Picture of the Month

We present a method to directly detect or constrain a stochastic background of gravitational waves (SBGW) at mHz and Hz frequencies by using helioseismic observations. We demonstrate the validity of this approach by deducing a direct upper bound around 0.17 mHz on both the astrophysical and cosmological component of the SBGW.

The universe is expected to be penetrated by a stochastic background of gravitational radiation of astrophysical and cosmological origin. This background is not accessible to conventional observations based on electromagnetic waves. In recent years an increasing number of experiments have set upper limits on the amplitude of this background at various frequencies. However, the astrophysically interesting band between 10-4 - 1 Hz remains largely unexplored. As shown by Boughn & Kuhn (1984) the Sun and stars can be employed as giant hydrodynamical detectors for the gravitational-wave background. Using recent high-precision radial velocity data for the Sun and a...

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Numerical simulations of the surface layers of four dwarf stellar models of effective temperatures 4000 K, 5000 K, 5770 K (the Sun), and 6500 K, corresponding to spectral types M3, K3, G2, and F5, respectively, have been carried out. All models show bright filamentary features in the intergranular space, which are due to small-scale magnetic flux concentrations (see figure).

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Sunspots are the most prominent manifestations of the solar magnetic activity visible on the solar surface (~6000 K), which is heated by convection bringing up heat from the interior. They are composed of a dark and cool (~4000 K) umbra surrounded by the filamentary penumbra (~5000 K). These different regimes are due to different magnetic field properties which produce different modes of convective heat transport. Studies of fully developed sunspots with data from Hinode satellite revealed that the umbra-penumbra boundary stays stationary, and the strength of the vertical component of the magnetic field is always the same.

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The Schauinsland observatory is used not only for solar observations: In 2013, an additional 14" Maksutov-Cassegrain telescope was installed that is used for night-time observations. It has a parallactical mount and is located in the old refractor tower. The telescope is connected to a GoTo software which allows the observer to easily point at different objects.

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NOAA 12192 is the identification number of one of the largest regions of strong magnetic activity seen in the current solar cycle 24, which started back in January 2008. The NOAA 12192 active region appeared on the solar disc on 17 October 2014, harbouring several large sunspots visible even to the naked eye. The size of the active region was gigantic, with an area extending over 2750 millionths of the visible solar hemisphere (MHS). The largest umbral diameter reached up to 22000 km, almost twice as big as the diameter of Earth. By 27 October 2014, NOAA 12192 ranked 33rd in the list of active region sizes since 1874.

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The highly dynamic magnetised solar atmosphere exhibits a wealth of oscillatory magneto-hydrodynamic (MHD) waves. These MHD waves are thought to play an important role in the transport of energy to the solar chromosphere and corona since they are channeled by the magnetic fields.

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Finding life on other planets is one of the ultimate goals of modern astrophysics. Prof. Dr. Svetlana Berdyugina and her team have proposed and developed a new approach for searching life on other planets. They have measured in the laboratory samples of terrestrial plants containing various biological photosynthetic pigments (biopigments, BP) and found that these biopigments modify reflected light in such a way that it becomes linearly polarized to a high degree. This means that the reflected electromagnetic wave oscillates preferably within one plane, and an external observer can see a very conspicuous signal of biopigments if the planet is observed in polarized light. The team has also measured non-biological samples like sand and rocks containing different mineral pigments. The measured data were used to model polarized and unpolarized spectra of Earth-like planets.

In contrast to biopigments, minerals do no show a very high polarization degree in the reflected light of planets and can be well distinguished from biopigments. This is an excellent news for ...

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Close binary stars with late-type, solar-like components are among the most active stellar objects known. The combination of vigorous convective motions with rapid rotation promotes efficient dynamo operation, which entails a plethora of magnetic activity considerably stronger than on the Sun. Examples include extensive dark spots in the photosphere, enhanced chromospheric emission, and high-energetic flaring events in the corona. The magnetic field has a decisive influence on the structural, dynamical and thermal properties of the atmosphere of these stars. However, since even in the case of the Sun direct observations of coronal magnetic fields are difficult to accomplish, extrapolation methods are frequently used to infer them from observed magnetic field distributions in the photosphere.

We have extended the potential field source surface extrapolation technique, a basic method which was originally developed for the case of the Sun, to binary star systems to...

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As of recently, the new German 1.5 m GREGOR telescope at the Observatorio del Teide (Tenerife) is fully operational. The first scientific data was taken in May of this year with hitherto unparalleled precision.

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Das KIS ist Gastgeber für das 12. Solar Orbiter PHI Team Meeting. Es findet im Hotel Brugger in Titisee statt, vom 1. bis 3. Juli 2014.

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