bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of Radial Abundances Gradients from Planetary Nebulae
Authors: Maciel W.J. , Köppen J
Published: June 2019

The presence of radial abundance gradients is now well established, both in our Galaxy and in other spirals. These gradients were originally derived from oxygen abundance in HII regions, but in the past few years, other elements produced by massive stars have also been shown to display radial abundance gradients similar to the oxygen gradient, which amounts to −0.07 dex kpc−1. Moreover, planetary nebulae (PN), belonging to the intermediate disk population (the so–called Peimbert “type II” PN) also exhibit gradients of the same order of magnitude as the HII regions.
Hipparcos Photometry of Minor Planets
Authors: Morando B. , Mignard F.
Published: June 2019

In addition to its astrometric capabilities the Hipparcos main detector proves to be a good phototometer. The main features of the photometric reduction applied to minor planets are outlined. The apparent magnitude measured by Hipparcos is transformed into absolute magnitude after corrections for the distance to the sun, the earth and for the phase effect, are applied. We show that the remaining signal contains information on the rotational properties of the planets.
CCD Astrometry with Wide-Field Astrographs
Authors: Gubanov V. S. , Shornikov O. E.
Published: June 2019

A principle of a CCD-Tracking System for wide-field astrographs is proposed. This system can be used for precise relative positioning of fixed and moving, bright and very faint optical objects with respect to reference stars. Estimates of the positioning accuracy are given for objects of the 10÷20th magnitudes when observing with the K. Zeiss wide-field astrographs.
Applications of Few-Hundred Microarcsecond VLBI Astrometry: Planetary Relativistic Deflection, PPN Gamma Determination and Deep-Space Tracking
Authors: Lowe S. T. , Treuhaft R. N.
Published: June 2019

This paper presents several applications of a few hundred microarcsecond (μas) astrometric technique which has been developed and demonstrated using differential very long baseline interferometry (VLBI). A brief description of the technique along with several applications will be discussed below. This technique was developed for high-accuracy deep-space tracking, but the first application tracked an extragalactic radio source in a measurement of Jovian relativistic deflection. Current work includes making a state-of-the-art solar deflection measurement, and thus, an improved determination of the Parameterized Post Newtonian (PPN) gamma parameter. A number a future spacecraft tracking applications, described below, are also enabled by this technique.
Geodetic VLBI Experiment at 22 GHz Band Between Japan and Italy
Authors: Takahashi Y. , Kiuchi H. , Kurihara N. , Grueff G. , Ambrosini R.
Published: June 2019

Geodetic VLBI experiments are usually conducted at S/X dual bands. Some advantages can be gained at some higher frequency band and in particular at 22 GHz band (K band). We organized a geodetic VLBI experiment on the 16th of February 1991 between Kashima 34m antenna of the Communication Research Laboratory (CRL), in Japan and Medicina 32 m telescope of the Institute of antenna(IRA), in Italy. The phase calibrator was developed using a new “up-conversion” scheme for K band. Data relative to 212 observations of 40 sources were correlated and for 152 scans we obtained correlated amplitudes, delays and delay rates. The r.m.s. residuals have been found to be 100 ps for delays, and 74 fs/s for delay rates. The coherence loss of correlation amplitude becomes large at higher frequency band than 22GHz due to the atmospheric scintillation. The estimated method of the coherence loss was presented. The correlated flux densities at K band evaluated from them were found to be smaller than the ones at X band in general.
Absolute Proper Motion of Galactic Globular Clusters
Authors: Scholz R.-D. , Irwin M. J.
Published: June 2019

Using automated scans of Tautenburg Schmidt plates with the APM facility in Cambridge (UK) the mean tangential motion of two globular clusters, M3 and M92, is determined directly with respect to a well defined extragalactic reference frame. In both fields five pairs of plates centred on the cluster with epoch differences from 20 to 27 years were measured. In the independent proper motion determination with 1200 to 2300 reference galaxies for each pair of plates we used 3rd order polynomials and a stepwise regression method. The mean absolute cluster p.m. corrected for systematic effects dependent on the coordinates was obtained with an accuracy of ±0.03 arcsec/century for M3 and ±0.06 arcsec/century for M92.
One Year of Daily Satellite Orbit and Polar Motion Estimation for Near Real Time Crustal Deformation Monitoring
Authors: Bock Yehuda , Zhang Jie , Fang Peng , Genrich Joachim , Stark Keith , Wdowinski Shimon
Published: June 2019

The Permanent GPS Geodetic Array (PGGA) in southern California consists of five continuously operating stations established to monitor crustal deformation in near real time. The near real time requirement has been problematic since GPS satellite ephemerides and predicted earth orientation values (IERS Bulletins A and B) have been found to be neither sufficiently timely nor accurate to achieve horizontal position accuracies of several mm on regional scales. Therefore, we have been estimating precise GPS ephemerides and polar motion since August 1991. An examination of overlapping 24-hour satellite arcs indicates worst-case orbital errors of approximately 0.2 meters in the radial components, 1 meter in the cross-track components and 2–3 meters in the along-track components. A comparison with very long baseline interferometry indicates an accuracy of less than 1 mas in our determination of 24-hour values of pole position. These products are sufficiently timely and accurate to achieve several mm long-term horizontal precision in regional scale measurements of crustal deformation in near real time, as has been demonstrated during the 28 June, 1992 Landers and Big Bear earthquakes in southern California. The PGGA stations were able to detect seismically induced, sub-centimeter-level motions with respect to a terrestrial reference frame defined by the global tracking stations.
IAU North Poles and Rotation Parameters for Natural Satellites
Authors: Lieske J. H.
Published: June 2019

In 1970 the IAU defined any object'snorthpole to be that axis of rotation which lies north of the solar system's invariable plane. A competing definition in widespread use at some institutions followed the “right hand rule” whereby the “north” axis of rotation was generally said to be that that of the rotational angular momentum.

A Working Group has periodically updated the recommended values of planet and satellite poles and rotation rates in accordance with the IAU definition of north and the IAU definition of prime meridian.

In this paper we review the IAU definitions ofnorthand of the location ofprime meridianand we present the algorithm which has been employed in determining the rotational parameters of the natural satellites.
Suggestion on the Problem of Time
Authors: Zongyi Cheng , Zongyuan Li , Kaiping Tian
Published: June 2019

Having analysed the real reason why the TDT second differs the TAI second, the TDT's property, unit as well as its definition, and the radical disadvantages existed in the problem of time, we present a new program on the problem of time.
The Conventional Geocentric Reference System within the Framework of Relativity
Authors: Chun-Hao Han , Bang-Xin Xu
Published: June 2019

Some basic conceptions of relativistic reference systems are given. The conventional solar-system barycentric reference system (B-system) and the conventional geocentric reference system (G-system) are discussed. It is suggested that the harmonic conditions be used in the definition of the B-system and the G-system be defined by the B-system and the coordinate transformation given by eqs (3–2), (3–3) and (3–4).
AIST Project: Scientific and Technological Foundations
Authors: Chubey M.S. , Kanayev I.I. , Makarov V.V. , Yershov V. N. , Il'in A.E. , Moklyak V.I. , Shaklein P.A. , Golovanov S.M. , Zinkov V.A. , Chebotarev V.E. , Arbuzov V.N. , Ashurkov E.A. , Bartenev V.A. , Titov G.A. , Bulynin Yu.L. , Zagar O.V. , Malyshev V.A. , Nikitenko A.N. , Sergeev Yu.D. , Yermashkevich Yu.B. , Bakerkin A.V. , Gashkin I.S. , Yefimkin V.I. , Zakharov A.N. , Znamensky I.V. , Tolstonozhenko V.E. , Pochukayev V.N. , Kuskov V.D. , Biryukov I.V. , Novikova E.L. , Peshkin A.A.
Published: June 2019

The results of an initial technical design of the AIST spacecraft and payload are presented. The spacecraft design is subjected to the main requirement: to supply the smooth rotation. Two telescopes are symmetrically placed around central beam combiner unit. The fine adjustment of the light pressure centre position by means of special-purpose sails is proposed. Scientific objectives of the project are the implementation of astrometric survey of the sky and obtaining a series of star position catalogues with milliarcsecond accuracy, including a second epoch of Hipparcos/Tycho catalogues. The survey list will consist of nearly 10–15 million stars brighter than 15th magnitude.
Nécessité de trois paramètres pour la classification précise des étoiles des premiers types spectraux
Authors: Chalonge D.
Published: June 2019

Une classification stellaire utilisant trois paramètres quantitatifs a été constitute : elle permet de classer des étoiles qui n'avaient pas place dans les anciens systèmes.

Une classification précise exige trois paramètres aussi bien pour la population I que pour la population II. Lorsque les valeurs des trois paramètres caractérisant une étoile sont connues, sa magnitude absolue semble déterminée sans ambiguité : ainsi toute « dispersion cosmique » disparaîtrait. Cette notion serait la conséquence du manque de precision de la classification à deux paramètres qui a été employée jusqu'ici.
Theoretical interpretation of the Hertzsprung-Russell diagram
Authors: Schwarzschild M.
Published: June 2019

The theory of the stellar interior indicates that for a star of given mass, given initial composition, and given age, all physical characteristics (including the luminosity and the effective temperature) are uniquely determined. Accordingly it should be possible to derive theoretically for a particular star of definite mass and initial composition a relation between luminosity and effective temperature, i.e., a curve in the Hertzsprung-Russell diagram along which the star must move during its evolution. With the help of such evolution curves it must then be possible to identify any observed star as to its mass, composition and age. This identification is possible at present only for certain stellar types, for two reasons. First, the theoreticians have not yet succeeded in deriving all the necessary evolution curves. Second, the evolution curves cross over each other in a complicated pattern in the Hertzsprung-Russell diagram so that observations in the two dimensional Hertzsprung-Russell diagram will not always suffice to identify uniquely the state of an individual star although it appears to suffice for the identification of a whole sequence of stars, like those which are observed in stellar clusters.
On the possible directions of evolutionary trends of stars in the Hertzsprung-Russel diagram
Authors: Krat V.
Published: June 2019

The evolution of a star depends on the initial conditions existing during its formation and on the course of the main processes changing its chemical composition and mass. If it is assumed that stars are formed from diffuse matter, the initial conditions are restricted to three factors: 1) mass, 2) chemical composition, 3) angular momentum. The mass of the star can be determined by the conditions of gravitational instability of diffuse matter, which, according to our hypothesis, consisted of solid primary bodies, similar to cometary nuclei, and a gas and dust nebula formed by them. The upper limit for the possible mass of a star is evidently determined by its angular momentum, which cannot exceed a certain critical value.
Mass Distributions in Elliptical Galaxies at Large Radii
Authors: Sarazin Craig L.
Published: June 2019

Recently, x-ray observations have shown that elliptical galaxies generally contain large quantities of hot gas. Central dominant cluster ellipticals have even more gas, which they have accreted from the surrounding clusters. The mass distributions in these galaxies can be derived from the condition of hydrostatic equilibrium. M87, the best studied central dominant galaxy, has a massive, dark halo with a total mass of about 4 × 1012 M⊙ within a radius of 300 kpc. The total mass-to-light ratio within this radius is at least 150 M⊙/L⊙. The x-ray observations of normal ellipticals also strongly suggest that they have heavy haloes, although the distribution of the mass is much less certain than in M87.
The Intrinsic Shapes of Elliptical Galaxies
Authors: Schechter P. L.
Published: June 2019

Distribution functions for the intrinsic shapes of elliptical galaxies are discussed, starting with the simplest and proceeding to the more complex. A variety of competing “proxy” observables, which can in principle be used to recover at least some of information lost in the projection of a galaxy onto the plane of the sky, are considered.
N-Body Simulations of Elliptical Galaxies
Authors: van Albada T.S.
Published: June 2019

N-body simulations are a useful tool for constructing equilibrium models of elliptical galaxies and for the exploration of their kinematical properties, in particular the tumbling rate of the figure about some axis and the internal streaming. As yet little is known about these, except that there is a large variety of possible equilibrium models. It is easy to make triaxial systems that tumble about the short axis, with internal streaming aligned with the rotation axis of the figure. Attempts to construct systems with figure rotation and internal streaming in opposite directions have not been successful. Use of current simulation codes for detailed studies of particle orbits is limited to several (about 10) dynamical times due to non-physical fluctuations in the force field.
Stability of Elliptical Galaxies. Numerical Experiments
Authors: Merritt David
Published: June 2019

The idea that dynamical instabilities might play an important role in determining the equilibrium structure of elliptical galaxies is a startling one, especially to those of us who are accustomed to associating instabilities with rapidly-rotating systems like disk galaxies. The shock is even greater when we learn that these instabilities have been taken seriously by workers in the Soviet Union for a long time. As Dr. Polyachenko points out in his talk, instabilities affecting spherical, non-rotating galaxies were being discussed by Soviet astronomers as long ago as 1972. Much of this work has recently become more accessible through the publication of an English-language version of Fridman and Polyachenko's monograph, Physics of Gravitating Systems (Fridman and Polyachenko 1984). In the West, it appears that only two people were prescient enough to systematically test the stability of spherical models before learning of the Soviet work (Hénon 1973; Barnes 1985). In particular, Barnes discovered independently that a spherical system composed of predominantly radial orbits evolves rapidly into a bar. Subsequent work has demonstrated that even some mildly anisotropic models can be unstable in this way.
The Core Properties of Elliptical Galaxies
Authors: Lauer Tod R.
Published: June 2019

The core structure of elliptical galaxies is determined by two parameters: total luminosity L and central luminosity density ρC. Scatter in ρC at any L may imply dissipational formation of core structure; once this scatter is accounted for, however, the pure L dependence of the core parameters can be isolated and perhaps used as a metric distance indicator.
Isophotometry of Brightest Cluster Ellipticals
Authors: Porter A.C. , Schneider D.P. , Hoessel J.G.
Published: June 2019

What are the two-dimensional distributions of projected luminosity in the brightest ellipticals in Abell clusters (hereafter called “El” s)? If we treat isophotes as ellipses, how do their properties vary as functions of surface brightness? Are the isophote parameters correlated with a galaxy's global properties? Are they correlated with any properties of the surrounding cluster? Are Els morphologically similar to other cluster or field ellipticals? This paper describes work in progress to the answers to these questions, and illustrates an interesting result.
Parent Structures in E and SO Galaxies?
Authors: Michard R. , Simien F.
Published: June 2019

Isophote shape and flattening are being used for studying a similarity between elliptical and lenticular galaxies.
A Method To Determine the Intrinsic Axial Ratios of Individual Triaxial Galaxies
Authors: Gerhard Ortwin E. , Vietri Mario
Published: June 2019

We present a method, partly geometrical and partly dynamical, to determine the intrinsic axial ratios of a triaxial galaxy. The method can be applied to bulges of spiral galaxies and to ellipticals containing sufficiently extended and kinematically regular gas disks. Required observational inputs are multi-colour surface photometry and the gas velocity field.
The Structure and Kinematics of the Ionized Gas In Centaurus A
Authors: Bland J. , Taylor K. , Atherton P. D.
Published: June 2019

The TAURUS Imaging Fabry-Perot System (Taylor & Atherton 1980) has been used with the IPCS at the AAT to observe the ionized gas within NGC 5128 (Cen A) at [NII]λ6548 and Hα. Seven independent (x, y,λ) data cubes were obtained along the dust lane at high spectral resolution (30 km/s FWHM) and at a spatial resolution limited by the seeing (~1″). From these data, maps of the kinematics and intensities of the ionized gas were derived over a 420″ by 300″ region. The maps are the most complete to date for this object comprising 17500 and 5300 fitted spectra in Ha and [NII]λ6548 respectively. The dust lane system is found to be well understood in terms of a differentially rotating disc of gas and dust which is warped both along and perpendicular to the line-of-sight.
Fabry-Perot Observations of Cen A
Authors: Hayes J.J.E. , Schommer R.A. , Williams T.B.
Published: June 2019

We present Fabry–Perot spectrophotometry of the well-known peculiar galaxy Cen A (NGC 5128). The observations were carried out using the Rutgers Fabry–Perot system and a CCD as a detector. We scanned the Hα and [NII] (λ6583) emission lines. From these data we were able to construct maps of the continuum, line emission, velocity and velocity dispersion. The velocity maps in both Hα and [NII] have smooth gradients and twists in the line of nodes. The deprojected emission maps strongly resemble emission maps of face-on spirals. We speculate that Cen A is a merger between an elliptical and a spiral.
Anisotropy of the Velocity Dispersion in ω Centauri
Authors: Meylan G.
Published: June 2019

By far the brightest and the most massive globular cluster in our Galaxy,ω Cen seems to be, in some of its properties, a kind of transition step between dwarf ellipticals and ordinary globular clusters. For this giant cluster, the comparison between observations and King-Michie multi-mass dynamical models appears possible only using models with strong anisotropy in the velocity dispersion. A more comprehensive description of this work is to be published (Meylan 1986).
The Local Density and Morphology Dependence of the Galaxy Luminosity Function
Authors: Choloniewski Jacek , Panek Miroslaw
Published: June 2019

We obtained the luminosity function (LF) for samples of galaxies from the CfA North catalogue (Huchra, Davis, Latham and Tonry, 1983). the criteria of selection of samples were the local density (range—more than 2 orders of magnitude) and/or the morphology. No difference in the combined LF for all morphological types is found for subsamples of different density. the LF of elliptical galaxies is found to be less steep at the faint end than the LFs for S and SO galaxies. E galaxies are on the average brighter than the other morphological types. the LFs measured for early–type galaxies (E + S0) in high and low density regions show marginal difference—the low density LF has a steeper faint end slope. (Such a difference is not found for S galaxies). If this feature is maintained for larger samples it may indicate that the LF determined at the moment of galaxy formation is only weakly influenced by the phenomena present in dense regions. This is because these phenomena would rather leave the opposite imprint on the LF—the tidal stripping in dense regions would populate them with faint remnants of disrupted, bright, low angular momentum galaxies. Mergers could not reverse this trend because they act mainly on the bright galaxies.
Natural Action–Angle Variables
Authors: Spergel David N
Published: June 2019

Since galaxies are collisionless relaxed systems, actions are an extremely useful tool for understanding their dynamics. There are many potential applications of actions: (1) When orbits in an N-body simulation are characterized by their actions, the six dimensional distribution function, can be reduced to a more tractable three dimensional function, f(J). (2) Actions are adiabatic invariants, and thus are useful for studying slowly evolving systems. Binney, May and Ostriker (1986) have applied this technique to study the response of the spheroid to the disc. (3) the spectral decomposition of an orbit can be used to help generate self–consistent galaxy models (Spergel 1987).
The Envelopes of Spherical Galaxies
Authors: Jaffe Walter
Published: June 2019

The light distribution in the envelopes of spherical galaxies seems to be caused by the existence of a break in the energy distribution, N(E) at E = 0. This, in turn is probably caused by the escape of positive energy stars.
Angular Momentum in Elliptical Galaxies
Authors: G. Wyse Rosemary F. , Lizano Susana
Published: June 2019

We have used the available published observations of the rotational properties of elliptical galaxies to test theories of galaxy formation which predict an anti-correlation between the angular momentum of a galaxy and its initial overdensity and hence formation epoch. We find that the prediction, at least in its simplest form, is not supported by the data for well studied elliptical galaxies which have a range in rotational support.
The Galactic Center: Outstanding Puzzles and Challenges (Introductory Review)
Authors: Townes C. H.
Published: June 2019

Over the last two decades, the refinement of radio and infrared techniques, as well as work in space, have provided a remarkable amount of information about the center of our galaxy. Much of it fits into a more or less understandable and increasingly well-defined pattern. However, some of this information seems to represent phenomena we do not yet understand, and still other measurements appear to challenge us with inconsistencies. Much of the material to be presented at this conference represents new results which will add both to our information and our understanding. It is hoped this first discussion will properly introduce the overall subject, paying particular attention to those areas which are still puzzling or under debate. Because of the wealth of material, the complexity of the subject, and my own limitations, not all of the many important points and questions will be treated, nor treated equally. Fortunately, the many gaps which I must leave will be filled by others, since there are review talks on most of the various, more specific aspects of the field.
The Distance to the Galactic Center: RO
Authors: Reid Mark J.
Published: June 2019

Great progress has been made toward measuring the size of the Milky Way. There are now several methods that employ independent calibrations to estimate the distance to the center of the Galaxy, Ro, and these methods have been applied to many types of astronomical objects. Ro estimates generally have been decreasing over the last 15 years. At this time a reasonable “best value” estimate for Ro is 7.7 ± 0.7 kpc.
Evidence against Formation of the Stellar Bulge by Mergers Taking Place over a Hubble Time
Authors: Rich R.M.
Published: June 2019

Data on abundances and ages of stars in the nuclear bulge of the Galaxy are in conflict with a scenario in which the bulge has been slowly accumulated by mergers of Magellanic Cloud-like systems taking place over a Hubble Time.

I review the abundance distribution of 88 K Giant stars in Baade's window, and show that the distribution is fit by the simple model of chemical evolution unmodified by gas infall. The metal rich stars in the bulge could not have formed in small galaxies of ≈ 1010 solar masses, which do not retain their metal-enriched gas.

Two large surveys of luminous evolved stars in the bulge–the M giant surveys of Blanco, and the carbon star surveys of Azzopardi, Lequeux, and Rebeirot, find no luminous carbon stars or M supergiants which would signify the presence of an intermediate-age population. I present infrared photometry of 33 bulge carbon stars which shows that they are intrinsically faint, confirming the lack of an intermediate age population.

The lack of young turnoff stars in the color-magnitude diagrams of bulge fields by Terndrup and Rich further strengthens the case against a substantial bulge population younger than 5 Gyr.
An IR Quintuplet Near the Galactic Center
Authors: Okuda H. , Shibai H. , Nakagawa T. , Matsuhara H. , Kobayashi Y. , Hayashi M. , Kaifu N. , Nagata T. , Gatley I. , Geballe T.
Published: June 2019

A cluster of luminous infrared sources has been found near the Galactic Center. It consists of five identical stars clustered in a compact volume, to be called an IR quintuplet. They are all highly reddened, strongly polarized and associated with deep absorptions of silicate band and CO vibration band. They seem to be a cluster of young stars newly born near the Galactic Center.
Electrodynamics at Galactic Center
Authors: Benford Gregory
Published: June 2019

Molecular clouds moving at Keplerian velocities can induce strong electric fields in ionized regions near the galactic center. The induced field can drive currents over equivalent circuits ~ 100 pc. along the highly ordered magnetic fields, B ~ 10−3G. Such current paths drive low-level ion acoustic turbulence, providing a resistance in the circuit. Small magnetic pinches form which are generally kink unstable, but can organize into larger, long-lived structures. Ohmic losses are energetically important in the molecular clouds, where high density regions should be most luminous. Electrons can accelerate in the induced fields to relativistic energies, yielding the radio luminosity. Electrodynamic flares may occur on year timescales. Such electrodynamic deceleration of clouds can powerfully increase accretion toward galactic centers and enhance their luminosities.
The Nature, Location and Environment of Sgr A East
Authors: Goss W. M. , Anantharamaiah K. R. , van Gorkom J. H. , Ekers R. D. , Pedlar A. , Schwarz U. J. , Zhao Jun-Hui
Published: June 2019

We have observed SgrA at 332 MHz (92 cm) with a resolution of 12 arcsec (0.6 pc) using the four configurations of the VIA. These results illustrate the dramatic and almost unique variation of radio spectral index within the central 3–4 arcmin of the galactic center. SgrA East is a non-thermal shell source that could be a supernova remnant or a very low-luminosity example of a radio component associated with the active nucleus of a spiral galaxy. The most dramatic aspect of the new 332 MHz observations is the appearance of the the SgrA West spiral features in absorption against SgrA East. Based on these results, SgrA East is situated behind SgrA West, the center of the galaxy. The halo is in front of or surrounds the former sources. The HII regions to the east of SgrA East (1 = −0°.02, b = −0°.07) are probably associated with the 50 km/s molecular cloud. The 7 arcmin halo (20 pc) has a non-thermal spectrum with turn-over below 1 GHz.
A Large Near-Infrared Image of the Galactic Center
Authors: Gatley Ian , Joyce R. , Fowler A. , Depoy D. , Probst R.
Published: June 2019

We have obtained a K band image of the central 30 × 40 arcminutes of the Galaxy at a scale of 1.4″/pixel using a 256 × 256 Pt: Si Schottky barrier diode array detector provided by the Hughes Aircraft Company. The excellent cosmetic quality and large field of this device provide an unprecedented view of the inner Galaxy. Images of the central 10 arcminutes at a scale of 0.9″/pixel in the H (1.65μm) and K (2.2μm) bands produced with the same detector array have been combined to produce a color picture, which clearly shows the circumnuclear molecular ring in absorption; this picture demonstrates directly that the southwestern side of the ring lies in front of, and the northeastern side behind, the Galactic center.
HI Absorption Against the 40 km s−1Cloud and the Circum-nuclear Disk in Sgr A
Authors: Lasenby Joan , Yusef-Zadeh F. , Lasenby Anthony N.
Published: June 2019

HI absorption studies of the Sgr A complex based upon recent VLA2observations, show that the 40 km s−1molecular cloud liesbehindthe Sgr A West region, and that the cloud may be physically associated with the Sgr A East non-thermal shell. The absorbing gas over the range +30 to +60km s−1lies mainly between the eastern edge of the Sgr A East shell and the western boundary of a cluster of HII regions. There is a pronounced velocity gradient over this region, and at 40 km s−1similar morphology is apparent between the distribution of atomic hydrogen and the edge of the Sgr A East shell. The physical association of the 40 km s−1cloud and the Sgr A East shell, and the placing of the 40 km s−1cloud behind Sgr A West, are consistent with recent evidence which has demonstrated that Sgr A West liesinfrontof Sgr A East. The HI optical depth maps of the circum-nuclear disk plus a new HI feature associated with the northern extension of Sgr A West will be presented.
Gas Feeding Toward the Central Neutral Ring in the Galactic Center
Authors: Ho P. T. P. , Jackson J. M. , Armstrong J. T. , Szczepanski J. C.
Published: June 2019

VLA observations in the (J, K)=(3,3) line of ammonia reveal new structures in the Galactic center region. An approximate ring of emission is centered on the central ionized streamers. This ring, seen previously in millimeter-wave interferometer maps, is very clumpy in the ammonia emission, with size scales ≲10″ (0.4 pc). The clumps show good spatial and velocity agreement with the ionized gas, and are warm with brightness temperatures exceeding 30 K. A comparison of the (3,3) to (1,1) ratio indicates considerably higher gas temperatures. This circumnuclear ring may not be the dominant feature in the mass distribution of the circumnuclear gas. A streamer, immediately to the south of the Galactic center, connects the gas complex at lII= −4′ (~10 pc) directly to the Galactic center. This streamer may define the path for gas flow into the nuclear region.
High Resolution 11.6 μm Images of the Central 1 Parsec of the Galactic Center With a New 58 × 62 Si:Ga Array Camera
Authors: Gezari Daniel Y.
Published: June 2019

Seeing-limited 11.6-μm images of the central 1 parsec (~20 arcsec) of the Galactic Center have been obtained with a new 58 × 62 pixel Si:Ga array camera system. Previous array observations (Gezari et al. 1985) were used to derive the color temperature structure of the region. This higher spatial resolution work resolves new structure, showing a strong similarity (and notable discrepancies) between the 11.6-μm emission and the 6-cm continuum VLA maps (cf., Morris and Yusef-Zadeh 1986) and closely correlated Brackett a infrared array images (Forrest et al. 1986). Careful comparison of the dust and ionized gas emission distributions shows most of the compact 11.6-μm dust sources are displaced from the gas peaks.
A Search for Variable Stars at the Galactic Center
Authors: Haller Joseph W. , Rieke Marcia J.
Published: June 2019

A study of the Galactic Center stellar population is continuing with a sensitive 2μm CCD camera. Using a 64 × 64 detector array, background limited images are recorded with modest amounts of observing time (tobs ≈ 20 sec to reach K=13). Magnitudes have been extracted using DAOPHOT from repeated imaging of the central 5′ × 5′ to search among approximately 1500 stars for long period variables (LPV's, P > 200d), particularily Miras. Miras have a well defined period-luminosity relationship as well as one in period-mass. This program investigates the nature of highly luminous stars at the Galactic Center. Presently 12 variables have been found and have several characteristics consistent with Miras. They have a maximum bolometric luminosity of −4.4 mag, which supports the case that high luminosity stars in the central 6 pc are young supergiants.
High Resolution Near-Infrared Imaging and Computer Simulations of a Lunar Occultation of the Galactic Center
Authors: Simons D. A. , Becklin E. E. , Hodapp K. -W
Published: June 2019

A high resolution K-band (2.2 μm) image of the Galactic center was acquired as part of an effort to develop computer simulations of a lunar occultation of the IRS 16 region that was previously observed in 1986 September. Through our computer simulations and recent observations of another occultation that occurred in 1988 September, confident identifications of the objects detected during the 1986 September occultation were acquired. In particular, IRS 16C, 16SW, and 16NE were all identified and found to be unresolved (<0.05″ in angular extent).
The flare activity of two peculiar red dwarfs
Authors: Ilyin I.V. , Shakhovskaya N.I.
Published: June 2019

Photoelectric observations of flares on the two red dwarfs Gliese 171.2A and CM Dra are reported.
NTT spectra of the flare stars HM1 and HM2 in the R Coronae Austrinae aggregate
Authors: Duerbeck H. W. , Tsvetkov M.K.
Published: June 2019

Spectroscopic observations of the flare stars HM1 and HM2 (V667 CrA) in the direction of the R Coronae Austrinae aggregate are presented. The respective spectral classes are dM1e and dM6e. Both stars are at the distance 40 pc, much closer than the R CrA association.
Balmer and soft X-ray emission from solar and stellar flares
Authors: Butler C. J.
Published: June 2019

Integrated soft X-ray (8-12A) fluxes for solar flares have been scaled to the equivalent EXOSAT fluxes using spectra obtained from a variety of rocket-based experiments. The data show good agreement with the soft X-ray - Hγ correlation established by Butler et al. (1988) for stellar flares and confirm the basic similarity, in this respect, of flares on the Sun to those on dMe stars.
Periodical variations of the brightness of T Tauri
Authors: Zajtseva G.V.
Published: June 2019

T Tauri-type stars are characterized by the fast irregular variability. It is possible to select several components in brightness variations: slow components with timescales of years and fast ones with timescales of days and tens of days. Besides, up to 1 mag flares in the ultraviolet part of the spectrum occur during some nights. The overall change of the brightness may reach 2-3 mag.
Axial rotation of BY Dra-type stars and related objects
Authors: Chugainov P. F.
Published: June 2019

Periods of the rotational modulation of the brightness of BY Dra-type stars, Pleiades spotted stars, naked T Tau stars and T Tau-type stars are compared with absolute bolometric stellar magnitudes. Arguments are given that the majority of BY Dra-type stars have the age of 10∗∗8 years and relatively fast as well as slowly rotating objects are met between them.
Flares on T Tauri stars
Authors: Gahm G. F.
Published: June 2019

An overview of the characteristics of short-term light variability on T Tauri stars is given. The evidence of the occurrence of flares comes from observations mainly at X-ray energies and from patrole observations in the ultraviolet spectral region. From such observations some limits on the peak fluxes and total energies of the largest flare-like events can be set. In addition, the frequency of such events can be deduced for a number of stars. It is demonstrated that there appears to be a qualitative difference between powerful flare-like events on the weak-line T Tauri stars (NTTs) and those on strong-line stars (CTTs). While it appears that the concept of surface flares occurring on NTTs may be correct there is the evidence that the disk-stars in addition produce flare-like events of a different nature. These events could be related to processes occurring not on the stars but in their circumstellar environment, for instance in a circumstellar disk. We also point at observations that could be of importance in clarifying the cause of flare-like activity on T Tauri stars and also comment on how this activity changes with stellar age.
High resolution spectroscopy of RY Tauri: variability of the Na D line profiles
Authors: Petrov P.P.
Published: June 2019

Ejection and accretion of gas clouds in the vicinity of RY Tau were discovered. The existense of large scale “stellar prominences” around young stars is suggested.
Polarimetric & Spectropolarimetric Properties of FGK Type Stars and Extrasolar Systems
Authors: Ortolani S. , Tamburini F. , Bianchini A.
Published: June 2019

The study of extra solar planets represents a new exciting frontier for modern astronomy. Most of the results on extrasolar systems are obtained with Doppler surveys. Here we suggest a different approach aimed to study the polarimetric properties of the residual interplanetary dust. Dust can produce observable effects such as infrared emission excess (Beckwith & Sargent 1996; Spangler et al. 2001) and partial polarization of the star light via scattering (Mauron & Dole 1998; Yudin 2000), like in β Pictoris (Voshchinnikov & Krügel 1999). Some polarization could also be produced by a giant planet in a close orbit around the star (Saeger et al. 2000), but the resulting effect is too weak to be responsible for the polarizations actually observed.
Detecting Extrasolar Planet Transits from the South Pole
Authors: Caldwell Douglas A. , Borucki William J. , Showen Robert L. , Jenkins Jon M. , Doyle Laurance , Ninkov Zoran , Ashley Michael
Published: June 2019

We have developed and tested a wide-field photometer to detect extrasolar planet transits from the South Pole. The discovery of transiting planets for which masses can be measured by radial velocity is vital to constrain the models of planet formation and evolution. Short of going to space, the South Pole is the best site from which to carry out a such a survey. Based on results from the Doppler velocity surveys and the Vulcan transit search, we expect to detect 10 to 15 transiting planets in two years of operation at the South Pole.
Habitability of Brown Dwarf Planets
Authors: Andreeshchev Andrey , Scalo John
Published: June 2019

The time during which the temperature of a terrestrial-like planet remains in the liquid water range during the fading of its parent brown dwarf is calculated as a function of brown dwarf mass and planetary semimajor axis using recent models for brown dwarf evolution and two criteria for habitable zone width. Durations of habitability range from 0.5–2 Gyr at a brown dwarf mass of 0.03 M⊙ to 2–10 Gyr at a brown dwarf mass of 0.07 M⊙ for planets within a few Roche radii.
An Interferometric Study of CO and CS in Comet Hale-Bopp (C/1995 O1)
Authors: Kuan Y.-J. , Pen M.-L. , Huang H.-C. , Veal J. M. , Woodney L. M.
Published: June 2019

We used the BIMA Array to observe CO and CS molecules in Comet Hale-Bopp (C/1995 O1) during the 1997 apparition. A spur-like structure around the cometary nucleus is observed. These molecular spurs may be attributed to gas or dust jets. Using Haser model, we find the theoretically predicted CO scale length agrees well with observations. A large fraction of CO is sublimated directly from the nucleus, with the remaining CO coming from icy dust grains in cometary coma. The [CO/H2O] abundance ratio of Hale-Bopp is consistent with that of icy dust grains in star forming regions. We conclude that Hale-Bopp was likely formed at the stage when there were still ample of icy grains in Solar Nebula; therefore, abundances of parent molecules in a comet may reflect the primordial chemical composition of the Nebula.
Evidence for Past Life on Early Mars: How the Evidence Stands
Authors: Gibson Everett K. , Thomas-Keprta Kathie L. , Clemett Simon J. , Mckay David S. , Romanek Christopher , Wentworth Susan J.
Published: June 2019

Martian Meteorite ALH84001 contains four unusual features which have been interpreted as possible signatures of relic biogenic activity. After six years of intense study by the world's scientific community, the current status of the biogenic hypothesis is reviewed and shown to still be valid. Furthermore additional features have been observed in two younger Martian meteorites. The strongest argument for possible evidence of biogenic activity within the ALH84001 meteorite is the presence of truncated hexa-octahedral magnetite crystals which are only known on Earth to be the products of biology.
Growth of Methanogens on a Mars Soil Simulant Under Simulated Martian Conditions
Authors: Kral Timothy A. , Bekkum Curtis R. , Mckay Christopher P.
Published: June 2019

Due to the hostile conditions at the surface, any life forms existing on Mars today would most likely inhabit a subsurface environment where conditions are potentially wetter and warmer, but organic compounds may be lacking and light energy for photosynthesis would be absent. Methanogens, members of the domain Archaea, are microorganisms from planet Earth that can grow under these relatively extreme conditions. We have demonstrated that certain methanogenic species can indeed grow on a Mars soil simulant, JSC Mars-1, with limited amounts of water, under conditions approaching a possible subsurface environment on Mars.
A Search for Dyson Spheres Around Late-type Stars in the Solar Neighborhood
Authors: Jugaku Jun , Nishimura Shiro
Published: June 2019

We continued our search for partial (incomplete) Dyson spheres associated with solar-type stars (spectral types F, G and K) within 25 pc of the Sun. No candidate objects were found in a total of 384 stars.
Large-Size Message Construction for ETI: Self-Interpretation in LINCOS
Authors: Ollongren Alexander , Vakoch Douglas A.
Published: June 2019

Messages for ETI written in a terrestrial language admitting linear notation, should be supplied with extra-linguistic annotations – also linearized in some way – as an aid for interpretation by recipients. In several papers the first author has advocated the use at the second level of an abstract system (a new Lingua Cosmica, still under development), based on constructive logic – with a minimal set of primitives. Expressions at the meta level explain the logic contents of messages.

The interaction between any LINCOS and text may suffice for interpretation of both – provided the messages and annotations are of considerable size. Finding a measure for the sizes involved is, however, a non-trivial problem. As a result, one is interested in methods for interpreting a LINCOS without recourse to natural languages. The present paper is concerned with the problem of interpretation of the new system within itself. For that purpose, interpretation of parts of it and (complete) propositional logic in terms of each other is considered (commutativity). This leads to self-interpretation as all semantic terms reside in the closed context of the system.
The Ultimate Hacker: SETI Signals May Need to Be Decontaminated
Authors: Carrigan Richard A.
Published: June 2019

Biological contamination from space is a remote but recognized possibility. SETI signals might also contain harmful information. Some argue that a SETI signal could not contaminate a terrestrial computer because the idiosyncratic computer logic and code constitute an impenetrable firewall. Suggestions are given below on how to probe these arguments and decontaminate SETI signals.
Ultraviolet classification of Wolf-Rayet stars
Authors: Rochowicz Krzysztof
Published: June 2019

The ultraviolet spectra of 94 WR stars obtained from Vilspa IUE archive are used here to look for classification criteria in the UV region alone. We have tried to select as many single and SB1 type stars as possible in the Galaxy and the LMC to get the complete, flux-calibrated spectra between 1150 and 3250 Å. Altogether 56 (34 of WN and 22 of WC type) stars in the Galaxy and 38 (31 of WN and 7 of WC type) in the LMC were found, for which at least single SWP and LWR (or LWP) low resolution images are accessible – note that this is about one third of the number of known galactic and LMC WR stars. The set of stars we study is representative according to spectral subtype and brightness (it is almost complete to 12 magnitude for galactic stars). See Niedzielski & Rochowicz (1994) for the list of program stars and associated IUE images as well as for the details of reduction.

To look for classification criteria of WR stars in the ultraviolet region we will use the equivalent width (EW) and line width (FWHM) data.
A search for spectral variability in WR1
Authors: Niedzielski A.
Published: June 2019

Preliminary results of spectroscopic monitoring of the WN5-B star WR1 (HD 4004) are presented, showing evidence for a 0d.775 period.
Periodic variations in the IUE data of HD 50896
Authors: Lloyd C. , Stickland D. J.
Published: June 2019

A periodogram analysis of the radial velocities and absorption line strengths from IUE spectra of HD 50896 show evidence of the 3.766 day period usually associated with this star. The dominant line variations occur on time scales of ∼ 1 day but may be interpreted as higher order harmonics of the 3.766 day period.
3.5 hour periodic variability of WR66 (HD 134877, WN8): the first example of non-radial pulsations among Wolf-Rayet stars?
Authors: Antokhin Igor I. , Bertrand Jean-François , Lamontagne Robert , Moffat Anthony F.J.
Published: June 2019

We report a first result from an extensive observing campaign for the WN8 star WR66 (HD 134877). We obtained 219 photometric observations of WR66 in a standard broadband V-filter during 61 nights, distributed in a T = 83d interval. Details of observations and data reduction can be found in Antokhin et al. (1994). The power spectra of WR66-C1, WR66-C2 and C2-C1 are shown in Fig.1. Both the WR66-C1 and WR66-C2 spectra clearly show high frequency components. The overall structure of the peaks is evidently determined by 1-day aliasing. The highest peak in both spectra has frequency v1 = 6.828 d−1 (period P = 3h.51). Inspection of the power spectra shows that C1 is a low-amplitude variable, but luckily at low frequencies only. We conclude that WR66 is significantly variable with a period of 3h.5. A phase plot of the data (WR-C2 and C2-C1) with this frequency is shown in Fig.2. Plausible scenarios which could potentially account for the observed variability are: (i) non-radial pulsations (NRP); (ii) rotational light-modulation by spots or (magnetic) loops at the stellar surface; (iii) spiral-in system (WR+c), like the massive X-ray binary Cyg X-3 (van Kerkwijk 1993).
Pulsations of Wolf-Rayet stars: observational results for five WR stars
Authors: Bratschi P.
Published: June 2019

Since the recent discovery of fast pulsations of a WR star (Blecha et al. 1992), we observed five WR stars intensively and we report here the detection of fast photometric variations for three of them. These variations have a quasi periodic features with a time-scale compatible with theoretical predictions (Maeder 1985, Glatzel et al. 1993). For all observed WR stars the period can vary significantly and even disappear, showing the erratic nature of this phenomenon.