way to the centre. This result can be approximately understood in terms of the frequency ratio Ωr/Ωθ remaining close to the harmonic value of 2 for many orbits in the corresponding spherical potential. Finally, I discuss observable consequences of the box orbit scattering process and future work, and use the presence of isophote twists in the central parts of a number of elliptical galaxies to obtain approximate upper limits on the masses of the black holes these systems may contain.
Formation and Secular Evolution of Elliptical Galaxies
Authors: Lake George
Published: June 2019

Three ways have been proposed to make elliptical galaxies: cooling by gas dynamical processes at late epochs, Compton cooling at early times and merging. These theories must address a variety of observational constraints, the most severe being the problems of slow rotation and high central phase densities. I look at some aspects of all three theories with particular attention to key numerical simulations and observations that can distinguish between the scenarios.
Summary
Authors: Tremaine Scott
Published: June 2019

This is the first IAU symposium devoted specifically to elliptical galaxies. I would like to congratulate the organizers for initiating a symposium on such a well-defined topic with so many interesting puzzles. I have been impressed at this meeting by the great strides made in this subject over the last ten years, both in the quality and quantity of data and in the sophistication of the theoretical models. In addition, I'm sure that I express the sentiments of the great majority of the participants when I say what a pleasure it was to attend a meeting on galaxies in which there was not a single paper on spiral structure!

Rather than attempting to give a general summary, I have chosen to concentrate on four specific topics which reflect some of my personal impressions of the meeting.
Intrinsic Shapes of Elliptical Galaxies From a Statistical Comparison of Two Different Isophotes
Authors: Fasano G.
Published: June 2019

Several statistical attempts were already made to discriminate between oblate forms vs. prolate forms (OF/PF) in elliptical galaxies (Marchant & Olson, 1979; Lake, 1979; Olson & de Vaucouleurs, 1981; Capaccioli et al., 1984). They fell in with the fundamental problem that the observed quantities (surface brightness, velocity dispersion, flattening etc.) whose projection should depend on the assumed shapes (OF/PF), could be intrinsically correlated each other. This can mask the simple projection–effect (Richstone, 1979; Merritt, 1982).
The Distribution and Kinematics of Neutral Hydrogen in NGC 807
Authors: Dressel L. L.
Published: June 2019

I have detected 21 cm line emission from neutral hydrogen in the giant elliptical galaxy NGC 807 at Arecibo Observatory, and I have mapped this emission with the VLA. Unlike the active and dwarf ellipticals that have been mapped thus far, NGC 807 has a fairly regular disk of gas rotating about the apparent optical minor axis. Combined with observations of active ellipticals, this observation suggests that two classes of HI-rich ellipticals may exist: ellipticals which have accreted gas and become active recently, and quiescent ellipticals which have either produced gas internally or accreted it so long ago that it has reached dynamical equilibrium.
Properties of the X–Ray Emitting Gas in Early Type Galaxies
Authors: Canizares C. R. , Fabbiano G. , Trinchieri G.
Published: June 2019

We have studied a sample of 81 E and SO galaxies (taken mostly from the literature) that were observed with the Einstein Observatory. Fifty–five galaxies are detected in X–rays, most of which come from a hot interstellar medium. It is possible that discrete sources make a significant contribution to the X–ray emission for 21 of the detected galaxies with the lowest X–ray luminosity, LX, for a given optical luminosity, LB. We examine the LX vs. LB distribution (see Figure 1), and derive approximate values of the central electron density, central cooling time and total mass in gas for the sample. Typical values are ~ 0.1cm−3, ~ 5 × 106 yr and 5 × 109M⊙, respectively. The short cooling times suggest the presence of cooling flows, and we consider heating by supernovae and by gravitational processes. Supernovae at the accepted rate would overproduce the observed X–ray luminosity: either the true rate is many times lower or the supernova energy is not well coupled to the hot gas. There are also difficulties in explaining the suppression of a strong galactic wind if supernova heating dominates, unless an external pressure confines the gas. Gravitational heating gives LX ∝ LBσ2, where σ is the line–of–sight velocity dispersion in the galaxy, and we find that this is roughly the case. Gravitational heating exceeds the mean observed Lx by a factor of ~ 3 — 4 if one uses the accepted rate of stellar mass loss and assumes that the gas falls all the way to the center of the galaxy. This could be reconciled if the mass injection rate were lower or if matter drops out of the flow at all radii. The sample properties provide no additional information about the presence or absence of heavy halos in early type galaxies.
The Hydrodynamical Evolution of Gas in Young Elliptical Galaxies
Authors: Kunze R. , Loose H.H. , Yorke H.W.
Published: June 2019

We calculate the partial inflow of gas fuelled by stellar mass loss at an early epoch (109yr after the birth of the galaxy) during the evolution of an elliptical galaxy assuming a modified King model stellar distribution. The influence of the partial thermalization of stellar mass lost on the amount of gas which can be stored in the nucleus of a typical elliptical during the time of partial inflow is investigated. Masses up to 105M⊙ of cool (≤ 104K) material can be stored in the nucleus of the galaxy before the fast dissipation of the “kinetic bulk energy” of the nuclear gas cloud leads to “thermal” instability and subsequent collapse. A supermassive star can form. A detailed discussion of the model and the results is subject of a forthcoming paper (Kunze et al., 1986).
Visual–IR Color Gradients in Elliptical Galaxies
Authors: Peletier R. F. , Valentijn E. A. , Jameson R. F.
Published: June 2019

Dissipational formation theories (e.g. Larson 1974) predict a metallicity change with distance from the center in elliptical galaxies. Several authors have reported small color gradients in visual colors like B–V and B–R. The interpretation of these data is not easy, due to uncertainties caused by the short wavelength–baseline, and by the presence of a hot stellar population suggested by IUE–data (e.g. Burstein et al. 1986). Simultaneous measurements of visual and visual-infrared colors provide the means to determine both the average temperature of the giant branch and the turnoff–temperature of the main sequence. This allows to model fractional contributions of different populations, including age– and metallicity–effects. The required continuity of solutions at different radii provides a strong constraint in selecting a more unique overall population model, and relieves the ambiguous interpretation of single measurements.
Direct IR Determination of the Stellar Luminosity Function to 0.2 M⊙ in Elliptical Galaxies
Authors: Gilmore G. , Arnaud K.
Published: June 2019

We present a determination of the stellar luminosity function in luminous elliptical galaxies which includes all stars more massive than 0.15 M⊙. This limit corresponds to masses beyond the maximum in the solar neighbourhood stellar mass function, and therefore includes effectively all the luminous mass. Galaxies with X-ray evidence for current massive star formation, also show no evidence for enhanced low mass star formation in their central regions. All elliptical galaxies studied to date have stellar luminosity functions for masses above 0.15 solar masses which do not differ significantly from that in the solar neighbourhood. Elliptical galaxies have stellar bolometric mass-to-light ratios of 2.5< M/L <5.0.
Dynamics of the Fornax Dwarf Spheroidal Galaxy
Authors: Paltoglou George , Freeman K.C.
Published: June 2019

The mass to light ratio of the inner parts of the Fornax system is 3.2 ± 1.1. Its major axis rotation is only 3.4 ± 2.4 km s-1 over ± 1 kpc, which argues against its origin as a stripped dwarf irregular.
Two Colour CCD Photometry of Malin–Carter Shell Galaxies
Authors: Wilkinson A. , Sparks W.B. , Carter D. , Malin D.A.
Published: June 2019

Shells may be the result of the disruption of a small companion in the potential of a much larger galaxy (e.g., Hernquist & Quinn, 1986; Dupraz & Combes, 1985), the disturbance of a disk system in a tidal encounter (Toomre, 1972), an accumulation of resonant stellar orbits (Binney, pers.comm.) or the result of some shock phenomenon in a hot galactic atmosphere (e.g., Williams & Christiansen, 1985; Wilkinson & Bailey, 1985;). To distinguish between these formation mechanisms, CCD direct images in B and R have been obtained at the Anglo-Australian 3.8m telescope for 66 of the 74 galaxies in the range 01h 40′ α < 13h 46' in the Malin-Carter (1983) catalogue of shell galaxies.
Shells around Tumbling Bars: The Mass Distribution Around NGC 3923
Authors: Dupraz Ch. , Combes F. , Prieur J.-L.
Published: June 2019

In previous articles (Dupraz & Combes, 1985, 1986a), we showed that shells form with different geometries around prolate and oblate galaxies. However, theory and observations suggest that some ellipticals could be tumbling bars (Miller & Smith 1980; Müllenhoff & Marenbach 1986). Here we simulate the accretion of a small galaxy by a tumbling bar; the tumble period T& is kept free. Let Tp be the typical period of motion of a particle in the potential of the elliptical galaxy. Then we find (Dupraz & Combes, 1986b):

a) When Tt > 3TP (Figure l a), shells form with the geometry of a static prolate potential, i.e., aligned with the major axis.

When Tb < 3Tp (Figure lc), the particles feel the time-averaged potential, which is oblate: the shells display the typical oblate geometry. But there is no confusion with a static oblate shell galaxy, because the tumbling bars must be seen edge -on for the shells to appear.

c) When Tb ~ 3Tp (Figure lb), the outer shells form with the oblate geometry, the inner shells with the prolate geometry. In between, no shells form, because particles follow resonant (non-radial) motions.
Initial Tidal Effects on Shell Formation
Authors: James R. A. , Wilkinson Althea
Published: June 2019

Sharp edged features have been observed by Malin and Carter (1980), Schweizer (1980) and others in the envelopes of many elliptical galaxies. the most promising of current models involves the disruption of a low mass galaxy penetrating close to the centre of a considerably larger ellipsoidal galaxy (Schweizer, 1980, Quinn, 1984, Hernquist and Quinn, 1986, Dupraz and Combes, 1986). the release of stars having a range of energies and with a definite relationship between velocity and position at the point of release generates sharp features by the “phase wrapping” mechanism.
Shells and Encounters of Disk Galaxies with Ellipticals
Authors: Piran Tsvi , Villumsen Jens Verner
Published: June 2019

Faint shells have been found around a large number of ellipticals (Malin and Carter 1980, 1983; Schweizer, 1980). Quinn (1984) has suggested that shells form around ellipticals when a small disk galaxy is tidally disrupted in a near radial orbit. According to this mechanism the remnants of the nearly two-dimensional disk maintain their dimensionality and form sheets. These sheets will phasewrap around the elliptical, and the shells are seen when the line of sight is tangent to one of these surfaces (Quinn 1984, Hernquist and Quinn 1986a,b,c).
Stochasticity in Models of Elliptical Galaxies
Authors: Pfenniger Daniel , Udry Stéphane
Published: June 2019

We measure quantitatively the growth of stochasticity due to various perturbations to a model of elliptical galaxy. This is achieved by computing the Liapunov characteristic exponents of randomly selected orbits.
Self–consistent Elliptical Disks
Authors: Teuben Peter
Published: June 2019

Self-consistent solutions for the perfect elliptic disk have been obtained. Velocity field, dispersion maps and the distribution function in action space have been derived.
Stellar Dynamics of Needles
Authors: Tremaine Scott , de Zeeuw Tim
Published: June 2019

One dimensional “needles” are a limiting case of general triaxial stellar systems. Self-consistent, finite needles can have arbitrary longitudinal density distributions but have a fixed, universal distribution function. All needles are stable to all longitudinal perturbations but neutral to transverse perturbations.
Dynamical Approach to the R1/4 Law of Ellipticals
Authors: Bertin G. , Stiavelli M.
Published: June 2019

The R1/4 luminosity law has often been used as an observational constraint in the construction of self-consistent models of ellipticals. In contrast, in this and in the following paper, developing some ideas proposed in the past (BS8A, SB85), we investigate certain theoretical arguments that may lead to a dynamical justification of this important empirical law.
Spherical Stellar Systems: Structure and Evolution
Authors: Ozernoy L. M. , Volodin V. A.
Published: June 2019

We analyze a class of spherical stellar systems with an isotropic, non-isothermal, one-particle distribution function which is truncated in energy ε as (εb —ε)ν (ν > 0) near the energy of truncatingεb and is the Maxwell-Boltzmannian at |ε| ≫ |εb|. the stellar systems which correspond to this distribution function appear to be isothermal in their central parts and polytropic in the external parts. Some qualitative results which follow from such a “polytropic-isothermal” distribution function (PIDF) are briefly discussed. A further extention of PIDF enables us to analyze in a new way the evolution of spherical stellar systems.
Collisional Effects on the Density Profiles of Spherical Galaxies
Authors: Aguilar L.A. , White S.D.M.
Published: June 2019

We use N-body simulations to study the time evolution and the final shape of the density profiles of non-rotating spherical galaxies that have undergone a tidal encounter. We consider models with de Vaucouleurs and King surface density profiles and with isotropic, tangential and radially biased velocity distributions.
Numerical Investigation of the Density Distribution of Stars and the Dispersion of Velocities in Spiral Galaxies
Authors: Zhou Hong-Nan
Published: June 2019

We use a three-component model of a spiral galaxy, given by (Huang et al., 1979):

1.

An outer halo with a gravitational potential of the form

where R2 = x2 + y2 + z2, M1 = 1.2 × 1011M⊙ and b1 = 1.1 Kpc.

2.

A nucleus, with a gravitational potential given by

where M0 = 1.1 × 107M⊙, and b0 = 0.61 × 10−2 Kpc.

3.

A self-gravitating disk containing N stars. The density distribution in the z-direction is assumed to be:

where α = 2.1 Kpc−1 is the equivalent semi-thickness of the galaxy, and σ(r) is the surface density. We consider three different initial expressions for σ(r):

i.

A Toomre (1963) disk.

ii.

A uniform distribution.

iii.

An exponential distribution.
On the Instability of Stationary Spherical Models with Purely Radial Motion
Authors: Antonov V.A.
Published: June 2019

Models of spherical, self-gravitating stellar systems in which all the trajectories pass initially near the center are interesting to examine from different perspectives. Such models are compatible not only with the idea of explosive cosmogony, but also with the concept of formation of stars from a gaseous, spherical cloud, if they are not affected during formation by significant peculiar motions and thus “fall” into the center. Another question is whether such a system is capable of remaining stable for a long period of time. We will show that such a system is unstable with respect to regular forces and must be reconstructed during the course of one period of revolution of an individual star.
Characteristics and Space Distribution of Stars in the Bulge of the Milky Way
Authors: Frogel Jay A.
Published: June 2019

Stars in Baade's Window at b = −4° are described. They are old, metal rich, and have a velocity dispersion greater than 100 km/sec. Their colors are unlike those of any other group of stars. Stars in other windows between b = −3 and −12° differ systematically from those in Baade's Window. The differences are best understood if they are caused by a metallicity gradient in the bulge. The distribution of surface brightness or surface density over the bulge has a much steeper falloff than that seen in other galaxies or in the very center of the Milky Way itself. It is now possible to link together stars in the immediate vicinity of the nucleus with those that are several hundred parsecs out. Understanding this linkage will help in understanding the history and evolution of stars throughout the bulge and that part of the inner disk with which it overlaps.
The Distribution of Stars Within 2° of The Galactic Centre Revealed by 1 to 2 μm Images
Authors: Catchpole R M , Glass I S , Whitelock P
Published: June 2019

We have produced images at 1.2, 1.6, and 2.2μm of a 1° × 2° region of the sky that includes the galactic centre using the drift scan techniques described by Catchpole et al. (1985) and Glass et al. (1987). These images were calibrated by observations of standard stars so that it is possible to make quantitative measurements of 3, H and K magnitudes for individual stars. Colour magnitude diagrams have been constructed, using K against H–K, for the stars within elliptical annuli centred on the galactic centre, with major axes along the galactic plane and an axial ratio of 2.2. The distribution of stars within each colour magnitude diagram is compared with a composite giant branch, based on 47 Tuc as seen at a distance of 8.2 Kpc, but extended to higher luminosity by including photometry of long period variables in the Baade windows. The assumption of a unique giant branch for the galactic centre stars is empirically justified by the small scatter in the colour magnitude diagrams beyond about 1.5° from the galactic plane. Fig. 1a & b give examples of colour magnitude diagrams for 400″ × 400″ areas of sky far from and near to the galactic centre. The observed distribution of stars relative to the 47 Tuc giant branch allows us to measure both the foreground absorption and the number distribution of stars within a given range of dereddened apparent magnitude. The number of stars counted must be corrected for the effect of crowding which is estimated by generating simulated star fields and comparing the number of stars found using our reduction programmes, with the number used to simulate the fields.
Observation of Diffuse CII Emission in the Galactic Center Region
Authors: Okuda H. , Shibai H. , Nakagawa T. , Matsuhara T. , Maihara T. , Mizutani K. , Kobayashi Y. , Hiromoto N. , Low F. J. , Nishimura T.
Published: June 2019

Spectroscopic observations of CII line emission at 157.7 μm have been made of the Galactic Center region with a Fabry-Perot spectrometer onboard a balloon telescope. Strong emission has been detected ubiquitously in a wide area extending between ± 0.7° in galactic longitude. A ring-like structure is suggested from the double lobed distribution of the emission around the Galactic Center.
158μm [CII] Mapping of the Galactic Center Molecular Clouds
Authors: Genzel R. , Stacey G. J. , Townes C. H. , Poglitsch A. , Geis N.
Published: June 2019

We have made 55″ resolution maps of the 158 μm [CII] emission line in the region of the curved, thermal filaments and the +20 / +50 kms−1 molecular clouds in Sgr A. The [CII] emission is spatially well correlated with the radio continuum in the filaments. The large intensity of the [CII] radiation excludes shocks as the origin of the ionization and we conclude that the curved filaments are most likely photo-ionized HII regions at the surface of dense molecular clouds. Our [CII] maps of the +20 / +50 kms−1 clouds indicate that the +50 kms−1 cloud is close to (<10pc) Sgr A west while the more massive +20 kms−1 cloud is at a greater distance from the center (>30pc).
On The Evolution of Accretion Disks in Galactic Centers
Authors: Duschl Wolfgang J.
Published: June 2019

I present the results of hydrodynamical model calculations for the evolution of accretion disks in an originally soft potential well. We follow the onset of selfgravity in the accretion disk and the formation of a central object, and find that for an ample set of possible parameter combinations of the “host galaxy” the evolution runs such that today, i.e. after an evolution time of the order of 1010yrs, compact objects of about 106 M⊙ have formed in the centers of galaxies. In the first Section, I concisely describe the basic ideas; Sect. 2 is devoted to the presentation of the results of hydrodynamical model calculations; and in the last Section, I shall discuss these results, interpreting them with the help of an analytical model that shows why the evolving central object is so independent of the conditions in the galaxy.
VLA Observations of Far-IR Sources Toward the Galactic Center
Authors: Odenwald Sten F.
Published: June 2019

Preliminary results are presented from a 4.8-GHz VLA study of 5 far-IR sources within 1° of the Galactic center. Sgr-D and FIR-27 appear to be nearly featureless radio sources similar to young blister type HII regions, and FIR-21 has a filamentary structure similar to bright rimmed HII regions or Crab-like supernova remnants. Also presented are additional observations of Sgr-C.
Galactic-Center Jet of 4-Kpc Length
Authors: Sofue Y. , Reich W. , Reich P.
Published: June 2019

We report the detection of a 4-kpc long, highly collimated radio feature emanating from the galactic center. This feature, which may be cylindrical in shape, is some 200 pc in diameter and extends almost perpendicular to the galactic plane. The structure may possibly be the remnant of a one-sided or highly asymmetric jet from the nucleus, or it might be a magnetic tornado produced by a twisted poloidal magnetic field between the disk and halo.
Symmetrical Structures in the Galactic Centre Region
Authors: Seiradakis J. H. , Reich W. , Sofue Y.
Published: June 2019

Symmetrical structures do exist, in the Galactic Centre region, In this article we attempt to summarize their properties and draw the attention of the scientific community to the advantages of taking them into account when working with models of the Centre of our Galaxy, Our work is corroborated by two new maps of the region at 10.7 GHz.
VLA Polarization Observation of the Radio Arc at 15 Ghz
Authors: Inoue M. , Fomalont E. , Tsuboi M. , Yusef-Zadeh F. , Morris M. , Tabara H. , Kato T.
Published: June 2019

Polarization measurements of the radio Arc were made with the VLA at 15 GHz. High frequency polarimetry made with high spatial resolution minimizes Faraday depolarization and reveals polarized filaments which correspond to the predominant filaments of the radio Arc. We notice a peculiar linear feature in the polarization map (“thorns”) which suggests the presence of a second magnetic field system. The total intensity maps show no evidence for an interaction between the two field systems, so the thorns may be foreground magnetized structures. However, if the two magnetic field systems do interact, it would allow a model in which the acceleration of relativistic particles takes place at their intersection. The accelerated particles would flow toward both ends of the radio Arc, and account for the intrinsic polarization observed along the entire length of the system. Thermal electrons responsible for the Faraday depolarization occuring at longer wavelengths may be supplied by the interaction of the streams of relativistic particles with relatively dense, ambient thermal clouds.
Mid-Infrared Observations of the Galactic Center Arc and the Sgr A East HII Region
Authors: Yusef-Zadeh F. , Telesco C. M. , Decher R.
Published: June 2019

We have used the 20-pixel IR camera to observe thermal IR emission from dust associated with the radio continuum Arc near the Galactic center and the cluster of HII regions in the immediate vicinity of Sgr A East. We detected strong 10μm emission from the eastern and western arched filaments (G0.1+0.08), from an unusual pistol-shaped structure known as G0.15–0.05 and from the brightest member of the Sgr A East HII region. Spatial maps of these features at 10μm with a resolution of 4.1″ × 4.2″ are presented and are compared with 5-GHz radio images. We find a general spatial correlation between the ionized gas and the dust distributions. The ratio of IR to radio flux densities is significantly different in the eastern and western arched filaments, which suggests that the source of heating has a softer spectrum along the eastern arched filaments. In addition, the ratio of IR to radio flux densities, which is typically ~10 in normal Galactic HII regions excited by O stars, is at least a factor of two higher than this value in almost all the sources we have observed. This suggests that additional mechanisms other than trapped Lymanαradiation should be present in heating the dust, e.g. stochastic heating of small dust grains by energetic particles associated with the nonthermal filaments.
MHD Mechanisms for the Formation of Galactic Center Lobes
Authors: Shibata Kazunari
Published: June 2019

I critically discuss three possible MHD mechanisms for the formation of Galactic center lobes (GCL) found by Sofue and Handa (1984) from the theoretical point of view. The three mechanisms I shall discuss are: (1) sweeping-magnetic-twist mechanism, (2) explosion in a disk with a vertical magnetic field, and (3) nonlinear Parker instability. I review the characteristics of these mechanisms, which are mainly obtained from nonlinear 2D MHD numerical simulations, and discuss their merits and demerits as possible mechanisms for the formation of GCL and related magnetic structures.
On The Galactic Dynamo
Authors: Rosner R. , Deluca E.
Published: June 2019

We critically review the status of our current understanding of galactic dynamo theory. In brief, a definitive model for the production of magnetic fields on galactic scales remains to be constructed.
Gas Dynamics in the Galactic Centre: Gravity vs. Magnetism
Authors: Pudritz Ralph E.
Published: June 2019

This contribution is a summary of an impromptu and extremely interesting discussion on the nature of the forces acting on gas in the galactic centre. The origins of the gas motions in the central few parsecs are crucial for clarifying many important problems about galactic nuclei. Some of the many gas dynamics issues that were raised include: 1. are there explosive events in the galactic centre which produce outward moving gas clouds (see Heyvaerts, these proceedings)? 2. are the streamers of gas due to the tidal disruption of molecular clouds that stray in too deep in the galactic centre's tidal field (see Serabyn, these proceedings)? 3. is there circular gas motion which would be important in constraining the nature of the mass distribution inside scales of a few pc (see review by Townes, these proceedings)?

The discussion centered on gas dynamics in the molecular torus and ionized gas streamers on the 2–5 pc scale. Because reliable measurements of the magnetic field strength in the galactic centre are not yet available, several of the key points of contention will not be finally settled until the data are in. Be this as it may, the discussion boiled down to the issue of whether gravity or magnetic fields were responsible for the structures and morphology on this scale. Accordingly I will label the arguments of the two relevant camps by G (for gravitational fields as the predominant shaper of things) and M (for magnetic fields as the important agents).
Continuum Observations of Sgr A at mm/submm Wavelengths
Authors: Mezger P.G. , Zylka R. , Salter C.J. , Wink J.E. , Chini R. , Kreysa E. , Tuffs R.
Published: June 2019

We have mapped the source complex Sgr A (containing Sgr A West and East) at λ2.8mm, 1.3mm and 350μm using the IRAM 30m MRT (Pico Veleta, Spain) and the 3m IRTF (Mauna Kea, Hawaii) telescopes. Detailed results have been published or will be published elsewhere (Mezger et al., 1986, Paper I; Zylka and Mezger, 1988, Paper II; Mezger et al., 1988, Paper III).
NH3 Observations of the Sgr A Complex Region with the Nobeyama Millimeter Array
Authors: Okumura S. K. , Ishiguro M. , Fomalont E. B. , Chikada Y. , Kasuga T. , Morita K.-I. , Kawabe R. , Kobayashi H. , Inoue M. , Hasegawa T.
Published: June 2019

We report NH3 observations of the Sgr A complex region including Sgr A West and the 20 km/s and 50 km/s molecular clouds (M–0.13–0.08 and M–0.02–0.07) using the Nobeyama Millimeter Array and the 45m telescope. NH3(1,1) and (2,2) lines were simultaneously observed to estimate the kinetic temperature. Our results suggest strong interaction between the molecular clouds and the continuum sources in the Sgr A complex. The interaction with continuum sources might be an important factor in determining the physical conditions of molecular gas in the galactic center region.
CS Multitransition Observations of the Circumnuclear Disk
Authors: Serabyn E. , Güsten R. , Evans N. J.
Published: June 2019

Three rotational transitions of the CS molecule were observed toward the negative longitude half of the molecular disk which orbits about the galactic center between radii of 2 and 10 pc. A comparison of the relative line strengths allows a determination of the radial run of density in the circumnuclear disk. In order to observe all of the transitions with a similar beamsize, the two lower frequency transitions were measured with the IRAM 30-m telescope, and the highest frequency transition with the NRAO 12-m. Table I lists the observing parameters.
The Luminosity of the Central Parsec of the Galaxy
Authors: Werner M. W. , Davidson J. A.
Published: June 2019

The luminosity of the central 5 pc of the Galaxy -encompassing the inner regions of the rotating ring of dust and gas which surrounds the galactic center - emerges primarily at infrared wavelengths in the form of thermal emission from heated dust. The nature and location of the sources which heat the dust can be inferred from the spatial and temperature distribution of the thermal infrared emission (λ>20um), from studies of the ionized gas in this region, and from direct imaging in the near infrared. These observations show that the principal heating sources within this 5-pc region are concentrated within the central parsec of the Galaxy and indicate that the luminosity of these sources is within a factor of two of 107 LO. The near-infrared observations of the compact sources at the galactic center do not reveal a single dominant source but suggest instead that the several components of the IRS-16 complex, taken together, may contribute the bulk of the luminosity; however, the data also permit a single object to dominate the energetics of this region. We draw attention to the striking morphological similarities between the galactic center and the innermost regions of the 30 Doradus nebula in the Large Magellanic Cloud and speculate that the luminosity sources in the galactic center may resemble the early-type supergiants in 30 Doradus.
Multi-Array λ2 and 6cm Radio Continuum Observations of Sgr A West
Authors: Yusef-Zadeh F. , Morris Mark , Ekers Ron
Published: June 2019

Sub-arcsecond (down to 0.1″ × 0.2″) radio continuum observations using the VLA2 in a number of configurations have been carried out in order to investigate the fine-scale morphological details of the ionized gas and the distribution of spectral index along the triskelian-shaped figure of Sgr A West. In addition to finding a number of isolated patches of thermally-emitting gas and an absorbing feature at λ6cm within three arcminutes of the Galactic center, we have observed:

1) radio continuum emission from IRS-7, implying that the stellar wind from this supergiant is externally ionized. An improved position for this object was obtained.

2) the circular mini-cavity located along the east-west bar of Sgr A West. This feature has a diameter of 2-arcseconds and may have been created by a spherical wind, the source of which is yet to be identified; the seemingly most plausible candidate, IRS-16, is offset by 3″ from the center of the cavity.

Spectral index maps having a resolution of 0.7″ × 0.3″ were made from scaled array observations at λ2cm and 6cm. They show that the eastern arm has a spectral index near −0.1, while the northern arm and the bar have positive spectral indices, indicating perhaps a partial opacity effect. The spectral index of IRS-7 is +0.6, consistent with that expected from a completely ionized stellar wind.
The Mass Distribution in the Central Few Parsecs of the Galaxy
Authors: Lacy John H.
Published: June 2019

The determination of the mass distribution in the central few parsecs of the Galaxy, primarily from the ionized gas dynamics, is discussed. The gas motions are described and interpreted assuming that the orbits are determined by gravitational forces. It is shown that there is good evidence for a central mass of ~ 2 × 106 M⊙. The primary uncertainty in this conclusion results from the possibility of significant magnetic forces. In the absence of corroborating evidence, the case for a massive black hole cannot be considered proven.
The Mass Distribution in the Galactic Centre Estimated from OH/IR Stars
Authors: Lindqvist M. , Winnberg A. , Habing H. J. , Matthews H. E. , Olnon F. M.
Published: June 2019

The preliminary results of a search for OH/IR stars in the Galactic Centre using the VLA are presented. The goal of this project is to determine the mass density distribution from a few parsecs up to about 120 pc of the Galactic Centre using stellar kinematics. Up to now, 125 OH/IR stars have been found. The distribution of the stars is clearly elongated with the major axis parallel to the galactic equator. The stars show a rotation of 117 km s−1 deg−1 with a dispersion of 90 km s−1. Two preliminary models have been applied in order to determine the enclosed mass, resulting in M(r)=4.0·106·r1.4 Mo, where r is the galactocentric distance in parsecs.
High Velocity Ionized Gas near IRS 16
Authors: Geballe T. R. , Lugten J. B.
Published: June 2019

An important means of studying the unusual activity within the central ~0.15 parsec of the galaxy is to obtain detailed information on the high velocity ionized gas there. This gas was first reported by Hall, Kleinmann, and Scoville (1982), who observed the He I line at 2.06 μm. Subsequent observations of this line and the Br ∝ and Br γ lines of H I (4.05 μm and 2.17 μm, respectively) by Geballe et al. (1984, 1987) have defined the coarse spatial and spectral properties more accurately. Briefly, the broad (i.e., |v| > 400 km/s) line emission, as observed at velocity resolutions as high as 400 km/s and angular resolutions as high as 2.5″ (1) extends approximately to +/– 700 km/s (e.g., see Fig. 1), (2) is spatially resolved, with a characteristic dimension of 3″, (3) is centered approximately on IRS 16C, and (4) appears to be due neither to rotational motion nor to a simple radial flow from or onto a single compact object. These properties are difficult to understand in terms of simple models, and point out the necessity for further measurements at higher spectral and spatial resolutions.
Constraints on and Alternatives to a Massive Black Hole at the Galactic Center
Authors: Ozernoy Leonid M.
Published: June 2019

Considerations are presented which could serve as nourishment for a “devil's advocate” with regard to the concept of a very massive (~ 106M⊙) black hole at the center of the Galaxy. Constraints on the BH mass given by various processes are summarized. Most attention is paid to a novel probe of the black hole by means of a “wind diagnostic,” i.e. by accounting for interaction of the BH with the wind responsible for the broad line region at the Galactic Center. All available data taken together do not require a very high mass for the BH, but a moderately massive black hole currently seems to present the prime candidacy from several alternatives.
Theoretical Perspective
Authors: Blandford R. D.
Published: June 2019

A conference devoted to the center of our Galaxy inevitably draws together astronomers from many different tribes speaking in tongues about what they each know to be truly important. We have heard from stellar dynamicists and users of magnificent infra-red arrays, (who are apparently only here by courtesy of a hole in the dust distribution), from molecular radio astronomers and experts on solar MHD, cosmic ray physicists and those who misguidedly believe that understanding the Galactic center is much easier than solving the mysteries of quasars. The Galactic center can lay claim to being the melting pot of astronomy and so it is quite appropriate that this conference should be held here in Southern California.
Photometrical, spectral and radio monitoring for EV Lac in 1986 and 1987
Authors: Gershberg R. E. , Ilyin I. V. , Nesterov N. S. , Shakhovskaya N. I. , Getov R. G. , Ivanova M. , Panov K. P. , Tsvetkov M. K. , Tsvetkova A. G. , Leto G.
Published: June 2019

During 9 nights in 1986-1987 we have carried out the patrol observations of red dwarf EV Lac within the wavelength range from 3500 Å to 8 mm and registered more than 50 optical flares. Some features of stellar flares, spots and active regions for the periods of cooperative observations are discussed.
Electrophotometric observations of the EV Lac flares in U, Hα and Hβ
Authors: Melkonian A.S.
Published: June 2019

Results of the patrol observations of the EV Lac flares in U, Hα and Hβ bands are given. The observations are carried out simultaneously in U and Hα or in U and Hβ. During (U, Hα) observations 21 U -flares are registered of which only comparatively strong one is accompanied by a real Hα - flare. And during (U, Hβ) observations among 7 U-flares the strongest and a “slow” one is accompanied with an increase of Hβ -signal. Small amplitude periodic light variations of EV Lac are detected with a period of 3d. 3 and amplitude 0m.02 in B and V bands.
Rapid spike flares on AD Leo and EV Lac
Authors: Panov K. P. , Ivanova M. S. , Antov A.
Published: June 2019

Photoelectric U - band observations of the flare stars A Leo and EV Lac during the last 9 years obtained at the Bulgarian National Astronomical Observatory revealed 8 rapid spike flares on AD Leo and 9 rapid spike flares on EV Lac which duration is less than 6 seconds. The corresponding total monitoring time is 173.6 hours for AD Leo and 173.3 hours for EV Lac.
Diagnostic possibilities of the Walrawen photometric system
Authors: Berdyugin A. V.
Published: June 2019

Diagnostic possibilities of the Walraven photometric system to analyze the UV Cet type flare stars have been studied. It was shown that the Walrawen system marks out the hydrogen spectrum features better than the standard UBV system. Observations of the UV Cet flare of 1985 December 23, carried out in the Walraven system were analyzed with computed two-colour diagrams, temperature and gaseous density at the maximum of brightness were estimated.
Some physical consequences from the flare statistics of the UV Cet type stars in the solar neighbourhood
Authors: Shakhovskaya N.I.
Published: June 2019

The observational data permit us to establish statistical correlations between different parameters of stellar flare activity and the characteristics of quiet stars. We discusss physical consequences following from these relationships.
Flare activity of stars in the Taurus region
Authors: Hojaev A.S.
Published: June 2019

Using the actual observational data on photometric and spectral stellar activity in the region of central area of the Taurus Dark Clouds complex, the question of flare activity of the stars and its connection with another kinds of activities is considered. The comparison of stellar flares in this region with that of in other associations and clusters (especially, Orion and Pleiades) is made and the youth of the group in Taurus is shown. The detection of flaring variables (including stars with T Tauri-type features) in Taurus region is the evidence in favour of evolutionary connection of these stages.
X-ray emission from solar neighbourhood flare stars
Authors: Pallavicini R. , Stella L. , Tagliaferri G.
Published: June 2019

A brief summary is given of a comprehensive analysis of EXOSAT observations of solar neighbourhood flare stars. Special attention is devoted to the discussion of quiescent X-ray emission and time variability.
Herbig-Haro phenomena associated with T Tauri: evidence for a precessing jet?
Authors: Schwartz Richard D.
Published: June 2019

A [S II] emission-line image of T Tauri and its surrounding nebulosity suggests the presence of a precessing jet in the system.
Subfuors in Orion association
Authors: Gasparian L.G. , Melkonian A.S. , Ohanian G.B. , Parsamian E.S.
Published: June 2019

Results of spectral and photometric observations of Sugano star = V1143 Ori in brightness minimum and near it are given. Emission lines of HI, CaII, FeI, TiI, TiII and TiO absorption bands are detected. The appearing envelope is observed also in minimum. A brightness increase of Shanalstar V1118 Ori is observed. In its spectrum lines of HI, CaII, FeI, FeII are found, testifying to formation of an envelope.

During the last ten years data on T Tau type stars which have fuor-like outburst-subfuors were obtained. Two such stars were found in Orion association. These are V1118 Ori [1] and V 1143 Ori [2,3]. In recent years, in Byurakan observatory observations of these stars have been made.
Slow flares and eruptive phenomena in early stages of stellar evolution
Authors: Ibrahimov M.A. , Shevchenko V.S.
Published: June 2019

Correlations between different eruptive phenomena (fast and slow flares, large-scale eruptive variations up to fuor phenomenon) in stellar instability during stage of evolution are analysed A conclusion is drawn on the difference in natures of eruptive phenomena lasting some ten minutes and slower variations lasting more than one day.
A new fuor?
Authors: Tovmassian H.M. , Hovhannessian R.Kh. , Epremian R.A.
Published: June 2019

During observations made in August and November 1987 with the ultraviolet telescope “Glasar” [1] installed at the module “Kwant” of the “Mir” Space Station a very blue star HD 269665 = Sk −68°110 in the region of the LMC was detected.
Quiescent chromospheric response to the (E)UV/optical flare radiation field on dMe stars
Authors: Houdebine E. R. , Butler C. J.
Published: June 2019

We examine the response of the quiescent chromosphere to the large (E)UV and optical continuum and spectral line radiation field arising from a flare. We show that during a UV Ceti type flare, which displays a large U-band enhancement, a major part of the Balmer line flux may arise from the “quiescent chromosphere”, rather than the heated flare plasma itself. This leads us to distinguish two main phases in the Balmer lines, as first proposed by Houdebine et al. (1989): an early, mainly impulsive, phase, driven by radiative pumping of the quiescent chromosphere, which is mainly correlated with continuum variations, and a later one, related to the thermal flare phase, which arises from the cooling of the flare plasma itself. The effect of the radiative pumping is much larger for stellar (dMe) than for solar flares, due to substantial differences in the flare, relative to the quiescent, level and the quiescent chromospheric density and temperature.
The hydrogen atom kinetics in flare star chromospheres
Authors: Bruevich E. A. , Livshits M.A.
Published: June 2019

The solution of steady-state equations for hydrogen is carried out. The diffuse radiation field was taken into account in these equations the value βs≡NRB - the escape probability of photons from the medium. This value is calculated for a layer of motionless plasma with finite optical depth. Our results are compared with analogical ones using Sobolev's method.
On the gamma-activity of stellar flares
Authors: Harutyunian H.A. , Hayrapetyan V.S.
Published: June 2019

The principal possibility of γ-ray manifestation of stellar flares in the framework of pinch-model is shown. Validity of assumption that, γ-bursts are connected with magnetically active dwarfs (MAD) is discussed.
On the origin of dwarf stars
Authors: Lada Charles J.
Published: June 2019

The origin of dwarf or low mass stars is one of the most interesting and challenging problems of modern astrophysics. In recent years advances in observational technology particularly at infrared and millimeter wavelengths, have produced an avalanche of revealing new data, unexpected discoveries and new mysteries about the process of star formation. From this new knowledge a complete empirical picture of stellar origins is being synthesized and a more profound and penetrating understanding of the physical process of star formation in our galaxy is beginning to emerge. It is now apparent, for example, that energetic bipolar outflows are a fundamental aspect of the formation of low mass stars and understanding how a star can form by the act of ejecting mass may be the key to unlocking the secrets of stellar genesis.
Prospects for studies of UV Cet-type flare stars
Authors: Rodono' M.
Published: June 2019

The present review addresses selected questions on UV Cet-type red-dwarf stars primarily concerning the physics involved in the various aspects and phases of the flare phenomenon, rather than the average activity behaviour of the flare stars. In fact, while flare activity level and general trend are reasonably well established, a fully consistent physical picture of both solar and stellar flare events is still missing. Some recent results are presented with the aim of showing which observations are needed and the relevant role that coordinated multiband studies can play.
PLANET II: A Microlensing and Transit Search for Extrasolar Planets
Authors: Sackett Penny D. , Albrow M. D. , Beaulieu J.-P. , Caldwell J.A.R. , Coutures C. , Dominik M. , Greenhill J. , Hill K. , Horne K. , Jorgensen U.-G. , Kane S. , Kubas D. , Martin R. , Menzies J. W. , Pollard K. R. , Sahu K. C. , Wambsganss J. , Watson R. , Williams A.
Published: June 2019

Due to their extremely small luminosity compared to the stars they orbit, planets outside our own Solar System are extraordinarily difficult to detect directly in optical light. Careful photometric monitoring of distant stars, however, can reveal the presence of exoplanets via the microlensing or eclipsing effects they induce. The international PLANET collaboration is performing such monitoring using a cadre of semi-dedicated telescopes around the world. Their results constrain the number of gas giants orbiting 1–7 AU from the most typical stars in the Galaxy. Upgrades in the program are opening regions of “exoplanet discovery space” – toward smaller masses and larger orbital radii – that are inaccessible to the Doppler velocity technique.