bluuebunny/crossref_metadata_2025 huggingface dataset:
3D: The New Near-Infrared Field Imaging Spectrometer
Authors: Tacconi-Garman L. E. , Weitzel L. , Cameron M. , Drapatz S. , Genzel R. , Krabbe A. , Kroker H. , Thatte N.
Published: June 2019

3D is a next-generation near-IR spectrometer developed at the MPE which offers, in a single integration, the opportunity to image an 8″ × 8″ field across almost the entire K-band at a simultaneous spatial resolution of 0.″5 wide strips which are then aligned optically on top of each other forming a single long slit. This long slit is then used as the input for a grating spectrometer which images it onto a two dimensional detector array. Each detector row then represents the spectrum of one spatial element of the two dimensional field of view. The central part of the optical system is the image slicer which is made of two complex plane mirror systems consisting of 16 segments each. The detector is a NICMOSIII HgCdTe array with 256 × 256 pixels. In the spectral domain the spectrometer provides a resolving power of R = 1000.

Here we present not only the design of the instrument but also first data obtained during instrument commissioning at the 3.5-m Calar Alto telescope in December, 1993.
Laboratory Experiments on Current Sheet Disruptions, Double Layers Turbulence and Reconnection
Authors: Stenzel R. L. , Gekelman W.
Published: June 2019

The role of laboratory experiments to the understanding of current systems in space plasmas is reviewed. It is shown that laboratory plasmas are uniquely suited to make detailed investigations of basic physical processes in current-carrying plasmas. Examples are given for double layers, current-driven instabilities, and the plasma dynamics at magnetic neutral points during reconnection. Observations of current sheet disruptions show the coupling between local plasma phenomena (double layers) and global circuit properties (magnetic energy storage).
On the Role of Double Layers in Astrophysical Plasmas
Authors: Smith Robert A.
Published: June 2019

Limitations of current knowledge of plasma double layers create difficulties in extrapolating double-layer concepts for application to astrophysical models. Some problems of this sort are described, and some central issues in structure and dynamics of double layers are identified, which must be addressed in astrophysical contexts. These include the determination of kinetic boundary conditions, and the relations of time and length scales of local dynamics and structure to those of the global circuit in which the double layer is contained.
Computer Simulation of Reconnection in Planetary Magnetospheres
Authors: Birn J.
Published: June 2019

The earth's magnetosphere provides an ideal opportunity to model reconnection in well known geometries that are close enough to the idealized analytic models to make a comparison of the computer models with analytic theory meaningful. In addition more detailed, even three-dimensional, models can be used for a comparison with extended data from in situ observations. The computer studies have basically confirmed the reconnection picture that was based on two-dimensional steady state models and linear analytic theory. The three-dimensional models in particular have also added a lot more information on the reconnection process and the structure of flow, magnetic fields, and currents including many features that are consistent with observations and empirical models of geomagnetic substorms.
Observations of the Earth's Cross-Tail Current Sheet and Their Implications
Authors: Lui A. T. Y.
Published: June 2019

Observations of the neutral sheet in the Earth's magnetotail are presented to show different magnetic signatures of the neutral sheet which have been used to infer (1) wave profiles on the neutral sheet surface, (2) magnetic islands embedded in the neutral sheet, and (3) localized turbulent magnetic field regions. The occurrence of these features even at magnetospheric quiet conditions suggests that the above features are intrinsic to the current sheet and may possibly play a role in its stability. There are indications that these features are common to other current sheets in space.
Instabilities in Astrophysical Jets: Disease and Cure
Authors: Eichler David
Published: June 2019

A striking feature of extragalactic radio jets is that they are so narrow. Theories of collimation should account for opening angles of order 1° or less (as opposed to those of laboratory jets which become turbulent and typically open up to more than 10°). This makes instabilities particularly troublesome for theories of collimation in which they are present. While instabilities might not entirely destroy the general bipolar nature of the flow, they decollimate it by definition.
Current Systems in Radio Jets
Authors: Eilek Jean A.
Published: June 2019

The structure of the magnetic field in radio jets is a topic of recent interest, especially due to the possibility that some high pressure jets are confined by a magnetic pinch. Several such jets have been found which cannot be confined by external cluster gas pressure, on which there are observational limits; nor can they be in free expansion, since they do not show evidence of adiabatic expansion losses. Recent radio interferometer observations of surface brightness and polarization allow the possibility of determining the magnetic field structure. In this paper I present some basic considerations of the current and field structure required if the observed jets are to be magnetically confined.
Theory of Strongly Turbulent Two-Dimensional Cross Field Convection of Current Carrying Space Plasmas
Authors: Keskinen M. J.
Published: June 2019

The “direct interaction approximation” of Kraichnan as modified by Kadomtsev is employed to develop a two-dimensional strong turbulence theory which predicts both nonlinear frequency broadening and a power law for the spectrum of a convecting plasma containing a gravitationally induced cross field current. These results are favorably compared with experimental observations, numerical simulations, and previous studies1 of turbulent cross field convection of current-carrying plasma.
Summary of Conference
Authors: Vasyliunas Vytenis M.
Published: June 2019

For a meeting of people from such widely different fields, this Symposium has exhibited a remarkable degree of unity. There has been one key concept running as a thread throughout the Symposium: the concept of magnetic field line reconnection, or magnetic field line merging as I prefer to call it. It was dealt with directly in many papers, and many others dealt indirectly with it and various related aspects. The concept was applied in the Symposium to an amazing variety of objects and was examined from many points of view and by many different techniques. Magnetic field line reconnection or merging is a paradoxical concept. It clearly depends upon magnetohydrodynamics (MHD); for example, constraints imposed by the MHD relation between the magnetic field and the plasma flow are essential to set it up - without these constraints (if, for example, the electric field parallel to the magnetic field could assume any desired value) the problems we discuss under the heading of magnetic reconnection would merely be moderately complicated problems of magnetostatics. At the same time, departures from ideal MHD are also an essential and unavoidable part of the concept.
Relativistic Reduction of Astrometric Observations
Authors: Brumberg V. A.
Published: June 2019

The nonuniqueness of the quasi-Galilean coordinates of general relativity leads to the emergence of unmeasurable coordinate-dependent quantities in astronomical practice. One may offer three possible ways to overcome the related difficulties:

1.

developing theoretical conclusions only in terms of measurable quantities

2.

using arbitrary coordinates and developing an unambiguous procedure for comparing measurable and calculated quantities

3.

agreement to utilize one and only one coordinate system.

In this paper we prefer the second way. After formulating the heliocentric planetary and geocentric satellite equations of motion, the general technique for relativistic reduction in astrometry and geodynamics is developed. Specific algorithms for the reduction of absolute and relative measurements are derived for the one- and the two- body problem. For illustration, the relativistic reduction of stellar parallaxes, Doppler satellite observations, navigation measurements with the aid of satellites and radiointerferometric measurements are presented in detail.
Brosche's Method for Representing Systematic Differences in Positions and Proper Motions of Stars
Authors: Vityazev V. V.
Published: June 2019

A variant of Brosche's well-known method is proposed which allows one to represent systematic differences (many times faster than with the original method) by the use spherical harmonics. The improved economy of computer memory requirements and reduction of calculating time are achieved by replacing the two-arguments approximation with a sequence of one-argument approximations, and by enforcing an equidistant distribution of the initial differences along the α and the δ directions. The proposed method was tested on models and used for representing the systematic corrections Δ δα and Δ μα to the catalogues GC and N30.
The Photoelectric Meridian Circle of the Pulkovo
Authors: Ershov V.N. , Pliss V.E. , Streletsky Yu. S.
Published: June 2019

The paper reports on the new semiautomatical meridian circle of the Pulkovo observatory. It is equipped with a scanning photoelectric micrometer and a photoelectric circle reading system. The standard errors of a single registration of a star are 0s.016 and 0″.35 in RA and declination, respectively. The limiting magnitude is 10.5m. The instrument can be used for IRS differential observations.
The Glass Meridian Circle
Authors: Høg E.
Published: June 2019

Some aspects of the design for a Glass Meridian Circle with 24 cm aperture are presented and discussed. Tangential ventilation will be used to minimize tube refraction. The air for the ventilation will be filtered and it will provide a clean atmosphere around all optical and critical mechanical components, thus improving reliability. The base frame and piers are particularly stable thanks to a sharp separation between parts with short and long thermal time constants. The instrument is compact and portable and it requires only a small dome.
VLBI Survey of a Complete Sample of Active Nuclei and Quasars
Authors: Pearson T. J. , Readhead A.C.S.
Published: June 2019

We have conducted a VLBI survey of a complete, flux-density limited sample of 65 extragalactic radio sources, selected at 5 GHz. We have made hybrid maps at 5 GHz of all of the sources accessible to the Mark-II system. The sources can be divided provisionally into a number of classes with different properties: central components of extended double sources, steep-spectrum compact sources, very compact (almost unresolved) sources, asymmetric sources (sometimes called “core-jet” sources), and “compact double” sources. It is not yet clear whether any of these classes is physically distinct from the others, or whether there is a continuous range of properties.
200 Milliarcsecond Structure in 3C 120
Authors: Benson J. M. , Walker R. C. , Seielstad G. A. , Unwin S. C.
Published: June 2019

We present VLBI and VLA maps of the superluminal radio source 3C 120 (z = 0.03). The 18 cm VLBI maps shown in Figures 1 and 2c were constructed from a 14 station VLBI observation on 10, 11 October 1982. The map in Figure 1 is at full spatial resolution. The Figure 2c map was made from a uv-tapered data set and shows the extended emission. The VLBI maps show a jet ~175 pc long with distinct knots and bends (H0 = 55 kms−1 Mpc−1). The 18 cm jet smoothly connects to the 6 cm superluminal jet (Figure 2d). The VLBI jet remains well collimated through several bends and only begins to spread out 100 pc beyond the core. At 175 pc from the core, the jet is wide and weak, and disappears into the under-sampled region of the uv-plane (< 2(10)6 λ's).
VLBI Observations of Weak Cores in Extended Quasars
Authors: Zensus J. A. , Porcas R. W.
Published: June 2019

We present Mark III VLBI results for a sample of weak cores associated with quasars with extended double lobes. The m.a.s. scale structure is found to be well aligned with the outer structure.
A New Geometry for Superluminal Motions
Authors: Salvati Marco
Published: June 2019

In the context of superluminal motions, the statistical difficulties intrinsic to the canonical jet geometry are alleviated if the relativistic flows occur on a plane screen, orthogonal to the source axis. The strongest superluminal effects should be detected when the source lies in the plane of the sky, rather than pointing at the observer. The polarization properties, the simplest deviations from the basic geometry, and the connection with other non-thermal phenomena are also indicated.
The September 1982 Radio Outburst of CYG X-3
Authors: Geldzahler B. J. , Johnston K. J. , Spencer J. H. , Klepczynski W. J. , Josties F. J. , Angerhofer P. E. , Florkowski D. R. , McCarthy D.D. , Matsakis D. N. , Hjellming R. M.
Published: June 2019

Cyg X-3 underwent a series of giant radio outbursts beginning on September 28, 1982 (Geldzahler et al. 1983). The flux densities at 2.7 and 8.1 GHz (11.1, 3.71 cm respectively, see Figure 1) were measured with the 2.4 km baseline of the Green Bank interferometer once every three days before October 5, 1982 (= JD 244 5248) and three times daily thereafter.
Circumstellar OH Masers
Authors: Booth R. S. , Diamond P. J. , Norris R. P.
Published: June 2019

Synthesis maps of stellar OH maser emission have revealed that the OH lies in expanding spherical shells typically about 1016 cm in diameter. From the maps and the expansion velocity, derived from the OH spectrum, stellar mass loss rates may be determined. Typical values are 10−5 M⊙/yr. An important application of the stellar OH masers is in the estimation of stellar distances.
The Choice of Standard Stars
Authors: Batten Alan H.
Published: June 2019

Standard stars should normally be constant in the characteristic for which they have been chosen to be standards. Individually they should be capable of testing the instrument used in their measurement, and collectively (usually together with a particular type of instrument) they must define a system of measurement. A star should not be adopted as a standard until several years' observation have demonstrated its constancy. The number ofindependentobservations in that interval is as important as its length. Many of these points are illustrated by particular reference to standard-velocity stars. Even 100 observations of such a star may fail to reveal a detectable variation that is present. A distinction is drawn between “primary” standards, meeting the above criteria, and “reference” or “comparison” stars which need not be so severely tested since their use is more limited. Standard stars must be calibrated in some fundamental way. Since random errors of observation can introduce systematic errors in calibration, the use of the intermediate step of standard stars may decline with increasing internal precision of observations.
The MK Classification and Its Calibration
Authors: Keenan Philip C.
Published: June 2019

I have been asked to describe the system of spectral classification as it has developed from the original Yerkes Atlas (Morgan, Keenan, Kellman, 1943) until to-day. I use the word “developed” because any system that is to remain useful must be flexible enough to adapt not only to improved techniques of measurement but also to new theoretical insights into the variables that actually determine the energy spectrum of a star in all its fascinating but sometimes frustrating detail.
Determination of Stellar Rotational Velocities
Authors: Slettebak Arne
Published: June 2019

The three basic methods for measuring axial rotation of stars had been suggested before the beginning of this century. These are (1) Modulation of starlight due to dark or bright areas on a rotating star; (2) Distortions in the radial velocity curves of eclipsing binary systems; and (3) Line profile analysis. Research in each of these areas is reviewed.
The Absolute Magnitudes of the Nearby Stars: Calibrations of mean luminosity relations
Authors: Gliese W. , Jahreiss H.
Published: June 2019

The nearby stars are most favored for determining precise absolute magnitudes and for calibrating spectral-type, luminosity relations and color, luminosity relations. To demonstrate the main problems we discuss the (Mv,B-V) relation since (B-V) data are available for most of our candidates. At Yale Observatory van Altena is compiling a new catalog of trigonometric parallaxes. We feel deeply indebted to van Altena for making available to us a preliminary version of this catalog.
Rotational Properties and Synchronization in Early-Type Close Binaries
Authors: Giuricin G. , Mardirossian F. , Mezzetti M.
Published: June 2019

We have rediscussed the synchronism between rotation and revolution in close binaries by an inspection of the published projected rotational velocities V sin i of about 250 early-type (from 0 to F5) eclipsing and double-lined spectroscopic binaries. Corrections of the V sin i - values (which are mainly taken from the catalog of Uesugi and Fukuda, 1982) for the aspect effect is straightforward for the eclipsing binaries with analyzed light-curves; in the other cases we have estimated the value of the orbital inclination angle i from the primary's minimum mass M1 sin3 i on the assumption that its mass follows Straižys and Kuriliené's (1981) mass-spectrum relations for different luminosity classes. For the components of non-eclipsing binaries, for which the absolute radii are not directly known, we have adopted values of the absolute radii in accordance with Straižys and Kuriliené's (1981) radius-spectrum relations for different luminosity classes. By using our estimates of the radii, for each component we have evaluated the synchronized velocity Vk (corresponding to the mean orbital angular velocity) and the pseudosynchronized velocity Ve, which corresponds to a synchronization with the instantaneous orbital angular velocity at periastron of an eccentric orbit; in close binaries with appreciably eccentric orbits synchronization is attained with V/Vk>1 and it is probably quickly reached at periastron (Hut 1981).
MKJ and MSS Classification of Solar-Type Stars Within 100 Parsecs of the Sun: Preliminary Results
Authors: Fracassini M. , Pasinetti L. E. , Borella M. , Pasinetti A.
Published: June 2019

A study of the distribution of spectral types of Solar Type Stars (STS) in the revised MKJ and MSS classifications is made on 3919 F8-K3 HD spectral-type stars brighter than mv=10. By means of the solar color indices U-B and B-V 697 STS were selected. The spectral types G3V and G5V have the highest percentages in MSS and MKJ, respectively, confirming statistically the results published by Keenan and Pitts (1980) and by Hardorp (1982). The distribution of the color indices U-B and B-V in the revised G2V spectral type shows that these are good selection criteria for STS and are in the range 0.06 ≤ U-B ≤ 0.10 and 0.58 ≤ B-V ≤ 0.65.
Elemental Abundances of Normal Sharp-Lined B and A Stars from Optical Region Analyses
Authors: Adelman Saul J.
Published: June 2019

Optical-region elemental-abundance analyses were performed for ten sharp-lined main sequence B and A stars. The derived abundances are generally in good agreement with those of the Sun. Multiple high dispersion spectrograms, fully line-blanketed solar composition model atmospheres, optical spectrophotometry, and the most accurate gf values were employed. This study provides initial parameters for studies of these stars in the ultraviolet and a consistent set of values for comparison with abundances of more exotic stars.
Mount Wilson Spectra of Standard Stars
Authors: Griffin R. F. , Griffin R. E. M.
Published: June 2019

We show part of a tracing of π Ceti, an example of a uniform series of high-quality tracings of standard stars covering the wavelength region 3850–4650 Å and derived from 10 Å/mm photographic spectrograms taken with the coudé spectrograph of the Mount Wilson 100-inch reflector.
Determination of Teff for Candidate Standard Stars Based on Comparison with Model Atmoshperes
Authors: Malagnini M. L. , Morossi C. , Ramella M.
Published: June 2019

A systematic analysis, as complete as possible, of early type standard stars has been undertaken at the Astronomical Observatory of Trieste, in order to obtain a sequence of carefully determined spectroscopic data to be used in the comparison of “normal” and “chemically peculiar” stars. As an intermediate and necessary step, effective temperatures are derived. The determination of Teff is performed either by comparing observed and computed flux distributions, or by using a calibration of UV-visual photometric index versus Teff. The results for a sample of stars in the spectral type range B2-F8 are presented, and an analysis of the influence of the adopted value of log g on the derived Teff values is reported. As a check on the validity of the results, the Teff and log g values are used to construct a synthetic spectrum which is compared with the IUE high resolution observations of the stars in our list.
The Principle of Equivalence and the Trojan Asteroids. Part II
Authors: Orellana R.B. , Vucetich H.
Published: June 2019

A new value for the Nordtvedt parameter and the mass of Saturn are computed using the ten first Trojan asteroids. From 1262 observations, we find the inverse mass of Saturn 3498.17±0.51 and the Nordtvedt parameter 0.0±0.3.
About the Secular Acceleration of Mimas
Authors: Vienne A. , Sarlat J.M. , Duriez L.
Published: June 2019

We explain the high values of the acceleration (≈ 2° cy−2) found in the longitude of Mimas by Kozai and Dourneau when they fit to observations their current theory of the Mimas' motion. In fact, we have found that very long-period terms are missing in these theories; their expansion in powers of t well agrees with the observed acceleration. Effects of tidal dissipation are far smaller and could be determined only after accounting of these long-period terms.
Some Aspects of Particle's Dynamics
Authors: Gomes R.S.
Published: June 2019

Some features of the dynamics of particles affected by drag, in the field of the Sun and planets, are presented here. In particular mean motion and secular resonances are investigated. When dust particles are considered as a whole in the zodiacal cloud, a simple secular theory can explain much of its geometry. Dynamics of particles near an inner planet is mostly dispersive, but an average behavior can be deduced from some analytical and numerical considerations.
Mappings in Astrodynamics
Authors: Froeschlé C.
Published: June 2019

We review mappings mainly devised for the study of the dynamics of comets and asteroids. An attempt of a typology according to the method used to devise the mapping and to its deterministic or stochastic character is made.
Infrared Emission Lines in Planetary Nebulae
Authors: Dinerstein Harriet L.
Published: June 2019

Advances in infrared spectroscopy have led to the detection of many forbidden fine-structure emission lines in planetary nebulae. Measurements of these lines offer sensitive probes of the physical conditions and ionization structure, and lead to improved abundance determinations. This paper reviews recent observations and discusses the ways in which infrared line measurements can contribute to our knowledge of planetary nebulae.
Recent Advances in Atomic Calculations and Experiments of Interest in the Study of Planetary Nebulae
Authors: Mendoza C.
Published: June 2019

Recent advances in the calculation and measurement of transition probabilities, electron excitation rate coefficients and photoionization cross sections relevant to the study of planetary nebulae are discussed. A compilation of these parameters is also presented.
Effects of Stellar Mass Loss on the Formation of Planetary Nebulae
Authors: Kwok Sun
Published: June 2019

Over the last decade, stellar mass loss has become recognized as an important factor in the evolution of stars. The magnitude of the mass loss rate is found to be greatest amongst high luminosity stars at both the red and blue sides of the HR diagram. Planetary nebulae (PN), which result from an evolutionary phase during which the parent star traverses from the red side to the blue in a relatively short time scale, are likely to be affected by these processes. In this talk, I shall review the mass loss processes relevant to the PN phase and discuss their affects on the formation and evolution of PN.
On the Strength of the CIV 155 nm Resonance Lines in Planetary Nebulae
Authors: Köppen J. , Wehrse R.
Published: June 2019

Ionization models for NGC 6210, 7009, 3242 and II 2003 have been constructed from optical and IUE spectroscopic data. The CIV 155 nm resonance line is predicted about ten times stronger than observed. Radiative transfer calculations of the CIV lines in a spherical nebula, assuming partial frequency redistribution, were made to investigate the effects of dust absorption and an additional depopulation of the upper level.
Optically Derived Carbon Abundances in Planetary Nebulae
Authors: French H. B.
Published: June 2019

Gas phase carbon abundances have been determined for a number of bright planetary nebulae from new photoelectric measurements of optical recombination lines (C II λ 4267, C III λ 4650 and C IV λ 4659). Because of blending problems for the latter two features, the abundance for any object may have substantial errors, but the average abundance should be reliable. For the twelve best observed planetaries, this average is C/H = (8.4 ± 2.9 s.d.) x 10−4 by number. If it is assumed that the planetary progenitors had essentially solar abundances, then, based on Cameron's most recent results (C/H = 4.2 × 10−4, O/H = 6.9 × 10−4), it appears that the planetary ejecta have been enriched in carbon, presumably because of dredging of newly synthesized triple α carbon by helium shell flashes during the late evolution of the progenitor. The helium abundance is also slightly high, as would be expected in this interpretation. Since the mean planetary carbon abundance exceeds the solar oxygen abundance, it is possible that the progenitor became a carbon star prior to the ejection of the planetary; that may even have caused the ejection. Because the planetaries in this study were drawn from Peimbert's samples with relatively low mass progenitors (1 – 2.5 M⊙; these are not significantly helium- and nitrogen-rich objects), such a process might be a general feature of late double shell source evolution.
An Optical and Ultraviolet Study of Nine Low-Excitation Planetary Nebulae
Authors: Adams S. , Barlow M.J.
Published: June 2019

Ultraviolet and optical observations of seven very low excitation nebulae (He 2-131, He 2-138, TC 1, M 1-11, M 1-12, M 1-26, H 2-1) and of two low-excitation nebulae (IC 418 and He 2-108) are discussed.
Nebular Abundances and Central Star Parameters for eight PN in the Magellanic Clouds
Authors: Barlow M.J. , Adams S. , Seaton M.J. , Willis A.J. , Walker A. R.
Published: June 2019

We have obtained ultraviolet and optical spectrophotometry for two PN in the SMC (N87, L302) and for six in the LMC (N28, N66, N97, N141, N201, N203). The data were obtained with the IUE (eight nebulae), the 3.9 m AAT (six nebulae) and the 1.9 m SAAO reflector (two nebulae). Nebular temperatures, densities and abundances are presented. The nebular continua were calculated and subtracted from the observed continua, allowing the central star energy distributions and hydrogen and helium Zanstra temperatures to be derived. Our results for the effective temperatures and absolute magnitudes and luminosities of the central stars are presented, including data on two Wolf-Rayet central stars (WC5 and WC8) and one Of central star.
Why is IC 4642 of such High-Excitation Class?
Authors: Penn C.J. , Flower D.R. , Barlow M.J. , Seaton M.J. , Aller L. H.
Published: June 2019

We have observed IC 4642 with the AAT and the IUE. It is of exceptionally high-excitation class, as judged by ratios such as He II/Hβ and (Ne V)/He II.
Three Symbiotic Stars Catalogued as Planetary Nebulae
Authors: Carrasco L. , Costero R. , Serrano A.
Published: June 2019

Three stellar-like objects, previously identified as planetary nebulae, were observed with the Image Intensifier-SIT multichannel spectrograph at the 2.1 m telescope in San Pedro Mártir. The mis-identified planetaries are B1 3-11, He 2-417 and He 2-468. All of them show strong permitted H and He lines, detectable stellar continuum with absorption late-type bands and several other emission lines, including the unidentified λ 6830 Å feature. Clearly, the three objects are symbiotic stars, and not planetary nebulae. We present low-dispersion spectra for the three objects in the 3800-7000 Å spectral range.
Magnetic Field Structure in Dark Clouds
Authors: Tamura M. , Nagata T. , Sato S. , Tanaka M. , Kaifu N. , Hough J. , McLean I. , Gatley I. , Garden R. , McCaughrean M.
Published: June 2019

The magnetic field geometry in the central regions of two dark clouds has been mapped by measuring the polarization at 2.2 μm of background stars and of stars embedded in the clouds. The observations were done with the Kyoto polarimeter on the Agematsu 1m IR telescope in December 1984 for Heiles Cloud 2 in the Taurus dark cloud complex, and on the UKIRT 3.8m in May and July 1985 for the ρ Ophiuchus dark cloud core. The main results are:

i)

Most of the stars in both regions show polarization and their maxima are 2.7% in Heiles Cloud 2 and 7.6% in ρ Oph, respectively. There are similar positive relations between polarization degree and extinct ion Av's.

ii)

The distribution of position angles for Heiles Cloud 2 shows a single mode at about 50° and that for ρ Oph shows a bimode, at about 50° and 150°.

iii)

The magnetic fields, as delineated by the infrared polarization, appear perpendicular to the flattened elongations of the molecular clouds.
13 CO(J = 1-0) Observations of the Filaments in the ρ Oph Dark Cloud
Authors: Mizuno A. , Fukui Y.
Published: June 2019

The ρ Oph dark cloud is located at a distance of 160 pc and is known as a site of active formation of low-mass stars. In optical photographs a central core of a ∼ 1° × 1° extent and two thin filamentary elongations of obscuring matter are apparent. The two filaments extend toward the east over ∼ 4° – 10°. The central core has been studied in the 2.6 mm CO lines (e.g., Wilking and Lada, 1980, Ap. J. 224, 698). On the other hand, the two filaments have not yet been mapped in molecular spectra. Interestingly, optical studies revealed that polarization vectors run along these remarkable filaments, suggesting that the magnetic field plays an important role in determining the structure of the filaments.
Molecular Line Observations in Sgr B2
Authors: Morimoto Masaki , Ohishi Masatoshi , Kanzawa Tomio
Published: June 2019

The ∼20 pc square region around the continuum peak, (α(1950.0) = 17h44m 10.6s, δ(1950.0) = −28°22′05″) of Sgr B2 was observed using the 45-m telescope of Nobeyama Radio Observatory. The observed molecules are H2O, NH3, CH3OH, SiO, H13CN, H13CO+, CO, HNCO, HC3N, and so on.
The Star Formation Region Associated with the Cometary Nebula GM24
Authors: Tapia M. , Roth M. , Rodríguez L.F. , Cantó J. , Persi P. , Ferrari-Toniolo M. , López J.A.
Published: June 2019

GM24 is a small visible nebulosity in the vicinity of a molecular cloud. In this contribution we present the results of continuum (6-cm) and CO line (J = 1 → 0) radio observations, infrared maps, broad-band photometry and low-resolution spectroscopy as well as long-slit Echelle Ha spectroscopy. We found evidence that the GM24 = PP85 nebula is part of a larger region where star formation occurred in the past 104 years; the region is embedded in a typical molecular cloud with a dimension of ∼ 10 pc and mass of ∼104 M⊙. A compact radio H II region seems to be associated with GM24 and with one of the mid-infrared peaks detected. The nebula is most probably the visible part of an embedded H II region that is starting to emerge from the cloud. The other infrared peaks found in its vicinity (∼ 1 pc) are probably associated with less evolved stellar objects. The complex also shows an extended near-infrared flux which we believe to arise in a reflection nebula. From energy arguments, we found that the luminosity required to power the H II region and keep the cloud at the observed large temperature (TK ≅33 K), is ∼105 L⊙ which is consistent with the infrared total flux from the present measurements and those from IRAS of 4x104 L⊙; this corresponds to the flux of ∼3 BO ZAMS stars. The details of the present work have appeared in the Revista Mexicana de Astronomía y Astrofísica, Volume 11, 83, 1985.
Mass Outflows Associated with Young Stellar Objects
Authors: Strom Stephen E. , Strom Karen M.
Published: June 2019

The fundamental properties of optical and molecular outflows associated with young stellar objects are reviewed. Particular emphasis is placed on a discussion of new results concerning outflow energetics, collimating structures and the relationship between outflow properties and the magnetic field geometry characterizing their host molecular clouds. IRAS observations of YSO mass outflows reveal extended far-IR emission associated with high velocity molecular gas; in the case of L1551 IRS5, the luminosity of the extended emission is ∼10 times the mechanical luminosity inferred from observation of the molecular flow (and thus ≳0.1 the bolometric luminosity of the YSO driving the outflow). Circumstellar disks of size ∼100 au appear to be a common, if not certain outcome of the stellar birth process for stars of ∼1M⊙. In a few cases, it has been possible to resolve disk-like structures associated with YSO outflow sources. In such cases, the disk axes appear to lie along the direction of molecular outflows or stellar jets. The mass outflows (and by inference, the axes of circumstellar disks) show a remarkable tendency to align along the direction of the magnetic fields which thread their host molecular clouds. This suggests that the cloud magnetic field must play an important role in determining the flattening (and perhaps the rotation) of protostellar structures.
New Herbig-Haro Objects Found by a New Method
Authors: Ogura Katsuo
Published: June 2019

So far discoveries of Herbig-Haro objects were done mainly by either of two different methods. The first relies on their non-stellar appearances on direct photographs, followed by low-dispersion slit spectroscopy; this is the most standard method. But sometimes only the former step is made; then picked-up objects are possible HH objects (e.g. Gyul'budagyan 1982, and Reipurth 1985). The second is based on objective-prism observations in the red with Schmidt telescopes. We have invented a third method to find new HH objects. This utilizes Schmidt telescopes, too, but can reach a fainter limiting-magnitude than that obtained with objective-prism observations.
Jets from Low Mass Accreting Stars
Authors: Kahn F. D.
Published: June 2019

There is excellent evidence that jets originate in protostars of low mass (M ∼ M⊙). Flow speeds are typically of order a few 100 km s−1; the energy for the motion must be generated close to or below the stellar surface, where the escape velocity is of the same order. Here it will be argued that the origin of the jets is connected with the thermodynamics of the accreted gas as it settles towards equilibrium. At some distance below the photosphere, in a spherically symmetrical star, the opacity of the material becomes so high that the outward flow of radiant energy is too slow to balance the inward convection of thermal energy. Consequently there can be no equilibrium, and the symmetry must be broken. The occurrence of jets can be led back to this effect, and the power required to drive them restores the energy balance.
A New CO Outflow Source near NGC 2071
Authors: Iwata T. , Fukui Y.
Published: June 2019

The region of NGC 2071 and NGC 2068 is one of the active sites of star formation in Orion. An extended CO cloud in this region has been studied previously (e.g., White et al. 1981). Here, we report new J = 1-0 CO, 13 CO, and C18 O observations of this region with a 2.7′ beam. Up to the present, we have obtained 400, 800, and 100 spectra for CO, 13 CO, and C18 O lines, respectively. The data cover an area of ∼ 1°x2°.
Polarization Mapping of Infrared Reflection Nebulae
Authors: Nagata T. , Yamashita T. , Sato S. , Tanaka M. , Suzuki S. , Kaifu N. , McLean I. , Hough J. , Gatley I. , Garden R.
Published: June 2019

Extensive reflection nebulae have been discovered around GGD27 IRS and around W75N IRS by mapping the infrared polarization in the K band.

It was found that the infrared radiation from both objects is extended at λ = 2.2 μm, by using the Agematsu 1-m, the UH 2.2-m, and the UKIR 3.8-m telescopes. We have carried out polarization mapping with the Kyoto polarimeter on the UKIRT in August 1985.
Star Formation Induced by Supersonic Turbulence
Authors: Tosa Makoto , Sabano Yutaka
Published: June 2019

Supersonic turbulent motion of gas plays a significant role in the dynamics and physics of a cosmic gas cloud. One of the most important effects of the supersonic turbulence is a strong compression of the gas by shock waves, that may trigger the gravitational instability of the shock-compressed layer leading to the formation of stars.
Resolution of the Angular Momentum and Magnetic Flux Problems During Star Formation, and Observational Consequences
Authors: Mouschovias Telemachos Ch.
Published: June 2019

Detailed calculations show that the two most important dynamical problems in the formulation of a theory of star formation (namely, the angular momentum and magnetic flux problems) can be resolved in that order by magnetic braking and ambipolar diffusion, respectively, relatively early during the collapse of an interstellar cloud or fragment. Although the physical processes involved are complicated and highly nonlinear and the formal solutions are mathematically nontrivial, they can often be elucidated by exact analogies with small-amplitude, transverse waves on strings, by a mechanical (or quantum mechanical) “leaky” system of N coupled oscillators, and by spinning coaxial metal disks joined by rubber bands and sharing (as well as losing to an external medium) energy and angular momentum (see Mouschovias and Morton 1985a, Astrophys. J. 298, 190; 1985b, Astrophys. J. 298, 205, Mouschovias and Paleologuo 1979, Astrophys. J. 230, 204; 1980, Astrophys. J. 237, 877).
Giant Molecular Clouds in the Galaxy: The Massachusetts-Stony Brook CO Galactic Plane Survey
Authors: Solomon P. M.
Published: June 2019

The CO Galactic Plane Survey consists of 40,572 spectral line observations in the region between 1 = 8° to 90° and b = −1°.05 to +1°.05 spaced every 3 arc minutes, carried out with the FCRAO 14-m antenna. The velocity coverage from −100 to +200 km/s includes emission from all galactic radii. This high resolution survey was designed to observe and identify essentially all molecular clouds or cloud components larger than 10 parsecs in the inner galaxy. There are two populations of molecular clouds which separate according to temperature. The warm clouds are closely associated with H II regions, exhibit a non-axisymmetric galactic distribution and are a spiral arm population. The cold clouds are a disk population, are not confined to any patterns in longitude-velocity space and must be widespread in the galaxy both in and out of spiral arms. The correlation between far infrared luminosities from IRAS, and molecular masses from CO is utilized to determine a luminosity to mass ratio for the clouds. A face-on picture of the galaxy locating the warm population is presented, showing ring like or spiral arm features at R ∼ 5, 7.5 and 9 kpc. The cloud size and mass spectrum will be discussed and evidence presented showing the presence of clusters of giant molecular clouds with masses of 106 to 107 M⊙. The two populations of clouds probably have different star forming luminosity functions. The implication of the two populations for star formation mechanisms will be discussed.
Star Formation in the Large Magellanic Cloud
Authors: Feitzinger J. V.
Published: June 2019

Methods used in pattern recognition and cluster analysis are applied to investigate the spatial distribution of the star forming regions. The fractal dimension of these structures is deduced. The new 21 cm, radio continuum (1.4 GHz) and IRAS surveys reveal scale structures of 700 pc to 1500 pc being identical with the optically identified star forming sites. The morphological structures delineated by young stars reflect physical parameters which determine the star formation in this galaxy. The formation of spiral arm filaments is understandable by stochastic selfpropagating star formation processes.
A 10-GHZ Radio Continuum Survey of the Galactic Plane
Authors: Handa T. , Sofue Y. , Nakai N. , Hirabayashi H. , Akabane K. , Inoue M.
Published: June 2019

A radio continuum survey of the galactic plane has been made with the 45-m telescope of the Nobeyama Radio Observatory at 10.55 GHz, which is the highest frequency among such surveys. The sensitivity of the telescope was Tb/S = 0.47 K/Jy and the HPBW was 2!6, which was a great advantage because of the same beam size of the Bonn 5-GHz survey (Altenhoff et al. 1978). The receiver was a cooled parametric amplifier. The instantaneous bandwidth was 500 MHz, and the system noise temperature was about 100 K. The calibration source was NGC 7027, which was assumed to be 6.6 Jy. One circular polarization component was observed. The observational parameters are summarized in Table I.
Dynamics of Giant Molecular Clouds in the Density Wave Potential
Authors: Fukunaga Masataka , Tosa Makoto
Published: June 2019

We performed an N-body simulation of a system of gravitating particles modeling the system of stable Giant Molecular Clouds (GMCs) in the background density wave potential. The system of gravitating GMCs forms shocks in the spiral potential well, and shows a prominent spiral structure.
Molecular Clouds in External Galaxies and the Efficiency of Star Formation
Authors: Young Judith S.
Published: June 2019

Observations of the molecular cloud distributions in spiral galaxies are reviewed. For the luminous, relatively face-on Sc galaxies, the azimuthally averaged CO distributions are centrally peaked, with H2surface densities which decrease as a function of radius. For the Sb and Sa galaxies, the CO distributions exhibit central CO holes up to 5 kpc across in a significant fraction of the galaxies studied. In galaxies with this CO morphology, the central hole is coincident with the nuclear bulge of the galaxy. Additionally, the radial distributions of CO and13CO emission are similar in 10 Sb and Sc galaxies.
Star Formation in Barred Galaxies
Authors: Mountain C. M. , Hawarden T. G. , Joseph R. D. , Leggett S. K. , Puxley P. J.
Published: June 2019

Examination of IRAS results for a sample of nearby galaxies with RC2 types between SO/a and Scd (inclusive) suggests that the only galaxies in which the IRAS colours are dominated by emission from warm dust in star formation regions are barred (Hawarden et al. 1985). Figure 1 is a 2-colour diagram of all Shapley-Ames spiral galaxies of the above types detected by IRAS in all four wavebands. It shows the ratio of fluxes in the IRAS 25 and 12 micron bands as a function of the ratio of fluxes in the 100 and 25 micron bands. On this diagram the SA systems, with the exception of a few Seyferts, have small 25/12 ratios and large 100/25 ratios. In sharp contrast, a large fraction of the SB galaxies and many SAB galaxies (not shown) have greatly enhanced 25 micron fluxes indicative of large amounts of dust at temperatures such as are commonly observed in regions of current star formation.
CO Observations of Bright IRAS Galaxies
Authors: Sanders D. B.
Published: June 2019

CO emission has been detected from 75 bright infrared galaxies with CZ = 2 000 – 16 000 km/s. These include the most distant and the most luminous galaxies (Arp 55, IR 1713+63) yet detected in CO. All of these galaxies are rich in molecular gas with Mtotal (H2) = 2 × 109 −6x1010 M⊙, and they have a strong far-infrared excess, with LFIR/LB = 2-40 and LFIR (40-400μ) = 1010 – 3 × 1012 L⊙. The primary luminosity source appears to be star formation in molecular clouds. A strong correlation is found between the FIR and 21-cm continuum flux, implying that the IMF is independent of the star formation rate. The ratio LFIR/M(H2) provides a measure of the current rate of star-formation, which is found to be a factor 3-20 larger in these galaxies than for the ensemble of molecular clouds in the Milky Way. VLA maps plus a few high resolution (14″-30″) CO (1-0) and CO (2-1) maps suggest that most of the luminosity comes from core regions 1-3 kpc in size. The abnormal concentration of molecular gas in these galactic cores is presumably the result of a collision or strong interaction with a nearby companion.
Star Formation and Galactic Evolution: From Protogalaxies to Starbursts
Authors: Silk Joseph
Published: June 2019

Three topics in star formation theory are reviewed: the initial mass function, the star formation efficiency, and the star formation rate. A physical mechanism for bimodal star formation is developed. Applications are made to the solar neighborhood, to the inner galaxy, to starburst galaxies, and to past star formation in protodisks and in protoellipticals. Implications are drawn for galactic morphology, for chemical evolution, and for the present density of stellar remnants.
The Galactic Globular Cluster System
Authors: Hesser James E.
Published: June 2019

“Although the evidence presented in the preceding discussion is still very fragmentary, there can be no doubt that, in dealing with galaxies, we have to distinguish two types of stellar populations, one which is represented by the ordinary H-R diagram (type I), the other by the H-R diagram of the globular clusters (type II). Characteristic of the first type are highly luminous O- and B-type stars and open clusters, of the second, globular clusters and short-period Cepheids…it should be pointed out that these same two types of stars were recognized by Oort as early as 1926. Oort showed that the high-velocity stars of our galaxy (our type II) are of a kind quite different from the slowmoving stars (type I) which predominate in the solar neighborhood.”
Stellar Populations in the Magellanic Clouds
Authors: Feast M.W.
Published: June 2019

There seems to be no strong evidence that the young globular clusters in the MC have metallicities differing significantly from the metallicities of MC field stars of the same age. The old globular clusters in the LMC are of the same age as, or slightly younger than, those in the outer halo of our Galaxy. It is suggested that the increase in the SFR in the LMC ~ 4 Gyr ago was related to the collapse of the system to a plane. Evidence for a spread in metallicities amongst young stars in either Cloud remains tentative. There is no strong evidence for bursts of star formation being triggered by LMC-SMC-Galaxy interactions but the possibility is raised that the SFR in the SMC has been strongly affected by this interaction.
Dark Matter in the Milky Way
Authors: Kuijken Konrad
Published: June 2019

If the Newtonian inverse-square law is an appropriate description of gravity, then disk galaxies, and the Milky Way in particular, contain large amounts of dark matter: in general, the observed shapes of rotation curves do not correspond to the gravitational potential of the observed stars and gas. The nature of this dark matter is still a topic of debate, the outcome of which will have important consequences for our ideas of how galaxies and larger structures in the universe formed.
Open Cluster System: Kinematics, Orbits
Authors: Nezhinskij E. M. , Ossipkov L. P. , Kutuzov S.A.
Published: June 2019

This study is based on the catalogue of 69 open clusters by Barkhatova et al. (1987) and cluster distances taken from Hagen (1970). Most of the dimensionless characteristics discussed here are insensitive to the distance scale. Galactocentric cylindrical coordinates of clusters and the corresponding velocities have been calculated with the accepted galactocentric distance of the Sun R⊙ = 8.2 kpc and the galactocentric velocity of the Sun sR = −9 km/s, sθ = 228 km/s, sz = 7 km/s.