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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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/s2 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. Bibcode: 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-1, 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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

\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. Bibcode: 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-1, while the downflows at the edges really are much stronger than observed, of order 1.5-3.3 km s-1. Title: The Diagnostic Potential of the MG i 4571.1 Å Line Authors: Langangen, Ø.; Carlsson, M.; Rouppe van der Voort, L. Bibcode: 2005ESASP.600E..65L Altcode: 2005ESPM...11...65L; 2005dysu.confE..65L No abstract at ADS