Picture of the Month

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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At GREGOR, the largest European solar telescope, another essential instrument is now operational: the slit scanner. Up to now, the slit of the spectropolarimeter GRIS (GRegor Infrared Spectrograph) could only stare at one position on the solar surface. Therefore, only spectra in one spatial dimension could be taken.

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The 11-year solar cycle has been known for centuries. During this time the activity level (measured as sunspot number) changed dramatically from the Maunder minimum (1650-1700) to the Modern maximum in mid 20th century. The extended minimum of the last solar cycle alerted solar physicists about possible long-term variations in the solar magnetic activity. While some argue that the Sun was unusually active in mid 20th century, others find it unusually inactive now. This caused speculations whether the solar activity cycle is overlaid with a long-term decline that may lead to another grand minimum in the near future. Some linear extrapolations predicted that there would be no sunspots in the next cycle. Since solar magnetic activity and space weather have a direct impact on our life, it is important to understand such variations. To this end, we compared the present cycle 24 with the previous one. We measured sunspot intensity, area, and magnetic field strength, seeking for...

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In the solar subsurface layers one can observe a meridional flow which stretches from the equator to the poles. In our group we developed and applied a new helioseismic analysis method to measure the extension of the meridional flow in the deeper solar interior. The method uses the deformation of deeply penetrating solar acoustic waves due to the flow. We have analyzed 6 consecutive years of doppler velocity data with this method. The data were obtained between 2004-2010 by the Michelson Doppler Imager (MDI) on board of the Solar and Heliospheric Observatory (SoHO), a spacecraft of ESA/NASA. Figure 1 depicts a cross-section of the meridional flow measured below the solar surface between 0.82-0.97 solar radii in the radius-latitude-plane. A dashed line marks the solar surface; dashed-dotted lines mark heliographic latitudes of +/-60 degree. Positive (negative) velocities correspond to a northward (southward) directed flow. Our measurement shows a complex flow profile in the solar interior with horizontal velocities less than 50 m/s. It is composed of multiple flow cells of larger and smaller scales.

The meridional flow is present at greater depths than depicted in Figure 1, but the current analysis does not yet allow measurements of the large-scale flow component at depths beyond 126 Mm.

In Figure 2 (bottom), we show the flow component consisting of small flow cells as a function of latitude and depth below the solar surface; positive (negative) values again correspond to a northward (southward) directed flow. For this flow component we obtain significant velocities down to a depth of about 200 Mm. Hence, the result provides evidence for a deeply penetrating meridional flow that permeates the whole solar convection zone. We compared our measurement with a subsurface measurement of the small-scale flow component (Bild 2, top) published by Komm et. al. (2004). This measurement reaches from 0.5-14 Mm depth. Near the surface, both results are in good agreement. The small-scale flow cells observed already near the surface stretch deep down into the interior and change their flow direction at a depth of about 100 Mm.

References:

Schad A., Timmer J., Roth M.: "Global helioseismic evidence for a deeply penetrating meridional flow consisting of multiple flow cells", ApJL, 778, L38-L44 (2013)

Komm, R., Howe, R., Hill, F., González Hernández, I., & Toner, C., ApJ, 631, 636 (2005) ...

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In collaboration with the Istituto Ricerche Solari Locarno (IRSOL) another instrument has been installed for the first time at the GREGOR telescope: ZIMPOL. First successful observations have been carried out.

The new instrument is a polarimeter for the visible wavelength range (390-700 nm) combined with the spectrograph at GREGOR. The polarimeter is based on technologies originally developed at ETH Zurich. It has been used for many years at IRSOL and is further developed in collaboration with SUPSI (University of Applied science in Locarno-Manno).

The system consists of two main components: a fast polarization modulator (composed of two ferro-electric liquid crystal modulators and two retarder plates) and a polarizer. It transforms polarization signals into modulated intensity signals. The second component is a camera system with a special masked CCD sensor. It demodulates the modulated intensity signal directly on the sensor. This concept allows a fast polarization modulation of 1 kHz, fast enough to avoid any disturbing seeing effects for the polarization measurements. Thus the polarimeter achieves a high sensitivity and is especially suited for the measurement of very small polarimetric signals.

End of October 2013 the new system has been installed at GREGOR for the first time with the goal to integrate the instrument into the other components (telescope, spectrograph and AO). Several observations have been recorded to demonstrate the performance of the instrument.

Another important point was the calibration of the measurements. Modern solar telescopes like GREGOR often have many inclined mirrors which change the polarisation state. Generally this is a difficult calibration problem. GREGOR, however, has the great advantage that there is a calibration unit installed before of the first tilted mirror. So the telescope and the polarimeter can be fully calibrated. The signals in the recorded data show that the system is already working successfully....

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Das Kiepenheuer-Institut für Sonnenphysik bildet nicht nur im wissenschaftlichen Bereich Studierende aus, sondern engagiert sich auch im gewerblich-technischen Bereich als Ausbildungseinrichtung.

Insgesamt 5 Ausbildungsstellen in der Form der dualen Ausbildung sind am Kiepenheuer-Institut etabliert.

Es werden Auszubildende in den Berufsfeldern Feinmechanik (2 Auszubildende), Elektronik, Fachinformatiker / Systemintegration und Fachinformatiker / Anwendungsentwicklung ausgebildet.

Im Rahmen ihrer Ausbildung haben die Auszubildenden am KIS die Möglichkeit in einem technisch wissenschaftlichen Bereich zu lernen und hierbei an technischen Entwicklungen und Produktionen mitzuwirken, die zu den führenden im Bereich der Astrophysik zählen.

Diese Aufgabenstellung motiviert die Auszubildenden und Ausbilder, was sich nun auch im Abschneiden  unseres Fachinformatiker /Systemintegration Auszubildenden  Marco Günter, der mit einer Gesamtpunktzahl 93 von 100 Punkten seine Prüfung abschloss zeigt....

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The ESA satellite Solar Orbiter will approach the Sun as close as 0.28 astronomical units, closer than any other satellite before. Start of the mission is planned for 2017.

KIS participates in the Solar Orbiter project by building the Image Stabilization System (ISS) for the Polarimetric and Helioseismic Imager (PHI).

During closest approach PHI will measure the magnetic field in the polar regions of the Sun with high accuracy. The ISS will provide the required pointing stability to obtain such accurate measurements.

The ISS consists of a fast tip-tilt mirror in the optical path of the telescope and a high-speed camera. The measured image motion is used to control the tipp-tilt mirror to compensate for that motion in real time.

Recently lab tests have shown that the prototype ISS system performance clearly exceeds the specifications.

Image 1 shows the required (thin curve) and actually measured (thick black and red curves) motion damping of the system.  The actual damping is...

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Three-dimensional computer simulations of magneto-acoustic wave propagation in a solar model atmosphere with a complex magnetic field structure, reveal the physics of a phenomenon known as "magnetic shadow''. In these simulations, acoustic waves of 10 mHz frequency are excited at the bottom of the simulation domain. On their way through the upper convection zone and through the photosphere and the chromosphere they become perturbed, refracted, and converted into different mode types. Synthesized oscillatory power-maps of the line-of-sight velocity of the upper photosphere and the lower chromosphere then show the magnetic shadow as is observed on the Sun: a seam of suppressed power surrounding the magnetic network elements (see Fig. 1).

We demonstrate how this shadow is linked to the conversion of the excited wave into different modes (see Fig. 2) and that power maps in these height levels show the signature of three different magneto-acoustic wave modes in three different regions: the...

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Das ballongetragene Sonnenobservatorium Sunrise, das am 12. Juni 2013 zu seinem mehr als fünftägigen Beobachtungsflug von Schweden nach Kanada gestartet war, ist nun – in Einzelteile zerlegt – auf dem Heimweg nach Deutschland. Obwohl bei der Landung am 18. Juni auf der kanadischen Halbinsel Boothia starke Winde in Bodennähe das Observatorium umwarfen, sind die wichtigsten Komponenten wie etwa die Datenspeicher, die Spiegel des Sonnenteleskops und die wissenschaftlichen Instrumente unversehrt. Das ergab die dreitägige Bergung vor Ort. Während der Großteil des Observatoriums nun in Containern verpackt den langen Heimweg auf dem Seeweg antritt, sind die Datenspeicher bereits am Max-Planck-Institut für Sonnensystemforschung (MPS) im niedersächsischen Katlenburg-Lindau angekommen.

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