1,675 research outputs found
Optically Controlled Excitonic Transistor
Optical control of exciton fluxes is realized for indirect excitons in a
crossed-ramp excitonic device. The device demonstrates experimental proof of
principle for all-optical excitonic transistors with a high ratio between the
excitonic signal at the optical drain and the excitonic signal due to the
optical gate. The device also demonstrates experimental proof of principle for
all-optical excitonic routers
Transport of Indirect Excitons in a Potential Energy Gradient
We realized a potential energy gradient - a ramp - for indirect excitons
using a shaped electrode at constant voltage. We studied transport of indirect
excitons along the ramp and observed that the exciton transport distance
increases with increasing density and temperature.Comment: 4 pages, 3 figure
An Empirical Ultraviolet Template for Iron Emission in Quasars as Derived from I Zw 1
We present an empirical template spectrum suitable for fitting/subtracting
and studying the FeII and FeIII line emission in the restframe UV spectra of
active galatic nuclei (AGNs), the first empirical UV iron template to cover the
full 1250 - 3090 A range. Iron emission is often a severe contaminant in
optical--UV spectra of AGNs. Its presence complicates and limits the accuracy
of measurements of both strong and weak emission lines and the continuum
emission, affecting studies of line and continuum interrelations, the
ionization structure, and elemental abundances in AGNs. Despite the wealth of
work on modeling the AGN FeII emission and the need to account for it in
observed AGN spectra, there is no UV template electronically available to aid
this process. The iron template we present is based on HST spectra of the
Narrow Line Seyfert 1, IZw1. Its intrinsic narrow lines (~900 km/s) and rich
iron spectrum make the template particularly suitable for use with most AGN
spectra. The iron emission spectrum and the line identifications and
measurements are presented and compared with the work of Laor et al. We
illustrate the application of the derived FeII and FeIII templates by fitting
and subtracting the iron emission from UV spectra of four high-z quasars and of
the nearby quasar, 3C273. We briefly discuss the small discrepancies between
this observed iron emission and the UV template, and compare the template with
previously published ones. We discuss the advantages and limitations of the
templates and of the template fitting method. We conclude that the templates
work sufficiently well to be a valuable and important tool for eliminating and
studying the iron emission in AGNs, at least until accurate theoretical iron
emission models are developed. (Abridged)Comment: 73 pages including 7 figures, 6 tables. To appear in ApJS. Preprint
is also available at
http://www.astronomy.ohio-state.edu/~vester/IronEmission
Spectral Variability of Quasars in the Sloan Digital Sky Survey. II: The C IV Line
We examine the variability of the high-ionizaton C IV line in a sample of 105
quasars observed at multiple epochs by the Sloan Digital Sky Survey. We find a
strong correlation between the change in the C IV line flux and the change in
the line width, but no correlations between the change in flux and changes in
line center and skewness. The relation between line flux change and line width
change is consistent with a model in which a broad line base varies with
greater amplitude than the line core. The objects studied here are more
luminous and at higher redshift than those normally studied for variability,
ranging in redshift from 1.65 to 4.00 and in absolute r-band magnitude from
roughly -24 to -28. Using moment analysis line-fitting techniques, we measure
line fluxes, centers, widths and skewnesses for the C IV line at two epochs for
each object. The well-known Baldwin Effect is seen for these objects, with a
slope beta = -0.22. The sample has a median intrinsic Baldwin Effect slope of
beta = -0.85; the C IV lines in these high-luminosity quasars appear to be less
responsive to continuum variations than those in lower luminosity AGN.
Additionally, we find no evidence for variability of the well known blueshift
of the C IV line with respect to the low-ionization Mg II line in the highest
flux objects, indicating that this blueshift might be useful as a measure of
orientation.Comment: 52 pages, 14 figures, accepted for publication in Ap
The UV Properties of the Narrow Line Quasar I Zwicky 1
I Zw 1 is the prototype narrow line quasar. We report here the results of our
study of the UV emission of I Zw 1 using a high S/N (50-120) spectrum obtained
with the HST FOS. The following main new results are obtained: 1. The Mg II and
Al III doublets are partially/fully resolved. The measured doublet ratios
verify theoretical predictions that the lines are thermalized in the BLR. 2. A
weak associated UV absorption system is detected in N~V, and possibly also in C
IV and Lya, suggesting an outflow with a velocity of 1870 km/s and velocity
dispersion <300 km/s. 3. Lines from ions of increasing ionization level show
increasing excess blue wing flux, and an increasing line peak velocity shift,
reaching a maximum blueshift of about 2000 km/s for He II 1640. This may
indicate an out-flowing component in the BLR, where the ionization level
increases with velocity, and which is visible only in the approaching
direction. The highest velocity part of this outflow may produce the associated
UV absorption system. 4. The small C III] 1909 EW, and the small C III]
1909/Lya and C III] 1909/Si III] 1892 flux ratios indicate a typical BLR
density of 10^11, i.e. about an order of magnitude larger than implied by C
III] 1909 in most quasars. A BLR component of a higher density is implied by
the EW and doublet ratio of the Al III 1857 doublet. 5. Prominent Fe II UV 191
emission is seen, together with weaker line emission at 1294 and 1871 A. These
three features have been proposed as evidence for significant Lya pumping of
the 8-10 eV levels of Fe II. 6. Significant Fe III emission is present. The Fe
III UV 34 and UV 48 multiplets are clearly resolved, and Fe III UV 1, UV 47, UV
50, and UV 68 may also be present. (Shortened version)Comment: 28 pages, 1 table and 7 figures included. Uses aas2pp4.sty. Scheduled
for the Astrophysical Journal November 10, 1997 issue, Vol. 48
Neutrino Spin Transitions and the Violation of the Equivalence Principle
The violation of the equivalence principle (VEP) causing neutrino
oscillations is of current interest. We study here the possibility of not only
flavor oscillation but spin flavor oscillation of ultra high energy ( 1
PeV) neutrinos emanating from AGN due to VEP and due to the presence of a large
magnetic field ( 1 Tesla) in AGN. In particular we look at the resonance
spin flavor conversion driven by the AGN potential. Interesting bounds on the
transition magnetic moment of neutrinos may therefore be obtained.Comment: Latex, 12 pages, no figures. To appear in Journal of Physics G:
Nuclear and Particle Physics. Two references adde
Electrostatic Conveyer for Excitons
We report on the study of indirect excitons in moving lattices - conveyers
created by a set of AC voltages applied to the electrodes on the sample
surface. The wavelength of this moving lattice is set by the electrode
periodicity, the amplitude is controlled by the applied voltage, and the
velocity is controlled by the AC frequency. We observed the dynamical
localization-delocalization transition for excitons in the conveyers and
measured its dependence on the exciton density and conveyer amplitude and
velocity. We considered a model for exciton transport via conveyers. The
theoretical simulations are in agreement with the experimental data.Comment: 4 pages, 4 figures + supplemental material including two video
Pattern formation in the exciton inner ring
We report on the two-beam study of indirect excitons in the inner ring in the exciton emission pattern. One laser beam generates the inner ring and a second weaker beam is positioned in the inner ring. The beam positioned in the inner ring is found to locally suppress the exciton emission intensity. We also report on the inner ring fragmentation and formation of multiple rings in the inner ring region. These features are found to originate from a weak spatial modulation of the excitation beam intensity in the inner ring region. The modulation of exciton emission intensity anticorrelates with the modulation of the laser excitation intensity. The three phenomena—inner ring fragmentation, formation of multiple rings in the inner ring region, and emission suppression by a weak laser beam in the inner ring—have a common feature: a reduction of exciton emission intensity in the region of enhanced laser excitation. This effect is explained in terms of exciton transport and thermalization
The Molonglo Reference Catalog 1-Jy radio source survey IV. Optical spectroscopy of a complete quasar sample
Optical spectroscopic data are presented here for quasars from the Molonglo
Quasar Sample (MQS), which forms part of a complete survey of 1-Jy radio
sources from the Molonglo Reference Catalogue. The combination of low-frequency
selection and complete identifications means that the MQS is relatively free
from the orientation biases which affect most other quasar samples. To date,
the sample includes 105 quasars and 6 BL Lac objects, 106 of which have now
been confirmed spectroscopically. This paper presents a homogenous set of
low-resolution optical spectra for 79 MQS quasars, the majority of which have
been obtained at the Anglo-Australian Telescope. Full observational details are
given and redshifts, continuum and emission-line data tabulated for all
confirmed quasars.Comment: 40 pages, ApJS in pres
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