27,039 research outputs found
Time variations of the narrow FeII and HI spectral emission lines from the close vicinity of Eta Carinae during the spectral event of 2003
The spectrum of Eta Carinae and its ejecta shows slow variations over a
period of 5.5 years. However, the spectrum changes drastically on a time scale
of days once every period called the 'spectral event'. We report on variations
in the narrow emission line spectrum of gas condensations (the Weigelt blobs)
close to the central star during a spectral event. The rapid changes in the
stellar radiation field illuminating the blobs make the blobs a natural
astrophysical laboratory to study atomic photoprocesses. The different
responses of the HI Paschen lines, fluorescent lines and forbidden
[FeII] lines allow us to identify the processes and estimate physical
conditions in the blobs. This paper is based on observations from the Pico dos
Dias Observatory (LNA/Brazil) during the previous event in June 2003.Comment: Accepted for publication in A&
Levitated droplet dye laser
We present the first observation, to our knowledge, of lasing from a
levitated, dye droplet. The levitated droplets are created by computer
controlled pico-liter dispensing into one of the nodes of a standing ultrasonic
wave (100 kHz), where the droplet is trapped. The free hanging droplet forms a
high quality optical resonator. Our 750 nL lasing droplets consist of Rhodamine
6G dissolved in ethylene glycol, at a concentration of 0.02 M. The droplets are
optically pumped at 532 nm light from a pulsed, frequency doubled Nd:YAG laser,
and the dye laser emission is analyzed by a fixed grating spectrometer. With
this setup we have achieved reproducible lasing spectra in the visible
wavelength range from 610 nm to 650 nm. The levitated droplet technique has
previously successfully been applied for a variety of bio-analytical
applications at single cell level. In combination with the lasing droplets, the
capability of this high precision setup has potential applications within
highly sensitive intra-cavity absorbance detection.Comment: 6 pages including 3 figure
iPTF16abc and the population of Type Ia supernovae: Comparing the photospheric, transitional and nebular phases
Key information about the progenitor system and the explosion mechanism of
Type Ia supernovae (SNe~Ia) can be obtained from early observations, within a
few days from explosion. iPTF16abc was discovered as a young SN~Ia with
excellent early time data. Here, we present photometry and spectroscopy of the
SN in the nebular phase. A comparison of the early time data with a sample of
SNe~Ia shows distinct features, differing from normal SNe~Ia at early phases
but similar to normal SNe~Ia at a few weeks after maximum light (i.e. the
transitional phase) and well into the nebular phase. The transparency
timescales () for this sample of SNe~Ia range between 25 and 41
days indicating a diversity in the ejecta masses. also weakly correlates
with the peak bolometric luminosity, consistent with the interpretation that
SNe with higher ejecta masses would produce more Ni. Comparing the
and the maximum luminosity, L\, distribution of a sample of SNe~Ia to
predictions from a wide range of explosion models we find an indication that
the sub-Chandrasekhar mass models span the range of observed values. However,
the bright end of the distribution can be better explained by Chandrasekhar
mass delayed detonation models, hinting at multiple progenitor channels to
explain the observed bolometric properties of SNe~Ia. iPTF16abc appears to be
consistent with the predictions from the M models.Comment: 13 pages, 8 figures, accepted for publication in MNRA
The information about the state of a charge qubit gained by a weakly coupled quantum point contact
We analyze the information that one can learn about the state of a quantum
two-level system, i.e. a qubit, when probed weakly by a nearby detector. We
consider the general case where the qubit Hamiltonian and the qubit's operator
probed by the detector do not commute. Because the qubit's state keeps evolving
while being probed and the measurement data is mixed with a detector-related
background noise, one might expect the detector to fail in this case. We show,
however, that under suitable conditions and by proper analysis of the
measurement data useful information about the initial state of the qubit can be
extracted. Our approach complements the usual master-equation and
quantum-trajectory approaches, which describe the evolution of the qubit's
quantum state during the measurement process but do not keep track of the
acquired measurement information.Comment: 5 pages, 3 figures; Published in the proceedings of the Nobel
Symposium 141: Qubits for Future Quantum Informatio
Non-colliding Brownian Motions and the extended tacnode process
We consider non-colliding Brownian motions with two starting points and two
endpoints. The points are chosen so that the two groups of Brownian motions
just touch each other, a situation that is referred to as a tacnode. The
extended kernel for the determinantal point process at the tacnode point is
computed using new methods and given in a different form from that obtained for
a single time in previous work by Delvaux, Kuijlaars and Zhang. The form of the
extended kernel is also different from that obtained for the extended tacnode
kernel in another model by Adler, Ferrari and van Moerbeke. We also obtain the
correlation kernel for a finite number of non-colliding Brownian motions
starting at two points and ending at arbitrary points.Comment: 38 pages. In the revised version a few arguments have been expanded
and many typos correcte
Atomic Processes in Planetary Nebulae and H II Regions
Spectroscopic studies of Planetary Nebulae (PNe) and H {\sc ii} regions have
driven much development in atomic physics. In the last few years the
combination of a generation of powerful observatories, the development of ever
more sophisticated spectral modeling codes, and large efforts on mass
production of high quality atomic data have led to important progress in our
understanding of the atomic spectra of such astronomical objects. In this paper
I review such progress, including evaluations of atomic data by comparisons
with nebular spectra, detection of spectral lines from most iron-peak elements
and n-capture elements, observations of hyperfine emission lines and analysis
of isotopic abundances, fluorescent processes, and new techniques for
diagnosing physical conditions based on recombination spectra. The review is
directed toward atomic physicists and spectroscopists trying to establish the
current status of the atomic data and models and to know the main standing
issues.Comment: 9 pages, 1 figur
Constant net-time headway as key mechanism behind pedestrian flow dynamics
We show that keeping a constant lower limit on the net-time headway is the
key mechanism behind the dynamics of pedestrian streams. There is a large
variety in flow and speed as functions of density for empirical data of
pedestrian streams, obtained from studies in different countries. The net-time
headway however, stays approximately constant over all these different data
sets. By using this fact, we demonstrate how the underlying dynamics of
pedestrian crowds, naturally follows from local interactions. This means that
there is no need to come up with an arbitrary fit function (with arbitrary fit
parameters) as has traditionally been done. Further, by using not only the
average density values, but the variance as well, we show how the recently
reported stop-and-go waves [Helbing et al., Physical Review E, 75, 046109]
emerge when local density variations take values exceeding a certain maximum
global (average) density, which makes pedestrians stop.Comment: 7 pages, 7 figure
Understanding the Structural Scaling Relations of Early-Type Galaxies
We use a large suite of hydrodynamical simulations of binary galaxy mergers
to construct and calibrate a physical prescription for computing the effective
radii and velocity dispersions of spheroids. We implement this prescription
within a semi-analytic model embedded in merger trees extracted from the
Bolshoi Lambda-CDM N-body simulation, accounting for spheroid growth via major
and minor mergers as well as disk instabilities. We find that without disk
instabilities, our model does not predict sufficient numbers of intermediate
mass early-type galaxies in the local universe. Spheroids also form earlier in
models with spheroid growth via disk instabilities. Our model correctly
predicts the normalization, slope, and scatter of the low-redshift size-mass
and Fundamental Plane relations for early type galaxies. It predicts a degree
of curvature in the Faber-Jackson relation that is not seen in local
observations, but this could be alleviated if higher mass spheroids have more
bottom-heavy initial mass functions. The model also correctly predicts the
observed strong evolution of the size-mass relation for spheroids out to higher
redshifts, as well as the slower evolution in the normalization of the
Faber-Jackson relation. We emphasize that these are genuine predictions of the
model since it was tuned to match hydrodynamical simulations and not these
observations.Comment: Submitted to MNRA
Infrared FeII Emission in Narrow-Line Seyfert 1 Galaxies
We obtained 0.8-2.4 micron spectra at a resolution of 320 km/s of four
narrow-line Seyfert 1 galaxies in order to study the near-infrared properties
of these objects. We focus on the analysis of the FeII emission in that region
and the kinematics of the low-ionization broad lines. We found that the 1
micron FeII lines (9997 A, 10501 A, 10863 A and 11126 A) are the strongest FeII
lines in the observed interval. For the first time, primary cascade lines of
FeII arising from the decay of upper levels pumped by Ly-alpha fluorescence are
resolved and identified in active galactic nuclei. Excitation mechanisms
leading to the emission of the 1 micron FeII features are discussed. A
combination of Ly-alpha fluorescence and collisional excitation are found to be
the main contributors. The flux ratio between near-IR FeII lines varies from
object to object, in contrast to what is observed in the optical region. A good
correlation between the 1 micron and optical FeII emission is found. This
suggests that the upper z4Fo and z4Do levels from which the bulk of the optical
lines descend are mainly populated by the transitions leading to the 1 micron
lines. The width and profile shape of FeII 11127, CaII 8642 and OI 8446 are
very similar but significantly narrower than Pa-beta, giving strong
observational support to the hypothesis that the region where FeII, CaII and OI
are produced are co-spatial, interrelated kinematically and most probably
located in the outermost portion of the BLR.Comment: Accepted for publication in ApJ - 35 page
Is the Mott transition relevant to f-electron metals ?
We study how a finite hybridization between a narrow correlated band and a
wide conduction band affects the Mott transition. At zero temperature, the
hybridization is found to be a relevant perturbation, so that the Mott
transition is suppressed by Kondo screening. In contrast, a first-order
transition remains at finite temperature, separating a local moment phase and a
Kondo- screened phase. The first-order transition line terminates in two
critical endpoints. Implications for experiments on f-electron materials such
as the Cerium alloy CeLaTh are discussed.Comment: 5 pages, 3 figure
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