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  • The frequency condition for the mixed modes of nonradial stellar oscillations is generally examined by a simple physical model based on a running-wave picture. The coupling coefficient between the gravity-wave oscillation in the core and the acoustic-wave oscillation in the envelope is expressed in terms of the reflection coefficient at the intermediate evanescent region. It is also argued that the eigenmode condition should appropriately be modified if the wave generated near the surface and transmitted to the core is (partially) lost either by damping or scattering in the core. The derived formulae should be helpful in understanding the physics of the mixed modes in general, the origin of the red giants with depressed dipolar modes, and the effect of radiative damping in the core of the red giant stars.
    Data Types:
    • Video
  • The detection and analysis of oscillations in binary star systems is critical in understanding stellar structure and evolution. This is because such systems have the same initial chemical composition and age. Solar-like oscillations have been detected in both components of the asteroseismic binary HD 176465 by Kepler (White et al., 2016). This study presents an independent modelling of the two stars in this binary system. Stellar models generated using MESA (Modules for Experiment in Stellar Astrophysics) were fitted to both the observed individual frequencies and some spectroscopic parameters. The individual theoretical oscillation frequencies for the corresponding stellar models were obtained using GYRE as the pulsation code. A Bayesian approach was applied to find the Probability Distribution Functions of the stellar parameters using AIMS (Asteroseismic Inference on Massive Scale) as the optimization code. The age of the individual stars was found to agree with that obtained by White et al., (2016) of about 3.0 $\pm$ 0.5 Gyr old.
    Data Types:
    • Video
  • In my presentation I will talk about my upcoming master thesis about EUV bright points in the solar corona with AIA (Atmospheric Imaging Assembly) data from SDO (Solar Dynamics Observatory). Therefore I did some research of statistical properties of solar coronal bright points to compare them with the first results of our average bright point statistic (e.g.: number of bright points and their lifetime). Additionally, I will also show individual coronal bright points with their number of pixels, maximum and FFT (Fast Fourier Transformation). There are several possible origins for bright points, so I will also discuss these possible origins too. Further I will give an outlook for my future work: possible oscillation effects, possible difference in different wavelengths?
    Data Types:
    • Video
  • Time series VI (14 min). Left panel - reconstructed white-light intensity-maps @ 656nm. Right panel - Hα Line Wing intensities. Remarkable feature - interaction of small-scale quiet-sun magnetic field at solar disk center, driven by the surrounding convection. Spicules are observed in consequence.
    Data Types:
    • Video
  • Time series VI (14 min). Left panel - reconstructed white-light intensity-maps @ 656nm. Right panel - Hα Line Wing intensities. Remarkable feature - interaction of small-scale quiet-sun magnetic field at solar disk center, driven by the surrounding convection. Spicules are observed in consequence.
    Data Types:
    • Video
  • This presentation was given at the Solar Orbiter Science Activity Plan Meeting #4. It is a review on the techniques and achievements of helioseismology during the last decades. Furthermore, it gives an outlook on the science to be facilitated with ESA's space misison Solar Orbiter.
    Data Types:
    • Video
  • The Solar Physics Research Integrated Network Group (SPRING) is a project to develop a geographically distributed network of instrumentation to obtain synoptic solar observations. Building on the demonstrated success of networks to provide nearly-continuous long-term data for helioseismology, SPRING will provide data for a wide range of solar research areas. Scientific objectives include internal solar dynamics and structure; wave transport in the solar atmosphere; the evolution of the magnetic field over the activity cycle; irradiance fluctuations; and space weather origins. Anticipated data products include simultaneous full-disk multi-wavelength Doppler and vector magnetic field images; filtergrams in H-Alpha, CaK, and white light; and PSPT-type irradiance support. The data will be obtained with a duty cycle of around 90% and at a cadence no slower than one minute. The current concept is a multi-instrument platform installed in at least six locations, and which will also provide context information for large-aperture solar telescopes such as EST and the DKIST. There is wide support for the idea within the EU and the US solar research communities. The project is currently completing a technical feasibility study, and we are open to and looking for participants in the science and instrument definition.
    Data Types:
    • Video
  • An overview of the James Clerk Maxwell Telescope on Mauna Kea, Hawaii and the East Asia Observatory
    Data Types:
    • Video
  • Public Talk - Volkssternwarte Darmstadt
    Data Types:
    • Video
  • Determining empirical atmospheric models for the solar chormosphere is difficult since it requires the observation and analysis of spectral lines that are affected by non-local termodynamic equilibrium (NLTE) effects. Here we present Sunspot’s umbra data taken with the 1.5 m GREGOR telescope are analyzed after the effects of the stray-light on the data are removed using a novel deconvolution technique. The full Stokes measurements of a sunspot near disk center in the near-infrared spectral range were obtained with the GRIS instrument installed at the GREGOR telescope. A point-spread-function (PSF) including the effects of the telescope, the Earth’s atmospheric seeing, and the scattered light is constructed using prior Mercury observations with GRIS and the information provided by the adaptative optics system of the GREGOR telescope during the observations. The data are deconvolved from the PSF using a Principal Component Deconvolution method. The data are then analyzed using the NICOLE inversion code which can take into account the NLTE effects in the Si i 1082.9 nm line. The information of the magnetic field in taken into account within the inversion. Results. We found that the Si i 1082.9 nm line appears in emission in sunspot umbra after the effects of the scattered light (stray-light coming from wide angles) is removed. We show how the spectral line shape changes dramatically with the amount of scattered light. Current umbral empirical models are not able to reproduce the detected emission, taking into account NLTE effects. This is, to our knowledge, the first time the Si i 1082.9 nm line is seen in emission in sunspot umbrae.
    Data Types:
    • Video
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