bluuebunny/crossref_metadata_2025_split huggingface dataset:
Towards a Truly Unified Model of AGN: Aspect, Accretion and Evolution
Authors: Dopita Michael A. 
Published: March 2011

AbstractThe Unified Model holds that the aspect-dependent effects primarily determine the nature of the active galactic nucleus that we observe. In this paper, I argue that three parameters; aspect, accretion rate into the nuclear regions, and the evolutionary status of the central black hole hold the key to unification. The mystery of why the epoch of quasar formation occurred so early in the evolution of the Universe, why radio-loud QSOs represent only a small fraction of the general population of QSOs, and why ellipticals are invariably the hosts of radio-loud active galaxies could be explained if (a) the most rapid growth of black holes occurred in galactic merger events, and if (b) an excess in the rate of nuclear feeding was able to choke off the radio jets, producing radio quiet QSOs. In this paper, I develop the idea that rate of nuclear feeding plays a dominant role and that feeding at super-Eddington rates into the broad-line region (BLR) during merger events is the means whereby massive black holes are grown. In particular, I develop a toy model for the radio-loud, radio-quiet dichotomy based on the rate of nuclear feeding, suggest an electron scattering model for the ‘big blue bump’ and its relation to the BLR, and emphasise the important diagnostic capabilities offered by analyses of the narrow line regions based on shock excitation models.
A Search for NH3 in the Large Magellanic Cloud
Authors: Osterberg Jürgen , Staveley-Smith Lister , Weisberg Joel M. , Dickey John M. , Mebold Ulrich 
Published: March 2011

AbstractWe report a search for the NH3 (J,K) = (1,1) inversion line in the Large Magellanic Cloud (LMC) using the Parkes 64–m telescope. Candidate positions were chosen with the help of recent H i data from the Australia Telescope Compact Array and published 12CO data from the Swedish–ESO Submillimetre Telescope. No detections of NH3 in emission were found at the positions surveyed. Upper limits are approximately 25 to 74 mK.
Limits on Source Distances for the Most Energetic Cosmic Rays
Authors: Lampard R. , Clay R. W. , Dawson B. R. 
Published: March 2011

AbstractThe propagation of the highest energy cosmic rays through the 2·7 K microwave background is considered. Photo-pion production interactions cause energy losses for primary cosmic ray protons which result in significant energy degradation over intergalactic distances. The process of energy loss is discussed and an estimate is made of the average distances travelled for observed cosmic rays with a range of energies, assuming a power law source spectrum. At energies over 1020 eV, the average distances travelled are a few tens of megaparsecs, limiting possible sources to the volume dominated by the supergalactic plane.
The Monash Spectrograph Simulation Program
Authors: Marsden S. C. , Coates D. W. 
Published: March 2011

AbstractThe Monash University Physics Department is constructing a spectrograph, to be attached to a 0·46-m Cassegrainian telescope. To help future users of the spectrograph determine the operational capabilities of the spectrograph a PC-based software package was created. This program allows the user to simulate the response of the spectrograph to various stellar types under differing observational constraints. We have estimated the precision of measurements of stellar radial velocities with the spectrograph. The estimates are reasonable but are yet to be compared with real data.
Special School Holiday Programs at the Carter Observatory
Authors: Leather Kay , Andrews Frank , Buckley Dawn , Carter Brian , Hall Lesley , Hall Richard , Hall Sacha , Leather Katrina , Leather Nyree , Matla Philippa , Orchiston Wayne , Sule Caroline 
Published: March 2011

AbstractAs an experiment, special holiday programs for primary school children were offered by the Carter Observatory during two different school holidays in 1995. One program focussed on Mars and the other on the Sun. This paper describes the two programs, expands on their strengths and weaknesses from different viewpoints, and (despite their overwhelming popularity) outlines the reasons why the Observatory has decided not to offer further holiday programs of this type in the foreseeable future.
Probing ISM Models with Hα Observations
Authors: Ferrara Andrea 
Published: March 2011

AbstractI review the capabilities of Hα observations to constrain some aspects of the current models of the interstellar medium. In particular, it is shown that turbulence is a necessary ingredient of any viable model, since most of the energy produced by supernova explosions and ionising radiation is stored in kinetic form in the ISM. Various forms of turbulent energy dissipation, including cloud collisions, are analysed. Two additional aspects, concerning the existence of galactic fountains and their relation with high-velocity Clouds, and the extended ionised layer of spiral galaxies are discussed; some crucial experiments are suggested.
The MSSSO Wide Field CCD HαImaging Survey
Authors: Buxton Michelle , Bessell Michael , Watson Bob 
Published: March 2011

AbstractA wide-field Hαsurvey of the Galactic Plane has been initiated by Mount Stromlo & Siding Spring Observatories in collaboration with the University of Sydney. The primary aim of the survey is to obtain images of the Galactic Plane in Hαand red continuum filters which will be compared with radio continuum images at 843 MHz from the Molonglo Observatory Synthesis Telescope (MOST). The secondary aim is to obtain images in [OIII] and [SII] to provide additional information on the nature of excitation in HII regions. Thirdly, additional images will be taken in B, V and I of interesting areas suitable for general publications as coloured reproductions. The images are taken with a 400 mm f/4·5 Nikkor-Q lens in conjunction with a 2K×2K SITe thinned CCD. The resolution is 12″ per pixel and the pixel size is 24 μm giving a 7°×7° field of view. Hαand red continuum observations are expected to be completed by the end of 1997. It is planned to make the results from the survey available on CD ROM and possibly video.
Background and First Results from the New AAO/UKST Hα Survey
Authors: Parker Quentin A. , Phillipps Steven 
Published: March 2011

AbstractThe UK Schmidt Telescope (UKST) of the Anglo-Australian Observatory (AAO) has just embarked on a new Hα survey of the Southern Galactic Plane, Magellanic Clouds and selected regions using a specially designed, high-specification, monolithic, interference filter. It is probably the largest of its kind for astronomy. It is being used in combination with Kodak Tech Pan film-based emulsion. This emulsion not only has a useful sensitivity peak at Hα but also possesses extremely fine grain and an exceptionally high DQE for the hypersensitised product (∼10%). This leads to excellent imaging, sensitivity and low noise. It is clear that CCDs cannot yet match the wide-area coverage, uniformity and resolution of the UKST/Tech Pan combination for undertaking such a survey. The survey will initially include about 233 Galactic Plane and 40 Magellanic Cloud fields on 4-degree centres and will take about 3 years to complete. Some preliminary images from the new survey are presented and compared with the best previously available from the UKST. Examples of the first survey discoveries, new resolved Galactic planetary nebulae, are also given. This survey will have an unprecedented combination of area coverage, depth and resolution, superior to those of any previous optical survey of ionised gas in the Galaxy. Many new discoveries and research avenues are expected.
Photographic Enhancement of Hα Films
Authors: Malin David 
Published: March 2011

AbstractThe appearance of Tech Pan film in sizes that were useful in large Schmidt telescopes immediately offered new opportunities and advantages to users of Schmidt telescopes. Among the advantages were a spatial resolution that was well matched to the image quality produced by the optics of the telescope under the best conditions. For the first time such images were well sampled on Schmidt telescopes. Tech Pan was initially formulated by Eastman Kodak as a 35 mm solar patrol film designed to have enhanced sensitivity around the 656·2 nm Hα line. It is this feature, combined with the excellent imaging characteristics, that we seek to exploit with the new UK Schmidt Telescope (UKST) Hα survey. This paper briefly reports some preliminary comparative tests of Tech Pan with the new Hα filter at UKST and suggests ways in which data from the new survey can be quickly exploited using advanced photographic techniques such as photographic amplification. This simple contact copying process rapidly reveals extended low surface brightness features that simple inspection cannot.
Digitisation, Archiving and Dissemination of the 275 Gbytes of the AAO/UKST Hα Survey Data
Authors: MacGillivray Harvey T. 
Published: March 2011

AbstractWe plan to digitise the AAO/UKST Hα survey of the Southern sky using the SuperCOSMOS facility at the Royal Observatory Edinburgh. The digitisation will be performed at 10 microns resolution (0·67 arcsec), and will result in a database of 275 Gbyte of pixel data for the 200 fields of the survey. These data will be processed to produce also a point source catalogue. As the Hα survey is an official AAO sky survey, both the pixel data and the point source catalogue will be made available to the community as a service facility. We give details of the digitisation process, archiving of the resulting data and the plans for dissemination of the database.
Diffuse Hα in a Fractal Interstellar Medium
Authors: Elmegreen Bruce G. 
Published: March 2011

AbstractObservations of cloud structure over the last 10 years have led to the conclusion that it is fractal in nature, with a fractal dimension characteristic of turbulence, as found in the laboratory. Such structure has an open texture, with a volume filling factor of nearly 90% for gas that is at low density. Turbulence makes such cavities by clearing away material during convective motions. We propose that most of the low-density intercloud medium is the result of turbulence and not overlapping supernova remnants. This model has important implications for diffuse Hα and ionisation of the halo. Fractal clouds have a gradually decreasing average density with increasing distance, so ionisation zones around these clouds can be very extensive. Fractal clouds are also highly clustered, making the mean free path for ionising photons at least twice as large as in the ‘standard cloud’ model. This long mean free path allows stray ionising photons from midplane H II regions to reach and ionise the halo.
The Warm Ionised Medium in Spiral Galaxies: A View from Above
Authors: Walterbos René A. M. 
Published: March 2011

AbstractThe warm ionised medium (WIM), also referred to as diffuse ionised gas (DIG), contains most of the mass of interstellar medium in ionised form, contributing as much as 30% of the total atomic gas mass in the solar neighborhood. The advent of CCDs has enabled unprecedented study of this medium in external galaxies, probing a variety of environments. In particular, we can derive the morphology of the WIM, its distribution across disks, and the correlation with other Population I material. Spectroscopy of the WIM makes it possible to test various ionisation models. I will review here our current understanding of the properties of the WIM in spiral galaxies. A perhaps unexpected result is that the Hα emission from the WIM contributes about 40% of the total observed Hα luminosity from spirals. This places severe constraints on possible sources of ionisation, since only photoionisation by OB stars meets this requirement. Spectroscopic measurements of forbidden line strengths appear in reasonable agreement with photoionisation models. It is not yet clear if the Lyman continuum photons that ionise the WIM are mostly from OB stars located inside traditional HII regions, or from field OB stars.
Diffuse Ionised Gas in Edge-on Galaxies
Authors: Rand Richard J. 
Published: March 2011

AbstractWe review observations of diffuse ionised gas (DIG) in edge-on spiral galaxies. Deep imaging has revealed a variety of morphologies for ‘extraplanar’ (above the HII region layer) or ‘halo’ DIG: some show widespread prominent layers of truly diffuse gas and filamentary structures, others show just one patch or a few patches of extraplanar emission, while still others show no detectable extraplanar DIG at all. The key galactic property which appears to govern the prominence of the DIG layer is the star-formation activity. Smaller-scale connections between DIG and local star formation activity can be seen in some of the galaxies.DIG halos are also related to radio continuum, X-ray and HI halos. Those galaxies with the most prominent DIG layers also have the most prominent radio halos. In NGC 891, there are spatial correlations between extraplanar DIG, radio emission, X-ray emission and HI, and these in turn are related to the underlying disk star-formation activity.Progress on identifying the sources of ionisation and heating of the gas has come from spectroscopy, imaging in different emission lines, and Fabry–Perot observations. By comparing with theoretical predictions, much evidence is found for photoionisation by disk stars as the primary ionisation and heating mechanism, but recent observations are beginning to point towards the need for additional sources of ionisation and/or heating.
Cosmological Applications of Hα Surveys
Authors: Valls–Gabaud David 
Published: March 2011

AbstractWe briefly review three main applications of Hα surveys in cosmology, namely: (1) the diffuse Hα emission as a tracer of the free–free foreground that contaminates the fluctuations in the cosmic microwave background radiation; (2) the Hα emission from galaxies as a measure of the formation rate of massive stars, both at low and high redshift; and (3) the diffuse Hα emission from ionised clouds as a constraint on the local ionising background radiation.
Neutral and Ionised Hydrogen in NGC 4214
Authors: McIntyre V. J. 
Published: March 2011

AbstractIt is not clear at present how the diffuse ionised gas (DIG) component in galaxies is ionised. The leading hypothesis is that ultraviolet photons from star clusters are responsible, but this requires a rather porous interstellar medium if the photons are to travel the large distances (≥ 1 kpc) between the bright clusters and diffuse-emission regions. To examine this hypothesis, we present high-resolution VLA observations of the neutral hydrogen in the Magellanic galaxy NGC 4214, and compare them with an Hα image. The data appear consistent with the idea that enough UV photons escape from supergiant H II regions to ionise the DIG.
Quantifying the Ionising Flux escaping from the Ultra-luminous H II Regions in Four Spiral Galaxies
Authors: Rozas M. , Zurita A. , Beckman J. E. 
Published: March 2011

AbstractThere are two principal problems in explaining, in terms of the emission from OB stars, the ionisation of gas which emits diffuse Hα in spiral galaxies. One is the long pathlength which the ionising photons need to traverse to reach their objectives, the other is whether sufficient photons can escape from within the H II regions which surround the hot stars. Here we treat the second point, assuming that the H II regions above a certain threshold luminosity are density bounded. We calculate the escaping Lyman continuum (Lyc) fluxes from the density bounded regions in four galaxies, and show that in each of them this is easily suffcient to produce the measured diffuse Hα emission.
Image Digitisation of Outflows and the AAO/UKST Hα Survey
Authors: Zealey W. J. , Mader S. L. 
Published: March 2011

AbstractThe Hα emission-line survey of the Southern Sky to be carried out by the AAO/UKST will provide deep, high resolution images of Galactic Plane sources allowing the detection of new and existing filamentary sources such as Herbig–Haro objects. Used in conjunction with the existing ESO/SERC Southern Sky Survey Plates, the Hα plates will provide us with the opportunity to study the morphology and environment of new and existing star forming regions.
Hipparcos Observations of Hydrogen-deficient Carbon Stars
Authors: Cottrell P. L. , Lawson W. A. 
Published: March 2011

AbstractParallax measurements for 21 hydrogen-deficient carbon stars have been made by the Hipparcos satellite. These stars include most of the brighter R Coronae Borealis (RCB) variables, other cool hydrogen-deficient carbon (HdC) stars, and several higher-Teff extreme helium (eHe) stars. Most of these stars have either negative or statistically insignificant parallaxes, indicating that they lie beyond the detection capability of Hipparcos. Although the distances to the galactic hydrogen-deficient carbon stars remain unknown, at least the Hipparcos observations do confirm that these objects must have high luminosity like the LMC RCB stars, for which Mbol = −4 to −5. Based upon Hipparcos proper motions, we derive UVW velocities for the RCB and HdC stars, assuming Mbol = −3 and −5. The UW -velocity dispersion of the RCB/HdC stars is similar to that already reported for the eHe stars, further supporting the idea that these groups of stars have predominantly bulge distributions. However, UW Cen may be a second example of a halo RCB star currently seen transitting the Galactic plane.
Near-IR Fluorescent Molecular Hydrogen Emission from NGC 2023
Authors: Burton Michael G. , Howe J. E. , Geballe T. R. , Brand P. W. J. L. 
Published: March 2011

AbstractSpectra from 1 to 2·5 μm, at 230–430 spectral resolution, are presented of the fluorescent molecular hydrogen line emission from two locations in the reflection nebula NGC 2023. Over 100 H2 lines can be identified in the spectra, although blending and poor atmospheric transmission mean that reliable level column densities can only be obtained from 35 lines. This latter group includes lines from v = 1–8 and v = 10, spanning an energy range from 6000 to 45,000 K above the ground state. These data may be used to constrain models of photodissociation regions and of fluorescent excitation for molecular hydrogen.
UNSWIRF: A Tunable Imaging Spectrometer for the Near-Infrared
Authors: Ryder Stuart D. , Sun Yin-Sheng , Ashley Michael C. B. , Burton Michael G. , Allen Lori E. , Storey John W. V. 
Published: March 2011

AbstractWe describe the specifications, characteristics, calibration, and analysis of data from the University of New South Wales Infrared Fabry–Perot (UNSWIRF) etalon. UNSWIRF is a near-infrared tunable imaging spectrometer, used primarily in conjunction with IRIS on the AAT, but suitable for use as a visitor instrument at other telescopes. The etalon delivers a resolving power in excess of 4000 (corresponding to a velocity resolution ∼75 km s−1), and allows imaging of fields up to 100″ in diameter on the AAT at any wavelength between 1·5 and 2·4 μm for which suitable blocking filters are available.
Torque Reversals in Disk Accreting Pulsars
Authors: Li Jianke , Wickramasinghe Dayal T. 
Published: March 2011

AbstractX-ray binaries in which the accreting component is a neutron star commonly exhibit significant changes in their spin. In the system Cen X-3, a disk accreting binary system, the pulsar was observed to spin up at a rate ḟ = 8 × 10−13 Hz s−1 when averaged over the past twenty years, but significant fluctuations were observed above this mean. Recent BASTE observations have disclosed that these fluctuations are much larger than previously noted, and appeared to be a system characteristic. The change in the spin state from spin-up to spin-down or vice-versa occurs on a time scale that is much shorter than the instrument can resolve (≤1 d), but appears always to be a similar amplitude, and to occur stochastically. These observations have posed a problem for the conventional torque–mass accretion relation for accreting pulsars, because in this model the spin rate is closely related to the accretion rate, and the latter needs to be finely tuned and to change abruptly to explain the observations. Here we review recent work in this direction and present a coherent picture that explains these observations. We also draw attention to some outstanding problems for future studies.
The Las Campanas/AAT Rich Cluster Survey
Authors: O'Hely Eileen , Couch Warrick J. , Smail Ian , Edge Alastair C. , Zabludoff Ann 
Published: March 2011

AbstractSome unsolved cosmological questions remain in relation to the formation of structure in the universe. One way of addressing such questions is to use rich galaxy clusters as tracers of the growth of large-scale structure. To date, studies of rich clusters of galaxies have concentrated on systems generally at either high redshift or in the local universe. The properties of clusters and their constituent galaxies at these extrema are becoming well understood. In particular, it is becoming clear that rich clusters have undergone considerable evolution both dynamically and in their galaxy populations over the last 5–8 Gyr. We are undertaking a detailed study of rich clusters of galaxies in the range 0·05 ≲ z ≲ 0·15. Our results will be directly comparable to those of previous studies both at high and low redshift and, for the first time, provide continuous coverage across this important and unexplored transitory epoch in terms of galaxy evolution and structure growth.
A Radio Survey of the SMC at 843 MHz with the MOST: I. The Survey
Authors: Turtle A. J. , Ye Taisheng , Amy S.W. , Nicholls Jennifer 
Published: March 2011

AbstractA radio survey at a frequency of 843 MHz of 36 square degrees containing the Small Magellanic Cloud (SMC) has been made with the Molonglo Observatory Synthesis Telescope (MOST). The angular resolution is around 45 arcsec and the rms noise is about 1 mJy per beam. The radio image of the region is presented showing over a thousand sources with a variety of angular sizes from unresolved to 10 arcmin. Most of the sources are presumed to be background objects but about 70 of the more extended sources are H II regions or supernova remnants within the SMC.
A Statistical Comparison of Line Strength Variations in Coma and Cluster Galaxies at z ~ 0·3
Authors: Jones Lewis A. , Couch Warrick J. 
Published: March 2011

AbstractWe present a statistical comparison between spectral line strength variations in Coma galaxies and galaxies in three rich clusters at z ~ 0.3. Using a principal component analysis, we have transformed the observable quantities, the line strengths, into new mutually orthogonal axes and found two specific results. First, more independent parameters are required to account for the line strength variations in the distant cluster data than in the Coma data, and second, line strengths which are not correlated in the distant cluster data are strongly coupled in the Coma data. These results suggest that galaxies in clusters have been homogenised such that most of the information from the conditions present at their formation has been destroyed. Hence, it may be possible that the present-day homogeneity of early-type galaxy properties, e.g. the fundamental plane relation, does not require a single formation scenario, but that a variety of formation scenarios for different galaxies could still yield the observed behaviour of nearby galaxies.
Observational Tests of a Double Loop Model for Solar Flares
Authors: Hardy S. J. , Melrose D. B. , Hudson H. S. 
Published: March 2011

AbstractA model for the energetics of solar flares, developed by Melrose (1997), is based on magnetic reconnection between two current-carrying magnetic loops. A detailed numerical investigation of the model has been made to identify those configurations that lead to energy release in a flare. Our results predict a strong relation between the ratio of currents in the interacting loops for a favoured flare configuration, and provide further support for a proposed method of generating long loops connecting different active regions. Both of these predictions are amenable to observational verification.