bluuebunny/crossref_metadata_2025 huggingface dataset:
Lunar Occultation Observations of Millimeter CO Emission in S255
Authors: Schloerb F. Peter , Scoville N. Z.
Published: July 2016

Observations of millimeter wavelength emission lines at the highest possible angular resolution are necessary to reveal the energetics and dynamics in compact regions of star formation activity. Lunar occultations of molecular clouds provide a means for obtaining angular resolution that is much better than that possible with a single radio telescope, and make it possible to study in more distant sources features at the same linear scale as those in Orion. We have recently used lunar occultations of the region around two infrared sources embedded in the S255 molecular cloud to determine the angular structure of the CO emission of the surrounding gas, and we have found that this region closely resembles the core of the Orion molecular cloud (Schloerb and Scoville 1980).
CN Observations in Taurus Dark Cloudlets
Authors: Churchwell Ed
Published: July 2016

CN(N = 1→0, J = 3/2→1/2) has been searched for toward 8 locations in the Taurus dark cloud complex where NH3 and HC3N and/or HC5N have been observed. CN was detected in TMC1(NH3) and TMC2(cont.) and was probably detected in L1533(NH3) and L1544(NH3). CN appears to be correlated with NH3 and anti-correlated with HC5N and HC3N. It is postulated that NH3 is likely a dominant precursor of CN and HCN but that CN and HCN are probably not important precursors of HC3N and heavier cyanopolyacetylenes.
High Resolution 4.8 Ghz Mapping of H2CO using the Westerbork Synthesis Radio Telescope
Authors: Forster J. R. , Goss W. M. , De Jong T. , Norman C. A. , Habing H. J. , Dickel H. R.
Published: July 2016

We mapped the distribution of 6 cm H2CO (110→111) absorption against the HII regions DR21 and W58 with an angular resolution of 6″8 (RA) and a velocity resolution of 0.73 km s-1. The Westerbork SRT was used with the newly completed 5120 channel digital line receiver. With all 14 telescopes, a maximum baseline of 1440 m, both linear polarizations and a bandwidth per channel of 10 kHz the rms noise in the channel maps was about 7 K. The goal of this work is to measure scale sizes of H2CO in molecular clouds near HII regions and to study the kinematics of the clouds in the molecular line.
Observations of the 3.4-mm HCO+ Line toward the Galactic Center
Authors: Fukui Yasuo , Kaifu Norio , Morimoto Masaki , Miyaji Takeshi
Published: July 2016

3.4-mm line of HCO+ has been mapped toward the galactic center. The telescope used was the 6-m mm-wave telescope at the Tokyo Astronomical Observatory, equipped with a GaAs Schottky barrier diode mixer and a 256-ch filter bank of 1-MHz resolution. Fig. 1 shows the observed positions on the antenna temperature contour map of HCN(Fukui et al. 1977). Intensive observations were made of the line SR where the HCN emission is strongest. Fig. 2 shows the HCO+ profile as well as the HCN profile, both of which are averages along SR().
Co (J=2-1) Observations of Several Galactic HII Regions
Authors: De Graauw T. , Lidholm S. , Fitton B. , Israel F. P. , Sargent A. , Kuiper T.B.H. , Nieuwenhuyzen H.
Published: July 2016

We used the new OVRO 10 meter millimeter telescope together with the Estec heterodyne receiver and backend to observe 12CO (J=2-1) emission in the direction of several galactic HII regions. At a frequency of 230 GHz our angular resolution was 30 arcsec and our velocity resolutions were 0.3 and 1.3 km s-1. We observed the cores of 16 molecular clouds associated mainly with compact and subcompact HII regions: S88, S106, S157, S158 (NGC 7538), S159, S187, S228, S255 (IC 2162), S269, ON-1, G45.5-0.1, Wl (center), W58 (K3-50), Cep A and Mon R2. Observations of all sources were in a cross pattern of at least five points. Four sources - Cep A, Mon R2, S158 and W58 - were mapped in more detail. Results for the latter two are shown in Figures 1 and 2.
Molecular Cloud Densities from Observations of Carbon Monosulfide
Authors: Linke Richard A. , Goldsmith Paul F.
Published: July 2016

We have made carefully calibrated measurements of the J=1→0 and J=2→1 transitions of CS in 32 molecular sources in order to obtain density and fractional abundance information from the excitation of this molecule. The antennas used provided beams of nearly equal size. The line intensities, which fall between 1 and 5K, have typically been determined with a (1σ) uncertainty of ∼10%. The two transitions show nearly equal intensities and linewidths which are, respectively, about one tenth and one half of the corresponding quantities for CO. Our observations are seen to be in good agreement with the results of excitation calculations involving either a velocity gradient model or a purely micro-turbulent model since in both cases optical depths are small (0.3 to 3.0). Values obtained for n(H2) and X(CS)/dv/dr from the velocity gradient model fall in the range 2×104 to 2×105 cm−3 and 3×10−11 to 3×10−10 (km s−1pc−1)−1 respectively.
The Extinction Efficiency of Dust Grains at 1 Mm
Authors: Sherwood W. A. , Arnold E. M. , Schultz G. V.
Published: July 2016

We have determined the extinction efficiency factor Q for the objects in the Table by means of maps, scans, or photometry at 1 mm using a composite bolometer at the prime focus of the ESO 3.6m telescope (Arnold et al., 1978; Arnold, 1979). The beam is 2′ in diameter.
Comparison of Submillimeter and CO Brightness in Orion and Mon R2
Authors: Cudaback David , Anderson Lawrence , Lynch David , Smith James
Published: July 2016

Emission from interstellar dust in L 1641 and Mon R2 was mapped with three arcminute resolution at 400 microns wavelength from White Mountain, California at 3.9 km elevation. Dust brightness distributions and 13CO antenna temperatures are shown below with equal linear scales, emphasizing that the core of Mon R2 is considerably larger and more massive than the core of the Orion region containing OMC-1 and OMC-2. Dust and 13CO brightness distributions for each object are similar, but some of the differences may be real. The differences become accentuated when mass distributions are compared.
The Structure and Evolution of the W3 Molecular Cloud
Authors: Dickel Hélène R.
Published: July 2016

A model of the W3 molecular cloud derived from molecular observations is presented and the evolution of the cloud is discussed.
The Interaction of T-Tauri Stars with Molecular Clouds
Authors: Silk Joseph , Norman Colin
Published: July 2016

Winds from T-Tauri stars may provide an important dynamical input into cold molecular clouds. If the frequency of T-Tauri stars exceeds 20 pc-3, wind-driven shells collide and form ram pressure confined clumps. The supersonic clump motions can account for cloud line widths. Clumps collide inelastically, coalescing and eventually becoming Jeans unstable. For characteristic dark cloud temperatures low mass stars form, and we speculate that in this manner clouds can be self-sustaining for 107 − 108 yr. Only when either the gas supply is exhausted or an external trigger stimulates massive star formation (for example, by heating the cloud or enhancing the clump collision rate), will the cloud eventually be disrupted. A natural consequence of this model is that dark cloud lifetimes are identified with the duration of low mass star formation, inferred to exceed 107 yr from studies of nearby star clusters. Other implications include the prediction of the existence of embedded low mass stars in turbulent cloud cores, the presence of an internal source of radiation in dark clouds, and a clumpy structure for cold molecular clouds.
Cold HI Gas in the Region of the Giant Molecular Cloud Near M17
Authors: Sato Fumio , Fukui Yasuo , Hasegawa Tetsuo
Published: July 2016

Sato and Fukui (1978, hereafter SF) studied the HI 21-cm line in the giant molecular cloud near M17 and showed that the self-absorption of the 21-cm line is a useful tool for probing star-forming clouds. The giant molecular cloud at V(LSR) ∼ 20 km s-1 has been found to extend 4° (∼170 pc) southwest of M17 (Elmegreen et al. 1979). To gain a better knowledge of its physical conditions, we used the data from the Maryland-Green Bank Survey (Westerhout 1973) to examine the self-absorption features of the 21-cm line in and around the whole molecular cloud except the two fragments adjoining M17. The HI profiles at every in galactic latitude and longitude in the region were analyzed in almost the same manner as in SF by assuming that the spin temperature of the cold HI gas is equal to 20 K. The distance was taken to be 2.5 kpc.
Search for CO in Atomic Hydrogen Clouds
Authors: Kazès I. , Crovisier J.
Published: July 2016

The relationship between dense molecular clouds and diffuse clouds, as well as the mechanisms connected with the formation of molecules in diffuse clouds, may be studied using HI 21-cm line observations and molecular line observations in the same directions. For this purpose we previously studied the OH 18-cm main lines (Kazès et al., 1977) and the 2.6-mm CO lines (Crovisier and Kazès, 1977) in directions where strong 21-cm absorption features had been detected in the Nancay survey (Crovisier et al., 1978). Liszt and Burton (1979) also measured CO lines toward 19 directions observed in the Arecibo 21-cm emission/absorption survey (Dickey et al., 1978). This paper presents preliminary results of a more comprehensive search for 12CO in directions previously studied in the Nancay survey.
Optical and Theoretical Studies of Giant Clouds in Spiral Galaxies
Authors: Elmegreen Bruce G. , Elmegreen Debra Meloy
Published: July 2016

An optical study of four spiral galaxies, combined with radiative transfer models for transmitted and scattered light, has led to a determination of the opacities and masses of numerous dark patches and dust lanes that outline spiral structure. The observed compression factors for the spiral-like dust lanes are in accord with our expectations from the theory of gas flow in spiral density waves. Several low density (102 cm-3) clouds containing 106 to 107 M⊙ were also studied. We discuss these results in terms of recent theoretical models of cloud and star formation in spiral galaxies. The long-term evolution of giant molecular clouds is shown to have important consequences for the positions and ages of star formation sites in spiral arms.
Molecular Clouds in Orion and Monoceros
Authors: Morris Mark , Montani J. , Thaddeus P.
Published: July 2016

A 1.2-meter millimeter-wave telescope has been used to survey CO in the constellations of Orion and Monoceros. Many new molecular clouds have been found. The distribution of molecular material shows two striking characteristics: 1) Most of the molecular clouds in this region appear to be connected by continuous extensions and filaments. To judge from continuity in radial velocity, most of these connections appear to be real, and are not merely the result of projection along the line of sight. 2) There are at least two slender filamentary features longer than 10° in angular extent. These filaments may connect the molecular clouds lying well out of the Galactic plane to clouds lying in the plane. Their shape and orientation suggest that magnetic fields may play a role in their evolution. The observed velocity gradients may be explained by accelerated gas flow along the filament.
NRCC 18508

: Recent Laboratory Work on Molecules of Possible Importance for Interstellar Studies
Authors: Herzberg G.
Published: July 2016

One of the aims of our work at the National Research Council (Ottawa) during the last thirty years has been to contribute laboratory data that are of possible astronomical interest especially for the study of the interstellar medium.
Optical Observations of Interstellar Molecules
Authors: Snow Theodore P.
Published: July 2016

Recent observational data are summarized on molecular species in diffuse interstellar clouds, and a comprehensive list of all species detected or sought is included. The discussion is focussed on the use of molecular observations to determine physical conditions in clouds, and on important species which provide constraints on cloud chemistry models. Directions for new research are suggested, including intensive work on the unidentified diffuse bands, which may have a molecular origin.
Laboratory Studies of Interstellar Carbon/Nitrogen Ion Chemistry
Authors: Schiff H. I. , Mackay G. I. , Vlachos G. D. , Bohme D. K.
Published: July 2016

Laboratory measurements are reported for ion-molecule reactions involving CN+, HCN+, C2N+ and HCN, and their implications for interstellar synthesis for C/N compounds are discussed. The reaction of C+ with HCN was found not to constitute a major loss process for HCN, which is regenerated by reactions of C2N+ with NH3, H20, CH4, C2H2 and H2S. These latter reactions lead to C addition rather than C-N bond formation. Rapid association reactions were observed for CH3+ and C2H2+ with HCN. These suggest efficient radiative association reactions under interstellar conditions to form ions which may form larger C/N compounds upon neutralization.
Molecular Evolution in Dense Clouds
Authors: Suzuki H.
Published: July 2016

Molecular abundances were calculated time-dependently using a chemical scheme which was carefully constructed to represent the molecular evolution in dense clouds. All ion-neutral reactions of species containing up to 2 heavy atoms (C, N, O, S and Si) were surveyed and a set of possible reactions was selected from numerous exothermic reactions. As molecules containing 3 to 4 heavy atoms are produced by condensation reactions, the scheme was extended. As a result, 234 species, their 2884 gas-phase reactions, and H recombination on grain surfaces were included in our chemical scheme.
The Determination of Electron Abundances in Interstellar Clouds
Authors: Wootten Alwyn , Snell Ronald , Glassgold A. E.
Published: July 2016

A new method for estimating electron fractions in shielded molecular clouds is proposed on the basis of gas phase ion-molecule reactions which involves measuring the quantity . Applied to existing data, it yields upper limits to Xe in the range from 10−8 to 10−7 for a variety of clouds, warm as well as cool. An upper bound to the cosmic ray ionization rate is also obtained.
Laboratory and Theoretical Results on Interstellar Molecule Production by Grains in Molecular Clouds
Authors: Greenberg J. M. , Allamandola L. J. , Hagen W. , Van De Bult C.E.P. , Baas F.
Published: July 2016

Laboratory and theoretical studies have been made of the effects of ultraviolet photolysis of interstellar grain mantles. It has been shown that grain photolysis should be important even in dense clouds. A large number of molecules and radicals observed in the interstellar gas appear in the irradiated ices of CO, H2O, NH3 and CH4 which are deposited at 10 K. Energy released during warm-up is seen from visible and infrared luminescence and inferred from vapor pressure enhancement relative to unirradiated samples. Grains are pictured as a source as well as a sink (capture) of molecules. The photolysis of an individual grain provides the stored chemical energy which is sporadically released by relatively mild triggering events (such as low velocity grain-grain collisions in turbulent molecular clouds) to produce the impulsive heating needed to eject or evaporate a portion of the grain mantle. An extremely complex and non-volatile substance possessing the infrared signatures of amino and carboxylic acid groups and having a mass of 514 amu has been produced at a rate corresponding to a mass conversion rate of interstellar grains of between 2% and 20% in 107 years.
The Formation of Hydrocarbons and Iron-Hydrides on Cold Interstellar Grains-Experimental Studies
Authors: Bar-Nun A. , Litman M. , Pasternak M. , Rappaport M. L.
Published: July 2016

Cold hydrogen atoms at T ≥ 7K were shown experimentally to react with graphite grains at the same temperature to produce CH4 and smaller amounts of C2H6, C2H4 and C2H2. At T < 20K the hydrocarbon mantle could polymerize to form carbonaceous substances, similar to those found in carbonaceous chondrites. Further encounters with H-atoms would result in their recombination on the hydrocarbon mantle around the grains. At higher grain temperatures, the hydrocarbons formed could be ejected into the gas phase.

Cold iron atoms at T < 5K were shown experimentally to react with molecular hydrogen in a T < 5K matrix. Mössbauer studies with 57Fe demonstrated the formation of an Fe-H2 bond. FeH2 and FeH molecules could be formed on grains by encounters of iron atoms with either H-atoms or H2 molecules.
The Chemical Identification of Grain Mantles by Infrared Spectroscopy
Authors: Allamandola L. J. , Greenberg J. M. , Norman C. A. , Hagen W.
Published: July 2016

The composition and physical properties of interstellar grain mantles continues to be an important problem in astrophysics. Part of this importance comes from the fact that grain mantle composition, photochemistry and photophysics are involved in interstellar chemistry (Greenberg et al. 1972, Greenberg, 1979, Greenberg et al. this volume). Because most molecules have a number of fundamental modes of vibration which possess activity between 2.5 and 25 μm (the middle infrared), spectroscopic measurement in this region can provide a direct probe of the molecules making up grain mantles. In addition to molecular composition, under favorable conditions, such measurements can yield molecular abundances, the solid/gas ratio for specific molecules and give an indication of such physical grain properties as temperature and thermal history.
The 12C/13C Ratio in Interstellar Dark Clouds
Authors: Mccutcheon W.H. , Dickman R. L. , Shuter W.L.H. , Roger R. S.
Published: July 2016

Since 13C is believed to be produced by non-equilibrium CNO processing in stellar evolution (Truran 1977), measurements of the carbon ratio Rc ≡ [12C] / [13C] in the interstellar medium may provide important information on nucleo-synthesis. Commonly, the ratio (N13/N18)LTE ≡ [13CO/C18O]LTE is measured and from this RLTE ≡ [12CO/13CO]LTE is deduced and these values are often identified with Rc. However, this line of reasoning can be misleading for two reasons (Dickman et al. 1979):

(1) The difficulty of determining accurate column densities, [13C16O] and [12C18O], because of the complexity of the radiative transfer problem;

(2) The possible role of fractionation, whereby RCO ≡ [12CO] / [13CO] does not necessarily reflect the initial atomic abundance ratio RC (Watson et al. 1976, Langer 1977, Liszt 1978).
Molecular Clouds near Supernova Remnants
Authors: Slysh V. I. , Wilson T. L. , Pauls T. , Henkel C.
Published: July 2016

A survey of 14 SNR's in the 4.8 GHz absorption line of H2CO shows that two of them, W28 and W44, possibly interact with molecular clouds. The interaction leads to acceleration of a part of the molecular cloud to a velocity of ∼5 km s-1 without a significant increase in the kinetic temperature or turbulence.
Behavior and Significance of Circumstellar Clouds
Authors: Zuckerman B.
Published: July 2016

We will discuss molecular envelopes around post main sequence stars. Topics that will be covered include chemical composition, physical properties, mass loss and evolution. In view of the following papers by Drs. Snyder and Goldreich we will have little to say about circumstellar masers here.
Radio Detection of Ammonia in IRC+10216
Authors: Bell M. B. , Kwok Sun , Feldman P. A.
Published: July 2016

IRC+10216 (CW Leo) is a carbon star surrounded by an expanding circumstellar envelope which is rich in molecules. Recently, Betz et al.1 reported the detection of rotation-vibration transitions of NH3 (ν2 band) in absorption against the infrared continuum of circumstellar dust. We now report the detection of the (1,1) and possibly the (2,2) inversion transitions of (para) NH3, the first radio detection of ammonia in a star. This information can be used to determine the thermal structure of the envelope of IRC+10216.
Molecular Abundances in IRC+10216
Authors: McCabe E.M. , Smith R. Connon , Clegg R.E.S.
Published: July 2016

The observed molecular column-densities in IRC +10216 can be matched by chemical-equilibrium calculations for T∼1250°K, P∼100 dyn cm-2 and no graphite grain formation. Condensation of silicon carbide into grains may explain the low observed abundances of SiO and SiS.
SiO Emission from the Orion Nebula
Authors: Baud B. , Bieging J. H. , Plambeck R. L. , Thornton D. D. , Welch W. J. , Wright M.C.H.
Published: July 2016

SiO emission in both a strong maser transition in the first excited vibrational state and in a weaker transition in the ground vibrational state both arise from the same small region in the Kleinmann-Low Nebula in Orion. Within the errors, the source position coincides with that of the infrared source IRc2.
Pumping of Strong H2O Cosmic Masers
Authors: Strelnitsky V. S.
Published: July 2016

All the existing models of H2O masers fail to explain such a strong source as W49 N. Observed and theoretical quantities are related by: nH2OWPℓ3 ≳ 1046 S, where S is the maser flux density (in Janskys), nH2O is the H2O number density (cm−3), Wp is pump rate (s−1), and ℓ is the length of amplification region on the line of sight (cm). Models involving vibrational activation (or deactivation) of H2O by H2 (Goldreich and Kwan, 1974; Norman and Silk, 1979), with the usual cross-section σν ≲ 10−19cm2, require ℓ > 1016 cm for the strongest H2O features (∼104 Jy), which is unacceptable in view of the VLBI results. Besides, because σν is so small, it is questionable if vibrational pumping could control rotational level populations at all. Depending on the energy source and sink there are four possible schemes of rotational pumping: CR, RC, RR, and CC (C - collisional, R - radiative). The first was modelled by de Jong (1973) and by Shmeld et al. (1976). Though difficulties with the sink (Goldreich and Kwan, 1974; 1979) are avoidable in the model by Shmeld et al. (Strelnitsky, 1979), ℓ ≳ 1015 − 1016 cm is still required for the strongest features. Therefore other possibilities of rotational pumping are being investigated. One CC-model is presented below.
The Interpretation of High Velocity H2O Masers
Authors: Burdyuzha V. V.
Published: July 2016

Kinematic and physical models of high velocity H2O masers are briefly discussed.
Far-Ultraviolet Objective Spectrographic Surveys for Mapping of Interstellar H2, H, and CO
Authors: Carruthers George R.
Published: July 2016

A far-ultraviolet, wide-field camera/spectrograph investigation has been proposed for Spacelab missions. By use of an objective grating, this experiment could survey large areas of the sky, obtaining spectra of early-type stars as faint as 12th visual magnitude in the 950-2000 Å wavelength range, with 1 to 2 Å spectral resolution.
Wideband Spectrometers for Millimetre Wavelengths
Authors: Robinson B. J.
Published: July 2016

Millimetre-wave spectral lines show a wide range of linewidths, from 0.1 km s-1 in dark clouds to 30 km s-1 in some massive molecular clouds; at 100 GHz the corresponding Doppler widths range from 33 kHz to 10 MHz. SiO masers at 86 GHz have two lines typically 1 MHz wide spaced by 6 MHz. For most applications a resolution of 100 or 250 kHz is suitable.
A 10 Micron Heterodyne Receiver for Ultra High Resolution Astronomical Spectroscopy
Authors: Buhl D. , Chin G. , Faris J. , Kostiuk T. , Mumma M. J. , Zipoy D.
Published: July 2016

Infrared heterodyne spectroscopy is extremely useful in determining by precise measurements of atomic and molecular infrared line spectra the molecular abundances, velocity structure, and excitation conditions of the interstellar medium, and the temperature- and pressure-profiles of planetary atmospheres (cf. Kostiuk et al. 1977, Betz et al. 1976, 1977, Abbas et al. 1978).
On the Correspondence of OH/H2O Maser Sources to the Stage of Proto-Star Formation
Authors: Kondo Masa-aki
Published: July 2016

VLBI observations have revealed that OH/H2O maser sources are the aggregations of blobes with the sizes of a few A.U., spreading over the distance of several 1017 cm. From the standpoint of masing mechanism, especially for the hydroxyl case, we will argue that the blobes correspond to proto-stars in the stage of forming an opaque core, and the aggregations correspond to proto-clusters.
On the Star Formation in Early Stage of Galactic Evolution
Authors: Yoshii Y. , Sabano Y.
Published: July 2016

Evolution and fragmentation of a gas cloud are investigated for the primordial chemical composition which is the same as the products of the Big Bang. A pure-hydrogen gas cloud collapses isothermally at 500–1000 K when a low fraction of molecular hydrogen works as a coolant, and breaks into small subcondensations with mass less than 10 M⊙ due to thermal instability associated with molecular dissociation. On the other hand a pure-hydrogen gas cloud which contains no molecular hydrogen collapses isothermally at 6000–8000 K in a thermally stable condition, and enters the region where thermal energy exceeds radiation energy when thermal equilibrium between matter and radiation is achieved in the cloud. Consideration of energetics in the subsequent stage of the cloud evolution leads to the mass range of 0.1–20 M⊙ for the stable nuclear-burning protostars of the first generation. The thermal behavior of a gas cloud in the regime of z (the ratio of heavy element abundance to solar one) less than 10−4 is essentially similar to that in the case of no heavy element, and the heavy element cooling brings about thermal instability in a wide range of parameters in the regime of z greater than 10−3. Linear perturbation analysis gives growth time of the instability much shorter than the free-fall time, and suggests the efficient excitation of density fluctuation driven by thermal instability. Thus the possibility of the initial mass function relatively enhanced in massive star at early times is denied, and the slow rate of metal enrichment in the interstellar medium is suggested.
An Observational Approach to the Early Stages of Stellar Evolution
Authors: Ambartsumian V. A. , Mirzoyan L. V.
Published: July 2016

During last three decades an observational approach was being applied at the Byurakan Astrophysical Observatory to the problems of the evolution of astronomical bodies and systems. In contradiction to the views developed by many theoreticians who postulate as an initial state of each body or system a gaseous nebula of some kind and suppose that the processes of condensation are dominant in the Universe this approach makes use of the observed predominance of expansions, ejections and explosions.
Fragmentation of Isothermal Gas Clouds
Authors: Gingold R. A. , Monaghan J. J.
Published: July 2016

An analysis of the collapse and fission of the isothermal gas cloud examined by Boss and Bodenheimer (BB, 1979) has been made using SPH (Lucy 1977, Gingold and Monaghan 1977, 1978). While SPH is not as effective as finite difference methods for problems with spherical symmetry, it has the advantage in fragmentation problems that the description of the fragments is independent of their position and orientation. Furthermore, the SPH algorithm has been tested by applying it to non axisymmetric problems for which accurate solutions are known as well as spherically and axially symmetric problems.
Magnetic Braking, the Solar Nebula and the Cometary Cloud
Authors: Mestel L.
Published: July 2016

Biermann (1979) has revived the earlier suggestion of Cameron and of Donn that the proto-cometary cloud and the proto-solar nebula were contiguous but distinct cloudlets, forming e.g. as fragments within the same massive interstellar cloud. As in Goldreich and Ward (1973) and Biermann and Michel (1978), the cometesimals are thought to have formed in a layer of dust that settled in the equator of a cloudlet maintained at a moderate density by a combination of thermal pressure and centrifugal force due to a high angular momentum. The solar nebula had much less angular momentum and so could contract to about the radius of Pluto's orbit before achieving centrifugo-gravitational balance. In this paper it is noted that modest variations in the initial parameters of fragments forming within the same massive magnetic cloud can yield both high and low angular momentum cloudlets (Mestel and Paris 1979). A fragment of mass M greater than a critical mass Mc, defined in terms of its magnetic flux F by GM2c~F2/π2, contracts in approximate mechanical equilibrium, at the rate determined by the magnetic transport of angular momentum, and with centrifugal force remaining comparable with gravity. Rapid flux-loss at molecular cloud densities leaves a weakly magnetic, rapidly rotating, low-density cloudlet which could be the locale of cometary formation. If M<Mc, the magnetic stresses both limit contraction and enforce corotation with the surroundings. As flux leaks out slowly, the cloudlet contracts in approximate magneto-gravitational equilibrium, with centrifugal forces becoming a steadily smaller fraction of gravity. At the molecular cloud phase, rapid flux-loss leaves now a slowly rotating cloudlet, which can therefore become the proto-solar nebula. Whether a cloudlet is super- or sub-critical in mass will depend on the details of the fragmentation process in the parent cloud, in particular on the amount of mass agglomeration down the field-lines.
The Rapidly Rotating Giants of the FK Comae-type
Authors: Bopp B. W. , Rucinski S. M.
Published: July 2016

We present new spectroscopic and photometric observations and discuss a small but important group of rapidly rotating G - K giants (FK Com=HD 117555, UZ Lib=BD−8°3999, HD 199178 possibly others) which are photometrically variable, show slightly redshifted and variable Ca II H and K emission and variable Hα emission, show rotationally broadened spectral lines (50–100 km/s), and yet show no large radial velocity variations. Possible explanations of the properties of these stars are discussed and coalescence of a W UMa binary system seems to be the most probable evolutionary state.

The most extreme of the group, FK Com is discussed in detail. Its type, G2IIIa (Keenan, priv.comm.) implying MV=−1 (the IR indices are consistent with a giant) suggests a reduction of log g (relative to Sun) −1.5 to −2.5; this can be only marginally reconciled with the dimensions of about 5 Ro resulting from the photometric period 2.4 d. and Vrot sin i about 100 km/s. The photometric variability (0.05 in I, 0.07 in R) is most probably due to spots asymmetrically distributed in longitude. The brightness minima observed by Chugainov in 1966 and 1974 and the new minimum observed in 1979 (JD 2443949.025) can be phased with one period 2.3995±0.0002 d. The erratic behavior of rotationally broadened spectral lines precludes obtaining a radial velocity orbit but an upper limit of 25 km/s for any periodic variations implies that the secondary must be a very low mass object. The strong Hα emission is variable in relative intensity of its double peaks but has a constant full width in excess of 20 A. The full half width at base implies rotational velocities of the order of 570 km/s; the half separation of peaks implies 300 km/s. Existence of an excretion disc of the type suggested by Webbink is possible.
Shell-Flashes on Accreting Neutron Stars and Mode Profiles of Type-I X-Ray Bursts
Authors: Miyaji Shigeki , Fujimoto Masayuki Y. , Hanawa Tomoyuki
Published: July 2016

Thermal stabilities of hydrogen and helium shell-burnings on accreting neutron stars are studied semi-analytically, the progress of nuclear reactions during the flash is followed numerically, and the mechanism which makes different modes of Type-I X-ray bursts is discussed.
The Current Status of Neutron Star Cooling Theories
Authors: Tsuruta S. , Murai T. , Nomoto K. , Itoh N.
Published: July 2016

There are serious discrepancies among some of the recent neutron star cooling calculations by various groups. We have been investigating the possible source of these discrepancies. In this paper, we report our findings. We also report the preliminary result of our most recent cooling calculations without assuming an isothermal stellar evolution code. In this work, we used the currently existing best energy transport theories, as well as general relativity, both in thermodynamics and hydrodynamics.
Cyclotron Line Emission from Accretion onto a Magnetized Neutron Star
Authors: Salpeter E. E.
Published: July 2016

For material accreting along the magnetic field axis of a neutron star, electrons are quantized into Landau orbits. Collisional excitation of the first excited Landau level, followed by radiative decay, leads to the emission of a cyclotron line. The expected line is broad, because the optical depth is large, and its shape is difficult to calculate. Redshifts due to the recoil of a scattering electron and blueshifts due to scattering from the infalling accretion column are being calculated by I. Wasserman, as well as the proton stopping length in the presence of a magnetic field.
Magnetic Fields and Stellar Evolution
Authors: Mestel L.
Published: July 2016

Magnetic fields are now observed or inferred in a wide variety of stellar objects. The class of early-type stars with strong large-scale fields extends from types B to F, with effective fields from 300 gauss up to several x 104 gauss (Borra and Landstreet 1980). Fields between 4 × 106 and 108 gauss have been inferred in a small percentage of white dwarfs, and of over 1012 gauss in neutron stars. Some Cepheids show measurable fields. Evidence has built up of solar-type activity in late-type stars. The pioneering work by Wilson (1978) on Ca activity has shown convincingly the occurrence of periodicity reminiscent of the solar cycle in a number of G, K and M stars. Ca II emission appears to be a good predictor of simultaneous X-ray emission from hot coronae around cool stars (Vaiana 1979, Mewe and Zwaan 1980). Fields of some 2 × 103 gauss have been reported in two late-type main sequence stars (Robinson, Worden and Harvey 1980).
On the Presence of Turbulent Diffusion in Stars and its Effect on Stellar Evolution
Authors: Schatzman E.
Published: July 2016

The presence of a mild turbulence inside rotating stars has been considered by Howard et al (1967) and by Bretherton et al (1968) in connection with the problem of the solar flattening, raised by Dicke (1970). The possibility of using abundance determination to test the existence of that turbulence has been considered by Schatzman (1969).
Enhancement of Thermonuclear Reaction Rate due to Strong Screening
Authors: Itoh N. , Totsuji H. , Ichimaru S. , DeWitt H.E.
Published: July 2016

The enhancement factor for the rate of thermonuclear reactions which involve two kinds of nuclei with charges Zi and Zj in the strong-screening regime is given for general cases of surrounding nuclear plasmas by the formula, exp[1.25Γij −0.095τij(3Γij/τij)2]. Here, Γij = 2ZiZje2/(ai+aj)T; ai = [3Zi/4πΣkZknk]1/3; τij = [(27π2/4)(2μijZi2Zj2e4Th2)]1/3; μij is the reduced mass for the two reacting nuclei Zi and Zj; and nk is the number density of nuclei Zk. The calculation is based on the recent results of Monte Carlo computations for binary ion mixtures, which have shown that the screening functions hij(r) at intermediate distances [0.5 ≤ r/[(ai+aj)/2] ≤ 1.6] can be expressed to a good degree of accuracy by

Application to the calculation of carbon ignition in the carbon-oxygen core of a highly evolved star is discussed. The carbon ignition temperature is found to be single-valued as a function of the density in contrast to the work of Graboske.
General Relativistic Collapse of an Axially Symmetric Star Leading to the Formation of Neutron Stars and Black Holes
Authors: Nakamura Takashi , Maeda Kei-Ichi , Miyama Shoken , Sasaki Misao
Published: July 2016

Using the [(2+1)+1]-dimensional representation of the Einstein equations, we have computed the general relativistic collapse of a rotating star. We adopt the cylindrical coordinate. The system is assumed to be axially and plane symmetric. The number of meshes is 28×28 in R and Z direction. The equation of state is P=1/3ρε for ρ< ρ*≡3×1014 g/cm3 and P=(ρ-ρ*)ε+1/3ρ*ε for We use the following initial conditions; ρ∝exp(-(R2+Z2)/λ), Ω∝exp(-R2/λ) where Ω and λ are angular velocity and a size parameter, respectively. We have calculated three models;

(1)

Model 1 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.05.

(2)

Model 2 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.12.

(3)

Model 3 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.22.

where α=Eint/|Egrav| and β=Erot/|Egrav|. In all models, an apparent horizon was formed, that is, a black hole was formed. In Model 1, the final density distribution is oblate shape. In Model 2, there is a ringlike peak of the proper mass density distribution at the final stage. In Model 3, the determinant of the metric tensor goes to nearly zero at the ring in the equatorial plane, so that the proper mass density shows strong ringlike peak which is inside the apparent horizon. As the curvature invariant made from the Riemann tensor becomes very large at this ring, this may be a ring singularity of the space-time. These rotating black holes look like the Kerr black hole.
Wolf Rayet Stars and the Origin of the 22Ne Excess in Cosmic Rays
Authors: Cassé M. , Paul J. A. , Meyer J. P.
Published: July 2016

First order Fermi acceleration at the boundary between supersonic stellar winds from OB and Wolf-Rayet stars and the surrounding interstellar medium could be influential in the bulk energization of the local cosmic radiation. Since wind acceleration is not supposed to accelerate thermal particles, a continuous injection of low energy particles (E ~ 1 to 10 MeV/n) is required. We keep open the possibility that these particles may be injected from the interior of the stellar cavity, i.e. by the mass-losing star itself via a flare-like surface activity for instance. Observations of flare activity on hot and massive stars are mandatory to settle this idea. In this context, we expect that the CR reservoir is the surface of young and active stars and that the difference between the CR source (CRS) composition (i.e. corrected for propagation effects in the interstellar medium, ISM) and the surface composition of young stars (reflecting for most of them the present local ISM) is principally due to selective effects at injection depending on the atomic properties of the elements. This idea is supported by 3 arguments (Cassé and Goret, 1978, Meyer et al., 1979) i) the general resemblance between solar CR elemental abundances and elemental CRS abundances (see e.g. Mewalt, 1980) ii) the correlation between the (CRS/local galactic) abundance ratio and the first ionization potential and iii) the fact that dust grains must have been thoroughly destroyed in the medium from which CR are extracted. In the interstellar gas in which dust grains are present, Ni, Fe, Mg and especially Ca and Al are highly depleted whereas they are normally abundant in CR.
Propagation Studies Related to the Origin of Cosmic Rays
Authors: Cowsik R.
Published: July 2016

Propagation of cosmic rays is discussed with the intent of deriving results relevent to the origin of cosmic rays. Starting from a brief description of the methods for demodulating the effects of the solar wind on the spectra of particles, we describe an accurate method for correcting for spallation effects on the cosmic-ray nuclei during their transport from the sources subsequent to their acceleration. We present the composition of cosmic rays at the sources and discuss its implications to their origin. We discuss briefly the effects of stochastic acceleration in the interstellar medium on the relative spectra of primaries and secondaries in cosmic rays and show that the observation of decreasing relative abundance of secondaries with increasing energy rules out such phenomena for galactic cosmic rays. The spectrum of cosmic-ray electrons is discussed in terms of contributions from a discrete set of sources situated at various distances from the solar system on the galactic plane. We show that unless there are at least 3.104 sources actively accelerating cosmis rays in the Galaxy the spectrum of electrons would have a premature cut-off at high energies. Finally we point out some important questions that need to be clearly resolved for making further progress in the field.
Interpretation of Cosmic Ray Composition: the Pathlength Distribution
Authors: Protheroe R. J. , Ormes J. F.
Published: July 2016

The chemical composition of cosmic ray nuclei with 3≤Z≤28 between ~100 MeV/nuc and a few hundred GeV/nuc are compared with a consistent set of propagation calculations. These include the effects of spallation (energy-dependent cross sections are used), escape and ionization loss in the interstellar medium and deceleration in the solar cavity. This has enabled a consistent study of the cosmic ray pathlength distribution to be made over this entire energy range. Details of the propagation calculation are left to a forthcoming paper.
A Self-consistent Multiple Compton Scattering Model for the X and ɣ-Ray Emission from Active Galactic Nuclei
Authors: Maraschi L. , Roasio R. , Treves A.
Published: July 2016

We refer to a model of active galactic nuclei where a massive black hole (M≃108M⊙) is accreting spherically (1–3). Turbulent dissipation of the magnetic field produces an efficient heating. For low Thomson optical depth the main cooling mechanism is selfabsorbed cyclo-synchrotron (c-s) radiation from thermal electrons. The energy transfer of the thermal electrons to the c-s photons via Compton scattering (comptonization) becomes increasingly important for increasing optical depth. In ref. 2 the temperature profile of the inflowing gas was calculated balancing the heating and cooling mechanism but neglecting comptonization due to the difficulty of an analytic estimate of this process.
Symmetry Breaking and Invariant Mass Approach to the Spiral Structure of Galaxies
Authors: Thielheim K. O.
Published: July 2016

The physical conditions in the centre of spiral galaxies as our own galaxy still are not very well known. They offer themselves to more or less exotic speculations, some of which involve the possible existence of black holes and mechanisms for the production of high energy cosmic rays. In view of such argumentations I feel it worthwhile to look in more detail into recent progress obtained in the understanding of the dynamics of the central region of spiral galaxies which turns out to be intimately related to the galaxy as a whole, especially its spiral structure.
ɣ-Ray Emission from Slow Pulsars
Authors: Morini M. , Treves A.
Published: July 2016

Among the COS-B Galactic γ-ray sources two have been identified with the young pulsars PSR0531+21 and PSR0833–45, while for most of the others there are no convincing counterparts. An obvious explanation is that at least part of them are also pulsars. Because of the rarity of pulsar formation, an important issue for testing this possibility is to discuss whether relatively old pulsars (~105y) may be sources of γ-rays of the luminosity observed by COS-B (φ (100 MeV) 10−6cm−2s−1). On this line it is of great interest the claim of observation of γ-rays with SAS II from PSR1747–46 and with COS-B from PSR0740–28 and PSR1822–09, communicated at other conferences, but yet not confirmed. The three slow pulsars mentioned above were reported to have γ-ray luminosities of 1033 erg s−1 close to their intrinsic energy loss LT = Iωω. Their periods are about 0.1–1s and their distance ~1 Kpc.
Distribution of Neutrino Fluxes from Pulsar Shells
Authors: Shapiro M. M. , Silberberg R.
Published: July 2016

Young pulsars apparently have a distribution of initial power outputs N (> Po−γ), with 1/2 < γ < 1 and Po ≳ 1038 ergs/sec. Assuming that ultra-high-energy (E ≳ 1015 eV) cosmic-ray nuclei are accelerated at the central pulsar, a young, dense supernova shell can be a powerful source of high-energy neutrinos. With an optical array placed in a volume of one km3 at great ocean depths, as proposed for the DUMAND detector, it is likely that ≳ 103 hadronic and electromagnetic cascades induced by neutrinos would be recorded for a stellar collapse within our Galaxy. Such supernovae occur about 8 times per century. Neutrinos from young supernova shells in the Virgo supercluster would be marginally detectable via neutrinos with N(> Po) ∝ Po−1/2, but unobservable if N(> Po) ∝ Po−1.
Cosmic Rays and Galactic Radio Noise
Authors: Sironi G. , De Amici G.
Published: July 2016

Size and shape of the “confinement volume Vo”, the region around our Galaxy where the c.r. particles live until they escape or loose completely their energy are essential parameters of models for the origin and propagation of the cosmic rays. Focussing the attention on the c.r. electrons, whose sources are definitely galactic and concentrated in the Disk, to confine Vo to the Disk or extend it to the Halo is full of consequences. For instance in the first case the sources can be everywhere inside Vo; by contrast in a Halo model the sources can reside only in some parts of Vo, the mechanisms of energy loss play different roles in different regions of the confinement volume and the particle lifetimes can be up to 100 times larger than in the Disk, (e.g. ref. 1).
The All-Sky 408 MHz Survey
Authors: Haslam C.G.T. , Salter C. J. , Stoffel H.
Published: July 2016

The 408 MHz All-sky Survey has been made from four radio continuum surveys observed between 1965 and 1978, using the Jodrell Bank MKI telescope, the Effelsberg 100 metre telescope and the Parkes 64 metre telescope. A detailed description of the survey data reduction and calibration methods, with preliminary astronomical results will soon be published and a second paper will give an atlas of maps at the full survey resolution of 51′ arc between half power points.
High-Density, Cool Regions of Interstellar Matter in the Galaxy
Authors: Burton W. B. , Liszt H. S.
Published: July 2016

The distribution of interstellar nucleons is dominated by gas at temperatures ranging from a few K to a few hundred K. At the warmer end of this temperature range, the gas is predominantly in the form of ubiquitously distributed atomic hydrogen. The colder gas is almost entirely molecular; it resides in compressed clumps, confined principally to the inner-galaxy, and is most effectively traced by observations of carbon monoxide. In this paper, we focus on some of the problems which currently hinder derivation of the morphology and total number of nucleons in the galaxy. For the atomic gas, these problems involve optical depth effects in HI profiles, the amount of cold HI residing in molecular clouds, and the form of the outer-galaxy rotation curve. For the molecular gas, the problems involve the uncertainties in the conversion from CO intensities to H2 densities, including the possibility of composition gradients across the galaxy, the total number and typical size of molecular clouds, and the possibility that the molecular material in the region of the galactic nucleus is distributed differently from the material in the galaxy at large.
Nonlinear Landau Damping of Alfven Waves and the Production and Propagation of Cosmic Rays
Authors: Stoneham R. J.
Published: July 2016

The existence of hydromagnetic waves (waves whose frequency ω is less than the ion gyrofrequency Ωi = eB/mic) in a collisionless magnetized plasma with β, the ratio of plasma pressure to magnetic pressure, much greater than unity is required in theories for Fermi acceleration of cosmic rays by converging scattering centres at a shock front, in theories for the adiabatic cooling of cosmic rays due to trapping by plasma instabilities in an expanding supernova remnant (Kulsrud and Zweibel 1975, Schwartz and Skilling 1978) and in theories for resonant scattering of cosmic rays by hydromagnetic waves in the hot phase of the interstellar medium (Holman et al. 1979). Hydromagnetic waves may be damped by thermal ion cyclotron damping for wavenumbers k≳Ωi/vi, where vi = (Ti/mi)1/2 is the average thermal ion speed, and by linear Landau damping for non-zero angles of propagation with respect to the ambient magnetic field (Foote and Kulsrud 1979). Damping by both these processes is strong in a high-β plasma where there are many particles travelling at the phase speed of the waves. Hydromagnetic waves propagating along may be damped by nonlinear wave-particle interactions, the most important of which is thermal ion Landau damping of the beat wave of two Alfvén waves. This nonlinear process has the effect of transferring energy from the waves to the particles and can therefore be considered as a damping process for the waves.