bluuebunny/crossref_metadata_2025 huggingface dataset:
Note On A Super-Horizon-Scale Inhomogeneous Cosmological Model
Authors: Tomita K.
Published: July 2016

Many observations of large-scale and cosmological structures in the universe have been collected, but so far there is no consistent theoretical explanation. In the region within 100 Mpc from us, the observed two-point correlations of galaxies and clusters of galaxies can be described well by low-density homogeneous cosmological models (Bahcall & Cen 1993; Suto 1993). On the other hand, the observed anisotropies of the cosmic microwave background radiation have been explained well by comparatively high-density cosmological models such as the Einstein-de Sitter model (Bunn & Sugiyama 1994). In the intermediate scale, the angular sizes of the cores of quasars have been measured and their redshift dependence has been shown to be more consistent with the Einstein-de Sitter model than with the low-density models (Kellermann 1993). The number count-magnitude relation for remote galaxies supports low-density models with a nonzero cosmological constant (for example, Fukugita et al. 1990), but these models may be inconsistent with the observed distribution of Lyα clouds (Fukugita & Lahav 1991).
Gravitational Lensing Of Quasar 0957+561 And The Determination Of H0
Authors: Rhee George , Bernstein Gary , Tyson Tony , Fischer Phil
Published: July 2016

The double quasar 0957+561 was the first discovered instance of multiple imaging via gravitational lensing. The galaxy cluster is an important deflector as well as the first ranked galaxy. This has so far precluded construction of a unique model of the lens, reducing the accuracy of the derived H0 value. We have obtained deep images of the system at CFHT. The cluster is sufficiently massive to cause distortions on distant background galaxy images. We have used a mass map derived from lensing distortions to improve the accuracy of the cluster center location and place new limits on H0.
Gravitational Magnification And Cluster Masses
Authors: Taylor A.N.
Published: July 2016

The shear distortion of galaxies behind a large cluster provides us with only a relative measure of the mass of the cluster (Tyson et al. 1990, Kaiser & Squires 1993) due the invariance of shear to a sheet of matter. Thus we can at best only place lower limits on cluster masses, with the constraint that the surface density, κ(θ)=Σ(θ)/Σc, is non-negative. However, an absolute measurement of the mass can be obtained via the magnification of background galaxies (Broadhurst, Taylor & Peacock 1995, hereafter BTP). Here we describe the magnification effect, its observational consequences and mass reconstruction in the linear and nonlinear regimes. We also describe a number of applications in progress.
Optimized Cluster Reconstruction
Authors: Seitz Stella
Published: July 2016

We outline the noise-filtering finite-field inversion kernel and the regularized maximum likelihood methods for cluster reconstruction.
The Distribution Of Dark Mass In Galaxies
Authors: Sackett Penny D.
Published: July 2016

Gravitational lensing is one of a number of methods used to probe the distribution of dark mass in the Universe. On galactic scales, complementary techniques include the use of stellar kinematics, the kinematics and morphology of the neutral gas layer, kinematics of satellites, and the morphology and temperature profile of X-ray halos. These methods are compared, with emphasis on their relative strengths and weaknesses in constraining the distribution and extent of dark matter in the Milky Way and other galaxies. It is concluded that (1) the extent of dark halos remains ill-constrained, (2) halos need not be isothermal, and (3) the dark mass is probably quite flattened.
Searching For Dark Matter With Gravitational Microlensing: A Report From The MACHO Collaboration
Authors: Stubbs C.W. , Alcock C. , Allsman R.A. , Alves D. , Axelrod T.S. , Becker A. , Bennett D.P. , Cook K.H. , Freeman K.C. , Griest K. , Guern J. , Lehner M. , Marshall S.L. , Peterson B.A. , Pratt M.R. , Quinn P.J. , Reiss D. , Rodgers A.W. , Sutherland W. , Welch D.L. ,   (The MACHO Collaboration)
Published: July 2016

Gravitational microlensing is the most straightforward interpretation of the stellar brightenings that have been observed by our team and other experiments. These data have provided some of the most stringent limits to date on the nature of the Galaxy's dark matter halo. The number of events seen towards the LMC indicate that our Galaxy is not surrounded by a “standard” halo of MACHOs in the mass range of 10–6 to 0.3 solar masses. The observed optical depth towards the Galactic Center is an important constraint on the distribution of mass in the plane of the Galaxy.
The PLANET Collaboration
Authors: Albrow M. , Birch P. , Caldwell J. , Martin R. , Menzies J. , Pel J.-W. , Pollard K. , Sackett P. D. , Sahu K. , Vreeswijk P. , Williams A. , Zwaan M. ,   (The PLANET Collaboration)
Published: July 2016

A newly-formed microlensing monitoring network, the PLANET collaboration, is briefly described.
Is IRAS F10214+4724 Gravitationally Lensed?
Authors: Lehár J. , Broadhurst T.
Published: July 2016

We show that the z = 2.3 IRAS source F10214+4724 is gravitationally lensed by an intervening galaxy, as suggested by the observed near-IR structures. Its many anomalous properties can be explained if the source is an ordinary Seyfert 2 nucleus whose central regions are much more highly magnified than the surrounding host galaxy. Confirming expectations, we find a counterimage to the near-IR arc, and find spectral evidence for the lensing galaxy at z ∼ 1. We present new optical images which show that the optical source is compact and highly magnified. F10214+4724 may represent a population of lensed AGNs whose central engines are obscured.
The Variability Of PG1115+080
Authors: Schechter Paul L.
Published: July 2016

PG1115+080 (Weymann et al. 1980), the first quadruple lens system, remains the most promising for an optical measurement of the Hubble constant through a time delay. Factors contributing to this assessment include the well constrained geometry, the apparent magnitudes of the four components (Christian et al. 1987), the expected time delay (Narasimha & Chitre 1992), and the position of the lensing galaxy (Kristian et al. 1993). There are nonetheless many factors which combine to render this a difficult measurement, among them the small separation of the images and the small variability amplitude and long variability time scale of the “typical” optically selected quasar (Hook et al 1994). The measurement is further complicated by the likelihood of microlensing of the individual components (Witt et al. 1995), which depends upon the degree to which the quasar is resolved and the fraction of the lens mass in microlenses.
Mapping The Extinction In Dusty Lenses: Optical And IR Imaging Of MG J0414+0534
Authors: Vanderriest C. , Angonin-Willaime M.-C. , Rigau F.
Published: July 2016

The source of the gravitational mirage MG J0414+0534, found in a radio survey (Hewitt et al. 1992), is an extremely reddened quasar at z ≃ 2.63 (Lawrence et al. 1995) but the redshift of its lensing galaxy is still unknown (≃ 0.8 ?). Whether the extinction occurs mainly in the lens galaxy or in the source itself is a matter in debate. Also, a discrepancy is observed between the radio and optical flux ratios for images A1 and A2, which could be due either to differential magnification near a caustic or to differential extinction (Schechter et al. 1992, hereafter SM92; Angonin-Willaime et al. 1994, hereafter AW94). The new IR and optical data discussed here could throw some light on these obscure issues.
The Statistics Of Nearly On-Axis Gravitational Lensing Events
Authors: Wang Yun
Published: July 2016

A small volume of space, nearly on-axis behind a gravitational lens with respect to a given source, will receive a greatly increased radiation flux. In the idealized case of a point mass lens acting on a point source in complete isolation, the volume will approach zero only as the flux tends to infinity; in fact, the volume weighted rms flux is divergent. In realistic cases, finite source size and the effects of other gravitational deflections (i.e., non-zero shear) limit the maximum flux and considerably complicate the physics, but very large fluxes are still produced in small volumes. We consider the physics and statistics of these Extreme Gravitational Lensing Events (EGLE) and present an initial examination of their possible astrophysical effects for various known and putative populations of lensing objects and sources, with particular attention to the case in which finite source size is important but shear is not.
Formation Of Giant Luminous Arcs And Arclets Using An Optical Gravitational Lens Experiment
Authors: Surdej J. , Refsdal S. , Pospieszalska-Surdej A.
Published: July 2016

It is well known that simple optical lenses simulating light deflection due to a foreground object may easily reproduce all types of image configurations observed among known multiply imaged QSOs and AGN (cf. simulations in Refsdal and Surdej 1992, 1994, Surdej et al. 1993). Such an optical lens experiment can also be used to simulate the formation of multiple giant luminous arcs and arclets seen near massive foreground galaxy clusters. The optical setup used to make this experiment is shown in Fig. 1 (a similar setup was presented during the Melbourne conference). A compact light source is located on the right side (not very clearly seen), then comes to the left a ‘spiral galaxy disk’ optical lens (manufactured by the authors) and a cardboard perforated by multiple pinholes. In the absence of light deflection (i.e. by simply removing the optical lens), direct (non distorted) images of the background galaxies are seen by an observer, like those projected on the distant white screen (see Fig. 2a). When the optical lens is inserted between the light source and the multiple pinholes screen (cf. Fig. 1), images of the background galaxies get distorted (arclets) and/or transformed into multiple images, including giant luminous arcs (see Figs. 2bc for examples). We showed during the conference that by covering the pinholes with various transparent colored filters and translating the multiple pinholes screen, it was possible to reproduce, in a very inexpensive way, distorted images of background galaxies like the very impressive strong lensing artifacts seen behind the rich cluster Abell 1689 (cf. the color videotape of simulations by Tony Tyson).
Ages of Galaxy Bulges and Disks from Optical and Near-Infrared Colours
Authors: Peletier R. F. , Balcells M.
Published: July 2016

For a sample of bright nearby early-type galaxies we have obtained surface photometry in bands ranging from U to K. Since the galaxies have inclinations larger than 50° it is easy to separate bulges and disks. By measuring the colours in special regions, we minimize the effects of extinction, and by looking at B – K colour gradients we can show that for these type of spirals the colours mainly give information about stellar populations, and not extinction. We find that the differences between bulges and disks in all colours is very small, and using simple population models we can show that on the average the age difference between the bulge and the disk at 2 scale length is smaller than 30%, and much smaller if part of the difference is caused by a gradient in metallicity.
The Star Formation History of Elliptical Galaxies
Authors: Davies Roger L.
Published: July 2016

There is a growing body of evidence indicating young ages, 8 ± 3 Gyrs, for elliptical galaxies and significant age gradients with a younger population residing at the centre. The data appear to be consistent with a scenario where elliptical galaxies are assembled hierarchically with low luminosity galaxies forming first. Late star formation, associated with the last merging event and usually involving only a small fraction of the galaxy mass, could then account for the low age estimates of some luminous galaxies.
Disky Ellipticals in the Hubble Sequence
Authors: Scorza Cecilia , Bender Ralf
Published: July 2016

About one third of the elliptical galaxies show disky isophotes (Bender et al. 1989). These are low luminosity objects, are rotationally flattened (Carter 1987, Bender 1988b, Nieto 1988), are much weaker radio emitters than ellipticals in average and show no strong X-ray emission in excess of their discrete sources contribution. They have pointed isophotes which are thought to reflect the presence of embedded stellar disks. A large number of these disks could be hidden due to low inclinations (Rix and White 1990). Because of these properties, which makes them strongly resemble S0 galaxies, it has been suggested that disky ellipticals form together with S0s and spirals a continuous transition in D/B ratio in the Hubble sequence (Bender 1988b, Nieto 1988). However, until the present, this hypothesis had not been investigated throughout.
The Rate of Supernovae in Normal Galaxies
Authors: Cappellaro Enrico
Published: July 2016

The rate of supernovae (SNe) is a key number linking stellar evolution with galaxy evolution models. Stellar evolution theories predict life times, fates and nucleosysntesis yields of individual stars which are used to predicted the galaxy chemical evolution once the star formation history in the galaxy is known. Constraints to the models are the present chemical content of galaxies but also the present observed SN rate (Arimoto & Yoshi, 1987; Ferrini & Poggianti, 1993; Matteucci, 1994; Renzini et al., 1993; Bressan et al., 1994; Elbaz et al., 1995).
An HST Survey of Cores of Early-Type Galaxies
Authors: Kormendy John , Byun Yong-Ik , Ajhar E. A. , Lauer Tod R. , Dressler Alan , Faber S. M. , Grillmair Carl , Gebhardt Karl , Richstone Douglas , Tremaine Scott
Published: July 2016

Photometry of the central parts of bulges and elliptical galaxies with the Hubble Space Telescope (HST) confirms and extends ground-based results. Most giant ellipticals have cuspy cores: at the “break radius” rb (formerly the core radius rc), the steep outer surface brightness profile turns down to a shallow inner power law I(r) ∝ r–γ, 0 ≤ γ ≲ 0.25. The corresponding slope of the deprojected profile is derived; the flattest cores allow box orbits to survive. Cores continue to satisfy fundamental plane parameter correlations like those found from the ground. In particular, HST confirms that the luminosity sequence of elliptical galaxies (from cDs to M 32) is physically unrelated to spheroidal galaxies like Fornax. The latter are closely related to late-type dwarfs. Low-luminosity ellipticals do not show cores: 0.5 ≲ γ ≲ 1.3. The most important new result is that global and core properties both show signs of a dichotomy between (i) low-luminosity ellipticals that rotate rapidly, that are nearly isotropic and oblate-spheroidal, that have disky-distorted isophotes, and that are coreless and (ii) giant ellipticals that are essentially nonrotating, anisotropic, and moderately triaxial, that are boxy-distorted, and that have cuspy cores.
Detecting CO at High Redshift
Authors: Tacconi Linda J.
Published: July 2016

Searches for molecular line emission from high redshift galaxies have become one of the recent highlights in millimeter astronomy, largely because detection of this emission enables one to study the potential for star formation in galaxies at epochs close to galaxy formation. Such information is crucial to models of galaxy evolution. Thus far, most of the searches have been to try to detect any of the rotational lines of CO, although many authors have also inferred the presence of molecular gas through detections of cold dust in the submillimeter region of the spectrum. In addition to providing information about the physical properties of the molecular gas in distant galaxies (when more than one transition or isotope is detected), the CO lines can be used to place stringent constrints on the dynamical masses of these systems. Moreover, since millimeter data has spectral resolutions of typically a few tens of km/s, one can pin down the redshift of the host galaxy with extremely high precision. One of the driving forces in most of the searches for CO emission at high redshift is the fact that molecular gas is known to be an important constituent in the low redshift counterparts to the types of objects that one expects to find at high redshifts, the Ultraluminous Infrared Galaxies (ULIRGs), (e.g. Mirabel and Sanders 1985; Sanders et al. 1986), powerful radio galaxies (e.g. Mazzarella et al. 1993), and nearby quasars (e.g. Barvainis et al. 1989), for example.
Dark Matter Halos
Authors: Saglia R.P.
Published: July 2016

The observational evidence for dark halos around galaxies is shortly reviewed. New and old techniques and results constraining the mass, the distribution, the shape and the nature of dark halos are discussed.
Mapping Stellar Evolution in the Wake of Density Waves in Ring Galaxies
Authors: Appleton P. N. , Struck-Marcell C. , Bransford M. A. , Charmandaris V. , Marston A. P. , Borne K. , Lucas R.
Published: July 2016

We have been conducting multi-color observations of a sample of classical ring galaxies with the aim of using them to study the formation and evolution of massive stars. We compare theoretical predictions for the expected color of the material inside the rings assuming that massive stars are created in the wake of the expanding wave. We present ground based data for VIIZw466 and HST data for IIZw28 and the Cartwheel which show strong color gradients.
A Possible Evolutionary Scenario for NGC 7217
Authors: Athanassoula E. , Bosma A. , Guivarch B. , Verdes-Montenegro L.
Published: July 2016

NGC 7217 is an ordinary spiral galaxy with three rings whose size ratios are such that they can be associated with resonances, as for barred spirals. From 21-cm HI line data and BVRI CCD-images of this galaxy we find (cf. Verdes-Montenegro et al. 1995) : 1) a nuclear ring strong in Hα, 2) an inner ring seen clearly in a B - I colour map, and 3) an outer ring, with blue colours and strong HI-emission. After deprojection the disk has a mean ellipticity of 0.04 ± 0.01, while the position angle of the deprojected galaxy changes suddenly at 65″ radius, where the minor axis becomes major axis. Thus a very mild oval distortion could exist, with the outer ring perpendicular to the oval. Merrifield and Kuijken (1994) find from the stellar kinematics that about 20 – 30 % of the stars are in retrograde orbits.
Estimation of MG/FE Ratio in Early-Type Galaxies
Authors: Barbuy B. , De Freitas Pacheco J. A. , Idiart T.
Published: July 2016

Through computed synthetic spectra for individual stars in the Mg2 index region where different values of [Mg/Fe] were considered, and observed features Fe5270 and Fe5335 in a sample of 80 stars, we derived relations Mg2 and  = f(Teff, log g, [Fe/H], [Mg/Fe]). These relations were used to compute integrated indices for single aged populations, where number counts in colour-magnitude diagrams were used. A multi-population model was then built through a convolution of the single stellar population indices with a metallicity and luminosity distribution for elliptical galaxies, where a chemical evolution model includes enrichment by type II and I supernovae. A grid of 80 multi-population models was computed, by varying the efficiency of star formation rate. In Figure 1 are shown the results for [Mg/Fe] = 0.0, 0.3 and 0.6 compared to observational data by Worthey et al. (1992). An average value of [Mg/Fe] = 0.3 is found for the sample ellipticals.
Emission Line Regions in M86
Authors: Döbereiner S. , Heidt J. , Wagner S. J.
Published: July 2016

We present broad- and narrow-band (B, R, Hα+[NII] and Hα continuum) observations of M86 obtained with a focal reducer at the Calar Alto 1.23m telescope, to look for any signs of material cooling out from the hot X-ray emitting ISM. The above figures show a quotient image (13′ × 13′, north up) (Hα cont. - Hα) to the left, and a Hα image (right) from which the light of the stellar spheroid of M86 has been subtracted. Both are overlayed with ROSAT PSPC X-ray contours.
NGC 2188: A Case Study for Disk-Halo Interaction
Authors: Domgörgen H. , Dahlem M. , Dettmar R.-J.
Published: July 2016

A deep Hα image of the nearly edge-on (i ∼ 86°; Tully, 1988) irregular galaxy NGC 2188 shows the presence of spectacular filaments of ionized gas extending from a large star-forming complex several hundred pc into the halo of the galaxy (Dettmar, 1994). The origin and ionization mechanism of such extraplanar diffuse ionized features is not yet clear. One promising idea is that the extraplanar DIG is due to large scale mass circulation, i.e. a galactic “fountain” (Shapiro & Field, 1976) or “chimney” (Norman & Ikeuchi, 1989). Hα filaments could then be the photoionized walls of such chimneys or fountains.

Recently obtained VLA HI data also show peculiar HI filaments. East of the center of NGC 2188 a giant superbubble with a radius of 550 pc and energy requirement 1.6×1053 erg is found. However, a correlation between HI structures and Hα filaments cannot be found.

The HI observations reveal large-scale deviations from symmetry which are present in both, the gas distribution and in the velocity field. These suggest that NGC 2188 is a perturbed system, although it is not obviously an interacting galaxy.
Keck Spectroscopy of Moderate Redshift Galaxies Imaged by HST
Authors: Forbes Duncan , Phillips A. , Koo D. , Illingworth G.
Published: July 2016

Combining the results from Keck spectral and HST imaging data (Forbes et al. 1994), we have derived various quantitative parameters for 17 faint (I ∼ 21), distant (z ∼ 0.5) galaxies. Such redshifts correspond to a look–back time that is about half the age of the Universe and for which some scenarios predict significant galaxy evolution. We have measured disk scale lengths (with sizes ranging from 1–5 kpc) from fits to the surface brightness profiles and internal velocities with a rest frame resolution of σ = 55 to 80 km s–1 by fitting to the emission lines. The luminosity–disk size and luminosity–internal velocity relations for our moderate redshift galaxies are similar to the scaling relations seen for local galaxies, albeit with modest ΔMB ∼ 1m brightening. We do not see evidence for a dominant population of starbursting dwarf galaxies, that have disappeared by the present epoch. Further details of this study can be found in Forbes et al. (1995). When large samples of kinematic data on distant galaxies are available, we will be able to trace galaxy evolution by mass as distinct from light.
Study of a Complete Sample of Hα Emission–Line Galaxies from the UCM Survey
Authors: Gallego J. , Zamorano J. , Rego M. , Vitores A.G. , Alonso O.
Published: July 2016

The Universidad Complutense de Madrid survey is a long-term project with the aim of finding and analyzing star forming galaxies using the Hα line as the tracer for star formation processes. In order to obtain a representative and complete sample of the population detected, spectroscopic observations were carried out for the full sample of Hα emission-line galaxy (ELG) candidates of the UCM lists 1 and 2. The ELGs types most commonly found (47%) are intermediate to low-luminosity objects with a very intense star-formation region which dominates the optical energy output of the galaxy. This kind of ELGs is similar to the galaxy population detected in the blue objective-prism surveys. And what is more important, a second population (43%) of star-forming galaxies with low ionization or high extinction properties has been found. This ELGs group is detected neither in the blue (University of Michigan survey, Case survey) nor in other surveys (Kiso, IRAS, Markarian) using other selection techniques.
Peculiar Kinematics in the Core of NGC 474
Authors: Hau G. K. T. , Balcells M. , Carter D.
Published: July 2016

We present absorption line profile analysis of NGC 474, an elliptical with prominent, irregular shells. Profiles are parameterized with Gauss-Hermite polynomials (van der Marel & Franx ApJ 407 1993; Rix & White MNRAS 254 1992). The fastest rotation (∼ 50 km s–1) and steepest central velocity gradient along the intermediate photometric axis rules out the possibility that NGC 474 is a face-on S0 (Schombert & Wallin AJ 94 1987) and suggests that it is triaxial. The asymmetry of the LOSVDs (h3 up to 0.08) indicates the presence of a subsystem with rapid, ordered rotation. The minor axis velocity curve shows a kinematic feature at 3–4″ east of the nucleus, with no associated h3 or h4 features. Non-parametric LOSVD analysis (unresolved Gaussian decomposition, Kuijken & Merrifield MNRAS 264 1993) reveals a double-peaked profile at that location. In all position angles line-profiles are distinctly pointy for radii up to 2″, and are consistent with zero further out. We have found similar central positive h4 terms in the shell galaxy NGC 2865 (Hau et al. MNRAS in prep). Cores with pointy LOSVDs are uncommon in ellipticals (Bender, Saglia & Gerhard MNRAS 269 1994). Positive h4 terms might contain important clues on the shell-formation mechanism in ellipticals.
Physical Properties of Subcritical Accretion Disks
Authors: Heinrich O. M.
Published: July 2016

Despite of the great interest in accretion disks around supermassive black holes there are still numerous controversies about their structure and their physical properties. Therefore we have calculated the structure of such disks for a wide range of parameters. For the viscosity we use a standard α-description with the main component of the stress tensor trϕ proportional to the gas pressure. The disk structure depends sensitively on material properties such as opacities and specific heats. In our calculations we have used an equation of state and mean opacities taking into account a list of the most important ionization processes as well as the radiation contributions to thermodynamic quantities.
Spectroscopic and Photometric Nearby Field Galaxy Survey
Authors: Jansen R.A. , Franx M. , Fabricant D.G. , Caldwell N.
Published: July 2016

Galaxy evolution is one of the key questions in current astronomy. Observations of strong and recent galaxy evolution conflict with previous ideas of orderly and early evolution of galaxies.
NGC 4569: X-Ray Observation of a Spiral Galaxy with Nuclear Starburst Activity
Authors: Junkes N. , Hensler G.
Published: July 2016

We investigate the distribution of soft X-rays and their spectral characteristics for a sample of nearby nuclear starburst galaxies in order to probe their evolution. NGC 4569 is a bright early-type spiral in the Virgo cluster, one of the few blue-shifted galaxies outside the local group. It is gas-deficient in the outer spiral arms, the neutral hydrogen strongly concentrated in the inner region [1]. The bright nucleus, embedded in a normal stellar bulge, is probably the result of a recent star formation episode [4]. Based upon optical spectroscopy of its nucleus [5], the galaxy has been classified as a LINER. The results on NGC 2903 will be presented separately [2].
Absorption Features of “Lα Damped” Type in Spectra of Very Distant QSO as an Indicator of Young Clusters of Galaxies
Authors: Komberg B.V.
Published: July 2016

It is shown that at present one can not exclude a possibility that rare, wide and deep absorption feature of Lα damped type could be formed in a rich gas medium of distant clusters of galaxies, not verialized yet. In future massive galaxies are likely to be formed in the central regions of these clusters. Nuclei of these galaxies become very active during a short time, i.e. they pass a stage of QSO. Narrower absorption lines of metals and/or 21 cm associated with Lα damped systems can be formed in the clouds belonging to separate galaxies of these clusters.
Self-Regulated Star-Formation in Galaxies
Authors: Köppen J. , Theis Ch. , Hensler G.
Published: July 2016

In the chemodynamical models of galaxies the energy input from massive stars into the ambient medium results in a self-regulation of the star formation rate (SFR). A thorough analytical and numerical study of this model shows that there is always a strong and negative feed-back, and the SFR becomes almost independent of the assumed stellar birth function (SBF). The time-scale to reach this equilibrium is much shorter than the gas consumption time-scale, hence the models evolve along this solution for most of the time. This mechanism provides a physical explanation for a quadratic dependence of the SFR on gas density. For more details cf. Köppen et al. (1995), A&A 296, 99 and in preparation.
Environmental Effects on the Properties of Spiral Galaxies: Isolated Pairs of Spirals
Authors: Márquez I.
Published: July 2016

We characterized isolated spiral galaxies as a reference for the properties of interacting ones: we selected all the spirals in CfA catalog with mB ≤ 13.0,δ ≥ 0, a≤ 4′ and 73° > i > 32°. The isolated ones were those having no companions in ΔD≤0.5Mpc and ΔV≤500 km/s and no satellites galaxies in their neighborhood (from Nilson catalog and Palomar charts). To select the isolated pairs of spirals we used Karachentsev's catalog applying similar conditions for mB, δ, a, i and the same isolation criteria. We used broad band CCD images (Johnson B,V e I), narrow band CCD images (Hα) and long slit spectra in Ha region. The BVI images analysis consisted on applying sharp-divided methods, obtaining simulated images (from bulge/disk decomposition and galaxy orientation in the sky) and Fourier analysis. From Hα images we determined total emission, size, distribution and flux of HII regions. We also obtained the rotation curves.
X-Ray Observations of Elliptical Galaxies by ASCA Satellite
Authors: Matsushita K. , Makishima K.
Published: July 2016

Using ASCA, we have confirmed that the ISM of X-ray bright elliptical galaxies are surprisingly metal poor, as compared to the theoretical predictions. In fact the exact values of the derived metallicity depend considerably on the plasma emission codes. However, the overall metallicity cannot be larger than ∼ 1 solar. For low LX/LB galaxies, all the available plasma codes suggest abundances less than half a solar. The ASCA spectra may be compatible with somewhat higher metallicity if we assume there is an additional low-temperature component (e.g. kTe ∼ 0.3 keV). However, the derived abundance can not be over 1 solar. In particular, the Si abundance turns out to be < 1.5 solar, confirming the metal-poor nature of the ISM. These ASCA results are in severe contradiction with most of the SN Ia rate, particularly that of Tammann (1982). Considering further that a fairly long time (109–10yr) is needed for the stellar mass loss to accumulates into the ISM, it is suggested that the SN Ia rate has remained quite low throughout Hubble time.
ARP 142: Another Interacting Galaxy with Very Large Internal Motions?
Authors: McCain C.M. , Freeman K.C. , Quinn P.J.
Published: July 2016

We present our study of Arp 142, an interacting system which consists of irregular (NGC 2936) and spheroidal (NGC 2937) components. We discovered that NGC 2936 has very high internal motions, much higher than what is expected from the dynamics of interaction of such galaxies.
The Influence of Spiral Arms and Bar on the Large-Scale Galactic Magnetic Field Evolution
Authors: Otmianowska-Mazur K. , von Linden S. , Lesch H.
Published: July 2016

Recent observations of radio polarization from nearby galaxies show that the large-scale galactic magnetic field is aligned with spiral arms and bars and the magnetic field vectors in the interarm regions possess a spiral structure which has the same pitch angle as that in spiral arms. Our present project is going to address the following questions: What is the structure and evolution of the large-scale galactic magnetic field under the influence of spiral and bar structure in a galactic disk? To which extent could the resulting magnetic field account for the observed spiral pattern of magnetic field in nearby galaxies? The model is based on the particle-particle numerical scheme (SPH) involving two components: stars and molecular gas. The magnetic field is connected with the latter one. The magnetic field computations were performed first in two dimensions for 100 velocity fields: from 107 to 109 yrs. The resultant magnetic field is strongly affected by spiral arms, however at the given evolutionary stage its structure is different from the velocity field at the same time. The magnetic pitch angle distribution shows that the magnetic field “remembers” all the past velocity steps. The magnetic pitch angle distribution resulting after beam smoothing could quite well fit observations. The present model with fully 3D velocity field of interstellar gas should clear the problem if the magnetic field under the realistic velocity evolution of gas could explain the observed structure of large-scale magnetic field with constant pitch angle in the whole disk.
The Galaxy Mass Distribution from Mergers in a Collapsing Spherical Cluster
Authors: Shaviv Nir J. , Shaviv Giora
Published: July 2016

We examine the role of mergers in the formation and statistics of galaxies and clusters of galaxies. First steps in this direction were carried out by Shaviv & Shaviv (1993, ApJ.Lett., 412, L25) where the OD case was treated. The work is extended to examine the effect of self gravity. Thus, we essentially explore the combined effect of violent relaxation and mergers on the resulting structure and mass distribution of galaxies in clusters of galaxies. We developed a numerical method to treat the spherical 2D problem (radial position and velocity) of the evolution of a collapsing cluster of gas clouds (Shaviv & Shaviv, 1995, ApJ., 448, 514).
A BVRIJKHα Survey of 355 Nearby Galaxies
Authors: Surma Peter
Published: July 2016

A multiband CCD-survey of 355 UGC galaxies in our local cosmological neighbourhood is undertaken in collaboration with S.D.M. White (MPI-fAstrophysik Garching), S. McGaugh (IoA, Cambridge), M. Dennefeld (IAP Paris), H. Ferguson (STScI), M. Rieke, A. Grauer (Steward Obs. Arizona). Optical observations are obtained on Calar Alto (MPIA Heidelberg) and at La Palma (RGO) – with data 40% complete at the moment. The selection criterion is diameter 1.5′ < D25 < 2.5′. A database of local galaxy properties is being established (including total luminosities, mean SB, diameters, colours, colour gradients, D/B-ratios, present SFRs). Using theoretical evolution models we can predict the bona fide appearance of the galaxy population at any given redshift and thus provide a secure reference point to interpreting galaxies observed at intermediate and high z (e.g. faint galaxy counts).
Magnetic Fields and the Interstellar Medium in Spiral Arms
Authors: Urbanik M. , Soida M. , Beck R.
Published: July 2016

We performed the high frequency radio studies of spiral galaxies using the 100 m MPIfR radio telescope at 10.55 GHz. Two objects: NGC 4254 and NGC 3627 possess perturbed spiral structures while two others, NGC 3521 and NGC 5055 are flocculent objects, lacking organized spiral patterns. NGC 3521 possesses also a peculiar dust lane. For NGC 4254, NGC 3627 and NGC 5055 deep polarization maps were made, for NGC 3521 the total power data only were analyzed (see Urbanik et al. 1989).
Spectrophotometric Population Synthesis of Early Type Galaxies
Authors: Vazdekis A. , Peletier R. , Casuso E. , Beckman J.
Published: July 2016

We have developed a new stellar population synthesis model for calculating colours and absorption line indices in early type galaxies. This model can work either for single-age stellar populations or in an evolutionary scheme following the chemical evolution. The model is based on the isochrones of the Padova group and we have developed our own method of conversion to colours. Details can be found in Vazdekis A., Casuso E., Peletier R. & Beckman J. (submitted, 1995). To test the model we have obtained accurate observations in many colours and line indices of the three standard galaxies: NGC 3379, NGC 4472 and NGC 4594.
Magnetic Structure Responsible for Coronal Disturbances: Observations
Authors: Altschuler Martin D.
Published: July 2016

Coronal disturbances are considered as consequences of the ejection of electric currents (or non-potential magnetic fields) from the photosphere and chromosphere into the corona. It may be that electric currents are generated near neutral lines in the photosphere and are later ejected into the corona.
Direct Measurements of the Directivity of Type I and Type III Radiation at 169 MHz
Authors: Caroubalos C. , Steinberg J. L.
Published: July 2016

A 169 MHz radiometer fed from a Sun-pointed 8 dB antenna was flown on the Soviet probe Mars-3 in 1971–1972. This experiment called Stereo-1 is part of a cooperation program between the U.S.S.R. and France.
A Theory of Type III Solar Radio Bursts
Authors: Zaitsev V. V. , Mityakov N. A. , Rapoport V. O.
Published: July 2016

This paper is an extension of an earlier paper by Zaitsev et al. (1972).
The Behaviour of the Outer Solar Corona (3R⊙to 10R⊙) During a Large Solar Flare Observed from OSO-7 in White Light
Authors: Brueckner G. E.
Published: July 2016

(Solar Phys.). A very bright coronal streamer was observed on December 13, 1971 by the Naval Research Laboratory's coronagraph on board of OSO-7. The next day, the streamer had changed it's brightness and configuration considerably. Three subsequent coronagraph images, taken on December 14 at 0407, 0418 and 0430 UT show a large plasma cloud moving outward from the Sun between 3 and 10 solar radii. They also show distinct smaller clouds moving outward with projected velocities between 950 and 1100 km s−1. Traced back in time to the lower solar corona, these clouds coincide with discrete type II radiobursts observed from Culgoora between 0241 and 0256 UT. Each single cloud shows it's signature in the radio recording between 100 and 20 MHz. The drift velocity of the radio bursts can be determined to be 1600 km s−1using Newkirk's coronal streamer model. Assuming, that the plasma clouds are ejected from an active region 30° behind the east limb vertically, their true velocities close to the surface of the Sun would be approximately 1400 km s−1, which is in good agreement with the drift velocities determined from the type II bursts, considering all uncertainties. Therefore, the type II burst disturbance moves with the same velocity as the driving material.
Type II Solar Radio Bursts in the Decimeter Band
Authors: Maxwell Alan
Published: July 2016

(Solar Phys.) The progress of shock waves generated by solar flares through the corona is delineated in the radio band by radio bursts of spectral type II. Previous discussion of these bursts has been mainly concerned with their characteristics at frequencies below 200 MHz. This paper discusses the characteristics of the bursts in the range 2000–200 MHz, and the information that may then be deduced about the propagation of shock waves through the lower corona. Particular attention is paid to the type II burst emitted by the flare of 1972 August 7, 1500 UT. The shock from this flare was subsequently tracked (by radio equipment on the IMP-6 satellite) through the interplanetary plasma right to the Earth.
Type II Bursts at Hectometric and Kilometric Wavelengths from Interplanetary Shocks
Authors: Malitson H. H. , Fainberg J. , Stone R. G.
Published: July 2016

The first type II radio burst to be observed at frequencies below the ionospheric cutoff was recorded by the Goddard radio astronomy experiment on the Interplanetary Monitoring Platform, IMP-6. It occurred on June 30, 1971; a tracing made from the intensity contour plot of the radio data is shown in Figure 1. On the original, intensity contours were plotted in dB above background as a function of frequency and time. The figure shows 32 discrete frequencies from 4.9 MHz to 30 kHz received by the IMP-6 experiment. The time scale covers a period of almost five hours. During this time, five individual type III bursts and one group of type III's occurred; they are shown by their outlines to be drifting rapidly from high to low frequencies. The relatively narrow-band, slowly-drifting radiation with clearly defined fundamental and second harmonic is the type II. The average drift rate, represented by the straight lines drawn through the burst, is approximately 2.5 kHz min−1 in this frequency range, and is roughly 100 times slower than that of the type III bursts. The ovals defining the type II emission were traced from the record and show modulation of the signal caused by the spin of the satellite and the resultant sweeping of the antenna pattern of the dipole across the source direction. On the original record, the outlines of the type III's are also filled with a pattern of modulation ovals that were omitted from the figure for clarity. The shaded portion of the record at the lower frequencies represents magnetospheric noise.
On Split-Band Structure in Type II Radio Bursts from the Sun
Authors: Smerd S. F. , Sheridan K. V. , Stewart R. T.
Published: July 2016

(Astrophys. Letters). The measured amount of band-splitting, Δf, in the spectra of nine harmonic type II bursts is illustrated in Figure 1. Here, as in previous, smaller samples (Roberts, 1959; Maxwell and Thompson, 1962; Weiss, 1965) Δf is found to increase with frequency, f.
Solar Radio Pulsations
Authors: Gotwols B. L.
Published: July 2016

(Solar Phys.). Several models for pulsating type IV radio bursts are presented based on the assumption that the pulsations are the result of fluctuations in the synchrotron emission due to small variations in the magnetic field of the source. It is shown that a source that is optically thick at low frequencies due to synchrotron self absorption exhibits pulsations that occur in two bands situated on either side of the spectral peak. The pulsations in the two bands are 180° out of phase and the band of pulsations at the higher frequencies is the more intense. In contrast, a synchrotron source that is optically thin at all frequencies and whose low frequency emission is suppressed due to the Razin effect develops only a single band of pulsations around the frequency of maximum emission. However, the flux density associated with the later model would be too small to explain the more intense pulsations that have been observed unless the source area is considerably larger than presently seems reasonable.
Coronal Magnetic Fields and Energetic Particles
Authors: Newkirk Gordon
Published: July 2016

**Magnetic fields in coronal and interplanetary space play a critical role in the propagation and storage of energetic particles from the flare site to 1 AU. The current investigation is designed to determine if the detailed configuration of the coronal magnetic fields below 2.5 R⊙ has a measurable influence on the escape of particles to 1 AU, can account for the observed broad longitudinal distribution of proton flares, and can provide a realistic site for storage of energetic particles.
Preliminary Results from the NRL/ATM Instruments from Skylab SL/2
Authors: Tousey R. , Bartoe J.-D. F. , Bohlin J. D. , Brueckner G. E. , Purcell J. D. , Scherrer V. E. , Schumacher R. J. , Sheeley N. R. , Vanhoosier M. E.
Published: July 2016

The Naval Research Laboratory prepared three instruments for ATM and also a series of rocket payloads for purposes of calibration, under the overall direction of R. Tousey, the Principal Investigator. In this preliminary report a summary of results from operations during the first mission (SL/2) and sample results are presented.
11. A characteristic line current in a fully ionized gas
Authors: Pease R. S.
Published: July 2016

Standard formulae for the electrical resistance and for the radiating properties of a fully ionized gas have been combined with pinch effect relations to obtain the stationary state radial distribution functions and current—voltage characteristics of a filamentary current. The calculations suggest that the radiation cooling permits a pinched discharge to exist, with a maximum current of about one or two million amperes.
14. The neutral point theory of solar flares
Authors: Sweet P. A.
Published: July 2016

It is shown that under certain conditions hydrostatic equilibrium becomes unstable in a conducting medium in the presence of a magnetic field containing a neutral point if the gas pressure is less than a limiting value.

The motion resulting from breakdown of hydrostatic equilibrium in the solar chromosphere above complex sunspot groups could produce solar flares and cosmic ray particles.
15. The neutral point discharge theory of solar flares. A reply to Cowling's criticism
Authors: Dungey J. W.
Published: July 2016

The discharge theory has been criticized by Professor Cowling in §5·3 of The Sun, ed. Kuiper (Chicago[1]). A discharge theory requires the thickness of the accelerating layer to be only 5 m, which he finds unacceptable. This criticism is not soundly based, because no lower limit for the layer width is obtained from observation.

Secondly, Cowling invokes Lenz's law: ‘the effect of induced currents is always to oppose the change to which they are due.’ Lenz's law needs verifying for conducting fluids, however, and though it is usually true, it is shown to be false when there is a neutral point. Since Lenz's law refers to electromagnetic induction, other effects such as the pressure gradient may be omitted in this test, and then a completely rigorous proof is possible: it is shown that in an ideal fluid which is perfectly conducting, perfectly compressible and inviscid, the current density at a neutral point must become infinite.

The pressure gradient is irrelevant to Lenz's law, but it usually opposes any motion and should also be discussed. A physical picture suggests that the pressure gradient will not stop a vortical motion, but merely retard it. The related problem of equilibrium between the pressure gradient and the electromagnetic force may be discussed mathematically for the special case with two-dimensional symmetry. It is found that equilibrium requires an infinite current density at the neutral point. This is a subsidiary argument in favour of discharges at neutral points.
23. Interpretation of the polarization measurements of the double cluster in Perseus
Authors: Serkowski K.
Published: July 2016

The stars in the Double Cluster in Perseus whose angular distance is small have similar polarization and similar colour excesses. Quantitative description of this effect is the purpose of this paper.
24. Harmonic analysis of the periodic spectrum variables
Authors: Deutsch Armin J.
Published: July 2016

Certain stars are known to be periodic magnetic variables, and to show synchronous changes in line strength and radial velocity. The hypothesis has been made that the atmosphere of such a star is in rigid rotation, and that it is characterized by a permanent magnetic field and associated abundance irregularities. The magnetic potential and the local equivalent widths have been developed in spherical harmonics, and the Laplace coefficients of these expansions have been related to the Fourier coefficients of the observed curves. The theory has been applied to the star HD 125248 in an attempt to verify the original hypothesis and to map the magnetic fields and abundance anomalies over the stellar atmospheres.
28. The magnetic fields of sunspots and the evershed effect
Authors: Jensen E.
Published: July 2016

The observational data on the magnetic fields and the physical parameters in sunspots indicate in a qualitative way how the magnetic lines of force run relative to the isobaric surfaces. If matter is confined to move only along the lines of force it is shown that for sufficient tilt between these lines and the isobars, matter will be accelerated outward along the lines of force. The flow corresponding to this forced convection works as a cooling cap for the core of the spot. It is indicated how a stationary state may be reached with the outward velocity adapted to the temperature difference between the spot and the photosphere.
30. The magnetic field in the corona
Authors: Gold T.
Published: July 2016

The shapes of coronal features are discussed, on the basis that they are indicative of the configurations of the magnetic fields. Some considerations about the strength of the fields are advanced, and the forces that must be responsible for streamers and for the quiet corona are discussed. The magnetic fields would seem to dominate over all inertial hydrodynamic forces, leaving only such magnetic configurations as can be set up by variations of the gas pressure.