bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variation of Broad Optical Emission Lines in AGN's
Authors: Bochkarev N.G. , Shapovalova A.I. , Nazarova L.S. 
Published: July 2016

AGN optical spectra (4000–5000Å) have been obtained with the TV scanner of the 6-m telescope at Special Astrophysical Observatory (N. Arkhiz-North Caucasus) from 1986 to now. Most spectra were obtained with dispersion of 1 Å/channel and with 3–4Å spectral resolution and signal-to-noise ratio S/N=10–25 for individual spectra. NGC 4151, NGC 3516, NGC 5548 and NGC 7469 are the main sources of the programme and are also being used in international AGN watch programmes for diagnosis, estimation of the size and structure of the BLR.NGC4151:In 1987 the broad components of the Hβ and Hγ lines decreased strongly (on about 65% as compared with 1986) and fell to a level comparable to that of 1984. In 1988 they increased up approximately to the level of 1986. During the photometrically low state of NGC 4151 satellites of the strong Hβ, Hγ, Hδ and He II4686Å lines were suspected at radial velocities of +9400 km/s and −7500 km/s. The data are could be interprite a two-jet model with jet velocity of 8400–24000 km/s. (Bochkarev et al., 1989). Analysis of the spectra shows that the broad component of HeII λ 4686Å changed its asymmetry over 6 years. Bochkarev et al. (1992), Nazarova et al. (1993) discussed a possible explanation of profile HeII λ 4686Å behavior by involving a precession of cones of ionizing radiation.NGC5548:Cross-correction of the optical emission line light curves with the UV continuum light curve reveals that the lines respond to continuum variations with a time delay from 7 days for HeII 4686Å to 18 days for Hβ. Hγ responds more rapidly than the lower order Balmer lines and there is a general trend towards higher amplitude variations in higher-order lines. The time lags for the line variations are consistent with the general pattern of radial ionization stratification of the BLR. During 1988–89 Fe II in blend 4130Å varies with an amplitude of aproximately 20% about the mean, similar the amplitude of the Hβ variations and Balmer continuum.NGC3516:Variations of Hβ during 1986–88 were small (20%), the shape of the profile (including the assymetry) did not change, but Hγ - to Hβ ratios of the profile integrated intensities of broad component increased from 0.43 in 1986 to 0.8 in 1988. The 30% variations of continuum on characteristic time scale 10–15 days during the spring of 1988 were not accompanied by any noticeable changes in the line profile (Bochkarev et al., 1990).
Time Dependent BLR Photoionization Models
Authors: O'Brien P.T. , Goad M.R. 
Published: July 2016

Recent intensive campaigns to monitor the variable broad emission lines of AGN have provided a wealth of observational data. To reliably derive the BLR structure from such data requires a detailed comparison with physically realistic models. To provide such models we have combined photoionization calculations with a BLR modelling code. We find that the line emission is significantly anisotropic for the majority of lines at some radii in our models, particularly where the ionization parameter is large. As both anisotropic line emission and negative responsivity can have a substantial impact on the form of response functions, they must be taken into account when comparing BLR models to monitoring data. Differentiating between the effects of anisotropy and negative responsivity requires comparison of the variability behaviour of lines covering a wide range in ionization state with detailed photoionization models similar to those presented here. Failure to take such physical effects into account will lead to incorrect conclusions regarding the BLR structure.Based on the form of the anisotropic response functions for our models, we argue that in NGC5548 the high ionization lines (including CIII] λ1909) can be explained by a spherical BLR component which has a significant radial ionization parameter gradient. The clouds in this component may be optically thin at the Lyman limit in the inner part of the BLR due to the high ionization parameter. The bulk of the low ionization lines, and in particular almost all of the Balmer line emission, arises from a non-spherical BLR component, possibly an accretion disc.We have also investigated the accuracy of the linear response approximation by implicitly calculating the emissivity as a function of continuum level. For several lines the response is significantly non-linear over the typical continuum variability range of AGN. The form of the response functions is therefore luminosity dependent. Work is under way to incorporate this effect into the maximum-entropy-method used to recover response functions from monitoring data.
Multifrequency Spectra of EXOSAT Blazars
Authors: Ghosh K. K. , Soundararajaperumal S. 
Published: July 2016

BL Lacs, Highly Polarized Quasars (HPQs) and Optically Violent Variables (OVVs) are classed as blazars. Based on the multifrequency spectral properties of these objects we have classified the blazars into two groups which are as follows:
– Group I - BL LacsBL Lac objects are soft X–ray sources (Hardness ratio is less than 5) with steep and flat spectral indices in the X–ray and ultraviolet bands, respectively. They are relatively less polarized (in the optical band) and low luminous objects (Mabs < −23). Radio to X–ray spectra of BL Lacs can be fitted with a single parabolic curve and these objects radiate most of their energies in the X–ray band (radio through X–ray frequencies).– Group II - HPQs/OVVsHPQs and OVVs are hard X–ray sources (Hardness ratio is greater than 5) with flat and steep spectral indices in the X–ray and ultraviolet bands, respectively. These are highly polarized and highly luminous (Mabs > −23) objects. Radio to X–ray continuum emission spectra of HPQs/OVVs can be fitted with two parabolic curves with the spectral break between UV and X–ray bands and these objects radiate most of their energies in the infrared band.
On X-ray radiation of the quiet Sun
Authors: Mandelshtam S. L. 
Published: July 2016

The conditions of production of the solar X rays are briefly discussed. The comparison of the results of recent calculations and experimental measurements supports the assumption of a thermal origin of the X ray radiation. In the “tail” of the solar spectrum below 15 Å, the main contribution comes from the free-bound radiation of electrons and ions of carbon, nitrogen, oxygen and other elements.The solar X ray radiation consist of a “quasi-stable” component, produced in undisturbed coronal regions and a “slowly varying” component generated in the active regions of the corona.
The interpretation of the Sun'S XUV radiation
Authors: Allen C. W. 
Published: July 2016

This paper reviews our understanding of (a) the earth's ionosphere, and (b) the solar atmosphere, in relation to the recent observations of solar XUV.The expected ionospheric characteristics are derived as directly as possible from the XUV observations and then compared with the well known E and F layer formation. Agreement does not come very naturally. There are indications of a high ionospheric recombination coefficient decreasing rather rapidly with height. It is found that radiations from the high ions have greater solar cycle variations than radiations from the low ions. This leads to some difficulty in explaining the constancy of the E to F critical frequency ratios. Both UV and X-rays appear to contribute to the E layer.There are about 250 identified XUV solar emission lines from about 50 ions. The flux measurements for each line gives information on the number of corresponding ions in the solar atmosphere. Each radiation comes from a region with a well specified temperature selected from the whole available range 20000° to 2000000°K. This makes it possible to derive, (a) the amount of solar material in each temperature range, (b) the chemical abundances, and (c) the physical differences between normal solar atmosphere, centres of activity, and flares. The analysis is held up at the present moment until the problem of the dielectronic recombination coefficient is cleared. In due course a good distribution of matter with temperature should be available but the fitting of such results to chromospheric and coronal models provides many problems.
On the determination of the solar chemical composition from a study of the ultraviolet resonance lines
Authors: Pottasch S. R. 
Published: July 2016

On the assumption that the ultraviolet resonance lines are formed by collisional excitation followed by direct radiative transition of a quantum which eventually escapes from the atmosphere, it is shown how the chemical composition may be found. These assumptions are discussed, as is the accuracy of the determinations. The effects of non-radial inhomogeneities are also discussed. Finally the question of the determination of the hydrogen abundance is raised, for which purpose the solar radio observations are used.The results of this analysis are compared with other solar abundance determinations.
Silicon in the solar corona
Authors: Widing K. G. , Porter J. R. 
Published: July 2016

Resonance lines of coronal ions of silicon are prominent in the spectral ranges 40–62 Å and 254–356 Å.An unexpected feature of the soft X-ray spectrum is the weakness or absence of the resonance lines of iron in ionization stages XI through XV.A second feature is the prominence of lines of the type (3d → 2p) relative to the resonance transitions (3p → 2s) in Li-like and Beryllium-like spectra. It is suggested that the upper levels (3d) are excited by quadrupole collisions from the ground 2s or 2s2levels.The intensity of the soft X-ray lines relative to the resonance lines in the 300 Å region seems to be more consistent with temperatures well above one million degrees than with temperatures as low as 700000°K, but the data are not adequate for a precise comparison. The relative intensity of the line emission from the various stages of silicon ionization may be interpreted as indicating that the ionization of silicon peaks in stages IX and X.The abundances of C, Mg, S, and Al relative to silicon do not seem to be greatly different from the chromospheric abundances reported by Pottasch or with the photospheric abundances.
Développements récents en spectroscopie des continus atomiques et des raies autoionisées
Authors: Kieffer Par Jean , Damany-Astoin Nicole 
Published: July 2016

Bibliographical study of the principal experimental research of the last ten years on atomic and autoionization continua. We have restricted ourselves to the alkaline, alkaline-ferrous and rare gas groups. Moreover, with one exception, all the work cited is concerned with absorption spectra.We indicate the connections with theory and give the most important of the theoretical references.
Comparison between model atmospheres and spectra from early-type stars
Authors: Avrett E. H. , Strom S. E. 
Published: July 2016

To assist in the interpretation of ultraviolet continuum observations, we present observational features of a grid of non-grey model atmosphères in strict radiative equilibrium which have effective temperatures in the range 10000 °K to 20000 °K and surface gravities 103 and 104. For three models, we add the blended wings of the higher Balmer and Lyman hydrogen lines and include in an approximate way further effects of line blanketing in the ultraviolet. Finally, we present a preliminary calculation of the effect of departures from L. T. E. on the continuous flux.To examine the validity of the models, we compare the predicted continuous flux and predicted line profiles with the corresponding observed quantities for Vega and Sirius.We consider the question of discrepancies between theory and observations in the ultraviolet from the viewpoint of these new calculations, and find generally good agreement with recent observations made by T. Stecher.
The Evolution of Angular Momentum of Intermediate Mass Stars: From the Birthline to the Main Sequence
Authors: Wolff S. C. , Strom S. E. , Hillenbrand L. A. 
Published: July 2016

Measurements of stars in the Orion OB association show that there is a continuous power law relationship between specific angular momentum (J/M) and mass (M) for stars on convective tracks having masses in the range ~0.5 to ~3 M⊙; this power law extends smoothly into the domain of more massive stars on the ZAMS. If we assume that stars are “locked” to circumstellar accretion disks via their magnetic fields until they are deposited on the stellar birthline, we can account for the observed slope and zero point of the power law fit to the upper envelope of the observed J/M vs M distribution.Pre-main sequence stars with M<2 M⊙ on radiative tracks do not follow the power law relationship. A sharp decrease in J/M with decreasing mass has been recognized for more than 30 years for older field stars, but remarkably is seen already among our Orion sample of stars that are only a few million years old. We show that this break in the power law is a consequence of loss of angular momentum on convective tracks, combined with core-envelope decoupling at the time of the transition from the convective to radiative tracks.
The Enigma of AA Dor
Authors: Rauch Thomas , Werner Klaus 
Published: July 2016

AA Dor (LB 3459) is an eclipsing, close binary (P = 0.26 d) consisting of a sdOB primary star and an unseen secondary with an extraordinary small mass. The secondary is possibly a former planet which may have survived a common-envelope phase and has even gained mass.In order to investigate on an existing discrepancy between the components' mass derived from NLTE spectral analysis and subsequent comparison to evolutionary tracks and masses derived from radial-velocity and the eclipse curves, we performed phase-resolved high-resolution and high-SN spectroscopy with the UVES attached to the ESO VLT. from the obtained spectra, we have determined AA Dor's orbital parameters (P = 22 600.702±0.005 sec, A = 39.19±0.05 km s–1, T0 = 2451917.152690) and the rotational velocity (vrot = 47±5 km s–1) of the primary.
H I Tidal Tails, Bridges and Clouds
Authors: Koribalski Bärbel S. 
Published: July 2016

There is plenty of intergalactic HI gas without any obvious stellar content ranging from (1) extended gas envelopes around some normal and peculiar galaxies, (2) tidal tails/bridges in interacting or merging galaxy systems, (3) large-scale rings around early type galaxies, and (4) detached clouds at varying distances from associated galaxies, but there are few or no isolated HI clouds.The HIPASS Bright Galaxy Catalog, which covers the whole southern sky, contains only one definite extragalactic HI cloud which is located close to the galaxy NGC 2442 whereas it is sensitive to isolated HI clouds with MHI > 106 x D2 M⊙. The space density of HI clouds is therefore about 1/1000th that of galaxies with the same MHI.
XMM Observations of Abundances in the Intracluster Medium
Authors: Matsushita Kyoko , Ikebe Yasushi , Finoguenov Alexis , Böhringer Hans 
Published: July 2016

Based on XMM-Newton observations of M 87 and the Centaurus cluster, abundance profiles of various elements of the intracluster medium (ICM) are derived. The abundances of Si and Fe show strong decreasing gradients. In contrast, the O and Mg abundances are about half of the Si abundance at the center.From the gas mass to stellar mass ratio and the comparison of Mg abundance with the stellar metallicity, the stellar mass loss from the central galaxies is indicated to be the main source of gas in the very central region of the clusters.The observed O, Si and Fe abundance pattern determines the contribution of supernova (SN) Ia and SN II, with the abundance pattern of ejecta of SN Ia. Most of the Si and Fe of the ICM in the central region of the clusters comes from SN Ia which occured in the central galaxies. In order to explain the observed O/Si ratio of a half solar, SN Ia products should have similar abundances of Si and Fe, which may reflect dimmer SN Ia observed in old stellar systems.
Large-scale structure of the Magellanic Clouds using planetary nebulae
Authors: Meatheringham S. J. 
Published: July 2016

The Small and Large Magellanic Clouds (SMC, LMC) are of considerable interest from a kinematical viewpoint. The tidal interation of the Clouds with each other and with the Galaxy appears to have been quite significant in recent times (Murai & Fujimoto 1980). The SMC in particular appears to have been considerably disrupted by a recent close passage to the LMC (Mathewson & Ford 1984, Mathewson 1984, Mathewson et al. 1986). For the LMC Freeman et al. (1983) found that the young and old populations have significantly different rotation solutions.Planetary Nebulae (PN) form a population with age intermediate between the HI and young clusters and the old Population II clusters. A large number of PN are known in the MCs. Sanduleak et al. (1978) compiled a list of 102 in the LMC and 28 in the SMC. Since then other authors have increased the total number known to approximately 140 in the LMC and 50 in the SMC.
Mass-to-light ratio of intermediate and old clusters in the Magellanic Clouds
Authors: Seitzer Patrick 
Published: July 2016

The observed central velocity dispersion of a stellar system is dependent on the mass distribution and the velocity distribution function. For the past several years a program has been undertaken to determine central velocity dispersions of LMC and SMC clusters for comparison with galactic clusters. The mass-to-light ratio (M/L) estimates so obtained should be considerably more accurate than those obtained by tidal arguments (Chun 1978, Elson & Freeman 1985).Accurate radial velocities (mean error = 1.3 km s−1) have been obtained for a sample of K-type giants with the CTIO 4m telescope and échelle spectrograph with CCD detector. All of the stars observed were within two core radii of the cluster centre. Multiple observations at several epochs (1984 and 1989) were used to determine the velocity errors.The central M/L in solar units has been estimated from single component isotropic King models (King 1966), with the assumption that the distribution of mass follows that of the light. Observed values for the total integrated light and core radius were taken from the literature (in particular, from Chun 1978, van den Bergh 1981, Mateo 1987).
Diffraction-limited 76 mas speckle-masking interferometry of the carbon star IRC+10 216 and related AGB objects with the SAO 6 m telescope
Authors: Weigelt G. , Blöcker T. , Hofmann K.-H. , Osterbart R. , Balega Y.Y. , Fleischer A. J. , Winters J. M. 
Published: July 2016

We present high-resolution J–, H–, and K–band observations of the carbon star IRC+10 216. The images were reconstructed from 6 m telescope speckle interferograms using the speckle masking bispectrum method. The H image has the unprecedented resolution of 70 mas. The H and K images consist of at least five dominant components within a 0.21 arcsec radius and a fainter asymmetric nebula. The J-, H-, and K—band images seem to have an X-shaped bipolar structure. A comparison of our images from 1995, 1996, 1997, and 1998 shows that the separation of the two brightest components A and B increased from ∼ 193 mas in 1995 to ∼ 246 mas in 1998.The cometary shapes of component A in the H and J images and the 0.79 μm and 1.06 μm HST images suggest that the core of A is not the central star, but the southern (nearer) lobe of the bipolar structure. The position of the central star is probably at or near the position of component B, where the H—K color has its largest value of H—K = 4.2.If the star is located at or near B, then the components A, C, and D are located close to the inner boundary of the dust shell at separations of ∼200 mas ∼30 AU (projected distance) ∼6 stellar radii for a distance of ∼ 150 pc, in agreement with our 2-dimensional radiative transfer modelling.In addition to IRC+ 10 216 we studied the stellar disks and the dust shells of several related objects. Angular resolutions of 24 mas at 700 nm or 57 mas 1.6 μm were achieved.
High-resolution, near-IR spectroscopy and imaging of the Egg and Rotten Egg nebulae (AFGL 2688 and OH 231.8+4.2)
Authors: Kastner Joel H. , Henn LeeAnn , Weintraub David A. , Gatley Ian 
Published: July 2016

Velocity-resolved 2.12 μm H2 maps of the Egg Nebula (AFGL 2688), obtained with the NOAO Phoenix spectrometer, elaborate on previous observations of large velocity gradients in molecular emission both along and perpendicular to the polar axis of the system. The measured gradients along the polar axis support the notion that the polar H2 emission regions are formed in shocks as fast, collimated winds collide with material ejected while the central star was still on the AGB. The kinematics of H2 emission along the equatorial plane, meanwhile, are consistent with a model combining spherical expansion with rotation about the polar axis, although a model invoking multiple outflow axes cannot be ruled out.We also obtained the first direct near-infrared images of QX Pup, a Mira variable embedded within the evolved bipolar nebula OH 231.8+4.2. The inferred absolute K magnitude of the central Mira appears “normal” given its ∼ 700 day period, which is remarkable in light of its position at the heart of such an unusual object.
RV Tauri stars and Type II Cepheids in the LMC
Authors: Pollard Karen R. , Evans T. Lloyd 
Published: July 2016

A review of the main results from the MACHO project for RV Tauri stars and Type II Cepheids in the LMC is presented. In light and colour curve behaviour, the RV Tauri stars appear to be a direct extension of the Type II Cepheids to longer periods. A single period–luminosity–colour relationship is seen to describe both the Type II Cepheids and RV Tauri stars in the LMC.Follow-up low resolution spectroscopy of the LMC RV Tauri stars has been undertaken. The spectra of the longest period RV Tauri star in the MACHO sample show that this star has strong C2 bands with a pronounced phase dependence, their strength being greater at minimum light. This and other spectral features are similar to those observed in proto-planetary nebulae. This LMC star therefore appears to combine the main spectral anomaly of the proto-planetary nebulae with RV Tauri-like photometric variability. This is an intriguing result which indicates a possible link between RV Tauri stars and proto-planetary nebulae, and strengthens the post-AGB interpretation of the RV Tauri stars.
The Sagittarius Dwarf Galaxy Survey (SDGS): Constraints on the Star Formation History of the Sgr dSph
Authors: Bellazzini M. , Ferraro F. R. , Buonanno R. 
Published: July 2016

The main characteristics of a wide photometric survey of the Sgr dwarf spheroidal galaxy are briefly presented. V and I photometry has been obtained for ~90000 stars toward Sgr and for ~9000 stars in a region devoid of Sgr stars (for decontamination purposes).The full potential of this large database is far from being completely explored. Here we present only preliminary results from the analysis of statistically decontaminated Color Magnitude Diagrams, trying to set a scheme of the Star Formation History of the Sgr Galaxy. A scenario is proposed in which star formation in Sgr began very early and lasted for several Gyr, with progressive chemical enrichment of the Inter-Stellar Medium (ISM). Nearly 8 Gyr ago the star formation rate abruptly decreased, perhaps in coincidence with the event that led to the gas depletion of the galaxy. A very small rate of star formation continued until relatively recent times (~ 1 Gyr ago).