122 research outputs found
A five colour photometry and polarimetry of the zodiacal light - A preliminary report
Five color photometry and polarimetry of the zodiacal ligh
The X-ray properties of the merging galaxy pair NGC 4038/9 - the Antennae
We report the results of an X-ray spectral imaging observation of the
Antennae with the ROSAT PSPC. 55% of the soft X-ray flux from the system is
resolved into discrete sources, including components identified with the
galactic nuclei and large HII regions, whilst the remainder appears to be
predominantly genuinely diffuse emission from gas at a temperature ~4x10^6 K.
The morphology of the emission is unusual, combining a halo which envelopes the
galactic discs, with what appears to be a distorted, but well-collimated
bipolar outflow. We derive physical parameters for the hot gas in both diffuse
components, which are of some interest, given that the Antennae probably
represents an elliptical galaxy in the making.Comment: 15 pages plus 9 figures, uuencoded encapsulated postscript file.
Accepted for publication in MNRA
The properties of highly luminous IRAS galaxies
From a complete sample of 154 galaxies identified with IRAS sources in a 304 sq deg area centered on the South Galactic Pole, a subsample of 58 galaxies with L sub IR/L sub B > 3 was chosen. Low resolution spectra were obtained for 30% of the subsample and redshifts and relative emission line intensities were derived. As a class these galaxies are very luminous with = 2.9 x 10 to the 11th power L sub 0 and (L sub IR) max = 1.3 x 10 to the 12th power L sub 0. CCD images and JHK photometry were obtained for many of the subsample. The galaxies are for the most part newly identified and are optically faint, with a majority showing evidence of a recent interaction. Radio continuum observations of all galaxies of the subsample were recently obtained at 20 cm VLA with about 75% being detected in a typical integration time of about 10 minutes
An Incremental Learning Method to Support the Annotation of Workflows with Data-to-Data Relations
Workflow formalisations are often focused on the representation of a process with the primary objective to support execution. However, there are scenarios where what needs to be represented is the effect of the process on the data artefacts involved, for example when reasoning over the corresponding data policies. This can be achieved by annotating the workflow with the semantic relations that occur between these data artefacts. However, manually producing such annotations is difficult and time consuming. In this paper we introduce a method based on recommendations to support users in this task. Our approach is centred on an incremental rule association mining technique that allows to compensate the cold start problem due to the lack of a training set of annotated workflows. We discuss the implementation of a tool relying on this approach and how its application on an existing repository of workflows effectively enable the generation of such annotations
Systematic identification of IRAS point sources
A large scale program was initiated to identify IRAS point sources. At ROE the ideal facilities are at hand to undertake such a large program, viz. the rapid scanning capabilities of the COSMOS measuring machine to exploit the depth and resolution of the U.K. Schmidt Telescope J survey plates. Sources in 44 Schmidt plate areas were identified including 1300 sources and covering 1100 square degrees. The identification comprise 700 galaxy identifications and 600 stellar identifications. There are also about 40 sources with no obvious identification but which can be most easily explained by cirrus, confusion between two sources or sources just outside the 2 sigma error box. A major aim with the galaxy identification is to provide a data base from which sound statistical analyses can be made. Accurate blue magnitudes and morphological classifications for each identification were produced
Evidence For A Precessing Accretion Disk in the Nucleus of NGC 1097
We present new spectroscopic observations of the LINER (and now Seyfert 1)
nucleus of NGC 1097, and discuss the evolution of its broad, double-peaked
Balmer lines. When originally discovered in 1991, the red peak of the
double-peaked H-alpha line was stronger than the blue, while by 1994 the
H-alpha profile had become almost symmetric and the integrated line flux had
decreased to half its original value. Our new spectrum, taken in 1996, shows
that the broad, double-peaked lines have returned to almost their original
strengths, the profiles of H-beta and H-alpha are identical to within errors,
and the broad-line emitting region is unreddened. However, the profile of the
Balmer lines is now such that the blue peak is stronger than the red, opposite
to the asymmetry observed in 1991. Various models are considered for the
observed behavior, all assuming that the emission lines originate in an
accretion disk. We present a refined version of the precessing, planar,
elliptical accretion ring model proposed by Storchi-Bergmann et al. and
Eracleous et al. This model provides an acceptable fit to the line profiles. We
also consider the possibility that the line profile evolution results from a
precessing warp in the disk, induced by irradiation from the center, and show
that the range of radii and precession time scales expected in this model are
consistent with the observations. The sudden appearance of the "disk-like"
broad line profiles in NGC 1097 could have resulted from the formation of a new
accretion disk due to, for example, the tidal disruption of a star, or the
illumination of a pre-existing disk by a transient ionizing source at the
center of the disk.Comment: Accepted for publication in the Astrophysical Journal. TeX file with
5 postscript figures embeded using psfig.tex, 13 page
Error Analysis for Dual-Beam Optical Linear Polarimetry
In this paper we present an error analysis for polarimetric data obtained
with dual-beam instruments. After recalling the basic concepts, we introduce
the analytical expressions for the uncertainties of polarization degree and
angle. These are then compared with the results of Monte-Carlo simulations,
which are also used to briefly discuss the statistical bias. Then we approach
the problem of background subtraction and the errors introduced by a
non-perfect Wollaston prism, flat-fielding and retarder plate defects. We
finally investigate the effects of instrumental polarization and we propose a
simple test to detect and characterize it. The application of this method to
real VLT-FORS1 data has shown the presence of a spurious polarization, which is
of the order of 1.5% at the edges of the field of view. The cause of this
effect has been identified with the presence of rather curved lenses in the
collimator, combined with the non complete removal of reflections by the
coatings. This problem is probably common to all focal-reducer instruments
equipped with a polarimetric mode. An additional spurious and asymmetric
polarization field, whose cause is still unclear, is visible in the B band.Comment: 13 pages, 11 figures. Accepted for publication in PAS
The ISO-IRAS Faint Galaxy Survey: Early results
We present preliminary results for AGNs and starburst galaxies the ISO-IRAS Faint Galaxy Survey (IIFGS). The goal of the survey is to produce a database of infrared-luminous galaxies at redshifts of about 0.1–1 to help explore the AGN-starburst relationship, study the cosmological evolution of luminous infrared galaxies, and identify possible protogalaxy candidates. The candidate list of ∼3700 sources has been extracted from the IRAS Faint Source Survey using criteria selecting for faint, infrared-bright galaxies. The ISO observations will confirm the IRAS detections, yield sensitive 12 & 90 μm fluxes, and provide positions to ∼6" accuracy which will allow unambiguous optical identifications. Confirmed sources are being followed up with ground-based observations to determine optical magnitudes and accurate redshifts. In this preliminary phase we have in hand ∼100 observed fields and are developing techniques to maximize the sensitivity of the observations. Early results for the ISOCAM 12 μm images indicate we can reliably detect sources as faint as ∼0.5 mJy; ∼80% of the fields contain at least one source
The Far-Infrared Spectral Energy Distributions of X-ray-selected Active Galaxies
[Abridged] We present ISO far-infrared (IR) observations of 21 hard X-ray
selected AGN from the HEAO-1 A2 sample. We compare the far-IR to X-ray spectral
energy distributions (SEDs) of this sample with various radio and optically
selected AGN samples. The hard-X-ray selected sample shows a wider range of
optical/UV shapes extending to redder near-IR colors. The bluer objects are
Seyfert 1s, while the redder AGN are mostly intermediate or type 2 Seyferts.
This is consistent with a modified unification model in which the amount of
obscuring material increases with viewing angle and may be clumpy. Such a
scenario, already suggested by differing optical/near-IR spectroscopic and
X-ray AGN classifications, allows for different amounts of obscuration of the
continuum emission in different wavebands and of the broad emission line region
which results in a mixture of behaviors for AGN with similar optical emission
line classifications. The resulting limits on the column density of obscuring
material through which we are viewing the redder AGN are 100 times lower than
for the standard optically thick torus models. The resulting decrease in
optical depth of the obscuring material allows the AGN to heat more dust at
larger radial distances. We show that an AGN-heated, flared, dusty disk with
mass 10^9 solar and size of few hundred pc is able to generate optical-far-IR
SEDs which reproduce the wide range of SEDs present in our sample with no need
for an additional starburst component to generate the long-wavelength, cooler
part of the IR continuum.Comment: 40 pages, 14 figures, accepted for publication in Astrophysical
Journal, V. 590, June 10, 200
AI-KG: an Automatically Generated Knowledge Graph of Artificial Intelligence
Scientific knowledge has been traditionally disseminated and preserved through research articles published in journals, conference proceedings, and online archives. However, this article-centric paradigm has been often criticized for not allowing to automatically process, categorize, and reason on this knowledge. An alternative vision is to generate a semantically rich and interlinked description of the content of research publications. In this paper, we present the Artificial Intelligence Knowledge Graph (AI-KG), a large-scale automatically generated knowledge graph that describes 820K research entities. AI-KG includes about 14M RDF triples and 1.2M reified statements extracted from 333K research publications in the field of AI, and describes 5 types of entities (tasks, methods, metrics, materials, others) linked by 27 relations. AI-KG has been designed to support a variety of intelligent services for analyzing and making sense of research dynamics, supporting researchers in their daily job, and helping to inform decision-making in funding bodies and research policymakers. AI-KG has been generated by applying an automatic pipeline that extracts entities and relationships using three tools:DyGIE++, Stanford CoreNLP, and the CSO Classifier. It then integrates and filters the resulting triples using a combination of deep learning and semantic technologies in order to produce a high-quality knowledge graph. This pipeline was evaluated on a manually crafted gold standard, yielding competitive results. AI-KG is available under CC BY 4.0 and can be downloaded as a dump or queried via a SPARQL endpoint
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