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Scientific interest for the spectral region around 1083 nm is growing over the last years following advances in theory as well as in IR instrumentation. Such facilities require further development of diagnostic tools.The aim of our study is to analyze the validity of the weak field approximation for the photospheric Si I 1082.7 nm line. We solve the NLTE formation problem of this line by means of multilevel radiative transfer calculations in a 3D snapshot model taken from the magneto-convection simulations with small-scale dynamo action. The spectral images of the snapshot are degraded because of the seeing and light diffraction by the telescope aperture. We apply the weak field approximation both to the original and smeared Stokes I, Q, U, V profiles supposing that they represent ``real Sun'' observations. We compare the longitudinal and transverse components of the magnetic field that one would expect from observations of the Si I 1082.7 nm line under perfect spatial resolution and under different seeing conditions of the observations done with the VTT, GREGOR and EST (DKIST) telescopes. We show that crucial condition for observation of polarization in the quiet photosphere using the Si i 1082.7 nm line is the best possible spatial resolution, clearly better than 0.5 arc sec. We find that with the spatial resolution close to the diffraction limit of the EST telescope the surface maps of the magnetic field inferred from this line using the weak field approximation are close to the maps of the real field derived on a surface with the single optical depth. The correlation between them is rather high, except that the inferred longitudinal component of the magnetic field strength turn out to be lower than the vertical component of the ``real Sun''. At the same time, the transverse component is rather close to the horizontal one.
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This is a copy of presentation given at 14th Quadrennial Solar-Terrestrial Physics Symposium held in Toronto, Canada July 9-13, 2018. Heliophysics research community is pushing hard to explore the Sun with new instruments in new wavelength bands, with the highest-possible spatial resolution and the fastest time cadence. We also have the societal "mandate" to develop a reliable space weather forecast. The developments in high resolution solar physics are fueled by the recent progress in adaptive optics, radiative transfer, full Stokes polarimetry, and realistic numerical modeling allowing the true fusion of state-of-the-art numerical modeling and equally sophisticated observations. Ground-based initiatives in high spatial resolution solar physics are now under development in USA (DKIST and GST), Europe and China (CLST). Future large-aperture solar telescopes have been also discussed in Europe (EST), India (NLST) and China (CGST). Measuring magnetic fields in the chromosphere and corona has been long considered as one of critical issues for proper understanding of magnetic field topology and in improving the space weather forecast. The instruments for observing coronal magnetic fields include direct measurements at the limb (CoMP, COSMO), full Stokes polarimetry in infrared and He I 10830A in prominences, and multi-frequency observations in radio frequencies (OVRO, CSRH). Solar phenomena often occur on large spatial scales (e.g., large-scale connectivity and flare/CME-related restructuring of solar corona) and long temporal scales of several decades or longer (solar cycles, Maunder minima). The long-term monitoring is critical for understanding of these solar phenomena, which calls for development of synoptic programs. Relevant projects include SPRING initiative (EU and USA), CHAIN project (Japan), synoptic "Solar Service" and STOP-2 network of magnetographs (Russia). In addition, there are smaller in scale projects aimed at creating facilities for specific research goals (flare prediction, sun-as-star, Brazilian magnetograph). This talk will review the present instrument initiatives in ground-based solar and solar-terrestrial physics, and emphasize the importance of close international collaboration in this area of research.
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  • Video
In 2011, the International Astronomical Union (IAU) created a working group now known as the IAU inter-Division B-E working group on Coordination of Synoptic Observations of the Sun. The mission of this group is to facilitate the international collaboration in synoptic long-term solar observations, which includes past, current, and future synoptic programs, preservation, calibration, and access to synoptic solar data products. This presentation provides a brief overview of activities of the group and outlines the current issues facing the synoptic solar groundbased observations.
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We study effects of the cross-helicity in the full-sphere large-scale mean-field dynamo models of the $\mathrm{0.3M_{\odot}}$ star rotating with the period of 10 days. In exploring several dynamo scenarios which are stemming from the cross-helicity generation effect, we found that the cross-helicity provide the natural generation mechanisms for the large-scale scale axisymmetric and non-axisymmetric magnetic field. Therefore the rotating stars with convective envelope can produce the large-scale magnetic field generated solely due to the turbulent cross-helicity effect (we call it $\gamma^{2}$-dynamo). Using mean-field models we compare properties of the large-scale magnetic field organization that stem from dynamo mechanisms based on the kinetic (associated with the $\alpha^{2}$ dynamos) and cross-helicity. For the fully convective stars both generation mechanisms can maintain a large-scale dynamos even for the solid body rotation law inside the star. The non-axisymmetric magnetic configurations become preferable when the cross-helicity and the $\alpha$-effect operate independently of each other. This corresponds to situations of the purely $\gamma^{2}$ or $\alpha^{2}$ dynamos. Combination of these scenarios, i.e., the $\gamma^{2}\alpha^{2}$ dynamo can generate preferably axisymmetric, dipole-like magnetic field of strength several kG. Thus we found a new dynamo scenario which is able to generate the axisymmetric magnetic field even in the case of the solid body rotation of the star. We discuss the possible applications of our findings to stellar observations.
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The 3rd Myanmar Infrastructure Summit 2017 is set to provide a platform for potential foreign investors, infrastructure developers, technology providers and infrastructure funders to be updated on the development plans and policies of investing in Myanmar’s urban and rural infrastructure and at the same time build potential business and investment networks with the local policy makers and industry players.
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Context. The Sun and solar-like stars undergo activity cycles for which the underlying mechanisms are not well understood. The oscillations of the Sun are known to vary with activity cycle and these changes provide diagnostics on the conditions below the photosphere. Kepler has detected oscillations in hundreds of solar-like stars but as of yet, no widespread detection of signatures of magnetic activity cycles in the oscillation parameters of these stars have been reported. Aims. We analyse the photometric short cadence Kepler time series of a set of 24 solar-like stars, which were observed for at least 960 days each, with the aim to find signatures of stellar magnetic activity in the oscillation parameters. Methods. We analyse the temporal evolution of oscillation parameters by measuring mode frequency shifts and changes in the height of the p-mode envelope. Results. For 22 of the 24 investigated stars, we find significant frequency shifts in time, indicating stellar magnetic activity. For the most prominent example, KIC 8006161, we find that, similar to the solar case, frequency shifts are smallest for the lowest and largest for the highest p-mode frequencies. Conclusions. These findings show that magnetic activity can be routinely observed in the oscillation parameters for solar-like stars. The large proportion of stars for which this is the case opens up the possibility to place the Sun and its activity cycle in the context of other stars.
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We present results on travel time measurements for different frequencies through Gaussian frequency filtering of time-distance cross-correlation signals. We show that the center-to-limb systematics inferred through WE travel time measurements have a dominant frequency dependence, peaking at about 4 mHz. The subtraction of such travel times from the NS travel times leads to a strong frequency dependence in the resulting meridional flow signals too thus yielding flow structures dependent on frequency. In particular, we find multiple-cell structure for frequencies above 3.7 mHz.
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We describe principles of gravitational lensing, macrolensing and microlensing. The physics of Quasars is shortly discussed and then quasar macro- and microlensing by galaxies is described. Own observations consist of photometric observations and spectroscopic observations. We show how from the lensing parameters quantities like the Hubble constant, the mass of the lensing galaxy, the size of the accretion disc and the mass of the supermassive black hole at the center of the quasar can be derived.
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Opening slides for Synoptic Programs meeting
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Synoptic observations are indispensable in studies of long-term effects pertinent to variation in solar radiative output, space weather and space climate, as well as for understanding the physics of global processes taking place on our nearest star. Synoptic data also allow putting the Sun in the context of stellar evolution. Historically, the main-stay of such observations has been ground-based, although the improving longevity of space-borne instruments puts some space missions into the category of synoptic facilities. Space- and ground-based (synoptic) observations are complementary to each other; neither is inferior or superior to the other. Ground-based facilities can have a long-term (50 years+) operations horizon, and in comparison with their space-based counterparts, they are less expensive to operate and have fewer restrictions on international collaboration and data access. The instruments can be serviced, upgraded, and cross-calibrated to ensure the continuity and uniformity of long-term data series. New measurements could be added in response to changes in understanding the solar phenomena. Some drawbacks such as day-night cycle and the variable atmospheric seeing can be mitigated e.g., by creating the global networks and by employing the adaptive optics. Furthermore, the ground-based synoptic observations can serve as a backbone and a back-up to space-based observations. In my talk I will review some existing ground-based synoptic facilities, describe plans for future networks, and outline the current efforts in strengthening the international collaboration in synoptic solar observations from the ground.
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  • Video
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