I. Arregui

Damping of transverse waves in different solar coronal structures is a commonly observed property and a source of information about coronal conditions. Although resonant damping seems to be the most accepted mechanism for damping of transverse waves, there are other possible mechanisms. We have carried out a Bayesian analysis comparing three different models which could explain the damping in coronal loops. Our results indicate that resonant absorption is the most probable mechanism for low ratios between damping time and wave period, while the wave leakage mechanism is the best candidate for high ratios. Nonetheless, the evidence for one model against another shows a strong dependence on the data errors.

Chloe Pugh, Valery Nakariakov

Quasi-periodic pulsations (QPPs) are a common feature of solar flares that are observed in many different wavelengths. Although QPPs appear not to be as abundant in white light Kepler flare light curves as they are in solar flares, albeit in different wavelengths the structure of the pulsations are strikingly similar, hinting that the same underlying processes govern both solar and stellar flares. Here we consider a special case, observed on KIC9655129, which shows evidence of multiple periodicities. We speculate that the presence of multiple periodicities is a good indication that the QPPs were caused by magnetohydrodynamic oscillations, further strengthening the case that the physical processes in operation during stellar flares are at least analogous to those in solar flares.

One of the outstanding and unforeseen results from the Kepler mission is our new insight and understanding of red giant stars. These highly evolved stars, which are in the last stages of their life, provide extremely useful information when trying to develop stellar evolutionary models. Furthermore, they show stochastically excited oscillations thus allowing to use asteroseismic techniques to derive conditions of the most internal layers. Bright giants stars are well suited to be studied with the 1m telescopes in the Stellar Observations Network Group project (SONG) using a high resolution echelle spectrograph performing high precision measurements of their the radial velocity. The prototype node- the Hertzsprung SONG telescope- was inaugurated in October 2014 and is located at the Teide Observatory on Tenerife and providing continuous and high quality observations since then, When selecting the best targets for SONG, a precision of 1-2 m/s per point is reachable using the iodine method and a number of red giants have been observed with the SONG telescope since scientific operation started. In this talk we present the first results of these specific campaigns for a few red giants in which eigenmodes have been identified and their global seismic parameters derived.

Wolfgang Schmidt

LARS is an Absolute Reference Spectrograph. It performs fiber-coupled solar observations with the high-resolution Echelle Spectrograph of the Vacuum Tower Telescope (VTT) at the Observatorio del Teide on Tenerife. The scientific instrument is operated by the Kiepenheuer Institute for Solar Physics, Freiburg. The spectral observation is supported by a Laser Frequency Comb which serves as an absolute ruler for the wavelength calibration of the solar spectrum. This novel technique of spectroscopic observations allows the determination of absolute velocities in the solar atmosphere with the best accuracy (m s-1).

The differences between the oscillation frequencies and uncertainty estimates of a star derived by different fitters can be large, sufficiently large so that, were one to find a stellar model that fitted one frequency set ($\chi^2\sim 1$), it does not fit an alternative set. I give 21 examples, comparing frequency sets in common between the Kepler Legacy project and frequency sets from Appourchaux et al (2014) and Davies et al (2015). For 16CygA\&B the differences are large; the $\chi^2$ of the fit of Legacy to Davies's values ranging from 1.64 to 11.47 for 16CygA and 1.62 to 1.79 for 16CygB, depending on which error estimates are used. I analyse both stars in some detail applying my own mode fitting code to both the Legacy and Davies's power spectra and find reasonable agreement with Davies's full frequency sets and very good agreement between values for modes with signal/noise > 1 ($\chi^2 = 0.06, \chi^2_B=0.03$). But the difference with the Legacy values remains large even for modes with S/N>1. I also examine the effects of different power spectra (weighted and unweighted) using the kasoc light curves for Q6-17.2 and Q7-Q16, the effect of different mode height ratios and different rotational splitting and inclination.

F. Berrilli, G. Consolini, D. Del Moro, F. Giannattasio, L. Giovannelli

The understanding of fluctuations in systems far from equilibrium is one of the key issues of non-equilibrium statistical thermodynamics. The Fluctuation Theorem of Gallavotti and Cohen (1995) [GCFT] portrays some symmetry features of entropy production rate and deviations in non-linear and far from equilibrium regime. In this framework, the turbulent solar convection, observed in the photosphere and viewed as a dissipative non-equilibrium system near a steady state, provides an incomparable laboratory where to attempt a test the GCFT. In fact, solar convection flows emerge in the photosphere in terms of a structured pattern: the granulation. High resolutions spectro-polarimetric data acquired with Interferometric BIdimensional Spectropolarimeter (IBIS) instrument installed at the Dunn Solar Telescope (DST) are used to perform this analysis. Here, we present a preliminary analysis of the validity of the GCFT in the solar convection field. The statistical features of entropy production rate, which is at the core of the irreversibility, is estimated through the vertical heat flux. The vertical heat flux along the line of sight (LOS), in its turn, is evaluated using temperature and LOS velocity map obtained with spectro-polarimetric inversion using the NICOLE code and with the simplest center of gravity method.

L. Bielak, Th. Berkefeld

The combination of adaptive optics with post processing of sequences of short exposures is a very successful technique to produce diffraction limited images of the solar photosphere throughout the visible spectral domain. Viable approaches are multi frame blind deconvolution and speckle imaging, and both approaches have been used with great success in the past 15 years. While blind deconvolution solves for both the undisturbed image and the optical transfer function for every frame in the sequence, speckle imaging makes assumptions about the statistics of the partially compensated wavefront and the resulting transfer functions which apply to the speckle signal. These depend on the shape of the entrance aperture and on the characteristics and performance of the adaptive optics system, and therefore need to be established separately for every telescope. We have calculated the speckle transfer function (STF) for the GREGOR solar telescope as a function of seeing and control performance of GREGORs adaptive optics system GAOS. The calculations are based on simulations of optical propagation through an extended, turbulent atmosphere and field dependent, partial compensation by a conventional adaptive optics system. The compensation characteristics are based on actual measurements of the performance of GAOS. We present the results of the simulations and compare image reconstruction using the simulated transfer functions with reconstructions based on the previously used analytic STF models.

Gömöry, P., Rybák, J., Schwartz, P., Kučera, A., Ambróz, J., Kozák, M., Koza, J., Tomczyk, S., Sewell, S., Aumiller, P., Gallagher, D., Summers, R., Sutherland, L., Watt , A.

We present actual status and observing possibilities of the Coronal Multi-channel Polarimeter (CoMP-S) and Solar Chromospheric Detector (SCD) installed at the Lomnicky Peak Observatory. The CoMP-S is a dual beam spectropolarimeter developed to detect full Stokes parameters of prominent coronal and chromospheric spectral lines in order to estimate magnetic and velocity fields in the solar corona and in prominences. The SCD is a single beam spectropolarimetric instrument designed for on disk measurements of Stokes parameters in the chromosphere. Both instruments were designed and manufactured by HAO/NCAR (Boulder, USA). We present technical parameters of the instruments and the acquired data which can serve as complementary observing material to high resolution measurements taken by the European Solar Telescope (EST).

Ariane Schad, and Markus Roth

Several hundred stars were observed in the short cadence mode of the Kepler satellite during the nominal mission phase. This generated a large pool of data which can provide insight into the characteristics of stellar activity cycles of solar-type stars through the methods of asteroseismology. From helioseismology it is known that the frequencies of solar acoustic oscillations (p modes) are positively correlated with the solar magnetic activity cycle. Evidence for a similar behaviour in the p modes of a star, which was observed by the CoRoT satellite, was provided by [1]. This showed that it is feasible to trace activity cycles of stars in their p mode frequencies. We analyse the Kepler time series of a set of solar-type stars with the aim to find signatures of stellar magnetic activity. We divide the time series of each star into shorter sub-series in order to analyse the temporal evolution of the p mode frequencies. The sub-series’ periodograms are cross-correlated to retrieve the shift of p mode frequencies over time. The errors on the shifts are computed by a resampling approach of the periodogram. We find significant frequency shifts, indicating stellar magnetic activity, for all stars we investigated. For the most prominent example, KIC 8006161, we find that, not unlike in the solar case, frequency shifts are smallest for the lowest and largest for the highest p mode frequencies.

SOLARNET III / HELAS VII / SpaceInn Conference "The Sun, the stars, and solar-stellar relations" Freiburg, August 31-September 4, 2015 The 3rd SOLARNET / 7th HELAS / SpaceInn international conference "The Sun, the stars, and Solar-stellar relations" will take place in Freiburg (Germany) between 31 August - 4 September 2015, organized by the Kiepenheuer-Institut für Sonnenphysik (KIS). SOLARNET (High-resolution Solar Physics Network) is an international project promoted by the European Association for Solar Telescopes (EAST) and funded by the European Commission FP7. HELAS is the European Helio- and Asteroseismology Network, which aims at coordinating the activities of the research groups active in helio-and asteroseismology. The purpose of this conference is to discuss the latest questions and results in solar and stellar physics. Solar and stellar seismology will be one particular focus but contributions on all aspects of solar-stellar relations will be welcome. We aim to establish links and synergies between the day- and night-time fields of astrophysics. In detail the following topics will be addressed in individual sessions as showed in the Scientific Program. Furthermore new and upcoming projects and missions shall be presented. Graduate students and early-career postdocs are particularly invited to participate in the conference to present their research work and to meet and discuss with their more senior colleagues. A limited amount of financial resources shall be available to grant travel support. Contact: mroth(at)kis.uni-freiburg.de

F. Zuccarello, P.R. Young, P. Romano, M. Murabito

We report multi-wavelength ultraviolet observations taken with the IRIS satellite, concerning the emergence phase in the upper chromosphere and transition region of an emerging flux region (EFR) embedded in the unipolar plage of active region NOAA 12529. These data are complemented by full-disk, simultaneous observations of the Solar Dynamics Observatory satellite, relevant to the photosphere and the corona. The photospheric configuration of the EFR is also analyzed by measurements taken with the spectropolarimeter aboard the Hinode satellite, when the EFR was fully developed. Recurrent intense brightenings that resemble UV bursts, with counterparts in all coronal passbands, are identified at the edges of the EFR and in the region of the arch filament system (AFS) cospatial to the EFR. Jet activity is also found at chromospheric and coronal levels, near the AFS and the observed brightness enhancement sites. The analysis of the IRIS line profiles reveals the heating of dense plasma in the low solar atmosphere and the driving of bi-directional high-velocity flows with speeds up to 100 km/s at the same locations. Comparing these signatures with previous observations and numerical models, we suggest evidence of several long-lasting, small-scale magnetic reconnection episodes occurring between the emerging bipole and the ambient field. This process leads to the cancellation of a pre-existing photospheric flux concentration of the plage with the opposite polarity flux patch of the EFR. Moreover, the reconnection appears to take place higher in the atmosphere than usually found in UV bursts, explaining the observed coronal counterparts. These observations provide a case study for the EST science requirements, as higher spatial and temporal resolution are necessary to better understand and characterize the onset and development of such small-scale reconnection events.

Georgia Tsiropoula, Kostas Tziotziou

We report preliminary results on the evolution of a small-scale bipolar magnetic feature, from its emergence at the photosphere to its brightening at the corona. We use imaging and spectral observations from the space-born Hinode (SOT/BFI, SOT/SP, EIS & XRT), TRACE (1550 Å, 1600 Å, 1700 Å) and SoHO (MDI hi-res) as well as the ground-based Dutch Open Telescope (G-band, CaII H and five positions along the Hα profile). The small-scale feature emerges, adjacent to the chromospheric network and shows all morphological characteristics of a small-scale magnetic bubble. The magnetic flux density increases, reaching a maximum value while fine-scale CaII H brightenings coalesce forming clusters of positive and negative polarity footpoints of a bipolar feature. The corresponding emerging magnetic flux tubes make their way to the chromosphere, pushing aside the ambient magnetic field, producing Doppler-shifted absorption features. At the upper chromosphere and transition region, imaged by EIS, the emission gradually increases. The connectivity of the quiet-Sun network gradually changes and part of the existing network connects to the newly emerged bipole. A few minutes after the bipole has reached its maximum magnetic flux density, the bipole brightens in soft X-rays forming a coronal bright point. The brightening is observed in all EIS transition region and coronal windows and is accompanied by Doppler-shifted Hα features.