bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance of Models for Radiocarbon Dating of Groundwater: An Appraisal using Selected Irish Aquifers
Authors: Gallagher D , McGee E J , Kalin R M , Mitchell P I 
Published: July 2016

Appropriate management strategies are essential for the protection and maintenance of groundwater resources. It is therefore important that aquifers are understood in terms of hydraulics, recharge, and yield potential, and that the vulnerability of aquifers to surface pollution is evaluated. A range of aquifer types were examined in this study, and water samples were analyzed for the radiocarbon content of the total dissolved inorganic carbon (TDIC), stable isotopes, and a suite of chemical and physical parameters. The data were input to a selection of models for the estimation of the initial activity of the TDIC, and groundwater ages were calculated. Eight commonly used models were comparatively assessed in the study. The Tamers, Mook, and IAEA models gave anomalous ages, probably because of their inability to correct for solid phase isotopic exchange in aquifers. The Pearson, F&G, Evans, Eichinger, and Mass Balance models produced results in broad agreement.The study shows that contrary to popular belief, there are sources of ancient groundwater in Ireland. Of the 19 sampling stations, two boreholes yielded waters with age estimates of greater than 10,000 BP. Water samples from a further six sites returned ages of between around 800 and 4000 BP. In contrast to borehole samples, spring wells yielded water of consistently young ages, demonstrating rapid recharge and flow mechanisms. Samples from several spring wells produced negative ages, indicating the presence of anthropogenic 14C. The findings demonstrate the potential for contamination of springs by surface runoff, while sources of greater age generally offer a greater degree of protection from surface pollution.
Observations of radio continuum emission from M31
Authors: Pooley G. G. 
Published: July 2016

Observations of continuum emission from M 31 have been made with the Cambridge One-mile radio telescope (Pooley, 1969). Two observing frequencies were used; maps of the whole of the visible nebula were obtained at 408 MHz, and spectral data for the central region at 1407 MHz. The results show that the radiation from the disc is confined to the nucleus and to the population I spiral arms.The nuclear region may be described in terms of two spherical radio components, with diameters of 200 pc and 1 kpc. Any more compact source at the nucleus has a luminosity less than 1/20 of that of the source Sgr A in our Galaxy.The intensity of the radio emission from the spiral arms is closely correlated with the number of H ii regions visible. The main spiral arms, corresponding to Baade's arms 4 and 5, cross the major axis at about 8 and 12.5 kpc from the nucleus. The spectrum of the radiation shows that it is non-thermal in origin; the spectral index is 0.8. The intensity is less than that which would be observed from our own Galaxy at the same distance.
Contribution to the study of the distribution of neutral hydrogen in the region 230° ≤ lII ≤ 280°
Authors: Goniadzki D. , Jech A. 
Published: July 2016

A sky survey of the 21 cm hydrogen line has been made with the 100-foot Radiotelescope of the I.A.R.-C.I.W. Radio Astronomy Station in the region 230° ≤ lII ≤ 280°, −15° ≤ bII ≤ −3°.We study the distribution of the local hydrogen and that in the Orion, Intermediate and Perseus arms. We find a new structure that starts at lII = 265°. We also study the concentrations which lie far below the plane; some of them seem to be related to Lindblad's G arm.
Spiral waves caused by a passage of the LMC?
Authors: Toomre A. 
Published: July 2016

This progress report on the deduction of an almost grazing orbit of the Large Magellanic Cloud from the warped shape of our Galaxy focused on two issues of special relevance to this Symposium:
(i)Distance R0. - An implausibly large mass (> 3 × 1010M⊙) of the LMC is needed to account for the observed warp even with the most optimal orbit, using Schmidt's (1965) disk model of our Galaxy, or any close variant thereof. Although as yet only tentative, the inference seems to be that our distance R0 from the galactic center has been overestimated; instead of the now ‘standard’ R0 = 10 kpc, these disk-bending calculations suggest a value more like the older R0 ≅ 8 kpc.(ii)Forced spiral waves. - Even with the revised R0, the sense of the LMC orbit remains ambiguous (though not the perigalactic distance of roughly 20 kpc nor the low absolute inclination of that orbit relative to the galactic plane). Neither the detailed shapes of the vertically bent model disks, nor any computed tidal effects of the Galaxy upon the LMC and SMC, either separately or as a system, rule out an LMC passage that is retrograde with respect to the galactic rotation, but all favor a direct passage as being the more plausible. The latter kind of passage, however, presents an embarrassment of riches.
Deviation of the vertex of the velocity ellipse of young stars and its connection with spiral structure
Authors: Woolley Sir R. 
Published: July 2016

The deviation of the vertex of the velocity ellipse of stars of spectral class A is shown clearly in a diagram published by Strömberg (1946); no such clear deviation is shown by the velocity ellipses of stars of other spectral types in his diagrams. This deviation of the vertex or tilt of the velocity ellipse can have some connexion with spiral structure, and there seem to be two possibilities, (a) that the tilt is confined to young stars only, and has something to do with an initial condition of their formation; and (b) that the tilt is a manifestation of the nature of the attracting field in the neighbourhood of the sun, which is not central on account of the attractions of spiral arms.The present note examines data taken from the velocities of nearby stars, and uses the classification of the late type main sequence stars put forward by Wilson, based on observations of the reversals in the Ca+ H and K lines.From this material it is concluded that the vertex deviation is confined to young stars, and that hypothesis (a) rather than hypothesis (b) is correct – or at least strongly indicated by available observations. The paper goes on to show that the deviation of the vertex can be explained by supposing that the stars were formed comparatively recently in a thin strip of the galaxy more or less at right angles to the direction of the galactic centre – in fact, in something like a spiral arm.
Hard X-rays from the southern sky
Authors: Lewin Walter H. G. , Mcclintock Jeffrey E. , Smith William B. 
Published: July 2016

On March 20, 1969, we scanned the Southern sky for 8 hours in a manner similar to that during our October 15, 1967 observations. A quick look at the data shows clearly that the brightness of Cen XR-2 in the energy range above 20 keV has significantly decreased since our first observation. At this stage of the data analysis we can put an upper limit on the intensity of Cen XR-2 which is 1/3 the intensity observed by us on October 15, 1967. From further data analyses we will be able to determine the intensity of the source more precisely.During the same flight we observed Sco X-l, Nor XR-2, and the sources M-l, M-2, M-3, and M-4. Results on these observations will become available by May 1970.
2–20 keV X-ray sky background
Authors: Boldt E. A. , Desai U. D. , Holt S. S. , Serlemitsos P. J. 
Published: July 2016

The diffuse background of 2–20 keV X-rays over a band of the sky extending from Scorpius to the North galactic pole is found to be isotropic to within 5%, with a spectrum given bywheren= (1.35 ±0.100.07).A comparison with spectra at higher energies indicates that the lower energy spectrum is flatter, corresponding to an apparent unit change in spectral index within the band 20–80 keV. A spectral break in this energy region has been discussed in connection with the collisional energy loss lifetime for metagalactic protons that radiate X-rays via inverse bremsstrahlung collisions with the ambient electrons of the intergalactic medium (Boldt and Serlemitsos, 1969; Hayakawa, 1970).
The Gaseous Content of Galaxies
Authors: Roberts Morton S. 
Published: July 2016

A general review is given of the content and distribution of interstellar gas within galaxies. The constancy of the ratio N(He)/N(H), independent of galaxy type (spirals and irregulars), is discussed and the possible mechanisms for this constancy are considered. The helium abundance does not vary across the disk of spirals, although nitrogen and possibly other elements do.The gross features of the neutral hydrogen distribution in our Galaxy and other systems are described. In spirals, the peak of the radial distribution of Hi is located well away from the optical center. This is not the case for irregular-type systems. A possible correlation of the relative location of the maxima of Hi and Hii distributions with galaxy type is described. Many spirals studied with high enough relative angular resolution show concentrations of Hi in their outermost regions. These may be due to hydrogen companions or warps in the hydrogen plane. Hydrogen ‘bridges’ are described and a new example for the triple system M81–M82–NGC 3077 is given. This latter case may be an extreme example of distortion by companion galaxies of the Hi associated with a massive galaxy.The neutral hydrogen content of a galaxy and its correlation with other integral properties is discussed. The absorption profile due to hydrogen associated with the radio galaxy Centaurus A is given. Comparison of optical and 21-cm measurements of galaxian redshifts shows excellent agreement over the radical velocity range −400 to + 5200 km s−1. There is, however, a systematic difference between 21 cm and optical redshifts over the range ∼ 1200 to ∼ 2400 km s−1 for optical values based on blue-sensitive spectra. The difference, ∼ 100 km s−1, is most likely due to blending of galaxian and night sky H and K absorption lines. The Hubble Constant is derived from a redshift-21 cm flux relation. Values in the range 78 to 109 km s−1 Mpc−1 are derived. A value of 97 kms−1 Mpc−1 is favored.
Structural and Kinematic Properties of Populations of the Andromeda Galaxy
Authors: Einasto J. 
Published: July 2016

New observational data (Spinrad, 1970; Van den Bergh, 1970; Rubin and Ford, 1970) are used to determine structural and kinematic parameters of the nucleus, the subsystem of globular clusters, and interstellar hydrogen in M31.The mass derived for the nucleus from the new spectrophotometric data is in good agreement with the virial mass 6 × 108M⊙. Model calculations show that there is no appreciable exchange of stars between the nucleus and the bulge. The rotation energy of the nucleus is only 7.5% of the total kinetic energy; the central density is 2 × 106M⊙ pc−3.The mean radius of the subsystem of globular clusters is 4.5 kpc. This indicates that the subsystem of old stars is not identical with the spheroidal component of the galaxy, whose mean radius is only 1 kpc. Radial velocity dispersion of globular clusters is only half of that of the nucleus. This shows a strong dependence of the velocity dispersion on distance to the center of the galaxy and a bias in mass determination of a galaxy from velocity dispersion near the nucleus.On the basis of data on rotation two mass distribution models have been found, differing from each other in respect of the mass concentration to the center. Spectrophotometric data on the stellar content of the bulge are urgently needed to solve the mass distribution problem.
Infrared Radiation from Compact Objects
Authors: Neugebauer G. 
Published: July 2016

Current infrared observations of Seyfert galaxies, QSOs, and compact galaxies in the lists of Markarian and Zwicky have been reviewed. The bright Seyfert galaxies generally show similar infrared excesses at the longer wavelengths accessible from the ground. Only NGC 1068 has been observed, by F. J. Low, in the 100μ region; if the spectral distributions of all Seyfert galaxies are similar to that of NGC 1068, the intrinsic luminosities vary from 1 to 100 × 1044 erg s−1. Measurements by Kleinmann and Low, Gillett and Stein, Pacholczyk, and Penston and Neugebauer at 10 and 2μ apparently confirm variability of NGC 1068 and NGC 4151 on a time scale too short to allow the infrared radiation to come predominantly from dust shells.The published infrared observations of QSOs have been limited to wavelengths shorter than 3.5μ except for 3C 273. The energy distributions either show a power law fall-off, a flat spectrum, or a combination of these two. Those four QSOs which show large variability all have steep power law spectra. If one accepts that the distance of QSOs are cosmological, the extrapolated luminosity at 2μ of several QSOs exceeds that of 3C 273. The integrated luminosity of 3C 273 depends critically on the spectrum in the unobserved 10–1000μ region, but is probably in the range 1047 to 1048 erg s−1.The infrared observations of the compact Markarian and Zwicky objects show a correlation between the infrared excess and the broad optical emission lines. Presumably the infrared can be used to differentiate between the stellar and non-thermal components of the radiation from these objects.
Dynamo Theory and the Solar Cycle
Authors: Stix M. 
Published: July 2016

In this paper solutions of the mean field induction equation in a spherical geometry are discussed. In particular, the 22-year solar magnetic cycle is considered to be governed by an axisymmetric, periodic solution which is antisymmetric with respect to the equatorial plane. This solution essentially describes flux tubes travelling as waves from mid-latitudes towards the equator. In a layer of infinite extent the period of such dynamo waves solely depends on the strength of the two induction effects, differential rotation and α-effect (cyclonic turbulence). In a spherical shell, however, mean flux must be destroyed by turbulent diffusion, so the latter process might actually control the time scale of the solar cycle.A special discussion is devoted to the question of whether the angular velocityincreaseswith increasing depth, as the dynamo waves seem to require, or whether itdecreases, as many theoretical models concerned with the Sun's differential rotation predict. Finally, theories for the sector structure of the large scale photospheric field are reviewed. These describe magnetic sectors as a consequence of the sectoral pattern in the underlying large scale convection, as non-axisymmetric solutions of the mean field induction equation, or as hydromagnetic waves, modified by rotational effects.
Effects of Abundance Changes on the Spectra of Very Cool White Dwarfs
Authors: Wehrse R. 
Published: July 2016

In order to study the atmospheres of cool white dwarfs of spectral types DA, DF and DG, model atmospheres have been calculated for temperatures 5000 ≤ Teff ≤ 7000 K and gravities 7 ≤ log g ≤ 8.5. The helium to hydrogen abundance ratio ranges from 0.1 to 1000. The abundances of the metals ∈M (relative to hydrogen) vary between the solar value ∈⊙M and ∈⊙M/1000. The models are hydrogen and metal line blanketed and in radiative equilibrium. The models with increased He abundance are characterized by a decreased mean opacity since the absorption cross-section of He is much smaller than that of H–. As a result, the spectral lines become stronger and – due to the much higher pressures – much broader. A reduction of the metal contents also increases the pressures. In this case it is caused by the shortage of electron suppliers. Here the spectral lines also become broader, but in general weaker.These effects strengthen the overlap of the lines due to the high gravity of white dwarfs and more or less lead to a quasi-continuum which may be much below the true continuum. Because of the wavelength dependence of the line density the depression is strongest in the UV and blue spectral region, whereas for wavelengths λ ≥ 4500 Å the difference from the true continuum is only a few per cent. The details will be published elsewhere.
The Helium-to-Hydrogen Ratio of Stars in Young Clusters and Associations
Authors: Nissen P. E. 
Published: July 2016

A photoelectric narrow-band index, I(4026), of the He I λ 4026 line has been observed with an echelle spectrometer for B-type stars in young clusters and associations.Model-atmosphere computations of the Strömgren [c1] index, the Hβ index, and I(4026) as functions of Teff, g and the helium-to-hydrogen ratio have been used to derive these atmospheric parameters from the observed indices for each star.For the OriOBIb, LacOBI and Sco-Cen associations 11 out of 48 stars in the temperature range from 14 000 to 20 000 K are found to be helium poor in the sense that the derived helium-to-hydrogen ratios lie in the range from 0.05 down to very low values. In the temperature range from 20 000 to 30 000 K no helium poor stars are found, but two stars in OriOBIb are helium rich. Both of these stars show rather strong variations of the I(4026) index.All stars in h + χ Per and CepOBIII are apparently helium deficient compared to nearby field stars.
Spectral Classification in the Small Magellanic Cloud
Authors: Dubois P. , Jaschek M. , Jaschek C. 
Published: July 2016

This paper presents results obtained in classifying 26 supergiants of the Small Magellanic Cloud. The main results are:
–The hydrogen lines are not as sharp as expected for such luminous stars.–Generally, for the A-type stars, the calcium K-line is too strong compared to the other metallic lines.–There are differences in the behaviour of the different metals.–Often, the stars present variations in their spectra.–50% of the stars brighter than mv = 11.3 have an enhancement of the H8 Balmer line, which is one of the characteristics of a shell star.–The comparison with the Radcliffe classification and Dachs classification is, except in very few cases, in good agreement.
Red Variables of the Halo and the Globular Clusters
Authors: Evans T. Lloyd 
Published: July 2016

The present state of knowledge of the red variables in the halo and globular clusters is summarized. Techniques for their discovery are described. The correlations between their properties and those of the globular clusters to which they belong are discussed. The evolutionary state of the variables is considered and stars are assigned tentatively to the first or second ascent of the giant branch or to the excursions from the asymptotic giant branch resulting from instabilities in the He-burning shell.The assumption that a recognizable type of variable represents a unique type of star leads to the conclusions that the bulk of the stars in the central bulge of the Galaxy are more metal-rich than 47 Tuc and that the Large Magellanic Cloud contains an old, moderately metal-deficient population similar to that represented by clusters such as 47 Tuc in the Galaxy while the Small Magellanic Cloud does not.
Energy Distributions of Be Stars: (Review Paper)
Authors: Schild R. E. 
Published: July 2016

Energy distributions from 0.32 to 1.06 μ for field Be stars having p designations in their spectral types show that stars with Balmer discontinuities in emission do exist. Furthermore, the filling in of the Balmer continuum near the discontinuity is usually observed. The continuum emission showing a peak near 1 μ is a common feature in the energy distributions presented here.Energy distributions for a number of bright field Be stars are also presented and discussed.
Two Types of Evolution of Massive Close Binary Systems
Authors: De Loore C. , De Greve J. P. 
Published: July 2016

It is well known that the outcome of case B evolution of the primaries of massive close binary systems (M1 ≥ 9 M⊙) depends on the initial primary mass. The most massive primaries finally ignite carbon, form iron cores and presumably end in a supernova explosion, whereas the lighter ones presumably end as white dwarfs, without carbon ignition. This paper derives an estimate of the mass boundary separating these two kinds of evolution.As an example of the first case, the evolution of a 20 M⊙ + 14 M⊙ system was computed; after the mass exchange, the primary star (with M = 5.43 M⊙) evolves through the helium-burning (Wolf-Rayet) stage towards a supernova explosion; finally the system evolves into an X-ray binary (BWRX-evolution).As a representative for the second case the evolution of a 10 M⊙ + 8 M⊙ system was examined. After the first stage of mass exchange, the primary (with a mass of 1.66 M⊙) approaches the helium main sequence; during later phases of helium burning the radius increases again, and a second stage of mass transfer starts; after this the star (with a mass of 1.14 M⊙) again evolves towards the left in the Hertzsprung-Russell diagram and ends as a white dwarf (BSWD-evolution). A system of 15 M⊙ + 8 M⊙ is found to evolve very similar to the 20 M⊙ + 14 M⊙ system. The mass Mu, separating the two types of evolution, must therefore be situated between 10 and 15 solar masses. An initial chemical composition X = 0.70, Z = 0.03 was used for all systems.
Unsteady Mass Loss in Close Binaries
Authors: Webbink R. F. 
Published: July 2016

The evolution of a system of 1.50M⊙ and 0.50M⊙ components with initial separation 3.00R⊙ is presented. The primary reaches its Roche lobe after 6.108 × 108 yr, and the mass loss rate grows quickly to ~ 1.1 × 10−7M⊙ yr−1. The deep convective envelope of the secondary contracts in response to accretion, however, and the system avoids contact, even though the main sequence mass-radius relationship crosses the Roche relationship at 0.758M⊙.The growth of the convective envelope of the primary with mass loss prevents thermaltimescale mass transfer from reaching any stable value. The mass loss rate continues to increase as a result of the tendency of the growing convective envelope to expand with mass loss. A Bath-type pulsational instability in the mass transfer rate is manifested as a longer-period thermal instability in the hydrostatic treatment. Eventually mass loss proceeds on a dynamical timescale, reaching 1.5 × 10−4M⊙yr−1. This is followed by a detached phase with the mass ratio not yet reversed, and a second dynamical episode leaving a 0.6666M⊙ + 1.3334M⊙ binary still in a semi-detached state. The original secondary, now more massive, has a surface luminosity of 0.0538L⊙ but a nuclear luminosity of 1540L⊙, and a convective core of 1.076M⊙ separated by a radiative zone of only 0.028M⊙ from its convective envelope.An attempt is made to follow the evolution of the secondary in the case where the stream energy, much greater than the intrinsic luminosity of the secondary, is dissipated spherically symmetrically at its surface. The outer envelope departs radically from the previous case, an optically deep radiative surface layer forming, and the convection zone splitting into two, the lower one remaining very massive. Because the mass transfer timescale is short compared with the thermal timescale of the secondary, however, it is concluded that the stream luminosity cannot significantly alter the evolution of the secondary.
Interpretation of Cosmological Information on Radio Sources
Authors: Burbidge G. 
Published: July 2016

The topic that I have to introduce today is concerned with the question as to whether or not we can obtain any cosmological information from radio astronomy. Alternatively, we may ask “Where does radio astronomy have an impact on cosmology?” There are several areas that must be discussed. They are:
1)The discovery and interpretation of the microwave background radiation.2)The identification of powerful radio sources and the discovery that many of them have large redshifts. If we can prove that the large redshifts mean that the objects are at great distances, then we can use these radio sources as follows:(a)We can attempt to obtain a Hubble relation for the optical objects which are identified with radio galaxies;(b)We can look for a relation between the angular diameters of the radio sources and the redshifts of the optically identified objects and we can also look at relations between the angular diameter and the radio flux;(c)We can construct log N - log S curves and we can carry out luminosity volume tests.