bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparison of the classification systems of luminous stars in the northern Milky Way II and IV, for stars assigned two-dimensional spectral types from objective-prism plates
Authors: Stephenson C. B. 
Published: July 2016

For some years a survey for early-type luminous stars in the northern Milky Way has been underway at the Warner and Swasey Observatory and the Hamburg Observatory, as a joint project by the two institutions (1). With the aid of ultraviolet-transmitting objective prisms (Schott UBK7 glass), it has been possible at both institutions to recognize OB stars at a dispersion of about 600Å/mm. Moreover, the appearance of the Balmer discontinuity at low dispersion affords a valuable aid to two-dimensional classification of stars of late B to late F types (2, 3). These two-dimensional classifications, which are based essentially upon the appearance of the continuum (especially the Balmer discontinuity), the hydrogen lines, the K line, and the G band, are assigned in the MK classification nomenclature since they are well correlated with classifications made by means of the real MK classification criteria. The quality of the correlation depends upon location in the HR diagram, but the random probable error appears to be upward of one MK luminosity class and about a quarter of a full letter division in temperature class, except that luminosity class IV is nowhere well distinguished from class V, and class Iab is not really well distinguished from Ia and Ib.The present Cleveland system of assigning two-dimensional spectral types to stars from ultraviolet-included objective-prism plates tends to assign lower luminosities than those of the LS II (–LS I?) system. This fact alone accounts for certainly most of the difference between the numbers of stars assigned two-dimensional spectral types in LS II and in LS IV. The origin of this systematic difference of over a luminosity class is not well explained, but the difference is hardly alarming. The numbers of OB stars in the two catalogues are quite comparable and this is consistent with the fact that no classification system difference for OB stars is known to exist between these two catalogues.Slit spectrograms so far available support the belief that LS IV agrees better in the mean with the MK system than does LS II, though LS IV may also be slightly overluminous in the mean. There is one factor always tending to confuse the transformation from this objective-prism system to MK spectral types: stars having abnormally strong Balmer discontinuities will usually be included in our catalogues with some kind of MK classification, While those with abnormally weak Balmer discontinuities will more often be excluded or assigned to the OB group. This problem is by no means so serious as to detract significantly from the desirability of making objective-prism surveys that pay special heed to the Balmer discontinuity.
Statistical analysis of classification
Authors: Deeming T. J. 
Published: July 2016

If we make a set of measurements, such as narrow-band or multicolour photo-electric measurements, which are designed to improve a scheme of classification, and in particular if they are designed to extend the number of dimensions of classification, i.e. the number of classification parameters, then some important problems of analytical procedure arise. First, it is important not to reproduce the errors of the classification scheme which we are trying to improve. Second, when trying to extend the number of dimensions of classification we have little or nothing with which to test the validity of the new parameters.Problems similar to these have occurred in other areas of scientific research (notably psychology and education) and the branch of Statistics called Multivariate Analysis has been developed to deal with them. The techniques of this subject are largely unknown to astronomers, but, if carefully applied, they should at the very least ensure that the astronomer gets the maximum amount of information out of his data and does not waste his time looking for information which is not there. More optimistically, these techniques are potentially capable of indicating the number of classification parameters necessary and giving specific formulas for computing them, as well as pinpointing those particular measurements which are most crucial for determining the classification parameters.
Spectrophotometry and multicolour photometry at the Royal Observatory, Edinburgh
Authors: Guthrie B. N. G. , Lawrence L. C. , Nandy K. , Pratt N. M. , Reddish V. C. 
Published: July 2016

During the past 2 years, the 16, 24, 60-inch Schmidt telescope of the Royal Observatory, Edinburgh, has been used intensively on programmes of multicolour photometry and objective-prism spectrophotometry. The objectives of these programmes are concerned broadly with how, when, and where stars form, and may be classified as follows:(a) To make a detailed examination of the wavelength dependence of interstellar obscuration, at different distances, and in different galactic longitudes. This will make an essential contribution to the distance determinations in (b) and (c); it is of importance to the study of the physics of interstellar matter and hence also perhaps of star formation; it is a necessary part of the information on which a choice of wavebands for multicolour photometry must be based.(b) To contribute to the determination of the ages, absolute magnitudes and distances of early-type stars, and the distribution of obscuring matter in selected regions of the Galaxy. This will give information on the rate of formation of stars, as a function of time, in various regions.(c) To contribute to the determination of the luminosity functions and ages of stars in open clusters and associations.
A Surface Polarization Survey of the Milky Way and the Zodiacal Light
Authors: Staude J. , Wolf K. , Schmidt Th. 
Published: July 2016

An elliptical Surface polarimetry of the Night Sky has been carried out at the Boyden Observatory, South Africa. The Milky Way is linearly polarized by p = 1 to 2 % (Figure 1); 11 regions also show a circular polarized light contribution (Table I).The amounts of circular polarization near v ≈ 0.1 % or less, observed within the Zodiacal Light, are generally not exceeding twice the error of measurement: see Staude and Schmidt (1972). (v > 0 is defined by clockwise rotation, looking against the light source).
Molecular Distributions in Galactic Sources
Authors: Dickel Hélène R. 
Published: July 2016

The 4830 MHz absorption line of formaldehyde has been observed in the SNR complex W44 and the H ii region complex W3. The results are presented as maps of apparent optical depth. The formaldehyde is concentrated toward the eastern edge of the shell and reaches a maximum apparent optical depth of 1.5 compared with 0.2 for OH; furthermore the centers of the H2CO and OH concentrations are displaced by about 6′. The velocities of the H2CO and OH agree and both molecular lines have the same velocity gradient across the source.The H2CO absorption profiles for W3 (IC 1795) exhibit at least two narrow components whose average velocity becomes more negative toward the NE. The greatest optical depth occurs where the optical obscurration is high but not at the position of maximum Av. A general agreement between the velocities of other molecules and the H2CO values is indicated.
Cyanoacetylene: New Lines and Sources in the Galaxy
Authors: Morris M. , Palmer Patrick , Turner B. E. , Zuckerman B. 
Published: July 2016

Microwave emission from the J = 8 → 7 through the J = 11 → 10 rotational transitions of HC3N has been detected in the directions of Sgr(NH3A), Sgr B2, and Orion A. A map of the J = 8 → 7 emission around Sgr B2 shows that the emitting region extends at least 2′ in galactic longitude and 3′ in galactic latitude. Column densities may be comparable to those of HCN in some sources. This molecule is thus more abundant in the interstellar medium than would be expected from its complexity, and may provide clues to formation processes where it is found.With a reasonable model for excitation of the rotational levels, we have used the ratio of antenna temperatures of these 2 lines to derive a value for the molecular density in the region where the lines originate. For Sgr B2, this yields NH2 ≈ 106, and for Sgr(NH3A), NH2 ≈ 6 × 104.
An observational study of the interaction of impulsive and periodic perturbations in the solar atmosphere
Authors: Deubner F.-L. , Kleineisel R. 
Published: July 2016

Time series of simultaneous high resolution filtergram observations in white light and in CaK2 have been employed to study the dynamical interdependence of the ‘low’ and the ‘high’ layers of the solar atmosphere, the 3-D propagation of perturbations in the stratification, and the excitation of p-mode and other oscillations. Impulsive and oscillatory perturbations have been isolated in the wavenumber and frequency regime, and their mutual interaction was also studied.Several of our findings challenge interpretation and deserve further study.
•The occurrence of a granule can be clearly recognized in the upper chromosphere.•A granule induces low brightness and low oscillation amplitudes at the CaK2 level, whereas the opposite happens at the intergranular border.•It is not always evident that the ‘source’ of the perturbation is located at the lower, i.e. the photospheric layer.•It is far from being clear which components of the various perturbations contribute to a net outward mechanical energy flux.
Refraction in radioastronomy
Authors: Altenhoff Wilhelm J. 
Published: July 2016

In the last few years there was no paper in the astronomical literature reporting on new measurements of radioastronomical refraction. But there are some important review papers on different aspects of this topic, e.g. on the ionosphere by M.M. Komesaroff (1960) and T. Hagfors (1976), on the prediction of tropospheric refraction with ground based meteorological data by B.R. Bean (1962), B.R. Bean and G. Teleki (1974), and R.K. Crane (1976), on range measurements, predicted again by surface weather data, by H.S. Hopfield (1971).For astrometry only interferometric observations give the necessary positional accuracy. The result of the interferometer is not affected, if the delay by the atmosphere is the same for each antenna, therefore this technique is not sensitive to normal refraction.Differential delays can originate in the uneven distribution of water vapor in the atmosphere. Wesseling et al (1974) measured these differential delays with an infrared hygrometer; their attempts to correlate the water vapor with the observed interferometer phase were only partially successful.Hinder (1970) has investigated the differential delays as function of baseline and of season. One can conclude that improvements of positional accuracy either by going to longer baselines or to shorter wavelengths depend on the success to predict the differential delays either by infrared hygrometers or similar means.
Environmental systematics and astronomical refraction II
Authors: Hughes James A. 
Published: July 2016

The role of urban heat islands in producing systematic isopycnic tilts is explored in more detail, and with greater rigor, than in Part I of this series. (Perth, 1974).Specifically, a three dimensional integration is carried out, and light rays are, in effect, “traced” through the resulting perturbation field by evaluating the integral of anomalous refraction. This is done for various values of the parameters, viz., wind direction and observatory location relative to the heat island, strength of the central perturbation, zenith distance of the observed object, etc.It is stressed that heat islands are not the only source of such systematic effects.Finally, a brief discussion of some possible methods of determining observationally the effects here treated theoretically, as well as other site dependent effects, is appended.
Path length variations due to changes in tropospheric refraction
Authors: Anderson Allen Joel 
Published: July 2016

An experiment is described in which microwave Doppler is used to determine very small changes in path length to spacecraft tracked by the Deep Space Tracking Network (DSN). The experiment was carried out to test the detection capabilities of the DSN system to gravitational radiation of very low frequency (10−2–10−4 Hz). In this work spectral analysis of Doppler variations were performed for periods over 4 hours and more.These results indicated that one of major sources of noise was due to rapid variations in tropospheric refraction. The results obtained a differential path length variation, ΔL/L, of 1 part in 1014 for periods between 100 and 1 000 seconds.Doppler spectra are shown and a general discussion of the experiment is given.
A Summary of the Observations of the Twin QSOs, 0957+561 A, B
Authors: Chaffee Frederic H. , Weymann Ray J. , Davis Marc , Carleton Nathaniel P. , Walsh D. , Carswell R. F. 
Published: July 2016

An analysis of all observations of the “twin” QSOs, 0957+561 A, B, to date does not yet allow us to distinguish between their being two nearly identical QSOs or a single QSO split into two images by an intervening gravitational lens. The more identical the two objects are found to be, the more difficult any explanation which postulates the existence of two distinct QSOs becomes. Jodrell Bank and VLA observations reveal additional radio structure to the northeast of the northern QSO image which, if physically associated with a single QSO doubly imaged by a gravitational lens, would itself be imaged weakly to the southwest. More detailed radio mapping should be able to test the existence of such an image.The VLBI map of Porcas and his collaborators reveals that the radio images corresponding to the optical ones are point sources separated by 6.175 arcsec having an angular extent to less than 20 milliarcseconds, whereas all further radio structure is resolved out.Optical spectroscopy of the twins reveals two nearly identical sources with indistinguishable emission line redshifts and with absorption line redshifts identical to within 15 km/sec. It is the identity of these optical characteristics which makes all non-gravitational lens hypotheses most difficult.The most compelling test of the lens hypothesis is the measurement of time variations of the two images at as many wavelengths as possible. If brightness variations of one image are repeated by the other after a time interval determined by the details of the observerlens-QSO geometry (such an interval could be of the order of many months or years) the lens hypothesis would be confirmed. Several observations indicate prior variations of the images, and programs to monitor their relative brightness in the future will be of great importance.
Waves and Oscillations in the Chromosphere in Active and Quiet Regions
Authors: Giovanelli R. G. 
Published: July 2016

Oscillations and waves have been observed in Hα in sunspot umbras and penumbras. They appear to be basically of the Alfvén type, but do not carry away sufficient energy to account for the sunspot energy deficit.There is a pronounced difference in the velocity structures of supergranule centres and boundaries. In the former it is oscillatory, of shorter period but bigger amplitude than in the photosphere. In the network there are oscillations of the fibrils but, on the whole, little evidence of wave motion along their lengths except perhaps near their diffuse ends.In plages, there are velocity oscillations which at times may be phase coherent over extensive regions up to 105 km apart; there are suggestions of a connection between these times and the occurrence of flares. There is also a report of a velocity pulse travelling along an active-region fibril with a velocity of propagation of 150 km s-1.
A Theoretical Model for the Convection of Magnetic Flux in and near Sunspots
Authors: Meyer F. , Schmidt H. U. , Weiss N. O. , Wilson P. R. 
Published: July 2016

In this paper we investigate the physical processes that lead to the growth and decay of magnetic flux in and near sunspots.An initial phase of rapid growth is characterized by the emergence of magnetic flux from the deep convection zone. As the flux rope rises through the surface the magnetic field is swept to the junctions of the supergranular network where sunspots are formed. These flux concentrations follow the footpoints of the emergent flux rope as they rapidly move apart.
The Chromospheric Energy Balance
Authors: Piddington J. H. 
Published: July 2016

The problem of the solar atmospheric heat and energy balances is here divided into three sections.
(i)Basically the problem is an outward temperature gradient involving additional radiation losses whose estimate involves a model atmosphere. Proposed models described are based on optical and radio emissions together with various theoretical considerations such as thermal conductivity. The models are useful in providing estimates of the required flux of mechanical energy from below. However, they are limited by the use of averaging processes, and the failure to take full account of the many structural features which make up the chromosphere.(ii)It has long been accepted that the main energy input is by acoustic waves generated in the ‘small-bubble’ Vitense model convection zone. We review recent observations of chromospheric magnetic and velocity fields and their interpretation which strongly suggest that this model is not valid and that the acoustic theory of heating is without basis. At the same time the new data remove the objections of Osterbrock and others to a theory of heating based on Alfvén and/or slow-mode hydromagnetic waves.(iii)Observations of a variety of individual magnetic-plasma chromospheric structures, together with the adoption of heating by waves which follow the field lines, suggest a new approach to the whole problem of the heat balance. We discuss the heating problem in a number of these magnetic-plasma structures including the emission network, spicules and related disk features, arch filament systems and flares.
Observations in Chile and Results Related to Southern Hemisphere Systems (Invited Paper)
Authors: Anguita C. 
Published: July 2016

The astrometric observations made at the Cerro Calán observatory with several instruments since 1962 are outlined. The resulting catalogues are in press or approaching publication, and are described in some detail. An account is given of the observational projects currently in progress.The various catalogues are combined in order to demonstrate the large and well-determined systematic differences in Δαδ cosδ between the Cerro Calán observations and the FK4. It is concluded that the FK4 system requires some improvement if it is to fulfil the requirements of a fundamental reference system in the southern hemisphere.
Position Solution of Compact Radio Sources Using Long Coherence VLBI
Authors: Gubbay J. S. , Legg A. J. , Robertson D. S. 
Published: July 2016

Compact components of several radio sources were observed in the course of VLBI observations at S-band between NASA-JPL Deep Space Stations located in Australia, South Africa and California, U.S.A., during the southern summer of 1971–72. These stations were equipped with H-maser frequency standards over this period so that the fringe frequency could be determined to better than 1 mHz.The internal consistency of the position solution could be assessed for sources observed at least three times. This varied with source declination from ± 0″.1 at a declination of 45° to ± 2″.0 near the equator.The spread in the position solution for P0727-11, a rapid variable at the observing frequency, was also large.Positions obtained for some other sources have been used to assist in the identification of associated optical objects.
The Present State and Future of the Astronomical Refraction Investigations
Authors: Teleki G. 
Published: July 2016

(1) Astronomical refraction is one of the oldest astronomical problems, which has been investigated many times, but the existing knowledge of refraction is not sufficient to meet modern requirements for accurate astrometric data. The present investigations cast light on several facts which might help the advancement in the calculation of astronomical refraction.(2) There are several questions concerning the calculation of the astronomical refraction, from the laws of refraction to meteorological factors. These difficulties have prevented the development of a satisfactory refraction theory for a long time, leading to the conservation of old methods, but the accuracy of the refraction determinations has not increased. We are using old refraction theories and tables based on them for the most part, while the anomalous refraction is not considered. Seeing that the calculated refraction values are not acceptable, we are determining the formal refraction corrections directly from astrometric measurements, but these corrections are not real from the physical point of view.The present uncertainty in the calculated refraction is of the order of 0″.01, increasing with zenith distance. For observations near the horizon the existing refraction theories cannot give acceptably accurate values.(3) The greatest progress in the knowledge of refraction influences would be achieved if instead of mean meteorological data we could use direct measurement. There are some propositions of this kind.The new refraction tables are in preparation. We are very careful in taking into consideration the local characteristics and the correct calculation of the chromatic refraction.Frankly speaking, we must say that it is practically impossible to calculate a real influence of refraction and for this reason certain precautions are advisable. A careful positioning of the instrument may simplify the density field and thus eliminate the greatest part of the anomalous refraction. But the best proposition is to observe at small zenith distances only, not larger than 45° if possible.(4) Our conclusion is that, in current astrometric practice, we must continue refraction investigations and in addition to the refraction at optical wavelengths, it is absolutely necessary to investigate the radio and laser-refraction too.
Les effets de la refraction atmospherique sur les coordonnees tangentielles en astrometrie
Authors: Dommanget J. 
Published: July 2016

RésuméOn montre que les coordonnées tangentielles considérées en astrométrie et affectées de la réfraction, peuvent toujours s'écrire, même pour des champs pouvant s'étendre théoriquement jusqu'à 90°, sous la forme:
oò a est le coefficient du premier terme de l'expression de la réfraction:
Xa et Ya, des expressions calculables aisément pour chaque point du cliché et Rx et Ry, les restes des développements des coordonnées réfractées Xr et Yr. Ces restes sont fonctions de a et de b théoriquement, mais leur calcul pour chaque point du cliché peut se faire en toute rigueur même avec des valeurs approchées de ces coefficients. Introduits sous cette forme dans les formules de réduction des clichés, les effets de la réfraction atmosphérique n'apparaissent que par le seul paramètre inconnu a, et de manière linéaire.
Precise Reduction to the Apparent Places of Stars
Authors: Yumi S. , Hurukawa K. , Hirayama Th. 
Published: July 2016

For a precise reduction to the apparent places of the stars in a uniform system during the 19th and 20th centuries, the ‘Solar Coordinates 1800–2000’ by Herget (Astron. Papers14, 1953) may conveniently be used, because no coordinates of the Sun, referred to the mean equinox of 1950.0, are given in the Astronomical Ephemeris before 1930.A maximum difference of 0″.0003 was found between the aberrations calculated from both the Astronomical Ephemeris and Herget's Tables for the period 1960–1969, taking into consideration the effect of the outer planets, which amounted to 0″.0109.The effect of the inner planets on the aberration is estimated to be of the order of 0″.0001 at the most and the correction for the lunar term due to the change in astronomical constants is 0″.00002. It is recommended that the solar coordinates be calculated directly from Newcomb's formulae taking the effects of all the planets into consideration, but the effect concerned with the Moon can be neglected.