bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparison of Nebular Distance Scales
Authors: Samland M. , Köppen J. , Acker A. , Stenholm B.
Published: June 2019

Determination of the positions of central stars of planetary nebulae in the HR-diagram requires the knowledge of nebular distances. For almost all nebulae, these can only be given in terms of statistical scales. These scales have in common that they assume all nebulae to have the same structure (e.g. constant density) and that a unique ionized mass-radius relation exists. If the mass-radius relation is given by Mion = M0 · (R/R0)η, the distance d(pc) of planetary nebulae can be expressed as a function the de-reddened Hβ-flux (erg cm−2s−1) and the angular radius θ(arcsec):
M0 and R0 are in solar masses and pc (Te = 10000 K, He/H = 0.1). The parameter η characterizes the distance scale: e.g. Shklovsky (1956) η = 0, Maciel L. Pottasch (1980) η = 1, Pottasch (1984) η = 3/2, Daub (1982) η = 5/3, and Kwok (1985) η = 9/4.
The Ionization Structure of Planetary Nebulae
Authors: Barker T.
Published: June 2019

Ground-based and satellite spectrophotometric observations of emission-line intensities over the spectral range 1400–7200 Å have been made in 5 or more positions in a total of 9 planetary nebulae.
The Ionization and Thermal Structure of NGC 2392 and NGC 3242
Authors: Liu Xiao-Wei , Danziger John
Published: June 2019

In Liu and Danziger(1992b) we present Te derived from the Balmer discontinuities for 14 objects by long slit spectrophotometry. It is found that on the average the Te derived in this way are systematically lower than those derived the forbidden line ratios, indicating the presence of large temperature fluctuations(Peimbert 1967, 1971). The spectra obtained have been analyzed point-by-point along the slit for NGC 2392 and NGC 3242, for which t2 = 0.13 and 0.058, respectively, as measured on the summed spectra integrated along the slits.
Self-Consistent Photoionization Models of Planetary Nebulae Luminescence
Authors: Golovaty V.V. , Malkov F
Published: June 2019

The modern self-consistent photoionization model of planetary nebula luminescence is described. All of the processes which play an important role in the ionization and thermal equilibrium of the nebular gas are taken into consideration. The diffuse ionizing radiation is taken into account completely. The construction of the model is carried out for the radial distribution of gas density in the nebular envelope which is consistent with isophotal map of the nebula. The application of the model is illustrated on the example of the planetary nebulae BD+30°3639 and NGC 7293. For each nebula, the intensities of the emission lines of ten basic chemical elements in the UV, optical and IR spectral ranges are calculated and matched with observational data. Both the chemical composition of the nebular gas and the continuum of the central star at the wavelengths ≤912Å are determined during the process of model calculation. It is shown that the continuum of the central star at ≤912Å does not correspond to the blackbody spectrum but agrees with the spectrum of the corresponding non-LTE model atmosphere. The radial distributions of electron density, electron temperature and other parameters in the nebular envelopes are found. The optical thickness of the nebulae in the Lyman continuum is derived.
Chemistry in the Molecular Envelope of NGC 7027
Authors: Cox P. , Bachiller R. , Huggins P.J. , Omont A. , Guilloteau S.
Published: June 2019

We report here a systematic study of the molecular content in the neutral envelope of NGC 7027. The measurements were done in September 1991 with the 30-meter IRAM telescope on Pico Veleta (Spain). The frequencies and transitions covered are given in Table 1. Long integrations were performed in each transitions toward the central position of NGC 7027, and for the strongest lines we obtained detailed maps. The results of the observation are given in Table 1 (in units of main beam temperature).
Mass-Losing AGB Stars in the Magellanic Clouds
Authors: Reid Neill
Published: June 2019

Asymptotic giant branch stars are the immediate precursors to the planetary nebula stage of stellar evolution. It is clear that the latter stages of a stars life on the AGB are accompanied by either continuous or episodic mass-loss, with the final convulsion being the ejection of the envelope (the future planetary shell), the gradual exposure of the bare CO core and the rapid horizontal evolution to the blue in the H-R diagram. Thus, the structure of the planetary nebula luminosity function, particularly at the higher luminosities (although this phase is extremely rapid), is intimately tied to the luminosity function of the AGB.
Ubvri Polarization Measurements of Post AGB Stars
Authors: Parthasarathy M. , Jain S.K.
Published: June 2019

UBVRI polarization measurements of 25 post AGB stars with circumstellar dust shells (CDSs) were made. Most of them show A, F, G, K supergiant type spectra. IRAS data of these stars show evidence for the presence cool detached circumstellar dust envelopes. Some of these stars also have warm dust shells. Many show significant polarization. The observed polarization in UBVRI is most likely due to scattering of the central star radiation by CDSs. Some of these stars show variation in polarization and position angle. The polarization data suggest that several may have aspherical or bipolar CDSs.
Deprojection of Planetary Nebula Images
Authors: Volk K. , Leahy D. A.
Published: June 2019

We present first results of the deprojection of some optical and radio images of planetary nebulae using an iterative technique based on the Lucy method, as discussed in Leahy (1991). This approach allows a greater range of possible geometries to be investigated and is less sensitive to the effects of noise compared with the direct matrix-inversion method which can be used for the spherical case. We assume that the emissivity function can be represented as
The Dust in the Hydrogen-Poor Ejecta of Abell 30
Authors: Harrington J.P. , Borkowski K.J. , Blair W.P. , Bregman J.
Published: June 2019

High-resolution images in [O III] λ5007 of the hydrogen-poor knots of Abell 30 reveal comet-like structures which may be indicative of interaction with the stellar wind. In the near IR, new, higher-resolution, K-band images show an equatorial ring of hot dust that corresponds closely to optical knots 2 and 4 of Jacoby and Ford, while their polar knots 1 and 3 show no comparable IR emission. Both the thermal IR emission and the heavy internal extinction of the central star demands an extremely dusty ejecta. Greenstein showed that the UV extinction curve is fit by amorphous carbon. Our comprehensive dust models consider both the UV extinction and the IR emission from a population of carbon grains. The thermal emission from larger grains produces the far IR emission, while the stochastic heating of very small grains to high temperatures is essential to explain the near IR flux. We are able to reproduce the shape of the near IR spectrum with an a−3.0 distribution of grain radii which extends down to a minimum grain radius of 8 Å.
The Formation of Single and Binary Nuclei of Planetary Nebulae
Authors: Yungelson L. R. , Tutukov A. V.
Published: June 2019

The present birthrate of binaries may be written as

where M1 is the mass of the primary in M⊙, 0 < q ≤ 1 — mass ratio of components, A — semimajor axis of the orbit in R⊙. The Eq.(1) implies that all stars are born as binaries with 10 ≤ A/R⊙ ≤ 106, and that one binary with M1 ≥ 0.8M⊙ is formed annually in the Galaxy. We study numerically evolutionary scenarii of binaries within abovementioned range of M1, A,q. As PN formation events we consider all ejections of common envelopes by close binaries and ejections of envelopes by red giants, after which one may expect a formation of a hot (Te ≥ 30 000K) star, surrounded by a nebula. Altogether about 20 different single and binary cores of PN can be formed. Combining the scenarii data with the Eq. (1) one can estimate the birthrates of most numerous kinds of PNN (single and with main-sequence, white dwarf, giant and relativistic companions) listed in the Table.
Precataclysmic Binaries in the Centre of Planetary Nebulae
Authors: Jasniewicz G. , Acker A.
Published: June 2019

We report at first on two old and large planetary nebulae (PN) of which central stars could satisfy the Ritter's criteria (1986) for being precataclysmic binaries: LoTr5 and Abell 35. Both nebulae have probably been ejected as a consequence of common-envelope evolution. A model of cataclysmic binary (CB) for the central star of Abell 35 has been tentatively attempted by Acker and Jasniewicz (1990). The nucleus of LoTr5 is a triple star (Jasniewicz et al., 1987; Malasan et al., 1991): action of a third body on the separation of the close binary could make this binary evolve into a CB (see Mazeh and Shaham, 1979). We report at second on the similarity between the spectrum of the central star of the extended PN HFG1 with that of a CB (Acker and Stenholm, 1990). The PN cited above could be fundamental objects just at the transition between the stage PN and the stage CB.
On Some Links Between Symbiotic Stars and Planetary Nebulae
Authors: Leedjärv Laurits
Published: June 2019

Some correlations found between different physical characteristics of symbiotic stars and planetary nebulae are discussed from the evolutionary point of view.
Theoretical Light Curves of Recurrent Novae
Authors: Kato M.
Published: June 2019

Theoretical light curves for the decay phase of recurrent novae are obtained using optically thick wind theory. With the OPAL opacity tables the decay time scale is drastically shortened.
Evolution of 1–5 Mm⊙ Stars by Mass Loss
Authors: Vassiliadis E. , Wood P.R.
Published: June 2019

Stars of mass 1–5 MM⊙ and composition Y=0.25 and Z=0.016 have been evolved from the main-sequence to the white dwarf stage with an empirical mass loss formula based on observations of mass loss rates in AGB stars. This mass loss formula (Wood 1990) causes the mass loss rate to rise exponentially with pulsation period on the AGB until superwind rates are achieved, where these rates correspond to radiation pressure driven mass loss rates. The formula was designed to reproduce the maximum periods observed for optically-visible LPVs and it also reproduces extremely well the maximum AGB luminosities observed in star clusters in the Magellanic Clouds (see Vassiliadis and Wood 1992 for details).
On the Fading of AGB Remnants
Authors: Blöcker T. , Schönberner D.
Published: June 2019

We investigated the question how the evolution of post-AGB models depends on their history, i.e. on their initial mass and AGB evolution. Therefore, we calculated the evolution of a 3 and 5M⊙ star from the main sequence towards the stage of white dwarfs. These models suffered from 9 and 17 thermal pulses on the AGB, resp., and the common mass-loss law led to final masses of 0.61 and 0.84M⊙, resp., which are consistent with reasonable initial-final mass relationships. It was found that more massive AGB remnants fade much more slower than hitherto assumed. Thus, we conclude that only a reliable combination of initial and final mass yields the right fading time scales for more massive post-AGB models. To prove that we have recalculated the evolution of the 3M⊙ model with another mass-loss law leading to 86 thermal pulses and a remnant mass of 0.84M⊙, a combination which, however, does not comply with initial-final mass relations. Comparing now the post-AGB evolution of the two massive models of equal remnant mass (0.84M⊙) but different initial masses (3 and 5M⊙, resp.) yields completely different fading time scales. Thus we confirm by direct calculations the suggestion of Blöcker and Schönberner (1990, A&A 240, L11) that not only the remnant mass but also the initial mass determines the time scales of more massive central stars.
Planetary Nebulae and Halo Dynamics in Early Type Galaxies
Authors: Hui X. , Ford H.C.
Published: June 2019

The study of extragalactic planetary nebulae has made rapid progress in recent years with the help of high quantum efficiency detectors. A brief but distinctive phase in the late stage of stellar evolution, planetary nebulae (PNe) are not only interesting objects in their own right, but also are extremely valuable and unique tools for probing the host galaxies. Recent studies have used planetary nebulae as test particles to investigate the dynamics and mass distributions in the halos of early type galaxies.
Spectrophotometry and Kinematics of the Newly Discovered PN in the Outher Field of the LMC
Authors: Dopita M.A. , Vassiliadis E. , Morgan D.H.
Published: June 2019

Recently a number of new planetary nebulae (PN) have been found in the outer field of the LMC using deep objective–prism J plates taken with a Schmidt Telescope at the AAO. For a number of these PN, we have obtained spectrophotometry on the 2.3m ATT and for a sub–sample, determined the radial velocities using the Echelle Spectrograph of the 2.3m Telescope. All this data is to appear in the ApJ.
A Reanalysis of C/O Ratios in Planetary Nebulae
Authors: Rola C. , Stasinska G.
Published: June 2019

It is often mentioned in the literature that, in planetary nebulae, carbon abundancesderived from optical lines are systematically much larger than derived from UV lines. Various explanations have been proposed: line blends, inaccurate atomic physics, temperature fluctuations, non uniform distribution of carbon inside nebulae… Here, we study the effect of random errors in the line intensity measurements.
The DCMT in Progress
Authors: Zhigang Li
Published: June 2019

The DCMT (Danish-Chinese Meridian Telescope) is jointly developed by the Shaanxi Astronomical Observatory, Nanjing Astronomical Instrument Factory and Copenhagen University Observatory. The instrument was set up at the Shaanxi Astronomical Observatory in 1990 and put in testing operation in the same year. The design of this horizontal meridian circle is very compact and allows direct real-time monitoring of the instrument parameters. We have studied the stability of the instrument and internal refraction in the telescope tube.
On the Current State of the Mahis Construction
Authors: Kirian T. R. , Naumov K. N. , Nikiforov V. V. , Pinigin G. I. , Bushuev F. I. , Protsyuk Yu. I. , Sibilev V. P. , Gumerov R. I. , Aupov F. G.
Published: June 2019

Information on the recent results of the tests of the mirror, measuring equipments and computer control is given. The astrometrical capabilities of the MAHIS are considered.
The Circle Reading System for DCMT
Authors: Huanxin Li
Published: June 2019

A multi-access automatic circle reading system for Chinese-Danish Meridian Telescope has been developed in CSAO. It consists of circle scanners and photon-electric counters. The method, in using TP-801B Single board computer as main controller for the system, is proved to be successful. It has advantages with low cost, high quality and easy operation. One CTC chip, three PIO chips and relational circuts are all of I/O interface. These programable chips are provided in the board or expanded by designer.
VLBI Relativistic Time Delay Model with Picosecond Precision
Authors: Yang Zhigen , Zhao Ming
Published: June 2019

The VLBI relativistic time delay model of transformation is reformuled with a precision of better than 1 ps, which is given as follows

where is geocentric newtonial potential, and are the barycentric velocity vector in B-frame and the geocentric velocity vector of antenna i. Ŝ is the unit vector of the direction from the barycenter of solar system to the source. c is the speed of light in vacuum. , where is the geocentric baseline vector. δtv can be expressed as

in which

and

where Δtatm, Δtion and Δtaxo are the tropospheric, the ionospheric and the axio offset refraction delays respectively, and Δtgrav is called the gravitational time delay. A straightforward differentation of expression (1), the equation of d(dτ)/dt can be obtained. The included in the can be expressed as

The orders of magnitude of the various correction terms in expression (4) and (5) are estimated respectively. Conclusion: expression (4) and (5) should be taken into account in the VLBI relativistic model of transformation for the 1 ps precision. Equation (1) and the expression of its differentation differ from all the models which have been published earlier.
Is the Vorticity Vector of the Galaxy Perpendicular to the Galactic Plane?
Authors: Miyamoto Masanori
Published: June 2019

The modern astrometric catalogue ACRS invites attempts to re-examine the systematic stellar motions, together with the luni-solar precessional correction and the fictitious equinoctial motion correction to the FK5 system, and gives encouraging results.

On the basis of the three-dimensional Ogorodnikov-Milne model for the overall pattern analysis of the proper motions, the systematic stellar velocity field of about 30000 K-M giants chosen from the ACRS is first examined in the heliocentric distance interval 0.5 to 1.0 kpc. We have found in an iterative fashion a solution for the K-M giants that yields neither deformation-nor vorticity-field other than the classical ones (the Oort constants A and B). The important point to note here is that the generally accepted idea such that the K-M giants are a steady-state constituent of the galaxy is compatible with the luni-solar precessional correction proposed by the VLBI and LLR observations. The K-M giants give the rational set of corrections to the FK5 system: the luni-solar precessional correction Δp = −0″.27 ± 0″.03 / cent and the equinoctial motion correction including the planetary precessional correction Δe + Δλ = −0″.12 ± 0″.03 / cent. Thus, the precessional correction previously proposed with the modern techniques has been confirmed by the pattern analysis of the proper motions.

Next, applying the corrections obtained above, we have performed the overall pattern analysis of the proper motions of about 3000 O-B5 stars, supergiants, and bright giants, which are chosen again from the ACRS, and considered as an entity of the galactic warp. It is found that the kinematics of these stars is quite different from that of K-M giants. These stars show additional shears and rotations around two mutually orthogonal axes lying in the galactic plane, besides the classical ones. The present finding implies that the young stars are streaming around the galactic center in a tilted sheet (the warp) with the velocity of 225 km/s, and the sheet itself is simultaneously rotating around the nodal line of the warp (galactic center — sun — anticenter line) with the angular velocity of 4 km/s/kpc in increasing sense of the present inclination of the warp.
The Velocity Distribution and the Masses of Stars from the Proper Motions in the Stellar Clusters
Authors: Petrovskaya I. V.
Published: June 2019

The velocity distribution for the stars of different masses in the typical open cluster was calculated, the velocity variations having been considered as a purely discontinuous random process. the comparison of calculated and observed mean square velocities for the different groups of stars in the Hyades cluster enables us to estimate the mean mass of the stars in the each group.
The Observation of Counterjets of Quasars and Galaxies
Authors: Gong (Kung) S. M.
Published: June 2019

The purpose of this paper is to point out the importance of the observation of the counterjet of subluminals, for it will settle up the question whether quasars redshifts are cosmological or not. If so, from the observed wavelength of the counterjet, one is able to find out the value of Hubble constant H0. What we observe as an apparent superluminal or subluminal motion is the resultant velocity of Hubble flow and a local ejection. Taking Hubble flow into account, one can explain problems posed for the relativistic beaming model, such as the one-sidedness problem and the untolerable extension of the deprojected structure of some superluminal sources. Our method is applied to two superluminals, 4C73.18 and 3C179, and two subluminals, M87 and 3C84. Our method can also be applied to investigate the problem of the ejection of the quasar from the galaxy in the framework of kinematics. Two quasar-galaxy pairs, Markarian 205-NGC4319 and 3C455-NGC7413, are studied.
An Analysis of Tidal Variations in the Length of Day
Authors: Mccarthy Dennis D. , Luzum Brian J.
Published: June 2019

Observations of the length of day (LOD), corrected for the effects of variations in the angular momentum due to changes in wind velocity and atmospheric pressure, ocean tide heights and currents, and solid Earth zonal tides, were analyzed. The apparent effect of atmospheric angular momentum (AAM) on the astronomically determined LOD is found to be much less at the highest frequencies than at lower frequencies. For periods shorter than ten days there appears to be essentially no correlation between AAM and LOD. The International Earth Rotation Service (IERS) Standards (1992) model for the effects of zonal tides on the Earth's rotation, which includes ocean tidal effects, adequately accounts for the observations of the variations in the length of day with periods between five and 180 days at the present level of accuracy. A currently unexplained semi-annual variation in the length of day remains, but this may be due to the unmodeled effects of stratospheric winds. The power spectrum of the remaining variations with periods less than twenty days is essentially that of a white-noise process. The amplitudes of the remaining unexplained variations in length of day are less than thirty microseconds. This paper has been accepted by Geophysical Journal International for publication.
Rapid Variation of LOD and Solar Flares
Authors: Li Chen , Zhian Li , Zhengfeng Zhou
Published: June 2019

The sequence of LOD in the period from 1988 to 1991 (which was published in Bulletin B by IERS) is analyzed. Using the method of multiple filter, all the periodic terms are removed. Therefore, the rapid and outstanding variations of LOD that greater than 0.1ms in May, 1989 and Jan., 1990 are shown in the residual series. Because of many bursts of solar flares in the period of Mar.8 to 16 and Nov.7 to 17, there are geomagnetic storms in Mar. and Nov.1989. The strong geomagnetic variation probably induces the rapid variation of LOD.
Comparative Analysis of Structures of Some Astrometrical and Geophysical Observational Series
Authors: Rykhlova L. V.
Published: June 2019

Some variations of geo and solar physical parameters are known to be observed simultaneously in the Earth's dynamic parameters changes. The evaluation of the influence of solar activity upon Atmospheric Angular Momentum (AAM) and Length of Day (LOD) within the short periods is made. The similarity between the amplitude and period variations of low-frequency components of polar motion parameters and geomagnetical AA-indices is discovered too.
Characteristics of 30–70 Day Fluctuations of the Length of Day and Atmospheric Angular Momentum
Authors: Zheng Dawei , Gu Hui
Published: June 2019

The length of day (LOD), the atmospheric angular momentum (AAM) and the relative sunspot number (RSN) time series at 5-day intervals, which are spanning 13 years from 1976 through 1990, have been analysed in order to study the 30–70 day fluctuations. The filtered series with the 30–70 day band-pass of the three kinds of data were obtained by the Multi-Stage Filter. The five spectral peaks in both filtered series have been detected by the AR spectrum with the order of AR models as less than 3 percent of the sample number of each series. The amplitude estimates for the five periods in each series appear basically in equal distribution, and there is not a dominant one. The amplitudes of the averaging period for the five periods of LOD and AAM series decrease obviously with the increasing of sample number. The randomness of three series of periodic variations calculated from LOD, AAM and RSN was inspected by using the independence test and the link test of Statistics. Both tests for LOD and AAM are satisfied but RSN is not. From the above mentioned analysis, it is shown that the 30–70 day fluctuations both in LOD and AAM have the features of random walks in time scale and do not have a stable and periodic oscillation.
“Proper Motions” of Extragalactic Sources and the Precession Constant
Authors: Wang Shuhe , Xu Tongqi , Lu Peizhen
Published: June 2019

From the observational catalogues of the extragalatic sources, the common sources with larger observational intervals are selected. After a reduction of optical catalogue systems to the FK5, the “proper motions” of these sources are obtained in the FK5 system. With these values the correction of the precession constant has been estimated and compared with that obtained from the new techniques.
Equator and Equinox Solutions from Meridian Circle Observations of the Sun, Mercury and Venus at the Cape of Good Hope and the U. S. Naval Observatory from 1907 to 1971
Authors: Yao Zhen-Guo , Smith Clayton
Published: June 2019

A total of 53,259 observations(26,793 in declination and 26,466 in right ascension) of the Sun, Mercury and Venus made with the Washington, six-inch and nine-inch transit circles from 1911 to 1971 and the Cape of Good Hope reversible transit circle from 1907 to 1959 are used to obtain equator and equinox solutions.
Comparison of the Catalogs ACRS, PPM, and Tokyo PMC
Authors: Sôma Mitsuru
Published: June 2019

The positions of about 306,000 common stars of the recently published catalogs ACRS and PPM are compared. The positions agree very well (rms < 0″.1) at the epoch of 1950, but the differences become larger as the epoch becomes farther from 1950 due to the deficiency in the accuracy of proper motions. The rms at the epoch of 2000 is about 0″.36. The agreement is better for the stars in the southern hemisphere, as is shown in the figures below, although the southern part of PPM (1991 April version) is still preliminary.
A New Method of Relative Coordinate-and-Time Determination
Authors: Gubanov V.S. , Malkin Z.M. , Solina N.I.
Published: June 2019

The paper deals with the relative coordinate-and-time determination in a ground based reference frame by using the NAVSTAR/GLONASS radio interferometry and duplex clock comparison techniques.
Report on the World Space Congress
Authors: Mccarthy Dennis D.
Published: June 2019

The World Space Congress comprised of the 43rd Congress of the International Astronautical Federation (IAF) and the 29th Plenary Meeting of the Committee of Space Research (COSPAR) was held in Washington, DC from 27 August to 4 September, 1992. Over 3000 people participated in the meetings where scientific papers were presented on such diverse topics as space travel, biological aspects of space travel, relativity, planetary atmospheres, space debris, space law, global change, launch vehicles, space station, space communication, navigation, Earth rotation, astrometry, satellite geodesy, use of lunar observations, and new observational techniques. Presentations dealing with the topics of this symposium are discussed, but complete reports will be forthcoming in the proceedings of the Congress.
The Small Magellanic Cloud
Authors: Arp Halton C.
Published: June 2019

In 1957 a two-year photometric study of the Small Magellanic Cloud, sponsored by Indiana University and supported by the National Science Foundation was completed. Six region swere investigated. They are three on the edge of the SMC centered on conspicuous star clusters and three nearer the center.
Intrinsic dispersion in early-type stars
Authors: Strömgren Bengt
Published: June 2019

The principal basic parameters of early-type stars being mass and age, two-dimensional classification according to the MK system corresponds to a mass-age classification.
Evolution of stars decreasing in mass
Authors: Massevitch A. G.
Published: June 2019

By a “steady” evolution of a star is understood such a change of its main parameters in the flow of time, which occurs in the range of an assumed equilibrium model and is caused by regular interior processes. So, for instance, the gradual conversion of hydrogen into helium in the convective core of a star, whose substance is not mixed fully, leads to a continuous change of its luminosity, radius, Tc and ρc, convective core dimensions. However, all these changes occur all the time in the limits of the model's state of equilibrium, and the structure of the star (radiative envelope and convective core) remains unchanged until a certain limit is reached in the ratio.
Empirical data on age and position in the Hertzsprung-Russell diagram for O and B-type stars
Authors: Blaauw A.
Published: June 2019

For satisfactory tests of the theory of the evolution of the massive stars, accurate data are required on their positions in the HR diagram together with the corresponding ages. The following remarks deal with two pieces of information relevant to this problem.
On the corpuscular emission theory of stellar evolution
Authors: Fessenkov V. G. , Idlis G. M.
Published: June 2019

Considerations regarding the evolutionary path of the main sequence stars depend essentially on the theorem of Vogt-Russell. According to this theorem the structure of stars with thermonuclear sources of energy is determined uniquely by their masses and chemical composition, as characterised by the mean molecular weight X, Y, Z being the relative amounts of hydrogen, helium and of the mixture of the heavy elements.
General Historical Introduction
Authors: de Vaucouleurs Gérard
Published: June 2019

A brief historical review of the discovery and exploration of elliptical galaxies in the past two centuries is presented.
Cores of Early-Type Galaxies
Authors: Kormendy John
Published: June 2019

Systematic study of galaxy cores has become possible through improved understanding of seeing and the reduction of photometric errors by the use of CCDs. Many cores are well resolved in a photometry program with the Canada-France-Hawaii Telescope (median stellar FWHM = 0″.80). Core profile shape correlates with galaxy luminosity L: the brightest galaxies have isothermal profiles; fainter ellipticals and bulges have profiles that do not completely flatten inward into a core. This may be due to velocity anisotropies. Core parameters are correlated: more luminous galaxies have larger core radii and fainter central surface brightnesses. Large deviations suggest special events: Fornax A has too small and bright a core for its luminosity; it may be the remnant of a merger with a smaller galaxy. Core mass-to-light ratio M/L ∝ L0.2, as expected from the metallicity-luminosity relation. A kinematic search shows strong evidence for a central black hole in M31 and weaker evidence in M32 and NGC 3115. The nucleus of M31 rotates very rapidly but has an outer dispersion of only 107 km s−1. This implies that it is a disk; it may have formed from gas falling into the center. Rapid rotation and a central velocity dispersion > 241 ± 7 km s−1 imply a central M/Lv ≳ 20 − 35. Velocity anisotropies are not a major uncertainty because of the rapid rotation. Therefore there is strong evidence for a nuclear point mass of ~ 2 × 107M⊙.
Properties of cD Galaxies
Authors: Tonry John L.
Published: June 2019

cD galaxies are the most luminous galaxies in the universe. They are characterized by a surface brightness profile that falls off more slowly with radius than most elliptical galaxies. In most respects D galaxies are a continuous extrapolation from other ellipticals: their M/L and their colors are comparable to other ellipticals, their inner parts are fitted by an r1/4 law, and they follow the same relation between L and σ. On the other hand, their luminosity is too bright to be consistent with the luminosity function of other ellipticals and they are always found at the center of a cluster of other galaxies. Being at the center of a cluster of galaxies often endows D galaxies with a very faint, very extended halo of luminosity and multiple nuclei, but these are more properly associated with the cluster than the D galaxy itself. The connection between the formation of cD galaxies and the formation of clusters remains a mystery. It is still unresolved whether cDs are a byproduct of cluster evolution, whether they formed in parallel with clusters, or whether primeval D are galaxies the seed around which clusters accreted.
Dissipationless Formation of Elliptical Galaxies
Authors: White Simon D.M.
Published: June 2019

Dissipationless formation mechanisms envisage elliptical galaxies as arising from the collective relaxation of an aggregate of stars. Their key ingredients are thus a set of initial conditions derived from consideration of prior evolution, and a treatment of the relaxation process. I review numerical studies of violent relaxation carried out over the last decade and purely theoretical treatments going back twice as far. Relaxation is always incomplete, and as a result the final structure of a “galaxy” depends sensitively on the initial conditions assumed. The viability of dissipationless formation thus rests on the identification of plausible stellar initial conditions which relax to the present structure. I discuss the extent to which such initial conditions are compatible with current ideas on the origin of structure in the universe.
Dissipation and the Formation of Galaxies
Authors: Carlberg R.G.
Published: June 2019

The evidence for dissipation in elliptical galaxies indicates neither the epoch of formation nor the rate of radiation. The hypotheses for the formation of ellipticals include mergers of pre-existing, mostly stellar, disk galaxies; accumulation of gassy fragments that subsequently turn into stars; and the dynamical collapse of a distinct protogalactic gas cloud with simultaneous star formation. Mergers of purely stellar disks seem unlikely, because the phase space density of disks is everywhere far below that of the cores of normal ellipticals. Allowing a few percent of the mass of the galaxy to dissipate into the core and turn into stars could remove this difficulty. In the Hubble sequence of galaxies, ellipticals are characterized by their low angular momentum content. As a start to understanding the general problem for galaxy formation and angular momentum acquisition in the presence of dissipation, a cosmological N-body experiment containing both a dominant collisionless component and an isothermal gas is described. The collisionless component clusters in the usual hierarchical manner appropriate to the spectrum of fluctuations. In contrast, the gas fragments only when the Jeans mass drops below the turnaround mass. The fragments subsequently shrink, becoming distinct entities with relatively low chances of being quickly incorporated in a larger unit. Gravitational torques transfer angular momentum outward in the dissipating gas, placing most of the gas angular momentum at large radii in the protogalaxy. The distant, high angular momentum gas has a relatively long infall time onto the galaxy. The gas may continue to rain down for some time if the galaxy remains undisturbed, or, the growth of clustering may strip the gas off, leaving a low angular momentum system.
Morphological Properties of Elliptical Galaxies
Authors: Djorgovski S.
Published: June 2019

In the poster as presented at the meeting, I described global morphological properties of elliptical galaxies, based on the data from a CCD surface photometry survey of ~ 200 ellipticals and ~ 50 SO's (Djorgovski 1985). In this brief summary, I emphasize two points: (1) there is a very weak and very noisy trend of radial shape with luminosity, in the sense that more luminous galaxies are less concentrated, and (2) there is no preference for low-luminosity ellipticals to show boxy isophotes, and they differ in that respect from the bulges.
On The Relation between Radius, Luminosity and Surface Brightness in Elliptical Galaxies
Authors: Recillas-Cruz E. , Serrano A.
Published: June 2019

We have analyzed luminosity profiles of E galaxies in six clusters of galaxies. We have found a relationship between radius, luminosity and surface brightness for galaxies in each of the clusters. Moreover, it seems that there is a dependence of the zero point of the relation with environment. This relationship implies that there is not a universal luminosity profile for elliptical galaxies.
Settling of Gas Disks in Elliptical Galaxies
Authors: Steiman-Cameron T.Y. , Durisenr R.H.
Published: June 2019

Prominent gas disks and dust lanes are found in a number of elliptical galaxies. It is widely believed that these disks are the result of the tidal capture of material from a nearby galaxy or the accretion of a gas rich companion into a larger galaxy. While a captured gas disk will ultimately settle into a steady-state orientation (“preferred plane”), the disk will initially be time varying due to precessional and viscous forces. We have developed methods for modeling the evolution of such inclined dissipative galactic gas disks (Steiman-Cameron 1984, Ph.D. dissertation, Indiana U.; Steiman-Cameron and Durisen 1986, Ap.J., in press, hereafter SCD), and we here present some of the results of this work.
HI Imaging of Radio Active Ellipticals
Authors: van Gorkom J.H.
Published: June 2019

Statistics on HI absorption in radio galaxies suggest that accretion of gas into the center might be a general phenomenon. Images of the HI emission from these galaxies show that the gas must have an external origin. The rotation curves derived from the HI data are flat.
Dwarf Galaxies in the Fornax Cluster
Authors: Caldwell Nelson , Bothun Gregory
Published: June 2019

We present the results of an observational study of the dwarf galaxies in the Fornax cluster of galaxies.
Shells and Dark Matter in Elliptical Galaxies
Authors: Hernquist Lars , Quinn P.J.
Published: June 2019

A new method for probing the distribution of matter in elliptical galaxies surrounded by shell systems is described. As an illustration we have applied this technique to the giant elliptical galaxy NGC 3923. If the potential is modeled as the sum of an r1/4 law and a non–singular isothermal halo, then the best fit to the shell number and shell distribution gives a halo mass (within the shell system ~ 100h−1 kpc) ~ 40 times the mass of the elliptical and a halo core radius ~ 3 times the effective radius of the luminous material.
Complex Instability Around the Rotation Axis of Triaxial Systems
Authors: Martinet Louis , Pfenniger Daniel
Published: June 2019

We examine the general instability at large amplitude of the radial periodic orbits along the rotation axis of bulges, spheroids and other rotating triaxial ellipsoidal systems.
Instability Through Anisotropy in Spherical Stellar Systems
Authors: Palmer P.L. , Papaloizou J.
Published: June 2019

We consider the linear stability of spherical stellar systems by solving the Vlasov and Poisson equations which yield a matrix eigenvalue problem to determine the growth rate. We consider this for purely growing modes in the limit of vanishing growth rate. We show that a large class of anisotropic models are unstable and derive growth rates for the particular example of generalized polytropic models. We present a simple method for testing the stability of general anisotropic models. Our anlysis shows that instability occurs even when the degree of anisotropy is very slight.
Non-Circular Gas Motions in the Inner Galaxy
Authors: Sanders Robert H.
Published: June 2019

It is shown that the observed motion of neutral hydrogen in the inner 1000 pc of the Galaxy is, for the most part, consistent with flow on circular streamlines in the potential of the Galactic bulge as derived from the observed distribution of near infrared emission. The implied mass distribution is also consistent with recent kinematic determinations of the stellar mass in the inner few parsecs of the bulge. The non-circular gas motion seen between two and four kpc is most likely due to flow on elliptical streamlines in the presence of a weak bar distortion of the Galactic disk. Circular gas motion in the region of the bulge and elliptical streaming further out is an observed characteristic of flow in barred galaxies and is consistent with our present theoretical understanding of such systems. The implication is that non-circular motions of the molecular clouds in the inner 200 pc have a non-gravitational origin. A possible mechanism for exciting such motions is an accretion event resulting from an encounter of a molecular cloud with a massive black hole. A starburst leading to a high supernovae rate 107 years ago in the inner 50 pc is an alternative explanation. Observations of molecular cloud regions in the nuclei of external normal galaxies could distinguish between alternative mechanisms.
Molecular Clouds in the Central 100-pc of the Galactic Center
Authors: Tsuboi M. , Handa T. , Inoue M. , Inatani J. , Ukita N.
Published: June 2019

We have observed CS (J=1–0/2–1) lines in a 60′×30′(1×b) area of the Galactic center region. There are two large-scale features with elliptical shape in the position–velocity maps, which suggest shell–like structures in the region. One is the ring with a radius of ~40 pc in the positive galactic latitude region and another is the shell with a radius of ~20 pc in the negative galactic longitude region. These could be due to suggest star bursts occurred in the Galactic center region.
Wide-Line Molecular Clouds and the Gamma-Ray Deficit Toward the Galactic Center
Authors: Stacy J. G. , Bitran M. E. , Dame T. M. , Thaddeus P.
Published: June 2019

The discrepancy between observed and predicted γ-ray emission toward the Galactic Center is attributed to a unique population of wide-line molecular clouds. The most prominent objects of this class show evidence of rotation and a significant stellar population. The observed 12CO emission traces the gravitational field produced primarily by stars, not molecular gas.
Filamentary Structures Near the Galactic Center
Authors: Yusef-Zadeh F.
Published: June 2019

Recent studies of the Galactic center environment have revealed a wealth of new thermal and nonthermal features with unusual characteristics. A system of nonthermal filamentary structures tracing magnetic field lines are found to extend over 200pc in the direction perpendicular to the Galactic plane. Ionized structures, like nonthermal features, appear filamentary and show forbidden velocity fields in the sense of Galactic rotation and large line widths. Faraday rotation characteristics and the flat spectral index distributions of the nonthermal filaments suggest a mixture of thermal and nonthermal gas. Furthermore, the relative spatial distributions of the magnetic structures with respect to those of the ionized and molecular gas suggest a physical interaction between these two systems. In spite of numerous questions concerning the origin of the large-scale organized magnetic structures, the mechanism by which particles are accelerated to relativistic energies, and the source or sources of heating the dust and gas, recent studies have been able to distinguish the inner 200pc of the nucleus from the disk of the Galaxy in at least two more respects: (1) the recognition that the magnetic field has a large-scale structure and is strong, uniform and dynamically important; and (2) the physics of interstellar matter may be dominated by the poloidal component of the magnetic field.
Observations of Linear Polarization at 32 Ghz of the Galactic Center Arc
Authors: Reich Wolfgang
Published: June 2019

The Galactic Center Arc has been observed with the Effelsberg 100-m telescope at 32 GHz. The percentage polarization is of the order of 50%. The magnetic field structure is uniform in a direction parallel to the Arc.
Comment on the Standard of Rest Associated With the Neutral Ring at the Centre of the Galaxy
Authors: Clube S.V.M.
Published: June 2019

The evidence for a large systemic motion of the neutral ring at the centre of the Galaxy is reviewed, indicating that the local standard of rest is probably receding from the centre at around 40 kms−1.
The Stellar Cluster
Authors: Sellgren K.
Published: June 2019

Observations of the stellar cluster in the central 10 pc of the Galaxy are reviewed. The stellar density law derived from the observed light distribution and the effects on this density law of variable extinction, the possibility of a varying mass-to-light ratio, and the current debate as to the core radius of the cluster are all important for establishing the true mass distribution of the stellar cluster. The presence of the supergiant IRS 7 in the Galactic Center establishes that some recent star formation has occurred, but the age and extent of a possible starburst are still being established. The kinematics of the stellar cluster show predominantly velocity dispersion, in contrast to the systematic gas motion observed, yet the total mass distributions derived from stellar and gas kinematics agree reasonably well. The core radius of the cluster is critical to establishing whether or not a central dark mass is required to explain the total mass distribution.
Velocity-Resolved Spectra of Brαand Brγon IRS16 SW and NE
Authors: Maillard J. P. , Gay J.
Published: June 2019

The source IRS16 has been observed with the FTS at the Canada-France -Hawaii Telescope, in July 1987 and May 1988, in an attempt of spectral resolution associated with spatial resolution. Three positions were observed with a 2.5 arcsec aperture, centered on the sub-structures SW, NE and NW. Brαand Brγspectra were obtained at respective velocity resolutions of 210 and 140 km s−1, allowing resolution of the line profiles. The detection of hydrogen emission was marginal on NW, and strong on SW and NE, showing a net velocity difference of the gas of 160 km s−1. The Brαline on SW has very extended wings suggesting two components of different origin. These observations imply a difference of physical nature of the objects located in the vicinity of Sgr A∗.
X-Ray Observations of the Galactic Centre
Authors: Skinner G. K.
Published: June 2019

Observations of the galactic centre region in the photon energy range 2–500 keV are reviewed. Point sources, transients, bursts and a patch of apparently diffuse emission ~1° in extent have all been observed. The relatively detailed information obtained with the Einstein observatory just above the bottom edge of the x-ray window is starting to be supplemented by observations at higher photon energies. Although there is known to be a strong, variable, source of high energy x-rays somewhere in the region there is little reason to associate it with Sgr A West, which is detectable, but relatively weak, in the energy range below 30 keV where detailed measurements have been possible.
Gamma-Ray Imaging of the Galactic Center Region
Authors: Cook W. R. , Palmer D. M. , Prince T. A. , Schindler S. M. , Starr C. H. , Stone E. C.
Published: June 2019

The Caltech imaging γ-ray telescope was launched by balloon from Alice Springs, NT, Australia and performed observations of the galactic center during the period 12.62 to 13.00 April 1988 UT. The first coded-aperture images of the galactic center region at energies above 30 keV show a single strong γ-ray source which is located 0.7±0.1° from the galactic nucleus and is tentatively identified as 1E1740.7-2942. If the source is at the distance of the galactic center, it is one of the most luminous objects in the galaxy at energies from 35 to 200 keV.