bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution and systematic motions of neutral hydrogen
Authors: Lindblad P. O. 
Published: July 2016

Recent work on the rotation curve of the Galaxy has confirmed the large-scale asymmetry of the motion of neutral hydrogen. In addition it seems that the radial velocities at the subcentral points of the lines of sight vary with longitude in a rather unsmooth manner. These irregularities of the motions may be associated with the distribution of matter in spiral arms. Large-scale systematic deviations from circular motion, ranging up to at least 30 km/sec in the outer regions of the Galaxy, are shown by observations across the anti-centre.Thus it presumably is impossible to describe the velocity field of the gas in terms of a simple general model, or to derive the force field without simultaneously solving the distribution problem. We may have to construct for each region, or for each separate feature of galactic structure, a special model that explains its radial-velocity properties. All these models must of course be in mutual agreement.The most coherent picture of the large-scale motion of the interstellar hydrogen is still given by the early Dutch and Australian surveys. A number of surveys with higher resolution are at present well on their way, although most of them are limited to a rather narrow strip along the galactic equator.In the interpretation of line profiles some method of analysis into Gaussian components is increasingly used, especially as an aid in following different structural features in diagrams giving velocity as a function of galactic longitude or latitude, and in separating these features in regions of velocity overlap. Applications of this technique and of simple model-making are demonstrated in connection with a discussion of the local and outer structure of the Galaxy.Large-scale deviations from the galactic plane as found in recent work indicate that the ‘bending’ of the plane may be a complicated phenomenon. New observations outlining the true character of this bending are necessary for a decision between the different theories about these deviations.The need for surveys with high frequency resolution and extending away from the galactic plane is emphasized. Optical identifications of members of the various structural features are highly desirable as an independent determination of parameters of structural models.
The hydrogen distribution in galaxies
Authors: Roberts Morton S. 
Published: July 2016

Results of 21-cm line observations with the 300-foot telescope are summarized. Along the major axis of M 31, the peaks in the distribution of neutral hydrogen correlate closely (but do not exactly coincide) with the optical spiral arms. The distribution of hydrogen over the galaxy shows a ring pattern; the same is true in M 33.Resolution of such ring structures may be facilitated by consideration of profile integrals over a restricted velocity range around the systemic velocity. Out of nine spiral systems studied, with minor axis &gt; 10′ (arc), only NGC 628 exhibits no ring. The ratios ring radius to ring width and optical radius to ring radius vary little about averages 2·5 and 1·7. In two irregular galaxies, no ring structure was observed.Neutral-hydrogen haloes, if present, can only be studied in large edge-on systems. In NGC 4244 and 7640, the upper limit to the density of neutral hydrogen in the halo is 0·001 cm-3. Qualitative considerations indicate that a similar value may apply in the Galaxy.
Interferometric studies of H 11 regions
Authors: Courtés G. 
Published: July 2016

The paper briefly summarizes the application of interference techniques to studies of structure and kinematics both of our Galaxy and of the nearest external galaxies.Since the principal results of our work have been published elsewhere (Courtès 1960, Courtèset al.1966), we shall restrict ourselves here to a brief summary of the most important points, especially those related to radio-astronomical investigations.
Sagittarius A
Authors: Lequeux J. 
Published: July 2016

The available high-resolution observations of the complex of radio sources in the region of the galactic centre are reviewed and analysed. As noted by Downes and Maxwell, the spectrum of the strong central source, Sagittarius A, is markedly non-thermal (index 0·7) at high frequencies; below 3000 MHz the spectrum may be flat, but flux values obtained at high angular resolution are badly needed.Various arguments indicate that the whole source complex is located near the nucleus of the Galaxy. From the short-wave observations collected by Downes and Maxwell dimensions, densities and masses are estimated for the thermal sources. The total mass of ionized hydrogen in these sources is about 106M⊙; the mechanism of ionization is uncertain.The non-thermal source Sgr A may be similar to the optical nuclei of external galaxies. Its synchrotron emission, as well as the outward motions and tilted features observed in the 21-cm line and continuum, are signs of activity in the galactic nucleus; but the time-scales of the various phenomena appear to disagree.
Spectrophotométrie intégrée des galaxies proches dans L'ultraviolet (expérience persée)
Authors: Cruvellier P. , Roussin A. , Valerio Y. 
Published: July 2016

Preliminary results obtained from a sounding rocket launched in December 1968 show a strong ultraviolet excess in the central part of the Andromeda nebula, as compared to the color of the sky background.The color index of M 31 in this spectral range may be explained by an abnormally high proportion of B stars.
Photoelectric rocket spectra at 10 Å resolution
Authors: Stecher Theodore P. 
Published: July 2016

Spectral scans of a number of early-type stars have been made with a three-channel spectrophotometer attached to a 32 cm telescope. The telescope was pointed at the individual program stars with an accuracy of at least 20 sec of arc. The spectral resolution was 10 Å over the range 1150 Å to 4000 Å. The data were recorded in digital form and processed in a computer.The profile of hydrogen Ly-α, as smeared by the exit slit, was obtained for α Lyr, α CMA, β Ori, and β Tau. For the earlier-type stars observed the Ly-α line of the star is masked by interstellar hydrogen absorption. For ζ Oph and ζ Per the Ly-α absorption is considerably larger than for the other early-type stars. The identification of lines is relatively simple for the light elements but becomes more difficult with the heavier ions since there are many more weaker lines and 10 Å is then insufficient resolution. Extreme P Cygni profiles are present in the earliest stars and are interpreted as mass loss at high velocity.A full description appears in Astrophys. J.159, Feb. 1970.
Observations of interstellar Lyman-α with the Orbiting Astronomical Observatory
Authors: Savage B. D. , Code A. D. 
Published: July 2016

The equivalent width of the blended line at Lyman α is given for 48 stars measured with the OAO-A2 scanning spectrometer. This provides an upper limit to the neutral hydrogen column density. In the Orion association these upper limits are significantly lower than the column densities determined from 21-cm emission line measurements. The determination of the Lyman α equivalent width for θ Ori by Carruthers is rediscussed and agreement between 21-cm absorption measures and Lyman α absorption is obtained for a spin temperature in the range of 40–70 K. It is suggested that the most likely explanation for the discrepancies found for the other Orion stars is that the 21-cm emission primarily occurs beyond the Belt stars.The correlation between the OAO blended equivalent widths and color excess, 4430 Å absorption, and interstellar sodium absorption are examined. Excellent correlation between sodium and hydrogen column densities is found.
Spectroscopic determination of surface pressure and elevation differences on Mars
Authors: Cruikshank D. P. 
Published: July 2016

Observations of a carbon dioxide band at 1.2206 μ (8192.6 cm−1) made at the opposition of Mars in June, 1969, are used with laboratory data to derive a value for the pressure at the surface of Mars. This band is especially suitable because it is sensitive to pressure, lying in the transition region of the curve of growth, but is relatively free of telluric contamination. The pressure derived is , corresponding to the Martian desert region Amazonis.Using a five-channel spectrometer, the strengths of two carbon dioxide bands at 1.5753 and 1.6057 μ (6347.8 and 6227.9 cm−1) were compared over a Martian dark area (Mare Acidalium) and a nearby bright area in Amazonis. The bands were 1.32 times stronger in the dark area than in the bright area. Interpreting this as evidence for elevation differences on the Martian surface, it is found that the dark Mare Acidalium is 2.5 km lower in elevation than the bright area with which it was compared.
Estimates of boundary layer parameters in the atmospheres of the terrestrial planets
Authors: Golitsyn G. S. 
Published: July 2016

The similarity theory of atmospheric boundary layers is applied to an estimate of the form of vertical profiles of average wind velocity and potential temperature in the atmospheres of the terrestrial planets in day- and night-time conditions.It is then considered, as in the case of the earth, that the magnitude of the turbulent heat flux qT during the day is about 0.1 of q(1 – A), where q is the solar constant for the planet and A is its albedo; at night, qT is several times smaller still. The friction velocity u* is taken equal to 2–5% (depending upon the stratification) of the mean wind velocity in the free atmosphere, which was adopted from previous calculations (Golitsyn, 1968).The boundary layers in the atmospheres of Mars and Venus and in the hypothetical atmosphere of Mercury are examined in detail. Sharp temperature drops are characteristic of Mars within a few tens of meters from the surface, attaining a magnitude of several tens of degrees, especially during the day. Large changes of the wind velocity also take place in this thin lower layer. This effect results from the low density of the Martian atmosphere.For Venus, owing to the very high density of the atmosphere, the stratification is close to neutral, i.e., the temperature profile is close to the adiabatic one and the wind profile is of a logarithmic shape.Owing to high winds, the stratification on Mercury must also be close to neutral with respect to the wind (the profile being close to the logarithmic), but because of the expected low density, the temperature changes near the ground may still be very great.
Optical Systems for UV Space Researches
Authors: Courtés G. 
Published: July 2016

This paper gives a general review of the best ways to adapt the UV optical designs to the peculiar conditions of guidance of space vehicles.(1)Conditions to obtain useful photometric direct images of the sky (stars and nebulae) with several different receptors (photographs, image tube, TV camera etc., …). New solutions of imagery are considered.(2)Selection of the different bandwidths of wavelengths (filters; gratings).An example of a new optical design, the BPM filter especially adapted to the poor conditions of guidance, is described. (Wave length selection is independent of the guidance.)The last part of this article is devoted to a review of the dispersive optical designs adapted to space research.Conclusions are in favour of the average size space vehicles on rockets for the time being and for large telescopes in the space platforms even if their guidance is several times worse than their optical quality.
Report on the precision of atomic standards of frequency
Authors: Essen L. 
Published: July 2016

Atomic frequency standards have been checked by laboratory investigations and by the intercomparison of different standards.Existing ammonia Masers enable a frequency to be defined in terms of a spectral line with an accuracy of ±1 part in 108 and give a reproducibility under stated conditions of ±2 parts in 1010. The cesium atomic beam standard enables a frequency to be defined in terms of a spectral line with a precision of ±1 part in 1010. Comparison between the U.K. and U.S. by the radio transmissions of standard frequencies and time signals gave an average agreement of a few parts in 1010 but revealed some systematic discrepancies. Direct comparisons between three U.S. standards and the U.K. standard gave agreement to 2.2, 3.2, and 1.5 parts in 1010.
On the existence of a third integral in a particular case
Authors: Perek L. , Peterson D. M. 
Published: July 2016

A simple galactic model with a finite mass and dimensions, non-negative densities everywhere, an axis, and a plane of symmetry, exhibits box-type orbits for low energies. Depending on initial conditions the envelopes of the boxes are at least of degree 2, 4, and 6 respectively. High-energy orbits show a tendency to fill out the whole permissible area thus indicating the absence of an isolating third integral of motion.A preliminary—but plausible—conclusion is suggested that the oscillations in a straight line are unstable in the present mass distribution.
Speckle v Non-Redundant Masking
Authors: Haniff C.A. 
Published: July 2016

Unlike their radio counterparts, optical astronomers have paid relatively little attention to the role of the aperture function when designing their high resolution imaging experiments. This is despite the fact that it can be easily modified with the use of a suitable pupil plane mask. While the defining characteristics of the two most favoured pupil configurations have never been in doubt – negligible atmospheric noise in the case of a non-redundant configuration of small holes and high photon rates for a filled pupil – the relative merits of these two choices in terms of imaging performance in the presence of turbulence appear not to have been carefully investigated until very recently.Most existing comparisons of fully-filled aperture (FFA) and non-redundant mask (NRM) based imaging strategies appear to have ignored a number of fundamental and practical difficulties that are often encountered in practice. In the intermediate regime, between very high and very low light levels, that characterizes most astrophysical applications hybrid imaging schemes seem most profitable. These utilize partially-redundant pupil geometries that combine the advantages of redundancy at low light levels without incurring the penalties associated with fully redundant beam recombination. Such pupil geometries are also useful in reducing the level of systematic effects that often plague speckle imaging experiments.
High Angular Resolution Observations of Protostellar Disks
Authors: Monin J.-L. , Bouvier J. , Malbet F. 
Published: July 2016

The existence of circumstellar disks around young stellar objects like T Tauri stars is now well accepted. Such disks would have solar system sizes and, at the distance of the nearest star forming cloud, an angular diameter of 0.01 to 1 arcsecond at most, requiring very high angular resolution to be detected. Due to the nature of the emission process in circumstellar disks and to chromatic properties of ground based observations, disk imaging is expected to be more efficient in the near infrared. Also, multi-aperture interferometry in this wavelength range (1 – 10 μm) is expected to bring considerable insight into the disks properties and evolution in revealing their inner physical structure.In this paper, we present synthetic images of circumstellar accretion disks. The images have been computed from a complete disk vertical structure model.
Simulated X-Ray Emission from Starburst Driven Winds
Authors: Strickland D. K. , Stevens I. R. , Ponman T. J. 
Published: July 2016

Winds from massive stars and supernovae in starburst galaxies drive global outflows of hot X-ray emitting plasma, as seen in M82 and NGC 253. These galactic winds are important for understanding galaxy evolution & formation, chemical enrichment of the IGM, and the starburst phenomenon itself.X-ray observations provide the only direct probe of the hot gas in these winds. However, the limitations of current X-ray observatories and factors such as complex temperature structure, mass loading by ambient material and projection effects all make the link between the observed data and existing 1 & 2-D modeling and theory difficult to make.We have therefore begun a program of numerical simulations of galactic winds, concentrating on predicting their observable X-ray properties. We present some initial results, comparing them to the archetypal starburst wind system M82.
Non-LTE line blanketed atmospheres for hot stars
Authors: Hillier D. J. 
Published: July 2016

The modeling of hot star atmospheres falls into two broad classes: those where the plane parallel approximation can be used, and those where the effects of spherical extension and stellar winds are important. In both cases non-LTE modeling is a necessity for reliable spectroscopic analyses.While simple ions (e.g., H, He I, and He II) have been treated routinely in non-LTE for many years it is only recently that advances in computing power, computational techniques, and the availability of atomic data have made it feasible to perform non-LTE line blanketing calculations. Present models, with varying degrees of approximation and sophistication, are now capable of treating the effects of tens of thousands of lines. We review the latest efforts in incorporating non-LTE line blanketing, highlighting recent advances in the modeling of 0 stars, hot sub-dwarfs, Wolf-Rayet stars, novae, and supernovae.
Atmospheric motions and granulation in cool stars - observations and theory
Authors: Cottrell P.L. 
Published: July 2016

This review presents a number of aspects in our quest for an understanding of the detailed structure of cool star stellar atmospheres through the study of atmospheric motion. It includes the observational tools (e.g. direct imaging, detailed analyses of line profiles) used to determine the type and amount of motion, as well as the modelling techniques (e.g. simulated images, velocity and pressure fields) used to interpret and describe these motions.Linkages will be made through the solar-stellar connection to provide insight into the structure of stars where detailed imaging is not possible, and to the determination of the fundamental parameters of stars, such as effective temperature, surface gravity and elemental abundances.
Results from HST Observations of Six LMC Globular Cluster Fields
Authors: Olsen K. A. G. , Hodge P. W. , Mateo M. , Olszewski E. W. , Schommer R. A. , Suntzeff N. B. , Walker A. R. 
Published: July 2016

We present deep HST color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005, and NGC 2019. Separate cluster and field star CMDs are shown. The time of formation of the LMC is studied from an analysis of the cluster CMDs. Based on a comparison of the CMDs with sequences of the Milky Way clusters M3, M5, and M55, we suggest that the LMC formed its first stars at the same time as the Milky Way to within 1 Gyr. We find additional evidence that these LMC globular clusters are as old as the oldest Milky Way clusters through a comparison of our data with the horizontal branch evolutionary models of Lee, Demarque, & Zinn (1994).The evolution of the LMC following its formation is studied through an analysis of the field star CMDs. Through an automated comparison with stellar evolution models, we extract the star formation histories implied by the CMDs. Our best-fit star formation histories imply that the LMC has been actively forming stars over the last 4 Gyr, in agreement with previous field star studies. The four fields that lie in the Bar also contain significant numbers of stars with ages of 4–8 Gyr in the best-fit cases. The most notable disagreement between the best-fit models and observed CMDs is in the color of the red giant branch.
On the tidal function between two real bodies
Authors: Shkodrov V. , Ivanova V. 
Published: July 2016

The general expression of the tidal function between two real bodies of arbitrary mass distribution has been derived. The case has been regarded when the distances between the bodies are comparable to their sizes. In this case, the effect of the body figure is substantial.The relations obtained are utilized for the tidal influence of Jupiter on the surface of Io. It has been shown that Jupiter's shape (with J2 = 0.015) causes a deformation in the sub-Jupiter point of about 15m. This is approximately 10% of the total tidal deformation of Io caused by Jupiter's gravitation.
The K-Band Hubble Diagram for X-Ray Selected Brightest Cluster Galaxies
Authors: Mann R.G. , Collins C.A. 
Published: July 2016

The Hubble (magnitude-redshift) diagram for brightest cluster galaxies (BCGs) is a classic cosmological tool, widely studied because of the remarkably small dispersion (∼ 0.3 mag) in the absolute optical magnitudes of low redshift BCGs (Postman and Lauer 1995). Extending the BCG Hubble diagram to higher redshifts would greatly enhance its role as a cosmological probe, but this has been frustrated by several technical problems:
– the conventional means of cluster selection in the optical become increasingly compromised by projection effects at z > 0.1– at higher redshifts the interpretation of optical magnitudes becomes increasingly complicated by the effects of possible star formation.
N-Body Simulation of Large Scale Structure in the Universe with Oscillating Scalar Field
Authors: Kawabata K. , Taguchi H. , Andoh Y. 
Published: July 2016

Using the particle-mesh method with 1283 grids and 643 particles, we have carried out a number of N-body simulations of the large scale structure for the cosmological model proposed by Fukuyama et al.(1996): this model contains the matter(Ω0) as well as a scalar field(Φ) with a finite mass that couples non-minimally with the scalar curvature R through the form of 1/2ηΦ2R, where η(= −80) is the coupling constant.For simplicity, we have adopted the same values as those employed by Fukuyama et al.(1996) for all the parameters other than Ω0, fo which we have varied from 0.001 to 0.15. In performing our simulation, we further assume that only the density of matter ρ spatially fluctuates. The initial condition is created by perturbing the homogeneous distribution of the particles by means of the random Gaussian Harrison-Zeldovich spectrum.The two-point correlation function ξ(r) is then compputed for each of the resulting structures to compare with the observational data(Davis and Peebles, 1983). It is interesting to note that the structure formation appears to be achieved rather straightforwardly with the scalar field model. However, in order to yield an agreement between the theoretical and the observational two-point correlation functions, we seem to require the Ω0 value much larger than 0.01 adopted by Fukuyama et al.(1996).
Association of X-ray Quasars with Active Galaxies
Authors: Arp H. 
Published: July 2016

Analysis of ROSAT observations demonstrate that X-ray sources are associated with bright Seyfert galaxies up to distances of about 40 arc min. These X-ray sources are predominantly identified with blue stellar objects (BSO's) some of which are already catalogued as quasars.The X-ray sources tend to pair and align across the nucleus of the active Seyfert. Enough redshifts are now available to indicate the similarities of the redshifts in the quasar pairs and to enable computation of ejection velocities of about 0.1c.