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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.
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This contribution provides a summary of not yet published technical innovations to the GREGOR Fabry-Perot Interferometer (GFPI) at the 1.5m GREGOR Solar Telescope (Europe's largest solar telescope) that I implemented in 2013 as the Instrument Scientist of the GFPI. It also represents an overview of first important and not yet published observational results that I achieved with the GFPI in 2013. The results and achievements can be considered as a milestone in the scientific verification and further development of the Instrument.
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The standard picture of solar spicules: elongated highly dynamic jet-like features best seen in emission beyond the solar limb. Temporal evolution of Hα Line parameters for solar off-limb spicules; from left to right and top to bottom: Full width at half maximum (standard estimate, Gaussian Fit), line wing intensity, line core intensity, height distribution.
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Main sequence turn-off (MSTO) stars are advantaged indicators of Galactic evo- lution since their ages could be robustly estimated by atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it will be benefited from accurate estimates of stellar param- eters. In this work, we select 150 MSTO candidates in the LAMOST MSTO stars sample and constrain their stellar parameters with theoretical models. Asteroseismic properties ∆ν, νmaxobtained from Kepler data are considered for accurate estimates. And furthermore, we examine the contamination rate of the LAMOST MSTO stars sample and validate the age estimation by the LAMOST spectra in Xiang et al. (2015). The results show that 79 of the candidates are MSTO stars and others are main-sequence stars or sub giants and a comparison between ages from this work and what have been obtained through interpolation method in Xiang et al. (2015) shows that there is a mean difference of 0.53 Gyr (7%) and a dispersion of 2.71 Gyr (28%). A considerable fraction of oldest stars in the LAMOST MSTO stars sample are likely contamination stars from much younger dwarf/subgiant stars. The main cause for high contamination rates are likely relatively large systematic bias of surface gravity and may not be ignored in the study of Galactic structure.
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In this contribution, we investigate to which degree strayligh influences results from the GREGOR Infrared Spectrograph. To this end, we use the synthesis module of the SIR code to perform radiative transfer calculations in a 3D-MHD model atmosphere of a full sunspot. We convolve the resulting Stokes spectra spatially and spectrally with theoretical point spread functions (PSF) as well as a PSF obtained during the Mercury transit and compare the results to GRIS observations.
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As a part of the SOLARNET project, the Transnational Access and Service Programme supports the access of the European solar physics community to some of the best European telescopes. To enhance the efficiency of data usage, external observers will receive also support for postfactum reduction of data, while standard pipelines are not fully developed, with the aim of providing them science-ready data. A successful Programme, which will bring together researchers of different nationalities, forms the basis for a long-term perspective of solar physics in Europe and for the operation of the European Solar Telescope, when it become a reality.
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  • Video
Synoptic observations of the Sun are very important to understand the long term behavior of the solar activity cycle. Our current understanding solar magnetic cycle is rather in its infancy, as can be inferred from our very poor prediction for the strength of solar cycle 24, based on various dynamo models. Solar magnetism is at the heart of all solar activity and therefore it is important to understand what parameters govern the magnetic cycle in the Sun. An important parameter that is realized more recently is the internal dynamics, i.e., profile of solar internal rotation and nature of large scale meridional flows. Therefore, it is important to study the solar interior by making use of helioseismology. Ground based helioseismology networks such as GONG are now quite few decades old and its possible failure poses risk to the continuity of solar oscillation data. Hence, a next generation of synoptic network SPRING is being proposed and is currently under design study. We will present science requirements and the details of the SPRING network.
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SPRING is an evolving concept for next generation solar synoptic observations network. It is envisaged that the new network will cater to the needs of (i) Helioseismology community, by providing improved resolution Doppler observations at multiple heights in solar atmosphere, (ii) Space weather research community, by providing full disk vector magnetograms at a cadence of few minutes and in multiple heights in the solar atmosphere, and (iii) Large solar telescopes, such as DKIST and EAST, by providing high resolution fulldisk context imaging in multiple wavelengths. We will present the conceptual designs currently being explored for SPRING.
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Presentation on the Fourier-Legendre decomposition technique shown at the LoHCo Meetin in Stanford in August 2011.
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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 in the early planning stages, and we are open to and looking for participants in the science and instrument definition.
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  • Video
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