bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Differences Between Radio-Loud and Radio-Quiet QSOs
Authors: Francis Paul J. 
Published: July 2016

We analyse the rest-frame UV spectra of a complete sample of optically selected radio-loud and radio-quiet QSOs. Our results are:
1:Broad absorption-line QSOs (BALQSOs) are all radio quiet, but they are strongly clustered toward the top end of the radio-quiet population in radio power.2:Radio-loud QSOs have higher equivalent-width, narrower high ionisation emission-lines than radio-quiet QSOs.3:Further ReadingSee Francis, Hooper & Impey, 1993, Astronomical Journal 106, 417 and references therein for more details and discussion.
The extreme Ultraviolet emission from the Sun between the Lyman-alpha lines of H I and C VI
Authors: Tousey R. , Austin W. E. , Purcell J. D. , Widing K. G. 
Published: July 2016

As a result of research carried out with rocket-borne grating spectrographs, the nature of the extreme ultraviolet spectrum of the Sun is now known to a short wavelength limit of 33.7 Å, the Lyman-alpha line of C VI. Most of the emission lines of wavelengths greater than 400 Å have been identified, as have those from 80 Å to 33.7 Å. Between 149 Å and 400 Å, however there are many intense emission lines whose identity has not as yet been established. Twenty or more have been proved to be from iron, since they appear in spectra obtained from high temperature plasmas into which iron has been introduced, but the stages of ionization have not yet been established. Lines from the elements most abundant in the Sun, H, He, O, N, O, Ne, Mg, Al, Si, S and Fe, in most of the stages of ionization requiring 500 eV or less for production have been found. The outstanding exceptions are the lines in the fluorine and neon sequences.Spectroheliograms, photographed with normal incidence spectrographs, show that the emission lines Fe XV 284 Å, Fe XVI 335, 361 Å, originate principally from active regions, in contrast to He II 304 Å, which is emitted with great intensity from the disc also. Continuum emission, in the wavelength range 170–300 Å, has been recorded from intense centers of activity.
Cosmic gamma rays — experimental
Authors: Kraushaar W. L. 
Published: July 2016

As yet no experiment, satellite-borne, balloon-borne or earth-based has provided compelling evidence for more than upper limits to the intensity of cosmic gamma rays of more than a few MeV energy. Even these upper limits have been useful in blocking in some of the large scale properties of energetic particles in interstellar and intergalactic space. Nevertheless, the smallest upper limit set on the intensity of diffuse gamma rays 3.10−4 cm−2 s−1 sterad−1 (from the satellite experiment in Explorer XI) is a factor of about 20 above the intensity prediction which can be made with rather good confidence for gamma rays made in cosmic ray collisions with interstellar atomic hydrogen.Predictions of the gamma ray flux from the various discrete-source emitters of synchrotron radio noise are model-sensitive and in general appreciably smaller than existing upper limits. These upper limits are in the 3.10−4 cm−2 s−1 region for gamma rays of E > 5.107 eV and in the 5.10−11 cm−2 s−1 region for gamma rays of E > 5.1012 eV.
Magnetic Activity of Pre-main Sequence Stars
Authors: D. Feigelson Eric 
Published: July 2016

I review here recent advances in our understanding of magnetic activity in pre-main sequence (PMS) protostars and T Tauri stars. Results are based on recent imaging, spectroscopic and temporal studies of nearby star forming regions from the Chandra X — ray Observatory and XMM — Newton, including a first look at an ultradeep Chandra exposure of the Orion Nebula Cluster.Pre-main sequence stars exhibit a high level of X-ray emission dominated by a bewildering variety of magnetic reconnection flares. Activity is linked to bulk stellar properties — Lbol, mass, surface area or volume — rather than rotation. This suggests that dynamo processes in deeply convective PMS stars may fundamentally differ from the tachocline dynamo operating in main sequence stars.X-rays and MeV particles from magnetic flares will affect the circumstellar environment in PMS systems, particularly the protoplanetary disk. X-ray emission may influence: disk ionization, turbulence and viscosity; Jovian planet formation and migration; the production of meteoritic isotopes and melting of meteoritic chondrules; the heating and chemistry of the disk. X-ray surveys are also effective in locating post-T Tauri stars for disk evolution studies.
SOHO/SUMER Results: Mass Flows
Authors: Peter Hardi 
Published: July 2016

Hardly any part of the chromosphere and the low corona of the Sun is in a static state. Spectrographs reveal line shifts and nonthermal broadening indicating mass supply to the corona, draining of coronal material, syphon flows, wave propagation and more. Imaging instruments show apparent motions of bright or dark structures indicating the presence of flows and waves, too.This paper will review recent observations of the EUV spectrometer SUMER onboard SOHO on Doppler shifts of lines from the transition region and low corona of the Sun. These results will be discussed with respect to the general picture(s) we have of the structure of the upper solar atmosphere.
Studying the Evolving Universe with XMM-Newton and Chandra
Authors: Hasinger Günther 
Published: July 2016

Two X-ray observatories, the NASA observatory Chandra and the ESA mission XMM-Newton, provide powerful new diagnostics of the “hot universe”. In this article I review recent X–ray observations of the evolving universe. First indications of the warm/hot intergalactic medium, tracing out the large scale structure of the universe, have been obtained lately in sensitive Chandra and XMM-Newton high resolution absorption line spectroscopy of bright blazars. High resolution X–ray spectroscopy and imaging also provides important new constraints on the physical condition of the cooling matter in the centers of clusters, requiring major modifications to the standard cooling flow models. One possibility is, that the supermassive black hole in the giant central galaxies significantly energizes the gas in the cluster.XMM-Newton and Chandra low resolution spectroscopy detected significant Fe Kα absorption features in the spectrum of the ultraluminous, high redshift lensed broad absorption line QSO APM 08279+5255, yielding new insights in the outflow geometry and in particular indicate a supersolar Fe/O ratio. Chandra high resolution imaging spectroscopy of the nearby ultraluminous infrared galaxy and obscured QSO NGC 6240 for the first time gave evidence of two active supermassive black holes in the same galaxy, likely bound to coalesce in the course of the ongoing major merger in this galaxy.Deep X–ray surveys have shown that the cosmic X-ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over the cosmic time. These surveys have resolved more than 80 % of the 0.1–10 keV X-ray background into discrete sources. Optical spectroscopic identifications show that the sources producing the bulk of the X-ray background are a mixture of obscured (type–1) and unobscured (type–2) AGNs, as predicted by the XRB population synthesis models. A class of highly luminous type–2 AGN, so called QSO-2s, has been detected in the deepest Chandra and XMM-Newton surveys. The new Chandra AGN redshift distribution peaks at much lower redshifts (z ≈ 0.7) than that based on ROSAT data, indicating that the evolution of Seyfert galaxies occurs at significantly later cosmic time than that of QSOs.
Inhibition of Wind-Compressed Disk Inhibition in Optically Thick Winds
Authors: Gayley K. G. 
Published: July 2016

There are three important effects in optically thin line-driven winds that have been shown to inhibit the equatorial compression inherent in the wind-compressed disk model:1) gravity darkening, which concentrates the driving flux over the poles,2) stellar oblateness, which rotates the flux vectors poleward, and3) nonisotropic opacity, which rotates the force vectors poleward.The first two of these effects tend to yield fairly spherical winds, while the last one actually reverses the wind compression and should generate prolate winds. This poster argues that this third mechanism is not present for multiline scattering in Wolf-Rayet winds. Hence, it is argued that rotating optically thick line-driven winds should have a more spherical UV photosphere, especially for CAK α ≅ 2/3. However, owing to flux migration from polar to equatorial regions, such winds should have an even more prolate optical photosphere.
First CCD observations of Magellanic Cloud variable stars from the Mt John University Observatory, New Zealand
Authors: Tobin William , Gilmore A. C. , Wadsworth Alan , West S.R.D. 
Published: July 2016

Late in 1988 the Mt John University Observatory acquired a cryogenic CCD system from Photometrics Ltd (Tucson). The chip is a Thomson CSF TH7882 CDA comprising 384 × 576 pixels. As part of the evaluation process, we have begun two differential photometry programs of the Magellanic Clouds using the Mt John 0.6m Boller & Chivens telescope. On this telescope each CCD pixel corresponds to 0.6 arcsec. Mt John's southerly latitude (44°S) permits year-round observations of the Clouds.The first program concerns B, V and I photometry of five blue eclipsing binaries selected, on the basis of Gaposchkin's (1970, 1977) photographic light curves, to have roughly equal components with minimal interaction. HV 12634 has also been observed for comparison with the CCD light curves published by Jensen et al. (1988). Fig. 1 shows the B observations so far obtained for HV 1761, but the reduction is preliminary, being based on aperture-integrated magnitudes. The field is populous, and a final reduction will require use of a crowded-field reduction package such as ROMAFOT.
The role of convective boundaries
Authors: Herwig F. , Blöcker T. , Schönberner D. 
Published: July 2016

We investigate the influence of convective overshoot on stellar evolution models of the thermal pulse AGB phase with MZAMS = 3M⊙. An exponential diffusive overshoot algorithm is applied to all convective boundaries during all evolutionary stages.We demonstrate that overshooting at the bottom of the pulse-driven convective zone, which forms in the intershell during the He-shell flash, leads to more efficient third dredge-up. Some overshoot at the bottom of the convective envelope removes the He-H discontinuity, which would otherwise prohibit the occurrence of the third dredge-up for this stellar mass. However, no correlation between the amount of envelope overshoot and the efficiency of the third dredge-up has been found.Increasingly efficient third dredge-up eventually leads to a carbon star model. Due to the partial mixing efficiency in the overshoot region a 13C-pocket can form after the third dredge-up event which may be crucial for n-capture nucleosynthesis.
Multiperiodicity in semiregular variables
Authors: Kiss L.L. , Szatmáry K. 
Published: July 2016

We present a detailed period analysis for 98 red semiregular variables by means of Fourier and wavelet analysis of long-term visual observations carried out by amateur astronomers. The overwhelming majority of the studied stars show multiperiodic behaviour. We found two significant periods in 62 variables, while there are definite signs of three periods in 13 stars. 20 stars turned out to be monoperiodic with small instabilities in the period. Since this study deals with the general trends, we want to find only the most dominant periods.The distribution of periods and period ratios is examined in the (log P1, log P0/P1) plots. Three significant and two less obvious sequences are present which can be explained as the straight consequence of different pulsational modes. This hypothesis is supported by the multiperiodic variables with three periods. A clear distinction between C-rich and O-rich stars has been found in these diagrams suggesting a connection between the chemistry and pulsational characteristics.
AGB and post-AGB stars at high angular resolution
Authors: Lopez Bruno 
Published: July 2016

High angular resolution observations have provided some valuable information on the circumstellar environment of AGB and post-AGB stars.We review the recent results obtained in this field and focus on observations showing evidence of non-sphericity at different spatial scales (envelope, jets, binarity, maser clumps, stellar “photosphere”, hot spots, etc.). Such studies provide many informations/constraints not yet fully understood and seldom included in models.Although the available observations are very nice and interesting, they sometimes show limited performances with regards to what is needed to analyse the onset of the winds. We try to show, here, what must be gained to improve our present knowledge.
Post-AGB Evolution
Authors: Van Winckel Hans 
Published: July 2016

This review focuses on the evolution of single and binary optically bright post-AGB stars and the relation between the photospheric chemical abundances and the circumstellar material.Surface abundance determinations of optically bright post-AGB stars offer a powerful tool, not only to clarify the evolutionary nature of the objects themselves, but also to constrain theoretical calculations for chemical evolution. However, a survey of recent results shows that the chemical patterns observed are very diverse and that several different classes can be distinguished. The most striking result is that only a minor fraction, namely the 21 μm objects, are conform to standard post third dredge-up theory.In recent years it became clear that binarity can influence the late evolutionary stages considerably. A second part therefore discusses the varied and fundamental impact of the presence of a companion on the evolution of post-AGB systems.
Are there carbon stars in the Bulge?
Authors: Ng Yuen Keong 
Published: July 2016

The Bulge carbon stars have been a mystery since their discovery by Azzopardi et al. (1991), because they are about too faint to be regarded as genuine AGB stars, if located inside the metal-rich Bulge . Part of the mystery can be solved if these carbon stars are related to the Sagittarius dwarf galaxy . They are in that case not old and metal-rich, but young, ∼0.1 Gyr, with SMC-like metallicity (Ng 1998).The σRV = 113 ± 14 km s−1 (Tyson & Rich 1991) radial velocity dispersion of the stars appears to be consistent with Bulge membership. On the other hand, a similar velocity dispersion could be the result from an induced star formation event when the SDG crosses the galactic midplane. It is suggested that the carbon stars are tracers of such an event and that they therefore are located at distances related to the SDG. However, the majority of the carbon stars are not member of the SDG, nor are they similar to the C-stars which are member of the SDG.The radial velocities can be used to determine a possible membership to the SDG. However, they do not give information about the distance of the stars. In particular, if the stars are located at a distance comparable to the SDG. This implies that only the period-luminosity relation (Groenewegen & Whitelock 1996) can be used to distinguish unambiguously if the carbon stars are located at Bulge-like or SDG-like distances. Thus far only carbon stars with reliable periods have been identified at a SDG related distance (Ng & Schultheis 1997; Whitelock 1998).
ISO Observations of AGB Stars in the Small Magellanic Cloud
Authors: Blommaert J.A.D.L. , Groenewegen M.A.T. , Cioni M. R. , Habing H. J. , van Loon J.Th. , Trams N. R. 
Published: July 2016

We used ISOCAM and ISOPHOT to observe the spectral energy distribution between 3.6 and 60 μm of AGB stars in the Small Magellanic Cloud detected by IRAS. CAM-CVF spectra are made which enable us to establish the carbon- or oxygen-rich nature of the stars.We are in the process of analysing this data using a radiative transfer model. This will provide us with accurate determinations of luminosity and mass loss rate. Combining the results on the SMC, LMC and Galaxy we hope to address the open question of the metallicity dependencies of the mass loss rate. This in turn is important in the ejection of matter by AGB stars into the interstellar medium.
Hydrodynamics of Clumpy Flows: Application to the PNe
Authors: Poludnenko A. Y. , Prank A. , Blackman E. G. 
Published: July 2016

Many astrophysical flows occur in inhomogeneous media. We present results of a hydrodynamic numerical study of the interaction of a steady, planar shock/supersonic postshock flow with a system of embedded cylindrical clouds in a two-dimensional geometry and describe an analytical model of the evolution of such systems. Finally we discuss mass-loading in such systems and the applicability of the results to the planetary nebulae (PNe).The most recent results and animations of the numerical experiments described in this paper can be found at www.pas.rochester.edu/~wma.
The Bizarre Central Star of SuWt2
Authors: Exter Katrina , Bond Howard , Pollacco Don , Dufton Philip 
Published: July 2016

SuWt2 has been found to contain a double lined and eclipsing binary system. Surprisingly, both components appear to be A-type stars with masses of about 3 M⊙ moving in essentially circular orbits with a period of 4.9 days. We see no indications of a hotter component in the optical or IUE spectra. We discuss the possibility that this is a triple system.Deep Hα + [N II] images show the nebula to be an inclined ring (≃600 to the line of sight) while spectra show anomalous line ratios (eg I([N II] 6584) ≥≥ I(Hα)) which maybe indicative of recombination in a changing radiation field. Further modeling is ongoing.
Evidence of Jets in the Bipolar Planetary Nebulae M 1-91 and M 1-92
Authors: Arrieta A. , Torres-Peimbert S. , Olguín L. , Georgiev L. 
Published: July 2016

For M1-91 we find that the ratio of the 6717/6731 [S II] narrow band images shows two symmetrical very collimated high density regions, or jets, along the major axis.We infer many properties of M 1-92 from the similarity of the spectral features with the symbiotic star MWC 560. We show that M 1-92 could also have a jet along the major axis and that from the NW knot we receive scattered light from the central region that has traveled along the line of symmetry.
The LMC Planetary Nebula N66 Revisited: Nebular Kinematics and Stellar Models
Authors: Peña M. , Hamann W.-R. , Ruiz M. T. 
Published: July 2016

LMC-N66 is an extraordinary planetary nebula whose central star underwent a violent mass loss event which has lasted for 10 years. The outburst reached its maximum in 1994. Since then the star has been slowly fading. During the stellar outburst, the nebular lines have shown no changes.The nebula shows a complex morphology. Two very bright lobes at both sides of the central star, almost aligned in the E-W direction, constitute the main body of the nebula. Several knots and filaments are conspicuous over the surface lying preferentially on the S-E and N-W directions. A couple of faint, extended loops are also detected in the S-E and N-W directions at both sides of the star. The extension of these loops are larger than 0.5 pc at the LMC distance. A no emitting-zone in the S-W quadrant, seems to be part of a dusty toroid around the central star, although the central star is not obscured by such a dark material (see Blades et ale 1992 for a description of N66 morphology).
Planetary Nebulae in the SMC
Authors: Jacoby George H. , De Marco Orsola , Ciardullo Robin 
Published: July 2016

Using the ESO 2.2m telescope with the 8K x 8K mosaic CCD, we surveyed 2.8 square degrees (~1.6° x 1.7°) of the SMC to search for faint planetary nebulae (PN). In this region, 34 PN were previously known; we identified 25 new objects. All of these are faint and have been spectroscopically confirmed. We estimate that there should be ~140 PN in the entire SMC to the limits of a survey like this one, which is complete to 6 mag down the planetary nebula luminosity function (PNLF). For a complete survey (8 mag down the PNLF), there should be ~220 PN. A strong new feature is evident in the PNLF as a deficiency at 4 mags below the brightest PN.The survey spectra that were used to confirm the candidates as PN show that the fainter PN exhibit a higher incidence (~28%) of strong [N II] emission (where I([N II]/I(Hα) > 1) relative to the bright Sanduleak et al. (1978) sample (~6%). We propose that the very faint SMC PN are selectively biased toward the chemically enriched Type I objects derived from younger, more massive progenitors.
Towards observations of Population III galaxies
Authors: Schaerer Daniel , Pelló Roser 
Published: July 2016

We are undertaking various studies of primordial galaxies with the following main aims:
(i)synthesize the properties of rest-frame UV-optical spectra of Population III galaxies and ‘transition objects’ between Pop III and normal starbursts;(ii)devise optimal search strategies for the detection of Pop III and related objects with ground-based and space observations;(iii)simulate photometric and spectroscopic observations of Pop III galaxies to quantify the feasibility of such studies especially for future ground-based instruments; and(iv)study the physics of Pop III and ‘transition’ galaxies and their implications on cosmology and the physics of galaxies
The Close Environment of Z CMa Binary System
Authors: Garcia Paulo J. V. 
Published: July 2016

We present echelle spectroastrometric observations of the Z CMa system in the Hα region showing its feasibility and underlining the astrophysical importance of the information stored in the spatial width of the spectra.The Hα profile dating from 12/1991 presents a “bullet” of blue-shifted emission superimposed on the broad absorption component. We interpret this material as an unresolved bullet of gas at the base of the jet. We show that the jet emission fills in the absorption component of the Hα profile and has a wide range of velocities.
The Sloan Digital Sky Survey
Authors: Hogg David W. 
Published: July 2016

The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey of 104 deg2 in the North Galactic Cap, currently underway with the 2.5-m SDSS Telescope at the Apache Point Observatory in New Mexico. The data products will include u, g, r, i and z-band imaging of several 108 sources and R = 2000 spectra of 106 galaxies. The imaging will have 10-sigma limiting (AB) magnitudes of (u, g, r, i, z) = (21.4, 22.6, 22.3, 21.7, 20.1). The “Main” sample of 9 x 105 galaxies, selected to have r < 17.7 mag, will have spectra with signal-to-noise ratio on the order of ~ 10 per resolution element, and median redshift z ~ 0.1. There will also be a sample of 105 luminous elliptical galaxies, selected on the basis of apparent color and magnitude, which will extend out to redshift z ~ 0.4. The data will be released steadily over the next five years.On the order of one percent of the eventual data volume has been assembled at the time of this meeting, with a few hundred square degrees of survey-quality 5-band imaging, and over 104 survey-quality spectra. In the refereed literature there are detailed descriptions of the survey design, goals and hardware (York et al 2000; Gunn et al. 1998) and first scientific results (e.g., Ivezic et al 2000; Fischer et al. 2000; Leggett et al. 2000; Yanny et al. 2000).Relevant to measures of the extragalactic background emission, the survey has found many z > 4 quasars and has measured the evolution in their space density (e.g., Fan et al. 2000). Measures of bright galaxy counts, the local galaxy luminosity function, and the evolution of elliptical galaxies are in preparation.