bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Grids of Synthetic Spectra for Abundance Derivation and Population Synthesis
Authors: Barbuy B. , Perrin M.-N. , Cayrel R. , Katz D. , Van't Veer C. , Schiavon R. P. 
Published: July 2016

We have built a new grid of synthetic spectra in the wavelength range λλ 4600-5600 Å for [α-elements/Fe] = 0.0, +0.2, +0.4 and +0.6. The Lick indices Mg2, Mgb, Fe5270 and Fe5335 are measured in all grid spectra, and their behaviour with stellar parameters is studied.For the calculation of this new grid, the set of atomic and molecular constants was revised and model atmospheres with overshooting and mixing length parameters appropriate to reproduce the wings of the Hβ line (suitable to indicate temperatures) were computed. We also present a grid in the wavelength range λλ 6000 – 10200 Å. A computation of a high-resolution grid of spectra in the range λλ 3800–7000 Å, as well as a full grid in the range λλ 3000–10200 Å, to be further used in conjunction with evolutionary population synthesis models, are also underway.
Neon abundances in three Wolf-Rayet stars observed with the ISO Short Wavelength Spectrometer
Authors: Morris Patrick W. , van der Hucht Karel A. , Willis Allan J. , Dessart Luc , Crowther Paul A. , Williams Peredur M. 
Published: July 2016

We are motivated to study the Ne/He abundance ratio at the surfaces of Wolf-Rayet stars by evolutionary models, which have predicted enhancements by more than an order of magnitude over cosmic levels during the WC stage (e.g., Maeder 1991). This should occur early in the WC phase, as core-hydrogen is exhausted and the CNO bi-cycle gives way to the following chain of reactions for the Galactic stars: The latest evolutionary models, which include the effects of interior mixing due to stellar rotation, indicate that the enhancement may be somewhat more gradual, but that the Ne/He ratio is essentially unchanged in its peak value, coinciding with complete H-depletion (e.g., Meynet, these Proceedings).
Evolution of star clusters moving on elliptic orbits
Authors: Baumgardt Holger 
Published: July 2016

We describe results of N-body simulations of star clusters moving on elliptic orbits. Our aim is to follow the evolution of these clusters and study how their dissolution times depend on particle number and eccentricity.We find that the scaling of the lifetimes is nearly independent of the eccentricity, despite the fact that the amount of tidal shocking changes with eccentricity. In addition, no leveling off of the lifetimes at the high-N end, which would indicate the influence of tidal shocking, is seen.
The Effects of Transition Time on the Populations of Post-AGB Stars, and on the Nebular Evolution
Authors: Villaver Eva , Stanghellini Letizia , Manchado Arturo , García-Segura Guillermo , Renzini Alvio 
Published: July 2016

We show how the different assumptions on the transition time (the time lag between the superwind quenching at the AGB and the illumination of the Planetary Nebula [PN]) reflect into very different theoretical outcomes, both in the characteristics of the stellar remnants, and in the evolution of the nebular shells.We use a Monte Carlo simulation of post-AGB stars with a set of assumptions on the transition time, to show the effect on the resulting location of the stars on the HR diagram, and on the derived core mass distributions.We have also performed numerical simulations of the PN formation process, and investigated the effects of the transition time on the resulting PN structure. We found that the transition time determines not only the size of the PN shell, but also its dynamical evolution.We show the important implications that the transition time has on the observable parameters during the PN stage.
CHAOS: The Cornell High-Order Adaptive Optics Survey for Brown Dwarfs
Authors: Carson Joseph , Eikenberry Stephen , Brandl Bernhard , Wilson J. C. , Hayward T. L. 
Published: July 2016

The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% complete, uses the Palomar Hale Telescope's adaptive optics system to survey 80 bright stars out to 13 parsecs. Using the telescope's AO Science camera, brown dwarf companions 4–200 AU can be identified using coronagraphic imaging and spectroscopic modes. We will be using monte carlo simulations to create population models consistent with the CHAOS data set.Currently, we have observed 70 systems out of a target sample of 80. Five candidate companions await follow-up observations. As of now, no systems in the target sample have shown strong evidence of having brown dwarf companions. These early results support previous speculations of a “brown dwarf desert” at orbital separations out to 200 AU.While the target sources revealed no evidence of brown dwarf companions, accompanying observations of calibration stars provided evidence of an early methane dwarf candidate around the binary system HD150451AB. Forty seven parsecs from earth, the candidate indicated a projected orbital separation of 280 AU.
Modeling of Optical and IR Spectra of M and Brown Dwarfs
Authors: Pavlenko Yakiv V. 
Published: July 2016

Procedure and results of computation of optical and infrared spectra of ultracool (1000 < Teff < 3000 K) objects are discussed. LTE synthetic spectra and spectral energy distributions in wide spectral region λλ 0.6–10 microns) are computed for model atmospheres from grids of different authors taking into account opacities provided by water and other molecules.Essential interest will be paid for problems of realization of lithium and deuterium tests which can be used for assessment of objects of sub-stellar masses and big planets and refining of scenarios of evolution of young stars and substellar objects.
Overstability of nonradial pulsations in rotating early type stars
Authors: Saio Hideyuki , Lee Umin 
Published: July 2016

We present the result of nonadiabatic analysis for nonradial pulsations in uniformly rotating main sequence models.The angular dependence of the amplitude of a nonradial pulsation mode with an azimuthal order m in a rotating star is represented by a sum of terms proportional to spherical harmonics Ylm(θ, ø) with l = |m|, |m| + 2,… (even mode) or l = |m| + 1, |m| + 3,… (odd mode; see e.g. Saio and Lee 1991 for detail). (In this paper we consider only even modes.) This property makes the analysis complex compared with the case without rotation, in which a single Ylm expresses the angular dependence of a given mode. In our numerical analysis the summation is truncated, in which only first two terms are taken into account. Lee and Saio (1987) give the differential equations for nonadiabatic nonradial pulsations in a uniformly rotating star. Treating the angular frequency of rotation as a free parameter, we applied the nonadiabatic analysis to a main-sequence evolutionary model, for which the effect of rotation is neglected.
Orbital Eccentricity Growth through Disc–Companion Tidal Interactions
Authors: Nelson Richard P. , Papaloizou John C.B. , Masset Frédéric 
Published: July 2016

We present the results of 2–D non linear hydrodynamic simulations performed to examine the driving of orbital eccentricity through disc-companion tidal interaction. We examine the eccentricity evolution for companion masses, mp, in the range 1 > mp >; 30 MJupiter. The disc model we employ is similar to a minimum mass solar nebula model.We find that there is a transition in behaviour, characterised by a rapid growth in eccentricity, for companion masses mp ≳ 20 MJupiter. Companions with masses below this limit show essentially no growth in eccentricity, for the disc model parameters that we examine. Our results suggest that if giant planets form from protostellar discs with properties similar to those studied in this paper, then the observed orbital eccentricities of the extrasolar planets are not a consequence of tidal interaction with their protostellar discs during formation.
Intraday Variability and Microarcsecond Structure in Blazar Cores
Authors: Jauncey David L. , Kedziora-Chudczer Lucyna , Lovell J. E. J. , Macquart Jean-Pierre , Nicolson George D. , Perley Rick A. , Reynolds John E. , Tzioumis A.K. , Wieringa Mark A. , Bignall Hayley E. 
Published: July 2016

The accumulation of evidence now strongly favours interstellar scintillation (ISS) as the principal mechanism causing intra-day variability (IDV) at cm wavelengths. While ISS reduces the implied brightness temperatures, they remain uncomfortably high. The distance to the scattering screen is an important parameter in determining the actual brightness temperature encountered. The high brightness temperatures, the presence of strong and variable circular polarization and the observed lifetimes of a decade or more for several IDV sources, pose significant problems for synchrotron theory.
“The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” William Shakespeare, Julius Caesar
A Population of Distant Luminous Infrared Galaxies Revealed by 15 μm ISOCAM Deep Surveys
Authors: Cesarsky Catherine J. 
Published: July 2016

The counts derived from the five mid-IR 15 μm (12–18μm LW3 band) ISOCAM Guaranteed Time Extragalactic Surveys performed in the regions of the Lockman Hole and Marano Field, the HDF-North and South (plus flanking fields), together with those of the lensing cluster A2390 at low fluxes and those of IRAS at high fluxes, cover four decades in flux from 50 μJy to ~0.3 Jy. The roughly 1000 sources detected with ISOCAM, 600 of which have a flux above the 80 % completeness limit, guarantee a very high statistical significance for the integral and differential source counts from 0.1 mJy up to ~5 mJy. The slope of the differential counts is very steep (α = −3.0) in the flux range 0.4-4 mJy, hence much above the Euclidean expectation of α = −2.5. When compared with no-evolution models based on IRAS, our counts show a factor ~ 10 excess at 400 μJy, and a fast convergence, with α = −1.6 at lower fluxes.Multiwavelength studies of a subsample of the ISOCAM sources in HDF and CFRS fields indicate that they are intrinsically bright galaxies (Luminous Infrared Galaxies, LIRGs), with median redshift 0.7. These galaxies, despite their low surface density, are responsible for a large part of star formation at z < 1 and contribute substantially to the cosmic infrared background at 140 μm.
Chemical Abundances and Models of WR Stars and Blue Supergiants
Authors: Maeder André 
Published: July 2016

Firstly, a brief account is given on the recent progresses in model assumptions, which influence the evolution of surface abundances in massive stars. A concise overview of this chemical evolution is presented.We discuss in detail the surface chemistry of WN and WC stars, in particular, the effects of the initial metallicity Z and mass loss rates on the resulting abundances. The abundances in WN stars are not very sensitive to model assumptions and are mainly a test on nuclear cross sections. Conversely, the chemical abundances in WC stars are very much model dependent. Major differences in the composition of WC stars (and subtype distributions) are expected according to their initial metallicity. The various models proposed to explain the N/C enrichments in blue supergiants and the properties of the progenitor of SN 1987A are reviewed.
Results From Five Years Of Monitoring Of The Einstein Cross With NOT
Authors: Østensen R. , Refsdal S. , Stabell R. , Teuber J. 
Published: July 2016

After some preliminary observations in 1990, a program was started in 1991 at the Nordic Optical Telescope (NOT) on the island of La Palma for monitoring mainly four well known gravitational lens systems: QSO0142-100, QSO0957+561, QS01413+117 and QSO2237+0305 (The Einstein Cross). Here we report results from the monitoring of the Einstein Cross. During the four year period the Monitor Program was active (1990-1993) we gathered 55 high quality observations of this well known lens system. In addition we have collected 32 more observations in 1994 and a further four so far in 1995, a total of 91 new observations of the Einstein Cross.Here we report results from the monitoring of the Einstein Cross. During the four year period the Monitor Program was active (1990–1993) we gathered 55 high quality observations of this well known lens system. In addition we have collected 32 more observations in 1994 and a further four so far in 1995, a total of 91 new observations of the Einstein Cross.
New Radio Observations Of ‘Old Faithful’
Authors: Porcas R.W. , Patnaik A.R. , Muxlow T.W.B. , Garrett M.A. , Walsh D. 
Published: July 2016

We present new arcsecond-scale radio images of the gravitational lens system 0957+561 A, B. Observations at 1.6GHz were made in 1991 October with the VLA in A/B configuration with a resolution of 1.5 arcsec (Fig. 1, left). The lowest contour is 0.37 mJy/beam. In addition to the compact A and B image components, and the familiar NE/SW radio double-lobe structure surrounding image A, this map shows two interesting new features:
(a)a long, thin feature extending south and west from the NE lobe, some 10 arcsec in extent, confirming the detection by Avruch et al. (1994). It is reminiscent of the ‘arc’ features seen in optical images of lensing clusters, and hopefully can be used to constrain models of the cluster mass distribution. (For the superstitious, one can note that the position angle of the arc, 17°, is identical to that of the VLBI jet in image B, a few arcseconds to the west.)(b)a low-level extension of the B image in the NW direction. We are not aware that this has been seen before. A possible interpretation of this feature is a continuation of the jet emission seen in VLBI images of B, whose counterpart in A is seen in higher resolution maps. The change of position angle between the VLBI and arcsec-scale jets would indeed have opposite parities in the A and B images.
Mergers and the Formation of Massive Ellipticals
Authors: Bender Ralf 
Published: July 2016

Many nearby luminous elliptical galaxies exhibit counter-rotating cores, minor axis rotation or peculiar velocity fields. These phenomena require that merging and accretion events played a major role in the formation of ellipticals and, equally important, that stars dominated significantly over gas in the merger progenitors. Low redshift analogues to the last stages in the formation of massive ellipticals can be observed in ultraluminous IRAS mergers. However, this does not imply that ellipticals generally formed in spiral-spiral mergers. Mergers can also occur as a consequence of inhomogenous collapse or hierarchical bottom-up structure formation and it is actually more likely that the progenitors of present-day ellipticals did not resemble present-day spirals.Although some ellipticals most certainly were and still are formed at low redshift, the general formation epoch of massive ellipticals is likely to be found at redshifts > 1. The evidence for this is threefold: (a) the homogenous stellar populations of ellipticals, most notably the tight correlation between colors/absorption linestrengths and velocity dispersion, (b) the high overabundance of light elements relative to iron and (c) the very weak evolution of colors and linestrengths of ellipticals with redshift.
The Evolution of Field Galaxies
Authors: Lilly S.J. , Le Fevre O. , Hammer F. , Crampton D. , Schade D.J. , Hudon J.D. , Tresse L. 
Published: July 2016

During the late 1980's, successively deeper redshift surveys carried out with
multi-object spectrographs on 4-m class telescopes produced growing evidence for evolution in the galaxy population. While some evolution had been expected from analysis of the galaxy number counts, the surprising indication from the first deep redshift surveys was that this appeared to involve moderate luminosity galaxies lying at moderate redshifts (Broadhurst et al. 1988, Colless et al. 1990, Cowie et al. 1991). However, while the results were suggestive, these early surveys suffered a number of significant problems that hampered their interpretation:
(a)the samples were small, especially at the faintest levels, so the statistical weight was limited and analysis was based on crude parameterizations of the data such as the median redshift of samples;(b)the typical redshifts were small (z << 0.5), so that evolutionary effects could only be seen against “local” populations whose selection was often quite different - indeed the local luminosity function of galaxies is still poorly defined (Loveday et al. 1992, Marzke et al. 1994);(c)the samples were selected in the observed B-band, so that comparison with local samples was based on the poorly constrained ultraviolet properties and relative numbers of galaxies of different types.
Faint Galaxy Number-Counts
Authors: Metcalfe N. , Shanks T. , Fong R. , Gardner J. , Roche N. 
Published: July 2016

Observers studying the cosmology and evolutionary history of our Universe through the statistical properties of ‘normal’ galaxies have four main tools at their disposal. (1) The number-redshift relation. Although a very powerful diagnostic, spectroscopic surveys are currently limited to B < 24m and significantly incomplete in the range, 23m< B < 24m. (2) Galaxy number-magnitude counts. Although by themselves, they cannot constrain models as tightly as spectroscopy, they can be measured ∼ 4m fainter, where cosmological effects are expected to be significant. (3) Galaxy colours over a wide wavelength range, which provide additional constraints. (4) The dependence of galaxy clustering with magnitude. ω(θ) can be measured to the limit of the counts.Here we report on the latest Durham count and clustering work.
Bars in Cusps
Authors: Dehnen Walter 
Published: July 2016

In order to investigate the stability properties of galaxy models with central density cusps, TV-body simulations of oblate models with density ρ ∝ m–1 (m+a)–3 where m2=R2+[z/q]2 and distribution functions f(E, Lz) (computed as in Dehnen, 1995) have been performed with the following results.
1.An E7 model with identical amounts of stars of either sense of rotation was stable over 30 tdyn(r=a). This is interesting for the bending instability has been argued to set in at about this flattening and be responsible for the absence of flatter elliptical galaxies (Merritt & Sellwood, 1994).2.Rapidly rotating E≳E5 models quickly form weak bars inside the cusp, which are stronger for the more flattened, faster rotating initial configurations. The bars grow in a self similar fashion from inside out: the pattern speed decreases with increasing bar length and time. This process is initiated at the origin, where, because of finite AT, the actual density no longer follows the power law, and stops when the edge of the cusp is reached. A typical example is given in the figure showing the z-y-coordinates of particles with |z|<0.1a after ≃20tdyn(r=a) for an initially rapidly rotating E7-model. The bar has axis ratios of about 5:3:1, and extends almost to corotation. However, it has no sharp edge, but an inhomogenous density with a cusp steeper than the initial model. No sign of a buckling insta-bility has been observerd.
Colour (≈Age?) Gradients in Spiral Galaxies
Authors: de Jong Roelof S. 
Published: July 2016

A sample of 86 galaxies was imaged in the B, V, R, I, H and K passbands to study their light and colour distribution as function of radius (de Jong & van der Kruit 1994). The radial colour gradients were compared with new dust models, which included both absorption and scattering, and with the stellar population synthesis models of Bruzual & Chariot (1993) and Worthey (1994). By requiring that the models had to fit all six passband photometry at the same time, the relative effects of dust, stellar age and stellar metallicity could be seperated (de Jong 1995a, 1995b). The main results from this investigation are:
–All galaxies become bluer with increasing radius. The colour at each radius correlates strongly with the average surface brightness at that radius, with Hubble type being an additional effect. Late type galaxies are bluer at the same surface brightness than early type galaxies.–The reddening profiles predicted by the dust models are incompatible with the data when all colours have to be fitted at the same time. Dust cannot be the major cause of the colour gradients.–The population synthesis models by Worthey (1994) indicate that the colour gradients cannot be caused by metallicity gradients alone.–The best fit to the data is reached in a model where the colour gradients are mainly caused by an age gradient across the disk, with an additional metallicity gradient to explain the very red central colours. The colours of galaxies of type later than Sc indicate that they have in general a lower metallicity at all radii than the earlier types.
On the Dynamics of very Flattened Ellipticals
Authors: Dejonghe H. , de Bruyne V. , Vauterin P. , Zeilinger W.W. 
Published: July 2016

Our aim is to study the generic phase-space structure of flattened ellipticals by investigating a few typical cases. Here we report on the E4 elliptical NGC 4697.The construction of 2-integral and 3-integral distribution functions asks for photometry and kinematic data. In the course of the data analysis, we additionally detected a nuclear dust lane at 3.4″ or 0.4 kpc from the centre, which could be confirmed with HST data. This was put to good use to constrain the inclination.
Properties of E & S0 Galaxies in the Coma Cluster
Authors: Mehlert Dörte , Bender Ralf , Saglia Roberto , Wegner Gary , Jørgensen Inger 
Published: July 2016

As one of the richest nearby clusters, Coma is the ideal place to study the structure of galaxies as a function of environmental density, thus to constrain the theories of galaxy formation and evolution. For a magnitude limited sample of ≈ 40 E and S0 galaxies we want to obtain spectra with sufficient S/N and spatial resolution, that we can derive the rotation curves, the velocity dispersions profiles and the radial gradients of the line indices of Mg, Fe and Hβ. Following questions will be addressed:
•Are the radial velocity dispersion profiles and the rotation of galaxies in high density environments similar to those in low density environments? Data for galaxies in low density environment are available from Bender et al. (1994, MNRAS, 269, 785). Are the centrally measured velocity dispersions representative for the mean kinetic energy of the galaxy?•Can the scatter in the Fundamental Plane (FP) - which tightly correlates the radii, surface brightnesses and (central) velocity dispersions (Djorgovski & Davis, 1987, ApJ, 313, 59; Dressier et al. 1987, ApJ, 313, 42) - for the Coma cluster be reduced if the mean kinetic energy is used instead of the central velocity dispersion? Can we derive stronger constraint on the variations in the M/L ratio than already implied by the FP?•The radial gradients of the line indices can be used to test the hypothesis that the metallicity gradient depends on the so-called “escape velocity” of the stars introduced by Franx & Illingworth (1990, ApJ, 359, L41). Also we can check whether the age of the stellar population varies with radius. Ages and metallicities can be estimated from the data with the use of stellar population models (Worthey 1994, ApJS, 95, 105; Bruzual & Chariot 1993, ApJ, 405, 538).•How does the radial variation of stellar populations and kinematics within the galaxies vary as a function of the clusters density profile?