10,615 research outputs found
The reverberation signatures of rotating disc winds in active galactic nuclei
The broad emission lines (BELs) in active galactic nuclei (AGN) respond to
ionizing continuum variations. The time and velocity dependence of their
response depends on the structure of the broad-line region: its geometry,
kinematics and ionization state. Here, we predict the reverberation signatures
of BELs formed in rotating accretion disc winds. We use a Monte Carlo radiative
transfer and ionization code to predict velocity-delay maps for representative
high- (C) and low-ionization (H) emission lines in both high- and
moderate-luminosity AGN. Self-shielding, multiple scattering and the ionization
structure of the outflows are all self-consistently taken into account, while
small-scale structure in the outflow is modelled in the micro-clumping
approximation. Our main findings are: (1) The velocity-delay maps of
smooth/micro-clumped outflows often contain significant negative responses.
(2)~The reverberation signatures of disc wind models tend to be rotation
dominated and can even resemble the classic "red-leads-blue" inflow signature.
(3) Traditional "blue-leads-red" outflow signatures can usually only be
observed in the long-delay limit. (4) Our models predict lag-luminosity
relationships similar to those inferred from observations, but systematically
underpredict the observed centroid delays. (5) The ratio between "virial
product" and black hole mass predicted by our models depends on viewing angle.
Our results imply that considerable care needs to be taken in interpreting data
obtained by observational reverberation mapping campaigns. In particular, basic
signatures such as "red-leads-blue", "blue-leads-red" and "blue and red vary
jointly" are not always reliable indicators of inflow, outflow or rotation.
This may help to explain the perplexing diversity of such signatures seen in
observational campaigns to date.Comment: 15 pages, 17 figures, 2 tables. Accepted by MNRAS 20/7/201
Differential cross section for neutron-proton bremsstrahlung
The neutron-proton bremsstrahlung process is known to be
sensitive to meson exchange currents in the nucleon-nucleon interaction. The
triply differential cross section for this reaction has been measured for the
first time at the Los Alamos Neutron Science Center, using an intense, pulsed
beam of up to 700 MeV neutrons to bombard a liquid hydrogen target. Scattered
neutrons were observed at six angles between 12 and 32, and the
recoil protons were observed in coincidence at 12, 20, and
28 on the opposite side of the beam. Measurement of the neutron and
proton energies at known angles allows full kinematic reconstruction of each
event. The data are compared with predictions of two theoretical calculations,
based on relativistic soft-photon and non-relativistic potential models.Comment: 5 pages, 3 figure
HI ``Tails'' from Cometary Globules in IC1396
IC 1396 is a relatively nearby (750 pc), large (>2 deg), HII region ionized
by a single O6.5V star and containing bright-rimmed cometary globules. We have
made the first arcmin resolution images of atomic hydrogen toward IC 1396, and
have found remarkable ``tail''-like structures associated with some of the
globules and extending up to 6.5 pc radially away from the central ionizing
star. These HI ``tails'' may be material which has been ablated from the
globule through ionization and/or photodissociation and then accelerated away
from the globule by the stellar wind, but which has since drifted into the
``shadow'' of the globules.
This report presents the first results of the Galactic Plane Survey Project
recently begun by the Dominion Radio Astrophysical Observatory.Comment: 11 pages, 5 postscript figures, uses aaspp4.sty macros, submitted in
uuencoded gzipped tar format, accepted for publication in Astrophysical
Journal Letters, colour figures available at
http://www.drao.nrc.ca/~schieven/news_sep95/ic1396.htm
Universal zero-bias conductance for the single electron transistor. II: Comparison with numerical results
A numerical renormalization-group survey of the zero-bias electrical
conductance through a quantum dot embedded in the conduction path of a
nanodevice is reported. The results are examined in the light of a recently
derived linear mapping between the temperature-dependent conductance and the
universal function describing the conductance for the symmetric Anderson model.
A gate potential applied to the conduction electrons is known to change
markedly the transport properties of a quantum dot side-coupled to the
conduction path; in the embedded geometry here discussed, a similar potential
is shown to affect only quantitatively the temperature dependence of the
conductance. As expected, in the Kondo regime the numerical results are in
excellent agreement with the mapped conductances. In the mixed-valence regime,
the mapping describes accurately the low-temperature tail of the conductance.
The mapping is shown to provide a unified view of conduction in the
single-electron transistor.Comment: Sequel to arXiv:0906.4063. 9 pages with 8 figure
Asteroseismic Theory of Rapidly Oscillating Ap Stars
This paper reviews some of the important advances made over the last decade
concerning theory of roAp stars.Comment: 9 pages, 5 figure
Phase separation and vortex states in binary mixture of Bose-Einstein condensates in the trapping potentials with displaced centers
The system of two simultaneously trapped codensates consisting of
atoms in two different hyperfine states is investigated theoretically in the
case when the minima of the trapping potentials are displaced with respect to
each other. It is shown that the small shift of the minima of the trapping
potentials leads to the considerable displacement of the centers of mass of the
condensates, in agreement with the experiment. It is also shown that the
critical angular velocities of the vortex states of the system drastically
depend on the shift and the relative number of particles in the condensates,
and there is a possibility to exchange the vortex states between condensates by
shifting the centers of the trapping potentials.Comment: 4 pages, 2 figure
Stability of vortex solitons in a photorefractive optical lattice
Stability of off-site vortex solitons in a photorefractive optical lattice is
analyzed. It is shown that such solitons are linearly unstable in both the high
and low intensity limits. In the high-intensity limit, the vortex looks like a
familiar ring vortex, and it suffers oscillatory instabilities. In the
low-intensity limit, the vortex suffers both oscillatory and Vakhitov-Kolokolov
instabilities. However, in the moderate-intensity regime, the vortex becomes
stable if the lattice intensity or the applied voltage is above a certain
threshold value. Stability regions of vortices are also determined at typical
experimental parameters.Comment: 3 pages, 5 figure
Observations of Cepheids with the MOST satellite: Contrast between Pulsation Modes
The quantity and quality of satellite photometric data strings is revealing
details in Cepheid variation at very low levels. Specifically, we observed a
Cepheid pulsating in the fundamental mode and one pulsating in the first
overtone with the Canadian MOST satellite. The 3.7-d period fundamental mode
pulsator (RT Aur) has a light curve that repeats precisely, and can be modeled
by a Fourier series very accurately. The overtone pulsator (SZ Tau, 3.1 d
period) on the other hand shows light curve variation from cycle to cycle which
we characterize by the variations in the Fourier parameters. We present
arguments that we are seeing instability in the pulsation cycle of the overtone
pulsator, and that this is also a characteristic of the O-C curves of overtone
pulsators. On the other hand, deviations from cycle to cycle as a function of
pulsation phase follow a similar pattern in both stars, increasing after
minimum radius. In summary, pulsation in the overtone pulsator is less stable
than that of the fundamental mode pulsator at both long and short timescales.Comment: accepted in MNRAS, 11 pages, 10 figure
Infrared nonredundant mask imaging at Palomar
A program of high resolution infrared imaging at Palomar Observatory, is presented. The use of nonredundant masks both as an imaging technique and as a method of analyzing various aspects of the imaging system are investigated. In particular, the technique is applied to a bright star and binary system using a three-hole mask. The method is useful for understanding certain systematic biases in data, as well as in producing high quality images despite sparse UV coverage. The use of multi-r(o) apertures along with a large bandwidth does not significantly hamper image reconstruction, but provides significant extra coverage in the UV plane
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