explanation blue bibcodes open ADS page with paths to full text
Author name code: langangen
ADS astronomy entries on 2022-09-14
author:"Langangen, Oystein"
---------------------------------------------------------
Title: Interference of Light in Michelson-Morley Interferometer:
A Quantum Optical Approach
Authors: Langangen, O.; Skagerstam, B. -S.; Vaskinn, A.
2011arXiv1102.4324L Altcode:
We investigate how the temporal coherence interference properties
of light in a Michelson-Morley interferometer (MMI), using only a
single-photon detector, can be understood in a quantum-optics framework
in a straightforward and pedagogical manner. For this purpose we make
use of elementary quantum field theory and Glaubers theory for photon
detection in order to calculate the expected interference pattern
in the MMI. If a thermal reference source is used in the MMI local
oscillator port in combination with a thermal source in the signal port,
the interference pattern revealed by such an intensity measurement
shows a distinctive dependence on the differences in the temperature
of the two sources. The MMI can therefore be used in order to perform
temperature measurements. A related method was actually used to carry
out high precision measurements of the cosmic micro-wave background
radiation on board of the COBE satellite. The theoretical framework
allows us to consider any initial quantum state. The interference of
single photons as a tool to determine the angular peak-frequency of a
one-photon pulse interfering with a single-photon reference pulse is,
e.g., considered. A similar consideration for coherent laser pulses
leads to a different response in the detector. The MMI experimental
setup is therefore in a sense an example of an optical device where
one can exhibit the difference between classical and quantum-mechanical
light using only intensity measurements.
---------------------------------------------------------
Title: Swaying Threads of a Solar Filament
Authors: Lin, Y.; Soler, R.; Engvold, O.; Ballester, J. L.; Langangen,
Ø.; Oliver, R.; Rouppe van der Voort, L. H. M.
2009ApJ...704..870L Altcode: 2009arXiv0909.2792L
From recent high-resolution observations obtained with the Swedish 1
m Solar Telescope in La Palma, we detect swaying motions of individual
filament threads in the plane of the sky. The oscillatory characters of
these motions are comparable with oscillatory Doppler signals obtained
from corresponding filament threads. Simultaneous recordings of motions
in the line of sight and in the plane of the sky give information
about the orientation of the oscillatory plane. These oscillations
are interpreted in the context of the magnetohydrodynamic (MHD)
theory. Kink MHD waves supported by the thread body are proposed as
an explanation of the observed thread oscillations. On the basis of
this interpretation and by means of seismological arguments, we give
an estimation of the thread Alfvén speed and magnetic field strength
by means of seismological arguments.
---------------------------------------------------------
Title: The Temperature Diagnostic Properties of the Mg I 457.1 nm Line
Authors: Langangen, Øystein; Carlsson, Mats
2009ApJ...696.1892L Altcode: 2009arXiv0903.1492L
We analyze the important formation processes for the Mg I 457.1 nm
line. This line is an intercombination line and the source function
is close to the local thermodynamic equilibrium (LTE) value. The
strong coupling to the local temperature and the relatively high
population of the lower level (the ground state of Mg I) makes this
line an ideal candidate for temperature diagnostics in the lower
chromosphere/temperature minimum region. Linking the temperature probed
to an absolute physical height is nontrivial because of non-LTE (NLTE)
ionization. We analyze the NLTE effects and find that photoionization
from the lower energy levels together with cascading collisional
recombination dominates the ionization balance. Taking properly into
account the line blanketing in the UV is essential for obtaining the
right photoionization rates. The identification of the main NLTE effects
in the line allows us to construct a "quintessential" model atom, ideal
for computationally demanding tasks, e.g., full three-dimensional
and/or time-dependent radiative transfer. Furthermore, we analyze
the diagnostic potential to temperature of this line in solarlike
atmospheres, by synthesizing the line from a series of parameterized
atmospheric models. These models have been constructed with fixed
effective temperature, but with a variable heat term in the energy
equation to obtain a chromospheric temperature rise at different
heights. We conclude that the line has a significant potential in
the diagnostics of the lower chromosphere temperature structure,
especially for cooler atmospheres, such as sunspots.
---------------------------------------------------------
Title: How fast could Usain Bolt have run? A dynamical study
Authors: Eriksen, H. K.; Kristiansen, J. R.; Langangen, Ø.; Wehus,
I. K.
2009AmJPh..77..224E Altcode: 2008arXiv0809.0209E
Since that memorable day at the Beijing 2008 Olympics, a big
question has been, “What would the 100 m dash world record have
been had Usain Bolt not celebrated at the end of his race?” Bolt's
coach suggested that the time could have been 9.52 s or better. We
consider this question by measuring Bolt's position as a function of
time using footage of the run, and then extrapolate the last 2 s with
two different assumptions. First, we conservatively assume that Bolt
could have maintained the runner-up's acceleration during the end of the
race. Second, based on the race development prior to the celebration, we
assume that Bolt could have kept an acceleration of 0.5 m/s<SUP>2</SUP>
greater than the runner-up. We find that the new world record in these
two cases would have been 9.61+/-0.04 and 9.55+/-0.04 s, respectively,
where the uncertainties denote 95% statistical errors.
---------------------------------------------------------
Title: Search for High Velocities in the Disk Counterpart of Type
II Spicules
Authors: Langangen, Ø.; De Pontieu, B.; Carlsson, M.; Hansteen,
V. H.; Cauzzi, G.; Reardon, K.
2008ApJ...679L.167L Altcode: 2008arXiv0804.3256L
Recently, De Pontieu and coworkers discovered a class of spicules
that evolve more rapidly than previously known spicules, with rapid
apparent motions of 50-150 km s<SUP>-1</SUP>, thickness of a few 100
km, and lifetimes of order 10-60 s. These so-called type II spicules
have been difficult to study because of limited spatiotemporal and
thermal resolution. Here we use the IBIS instrument to search for the
high velocities in the disk counterpart of type II spicules. We have
detected rapidly evolving events, with lifetimes that are less than a
minute and often equal to the cadence of the instrument (19 s). These
events are characterized by a Doppler shift that only appears in the
blue wing of the Ca II IR line. Furthermore, the spatial extent,
lifetime, and location near network all suggest a link to type II
spicules. However, the magnitude of the measured Doppler velocity is
significantly lower than the apparent motions seen at the limb. We
use Monte Carlo simulations to show that this discrepancy can be
explained by a forward model in which the visibility on the disk of
the high-velocity flows in these events is limited by a combination
of line-of-sight projection and reduced opacity in upward propelled
plasma, especially in reconnection driven jets that are powered by a
roughly constant energy supply.
---------------------------------------------------------
Title: Measurements of Plasma Motions in Dynamic Fibrils
Authors: Langangen, Øystein; Rouppe van der Voort, Luc; Lin, Yong
2008ApJ...673.1201L Altcode: 2007arXiv0710.1011L
We present a 40 minute time series of filtergrams from the red and
blue wings of the Hα line in an active region near the solar disk
center. From these filtergrams we construct both Dopplergrams and summed
"line center" images. Several dynamic fibrils (DFs) are identified
in the summed images. The data are used to simultaneously measure the
proper motion and the Doppler signals in DFs. For calibration of the
Doppler signals, we use spatially resolved spectrograms of a similar
active region. Significant variations in the calibration constant for
different solar features are observed, and only regions containing
DFs have been used in order to reduce calibration errors. We find
a coherent behavior of the Doppler velocity and the proper motion
that clearly demonstrates that the evolution of DFs involves plasma
motion. The Doppler velocities are found to be a factor of 2-3 smaller
than velocities derived from proper motions in the image plane. The
difference can be explained by the radiative processes involved, as
the Doppler velocity is a result of the local atmospheric velocity
weighted with the response function. As a result, the Doppler velocity
originates from a wide range of heights in the atmosphere. This is
contrasted with the proper-motion velocity, which is measured from the
sharply defined bright tops of the DFs and is therefore a very local
velocity measure. The Doppler signal originates from well below the
top of the DF. Finally, we discuss how this difference, together with
the lower spatial resolution of older observations, has contributed to
some of the confusion about the identity of DFs, spicules, and mottles.
---------------------------------------------------------
Title: Spectroscopic Measurements of Dynamic Fibrils in the Ca II
λ8662 Line
Authors: Langangen, Øystein; Carlsson, Mats; Rouppe van der Voort,
Luc; Hansteen, Viggo; De Pontieu, Bart
2008ApJ...673.1194L Altcode: 2007arXiv0710.0247L
We present high spatial resolution spectroscopic measurements of dynamic
fibrils (DFs) in the Ca II λ8662 line. These data show clear Doppler
shifts in the identified DFs, which demonstrates that at least a subset
of DFs are actual mass motions in the chromosphere. A statistical
analysis of 26 DFs reveals a strong and statistically significant
correlation between the maximal velocity and the deceleration. The
range of the velocities and the decelerations are substantially lower,
about a factor 2, in our spectroscopic observations compared to the
earlier results based on proper motion in narrowband images. There
are fundamental differences in the different observational methods;
when DFs are observed spectroscopically, the measured Doppler shifts
are a result of the atmospheric velocity, weighted with the response
function to velocity over an extended height. When the proper motion
of DFs is observed in narrowband images, the movement of the top
of the DF is observed. This point is sharply defined because of the
high contrast between the DF and the surroundings. The observational
differences between the two methods are examined by several numerical
experiments using both numerical simulations and a time series of
narrowband Hα images. With basis in the simulations we conclude that
the lower maximal velocity is explained by the low formation height of
the Ca IR line. We conclude that the present observations support the
earlier result that DFs are driven by magnetoacoustic shocks excited
by convective flows and p-modes.
---------------------------------------------------------
Title: Spectral analysis of fine structure in the lower solar
atmosphere
Authors: Langangen, Øystein
2008PhDT.......359L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric Spectrometry at High Spatial Resolution
Authors: Langangen, Ø.; Carlsson, M.; Rouppe van der Voort, L.;
Hansteen, V. H.; de Pontieu, B.
2007ASPC..368..145L Altcode:
In this summary we present spectrograms and images of the
chromosphere obtained in a co-observation campaign with the SST and
the DOT. The data are used to identify and measure the Doppler shifts
of dynamic fibrils. Quantitative comparison with the results of <P
/>\citep{ol-2006ApJ...647L..73H} requires compensation for several
observational issues.
---------------------------------------------------------
Title: Velocities Measured in Small-Scale Solar Magnetic Elements
Authors: Langangen, Øystein; Carlsson, Mats; Rouppe van der Voort,
Luc; Stein, R. F.
2007ApJ...655..615L Altcode: 2006astro.ph.11741L
We have obtained high-resolution spectrograms of small-scale magnetic
structures with the Swedish 1-m Solar Telescope. We present Doppler
measurements at 0.2" spatial resolution of bright points, ribbons,
and flowers, and their immediate surroundings, in the C I λ5380.3 line
(formed in the deep photosphere) and the two Fe I lines at 5379.6 and
5386.3 Å. The velocity inside the flowers and ribbons are measured to
be almost zero, while we observe downflows at the edges. These downflows
are increasing with decreasing height. We also analyze realistic
magnetoconvective simulations to obtain a better understanding of the
interpretation of the observed signal. We calculate how the Doppler
signal depends on the velocity field in various structures. Both the
smearing effect of the nonnegligible width of this velocity response
function along the line of sight and of the smearing from the telescope
and atmospheric point-spread function are discussed. These studies lead
us to the conclusion that the velocity inside the magnetic elements
is really upflow of order 1-2 km s<SUP>-1</SUP>, while the downflows
at the edges really are much stronger than observed, of order 1.5-3.3
km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: The Diagnostic Potential of the MG i 4571.1 Å Line
Authors: Langangen, Ø.; Carlsson, M.; Rouppe van der Voort, L.
2005ESASP.600E..65L Altcode: 2005ESPM...11...65L; 2005dysu.confE..65L
No abstract at ADS
