Author name code: settele ADS astronomy entries on 2022-09-14 author:"Settele, Axel" ------------------------------------------------------------------------ Title: Acceleration Effects in MDI Magnetogram Data Authors: Norton, A.; Settele, A. Bibcode: 2003SoPh..214..227N Altcode: Acceleration effects are found in the Michelson Doppler Imager (MDI) magnetogram data because changes in the line profiles during the 30-s measurement are introduced by underlying p-mode velocity variations. This imparts an oscillatory component to the magnetic flux signal. Simulated profiles using Maltby M and Harvard Smithsonian Reference Atmospheres (HSRA) are shifted in accordance with a given velocity amplitude and period and the MDI algorithm for data measurement is applied. The simulated oscillatory component to the magnetic flux density always has a phase difference with respect to the underlying velocity of −90°. The maximum introduced RMS amplitude is a function of velocity amplitude and field strength, but realistic errors are on the order of 5/2000 G, or 0.25% of field strength. Comparison of simulations with observations shows RMS amplitudes of MDI flux density are much greater than predicted by this effect. A 2-component HSRA model, tested to determine if stronger fields with smaller fill factors could fit the data, still can not reproduce the observations. It is concluded that oscillatory amplitudes of magnetic flux density measured with MDI are not due to acceleration effects, although the effect could contribute up to 25% of the measured amplitude. Attempts to remove acceleration effects from the magnetic flux signal are not successful. Also, we confirm that velocities measured in linearly polarized light in the vicinity of a strong magnetic field contain larger errors than velocities measured in circularly polarized light (Yang and Norton, 2001). Title: Temporal and spatial variations of the magnetic field vector in sunspots Authors: Settele, A.; Sigwarth, M.; Muglach, K. Bibcode: 2002A&A...392.1095S Altcode: In order to look for magnetic field vector oscillations in sunspots we used data measured with the Advanced Stokes Polarimeter at the Dunn Solar Telescope. We analyzed two time series of 65 and 110 min that were taken by scanning repeatedly a 6" 24 x 75" field of view, while obtaining the full Stokes vector in the lines FeI 630.15 nm and 630.25 nm. An inversion was carried out and a Fast Fourier Transform (FFT) analysis was used to find oscillatory phenomena. We discuss possible unwanted effects that lead to apparent magnetic field oscillations and find an average amplitude of (B, psi ) 5.8 G/0.23o rms by excluding these effects, which also means that only 6% and 22% of the two sunspot umbrae respectively remained for analysis. If we smooth the power spectra over 2x2 pixels, all significant power disappears. Title: Systematic errors in measuring solar magnetic fields with a FPI spectrometer and MDI Authors: Settele, A.; Carroll, T. A.; Nickelt, I.; Norton, A. A. Bibcode: 2002A&A...386.1123S Altcode: We will show the potential errors of observations using instruments, where a line spectrum is obtained not instantly but by scanning through the spectral line in time. We give two examples in simulations of a sunspot observation with the measuring procedure of a typical Fabry-Perot interferometer (FPI) spectrometer and the Michelson Doppler Imager (MDI) on board of the Solar and Heliospheric Observatory (SOHO). The effect described is inherent for observations with a low intensity input signal, where the accumulation time for one image and therefore the whole process of measuring a spectrum is relatively high compared to the timescale of the underlying physical processes. We show that our simulated data produce an error in magnetic field strength and - in a time series - result in an apparent oscillation of the magnetic field strength, while the input contained only velocity oscillations. As the FPI spectrometer is being used more and more widely, one has to be aware of the disadvantages and potential errors when interpreting its data. We encourage every observer to do the simple simulation as described for every specific setup used. Title: Waves in Sunspots: Resonant Transmission and the Adiabatic Coefficient Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D. Bibcode: 2001SoPh..202..281S Altcode: We investigate linear acoustic-gravity waves in three different semi-empirical model atmospheres of large sunspot umbrae. The sunspot filter theory is applied, that is, the resonant transmission of vertically propagating waves is modelled. The results are compared with observed linear sunspot oscillations. For three umbral models we present the transmission coefficients and the energy density of the oscillations with the maxima of transmission. The height dependence of the adiabatic coefficient (the ratio of specific heats) γ strongly influences the calculated resonance frequencies. The variable γ can explain the observed closely spaced resonance period peaks. The first resonance in the 3 min range is interpreted as a resonance of the upper chromosphere only, while the higher order peaks are resonances of the whole chromosphere. Title: Magneto-Atmosphaerische Wellen in der Umbra von Sonnenflecken; Magnetoatmospheric waves in the umbra of sunspots Authors: Settele, A. Bibcode: 2001PhDT.........3S Altcode: No abstract at ADS Title: Problems in the interpretation of sunspot oscillation measurements Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D. Bibcode: 2001ESASP.464..247S Altcode: 2001soho...10..247S Sunspot oscillations are observed in spectral lines formed at different depths in the sunspot atmosphere. The interpretation of measurements in chromospheric lines is problematic as the lines are formed in NLTE. So the measured power spectra do not originate from one specific depth in the atmosphere but are smoothed out over a larger region. This will also influence the phase shifts of the waves measured in different spectral lines and might cause some misinterpretation. These complications are illustrated by our model calculations: Modelling the transmission of magneto-atmospheric waves through the sunspot atmosphere by means of the sunspot filter approach, we show the "real" power spectra at different atmospheric depths. These results are compared with Ca II-H/K power spectra gained from the NLTE calculations of the Ca II-H/K lines in an atmosphere perturbed by our waves. All results are preliminary. Title: Magneto-Atmosphärische Wellen in der Umbra von Sonnenflecken Title: Magneto-Atmosphärische Wellen in der Umbra von Sonnenflecken Authors: Settele, Axel Bibcode: 2001PhDT.......431S Altcode: No abstract at ADS Title: Resonant Transmission of Magneto-atmospheric Waves in Sunspot Umbrae Authors: Staude, J.; Rendtel, J.; Settele, A. Bibcode: 2001IAUS..203..320S Altcode: Oscillations of velocity and intensity, of the magnetic field in the photosphere as well, have been observed at all height levels of the atmosphere above sunspots from the photosphere up to the lower corona. We discuss the nonstationary behavior of intensity and velocity oscillations; they have been observed by SOHO in transition region lines formed in the EUV plume of a sunspot during a continuous time series of 4.3 hours. Applying a wavelet analysis, we find periods around 3 mHz with different periods in the observed EUV lines. Moreover, we discuss the observed oscillations within the frame of model calculations for the resonant transmission of magneto-atmospheric waves through realistic models of the sunspot subphotosphere and atmosphere. Title: The Influence of the Adiabatic Coefficient and the Magnetic Field on Sunspot Oscillations Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J. Bibcode: 1999ESASP.448..367S Altcode: 1999ESPM....9..367S; 1999mfsp.conf..367S No abstract at ADS Title: A new method to calculate the resonant response of a sunspot model atmosphere to magneto-atmospheric waves Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J. Bibcode: 1999AN....320..147S Altcode: In order to understand the observed oscillations in sunspots we present a new method for calculating the resonant response of a realistic semi-empirical model of the sunspot umbral atmosphere and subphotosphere to magneto-atmospheric waves in a vertical magnetic field. The depth dependence of both the adiabatic coefficient and the turbulent pressure is taken into account. This requires an extension of the wave equations by Ferraro & Plumpton (1958). We compare the coefficients of wave transmission, reflection, and conversion between fast mode and slow mode waves for different assumptions, compare the results with those from earlier modelling efforts, and point out possible sources of mistakes. The depth dependence of the adiabatic coefficient strongly influences the resulting spectrum of resonance frequencies. The condition of a conservation of wave flux is violated if the depth dependence of the turbulent pressure is not properly considered.