4,782 research outputs found
An Empirical Ultraviolet Iron Spectrum Template Applicable to Active Galaxies
Iron emission is often a severe contaminant in optical-ultraviolet spectra of
active galaxies. Its presence complicates emission line studies. A viable
solution, already successfully applied at optical wavelengths, is to use an
empirical iron emission template. We have generated FeII and FeIII templates
for ultraviolet active galaxy spectra based on HST archival 1100 - 3100 A
spectra of IZw1. Their application allows fitting and subtraction of the iron
emission in active galaxy spectra. This work has shown that in particular CIII]
lambda 1909 can be heavily contaminated by other line emission, including iron
transitions. Details of the data processing, generation, and use of the
templates, are given by Vestergaard & Wilkes (2001).Comment: 4 pages, including 1 figure, to appear in "Spectroscopic Challenges
of Photoionized Plasmas", ASP Conf. Series, Eds. Gary Ferland and Daniel Wolf
Savi
Exciton effective mass enhancement in coupled quantum wells in electric and magnetic fields
We present a calculation of exciton states in semiconductor coupled quantum
wells (CQWs) in the presence of electric and magnetic fields applied
perpendicular to the QW plane. The exciton Schr\"odinger equation is solved in
real space in three dimensions to obtain the Landau levels of both direct and
indirect excitons. Calculation of the exciton energy levels and oscillator
strengths enables mapping of the electric and magnetic field dependence of the
exciton absorption spectrum. For the ground state of the system, we evaluate
the Bohr radius, optical lifetime, binding energy and dipole moment. The
exciton mass renormalization due to the magnetic field is calculated using a
perturbative approach. We predict a non-monotonous dependence of the exciton
ground state effective mass on magnetic field. Such a trend is explained in a
classical picture, in terms of the ground state tending from an indirect to a
direct exciton with increasing magnetic field.Comment: 20 pages, 7 figure
The Velocity Field of Quasar Broad Emission Line Gas
In this Letter, the broad emission line (BEL) profiles of superluminal
quasars with apparent jet velocities, , (ultraluminal QSOs, or
ULQSOs hereafter) are studied as a diagnostic of the velocity field of the BEL
emitting gas in quasars. The ULQSOs are useful because they satisfy a very
strict kinematical constraint, their parsec scale jets must be propagating
within of the line of sight. We know the orientation of these
objects with great certainty. The large BEL FWHM, , in ULQSOs tend to indicate that the BEL gas has a larger
component of axial velocity (either random or in a wind) along the jet
direction than previously thought.Comment: To appear in ApJ Letter
Studies in the roman province of Dalmatia
This study was undertaken while the author held a Ministry of Education State Studentship at the Department of Archaeology in Durham and, since October 1961, a Research Fellowship in the University of Birmingham. I would like to record my debt of gratitude to my supervisor Professor Eric Birley and Dr. J.C Mann of the Department of Archaeology in Durham. In the Spring and early Summer of 1960 I spent some time travelling in Yugoslavia, and here I would like to thank some of the many people who helped me to carry out my research. In particular I would like to express my gratitude to Professor Grga Novak, President of the Yugoslav Academy of Arts and Sciences in Zagreb; Professor D. Rendic-Miocevic and Mr. M. Zaninovic of the University of Zagreb; Dr. Esad Pasalio of the University of Sarajevo; Dr. Dimitri Sergejevski and Miss Irma Crremosnik of the Museum in Sarajevo; Dr. B. Gabricevic and Dr. N. Nikolanc of the Archaeological Museum in Split; Dr. M. Suic of the Museum and Historical Faculty in Zadar. Without the generous co-operation of many of the above it would have proved impossible for me to have visited many of the key sites in Dalmatia which lie far away from public transport routes. On this point especially, I would like to thank the Secretaries of the Communes of Zadar and Sinj for placing vehicles at my disposal. For assistance in the preparation of this thesis I would like to acknowledge the help of Mr. C.D.N. Costa and Dr. J.D. Eshelby of the University of Birmingham, and Miss Christine Pittarn of the University Library in Birmingham for undertaking the typing. The absence of a map calls for explanation. For points of topography only detailed maps of the largest scale would be of any value. However, all the places referred to are recorded on Kiepert’s map in CIL III (suppl ii taf. VI), and in the very few instances where this is not the case more precise details of location with regard to neighbouring centres are given
Apollo experience report: A use of network simulation techniques in the design of the Apollo lunar surface experiments package support system
A case study of data-communications network modeling and simulation is presented. The applicability of simulation techniques in early system design phases is demonstrated, and the ease with which model parameters can be changed and comprehensive statistics gathered is shown. The discussion of the model design and application also yields an insight into the design and implementation of the Apollo lunar surface experiments package ground-support system
Quasar x-ray spectra revisited
A sample of 45 quasars observed by the Imaging Proportional Counter (IPC) on the Einstein satellite is used to re-examine the relationship between the soft (0.2-3.5 keV) X-ray energy index and radio-loudness. We found the following: (1) the tendency for radio-loud quasars to have systematically flatter X-ray slopes than radio-quiet quasars (RQQ's) is confirmed with the soft X-ray excess having negligible effect; (2) there is a tendency for the flatness of the X-ray slope to correlate with radio core-dominance for radio-loud quasars, suggesting that a component of the X-ray emission is relativistically beamed; (3) for the RQQ's the soft X-ray slopes, with a mean of approximately 1.0, are consistent with the slopes found at higher energies (2-10 keV) although steeper than those observed for Seyfert 1 galaxies (also 2-10 keV) where the reflection model gives a good fit to the data; (4) the correlation of FeII emission line strength with X-ray energy index is confirmed for radio-quiet quasars using a subset of 18 quasars. The radio-loud quasars show no evidence for a correlation. This relation suggests a connection between the ionizing continuum and the line emission from the broad emission line region (BELR) of radio-quiet quasars, but in the opposite sense to that predicted by current photoionization models; and (5) the correlations of X-ray slope with radio core dominance and FeII equivalent width within the radio-loud and radio-quiet sub-classes respectively imply that the observed wide range of X-ray spectral slopes is real rather than due to the large measuring uncertainties for individual objects
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