bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Investigation of Lunar Limb Structure by Means of Stellar Occultations
Authors: Evans David S. 
Published: March 2016

It has long been recognized that the analysis of occultation traces from point source stars might provide a means of investigating the structure of the lunar limb on a remarkably small scale, certainly of tens of meters, possibly on a scale of meters.The routine process of analysis of such an occultation trace produces a curve fitted to the standard model for a point source, in which the observed rate of fringe passage is matched to that computed from the rate and position angle of the relative motion of the moon with respect to the star background and the position angle of the point at which the occultation occurs. If θυ is the position angle towards which the relative motion of the lunar center takes place, θ that at which the occultation occurs, and ψ = θν — θ, then the predicted rate of the lunar limb perpendicular to itself at this point isRp = V cos ψwhere V is the velocity of the lunar center.
The Effects of Filters and Colour on Stellar Occultations and Appropriate Deconvolution Procedures
Authors: Krishnan T. 
Published: March 2016

AbstractThe theory of the effect of bandwidth of lunar occultations is reviewed. It is recalled that effective beamshapes can be calculated for symmetrical bandpasses and that their widths are related to the absolute width in wavelength of the bandpasses. Restoration with the second differential of the theoretical Fresnel diffraction curves at the central wavelength, at the correct rates, yield source distributions as viewed by these beamshapes. It is shown that for asymmetric bandpasses, the real and odd parts taken about the centroids lead to equivalent even and odd beams. Assuming an approximate color temperature for the stars, the total system response can be evaluated and hence the even and odd parts. Restoration of the data should then be performed using the second differential of the Fresnel curve at the centroid wavelength to minimize the odd part, adjusting zeroes, rates, and centroids by inspection. The even part should then represent the even theoretical response convolved with the one-dimensional stellar distribution, provided the latter is circularly symmetrical.The technique is applied to the occultation observation of λ-Aquarii by Nather et al. (1970) leading to closely similar results.
Analysis of Lunar Occultation Data
Authors: McCants M. M. , Nather R. Edward 
Published: March 2016

AbstractThe technique of model fitting has been applied to the analysis of data obtained from photoelectric measurements of lunar occultations. A model occultation curve is generated and fitted, by least squares, to the observed light curve, and by this method the values of the model parameters are determined, together with their formal errors. This technique is contrasted with Scheuer’s deconvolution procedure by applying both methods to the same observed data.
Angular Diameters of the Red Giants 46 Leo and φ Aqr and Parameters of some Binary Systems from Occultation Observations
Authors: Poss Howard L. 
Published: March 2016

AbstractAngular diameters of 0″.0056 ± 0.0011 and 0″.0049 ± 0.0008 have been calculated for the red giants 46 Leo and φ Aqr respectively from occultation observations. The occultation curves of α Lib and ε Cap show that they are binary systems. The separation of the components of the visual binary ε Ari, as calculated from its occultation curve, is 1.3 times its reported value. The occultation curve of α Leo shows distortion effects which are attributed to irregularities in the lunar limb.
Pulsars and the Origin of Cosmic Rays
Authors: Gold T. 
Published: March 2016

The basic idea that pulsars may be the origin of cosmic rays arises when one realizes that they meet some of the criteria, perhaps not all as yet, for an origin theory of cosmic rays. Those criteria are: (1) there must be some possible mechanism that one can recognize for the acceleration of particles; and the pulsars have given us a very clear hint that particles are accelerated to at least the medium range of energies of cosmic rays - 1013 eV. (2) The objects that are thought responsible for cosmic rays must have enough total energy available to them to produce the entire cosmic ray beam in the Galaxy. I will come back to that, but it is clear that the total number of pulsars that one might expect in the Galaxy can indeed produce an adequate supply and even a good margin above that, if one makes the estimate on the basis of one plausible set of assumptions. (3) One would like of course that the mechanism proposed should generate the right spectrum; but there we as yet know too little. We do not understand what the energy spectrum of particles accelerated in pulsars should be, and we cannot as yet make any conclusive statement as to whether this spectrum can or cannot match the observed cosmic ray spectrum in the Galaxy. There is no reason for thinking otherwise, but there is no positive evidence in favor at the moment.Then we have (4) the problem that the process selected must generate the correct composition. There we have the problem that we have just discussed, which is certainly a difficult one; I don’t know that it is completely clear what type of particles you must expect to come from pulsars; how much of the material accelerated in the vicinity of the pulsar is material that is being cycled into it at the time and going out again; and how much is material which is preferentially sucked out of the surface, perhaps by reason of a high charge-to-mass ratio.
Some Problems and Instrumental Features of Submillimeter Astronomy
Authors: Salomonovič A. E. 
Published: March 2016

Modern astronomy includes optical, ultraviolet, infrared and, in recent years, radio, γ-ray, and X-ray astronomy. Such a classification is justified to a certain degree. In fact, the difference in wavelength ranges causes a distinction in the methods and techniques of receiving radiation. Also, the solution of specific problems requires observation in different wavelength regions. In this respect it is possible to describe a new astronomical branch, the submillimeter one.The submillimeter range is intermediate between the infrared and microwave regions, as shown in Table 1. The boundaries of this region are not very definite. Some authors include in the submillimeter range the wavelengths longer than 50 microns, others, those longer than 100 microns. The long wavelength edge of the range is also diffuse. Formally it is a wavelength of 1 mm, but in some cases the 2-mm or 4-mm wavelengths are also included in the submillimeter range. The measurements of submillimeter receiver performances are sometimes carried out at wavelengths up to 8 mm. The uncertainty of the boundaries is very understandable: their shifting depends on the methods of generation, transmission, and detection of radiation. In this review paper, following Martin’s (1962, 1963) terminology, wavelengths between 50 microns and 2 mm will be attributed to the submillimeter range.
Preliminary Results of the Determination of Absolute Proper Motions of Stars Referred to Galaxies
Authors: Fatčihin N.V. 
Published: March 2016

Absolute proper motions have been determined for 14000 stars in the 82 areas indicated in Figure 1. These proper motions result from measures made on 105 plate pairs taken with the Pulkovo normal astrograph which has a focal length of 3·5 m. The plates, which had an average epoch difference of 22·4 years, were measured film-to-film in a Repsold measuring machine. The number of galaxies used for defining zero proper motion was 271, and among the stars measured were 1283 from the AGK3. The probable error of a determination of proper motion from one plate pair wasThe images of the galaxies were estimated as having an average quality of 6 on a scale of 10. (Deutsch et al., 1955).
Radio-Source Spectra and their Time Variations
Authors: Kellermann K.I. , Pauliny-Toth I.I.K. 
Published: March 2016

During the past few years there has been a large increase in the available data on the spectra of radio sources, particularly at short wavelengths, where a number of sources have shown unexpectedly large time variations, with time-scales of 1 year or less.The simple power-law spectrum, which is a straight line on a log-log plot of flux density against frequency, is shown by about 30% of sources. Most sources have a spectrum with negative curvature, which steepens at high frequencies. Many have a sharp cut-off, which is almost certainly due to synchrotron self-absorption, at low frequencies. In several of these sources, such as 3C 48, 3C 147 and 3C 295, the spectrum begins to flatten at a considerably higher frequency than the cut-off frequency. This flattening is too sharp to be caused by a change in the energy distribution of the electrons and is probably due to parts of the source becoming optically thick at higher frequencies. Some sources have components which are optically thick even at centimetre wavelengths. These must have angular sizes of 10−3″ or less. The energy density in relativistic electrons in these compact sources is much larger than the magnetic-energy density, so that the source cannot be stable and variations in the flux density are to be expected.
Hard Solar X-Ray Bursts
Authors: de Jager C. 
Published: March 2016

A tentative spectrum of the Sun in the X-ray region is shown in Figure 1 (De Jager, 1967). The quiet Sun emits a measurable spectrum at photon energies below about 3 keV. During the occurrence of solar flares an enhancement of the emitted energy, and a hardening of the spectrum is clearly visible. The soft X-ray bursts apparently show a maximum radiation flux at wavelengths of about 10 Å.In the spectral region above about 10 keV hardly any quiet solar radiation is observable. During the occurrence of solar flares hard X-ray bursts are occasionally observed. From the point of view of observational techniques these bursts may be divided in the so-called deka-keV bursts, covering the range 10-200 keV, and the deci-MeV bursts in the range between 0·2 and 1 MeV. Many deka-keV bursts have been observed during the years 1966-67 by Winckler et al., by means of the OGO-I and OGO-III satellites (see Arnoldy et al., 1967). The existence of deci-MeV bursts has been doubted various times (see e.g. Chubb et al., 1966). Its reality seems now to be proved (see also De Jager, 1967). However, they may be much rarer than the deka-keV bursts, although it is not yet completely sure that the selection is not observational.
The Physics of the Interstellar Matter
Authors: Field G. B. 
Published: March 2016

Some of the most striking recent discoveries about interstellar matter involve molecules. It has been known for a long time that there are atoms and ions in space - mainly hydrogen and helium, of course - but also heavier elements like sodium and calcium. In addition, there are solid particles of dust, about 10-5cm across, which must be composed of heavier elements, as hydrogen and helium cannot condense under interstellar conditions.In 1972, the Orbiting Astronomical Observatory-3, which employs an 80-cm telescope at wavelengths between 1000Å and 3000Å, was launched in the United States and put into operation. In the ensuing year, it has demonstrated that much of the interstellar medium is composed of hydrogen molecules. This result, based upon the observation of Lyman-band absorption in the spectrum of early-type stars, had been anticipated by a rocket observation of H2 by Carruthers in 1970.The same OAO-3 instrument observed resonance lines of many cosmically abundant elements, and found that these elements often appear to be less abundant in interstellar space than in the solar system, relative to hydrogen. As young stars born recently from the interstellar medium do not show this effect, the heavy elements must in fact be present in some other form. Here I will argue that the heavy elements are largely locked up in the form of the dust and, further, that dust is critical for the formation of the molecules in interstellar space.It is appropriate that the Orbiting Astronomical Observatory-3 which made these discoveries has been named in honor of Copernicus, the Polish astronomer we honor here on the 500th anniversary of his birth. Just as his discoveries were revolutionary for the understanding of the solar system, those made using the Observatory named in his honor have been revolutionary for the understanding of the Galaxy.
Scans and Narrow-Band Photometry of Late-Type Stars in the One-Micron Region
Authors: Wing R. F. 
Published: March 2016

AbstractA summary is given of the molecular bands occurring in the near-infrared spectra of cool stars, especially those having sufficient strength and freedom from contamination to be measurable by narrow-band photometry. In some cases useful indices of both temperature and luminosity can be obtained from such measurements. Several bands remain unidentified, including the 9910 Å band in late M dwarfs and at least nine bands in cool S stars.Three topics of a spectroscopic nature are discussed. (1) In Mira variables, grossly different spectral types are sometimes obtained from zero-volt and excited TiO bands of the same band system. (2) A few M stars have been found to show bands of’ both VO and CN at the same time. They may be the coolest known supergiants, although there remains some doubt as to their luminosities. (3) The first results are given from a program of measuring crude C12/C13 ratios from narrow-band photometry of sensitive points on the profile of the ∆υ = + 2 band sequence of CN. The observations require only a few minutes per star, and the method can be applied to G and K giants and supergiants as well as to carbon stars.
Medium Resolution Stellar Spectra in the Two-Micron Region
Authors: Hyland A. R. 
Published: March 2016

AbstractThe role of medium resolution spectroscopy in the two micron region is discussed. Examples of the spectral features amenable to observation are shown. These include the vibration rotation bands of the important molecules 12C16O, 13C16O, H2O and CN, as well as the By line of hydrogen. Band strength-colour and -luminosity relations for the CO and H2O bands have been derived from observations of approximately 100 stars of spectral types later than G5. The interpretation of these and the outstanding problems (such as the colour dependence of the CO band strengths in carbon stars) are discussed.Examples of the use of two-micron spectroscopy in the spectral classification of infrared sources, and the infrared components of symbiotic stars, etc., are shown. The extension of this kind of observation to the nuclei of galaxies is briefly discussed in relation to stellar population studies.
Fourier Transform Spectrophotometry and its Application to the Study of K-Giants
Authors: Ridgway S. T. 
Published: March 2016

AbstractA Fourier Transform Spectrometer has been employed to obtain low and medium resolution spectrophotometry in the range 700 to 10000 cm-1. The method is described briefly and typical data are shown. The technique is applied to a study of 15 K giants, and spectra of 4 and 16 cm-1resolution in the range 4000 to 6500 cm-1 are discussed briefly. CN strong stars are found to be CO strong as well. Five K giants are found to have a relative 13C enhancement over probable primordial abundances.
Stellar Spectroscopy at 1.1 μ
Authors: Zirin H. 
Published: March 2016

This is a progress report on the program of stellar spectroscopy at 1.1 μ reported on by Vaughan and Zirin (1968) and by Zirin (1971). About 450 plates of about 200 stars have been obtained, using a magnetically focused RCA image converter with the 144” and 72” Palomar coudé cameras, giving dispersion of 8 and 17 Å mm-1 respectively. Most of the plates were taken at the latter dispersion and cover about 300 Å. In good seeing a star with J = 3 is obtained in about 90 min. A tube with a fibre optic backplate is now in use. Cooling such a tube is difficult because the cathode is held at high voltage. By completely insulating the cold box, we may use dry ice cooling, and 2 h exposures, reaching J = 5, may be made with this ITT tube.Our principal interest in this region of the spectrum is the He I 10830 line, but there are other features of interest such as Paschen y and a series of CN bands, λ 10830 is of particular interest because it is produced at relatively high temperatures and thus its presence in stars later than B5 can only be explained by the existence of a high temperature corona or chromosphere or of a strong ultraviolet source, which amounts to the same thing. Vaughan and Zirin found the presence of such chromospheres in a number of stars, and I have pursued the matter since then to determine the existence of chromospheric variability. The 10830 absorption in the Sun is very small from the normal chromosphere and is principally due to the presence of active regions. Emission is only found in large flares. Thus cyclic variations in Sun-like stars could be attributed to sunspot cycles. Unfortunately, main sequence stars are near the limit of our observations. Although definite 10830 absorption has been found in such main sequence stars as 61 Cyg A and B, 70 Oph br, K Cet and ε Eri, the absorption is just barely detectable and variation from plate to plate could be explained by variable quality.
The Ages of Stars in the Neighbourhood of the Sun
Authors: de Strobel G. Cayrel 
Published: March 2016

This introductory paper is divided into two sections.In the first section a short summary is given of the IAU Colloquium No. 17 on Stellar Ages held in Paris-Meudon Observatory in September 1972. The summary will concern particularly those subjects relevant to this Joint Discussion.In the second part the ages of nearby stars located in the subgiant region of the (log Teff, Mbol) diagram are discussed.
The Shell of V603 Aql and the Early Stages of the Nova Event
Authors: Weaver H. 
Published: March 2016

Nova V603 Aql 1918 was uniquely suited for studies of the structure of its shell because of the very favorable orientation of the shell in space. Additionally, almost by chance, spectroscopic observations were made in such a way that they permitted derivation of a three dimensional model of the shell.V603 Aql, as we see from its light curve (Figure 1), was a typical fast nova which showed strong periodic fluctuations in light during the transition stage. The period of fluctuation was approximately 10 days, during which time the visible light changed by roughly 50%.
Exploration of the Planets: An Invited Discourse Presented before the Sixteenth General Assembly of the International Astronomical Union Grenoble, France, August, 1976
Authors: Sagan Carl 
Published: March 2016

Until recently the entire astronomical endeavor was restricted to passive observations from the surface of the Earth. Natural experiments — such as stellar occultations, eclipsing binaries, or supernova explosions — might fortuitously arrange themselves, and systematic inventories were performed of information carried by reflected or emitted electromagnetic radiation. But it is only in the last twenty years that our species has been able to carry out in situ experiments on astronomical objects.Radar astronomy permits a kind of experimentation on solar system objects not too distant from Earth, and has made a number of major discoveries, including the determination of the 3:2 spin/orbit coupling of Mercury, the Earth-locked retrograde rotation of Venus, and major elevation differences on Mars. Radar is the tool of choice for geomorphological mapping of cloud-enveloped Venus, and efforts now underway at the Arecibo Observatory should lead to complete mapping of one hemisphere of Venus down to 10 km resolution. The radar reflectivity of the rings of Saturn has forced a rethinking of the nature of the constituent particles in the rings; and a determination of the radar cross-section of Titan is an experiment which can resolve much of the uncertainty about the atmospheric structure and surface pressure for that enigmatic and fascinating object.
The Galaxy Content of Clusters
Authors: Oemler Augustus 
Published: March 2016

Clusters of galaxies are easily identifiable collections of galaxies, all at the same distance and all observed under similar conditions of galactic obscuration, etc. They are, therefore, very convenient samples with which to study the matter content of the universe. However, clusters are also very particular physical environments, and from this latter point of view it is their atypical character which is of interest. The differences in the contents of one cluster from another, and of each from the contents of small groups and the “field” can teach us much about how the properties of galaxies depend on the environments in which they were born and have evolved.Because of the interrelatedness of these two points of view, one cannot really understand the galaxy populations of clusters until one also understands the populations of galaxies which are not in clusters. Therefore, while this review will concentrate on the contents of rich clusters of galaxies, it will also be necessary to discuss the properties of non-cluster galaxies.
The Existence of High-Order Clusters of Galaxies
Authors: Kalinkov M. 
Published: March 2016

The problem of the existence of high-order clustering of galaxies is a basic one in extragalactic astronomy and cosmology. In a conventional formulation this problem consists of indicating the largest configurations in the spatial distribution of galaxies.All treatments are carried out generally on the material presented in the catalogues of Abell (1958) and Zwicky et al. (1961-1968). However catalogues of the Jagellonian type (Rudnicki et al. 1973) may turn out to be extremely valuable. The nature of the observational material demonstrates that only statistical methods may be applied effectively. It is already clear that the expected effects are not large even if high-order clustering is a basic property in the Universe.
Some Research Programmes Into Galactic Structure at the Galactic Caps Under Way at the Royal Greenwich Observatory
Authors: Jones D. H. P. 
Published: March 2016

The R.G.O. has a continuing programme to investigate both the density and motions of the stellar content of the solar neighbourhood. Gaps in current knowledge are wider for the fainter stars which are found in proportionally greater numbers near the galactic poles. Our approach divides naturally into two questions: (i) What are the proportions of red dwarfs to giants at each apparent magnitude? and (ii) What are the corresponding total numbers of red stars?Question (i) was first tackled by a narrow-band photometric search for M dwarfs (Jones 1973). This approach is continuing and a progress report has been delivered (Jones 1976). To push the search deeper 41 stars in the South Galactic Cap (mostly fainter than V = 15) selected by P.S. Thé from a survey with the Lembang Schmidt as being M2 or later were observed with the Robinson-Wampler Scanner on the 150-inch A.A.T. The Na D lines, CaH and the band at λ5500 tentatively identified by Pesch with CaOH have been measured. Column density calculations of CaOH for giants and dwarfs of different temperatures support Pesch’s identification. Nearly all the stars are dwarfs but only seven appear in proper motion catalogues, (Thé and Staller 1974). At the galactic caps most stars brighter than V = 12 are giants and fainter dwarfs. The transition zone is only 10-14.
Galactic Mass Density in the Vicinity of the Sun
Authors: Joeveer M. , Einasto J. 
Published: March 2016

It is possible to estimate the galactic mass density in the solar neighbourhood either directly by summing up the mass densities of individual subsystems of stars and interstellar matter or indirectly from dynamical considerations.Observational data on the number density of visible stars lead to mutually consistent results on the stellar component of the mass density. The mean of different estimates is ⍴stars=0.052±0.010 Mʘpc−3. By adding the probable contributions of intrinsically faint undetected objects and of interstellar matter the value ⍴=0.09±0.02 Mʘpc−3 has been obtained for the total mass density.