bluuebunny/crossref_metadata_2025_split huggingface dataset:
Star Clusters as Touchstones for Theories of Galactic Evolution — A Few Examples
Authors: van den Bergh Sidney 
Published: July 2016

Observations of NGC 5128 (Cen A) show that this giant elliptical galaxy contains few globular clusters. The fact that the number of globular clusters per unit luminosity in E galaxies has a range of ∼ 102 indicates that different ellipticals were formed in differing physical environments. It is pointed out that more data on the frequency with which globular clusters occur in elliptical galaxies might place interesting constraints on theories of galaxy clustering.Intercomparison of the Local Group galaxies IC 1613 and the SMC shows that differences in the frequency of cluster formation also occur among Irregular galaxies.It is pointed out that globular clusters associated with distant galaxies probably start to outnumber galactic stars for B > 31.The discovery that the LMC supernova remnant N63A is situated in the small association N2030 shows that this object must have been formed from a star with a main sequence mass > 30 M⊙.Finally we show that E3, which is one of the faintest known galactic globular cluster, was decimated by tidal forces. Due to the interplay of equipartition and tidal effects this cluster has been severely depleted in single stars while retaining many (presumably binary) blue stragglers.
A Computer Based Catalogue of Open Cluster Data
Authors: Lyngå Gösta , Lundström Ingemar 
Published: July 2016

The catalogue contains data for 1130 galactic clusters. Each cluster has 255 available storage places. Most of these are reserved for positional, descriptional and physical parameters. In the present version the following items are included:
–Cluster name, OC1 No. (Alter et al. 1970)–R.A., Dec (1950.0), R.A., Dec. (2000.0), precession for 10 years, galactic longitude, galactic latitude–Data on peculiar stars (Feinstein 1979): Type, number, references–Part of Dixon's (1976) catalogue: POSS chart type, chart No., coordinates for chart centre (R.A., Dec), position on chart, largest published angular diameter, magnitude of brightest star, Trumpler class, nebulosity–Part of Bochum-Strasbourg catalogue (Kluke et al. 1975): Selected angular diameter, distance, magnitude of brightest star, spectral class, total magnitude, colour excess–Buscombefs (1978) compilation: Radial velocity, distance, colour excess, total apparent magnitude, total absolute magnitude, linear diameter, age, mass–Basel data (Becker and Fenkart 1971; Fenkart and Binggeli 1979): Photometric system, colour excess, interstellar extinction, distance, spectral type of hottest star, colour type of bluest star, linear diameter, type of observation–van den Bergh-Hagen (1975) data: Angular diameter, richness–Lyngå (1979) compilation: Selected angular diameter, references (various other parameters with references will be included later).
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.
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.
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.
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.
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.
A Laser Polar Motion Experiment
Authors: Smith David E. , Dunn Peter J. , Kolenkiewicz Ronald 
Published: July 2016

SummaryFor 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 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.
Classification des étoiles B à partir des raies de l'hydrogéne–Comparaison avec d'autres classifications
Authors: Herman R. 
Published: July 2016

RésuméComparaison 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.
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.
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.
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.
Theory of interstellar molecules
Authors: Salpeter E. E. 
Published: July 2016

Various estimates are described for the rate of formation of hydrogen molecules on the surface of interstellar grains in H 1 regions. The average abundance of molecular hydrogen relative to atomic hydrogen remains uncertain by a few orders of magnitude.Possibilities are presented for the formation of OH molecules (and, more briefly, for other diatomic molecules), either on the surface of dust grains or by exchange reactions in the interstellar gas after cloud-cloud collisions. The rate for photodissociation of OH in H 1 regions is uncertain.A brief discussion is given of various possible mechanisms for maser action in the OH molecule, such as optical pumping of microwave levels by UV radiation at the edge of an H 11 region. It appears that the narrow OH emission lines must originate in cool gas bordering an H 11 region.
General characteristics of interstellar clouds and their interpretation
Authors: Kahn F. D. 
Published: July 2016

This report is concerned with recent progress on various aspects of interstellar gas dynamics, including an investigation of the Orion Nebula, studies of H 11 regions and of ionization fronts, a statistical model of H 1 clouds and a re-appraisal of the heating and cooling processes in H 1 regions.Dyson has worked out a new model for the Orion Nebula, in which it is supposed that dense pockets of non-ionized gas exist within the H 11 region. He makes predictions concerning the flow of ionized gas around these pockets, and about the possible presence of shock-waves nearby.Mendis has extended Axford's classical description of ionization fronts to include the case in which a front advances into a region where the hydrogen is molecular, and finds that there are a number of consequent changes in the nature of the front. Hjellming has given a comprehensive account of the processes by which a thermal balance is achieved in an H 11 region, and has shown how the temperature in its various parts depends on the distance from the exciting star and on the stellar surface temperature. Mathews has integrated the equations of motion for a growing H 11 region, and has described how ionization fronts develop and when shocks will occur. Lasker has followed the motion further, and has given examples to show how older H 11 regions evolve.By means of a simple model of H 1 clouds, Field and Saslaw have tried to estimate how long it would take to form a massive interstellar complex which would become gravitationally unstable. They find that the time required is relatively short. One must therefore assume that only a small fraction of an unstable cloud can condense into stars, or else the rate of star formation would be too rapid.Finally an estimate is made of the rate at which early-type stars supply kinetic energy to the H 1 clouds, via the expansion of H 11 regions. One cannot, with the present data, decide definitely whether this process is important. A possible alternative would be the acceleration of gas clouds by supernova shells.
Local structure and large-scale motions from young objects
Authors: Schmidt-Kaler Th. 
Published: July 2016

Substitution of the value 3·2 for the ratioRof total visual extinction to reddening leads to a revision of the galactic rotation curve determined by Feast and Shuttleworth. The new results agree very well with the 21-cm rotation curves, particularly with those by Kwee, Muller and Westerhout and by Shane and Bieger-Smith. The corresponding local value for Oort's constant isA= + 15.2 km sec-1kpc-1.With the exclusion of special regions like Orion, the ratioRappears to vary only little about an average of 3·2. This value gives a clearer spiral pattern than the strong variations ofRwithladvocated by Johnson; also it leads to better correlation of velocity with distance at the maxima of differential galactic rotation.
Places of formation of young and moderately young stars
Authors: Strömgren Bengt 
Published: July 2016

Narrow-band photoelectric photometry can furnish classification indices allowing accurate determination of stellar ages. From these ages, together with well-determined space motions, the places of formation of stars, and their relationship to the spiral structure of the Galaxy, may be determined. This procedure has been successfully followed for 52 B8–B9 stars within 200 pc from the Sun. It turns out that seven of these have originated in the Perseus Arm, with local peculiar velocities of about 22 km/sec.A simple model is developed describing places of star formation in the Perseus Arm and velocities at formation. The distribution of space velocities and of ages for stars formed according to this model appears to be in agreement with observation.
An investigation of the properties of vacuum-ultraviolet radiation detectors
Authors: Tiyt Valdur M. 
Published: July 2016

At the Institute of Physics and Astronomy of the Academy of Sciences of the Estonian S.S.R. there is a laboratory for the research on the properties of detectors for vacuum ultraviolet radiation. The laboratory has also the necessary measuring equipment, including a beam double vacuum monochromator for the wavelengths 1000–2700 Å with a balancing-out system of registration attached to it. The last-named device automatically eliminates effects on the results of measurement caused by the distribution of energy in the spectrum of the light source as well as by absorption in the apparatus.Earlier the absolute efficiency of detectors was determined by means of a thermocouple but at present it is calculated from the data obtained from the photoionisation cross sections of gases.The present report throws light on some results of the investigation of the properties of radiation detectors under different operating conditions.
The stellar temperature scale from O5 to A0
Authors: Hayes D.S. 
Published: July 2016

An absolute spectrophotometric calibration of Vega and eleven other standard stars was completed by the author in 1967. This calibration extends from 3200 to 10870 Å, and therefore gives a useful calibration of the Paschen discontinuity as well as the Balmer discontinuity, for which calibrations have been available for some time.The measured values of the ratio of the size of the Paschen discontinuity to the size of the Balmer discontinuity have been compared with corresponding values predicted by model atmospheres. The comparison shows that LTE models satisfactorily predict the continuum in the wavelength range given above.A stellar temperature scale has been determined by fitting the measured sizes of the Balmer discontinuity of 43 stars to blanketed model atmospheres. This temperature scale agrees very well with Morton's modified form of the Morton-Adams temperature scale for all except the latest B-stars, for which higher temperatures are predicted.
Ultraviolet photometry of stars from OSO II
Authors: Hallam Kenneth L. 
Published: July 2016

Ultraviolet stellar fluxes from 1500 to 3200 Å were from February through August 1965 on OSO II. A 15-cm diameter Gregorian telescope with a stepped grating spectrophotometer provided flux measurements in ten adjacent 180 Å wide band passes.By comparing fluxes of stars showing B-U color excesses smaller than 0.19 and larger than 0.26, an ultraviolet extinction curve has been derived, which agrees with others which have been published as far as the magnitude effect is concerned, but the shape differs somewhat, the slope at 1/λ = 3.8 μ−1 being somewhat greater than at 1/λ = 5.0 μ−1.If the stars' fluxes are corrected for reddening, it is found that there is a good agreement between observation and models for stars earlier than B3, but that many of the later type stars have a residual apparently intrinsic reddening.