bluuebunny/crossref_metadata_2025 huggingface dataset:
Metallicities and Dust in High-z Galaxies
Authors: Möller C. S. , Fritze-v. Alvensleben U. , Calzetti D. , Fricke K. J.
Published: July 2016

By consistently connecting the chemical and spectrophotometric evolution of galaxies we are able to include the effect of dust absorption. The time and redshift evolution of the extinction is based on the evolution of the gas content and metallicity. We present our evolutionary synthesis models which include dust absorption to analyze the UV emission in various galaxy types. We are able to predict the extinction E(B-V) for different galaxy types as a function of redshift. We further use these models to explore the range of metallicities in normal and starbursting galaxies and the metallicity distribution of the stellar population. Comparing our model spectral energy distributions (SEDs) with templates from R. C. Kennicutt's (1992, ApJS 79, 255) and A. L. Kinney et al.'s (1996, ApJ, 467, 38) atlas we show the detailed agreement with integrated spectra of galaxies and point out the importance of aperture effects. Combined with a cosmological model we show the differences in the evolutionary and K-corrections by comparing models with and without dust.
Evolution of Abundance Gradients along the Galactic Disk
Authors: Hou J. L. , Prantzos Nikos , Boissier Samuel
Published: July 2016

A detailed investigation of the abundance gradients and their evolution along the Galactic disk has recently appeared (Hou, J. L., Prantzos, N., & Boissier, S. 2000, A&A, in press; astro-ph/0007164). A chemical evolution model of S. Boissier & N. Pranzos (1999, MNRAS, 307, 857) was quite successful in reproducing the main observational constraints both in the solar neighborhood and the entire Milky Way disk. Studied elements include He, C, N, O, Ne, Mg, Al, Si, S, Ar and Fe. We use metallicity dependent yields for massive stars with and without mass loss. We find that most observed abundance profiles are correctly reproduced by massive star yields, but C and N require supplementary sources. We argue that massive, mass losing stars can totally account for the abundance profile of C, while intermediate mass stars are the main source of N. We also find that the adopted “inside-out” formation scheme for the Milky Way disk produces abundance profiles steeper in the past. Using current data on planetary nebulae of type I, II, and III, on N, Ne, S, Ar as observational constraints for gradient evolution, we find that it is difficult to conclude whether the gradient steepens or flattens with time. However, for a given interval of Galactic age, our model predicts that the corresponding abundance scatter is smaller in the inner disk than in the outer regions.
Chemical Evolution of Galaxies: Abundance Trends and Implications
Authors: Truran James W.
Published: July 2016

Recent spectroscopic studies of the elemental abundance patterns associated with extremely metal deficient field halo stars and globular cluster stars are briefly reviewed. These metal deficient stellar populations have been found to be characterized by abundance patterns which differ quite distinctly from those of solar system abundances, but are consistent with the view that they reflect primarily the nucleosynthesis products of the evolution of massive stars and associated Type II supernovae. Guided by our current knowledge of nucleosynthesis as a function of stellar mass occurring in stars and supernovae, we identify some interesting constraints upon theories of the formation and early history of our Galaxy.
Lithium and Beryllium in Main Sequence Stars
Authors: Rebolo R.
Published: July 2016

Li and Be abundances in Main Sequence stars later than F0 are reviewed. Observations of Li in open cluster stars and metal-poor dwarf halo stars has promoted the development of a great variety of models invoking transport processes in the outermost layers of these stars. Although measurements in their present state do not allow to establish definitive conclusions on which process is the most important for each range of masses, they do manifest that metallicity and stellar rotation play an important role in controlling the processes which trigger disappearance of these elements from stellar atmospheres.
Diffusion, Meridional Circulation and Mass Loss in Main Sequence and Horizontal Branch Stars
Authors: Michaud G.
Published: July 2016

Photospheric abundances are used to determine the importance of atomic diffusion, meridional circulation, mass loss and turbulence in main sequence and horizontal branch stars. Atomic diffusion leads to the appearance of the Li gap and the AmFm and HgMn phenomena at approximately the Teff at which they are observed. It leads to a 12 to 25% reduction in the age of halo stars. The Li abundance in Halo stars is probably 50% of the original abundance. Atomic diffusion competes with meridional circulation. The V sin i at which the HgMn and AmFm phenomena disappear give an argument in favour of the meridional circulation model of Tassoul and Tassoul. Mass loss is probably present in AmFm stars and cooler F stars but only at the rate of 10-15 M⊙ yr-1. In many objects, the turbulent particle diffusion coefficient is at most 10 times larger than the atomic diffusion coefficient.
Abundances in Wolf-Rayet Stars, LBVs and OBN Stars
Authors: Willis Allan J
Published: July 2016

Current knowledge of the chemical nature of WR stars determined from UV, optical and IR spectral analyses, is reviewed. By number, the H/He ratio is low in most WN stars: 10 ≥ H/He ≥ 0.4 for WNL stars; 3.0 ≥ H/He ≥ 0.0 for WNE stars with most having near zero H-abundances. The C/N ratio in WN stars lies in the range 1–6 × 10−2, whilst N/He ∼10−4 − 4 × 10−3. These abundances for WN stars are broadly consistent with equilibrium CNO-burning products. In WC stars H/He=0 whilst C/He ∼ 0.1 − 0.7 with some evidence for increasing values from WC7 → WC4. N is highly deficient in WC stars, with C/N≥ 60, and for HD 165763 O/C ≤ 0.2 is deduced. In γ Velorum (WC8+O9), IR spectra give a value of Ne/He = 1.0×10-3 (about twice solar). Thus WC abundances are broadly consistent with He-burning products, although the Ne abundance appears lower than predicted. WO stars show C/He ∼ 0.2 − 0.7, and O/He ∼ 0.03 − 0.1, revealing both He-burning and α-capture products. Ring nebulae around several WN stars shown enhanced He and N, consistent with mass loss enrichment expectations from their chemically evolved central stars. Enhanced He (and probably N) is also seen in the atmospheres of several LBVs, OBN and Of stars - potential precursors of, at least, some WN subtypes.
CNO Abundances of Stars Undergoing First Dredge Up Mixing
Authors: Sneden Christopher
Published: July 2016

The abundances of C, N, O and the C and O isotopic ratios of stars undergoing the first dredge up phase of convective mixing are summarized in this paper. It is shown that rough agreement between predictions and observations of the surface abundances may be achieved for young Pop I giants, but that the observations deviate increasingly from the predictions in old disk field giants and especially in Pop II field and globular cluster giants. Recent investigations containing new information on the correlations among these elements in globular cluster giants are discussed.
Abundance Patterns in White Dwarfs
Authors: Liebert James
Published: July 2016

Various evidence indicates that the atmospheric compositions of white dwarfs may switch from hydrogen- to helium- dominated, and vice versa, over wide ranges of surface temperature (luminosity). This envelope evolution may be understood only by assuming that the hydrogen (DA) sequence retains only a tiny residual mass of hydrogen, many orders of magnitude less than that predicted by stellar evolution theory. A corresponding problem may exist for the helium envelopes of some lot stars with helium-rich atmospheres.
The Abundance Connection - the View From the Trenches
Authors: Lambert David L.
Published: July 2016

On Sunday morning, the day before our symposium opened here by the Black Sea, Georges Michaud asked me if I would be willing to be one of three speakers at this closing session. When he intimated that I was to be a stand-in for Wal Sargent who is unable to be here, I set aside all remnants of reluctance and agreed to entertain you for approximately twenty minutes. Wal was one of my earliest inspirations as I trod a path from solar physics into stellar spectroscopy.
Gravitational Lenses Among Highly Luminous Quasars: Large Optical Surveys
Authors: Claeskens J.-F. , Jaunsen A.O. , Surdej J.
Published: July 2016

The search for multiply imaged quasars among highly luminous quasars (HLQs) is a very good strategy to determine the fundamental parameters of the Universe. We report on the present observational status of a combined sample of HLQs, including new observations obtained with the Nordic Optical Telescope (NOT) and at ESO. This combined sample of HLQs now contains 1178 distinct HLQs. A complete list of the total sample will be soon made available, through a World-Wide-Web page. Preliminary maximum likelihood results are also presented, using a simple statistical model to constrain the values of galactic parameters, of the number counts of QSOs, and of the cosmological constant.
The Q0957+561 Time Delay
Authors: Schild Rudolph E. , Thomson David J.
Published: July 2016

The Q0957+561 time delay remains controversial, and we present four new time delay calculations based upon the intensively sampled data of the last three years.
Weak Lensing And The Sloan Digital Sky Survey
Authors: Stebbins Albert , Mckay Tim , Frieman Joshua A.
Published: July 2016

While the strategy for the first applications of weak lensing has been to “go deep” it is equally interesting to use one's telescope time to instead “go wide”. The Sloan Survey (SDSS) provides a natural framework for a very wide area weak lensing survey.
Association Of Distant Radio Sources And Foreground Galaxies
Authors: Martínez-González E. , Benítez N.
Published: July 2016

A statistically significant (99.1%) excess of red galaxies from the APM Sky Catalogue is found around a sample of z ∼ 1 1Jy radio sources. The most plausible explanation for this result seems to be the magnification bias caused by the weak gravitational lensing of large scale structures at intermediate redshifts.
The Clustering Evidence Of Lyman α Forest
Authors: Yingen Wu , Keliang Huang
Published: July 2016

Using high resolution spectral data of the Ly α forest, we found evidence for clustering of Ly α absorbers on scales of 8-10h0–1 Mpc.
The Cores of Cluster Lenses
Authors: Kneib J.P. , Soucail G.
Published: July 2016

The gravitational lensing of faint background galaxies by rich clusters is emerging as a very efficient method both to constrain the mass distribution of clusters of galaxies and to probe the statistical properties of faint background galaxies. We review results concerning the cores of cluster lenses, where recent Hubble Space Telescope (HST) images are giving new insights into the gravitational distortion phenomena.
A Luminous Arc In A Z=0.042 Cluster Of Galaxies
Authors: Campusano Luis E. , Hardy Eduardo
Published: July 2016

We report the discovery of a bright, arc-like feature with a redshift of z= 0.073 associated with the nearby cluster of galaxies ACO3408, at z = 0.042. The redshift, position, and geometry of the arc with respect to the central cD galaxy of the cluster strongly suggest that this is by far the nearest case known of gravitational lensing of a faint background galaxy.
The Mass Distribution In Clusters Of Galaxies From Weak And Strong Lensing
Authors: Miralda-Escudé Jordi
Published: July 2016

This paper is intended as an introduction to the theory of weak lensing. A review of the inversion formula introduced by Kaiser and Squires is presented. We then prove the formula of the aperture densitometry method in a simple way that allows a clear understanding of where the various terms come from. This is particularly useful to measure quantitatively masses in any region of a lens. We then summarize what has been learned from observations of strong lensing about the dark matter distribution; weak lensing should provide similar information on larger scales in clusters of galaxies.
The Reconstruction Of Cluster Mass Profiles From Image Distortions
Authors: Schneider Peter
Published: July 2016

I will review the basic principles and some of the most recent developments of parameter-free reconstructions of cluster mass profiles from the distortions of background galaxy images.
Observations And Predictions Of The Ratio Of 3-Image To 5-Image Systems In JVAS
Authors: King L.J. , Browne I.W A. , Wilkinson P.N. , Patnaik A.R.
Published: July 2016

In JVAS we find more 5-image systems than 3-image systems. On conventional assumptions, we predict the ratio to be ∼5:1.
MG2016+112: A Double Gravitational Lens Model
Authors: Nair S. , Garrett M. A.
Published: July 2016

MG2016+112, discovered by Lawrence et al. (1984) is one of the best–studied among multiply–imaged systems, but is still only partially understood. Ostensibly a three–image system consisting of images A, B and C of a quasar at z = 3.273, the observed lensing galaxy D (a giant elliptical at z = 1.01) at the centroid of the image system seems inadequate to provide the minimum mass of ∼ 2.5 × 1012 M⊙ within 10 kpc of its center (in projection along the l.o.s.) required to produce the observed 3.″9 image–splitting. C itself appears to consist of two components, radio emission that may be associated with the faint optical image counterpart of A and B (called C2, see Garrett et al. 1994) and flat-spectrum C1, which dominates radio observations of the system and apparently consists of at least three linearly stretched subcomponents, C11 to C13 (see Garrett et al. in these proceedings).
Gravitational Microlensing, The Distance Scale, And The Ages
Authors: Paczyński Bohdan
Published: July 2016

A high optical depth to gravitational microlensing towards the galactic bulge is consistent with current models of the galactic bar. The low optical depth towards the LMC can probably be accounted for by the ordinary stars in our galaxy and in the LMC itself. No conclusive evidence is available yet for the presence or absence of a large number of brown dwarfs or other non-stellar compact objects which might account for the dark matter. There is little doubt that the amount of mass in objects in the range 10–8 ≤ M/M⊙ ≤ 106 will be determined within the next few years with the continuing and expanding searches.

Billions of photometric measurements generated by the microlensing searches have lead to the discovery of ∼ 105 variable stars. In particular, a number of detached eclipsing binaries were discovered in the galactic bulge, in the LMC, and in the globular cluster Omega Centauri. The follow-up observations of these binaries will allow the determination of accurate distances to all these objects, as well as robust age determination of globular clusters.
Polarization During Caustic Crossing
Authors: Agol Eric
Published: July 2016

The limbs of hot stars are polarized due to electron scattering, but this polarization cancels out due to rotational symmetry. During microlensing, the star is amplified by different amounts across its surface so that the limb polarization no longer cancels out, but can be observable. Polarization can be much higher for a caustic crossing during microlensing by a binary lens than for a single lens.
Scintillations And Microlensing
Authors: Melrose D.B.
Published: July 2016

It is shown how the theory of scintillation may be applied to treat gravitational lensing. The theory is applied to microlensing by a system of N point masses. It is shown that scintillation theory reproduces a known result for the angular broadening due to multiple microlensing. Some unresolved differences between scintillation and microlensing theories for intensity fluctuations are pointed out.
Observations Of Lens Systems With Keck I
Authors: Lawrence C. R.
Published: July 2016

The extreme difficulty of many essential optical and infrared observations of lens systems has impeded progress and contributed to the popular but erroneous view that lensing is a curiosity rather than an important astrophysical tool. Keck I, with its unprecedented sensitivity for spectroscopy and infrared imaging, will have a major impact on lensing observations.
Milliarcsecond Structures In Gravitationally Lensed Systems
Authors: Patnaik Alok R. , Porcas Richard W.
Published: July 2016

VLBI studies of small-scale structures in gravitationally lensed systems can provide important constraints on the lens mass distribution. We review the current status of VLBI observations of a number of lensed systems.
Gravitational Telescopes
Authors: Blandford R. D. , Hogg D. W.
Published: July 2016

Some ways in which gravitational lenses can act as crude telescopes are reviewed. Magnification limits associated with finite source size, corrugation of the gravitational potential and finite wavelength are specified. It should be possible to obtain rotation curves for a small sample of ultra-faint galaxies imaged as giant arcs. There is an appreciable chance of eventually observing a radio jet component cross a caustic. The successful observation of microlensing in 2237+031 suggests that the continuum emission from this source at blue wavelengths is at least partly non-thermal. The maximum possible magnification observable, granted existing constraints is argued to be from γ-ray pulsars crossing caustic sheets formed by galaxies or a hypothetical population of intergalactic massive objects.
Gravitational Lensing By Curved Cosmic Strings
Authors: Anderson Malcolm R.
Published: July 2016

I briefly summarize all that is known about gravitational lensing by cosmic strings.
Prognosticating The Future Of Gravitational Lenses
Authors: Press William H.
Published: July 2016

About 20 years elapsed between my first and second papers on gravitational lenses (Press & Gunn 1973; Press, Rybicki & Hewitt 1992ab). Therefore, the conference organizers have asked me to prognosticate on the future of gravitational lenses. Their reasoning, if I understand it correctly, is that I will likely go to sleep for another 20 years immediately following this conference. So, if I simply look ahead to my very next paper on the subject, I will be in effect prognosticating over two decade's span.
The Galaxy Population of two Distant Galaxy Clusters: 0016+16 (z=0.54) and 0939+47 (z=0.41)
Authors: Belloni Paola , Röser Hermann-Josef
Published: July 2016

We analyzed the galaxy population of two distant clusters of galaxies by means of optimized multi filter photometry. To this purpose, broad and narrow band filters have been chosen to detect features characteristic of elliptical (4000 Å break and the Mg2 band) and E+A galaxies (Hβ, Hγ and Hδ in absorption). Cluster membership and morphological types of the galaxies have been obtained by fitting the low-resolution spectral energy distributions with template spectra. Ten templates for E+A galaxies have been built up using Bruzual & Chariot (1993, ApJ 405, 538) population synthesis models with the assumption that these galaxies result from a strong star formation episode occuring in an early-type galaxy.
A Survey of the Interstellar Medium in Elliptical Galaxies: the Ionized Gas
Authors: Caon N. , Macchetto F. , Pastoriza M.
Published: July 2016

We have carried out an extensive program of observations of the ionized gas in 74 luminous elliptical and lenticular galaxies, selected to include a variety of properties in radio and X-ray emission, and in kinematical behavior. For each galaxy we have obtained broad-band R and V images and narrow-band images, centered at the Hα and [NII] emission lines, to derive the luminosity and distribution of the ionized gas. We found that a large fraction (≃ 70%) of E and S0 galaxies in our sample contain ionized gas. The gas morphology and size varies from small disks (mean diameter 1 – 4 kpc) to large filamentary structures (extending up to 10 kpc from the galaxy center). Comparison with previous measurements shows reasonable agreement for a few galaxies, but considerable scatter for a large fraction, possibly due to differences in the limiting flux thresholds.
NIR Imaging of the Box/Peanut Bulge in NGC 4302
Authors: Dettmar R.-J. , Ferrara A.
Published: July 2016

The central, spheroidal component of spiral galaxies is frequently found to be “box- or peanut” (b/p) shaped. More than 30% of edge-on galaxies may show this phenomenon (Dettmar 1995). To explain this large frequency a very common process for the origin of this specific shape is required. N-body simulations have shown that this can be attributed to instabilities and resonances caused by bars in spiral disks (e. g., Combes et al. 1990, Raha et al. 1991).

Previous statistics (Jarvis 1986, Shaw 1987, de Souza & dos Anjos 1987) are hampered by the low dynamic range of the photographic material used as well as by dust absorption in late type spirals and the difficulty to disentangle disk and bulge in such systems. We present K-band imaging of the very dusty edge-on galaxy NGC 4302 in the Virgo cluster supporting the presence of b/p bulges in late type spirals.

NIR Observations were obtained with the NICMOS-3 ARNICA camera at TIRGO1 in spring 1994. The combined image of NGC 4302 clearly shows a flat-top “boxy” structure of the spheroid and an additional very thin component appears on the major axis cut. This latter component could be identified with a bar. The example of NGC 4302 demonstrates that b/p bulges are indeed present in disks of late type spirals and that bars can account for a significant fraction of these structures. As a consequence, the bulge/disk ratio of late type spirals has to be interpreted in an evolutionary scenario rather than as a primordial property.
Polarized Radio Emission of Edge-on Galaxies: Observational Results and Implications
Authors: Dumke M. , Krause M. , Wielebinski R. , Klein U.
Published: July 2016

We performed a small survey of the total and linearly polarized emission of six edge-on galaxies at λ2.8 cm. The selected galaxies show very different levels in their star forming activity, their environment (interacting or not), and many other properties. In the following we present the main results of these observations.
Dynamical Stability and Dynamical Evolution of the Disks of Sc Galaxies
Authors: Fuchs B. , Wielen R. , von Linden S.
Published: July 2016

We give a detailed description of the dynamical interaction of the stellar and gaseous components of a galactic disk. The stability of the two-component system against axisymmetric density perturbations is analyzed and the critical velocity dispersions of the stars and the gas, which control the instability, are determined. By comparison with the observed velocity dispersions it is shown that NGC 6946, a typical Sc galaxy, seems to be stable in the outer parts of the disk, but is dynamically unstable in the inner parts. The transition occurs exactly at the HII region disk boundary, so that the onset of gravitational instability appears to be related to the threshold of massive star formation (Kennicutt 1989). We study the dynamical evolution of the instability by numerical simulations using a code (cf. Casoli & Combes 1982), which implements both the stellar and gaseous components. It is shown that the gas forms after a short initial period of growing ring–like perturbations large cloud complexes, which induce by ‘swing-amplification’ (Toomre 1990) multi-armed spiral structures in the stellar and gas disks, exactly as observed.
3D N-Body Simulation of the Milky Way with Gas
Authors: Fux R. , Friedli D.
Published: July 2016

We present the first self-consistent 3D barred model of the Milky Way including gas, as an evolved stage of an unsymmetrised N-body simulation with axisymmetric initial conditions (fig.1). The corotation lies at about 4 kpc and the central gas particles have condensed into a nuclear ring/disc. Distortions of the bar and other odd modes in the stellar distribution (a) affect the gas flow by producing one-side gas voids (b) and instabilities of the nuclear component like tilting, warping and off-centering (c-d). These peculiarities may help to reproduce the intriguing asymmetries and densely populated “forbidden” regions in the Galactic HI and CO (l – v) maps (e-f). More details are given in the proc. of IAU Coll. 157 “Barred Galaxies”.
Spectroscopy of Three SBS Galaxies
Authors: Gyulzadian M.V.
Published: July 2016

Three galaxies from Second Byurakan Sky Survey have been studied. The spectra of these galaxies were obtained at 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. For these objects line widths and emission line ratios were measured and ionization mechanism and chemical abundances were determined.
Line Strength Gradients in Low Luminosity Galaxies
Authors: Halliday C. , Baggley G. , Davies R. L. , Birkinshaw M. , Bender R. , Saglia R.
Published: July 2016

Line strength gradients in luminous ellipticals show changes in metallicity of roughly a factor of two out to an effective radius (Worthey, Faber & Gonzalez, 1992; Davies, Sadler & Peletier (DSP), 1993; Gonzalez, 1993). The observed decline in Mg2 line strength with increasing radius, while Hβ remains roughly constant, has been interpreted to indicate an age gradient with the central parts of ellipticals being younger than the outer regions.
Field Galaxy Evolution Studies with an Optical Multicolor Deep-Sky Survey
Authors: Liu Charles T. , Green Richard F. , Hall Patrick B. , Osmer Patrick S.
Published: July 2016

We are investigating field galaxy evolution with the optical multiband survey of Osmer et al. (1995, in preparation; Hall et al. 1992, Bull. A.A.S., 24, 1136), which covers some 3000 sq. arcmin of sky with CCD photometry in six broad-band filters from 3000-10000Å, complete down to R∼23. The sample contains some 9000 cataloged galaxies, of which 7000 have data in at least three colors.
A Linkup Between Seyfert's and their Surroundings
Authors: Mahtessian A.P. , Khachikian E.Ye. , Tiersch H.
Published: July 2016

The observed physical characteristics of galaxies are (at least partly) determined by the influence of the surroundings after the formation of the galaxies. The examination of the frequency of the occurence of active galaxies, i.e. Seyfert galaxies, in different galaxy systems compared to a sample of field galaxies gives possibly an insight into this problem.

The galaxy groups were taken from the CfA redshift survey, the list of them is published in Mahtessian (1992, Soob. Byurakan. Obs. 65).
Flare Activity in the NGC 1275 Nucleus
Authors: Merkulova N.I. , Metik L.P.
Published: July 2016

The simultaneous UBVRI – observations of some Seyfert galaxies have been carried out at Crimean Astrophysical Observatory using the 1.25m telescope. Photometric errors are less than 0.01 mag. By analysis of the NGC 1275 light curves within one night we are discovered at least two types of variability: 1) The flares with the maximal amplitudes of 5 – 30 % in the U-band and durations of 15 – 30 minutes. 2) For the first time we have found rapid red flares. For instance, the red flare on the light curve 22-23.10.1992 lasted ∼ 65 minutes (see Figure. Vertical axes are in magnitudes). The amplitude in the filter I is ∼ 25 % (top panel). The light curve in the U-band is on the bottom panel. Fluxes in the U,B,V-bands were almost constant. One can see the flux decreasing in some filters before this flare. We conclude, that light curve of NGC 1275 nucleus could be represented by a superposition of rapid flares of different types.
The Anatomy of Starbursts in the Ultraviolet
Authors: Meurer G.R.
Published: July 2016

We have obtained Hubble Space Telescope ultraviolet (UV; λc = 2320 Å) images of nine starburst galaxies using the FOC, with the aim of characterizing the anatomy of starbursts with ∼pc resolution at a wavelength where hot massive stars dominate the luminosity output. The images have been analysed in detail, and full results can be found in Meurer et al. (1995).
The Energetics of Flat and Rotating Early-Type Galaxies and their X-Ray Luminosity
Authors: Pellegrini S. , Ciotti L.
Published: July 2016

A multivariate statistical analysis of data measuring the optical and X-ray properties of the Einstein sample of early-type galaxies (Eskridge et al. 1995) showed that: 1) on average S0s have lower X-ray luminosity LX at fixed optical luminosity LB than do Es; 2) at fixed LB the X-ray brightest galaxies are also the roundest; this correlation holds for both morphological subsets of Es and S0s. We investigate whether a flat and partially rotationally supported galaxy is expected to host a different gas flow phase (and so a largely different amount of hot gas) with respect to a spherical pressure supported galaxy of the same LB. This is accomplished using the global energetic balance of the hot gas flows, and axisymmetric two-component galaxy models (Ciotti and Pellegrini 1995).
Stellar Populations of Dwarf Irregular Galaxies
Authors: Schulte-Ladbeck R.E. , Hopp Ulrich
Published: July 2016

We recently completed two-color CCD photometry of resolved stars in 11 dwarf irregular galaxies (Hopp & Schulte-Ladbeck, 1995, A&AS 111, 527), selected because of their relative isolation from massive galaxies in the Kran-Korteweg – Tammann sample (1979, AN 300, 181). The B-R color magnitude diagrams (CMD) show that all galaxies studied had star formation activity in the last ∼ 108 yr. Several of them continue to form stars, the most active being UGC 5272 A (see Hopp & Schulte-Ladbeck, 1991, A&A 248, 1) while others, like DDO 210 (Hopp & Schulte-Ladbeck, 1994, ESO Conf. Workshop Proc. 49, 511), are pausing in their star formation activity. The CMDs enable us to select the brightest blue supergiants in these galaxies and to estimate their distances, D. Our values agree with the estimates based on the Virgo inflow model of Kran-Korteweg (1986, A&AS 66, 255) at the 30%-level. Prelimanary values are given in the table below.
Low Surface Brightness Galaxies and the Field Galaxy Luminosity Function
Authors: Sprayberry D. , Impey C. D. , Bothun G. D. , Irwin M. J.
Published: July 2016

We have developed a catalog of local low surface brightness galaxies (LSBGs) which is selected by objective criteria. We present here a luminosity function (LF) for LSBGs based on that catalog. This LF includes the effects of the completeness corrections to the LSBG catalog, and includes only galaxies with surface brightnesses (22.25 ≤ μB(0) ≤ 24.5) fainter than those included in the CfA Redshift Survey (see Marzke et al. 1994, AJ 108, 437). The best-fitting Schechter function has parameters α = –1.42, M∗B = −18.34, and Φ∗ = 0.0036 h3 Mpc–3 mag–1. Thus, surveys which do not take account of the observational selection bias imposed by surface brightness are missing a substantial fraction of the local galaxies, but, this missed fraction is not large enough to explain the counts of faint blue galaxies observed at moderate redshift.
Introduction to the JCMT-CSO Interferometer
Authors: Wiedner M.C. , Hills R.E. , Carlstrom J.E. , Lay O.P.
Published: July 2016

The James Clerk Maxwell Telescope (JCMT) and the Caltech Submillimeter Observatory (CSO) are located 160m apart on Mauna Kea, Hawaii. Recently they have been linked together to allow the first submillimetre interferometric observations (between 300GHz and 490GHz, soon to 690GHz). Submillimetre observations can be used to probe the physical conditions of molecular clouds and dust in starforming regions. Lines from rotational transitions of molecules such as CO, HCN and HCO+ trace densities, temperatures and masses of molecular gas. The thermal emission of cold dust, typically found in dense clouds, also peaks in the submm regime.
The Ursa Major Molecular Clouds
Authors: Pound Marc W. , Goodman Alyssa A.
Published: July 2016

The Ursa Major molecular cloud complex lies in the direction of an expanding HI shell known as the North Celestial Pole loop. The NCP loop, which is centered at (l, b) ∼ (138°,30°) and easily seen in IRAS 100 μm emission, is some 60 pc across and 150 pc distant (Meyerdierks et. al 1991). At 100 μm, the Ursa Major clouds appear in projection as “finger” (l ∼ 140, b ∼ 38) which “hangs down” towards the center of the loop and the plane of the Galaxy. Distance estimates to the molecular clouds (Penprase 1993) are consistent with that of the NCP loop, indicating that the clouds are physically associated with the loop.
Spectral Association of the 7 August 1972 Solar Radio Burst with Particle Acceleration
Authors: Castelli J. P. , Carrigan A. L. , Ko H. C.
Published: July 2016

(Solar Phys.). Microwave burst data from the August 7, 1972 event recorded on nine discrete frequencies between 245 and 35000 MHz at the Sagamore Hill Radio Observatory (Figure 1) provide a basis for correlation studies (especially timing information) of the associated white light flare, the high energy particle emission, type II bursts, and many other phenomena. This is perhaps the first time that sufficient radio coverage (i.e., data above 10000 MHz) was available to obtain the spectral slope information (related to electron-energy distribution) which is inherent in this part of the spectrum. Heretofore, timing was related to burst flux density profile variations. Improved correlations resulted from shorter centimeter wavelength data which supplied more accurate timing information than that derived from Hα observations. The shape and intensity of the burst peak flux density spectrum has also been used for qualitative analysis of energetic particle and white light events. The ultimate good may possibly come from spectral analysis of the minute by minute variation of the burst microwave radiation spectral slope α (above fmax) in the area between 15000 and 35000 MHz. This may be used alone or in relation to the position of fmax, where fmax is the frequency of burst maximum emission at a given time. This is basically our present investigation.
Mechanisms for Flash Phase Phenomena in Solar Flares
Authors: Smith Dean F.
Published: July 2016

Mechanisms for explaining the various forms of particles and radiation observed during the flash phase of solar flares are reviewed under the working hypothesis that the flash phase is the time in which electrons and to a lesser degree protons are accelerated in less than one second. A succession of such accelerations is allowed to explain longer lasting or quasi-periodic phenomena. Mechanisms capable of such acceleration are reviewed and it is concluded that first-order Fermi acceleration in a reconnecting current sheet is the most likely basic process. Such acceleration, however, gives rise to a rather narrow distribution of particle velocities along a given field line which is unstable to the production of electron plasma and ion-acoustic waves. This plasma turbulence can heat the plasma to produce soft X-rays and filter the initially narrow velocity distribution to produce a power law energy distribution. Electrons travelling inward from the acceleration region produce hard X-rays by bremsstrahlung and microwave bursts by gyro-synchrotron emission. Whereas the interpretation of X-ray spectra is relatively straightforward, the interpretation of microwave spectra is difficult because the source at low frequencies can be made optically thick by several different mechanisms.

Electrons travelling further inward presumably thermalize and produce impulsive EUV and Hα emission. The theory for these emissions, although amenable to present techniques in radiative transfer, has not been worked out. Electrons travelling outward give rise to type III radio bursts by excitation of electron plasma waves and the electrons observed at the Earth. Study of the interaction of a stream of electrons with the ambient plasma shows that the electron spectra observed at the Earth do not necessarily reflect their spectrum at the acceleration region since they interact via plasma waves as well as through Coulomb collisions. The mechanisms for the conversion of plasma waves into radiation and the propagation of the radiation from its source to the observer are reviewed.
Optical Evidence for Plasma Ejections and Waves in the Solar Corona
Authors: Bruzek A.
Published: July 2016

Plasma ejections and waves in the solar corona are almost exclusively flare associated phenomena. Ejections of relatively cool and dense plasma are frequently observed in Hα whereas observations in coronal light (visible, EUV- and X-radiation) are still rather scarce. Occurrence of coronal waves is so far best known from their effects on the Hα chromosphere and, of course, from the production of radio bursts. Only in relatively few cases have observations been made in coronal lines and in coronal continuum by ground based as well as by satellite borne equipment. We may expect, however, that the white light coronagraph and the X-ray telescopes on board of the Skylab will detect quite a number of events in front of the solar disk and high in the solar corona and will considerably increase and improve our imperfect knowledge and understanding of coronal ejections and waves as it is presented in this review.
The Coronal Disturbance of 12 August 1972
Authors: Riddle Anthony C. , Tandberg-Hanssen Einar , Hansen Richard T.
Published: July 2016

(Solar Phys.). The association of flare sprays, distortions of the overlying coronal structures and moving type IV radio bursts is a reasonable one and is well accepted despite the paucity of observational evidence. On 12 August 1972 there occurred a flare spray observed optically by both flare patrol (National Oceanographic and Atmospheric Administration) and coronagraph (High Altitude Observatory) instruments. A subsequent moving type IV radio burst was recorded on two swept frequency interferometers (Universities of Colorado and Maryland). In addition distinct changes in the K-coronal brightness at 1.6 R⊙ were measured (High Altitude Observatory K coronameter). These observations combine to form one of the most complete sequences of measurements yet recorded covering the range from the chromosphere to about 6 R⊙. The separate measurements are discussed and we show that they can be combined to form a relatively simple physical picture of the whole event.
East-West Asymmetry of Magnetic Bottle Expansion and Its Relation to Shock Waves Propagating in the Solar Atmosphere
Authors: Sakurai Kunitomo
Published: July 2016

(Solar Phys.). It is known that the sources of metric type IV radio bursts generally move outwards with speed of a few to several hundred km s−1 in the solar atmosphere and envelope (e.g., Kundu, 1965; Smerd and Dulk, 1971; Wild and Smerd, 1972). These sources consist of magnetic lines of force being stretched out from the flare regions and relativistic electrons being trapped by these field lines. They are often observed as expanding magnetic bottles (e.g., Smerd and Dulk, 1971). As a result of this expanding motion, the frequency range of type IV burst extends with time to lower frequencies, because of the decrease of both magnetic field intensity and energy of radiating electrons (Dulk, 1970; Sakurai, 1973a). By considering the observed expansion rate of emission frequency range, it seems possible to estimate the pattern of expansion of these radio sources: in doing so, we have analyzed the onset time differences between microwave and metric emissions of type IV bursts by referring to the longitudinal positions of parent solar flares on the solar disk, since the dependence of these differences on parent flare positions in the solar longitude seems to give a clue to estimate a general pattern of the expansion of magnetic bottles. The result thus analyzed is shown in Figure 1. Furthermore, peak flux intensities at metric frequencies for these type IV bursts have been also analyzed as a function of the longitude positions of parent flares (Figure 2). The results shown in Figures 1 and 2 are explained by assuming that, while moving outwards, the magnetic bottle tends to expand a few 10 deg east of the meridian plane which crosses the flare region (Sakurai, 1973a).
Theory of Shock Waves and Plasma Wave-Emission
Authors: Krall Nicholas A.
Published: July 2016

The theory of shock waves in a hot plasma is reviewed, and the types of shock waves which can exist are summarized. The detailed application of shock wave theory to the explanation of laboratory experiments is described; a comparison is made between the results of these experiments and the observations made of type II radio bursts from the Sun.
On the Thermal Interpretation of Hard X-Ray Bursts from Solar Flares
Authors: Brown John C.
Published: July 2016

The possible validity of thermal bremsstrahlung models of flare hard X-ray bursts is investigated quantitatively. In particular, the problem of rapid thermal conduction in ‘multi-temperature’ models is adequately examined for the first time by using a continuous temperature distribution consistent with the observed X-ray spectrum. This distribution is obtained from a general analytic solution for the temperature structure required to mimick any ‘non-thermal’ spectrum, the method being equally applicable to cosmic sources.

It is concluded that the thermal interpretation might extend to X-rays of hundreds of keV, a result with important consequences for flare energetics. The relationship of such a model to observations of X-ray polarization and rapid time variations is also considered.
2. Magneto-hydrodynamic waves in compressible fluids by finite viscosity and heat conductivity
Authors: Baños Alfredo
Published: July 2016

The general theory of magneto-hydrodynamic waves in an ideal conducting fluid embedded in a uniform field of magnetic induction, and the application of the theory to the systematic analysis of the various modes of propagation in incompressible and compressible fluids have been presented by the author in two earlier papers[1, 2]. In these papers, however, no effort was made to include the thermodynamics of the situation, which amounts to the tacit assumption that the fluid is of zero heat conductivity. In this case the resulting modes are of two kinds: isothermal (v-modes) and adiabatic (p-modes).

In this paper we first establish the conservation laws of momentum and energy for a (macroscopic) compressible fluid with finite viscosity and finite thermal and electrical conductivities, which is embedded in a uniform field of magnetic induction, and we then derive quite generally the exact (nonlinearized) equation governing the distribution of temperature in such a fluid. Next, making use of the linearized magneto-hydrodynamic wave equation in the fluid velocity, combined with the resulting heat diffusion equation and with the equation of state of the fluid, and applying the mathematical techniques developed earlier, we obtain a higher order partial differential equation in the fluid temperature from which ensue all the temperature modes.

In particular, we examine in detail the behavior of plane homogeneous waves, and it is shown that a compressible fluid with the indicated properties sustains altogether six different modes, two of which are pure shear modes, devoid of density, pressure, and hence temperature fluctuations (v-modes), while the remaining four are shear-compression waves accompanied necessarily by density, pressure, and temperature fluctuations (p-modes). The two shear modes, which are isothermal, comprise a slightly attenuated Alfvén wave, and a highly attenuated viscous mode, sometimes referred to as a vorticity mode. The four shear-compression modes have in general very complex properties, but in the low frequency and low heat conductivity case they are easily identified as (1) a modified (adiabatic) sound wave slightly attenuated; (2) a slightly attenuated modified Alfvén p-wave; (3) a highly attenuated viscous wave; and (4) a highly attenuated thermal wave governed in the main by the thermal properties of the medium.
4. Non-stable magneto-hydrodynamical processes in stars
Authors: Kipper A. J.
Published: July 2016

1. The behaviour of the magnetic field of a star was investigated by Cowling, Lamb and Wrubel on the assumption of the star as a solid body and on the assumption that the field variations caused by the extinction do not create any motions of the stellar matter. The important results obtained make possible the interpretation of magneto-hydrodynamical processes in stars only quite roughly. When motions of stellar matter caused by the electromagnetic forces are taken into account new properties may be revealed and the non-stability of the magneto-hydrodynamical processes in stars established. Entangled magnetic fields are the general expression of non-stability.

2. The mathematical criterion of a confused stellar magnetic field is given in the preceding paper from the magneto-hydrodynamical equations for an ideal incompressible fluid. The conception of a confused field as a superposition of various fields of different scales is introduced.

3. It is known that the presence of a magnetic field causes an increase of the stability of hydrodynamical processes, as compared with processes in the absence of a magnetic field. It may most probably be concluded that the extent of confusion of a magnetic field is not the same, as it happens as a result of ordinary turbulent motions in a liquid. However, owing to magneto-hydrodynamical formulae, it may be stated in the present paper that if the field confusion is considered as a superposition of fields of different dimensions and not as a field of entangled magnetic lines, no stability of the above kind can be expected.

4. The theory of a totally entangled magnetic field, as a field in a state of maximum confusion is examined. A very close similarity between a totally entangled magnetic field and the turbulent motion in a viscous liquid is established. The question of the time of extinction of a magnetic field of a star is discussed.

Note. Sections 1, 2, 4 of the paper are based upon the results obtained by the author, reported by him at the 4th Cosmological Conference. Section 3 contains unpublished results.
18. Stellar magnetic fields
Authors: Babcock Horace W.
Published: July 2016

A report is given of a ten-year observational program directed toward the discovery and investigation of the magnetic fields of stars through the Zeeman effect in their spectra. The emphasis has been on the sharp-line stars of type A, of which ten have been found to show irregular magnetic fluctuations without reversal of polarity, ten others to fluctuate irregularly with occasional reversals of polarity, and six to show essentially periodic variations; of the latter group, four are large-amplitude reversers with periods near one week.
37. Correlation between cosmic ray intensity and geomagnetic activity
Authors: Venkatesan D.
Published: July 2016

The Chree method of analysis has been adopted for the analysis of the Ionization Chamber data for Huancayo, Cheltenham and Godhavn for 1946 and for the former two stations for 1945. The same procedure is adopted for the planetary index Kp also.

The cosmic ray minimum (or maximum) precedes the minimum (or maximum) of Kp by about 4–5 days. It is also observed that the relative decrease in cosmic ray intensity per day, – ΔI/(I. Δt), follows the changes in Kp in a general way, and hence the electric field as would be expected from the consideration of the theory of emission of beams of particles from the sun with the associated frozen magnetic field and the electric field arising due to polarization.