bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal Abundances of Young Stellar Groups
Authors: Grenon M.
Published: July 2016

The metal abundances of young stellar groups in the solar vicinity are obtained from the photometric [Fe/H] ratios observed for the red giant group members. The definition of the groups has been rediscussed with the help of a sample of B5-A0 stars whose physical properties are derived by Cramer (1979). The young G3-K5 giants have been selected according to their spatial velocities and their age derived from the Geneva colours (Grenon 1978). They show the kinematics of A stars (Eggen 1963). The star concentrations coincide in both (U,V) planes (red giants and B & A stars) in the zones listed below with the value of the mean [Fe/H] and galactocentric distance, .
A New Photometric Investigation of the Young Open Cluster NGC 663
Authors: Hassan S. M. , Othman A. I.
Published: July 2016

The investigation of the open cluster NGC 663, based on the application of the method of UBV three colour photometry and the use of new photographic material, lead to a new distance to the cluster of 2550pc, E(B-V) & E(U-B) colour excesses of 0.74 & 0.53 mag and consequently a total visual absorption AV of 2.22 mag. An age of 3.9 × 107 y and a spectral type B2-B3 can be estimated for it; accordingly, it fits well the Perseus Arm (+1) near the outer edge and lies below the galactic plane at a distance of 47 pc.

From the distribution of 476 stars investigated, around both the ZAMS and the apparent centre of the cluster, 270 probable physical member stars could be separated from the field stars and neither late type giants nor a giant branch are in existence.
Binary Stars in Globular and Open Clusters
Authors: Trimble Virginia L.
Published: July 2016

In erecting the edifice we call science, it is given to some to draw the plans by which the entire effort will be guided, to others to lay the foundation stones on which the rest is built, to another group to place the windows that let in light upon the whole, and to still others to cover the result with the paint that will make it acceptable to the populace and the sponsoring agencies. In this review, it is, I fear, my task to run around the construction site, pick up odd bricks and pieces of brick, and ask whether they do not perhaps belong somewhere in the building. After the customary bit of folk history, this will be done in the order globular clusters, open clusters, with observations and theory inextricably mingled, as indeed they really are.
LMC Clusters: Young
Authors: Freeman K. C.
Published: July 2016

The young globular clusters of the LMC have ages of 107–108 y. Their masses and structure are similar to those of the smaller galactic globular clusters. Their stellar mass functions (in the mass range 6 m⊙ to 1.2 m⊙) vary greatly from cluster to cluster, although the clusters are similar in total mass, age, structure and chemical composition. It would be very interesting to know why these clusters are forming now in the LMC and not in the Galaxy.

I will talk about the “young globular” or “blue populous” clusters of the LMC. They were first identified as a family by Hodge (1961). The ages of these objects are 107 to 108 y, and their masses are 104 to 105 m⊙, so they are populous enough to be really useful for studying the evolution of massive stars. I will not discuss this aspect (see the extensive work by Flower and Hodge and Robertson since 1974), but will concentrate on the structure and stellar content of these young clusters.
Magellanic Cloud Halo RR Lyrae Stars: The NGC 2257 Field in the Outskirts of the LMC
Authors: Hesser James E. , Nemec James M. , Patricio Ugarte P.
Published: July 2016

The discovery of three RR Lyrae stars beyond the limiting radius of NGC 1841, a globular star cluster in the extreme halo of the Magellanic Cloud system, led Kinman, Stryker and Hesser (1976) to suggest that they might represent a stellar component of a tenuous halo that could have resulted from tidal interactions with the Galaxy. The field of NGC 2257, a “red” globular about 7° east of the LMC, is ideal for evaluation of the gradient in RR Lyrae surface density at intermediate distance in the Magellanic Cloud halo system. Sixty plates taken by Graham, Hesser and Kinman are available (6 from the 1.5-m telescope taken in 1971, and 54 from the 4-m telescope taken in 1974–1977); the 4-m plates are usually IIaO+GG385 exposed for 5 to 10 minutes with a 7 to 21 day Moon (avoiding full Moon by ± 3 days). Extreme hour-angle coverage during two 4-m telescope runs consisting of three consecutive nights each and separated by one month aided in detection and period determination for the short-period variables. Walker's (1972) electronographically measured stars were used as standards, after being made brighter by B=0.10 mag to bring them nearer to Gascoigne's (1978) photoelectric scale. Care was taken to account for increasing background near the cluster center in the iris-to-magnitude conversion. Twenty-eight variables were known in the cluster from the early work of Alexander (1960) who was able to determine periods of six of them. He has kindly made his original step estimates available to us, and they have yielded corresponding increases in the precision of our period estimates. Among our results are: (1) We have found 16 new RR Lyrae variables in the cluster and ~ 12 in the surrounding field; 3 of Alexander's variables appear constant on the CTIO plates. (2) The period-frequency diagram for stars within 8 arcmin of the cluster shows a high ratio, N(c)/N(ab), in contradistinction to the variables in the surrounding field. (3) If the effects of the variable background have been properly removed, then the mean B magnitudes of the cluster variables implies that they, like the cluster, lie about 9 kpc closer to the Galaxy than do the field variables. (4) Walker star 95 is a c-type variable with P=0.360d, 〈B〉 =19.44 mag, and AB ≃ 0.60 mag, and should not be used as a local standard star.
The Globular Cluster NGC 6144 and its Neighbouring Region
Authors: Alcaino G.
Published: July 2016

NGC 6144 is situated in the general area behind the nebulosity in Scorpio-Ophiuchus between its counterpart M4 and the bright red giant star Antares. The color magnitude diagram (CMD) is characterized by a steep giant branch, a group of exclusively blue horizontal branch stars, and a well defined instability gap within the colour range ~0.4 < B-V < 0.8. The CMD has the typical features of metal poor clusters, similar to M3, M15, and M92. From the analysis of five circular areas equal to the one measured in the cluster, it is shown that absorption increases towards the NE direction. The deduced reddening of E(B-V)=0.40 places the object at 15.8 kpc from the Sun, 4.3 kpc from the galactic plane and 7.8 kpc from the galactic centre, assuming Ro=9 kpc. The inferred values of δV~3.1 and S~5, corroborate the tendency of metal deficiency suggested by the integrated colours, which render Q=-0.41.
Inward Diffusion of Helium in Horizontal-Branch Stars of Globular Clusters
Authors: Giannone P. , Rossi L.
Published: July 2016

The diffusion process of helium was studied in evolutionary star models. A typical horizontal-branch (HB) star (M=0.53 M⊙, Y=0.3, Z=0.001) was evolved up to the beginning of the asymptotic giant-branch phase. Helium was shown to diffuse inwards in the atmosphere and subatmosphere in a rather short interval of time. Therefore the suggested efficiency of diffusion in explaining the helium deficiency in old B- and HB-stars in globular clusters received a significant support. In models where the surface convection is not efficient enough to restore the original helium content in the outermost stellar layers, stars in subsequent evolutionary stages (such as blue and white dwarfs) should still be deficient of helium.
Globular Cluster Luminosity Functions and Helium Abundance Differences Across the Galaxy
Authors: Green Elizabeth M.
Published: July 2016

This is a preliminary report on a project in which I have been comparing observed and theoretical giant branch luminosity functions for a relatively large number of globular clusters. I believe that I have found some novel evidence to support significant He differences among globulars, especially for the inner part of the galaxy, where He appears to be increasing toward the galactic center.
Plasma Distribution Near Pulsars
Authors: Michel F. Curtis , Pellat R.
Published: July 2016

We argue that the aligned rotator model originally introduced by Goldreich and Julian possesses “static” solutions wherein particles of both sign are trapped within the magnetosphere. Simple models of such distributions are given. For such models to have dynamic properties (constant particle emission, relativistic stellar wind, etc.) one must suppose that the equatorial particles are transported away by (e.g.) flux tube interchange, rather than by flow along field lines as originally proposed.
The Location, Spectrum and Beamwidth of Pulsar Radiation from Polar Cap Models
Authors: Rickett B. J. , Cordes J. M.
Published: July 2016

In the rotating “lighthouse” interpretation of pulsars, the average radio pulse profile is generally assumed to be a section through the average beam shape radiated by a spinning neutron star. The radio emission received in any one particular period usually differs markedly from the average profile. Such variations have been classified as subpulses (~ 3 ms) and micropulses (~ .3 ms); see Cordes (1979) for examples. However, there is not general agreement as to whether these variations are caused by the rotation of a steady narrow beam or by temporal variations of a wider beam. We first discuss these questions independently of the emitting particle location, and then apply them to a particular model.
Multifrequency Polarization Observations of Integrated Pulse Profiles
Authors: McCulloch P.M. , Hamilton P. A. , Manchester R. N.
Published: July 2016

Polarization observations of integrated pulse profiles have been made in seven frequency ranges between 170 MHz and 2700 MHz. Forty-nine pulsars have been observed at three or more of these frequencies. The frequency variation of the degree of linear and circular polarization is discussed for these pulsars.
Polar Cap Relief and Integrated Pulse Structure
Authors: Vivekanand M. , Radhakrishnan V.
Published: July 2016

An explanation is offered for the complexity and stability of integrated pulse profiles. We propose that the pulse structure arises from surface irregularities at the polar caps, and we indicate how the surface relief affects the number of charges which are released into the magnetosphere and create the observed radio radiation. The electrons produced in the vacuum break-down in the polar gap carry enough energy to continually modify the surface relief of the polar caps, and we suggest one way in which the surface could be modified in a timescale of a million years.
Multi Radio Frequency Observations of Pulsars
Authors: Bartel Norbert
Published: July 2016

An investigation of the frequency dependence of the radio emission of pulsars promises to contribute considerably to the understanding of such outstanding questions as:

1.

Is the emission mechanism narrowband or broadband?

2.

What is the coherence time of the radiation?

3.

Does a radius-to-frequency mapping exist?

4.

Is pulsed radiation absorbed in the magnetosphere?

The 100-m telescope in Effelsberg is satisfactorily sensitive in the GHz frequency range so that we could observe averaged pulses up to 22.7 GHz (Bartel et al., 1977; Bartel et al., 1978) and single pulses at 8.8 GHz (Bartel et al., 1980a), which are the highest radio frequencies respectively at which pulsars have been detected. Therefore quite naturally the analysis of the frequency dependent pulsar emission became one of the focal points of interest in pulsar research at the MPIfR.
PSR 0031–07: The Harmonic Pulsar
Authors: Wright G.A.E. , Fowler L. A.
Published: July 2016

PSR 0031-07 has a period of 0.94 seconds and the relatively old timing age of 37 million years. Its properties were first established by Huguenin et al. (1970), based on observations at 145 and 400 MHz.
Radio Radiation Characteristics of Pulsars and Magnetic Dipole Angle
Authors: Zhen-ru Wang , Yi Chu
Published: July 2016

The structure of the pulsar magnetosphere, the location of the radio emission region and the radio emission mechanism are important theoretical subjects in the research of pulsars. There may be close relations between these subjects. Nevertheless, it should be possible to set up some empirical relations among them which can be considered as a foundation for studying these important subjects. In this paper some of these relations are studied.
Pulsar Optical Emission as Amplified Synchrotron Emission
Authors: Stoneham R. J.
Published: July 2016

Pulsed optical emission has been observed from the Crab and Vela pulsars (Manchester and Taylor 1977). The pulse profile of the Crab pulsar has a main pulse and a strong interpulse separated by about 40% of the pulsar period; the peak of the main pulse is just resolved at 20 μs resolution; the spectrum is peaked at about 1014.8 Hz; the pulse profile is constant over long time intervals; both the main pulse and the interpulse are strongly linearly polarized with position angle varying smoothly through each profile and with a minimum of polarization near each peak; the pulses are not significantly circularly polarized. A number of models have been proposed to explain the optical emission from the Crab pulsar but none is completely satisfactory. The spectral peak is too low for incoherent synchrotron emission, the pulse profile is too constant for inverse Compton scattering of radio emission and the similarity with the low-energy X-ray emission argues against coherent curvature emission.
High Energy Gamma Rays from Pulsars
Authors: Bhat P. N. , Gupta S. K. , Ramana Murthy P.V. , Sreekantan B. V. , Tonwar S. C. , Viswanath P. R.
Published: July 2016

We present here the results from observations of pulsed gamma ray emission from the Crab and Vela pulsars for energies above 100 GeV using the atmospheric Cerenkov technique. The results suggest a very steep energy spectrum for gamma rays emitted from pulsars at high energies. Our observations over the last 4 years suggest also that the flux is highly variable with time.
Pulse Timing and Neutron Star Structure
Authors: Boynton Paul E.
Published: July 2016

The implementation of pulse timing analysis as a probe of neutron star structure is reviewed for both pulsars and X-ray pulsators. Current results are particularly significant for the Crab pulsar.
Neutron Star Properties from Observations of Pulsars and Pulsing X-ray Sources
Authors: Lamb F. K.
Published: July 2016

This paper reviews the information on neutron stars that has been obtained from radio and X-ray observations, with emphasis on recent results from timing studies. Included are summaries of the current theoretical picture of neutron stars, and the most recent evidence concerning stellar masses, radii, inertial moments, and magnetic fields. Also included are discussions of large frequency jumps (“macroglitches”), small-scale timing irregularities (“microglitches”), the characterization of the latter phenomenon in terms of random noise processes, and the use of both as probes of the internal structure and dynamics of neutron stars. Finally, some of the most promising directions for future work are briefly noted.
Cooling of Neutron Stars: Accurate Treatment of Thermal Conduction
Authors: Itoh N. , Nomoto K. , Tsuruta S. , Murai T.
Published: July 2016

Most of the neutron star cooling calculations with the only exception of Malone's (1974) have assumed an isothermal stellar core. Here we report on a neutron star cooling calculation which makes full use of the stellar evolution code and the recent thermal conductivity calculations by Flowers and Itoh (1976, 1979).
Unpulsed X-rays from Pulsars
Authors: Helfand David J.
Published: July 2016

The radio emission from pulsars is energetically insignificant, yet its distinctive character led to their discovery and subsequent identification with rotating magnetized neutron stars. In the intervening thirteen years, a wealth of radio data have been accumulated from which we have learned something of the magnetospheric properties, stellar structure, and evolutionary history of these objects. Yet we still do not know how pulsars pulse, what the neutron star interior is like or, with certainty, how and where pulsars are formed. And, we have not yet ‘seen’ a radio pulsar, in the sense that we see other stars, i.e., by detecting thermal photons from its surface. The Einstein Observatory soft X-ray telescope offers a new opportunity to attempt such an observation. We report herein the preliminary results of several programs aimed at the detection of thermal X-ray emission from isolated neutron stars.
The Magnetic Fields and Original Spins of Binary and Runaway Pulsars
Authors: Lamb F. K.
Published: July 2016

Pulsing X-ray sources are believed to be the progenitors of binary and runaway pulsars. Thus, their observed properties and predicted fates furnish information about the initial properties and evolution of these pulsars. Evidence is discussed which suggests that many binary and runaway pulsars are born with periods ~ seconds and dipole magnetic fields ~ 1011 – 1013 G, and that the turnoff of at least some is not due to decay of their dipole magnetic fields.
2. Red Subluminous Stars
Authors: Eggen O. J.
Published: July 2016

(UBVRI) observations of known subluminous stars were published in a previous discussion (Eggen, 1970a) where the bulk of the objects, both red (RSL) and blue (BSL) populated a sequence extending for M(I) near + 11.m5 at (R – I) near 0.m0 to M(I) of + 15m near R – I = +0.m3. However, four RSL stars appeared to form a separate sequence near M(I)= +11m and R–I between +0.m3 and +0.m7. These four stars, plus an additional object (LTT 2236) are listed in Table I together with the source of luminosity; the weights of the trigonometric parallaxes are given in parentheses following the parallax. These five stars are represented in Figure 1 by crosses; the top of the steep sequence of subluminous stars is shown as the hatched region in the figure. For reference, Figure 1 also contains (1) the Hyades main sequence (Eggen, 1969b), indicated by a broken curve, (2) the evolved main sequence of the old disk population (Eggen, 1970b), shown by open circles, and (3) the subdwarfs, which are listed in Table II. In addition to the photometric results, Table II contains the Yale Parallax Catalogue number, the mean trigonometric parallax and its weight, in parentheses, as well as the resulting values of M (I).
3. Parallaxes of White Dwarfs
Authors: Strand K. Aa.
Published: July 2016

The U.S. Naval Observatory program on trigonometric stellar parallaxes with the 61-inch Astrometric Reflector has been in progress since 1964.
5. The Identification of White Dwarf Suspects in the Lowell Proper Motion Program
Authors: Giclas H. L.
Published: July 2016

During the course of the Lowell proper motion survey that has been in progress since 1957, an effort has been made to identify the very blue stars and more recently the extremely red ones. The proper motions are detected and measured directly by projection on the calibrated grid of the blink microscope. The regular program catalogs all motions found >0″.26/year and fainter than the eighth magnitude. From this portion of the program, we have identified 179 white dwarf suspects, 48 of color class– 1 and 131 of color class 0, which have been published in the Lowell Bulletins under the title of ‘Lowell Proper Motions II through XV’. These lists cover the entire northern hemisphere, and a few regions down as far as −;10° South, and contain 10382 different individual stars. Finding charts are provided for each object.
6. An Astrometric Study of Van Maanen'S Star
Authors: van de Kamp P.
Published: July 2016

Van Maanen's star (1950: 0h46.m5, + 5°.09′) is a white dwarf (visual magnitude 12.4, spectrum DF) with a proper motion of 2″.95 in 155°.5 and parallax 0″.234. An early determination of radial velocity yielded +238 km/sec (Adams and Joy, 1926). It was suggested by Russell and Atkinson (1931) that van Maanen's star might show a very large Einstein shift of at least +700 km/sec. Oort (1932) pointed out that the observed value of +238 km/sec is incompatible with the theory of galactic rotation: this would support the Einstein shift interpretation.
7. The White Dwarfs in the Catalogue of Nearby Stars of 1969
Authors: Gliese W.
Published: July 2016

The Catalogue of Nearby Stars (Gliese, 1969) contains 1529 single stars and systems with altogether 1890 components. It includes 54 white dwarfs with apparent magnitudes from 8.5 to 17; namely 38 single stars and 16 degenerate stars which are components of binaries or triples. Only 48 of these objects have parallaxes larger than 0″.050. But our knowledge is very incomplete.
8. High Frequency Stellar Oscillations: IV: Photoelectric Monitoring of Southern White Dwarfs
Authors: Hesser J. E. , Lasker B. M.
Published: July 2016

Time-series data for 14 stars in the list of Eggen and Greenstein have been used to compute their power spectra, which confirm previously found quiescency in the 4 to 700 sec period range. Additionally, characteristics of the continuous power spectra are considered.
16. The Line Spectra of White Dwarfs
Authors: Strittmatter P. A. , Wickramasinghe D. T.
Published: July 2016

Model atmospheres with temperatures in the range 10000 ≤ Teff ≤ 25000 K and with gravities 6 ≤ log(g) ≤ 9 have been constructed for various helium abundances with a view to understanding the spectra of the hotter white dwarfs. It is shown that the DB stars are confined to the temperature range 15000 ≤ Teff ≤ 18000 K in which convection also becomes important in the outer layers of helium rich stars. The DA stars seem to avoid this temperature range. The hydrogen and metal abundances in DB atmospheres are shown to be reduced by factors 105 and 103 respectively compared to solar values. Possible explanations of DB and DC spectra are discussed.
21. Models of White Dwarfs, Radial Pulsations and Vibrational Stability
Authors: Vauclair G.
Published: July 2016

We have computed a set of models of white dwarfs. The equation of state is the Chandrasekhar (1939) one corrected by Salpeter (1961). It takes into account both the interactions between particles and the effect of non-zero temperature.

The models consist of an isothermal core with 50% of carbon and 50% of oxygen, surrounded by an envelope of population I composition with 70% of hydrogen and 3% of metals by mass. Nuclear energy is liberated by p-p reactions located in a shell at the edge of the isothermal core. Equilibrium models of various masses and luminosities have been built; Table I gives the values of their characteristic parameters. The central temperature-luminosity-mass relation for our models is compared with the Schatzman (1952) one for pure hydrogen envelopes (S), the Hubbard and Wagner (1970) one for Mg core and solar composition envelope models (HW) and the Van Horn (1970) one for carbons models (VH) (Figure 1). At high luminosities there is a sensible departure from the linear relation. Though our models are not evolutionary sequence ones, they fit very well with the sequences calculated by Vila (1966, 1967). The models studied here are of the type expected from the calculation of the evolution of some double systems (Lauterborn, 1970) after the white dwarfs have lost their very diluted envelopes.
Analysis of Pole Position from 1846 to 1970
Authors: Gaposchkin E. M.
Published: July 2016

One- and two-component models for the Chandler motion are investigated with the use of historical data. Evidence for a two-component motion is more convincing from both the data-analysis and the geophysical point of view.
An Interpretation of the Ambiguity between Annual Terms Obtained by Time and Latitude Observations
Authors: Okuda Toyozo
Published: July 2016

Guinot and Feissel (1968), Okazaki and Nasaka (1970) reported the marked discrepancy between annual terms of the polar motion obtained by time and latitude observations. The disturbing effects of local non-polar terms in latitude variation on pole coordinates are discussed in the first half of this paper.

From an analogy between time and latitude observations, we can conclude that Δx and Δy in the pole coordinates obtained from time observations are proportional to a part of the common fictitious term ΔT in the rotation of the Earth. Using ΔT obtained from Okazaki's data for the same interval as Guinot's and Feissel's data, a test example is given as follows:
If we apply the above corrections to the pole coordinates obtained from time observations, we can derive the coordinates x and y which are comparable to those of the ILS. Δαα, ΔS and local non-polar terms (z5 – z4) in the ILS latitude determination may be considered as the sources of ΔT.
Comparisons between Results of Polar Coordinates Derived from Time Data and Those from Latitude Ones
Authors: Okazaki Sêichi , Nasaka Mitsuko
Published: July 2016

Computations of the polar coordinates are carried out by the use of time data and of latitude data separately. The results from time data and those from latitude data are proved to have mutual differences in annual term in particular. That is, polar loci obtained from latitude results give almost circular forms, while those from time results give elliptic forms elongated rather seriously on the X-axis.
A Laser Polar Motion Experiment
Authors: Smith David E. , Dunn Peter J. , Kolenkiewicz Ronald
Published: July 2016

For three months in 1970, NASA, Goddard Space Flight Center conducted an experiment to try and detect the motion of the Earth's pole of rotation by laser ranging to an Earth satellite. Two laser tracking stations were used, one at Goddard Space Flight Center and one near Seneca in New York State, 408 km away and on the same meridian as the Goddard station. The objective of the experiment was to precisely measure the orbital inclination of the Beacon Explore C spacecraft, on a daily basis and with a resolution of a few hours, to a few hundredths of an arc second by the simultaneous tracking of the spacecraft as it passed between the two stations. During the experiment over fifty thousand range measurements on over two hundred revolutions of the satellite were obtained and on fifty occasions the satellite was simultaneously tracked at both stations. The noise accuracy of the tracking varied between 20 and 60 cm during most of the experiment and the orbital inclination obtained from the measurements showed a systematic change of about 25 arc sec, due primarily (about 80%) to the gravitational perturbation of the orbit by the Sun and the Moon. Perturbations by solar radiation pressure and the solid-Earth tides appear to account for most of the remaining systematic changes in the inclination and from which it has been possible to derive a value of Love's number for the Earth as
A preliminary determination of the motion of the pole in the meridian containing the stations by subtracting the known perturbations (including tides) from the observed perturbation suggests that an accuracy of 3 to 5 m has been obtained, over periods of about 6 hr, during the latter part of the experiment. The experiment has also demonstrated that the present laser tracking systems are able to measure the chord distance between the two tracking stations with a repeatability of 25 to 30 cm.

The present analysis of the data is directed towards an improved extraction of the gravitational perturbations and an improved determination of the Love number k2.

A full account of the experiment and its results so far will be published elsewhere.
The Use of the Refractional Pair Observations
Authors: Teleki G.
Published: July 2016

The author propose the inclusion in observational program of latitude services a number of Talcott pairs with greater zenithal distances (refraction pairs). It is specially advisable for the stations, forming a chain, where the comparison of local latitude data is necessary. Refraction pairs could be very useful for investigations of the local anomalous refraction influences.
Rotational Accelerations
Authors: Markowitz Wm.
Published: July 2016

Rotational accelerations of the Earth arise from changes in speed of rotation: periodic, irregular, and secular. Changes are caused by winds, Earth tides, ocean tides, and motions of the core. The semimonthly lunar body tide produces the maximum acceleration.
Random Variations in the Earth Rotation
Authors: Giacaglia G. E. O.
Published: July 2016

Researches on random variations in the Earth rotation, published in the last decade, are analyzed. The basic conclusions are that both mechanical and electromagnetic interactions between mantle and core have definite and measurable influence in the rate of rotation; turbulent motion within the core and non-periodic flows in the mantle must also be taken into account; atmospheric and irregular tidal effects have possible influence. A statistical approach based only upon observations and a simple description of the above phenomena is proposed as an extension of previous works.
The Excess Secular Change in the Obliquity of the Ecliptic and Its Relation to the Internal Motion of the Earth
Authors: Kakuta Chuichi , Aoki Shinko
Published: July 2016

The previous result (Aoki, 1969) on the explanation of the excess secular change in the obliquity of the ecliptic frictional couplings in the rigid constituents, the mantle and the core, is extended by using a model of an elastic and electrically conducting mantle and a hydromagnetic core. The secular change of the obliquity of the ecliptic referred to the mantle is found to be 1/3.2 times of the observed value, if the electrical conductivities of the fluid core and the mantle are assumed to be 3·10−6 emu and 3·10−9 emu respectively. A large secular deceleration of the Earth's rotational speed obtained in the previous result is proved to be strongly reduced because of weak excitation of the perturbing potential for a long time variation.
Excitation of the Chandler Wobble by Large Earthquakes
Authors: Shimazaki Kunihiko , Takeuchi Hitoshi
Published: July 2016

The direction of anomalous polar motion is compared with that of the motion expected from the source mechanism generating the earthquakes associated with the motion. The result supports the hypothesis that major earthquakes excite the Chandler wobble.
The Determination of Love's Number K from Tidal Variations of Rotation of a Compressible Earth
Authors: Pariisky N. N. , Pertsev B. P.
Published: July 2016

Long period bodily tides (fortnightly and monthly) cause periodic changes of the Earth's moment of inertia and consequently the angular speed of its rotation.

During the past few years the use of atomic clocks has made it possible to determine the amplitudes of these periodic variations of the Earth's rotation with high accuracy and has made this method very effective in determining Love's number K, which is dependent on the internal structure of the Earth (the most detailed studies were made in the U.S.S.R. – Pilnik and Gubanov).

But up to now it was taken (Anderson, Woolard, Melchior, and others), that the formulae of Jeffreys and Woolard, which are used in this method, are valid only for incompressible Earth models.

It is shown in this paper that the formulae are valid for the case of an actual compressible heterogeneous Earth. Thus, the method receives a real practical value. The use of lasers and radio methods in the near future will make this method even more effective.

The full text of the paper will be published in the magazine Physics of the Earth in No. 3, 1972.
On the Torques Due to Tidal Friction of the Oceans and Adjacent Seas
Authors: Brosche P. , Sündermann J.
Published: July 2016

The torques of the frictional forces on the bottoms of the seas are calculated in an approximate inertial system and not in the corotating system used hitherto. In this way, the loss of rotational energy of the Earth – corresponding to the mean torque – can be compared with the value obtained from astronomical observations. The calculations are based on velocities which are computed by numerical integrations of the hydrodynamical equations. Initial results are presented for the North Sea, the Bering Sea and rough models of theworld ocean.
The Wolf-Rayet Stars – The General Problems of Extended Atmospheres and Non-Classical Atmospheric Models
Authors: Thomas Richard N.
Published: July 2016

The Organizers of this Symposium asked that I make some introductory remarks on the general problems of extended atmospheres, the degree of common behaviour among stars having such a feature, and how the Wolf-Rayet stars may contribute to the progress of our inference in this area. In a Symposium entitled Wolf-Rayet and High Temperature Stars, not ‘Stars With Extended Atmospheres’, the implication of your charge to me is clear. You are implicitly assuming that the Wolf-Rayet phenomenon is primarily one of extended atmospheres. I can indeed give you a succinct summary of my outlook on these three points under such an implicit assumption, elaborating in more detail only to the extent as is necessary in order to be specific. And, as I am sure you had planned, because my outlook is considerably contrary to this implicit assumption, at least my remarks will spark controversy from the outset of this Symposium. I would like to emphasize that it is the summary of outlook to which I attach most weight and which I think is correct. The more specific details may change as we develop the mosaic of the summary, which has two main points. First, when you ask the physical picture of the general structure of a stellar atmosphere, you will eventually reach the conclusion that part of this general structure is an extended atmosphere for all stars. A focus upon some class, or classes, of them as exhibiting ‘extended atmospheres’ simply reflects the degree to which particular observations focus upon a particular part of the atmosphere as a function of the particular characteristics of the considered star. Second, in this context, I think that the implication that the Wolf-Rayet phenomenon is primarily one of extended atmospheres is incorrect. You are confusing a single system with a more deep-seated disease. My emphasis will lie on the disease as a whole, and the Wolf-Rayet stars as a guide to its diagnostics. I want to emphasize that this outlook on the general model of an atmosphere has developed jointly with K. B. Gebbie, J-C. Pecker, and F. Praderie; so most of what I say simply reflects this joint work.
Wolf-Rayet Binaries and Atmospheric Stratification
Authors: Kuhi Leonard V.
Published: July 2016

Considerable effort has been expanded on both of these topics ever since the binary nature of most bright WR stars was revealed by radial velocity and eclipse observations and the basic correlation of line-width with ionization potential was discovered. I would like to describe briefly the methods of detection of binaries, to review the percentage of known binaries and to summarize the mass determinations that result from the study of WR binaries.
Summary of Problems and Conclusions on the Nature and Physical Structure of Wolf-Rayet Stars
Authors: Underhill Anne B.
Published: July 2016

The Wolf-Rayet stars were the subject of a symposium held at the Joint Institute for Laboratory Astrophysics in Boulder, Colorado in June 1968. Here there was considerable discussion about whether one should talk about a class of objects called ‘Wolf-Rayet stars’ or whether it was more appropriate to talk about something called the ‘Wolf-Rayet phenomenon’ (Gebbie and Thomas, 1968). The point of view taken in this review is that it is more advantageous for obtaining an understanding of Wolf-Rayet objects to collate the available material under the broad category Wolf-Rayet phenomenon than to attempt to demonstrate that there is a homogeneous set of stars which can be called Wolf-Rayet stars and which occupy a significant stage in the evolution of stars, this stage being traversed routinely by all stars of a certain range of mass.
Classification des étoiles B à partir des raies de l'hydrogéne–Comparaison avec d'autres classifications
Authors: Herman R.
Published: July 2016

Comparaison entre notre classification, basée sur les raies de l'hydrogène (Rc γ, δ, ε W γ, δ, ε), et les classifications Chalonge, Barbier-Morguleff et J. Rountree-Lesh. Il semble que notre classification soit voisine de ces trois autres mais qu'elle est plus sûre dans le cas des étoiles Be.
Some Notes on Stars Near K0
Authors: Roman N. G.
Published: July 2016

Two hundred giant and subgiant stars near K0 were classified twice by somewhat different techniques. The resulting types were in excellent agreement but a comparison of the assigned types with U, B, V colors indicated both an intrinsic scatter in the colors for stars of similar spectroscopic appearance and a problem in either the luminosity classifications or the standard colors or both. Several peculiar stars and a luminous supergiant were also detected.
On the Precision of the MK Spectral Classification System
Authors: Jaschek C. , Jaschek M.
Published: July 2016

It is shown that a large scatter exists in all color-color and color-spectral type diagrams. This scatter can not be neglected and its importance is shown in several examples. A new approach is then developed for the study of the precision attainable in spectral classification. It is found that for A-type stars MK classification is about as accurate as photometry, whereas for B-type dwarfs photometry is at least two times more precise than MK classification. A precision of ±0.6 tenths of a spectral class seems attainable in both groups.
Photometric Classification of B-Type Stars
Authors: Crawford D. L.
Published: July 2016

Several photometric techniques for classification of B-type stars exist. This note describes another one, now nearly ready for publication.
New Standards for the Spectral Classification of M Dwarfs
Authors: Wing R. F.
Published: July 2016

Spectral types based upon photoelectric measurements of the strong TiO band near 7100 Å and having an internal accuracy of one-tenth of a subclass are presented for 26 dwarf stars in the range K4 to M6. For the calibration of the TiO index into spectral type, the MK scale for giants established by Wing and Keenan was adopted. Accordingly the types differ systematically from those previously published on any of the systems used for dwarfs, being closest to Joy's. The advantages of the MK giant scale are discussed, and it is suggested that the stars classified here be adopted as standards for a revised system of MK classification for dwarfs.

The relation between TiO band strength and near-infrared color temperature for dwarfs differs significantly from the giant relation. The coolest dwarfs observed were Wolf 359 and Proxima Centauri; although Wolf 359 is both cooler and less luminous than Proxima, they have nearly identical TiO band strengths.
Quelques sous-naines dans la direction du Grand Nuage de Magellan
Authors: Perrin M.-N.
Published: July 2016

Six G and K type stars, chosen among Fehrenbach's stars, in the direction of the Large Magellanic Cloud, were recognized as metal deficient galactic stars, on ground of multicolour photometry (UBV system and Lick six-color system). Data concerning these stars are given in Tables I and II. The stars are plotted in a U – B/B - V, and in a U – G/G – I diagram.

Three more of Fehrenbach's stars also appear in the Tables and Figures. They are: HD 30 229 and HD 268 957 – Thackeray's extreme and moderate subdwarfs – and HD 270 011, already recognized by Fehrenbach et al. as an extremely deficient galactic giant. This last star falls close to HD 122 563 in the U – G/G – I diagram. The I-Colour of HD 30 229 is probably contaminated by nearby cooler stars.
A Method for Determining Radial Velocities from Objective Prism Plates
Authors: Stock J. , Osborn W.
Published: July 2016

A simple method by which radial velocities of stars may be determined from Schmidt telescope objective prism plates is described, and the results from the initial application of the method are given.
The Theory of Extended and Expanding Atmospheres
Authors: Böhm Karl-Heinz
Published: July 2016

(A) The possibilities and the difficulties of a theoretical study of extended atmospheres in binaries are briefly discussed.

(B) We try to summarize and discuss critically the present status of the theory of three types of extended atmospheres (i.e. atmospheres in which the average photon mean-free-path is the same order of magnitude or larger than the stellar radius):

(1) Extended atmospheres in hydrostatic and in grey or non-grey radiative equilibrium.

(2) Dynamic (expanding) atmospheres which occur if the radiative acceleration is slightly smaller than the acceleration of gravity.

(3) Stellar coronae which are formed in the presence of a mechanical energy flux.

In (1) we study the importance of the ‘forward peaking’ of the radiation field in the outer layers of the atmosphere. The possibilities for the solution of the non-grey transfer problem in an extended atmosphere are discussed.

In (2) we pay special attention to Marlborough's and Roy's (1970) result that the atmospheric gas cannot be accelerated directly to supersonic velocities by the action of the radiation force.

In (3) the large differences in the coronal properties of stars of different chemical composition are emphasized. We draw attention to the partially unexplored but probably very interesting properties of coronae of helium-rich stars.
Equation of State at Densities Greater than Nuclear Density
Authors: Bethe H. A.
Published: July 2016

An equation of state is developed for densities from nuclear density (3 x 1014 g cm−3) to about 1016 g cm−3. The repulsive interaction between baryons dominates and empirical arguments for its existence are given. This interaction is attributed to vector meson exchange, and is derived from classical field theory whereupon a Yukawa potential results. The potential actually assumed is a modification of the Reid potential. Arguments are given that the baryons will not form a crystal lattice. The actual calculations were done using Pandharipande's method. The particles present at high density certainly include nucleons, Λ and Σ. The presence of Δ is questionable but that of π is likely. Results are given for the concentration of various species. With the more likely assumption about interactions, the concentration of each permissible species of particle is about equal at ϱ = 1016 g cm−3. The relation between energy and density is nearly independent of the assumptions on the species permitted and the energy is about 3 GeV particle−1 at ϱ = 1016 g cm−3. The relation between pressure and energy density is given, which yields a sound velocity equal to c at a few times 1015 g cm−3. Results for the structure of neutron stars are given. The maximum mass is about 2 solar masses and the maximum moment of inertia 1045 g cm2.
Phase Diagram of a Charged Bose Gas
Authors: Hansen J. P. , Jancovici B. , Schiff Daniel
Published: July 2016

The phase diagram of a charged Bose gas is drawn. The domains of existence of the solid, fluid and superfluid phases are discussed. It is predicted that superdense helium can be superfluid at densities higher than 106 g cm−3.
Pulsar Observations and Neutron Star Models
Authors: Börner Gerhard , Cohen Jeffrey M.
Published: July 2016

Information about the physical parameters of neutron stars is obtained from pulsar observations. The energy balance of the Crab Nebula and the Vela X remnant allows one to derive limits for the masses of the Crab and Vela pulsars. Glitch observations provide further clues on the masses of these two pulsars. The degree of confidence with which one should believe the derived numbers is pointed out. The possibility of observing neutron stars in binary systems as pulsating X-ray sources is discussed. Finally, the importance of observing redshifted gamma ray lines from the surface of neutron stars, and thus directly measuring either individual or statistical properties of these objects, is pointed out.
Continuum Polarization in Magnetic White Dwarfs
Authors: Lamb F. K. , Sutherland P. G.
Published: July 2016

We discuss some of the effects which magnetic fields in the range 104–108 G have on the continuum emission of white dwarfs. In order to show how atomic processes are related to the transport of radiation in an anisotropic medium we introduce the radiative transfer equation for polarized light. Using this transfer equation as a guide we develop a greatly simplified model of a white dwarf atmosphere: anisotropic absorption of unpolarized light passing through a cold, optically-thin layer. Two possible sources of continuum polarization in white dwarfs with strong magnetic fields are explored, namely bound-free transitions and cyclotron absorption. Within the hydrogenic approximation we develop a further approximation which is valid for bound-free transitions when B is in the range 104–107 G. Using this approximation it is possible to obtain simple expressions for the net circular and linear polarization in terms of the zero-field opacity. In the case of cyclotron absorption, the cross section is large and strongly peaked at the cyclotron frequency, which falls in the infrared or optical for B ⩾ 108 G. This process can lead to net circular and linear polarization of comparable magnitude. For stars with non-uniform magnetic fields, the cyclotron absorption effects are spread over considerable wavelength ranges, with possibly quite complicated wavelength-dependent polarization.
Radio Observations of X-Ray Sources
Authors: Braes L. L. E. , Miley G. K.
Published: July 2016

Observational work on radio emission from galactic X-ray sources is reviewed. Some problems associated with the detection of these weak radio sources are mentioned and our present knowledge of radio identifications is summarized. The radio properties of the most studied objects are discussed in detail.
Galactic X-Ray Polarimetry and High-Resolution X-Ray Spectroscopy
Authors: Novick R.
Published: July 2016

Stellar X-ray spectroscopy and polarimetry are discussed in terms of the source parameters that can be determined through such studies and in terms of the constraints that these studies will place on theoretical models. The spectroscopic and polarimetric results that have been obtained to date are reviewed. These include the recent discovery of X-ray polarization in the Crab Nebula and the recent evidence for X-ray coronal line emission in the Cygnus Loop. Finally, the properties and predicted performance of a number of satellite-borne spectrometers and polarimeters are presented.
High-Energy Discrete Sources
Authors: Fazio G. G.
Published: July 2016

The origin of the gamma-radiation from the galactic plane and the region near the galactic center is still uncertain. However, during this meeting, several groups reported evidence for discrete sources of cosmic gamma-rays. Most of the sources are located near the galactic plane, and some are associated with X-ray sources. The galactic gamma-radiation may be due to these previously unresolved sources. Other sources detected may be associated with variable radio galaxies.

The Crab Nebula still remains the most investigated source at gamma-ray energies. Pulsed emission from NP0532 was detected in the 10 to 30 MeV region, but no continuous emission was observed. At the highest energies, pulsed emission was reported at ∼1012 eV. Continuous emission from the Crab Nebula was observed at ∼1011 eV; the radiation may be time variable.

The recent gamma-ray experiments on Apollo 15 and 16 and the ESRO satellite TD-1 are described, as well as future experiments on the satellites SAS-B, COS-B, and HEAO-B.
Observations of neutral hydrogen in open clusters
Authors: Schmidt-Kaler Th. , Schwartz R.
Published: July 2016

Neutral hydrogen is found in every young cluster observed, usually extending beyond the optical diameter, and in some cases showing expanding motions.