bluuebunny/crossref_metadata_2025 huggingface dataset:
II. The Galaxy
Authors: Larsson-Leander G.
Published: July 2016

According to the general evolutionary ideas outlined in section (A), p. 13 above, we should find in the disk both old objects, formed immediately after the contraction of the primeval cloud into the disk, and recently formed stars. The study of the interarm population of our Galaxy is a difficult problem due to the interstellar absorption. Information from nearby galaxies, especially from M 31, is in some ways more readily obtainable. In the disk of M 31 we find stars of absolute magnitude about – 3 photovisual, which are similar to the brightest stars observed in globular clusters. Observations with the 200-inch telescope have shown that the number of these stars of population II decreases rapidly from the nucleus to the adjacent regions, and then slower towards the limit to which the system can be traced by optical means.
International determination of the total motion of the pole
Authors: Markowitz Wm.
Published: July 2016

A symposium on the future of the International Latitude Service (I. L. S.) is to be held in Helsinki in July 1960. My report for the symposium consists of two parts. Part I, denoded (Mk I) was published [1] earlier in 1960 under the title “Latitude and Longitude, and the Secular Motion of the Pole”. Part II is the present paper, denoded (Mk II).
Polhodie et catalogues d'etoiles
Authors: Guinot Bernard
Published: July 2016

I - L'étude de la polhodie résulte de l'observation des mouvements du zénith sur la sphère des fixes en plusieurs stations. La part commune de ces mouvements est attibuée aux déplacements des pôles terrestres. Mais le réseau de coordonnées défini sur la sphère des fixes par les valeurs attribuées aux ascensions droites et aux déclinaisons des étoiles, présente des irrégularités de l'ordre de grandeur des phénomènes à mesurer. L'étude simultanée de la polhodie et des catalogues d'étoiles s'impose.
Schematic Chart of the Far Side of the Moon
Authors: Breido I. I. , Shchegolev D. E.
Published: July 2016

The photographs of the far side of the Moon, obtained on 7 October 1959 by the automatic interplanetary station, were studied at the Pulkovo Observatory independently from other observatories. The purpose of this work was to detect authentic objects on the far side of the Moon, to determine their selenographic coordinates, and to draw—on this basis—a schematic chart with an approximate distribution of the brightness of detected features. In contrast with the work conducted at the Sternberg Astronomical Institute [1], the Pulkovo Observatory did not apply the method consisting of an artificial increase of the contrast of features within a specific range of densities (the so-called method of photometric cross-sections). Therefore, we detected only the topographically most distinctive features, which can be examined directly on photographs and compared with others.
Precision des Distances “Cratere-Centre Globe Lunaire” en Fonction de la Precision des Mesures
Authors: Weimer Th.
Published: July 2016

Le problème est complexe dans le cas général. C'est pourquoi nous supposons que les librations et les quantités qui en dérivent sont connues sans erreur. Les formules utilisées pour définirRg (distance du cratère au centre de la Lune) sont celles données dans le chapitre VII de nos “Recherches sélénographiques”:oòest le rayon de la sphere lunaire; ρ, la distance de l'image du cratère au centre du disque;R1le rayon de ce disque;a, l'angle dont le sommet est au centre du globe lunaire et dont les côtés passent par le centre du disque et le cratère; σ, Tangle dont les côtés passent par ces mêmes points, mais dont le sommet est l'observateur.
Lunar Multiangular Statistical Adjustment (A Geometrical Approach to Lunar Control)
Authors: Eckhardt Donald H. , Hunt Mahlon S.
Published: July 2016

Due to the continued and increased scientific interest in the Moon, the current international effort regarding the accumulation of usable selenodetic inputs for the purpose of compiling adequately controlled lunar charts has been undertaken. This is exemplified by the Bagnères Lunar Conference held in April 1960 and the present lunar symposium.
The Origin of the Moon
Authors: Ruskol E. L.
Published: July 2016

The difference between average densities of the Moon and Earth was interpreted in the preceding report by Professor H. Urey as indicating a difference in their chemical composition. Therefore, Urey assumes the Moon's formation to have taken place far away from the Earth, under conditions differing substantially from the conditions of Earth's formation. In such a case, the Earth should have captured the Moon. As is admitted by Professor Urey himself, such a capture is a very improbable event. In addition, an assumption that the “lunar” dimensions were representative of protoplanetary bodies in the entire solar system encounters great difficulties.
The Geosciences Applied to Lunar Exploration
Authors: Green J.
Published: July 2016

The term geo-sciences has been used here to include the disciplines geology, geophysics and geochemistry. However, in order to apply geophysics and geochemistry effectively one must begin with a geological model. Therefore, the science of geology should be used as the basis for lunar exploration. From an astronomical point of view, a lunar terrain heavily impacted with meteors appears the more reasonable; although from a geological standpoint, volcanism seems the more probable mechanism. A surface liberally marked with volcanic features has been advocated by such geologists as Bülow, Dana, Suess, von Wolff, Shaler, Spurr, and Kuno. In this paper, both the impact and volcanic hypotheses are considered in the application of the geo-sciences to manned lunar exploration. However, more emphasis is placed on the volcanic, or more correctly the defluidization, hypothesis to account for lunar surface features.
Photographies à Grande Resolution de Certaines Regions Lunaires
Authors: Dollfus Audouin
Published: July 2016

En vue d'une étude très détaillée de la surface de la Lune et des planètes B. Lyot avait installé en 1941 un réfracteur de 38 cm à l'Observatoire du Pic-du-Midi. Le but était de mettre à profit les conditions atmosphériques souvent excelléntes recontrées sur ce sommet de 2860 m d'altitude. En 1944 cet instrument fut remplacé par un réfracteur plus puissant dont l'ouverture de 60 cm permettait de tirer un encore meilleur parti des nuits assez fréquentes ou la turbulence atmosphérique reste réduite.
Cine Photography of the Moon from Pic-du-Midi
Authors: Kopal Zdeněk , Rackham Thomas W.
Published: July 2016

The aim of our present communication should be to give you a brief account of the current photographic work on the Moon which the Manchester astronomers have been carrying out, for some time, from the French high-altitude observatory at Pic-du-Midi under the auspices of the United States Air Force‡. This work, today, includes a variety of lines of lunar studies but since the inception of the entire programme in 1958 our principal aim has been to secure adequate data for extensive three-dimensional topography of the surface of our satellite; and it is this work whose recent developments we should mainly like to describe to you today.
The Rocks that May Constitute the Lunar Surface
Authors: Barabashev N. P.
Published: July 2016

In investigating the lunar surface it is necessary to use all possible methods of observation, and draw conclusions on the basis of a simultaneous comparison of the results obtained by different methods. The comparison should be made statistically by making use of a sufficient number of specimens of the rock of each type. The comparison should be made in accordance with the following characteristics and parameters: (a) the light or brightness factor; (b) the law of reflection; (c) the smoothness factor; (d) the spectral distribution of reflectivity; (e) the degree of polarization in dependence on the angle of incidence, reflection and phase in the different spectral regions; (f) heat conductivity; and (g) luminescence. At the Kharkov Astronomical Observatory such a research has basically been completed [1].
The Radio Emission of the Moon on 4 mm
Authors: Kislyakov A. G.
Published: July 2016

The aim of this communication is to present the results of an experimental research on the intensity of the radio emission of the Moon at 4 mm and to describe the method followed in observations and reductions. It was established that the radio brightness of the Moon,Tl, varies during the lunation according to the law:Tl= 230° + 73° cos (Ω0t-24°)K. The accuracy in measuring the absolute value of Moon's radio temperature is about ± 10%. The comparison between the phase dependence of the radio emission of the Moon at 4 mm and the data from observations of the radio temperature of the lunar disk on other wave lengths demonstrated that the homogeneous model of Moon's surface is in good agreement with the experimental data.
Some Physical Constants of the Lunar Surface as Indicated by its Radar Scattering and Thermal Emission Properties
Authors: Senior T. B. A. , Siegel K. M. , Giraud A.
Published: July 2016

The purpose of this paper is to summarize some of the results of lunar studies carried out in the Radiation Laboratory of The University of Michigan during the past 3 years. Apart from an associated program which is the subject of a later paper [1] by Fensleret al., these studies have been confined mainly to an analysis of radar scattering and thermal emission data, but in the course of this work, values have been obtained for some of the physical constants of the lunar surface.
Solar X radiation
Authors: de Jager C.
Published: July 2016

X-ray bursts are defined as electromagnetic radiation originating from electronic transitions involving the lowest electron shells; gamma rays are of nuclear origin. Solar gamma rays have not yet been discovered.

According to the origin we have :

1.

Quasi thermal X-rays, emitted by (a) the quiet corona, (b) the activity centers without flares, and (c) the X-ray flares.

2.

Non-thermal X-ray bursts; these are always associated with flares.

The following subdivision is suggested for flare-associated bursts :
Dielectronic recombination in the Corona
Authors: Burgess A.
Published: July 2016

The full importance of dielectronic recombination in plasmas has only recently been realized. The process is discussed in detail for the case of low density plasmas, and formulae for the rate of the process are derived using Correspondence Principle and Detailed Balance arguments. Recent work in the derivation of a simple Gener ral Formula for estimation of dielectronic recombination coefficients and on the ionization balance for Iron and Calcium ions in the corona is reviewed. The new ionisation balance curves are in much better agreement with observations on the Doppler widths of coronal lines.
Theoretical line profiles in the ultraviolet spectra of early B-type stars
Authors: Morton Donald C.
Published: July 2016

The blended profiles of 106 ultraviolet lines, including all those expected to have equivalent widths greater than 2 Å in the wavelength range 911,6 to 3000 Å, have been computed for Bz V and B0 V model atmospheres. Most of the lines are found shortward of 1410 Å, where they have deep cores and many have extensive wings. This blanketing amounts to 31% at Bz V and 20 % at B0 V.
Observational Manifestations of Young Neutron Stars: Spin-powered Pulsars
Authors: Kramer Michael
Published: July 2016

The largest number of known young neutron stars axe observed as spin-powered pulsars. While the majority of those are detected at radio frequencies, an increasing number can be studied in other parts of the electromagnetic spectrum as well. The Crab pulsar is the prototype of a young pulsar which can be observed from radio to gamma-ray frequencies, providing a red thread of discussion during a tour through the pulsar properties observed across the electromagnetic spectrum. The basic observational features of pulsar emission are presented, preparing the ground for more detailed reviews given in these proceedings. Here, particular attention will be paid to those emission features which may provide a link between the radio and high-energy emission processes.
Testing Pulsar Thermal Evolution Theories with Observation
Authors: Tsuruta Sachiko
Published: July 2016

With the successful launch of Chandra and XMM-Newton, the time has arrived when careful comparison of thermal evolution theories of isolated neutron stars with observations will offer a better hope for distinguishing among various competing neutron star cooling theories. For instance, the latest theoretical and observational developments may already exclude both nucleon and kaon direct Urea cooling. In this way we can now have a realistic hope for determining various important properties, such as the composition, superfluidity, the equation of state and stellar radius. These developments should help us obtain deeper insight into the properties of dense matter.
Mixing of Young Neutron Star Debris Into Supernova Envelopes
Authors: Noro A. , Miyaji S. , Yamashita K. , Ogawa T. , Den M.
Published: July 2016

We have simulated the 3D growth of a Rayleigh-Taylor instability in the expanding envelope of SN 1987A using the Adaptive Mesh Refinement Scheme utilizing a resolution of 4096−3. When the sinusoidal velocity perturbation amplitude is 10%, heavy element tongues of the He/H interface penetrate into the envelope with a high velocity.
The Distance and Distribution of Galactic Supernova Remnants from the PMN Survey Sample
Authors: Stupar M. , Filipović M. D. , Pannuti T. G. , Parker Q. A.
Published: July 2016

We have used the Parkes-MIT-NRAO (PMN) radio survey, at a common frequency of 4.85 GHz (λ=6 cm), to study the distribution of Galactic shell supernova remnants (SNRs). We estimate distances and distribution of the Galactic shell SNRs and find the peak of distances to be between 4 and 6 kpc. Our two-dimensional model of the distribution of Galactic shell SNRs shows a concentration between the Sagittarius and the Scutum arms.
The Chandra Supernova Remnant Catalog
Authors: Seward Fred , Smith Randall , Hagler Joan , Portolese Lisa , Gaetz Terrance , Slane Patrick , Koo Bon-Chul , Lee Jae-Joon
Published: July 2016

We show some examples from a WWW-based catalog, containing Chandra archive data, that is now under construction. Many remnants show manifestations of internal neutron stars, which are of particular interest to this conference.
New Pulsars from Arecibo Drift-Scan Searches
Authors: McLaughlin M. A. , Lorimer D. R. , Champion D. J. , Xilouris K. , Arzoumanian Z. , Backer D. C. , Cordes J. M. , Fruchter A. S. , Lommen A. N.
Published: July 2016

We report on new pulsars discovered in Arecibo drift-scan datA. Processing of 2200 deg2 of data has resulted in the detection of 41 known and 12 new pulsars. New pulsars include two millisecond pulsars, one solitary and one binary recycled pulsar, and one pulsar with very unusual pulse profile morphology and complex drifting subpulse behavior.
Searching for Submillisecond Pulsars from Highly Polarized Radio Sources
Authors: Han J. L. , Manchester R. N. , Lyne A. G. , Qiao G. J.
Published: July 2016

Pulsars are among the most highly polarized sources in the universe. The NVSS has cataloged 2 million radio sources with linear polarization measurements, from which we have selected 253 sources, with polarization percentage greater than 25%, as targets for pulsar searches. We believe that such a sample is not biased by selection effects against ultra-short spin or orbit periods. Using the Parkes 64-m telescope, we conducted searches with sample intervals of 50 μs and 80 μs, sensitive to submillisecond pulsars. Unfortunately we did not find any new pulsars.
20 Pairs of Real Pulsar/Supernova Remnant Associations
Authors: Tian Wenwu , Leahy Denis
Published: July 2016

We trace all pulsar/SNR associations proposed in the literature, and find that 20 pairs of associations are highly likely real because the pulsar wind nebulae around the pulsars have been detected.
Shocks and Wind Bubbles Around Energetic Pulsars
Authors: Gaensler Bryan M.
Published: July 2016

The Crab Nebula demonstrates that neutron stars can interact with their environments in spectacular fashion, their relativistic winds generating nebulae observable across the electromagnetic spectrum. At many previous conferences, astronomers have discussed, debated and puzzled over the complicated structures seen in the Crab, but have been limited to treating most other pulsar wind nebulae (PWNe) as simple calorimeters for a pulsar's spin-down energy. However, with the wealth of high-quality data which have now become available, this situation has changed dramatically. I here review some of the main observational themes which have emerged from these new measurements. Highlights include the ubiquity of pulsar termination shocks, the unambiguous presence of relativistic jets in PWNe, complicated time variability seen in PWN structures, and the use of bow shocks to probe the interaction of pulsar winds with the ambient medium.
Millimeter-wave Imaging of Pulsar Wind Nebulae
Authors: Bock Douglas C.-J. , Gaensler Bryan M.
Published: July 2016

We have observed the supernova remnants G16.7+0.1 and G29.7−0.3 at millimeter wavelengths with the Berkeley-Illinois-Maryland Association array, measuring total flux densities of the pulsar wind nebulae in the remnants. Our results imply a break at ∼50 GHz in the spectrum of the PWN in G29.7−0.3, lower than previously estimated. The PWN in G16.7+0.1 either has a break < 100 GHz, or a steep radio spectrum.
Peculiar Differences in Radio and X-ray Synchrotron Radiation from Pulsar Wind Nebulae
Authors: Dickel John R. , Wang Shiya
Published: July 2016

Several Crab-type supernova remnants appear to have very bright non-thermal X-ray cores just around the pulsar or expected pulsar. This X-ray brightness is often not matched by a corresponding increase in radio emission. The best example of this phenomenon is in N157B in the LMC. G21.5−0.9 and possibly 3C 58 also show it while the Crab Nebula and 0540−69.3 do not. Some method to enhance the higher energy particles must be present in these objects.
A Spin-down Power Threshold for Pulsar Wind Nebula Generation?
Authors: Gotthelf E. V.
Published: July 2016

A systematic X-ray survey of the most energetic rotation-powered pulsars known, based on spin-down energy loss rate, shows that all energetic pulsars with Ė > Ėc ≍ 4 × 1036 ergs s−1 are X-ray-bright, manifest a distinct pulsar wind nebula (PWN), and are associated with a supernova event, with over half residing in shell-like supernova remnants. Below Ėc, the 2–10 keV flux ratio FPWN/FPSR decreases by an order-of-magnitude. This threshold is consistent with the lower limit on the spectral slope γmin ≍ 0.6 observed for rotation-powered pulsars (Gotthelf 2003). The apparent lack of bright PWNe below Ėc suggests a change in the particle injection spectrum and serves as a constraint on emission models for rotation-powered pulsars. Neither a young age nor a high density environment is found to be a sufficient condition for generating a PWN, as often suggested, instead Ė is likely the key parameter in determining the evolution of a rotation-powered pulsar.
Soft Gamma Repeaters and Anomalous X-ray Pulsars: Together Forever
Authors: Kaspi Victoria M.
Published: July 2016

I review the observational properties of Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs), two unusual manifestations of neutron stars. I summarize the reasoning for SGRs being “magnetars,” neutron stars powered by the decay of a very large magnetic field, and the now compelling evidence that SGRs and AXPs are in fact members of the same source class, as predicted uniquely by the magnetar model. I discuss some open issues in the magnetar model, and the prospects for future work.
Orthogonal Polarization Modes in Pulsar Radio Emission
Authors: Petrova S. A.
Published: July 2016

General features of polarization transfer in the plasma of pulsar magnetospheres are outlined. A technique of plasma density diagnostics based on observed polarization profiles of radio pulses is developed. For the first time, it appears possible to obtain the profiles of the plasma density across the open field line tube from observations. The multiplicities derived are compatible with those predicted by modern theories of pair cascade and show a perfect exponential decrease towards the tube edge. Implications of the results are briefly discussed.
Ground-Based Gamma-Ray Detection of High Energy Galactic Sources: An Update
Authors: Rowell G. P.
Published: July 2016

I review the present status of ground-based γ-ray astronomy, concentrating on the population of Galactic TeV sources. A number of new telescope systems are now being completed, and promise to yield exciting new discoveries, expanding rapidly the number of sources. The TeV Galactic sources today include a number of plerions, shell-type supernova remnants, an X-ray binary, and also one unidentified candidate. Their present status, and our understanding of their TeV γ-ray emission processes are summarized and some motivation driving development of the field is outlined.
New Results from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) Mission
Authors: Lin R. P.
Published: July 2016

The primary scientific objective of RHESSI Small Explorer mission is to investigate the physics of particle acceleration and energy release in solar flares, through imaging and spectroscopy of X-ray/gamma-ray continuum and gamma-ray lines emitted by accelerated electrons and ions, respectively. Here we briefly describe the mission and summarize the new solar observations, including the first hard X-ray imaging spectroscopy, the first high resolution spectroscopy of solar gamma-ray lines, and the first imaging of solar gamma-ray lines and continuum.
Mass and Energy Supply of Fine Structure to the Solar Corona
Authors: Tziotziou Kostas , Tsiropoula Georgia
Published: July 2016

We investigate the role of chromospheric fine structures, e.g. mottles (spicules), in the mass balance and heating of the solar atmosphere by studying two-dimensional high-resolution Hα observations. The temporal and spatial variations of the line-of-sight (LOS) velocity, obtained with an inversion technique based on a cloud model, provide strong indications that the mechanism responsible for the driving of the observed flows is magnetic reconnection. Apart from the LOS velocity, application of the cloud model enables the derivation of several other physical parameters, like pressure, temperature, density etc. Mean values of these parameters permit the estimation of the role of these structures in the mass balance of the solar atmosphere. They, furthermore, permit a reasonable estimate of the energy provided by magnetic reconnection which is available for the heating of the solar corona.
X-ray Emission from Brown Dwarfs
Authors: Preibisch Thomas
Published: July 2016

During the last few years, X-ray emission has been detected from numerous brown dwarfs. Most of the X-ray detected brown dwarfs are very young objects with ages of at most 107 years, and all are still relatively warm, with late M spectral types. Their typical fractional X-ray luminosities are (LX/Lbol) ∼ 10—4 — 10—3, i.e. very similar to the values observed for active very-low mass stars. Their X-ray lightcurves show low-level variability, but in most cases no large flares; this implies that the young brown dwarfs are able to produce quiescent X-ray emission, not only occasional flares. An analysis of the Chandra X-ray spectra of several brown dwarfs yields surprisingly low plasma temperatures between 3 MK and 10 MK for some of the M8-9 dwarfs and indicates a decline in plasma temperature with decreasing effective temperature (or increasing age). The lack of X-ray detections for dwarfs cooler than spectral type M9 is consistent with the strong drop of activity observed in Hα at spectral types around M9. The observed X-ray emission from the young brown dwarfs with late M spectral type can be understood as a consequence of the fact that these objects are still warm enough to maintain partially ionized atmospheres which are capable of sustaining electrical currents. In the cooler, essentially neutral atmospheres of the older L and T dwarfs such currents are probably shut off, preventing the buildup of magnetic free energy and the support for magnetically heated chromospheres and coronae.
Circumstellar Disks around Young Solar-type Stars
Authors: Kamp Inga , Sammar Fatima
Published: July 2016

The chemistry of circumstellar disks around young (a few 10 Myr) solar-type stars is mainly driven by the strong UV radiation field of the central star. As a starting point for a detailed UV radiation field, the rocket and satellite observations of the solar chromosphere are used and scaled according to the time-dependent behaviour of stellar activity. The disk chemistry as well as dust and gas temperatures are then derived self-consistently from the model. The results of these calculations can be used for the identification of the most promising gas tracers as well as for the interpretation of present and future observations.
Heating of Stellar Chromospheres and Transition Regions
Authors: Musielak Zdzislaw E.
Published: July 2016

To explain the heating of stellar chromospheres and transition regions, two classes of heating mechanisms have been considered: dissipation of acoustic and magnetic waves generated in stellar convection zones; and dissipation of currents generated by photospheric motions of surface magnetic fields. The focus of this paper is on the wave heating mechanisms and on recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating can explain the “basal flux” and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. The obtained results clearly show that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres and transition regions.
Waves in the Solar Corona
Authors: Marsch Eckart
Published: July 2016

Waves at all scales, ranging in wavelength from the size of a loop (fraction of a solar radius) down to the gyroradii of coronal ions (about hundred meters), are believed to play a key role in the transport of mechanical energy from the chromosphere to the Sun's corona and wind, and through the dissipation of wave energy in the heating and sustaining of the solar corona. A concise review of new observations and theories of waves in the magnetically confined (loops) as well as open (holes) corona is given. Evidence obtained from spectroscopy of lines emitted by coronal ions points to cyclotron resonance absorption as a possible cause of the observed emission-line broadenings. Novel remote-sensing solar observations reveal low-frequency loop oscillations as expected from MHD theory, which appear to be excited by magnetic activity in connection with flares and to be strongly damped. Kinetic models of the corona indicate the importance of wave-particle interactions that hold the key to understand ion acceleration and heating by high-frequency waves.
An Ab Initio Approach to the Solar Coronal Heating Problem
Authors: Gudiksen B.V. , Nordlund Â.
Published: July 2016

We approach the solar coronal heating problem ab initio. Starting from a potential extrapolation of a SOHO/MDI magnetogram, a FAL—C atmospheric stratification, and a realistic photospheric velocity field, Spitzer conductivity and magnetic dissipation creates a corona where more than 2 106ergs s—1 cm—2 is dissipated. The winding of the magnetic field by the horizontal velocities in the solar photosphere is sufficient to provide a major part of the heating in the solar corona. The heating is intermittent on the smallest scale, but on average follows the magnetic field strength squared, as is expected from a force free magnetic field configuration. The intermittent heating creates large temperature and density fluctuations in the corona. The total dissipated energy in the corona is at least constant if not increasing with magnetic Reynolds number, making this heating process unavoidable as a major contributor to the heating of the solar corona.
Solar Magnetic Loops Observed with TRACE and EIT
Authors: Aschwanden Markus J. , Title Alan M.
Published: July 2016

We select some highlights and new results that have been obtained from detailed “microscopic” observations of coronal loop structures with the Transition Region and Coronal Explorer (TRACE) and Extreme Ultraviolet Imager (EIT) instruments, including: (1) the inhomogeneous substructure of EUV loops, (2) the dynamic and non-hydrostatic nature, (3) the non-uniform heating, (4) the magnetic topology at the loop foot-points, (5) the magnetic energy budget for heating, and (6) oscillations and waves in coronal loops.
Magnetic Loop Models: from Sun to Stars
Authors: Jardine M. , Collier Cameron A. , Wood K. , Donati J.-F.
Published: July 2016

I review recent progress in determining the nature of the loop structures that form the coronae of solar-like stars. This progress has been driven by observational advances, in particular the new results from X-ray satellites (Chandra and XMM-Newton) and the availability of surface magnetograms from Zeeman-Doppler imaging. It is now clear that stars that are similar to the Sun in mass, but which rotate more rapidly, have a very different magnetic field structure. Their surfaces are more heavily spotted, with spots appearing at all latitudes, extending all the way up to the rotation pole. Their coronae are correspondingly much brighter in X-rays, containing plasma that is hotter and denser than on the Sun. In addition, stellar coronae can support massive co-rotating prominences out to many stellar radii. Recent efforts in modelling these magnetic structures are now bringing together both the surface magnetograms and also the coronal X-ray emission. The resulting coronal loop models show complex loop structures on all scales, with much of the X-ray emission coming from high latitudes where is does not suffer rotational self-eclipse. The observed high densities and X-ray emission measures are a natural consequence of the high magnetic flux density at the surface. The stripping of the corona due to centrifugal effects at high rotation rates can also explain the saturation and supersaturation of X-ray emission with increasing rotation rates, and the recent observation of a high rotational modulation in a supersaturated star.
Lensing Diagnostics of Halo Substructure
Authors: Mao Shude
Published: July 2016

The Cold Dark Matter (CDM) hierarchical structure formation theory predicts substructures in dark matter halos. the number of predicted subhalos seems to exceed the observed number of luminous satellite galaxies. Gravitational lenses can be used to probe luminous or dark substructures. Image positions and flux ratios in broad-band (including radio and optical) and emission lines can all be used to probe substructures on different mass scales. the observed gravitational lenses appear to require a few percent of the mass surface density in substructures within the mass range of 104M⊙ − 109M⊙. Numerical simulations predict roughly the same mass fraction in substructures within the virialised region. But at typical image positions (a few percent of the virial radius), the predicted surface mass density in substructures appears to be lower than required. Both observations and numerical simulations are somewhat uncertain at present so it is not yet clear whether the discrepancy is severe.
Astrometric study of MACHO halo distribution in our Galaxy
Authors: Ohnishi Kouji , Hosokawa Mizuhiko , Fukushima Toshio
Published: July 2016

We estimated the optical depth and event rate of μas level astrometric microlensing for the stars outside our galaxy caused by MACHOs. For the stars in the LMC and the SMC, the optical depth of a 1 μas detection threshold is on the order of 10–1 and the event rate of the induced proper motion of 1 μas/year is on the order of 10–3/yr with the event duration of around a hundred years. They depend on the distribution of lenses and sources. This poses a constraint on the expected probability of photometric self-lensing in LMC and SMC.
Dark Matter Constraints from the Sagittarius Dwarf and Tail System
Authors: Majewski Steven R. , Law David R. , Johnston Kathryn V. , Skrutskie Michael F. , Weinberg Martin D.
Published: July 2016

2MASS has provided a three-dimensional map of the > 360°, wrapped tidal tails of the Sagittarius (Sgr) dwarf spheroidal galaxy, as traced by M giant stars. With the inclusion of radial velocity data for stars along these tails, strong constraints exist for dynamical models of the Milky Way-Sgr interaction. N-body simulations of Sgr disruption with model parameters spanning a range of initial conditions (e.g., Sgr mass and orbit, Galactic rotation curve, halo flattening) are used to find parameterizations that match almost every extant observational constraint of the Sgr system. We discuss the implications of the Sgr data and models for the orbit, mass and M/L of the Sgr bound core as well as the strength, flattening, and lumpiness of the Milky Way potential.
The Mass of the Galaxy from Large Samples of Field Horizontal-Branch Stars in the SDSS Early Data Release
Authors: Beers Timothy C. , Chiba Masashi , Sakamoto Tsuyoshi , Wilhelm Ron , Prieto Carlos Allende , Sommer-Larsen Jesper , Newberg Heidi J. , Yanny Brian , Marsteller Brian , Pier Jeffrey R.
Published: July 2016

We present a new estimate of the mass of the Milky Way, making use of a large sample of 955 field horizontal-branch (FHB) stars from the Early Data Release of the Sloan Digital Sky Survey. This sample of stars has been classified on the basis of an automated analysis approach, in combination with other methods, in order to obtain estimates of the physical parameters of the stars, i.e., Teff, log g, [Fe/H], and should be relatively free of contamination from halo blue stragglers. the stars all have measured radial velocities and photometric distance estimates, and the sample includes objects as distant as ~ 75 kpc from the Galactic center. Application of a Bayesian likelihood method, for a specific model of the Galaxy, indicates that the total mass of the Galaxy lies in the range 1.5 − 4.0 × 1012 M⊙. Our sample appears to reveal a clear signature of a dual halo population of FHB stars, with the boundary between the inner and outer halo around 20 kpc, and the possibility of rather striking differences in the rotational properties of the Galaxy at low metallicity.
Mapping the Remote Milky Way Halo using BHB stars at 70 < r < 130 kpc
Authors: Clewley L. , Warren S. J. , Hewett P. , Wilkinson M. , Evans N. W.
Published: July 2016

We increase the number of remote halo tracers by using blue horizontal branch (BHB) stars out to Galactocentric distances of 130 kpc. We use SDSS EDR photometry and the VLT to detect 16 BHB stars at Galactocentric distances 70 <r < 130 kpc, and to measure their radial velocities. We find the mass of the Milky Way is M = 1.7+3.0–0.6 × 1012M⊙. When completed this survey will: (i) substantially reduce the errors in the total mass and extent of the Milky Way halo, and (ii) map the velocity space in a hitherto unexplored region of the halo.
Using Globular Clusters to Test Newton's Law of Gravity
Authors: Scarpa Riccardo , Marconi Gianni , Gilmozzi Roberto
Published: July 2016

New measurements of the velocity dispersion of the globular cluster ω Centauri allow us to trace its gravitational potential down to an acceleration of 8 × 10–9 cm s–2. It is found that the dispersion profile remains flat well inside the tidal radius as soon as the acceleration of gravity approaches a0, a result that finds its simplest explanation within the context of MOND. A similar behaviour is observed in the globular cluster M15 showing this is not a peculiar feature of ω Centauri. This result is surprising and suggestive of a failure of Newton's law at low accelerations.
The visible matter – dark matter coupling
Authors: Sancisi Renzo
Published: July 2016

In the inner parts of spiral galaxies, of high or low surface brightness, there is a close correlation between rotation curve shape and light distribution. For any feature in the luminosity profile there is a corresponding feature in the rotation curve and vice versa. This implies that the gravitational potential is strongly correlated with the distribution of luminosity: either the luminous mass dominates or there is a close coupling between luminous and dark matter. in a similar way, the declining rotation curves observed in the outer parts of high luminosity systems are a clear signature of the stellar disk which either dominates or traces the distribution of mass.

The notion that the baryons are dynamically important in the centres of galaxies, including LSBs, undermines the whole controversy over the cusps in CDM halos and the comparison with the observations. If the baryons dominate in the central regions of all spirals, including LSBs, how can the CDM profiles be compared with the observations? Alternatively, if the baryons do not dominate but simply trace the DM distribution, why, in systems of comparable luminosity, are some DM halos cuspy (like the light) and others (also like the light) are not?
Evolution of Galaxies in Triaxial Halos with Figure Rotation
Authors: Bekki Kenji , Freeman K. C.
Published: July 2016

Firstly, we demonstrate that unusually large outer HI spiral arms observed in NGC 2915 can form in an extended gas disk embedded in a massive triaxial dark matter halo with slow figure rotation, through the strong gravitational torque of the rotating halo. Secondly, we show that the figure rotation of a triaxial dark matter halo can influence dynamical evolution of disk galaxies by using fully self-consistent numerical simulations. We particularly describe the formation processes of “halo-triggered” bars in thin galactic disks dominated by dark matter halos with figure rotation and discuss the origin of stellar bars in low luminosity, low surface brightness (LSB) disk galaxies. Thirdly, we provide several implications of the present numerical results in terms of triggering mechanism of starbursts in galaxies and stellar bar formation in high redshifts.
SAURON dynamical modeling of NGC 2974
Authors: Krajnović Davor , Cappellari Michele , Emsellem Eric , Mcdermid Richard , De Zeeuw P. Tim
Published: July 2016

We present a three-integral orbit superposition Schwarschild model of NGC 2974, observed with the integral-field unit SAURON. We explore the dynamical structure of the stars and gas.
Radial Distributions of Dark and Luminous Matter in Bright Spiral Galaxies
Authors: Kassin Susan A. , De Jong Roelof S. , Pogge Richard W.
Published: July 2016

We present a work in progress investigating the radial distributions of dark and luminous matter in local bright spiral galaxies spanning a range of Hubble types. the distributions are derived from multiband imaging (BVRJHK) predominately from the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS) and rotation curves from the literature. We use stellar colour-MIL relationships from Bell & de Jong (2001, ApJ, 550, 212) to create radial stellar mass surface density profiles for each of our galaxies. These profiles are used to create rotation curves for the stellar component; gas masses are derived from HI when available. the resulting stellar and gas mass rotation curves are compared to observed (total mass) rotation curves, and the rotation due to dark matter is determined for each galaxy. Fits to Navarro, Frenk, & White (1996, ApJ, 462, 563; NFW) halo profiles are shown. We present this analysis for 2 example galaxies from our sample of nearly 50. We will use this data to investigate correlations between these mass components and physical properties of galaxies.
The stellar Mass–to–Light ratio in disc galaxies
Authors: Portinari L. , Sommer–Larsen J. , Tantalo R.
Published: July 2016

The mass and distribution of baryons in galaxies is closely related to the inferred structure of the dark halo. A robust estimate of the baryon content requires knowledge of the typical mass–to–light (M/L) ratio of the stellar component. Various arguments favour a low M*/LI < 1 for late–type spirals. We show that “bottom-light” Initial Mass Functions (IMFs) favoured by recent literature do yield so low M/L ratios, for Sbc/Sc discs. We also predict the stellar M/L ratio, and hence the zero–point of the Tully–Fisher relation, to vary significantly with Hubble disc type. Finally, we provide colour–M/L relations to derive the stellar M/L ratio from the observed photometry, for different IMFs.
Tracing the relation between black holes and dark haloes
Authors: Buyle Pieter , Baes Maarten , Dejonghe Herwig
Published: July 2016

We present new velocity dispersion measurements for a set of 12 spiral galaxies and use them to derive a more accurate υc – σ relation which holds for a wide morphological range of galaxies. Combined with the MBH – σ relation, this relation can be used as a tool to estimate supermassive black hole (SMBH) masses by means of the asymptotic circular velocity. Together with the Tully-Fisher relation, it serves as a constraint for galaxy formation and evolution models.
Dark Matter in Dwarf Galaxies: High Resolution Observations
Authors: Bolatto Alberto D. , Simon Joshua D. , Leroy Adam , Blitz Leo
Published: July 2016

We present observations and analysis of rotation curves and dark matter halo density profiles in the central regions of four nearby dwarf galaxies. This observing program has been designed to overcome some of the limitations of other rotation curve studies that rely mostly on longslit spectra. We find that these objects exhibit the full range of central density profiles between ρ ∝ r0 (constant density) and ρ ∝ r–1 (NFW halo). This result suggests that there is a distribution of central density slopes rather than a unique halo density profile.
Extreme Dark Matter Dominated Dwarfs
Authors: Wilkinson Mark I. , Kleyna Jan T. , Evans N. Wyn , Gilmore Gerard F.
Published: July 2016

The results of a large radial velocity survey of the Draco and Ursa Minor dwarf spheroidal galaxies are presented. the velocity dispersion profiles of both objects are very similar: initially the dispersion increases with radius, while at radii approaching the outer limit of the stellar distribution we observe a sharp fall-off. We present the results of mass modeling based on these new data – the mass to light ratios are found to be about 400M⊙/L⊙. Evidence is also presented that the dark matter in the central regions of UMi has a core-like distribution. Finally, we demonstrate that the inner regions of UMi have not been affected by tides and discuss the implications of our data for MOdified Newtonian Dynamics (MOND).
Evidence for Light-weight Local Group Dwarf Spheroidal Galaxies
Authors: Kuhn J. R. , Kocevski D.
Published: July 2016

A simple and natural explanation for the dynamics and morphology of the Local Group Dwarf Spheroidal galaxies, Draco (Dra) and Ursa Minor (UMi), is that they are weakly unbound stellar systems with no significant dark matter component. A gentle, but persistent, Milky Way (MW) tide has left them in their current kinematic and morphological state (the “parametric tidal excitation”). A new test of a dark matter dominated dS potential follows from a careful observation of the “clumpiness” of the dS stellar surface density.
A high-resolution rotation curve of NGC 6822
Authors: De Blok W. J. G , Weldrake D. T. F. , Walter F.
Published: July 2016

We present a high-resolution rotation curve of the Local Group dwarf irregular NGC 6822, obtained with the Australia Telescope Compact Array. the best curve has a resolution of 8″ or 20 pc and contains some 250 independent points. NGC 6822 is a very dark matter-dominated galaxy. There is no evidence for the presence of a steep density cusp down to scales of ~ 20 pc, in conflict with the predictions of CDM.
The Tully-Fisher Relation in Cl0024+1654 at z=0.4
Authors: Metevier Anne J. , Koo David C.
Published: July 2016

We present the Tully-Fisher relation in cluster Cl0024+1654 at z=0.4. We find that our sample of 15 distant cluster members are ⋐ 0.5 mag overluminous as compared to local galaxies, and they exhibit slightly more Tully-Fisher scatter. This scatter is correlated with galaxy colours and sizes such that the smallest and bluest Cl0024 members in our sample are most overluminous.
Galaxy Scaling Relations as a Result of Secular Evolution
Authors: Zhang Xiaolei
Published: July 2016

The secular evolution process which slowly transforms the morphology of a given galaxy over its lifetime through mostly internal dynamical mechanisms could naturally account for most of the observed properties of physical galaxies (Zhang 2003a). As an emerging paradigm for galaxy evolution, its dynamical foundations had been established in the past few years (Zhang 1996, 1998, 1999). in this paper, we explore further implications of the secular morphological evolution process in reproducing the well-known scaling relations of galaxies.
The Galactic Halo and CDM
Authors: Merrifield Michael R.
Published: July 2016

This paper reviews the available information on the central density distribution and shape of the Milky Way's halo. At present, there is no strong evidence that the Milky Way's halo properties conflict with the predictions of cold dark matter (CDM): a primordial central power law cusp can be accommodated by the observations, and the current constraints on flattening are also consistent with the predictions of the theory. If you want to pick a fight with CDM, then the Milky Way is probably not the place to do it.
The Origin and Distribution of Angular Momentum in Galaxies
Authors: Primack Joel R.
Published: July 2016

Cold Dark Matter with a large cosmological constant (ACDM) appears to fit large scale structure observations well. of the possible small scale problems, the Central Cusps and Too Many Satellites problems now appear to be at least partly solved, so Angular Momentum has become the most serious remaining CDM problem. There are actually at least two different angular momentum problems: A. Too much transfer of angular momentum to the dark halo to make big disks, and B. Wrong distribution of specific angular momentum to make spiral galaxies, if the baryonic material has the same angular momentum distribution as the dark matter. the angular momentum of dark matter halos, and presumably that of the galaxies they host, appears to arise largely from the orbital angular momentum of the satellites that they accrete. Since the dark and baryonic matter behave very differently in such accretion events, it is possible that the resulting angular momentum distribution of the baryons is different from that of the dark matter, as required to make the sort of galactic disks that are observed. the latest hydrodynamical simulations give some grounds for hope on this score, but much higher resolution simulations are needed.
Angular Momentum in Groups from Cosmological Simulations
Authors: Bailin Jeremy , Steinmetz Matthias
Published: July 2016

We have performed high resolution cosmological N-body simulations in which halos of 1011 M⊙ are resolved with over 700 particles. We report on the internal structure of group-sized halos (masses between 1011M⊙ and 1014 M⊙), particularly on how the angular momentum within the halo correlates with the shape of the halo and with the angular momentum at other radii. We find that many halos have an inner region whose angular momentum is disconnected with that of the outer halo.
On the angular momenta of galaxy structures
Authors: Flin Piotr , Godlowski W. , Szydlowski M.
Published: July 2016

We discuss the possibility that angular momenta of galaxy structures are due to the global rotation of the Universe.
Dark Matter Search Experiments At Boulby Mine
Authors: Paling S. M.
Published: July 2016

The status of the dark matter search program at the Boulby Underground Laboratory is reviewed. Recent results are presented and plans for future generation experiments are discussed.