Author name code: cameron ADS astronomy entries on 2022-09-14 author:"Cameron, Robert H." ------------------------------------------------------------------------ Title: Erratum: "Faculae Cancel out on the Surfaces of Active Suns" (2022, ApJL, 934, L23) Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.; Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L. Bibcode: 2022ApJ...936L..17N Altcode: No abstract at ADS Title: Faculae Cancel out on the Surfaces of Active Suns Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.; Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L. Bibcode: 2022ApJ...934L..23N Altcode: 2022arXiv220706816N Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterization of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in stellar data are quite different, for instance, they have distinct temporal and spectral profiles. Consequently, corrections of stellar data for magnetic activity can greatly benefit from the insight on whether the stellar signal is dominated by spots or faculae. Here, we utilize a surface flux transport model to show that more effective cancellation of diffuse magnetic flux associated with faculae leads to spot area coverages increasing faster with stellar magnetic activity than that by faculae. Our calculations explain the observed dependence between solar spot and facular area coverages and allow its extension to stars that are more active than the Sun. This extension enables anticipating the properties of stellar signal and its more reliable mitigation, leading to a more accurate characterization of exoplanets and their atmospheres. Title: Chromospheric extension of the MURaM code Authors: Przybylski, D.; Cameron, R.; Solanki, S. K.; Rempel, M.; Leenaarts, J.; Anusha, L. S.; Witzke, V.; Shapiro, A. I. Bibcode: 2022A&A...664A..91P Altcode: 2022arXiv220403126P Context. Detailed numerical models of the chromosphere and corona are required to understand the heating of the solar atmosphere. An accurate treatment of the solar chromosphere is complicated by the effects arising from non-local thermodynamic equilibrium (NLTE) radiative transfer. A small number of strong, highly scattering lines dominate the cooling and heating in the chromosphere. Additionally, the recombination times of ionised hydrogen are longer than the dynamical timescales, requiring a non-equilibrium (NE) treatment of hydrogen ionisation.
Aims: We describe a set of necessary additions to the MURaM code that allow it to handle some of the important NLTE effects. We investigate the impact on solar chromosphere models caused by NLTE and NE effects in radiation magnetohydrodynamic simulations of the solar atmosphere.
Methods: The MURaM code was extended to include the physical process required for an accurate simulation of the solar chromosphere, as implemented in the Bifrost code. This includes a time-dependent treatment of hydrogen ionisation, a scattering multi-group radiation transfer scheme, and approximations for NLTE radiative cooling.
Results: The inclusion of NE and NLTE physics has a large impact on the structure of the chromosphere; the NE treatment of hydrogen ionisation leads to a higher ionisation fraction and enhanced populations in the first excited state throughout cold inter-shock regions of the chromosphere. Additionally, this prevents hydrogen ionisation from buffering energy fluctuations, leading to hotter shocks and cooler inter-shock regions. The hydrogen populations in the ground and first excited state are enhanced by 102-103 in the upper chromosphere and by up to 109 near the transition region.
Conclusions: Including the necessary NLTE physics leads to significant differences in chromospheric structure and dynamics. The thermodynamics and hydrogen populations calculated using the extended version of the MURaM code are consistent with previous non-equilibrium simulations. The electron number and temperature calculated using the non-equilibrium treatment of the chromosphere are required to accurately synthesise chromospheric spectral lines.

Movies associated to Fig. 2 are only available at https://www.aanda.org Title: Impact of spatially correlated fluctuations in sunspots on metrics related to magnetic twist Authors: Baumgartner, C.; Birch, A. C.; Schunker, H.; Cameron, R. H.; Gizon, L. Bibcode: 2022A&A...664A.183B Altcode: 2022arXiv220702135B Context. The twist of the magnetic field above a sunspot is an important quantity in solar physics. For example, magnetic twist plays a role in the initiation of flares and coronal mass ejections (CMEs). Various proxies for the twist above the photosphere have been found using models of uniformly twisted flux tubes, and are routinely computed from single photospheric vector magnetograms. One class of proxies is based on αz, the ratio of the vertical current to the vertical magnetic field. Another class of proxies is based on the so-called twist density, q, which depends on the ratio of the azimuthal field to the vertical field. However, the sensitivity of these proxies to temporal fluctuations of the magnetic field has not yet been well characterized.
Aims: We aim to determine the sensitivity of twist proxies to temporal fluctuations in the magnetic field as estimated from time-series of SDO/HMI vector magnetic field maps.
Methods: To this end, we introduce a model of a sunspot with a peak vertical field of 2370 Gauss at the photosphere and a uniform twist density q = −0.024 Mm−1. We add realizations of the temporal fluctuations of the magnetic field that are consistent with SDO/HMI observations, including the spatial correlations. Using a Monte-Carlo approach, we determine the robustness of the different proxies to the temporal fluctuations.
Results: The temporal fluctuations of the three components of the magnetic field are correlated for spatial separations up to 1.4 Mm (more than expected from the point spread function alone). The Monte-Carlo approach enables us to demonstrate that several proxies for the twist of the magnetic field are not biased in each of the individual magnetograms. The associated random errors on the proxies have standard deviations in the range between 0.002 and 0.006 Mm−1, which is smaller by approximately one order of magnitude than the mean value of q. Title: Theory of solar oscillations in the inertial frequency range: Amplitudes of equatorial modes from a nonlinear rotating convection simulation Authors: Bekki, Yuto; Cameron, Robert H.; Gizon, Laurent Bibcode: 2022arXiv220811081B Altcode: Several types of inertial modes have been detected on the Sun. Properties of these inertial modes have been studied in the linear regime but have not been studied in nonlinear simulations of solar rotating convection. Comparing the nonlinear simulations, the linear theory, and the solar observations is important to better understand the differences between the models and the real Sun. We wish to detect and characterize the modes present in a nonlinear numerical simulation of solar convection, in particular to understand the amplitudes and lifetimes of the modes. We developed a code with a Yin-Yang grid to carry out fully-nonlinear numerical simulations of rotating convection in a spherical shell. The stratification is solar-like up to 0.96R. The simulations cover a duration of about 15 solar years. Various large-scale modes at low frequencies are extracted from the simulation. Their characteristics are compared to those from the linear model and to the observations. Among other modes, both the equatorial Rossby modes and the columnar convective modes are seen in the simulation. The columnar convective modes contain most of the large-scale velocity power outside the tangential cylinder and substantially contribute to the heat and angular momentum transport. Equatorial Rossby modes with no radial node (n=0) are also found: They have the same spatial structures as the linear eigenfunctions. They are stochastically excited by convection and have the amplitudes of a few m/s and mode linewidths of about 20-30 nHz, which are comparable to those observed on the Sun. We also confirm the existence of the mixed modes between the equatorial Rossby modes and the columnar convective modes in our nonlinear simulation, as predicted by the linear eigenmode analysis. We also see the high-latitude mode with m=1 in our nonlinear simulation but its amplitude is much weaker than that observed on the Sun. Title: Small-scale dynamo in cool stars. I. Changes in stratification and near-surface convection for main-sequence spectral types Authors: Bhatia, Tanayveer S.; Cameron, Robert H.; Solanki, Sami K.; Peter, Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander Bibcode: 2022A&A...663A.166B Altcode: 2022arXiv220600064B Context. Some of the small-scale solar magnetic flux can be attributed to a small-scale dynamo (SSD) operating in the near-surface convection. The SSD fields have consequences for solar granular convection, basal flux, and chromospheric heating. A similar SSD mechanism is expected to be active in the near-surface convection of other cool main-sequence stars, but this has not been investigated thus far.
Aims: We aim to investigate changes in stratification and convection due to inclusion of SSD fields for F3V, G2V, K0V, and M0V spectral types in the near-surface convection.
Methods: We studied 3D magnetohydrodynamic (MHD) models of the four stellar boxes, covering the subsurface convection zone up to the lower photosphere in a small Cartesian box, based on the MURaM radiative-MHD simulation code. We compared the SSD runs against reference hydrodynamic runs.
Results: The SSD is found to efficiently produce magnetic field with energies ranging between 5% to 80% of the plasma kinetic energy at different depths. This ratio tends to be larger for larger Teff. The relative change in density and gas pressure stratification for the deeper convective layers due to SSD magnetic fields is negligible, except for the F-star. For the F-star, there is a substantial reduction in convective velocities due to Lorentz force feedback from magnetic fields, which, in turn, reduces the turbulent pressure.
Conclusions: The SSD in near-surface convection for cool main-sequence stars introduces small but significant changes in thermodynamic stratification (especially for the F-star) due to a reduction in the convective velocities. Title: Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone Authors: Bekki, Yuto; Cameron, Robert H.; Gizon, Laurent Bibcode: 2022A&A...662A..16B Altcode: 2022arXiv220304442B Context. Several types of global-scale inertial modes of oscillation have been observed on the Sun. These include the equatorial Rossby modes, critical-latitude modes, and high-latitude modes. However, the columnar convective modes (predicted by simulations and also known as banana cells or thermal Rossby waves) remain elusive.
Aims: We aim to investigate the influence of turbulent diffusivities, non-adiabatic stratification, differential rotation, and a latitudinal entropy gradient on the linear global modes of the rotating solar convection zone.
Methods: We numerically solved for the eigenmodes of a rotating compressible fluid inside a spherical shell. The model takes into account the solar stratification, turbulent diffusivities, differential rotation (determined by helioseismology), and the latitudinal entropy gradient. As a starting point, we restricted ourselves to a superadiabaticity and turbulent diffusivities that are uniform in space. We identified modes in the inertial frequency range, including the columnar convective modes as well as modes of a mixed character. The corresponding mode dispersion relations and eigenfunctions are computed for azimuthal orders of m ≤ 16.
Results: The three main results are as follows. Firstly, we find that, for m ≳ 5, the radial dependence of the equatorial Rossby modes with no radial node (n = 0) is radically changed from the traditional expectation (rm) for turbulent diffusivities ≳1012 cm2 s−1. Secondly, we find mixed modes, namely, modes that share properties of the equatorial Rossby modes with one radial node (n = 1) and the columnar convective modes, which are not substantially affected by turbulent diffusion. Thirdly, we show that the m = 1 high-latitude mode in the model is consistent with the solar observations when the latitudinal entropy gradient corresponding to a thermal wind balance is included (baroclinically unstable mode).
Conclusions: To our knowledge, this work is the first realistic eigenvalue calculation of the global modes of the rotating solar convection zone. This calculation reveals a rich spectrum of modes in the inertial frequency range, which can be directly compared to the observations. In turn, the observed modes can inform us about the solar convection zone. Title: The crucial role of surface magnetic fields for stellar dynamos: ϵ Eridani, 61 Cygni A, and the Sun Authors: Jeffers, S. V.; Cameron, R. H.; Marsden, S. C.; Boro Saikia, S.; Folsom, C. P.; Jardine, M. M.; Morin, J.; Petit, P.; See, V.; Vidotto, A. A.; Wolter, U.; Mittag, M. Bibcode: 2022A&A...661A.152J Altcode: 2022arXiv220107530J Cool main-sequence stars, such as the Sun, have magnetic fields which are generated by an internal dynamo mechanism. In the Sun, the dynamo mechanism produces a balance between the amounts of magnetic flux generated and lost over the Sun's 11-year activity cycle and it is visible in the Sun's different atmospheric layers using multi-wavelength observations. We used the same observational diagnostics, spanning several decades, to probe the emergence of magnetic flux on the two close by, active- and low-mass K dwarfs: 61 Cygni A and ϵ Eridani. Our results show that 61 Cygni A follows the Solar dynamo with a regular cycle at all wavelengths, while ϵ Eridani represents a more extreme level of the Solar dynamo, while also showing strong Solar-like characteristics. For the first time we show magnetic butterfly diagrams for stars other than the Sun. For the two K stars and the Sun, the rate at which the toroidal field is generated from surface poloidal field is similar to the rate at which toroidal flux is lost through flux emergence. This suggests that the surface field plays a crucial role in the dynamos of all three stars. Finally, for ϵ Eridani, we show that the two chromospheric cycle periods, of ∼3 and ∼13 years, correspond to two superimposed magnetic cycles.

The spectropolarimetic data are available from the Polarbase data archive: http://polarbase.irap.omp.eu/. Title: Testing solar surface flux transport models in the first days after active region emergence Authors: Gottschling, N.; Schunker, H.; Birch, A. C.; Cameron, R.; Gizon, L. Bibcode: 2022A&A...660A...6G Altcode: 2021arXiv211101896G Context. Active regions (ARs) play an important role in the magnetic dynamics of the Sun. Solar surface flux transport models (SFTMs) are used to describe the evolution of the radial magnetic field at the solar surface. The models are kinematic in the sense that the radial component of the magnetic field behaves as passively advected corks. There is, however, uncertainty about using these models in the early stage of AR evolution, where dynamic effects might be important.
Aims: We aim to test the applicability of SFTMs in the first days after the emergence of ARs by comparing them with observations. The models we employ range from passive evolution to models where the inflows around ARs are included.
Methods: We simulated the evolution of the surface magnetic field of 17 emerging ARs using a local surface flux transport simulation. The regions were selected such that they did not form fully fledged sunspots that exhibit moat flows. The simulation included diffusion and advection by a velocity field, for which we tested different models. For the flow fields, we used observed flows from local correlation tracking of solar granulation, as well as parametrizations of the inflows around ARs based on the gradient of the magnetic field. To evaluate our simulations, we measured the cross correlation between the observed and the simulated magnetic field, as well as the total unsigned flux of the ARs, over time. We also tested the validity of our simulations by varying the starting time relative to the emergence of flux.
Results: We find that the simulations using observed surface flows can reproduce the evolution of the observed magnetic flux. The effect of buffeting the field by supergranulation can be described as a diffusion process. The SFTM is applicable after 90% of the peak total unsigned flux of the AR has emerged. Diffusivities in the range between D = 250-720 km2 s−1 are consistent with the evolution of the AR flux in the first five days after this time. We find that the converging flows around emerging ARs are not important for the evolution of the total flux of the AR in these first five days; their effect of increasing flux cancellation is balanced by the decrease in flux transport away from the AR. Title: A solar coronal loop in a box: Energy generation and heating Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S. K.; Przybylski, D.; Rempel, M.; Chitta, L. P. Bibcode: 2022A&A...658A..45B Altcode: 2021arXiv211211549B Context. Coronal loops are the basic building block of the upper solar atmosphere as seen in the extreme UV and X-rays. Comprehending how these are energized, structured, and evolve is key to understanding stellar coronae.
Aims: Here we investigate how the energy to heat the loop is generated by photospheric magneto-convection, transported into the upper atmosphere, and how the internal structure of a coronal magnetic loop forms.
Methods: In a 3D magnetohydrodynamics model, we study an isolated coronal loop rooted with both footpoints in a shallow layer within the convection zone using the MURaM code. To resolve its internal structure, we limited the computational domain to a rectangular box containing a single coronal loop as a straightened magnetic flux tube. Field-aligned heat conduction, gray radiative transfer in the photosphere and chromosphere, and optically thin radiative losses in the corona were taken into account. The footpoints were allowed to interact self-consistently with the granulation surrounding them.
Results: The loop is heated by a Poynting flux that is self-consistently generated through small-scale motions within individual magnetic concentrations in the photosphere. Turbulence develops in the upper layers of the atmosphere as a response to the footpoint motions. We see little sign of heating by large-scale braiding of magnetic flux tubes from different photospheric concentrations at a given footpoint. The synthesized emission, as it would be observed by the Atmospheric Imaging Assembly or the X-Ray Telescope, reveals transient bright strands that form in response to the heating events. Overall, our model roughly reproduces the properties and evolution of the plasma as observed within (the substructures of) coronal loops.
Conclusions: With this model we can build a coherent picture of how the energy flux to heat the upper atmosphere is generated near the solar surface and how this process drives and governs the heating and dynamics of a coronal loop.

Movie associated to Fig. 2 is available at https://www.aanda.org Title: On the size distribution of spots within sunspot groups Authors: Mandal, Sudip; Krivova, Natalie A.; Cameron, Robert; Solanki, Sami K. Bibcode: 2021A&A...652A...9M Altcode: 2021arXiv210403534M The size distribution of sunspots provides key information about the generation and emergence processes of the solar magnetic field. Previous studies of size distribution have primarily focused on either the whole group or individual spot areas. In this paper we investigate the organisation of spot areas within sunspot groups. In particular, we analysed the ratio (R) of the area of the biggest spot (Abig_spot) inside a group, to the total area of that group (Agroup). We used sunspot observations from Kislovodsk, Pulkovo, and Debrecen observatories, together covering solar cycles 17-24. We find that at the time when the group area reaches its maximum, the single biggest spot in a group typically occupies about 60% of the group area. For half of all groups, R lies in the range between roughly 50% and 70%. We also find R to change with Agroup, such that R reaches a maximum of about 0.65 for groups with Agroup ≈ 200 μHem and then remains at about 0.6 for larger groups. Our findings imply a scale-invariant emergence pattern, providing an observational constraint on the emergence process. Furthermore, extrapolation of our results to larger sunspot groups may have a bearing on the giant unresolved starspot features found in Doppler images of highly active Sun-like stars. Our results suggest that such giant features are composed of multiple spots, with the largest spot occupying roughly 55-75% of the total group area (i.e., the area of the giant starspots seen in Doppler images). Title: Slow magneto-acoustic waves in simulations of a solar plage region carry enough energy to heat the chromosphere Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K. Bibcode: 2021A&A...652A..43Y Altcode: 2021arXiv210502932Y
Aims: We study the properties of slow magneto-acoustic waves that are naturally excited as a result of turbulent convection and we investigate their role in the energy balance of a plage region using three dimensional radiation magnetohydrodynamic simulations.
Methods: To follow slow magneto-acoustic waves traveling along the magnetic field lines, we selected 25 seed locations inside a strong magnetic element and tracked the associated magnetic field lines both in space and time. We calculate the longitudinal component (i.e., parallel to the field) of velocity at each grid point along the field line and compute the temporal power spectra at various heights above the mean solar surface. Additionally, the horizontally-averaged (over the whole domain) frequency power spectra for both longitudinal and vertical (i.e., the component perpendicular to the surface) components of velocity are calculated using time series at fixed locations. To compare our results with the observations, we degrade the simulation data with Gaussian kernels having a full width at half maxium of 100 km and 200 km and calculate the horizontally-averaged power spectra for the vertical component of velocity using time series at fixed locations.
Results: The power spectra of the longitudinal component of velocity, averaged over 25 field lines in the core of a kG magnetic flux concentration reveal that the dominant period of oscillations shifts from ∼6.5 min in the photosphere to ∼4 min in the chromosphere. This behavior is consistent with earlier studies that were restricted to vertically propagating waves. At the same time, the velocity power spectra, averaged horizontally over the whole domain, show that low frequency waves (∼6.5 min period) may reach well into the chromosphere. In addition, the power spectra at high frequencies follow a power law with an exponent close to −5/3, suggestive of turbulent excitation. Moreover, waves with frequencies above 5 mHz propagating along different field lines are found to be out of phase with each other, even within a single magnetic concentration. The horizontally-averaged power spectra of the vertical component of velocity at various effective resolutions show that the observed acoustic wave energy fluxes are underestimated by a factor of three, even if determined from observations carried out at a high spatial resolution of 200 km. Since the waves propagate along the non-vertical field lines, measuring the velocity component along the line-of-sight, rather than along the field, contributes significantly to this underestimation. Moreover, this underestimation of the energy flux indirectly indicates the importance of high-frequency waves that are shown to have a smaller spatial coherence and are thus more strongly influenced by the spatial averaging effect compared to low-frequency waves.
Conclusions: Inside a plage region, there is on average a significant fraction of low frequency waves leaking into the chromosphere due to inclined magnetic field lines. Our results show that longitudinal waves carry (just) enough energy to heat the chromosphere in the solar plage. However, phase differences between waves traveling along different field lines within a single magnetic concentration can lead to underestimations of the wave energy flux due to averaging effects in degraded simulation data and, similarly, in observations with lower spatial resolution. We find that current observations (with spatial resolution around 200 km) underestimate the energy flux by roughly a factor of three - or more if the observations are carried out at a lower spatial resolution. We expect that even at a very high resolution, which is expected with the next generation of telescopes such as DKIST and the EST, less than half, on average, of the energy flux carried by such waves will be detected if only the line-of-sight component of the velocity is measured. Title: Solar inertial modes: Observations, identification, and diagnostic promise Authors: Gizon, Laurent; Cameron, Robert H.; Bekki, Yuto; Birch, Aaron C.; Bogart, Richard S.; Brun, Allan Sacha; Damiani, Cilia; Fournier, Damien; Hyest, Laura; Jain, Kiran; Lekshmi, B.; Liang, Zhi-Chao; Proxauf, Bastian Bibcode: 2021A&A...652L...6G Altcode: 2021arXiv210709499G The oscillations of a slowly rotating star have long been classified into spheroidal and toroidal modes. The spheroidal modes include the well-known 5-min acoustic modes used in helioseismology. Here we report observations of the Sun's toroidal modes, for which the restoring force is the Coriolis force and whose periods are on the order of the solar rotation period. By comparing the observations with the normal modes of a differentially rotating spherical shell, we are able to identify many of the observed modes. These are the high-latitude inertial modes, the critical-latitude inertial modes, and the equatorial Rossby modes. In the model, the high-latitude and critical-latitude modes have maximum kinetic energy density at the base of the convection zone, and the high-latitude modes are baroclinically unstable due to the latitudinal entropy gradient. As a first application of inertial-mode helioseismology, we constrain the superadiabaticity and the turbulent viscosity in the deep convection zone.

Movie associated to Fig. 2 is available at https://www.aanda.org Title: A journey of exploration to the polar regions of a star: probing the solar poles and the heliosphere from high helio-latitude Authors: Harra, Louise; Andretta, Vincenzo; Appourchaux, Thierry; Baudin, Frédéric; Bellot-Rubio, Luis; Birch, Aaron C.; Boumier, Patrick; Cameron, Robert H.; Carlsson, Matts; Corbard, Thierry; Davies, Jackie; Fazakerley, Andrew; Fineschi, Silvano; Finsterle, Wolfgang; Gizon, Laurent; Harrison, Richard; Hassler, Donald M.; Leibacher, John; Liewer, Paulett; Macdonald, Malcolm; Maksimovic, Milan; Murphy, Neil; Naletto, Giampiero; Nigro, Giuseppina; Owen, Christopher; Martínez-Pillet, Valentín; Rochus, Pierre; Romoli, Marco; Sekii, Takashi; Spadaro, Daniele; Veronig, Astrid; Schmutz, W. Bibcode: 2021ExA...tmp...93H Altcode: 2021arXiv210410876H A mission to view the solar poles from high helio-latitudes (above 60°) will build on the experience of Solar Orbiter as well as a long heritage of successful solar missions and instrumentation (e.g. SOHO Domingo et al. (Solar Phys. 162(1-2), 1-37 1995), STEREO Howard et al. (Space Sci. Rev. 136(1-4), 67-115 2008), Hinode Kosugi et al. (Solar Phys. 243(1), 3-17 2007), Pesnell et al. Solar Phys. 275(1-2), 3-15 2012), but will focus for the first time on the solar poles, enabling scientific investigations that cannot be done by any other mission. One of the major mysteries of the Sun is the solar cycle. The activity cycle of the Sun drives the structure and behaviour of the heliosphere and of course, the driver of space weather. In addition, solar activity and variability provides fluctuating input into the Earth climate models, and these same physical processes are applicable to stellar systems hosting exoplanets. One of the main obstructions to understanding the solar cycle, and hence all solar activity, is our current lack of understanding of the polar regions. In this White Paper, submitted to the European Space Agency in response to the Voyage 2050 call, we describe a mission concept that aims to address this fundamental issue. In parallel, we recognise that viewing the Sun from above the polar regions enables further scientific advantages, beyond those related to the solar cycle, such as unique and powerful studies of coronal mass ejection processes, from a global perspective, and studies of coronal structure and activity in polar regions. Not only will these provide important scientific advances for fundamental stellar physics research, they will feed into our understanding of impacts on the Earth and other planets' space environment. Title: Coronal loops in a box: 3D models of their internal structure, dynamics and heating Authors: Breu, C. A.; Peter, H.; Cameron, R.; Solanki, S.; Przybylski, D.; Chitta, L. Bibcode: 2021AAS...23810606B Altcode: The corona of the Sun, and probably also of other stars, is built up by loops defined through the magnetic field. They vividly appear in solar observations in the extreme UV and X-rays. High-resolution observations show individual strands with diameters down to a few 100 km, and so far it remains open what defines these strands, in particular their width, and where the energy to heat them is generated.

The aim of our study is to understand how the magnetic field couples the different layers of the solar atmosphere, how the energy generated by magnetoconvection is transported into the upper atmosphere and dissipated, and how this process determines the scales of observed bright strands in the loop.

To this end, we conduct 3D resistive MHD simulations with the MURaM code. We include the effects of heat conduction, radiative transfer and optically thin radiative losses.We study an isolated coronal loop that is rooted with both footpoints in a shallow convection zone layer. To properly resolve the internal structure of the loop while limiting the size of the computational box, the coronal loop is modelled as a straightened magnetic flux tube. By including part of the convection zone, we drive the evolution of the corona self-consistently by magnetoconvection.

We find that the energy injected into the loop is generated by internal coherent motions within strong magnetic elements. The resulting Poynting flux is channelled into the loop in vortex tubes forming a magnetic connection between the photosphere and corona, where it is dissipated and heats the upper atmosphere.

The coronal emission as it would be observed in solar extreme UV or X-ray observations, e.g. with AIA or XRT, shows transient bright strands.The widths of these strands are consistent with observations. From our model we find that the width of the strands is governed by the size of the individual photospheric magnetic field concentrations where the field line through these strands are rooted. Essentially, each coronal strand is rooted in a single magnetic patch in the photosphere, and the energy to heat the strand is generated by internal motions within this magnetic concentration.

With this model we can build a coherent picture of how energy and matter are transported into the upper solar atmosphere and how these processes structure the interior of coronal loops. Title: Small-scale Dynamo in Cool Main-Sequence Stars: Effect on Stratification, Convection and Bolometric Intensity Authors: Bhatia, T.; Cameron, R.; Solanki, S.; Peter, H.; Przybylski, D.; Witzke, V.; Shapiro, A. Bibcode: 2021AAS...23830404B Altcode: In cool main-sequence stars, the near-surface convection has an impact on the center-to-limb variation of photospheric emission, with implications for stellar lightcurves during planetary transits. In the Sun, there is strong evidence for a small-scale dynamo (SSD) maintaining the small-scale magnetic flux. This field could affect the near-surface convection in other cool main-sequence stars.

An SSD could conceivably generate equipartition magnetic fields, which could lead to non-negligible changes not only in convection and intensity characteristics, but also in stratification. We aim to investigate these changes for F, G, K and M stars. 3D MHD models of the four stellar types covering the subsurface region to lower atmosphere in a small cartesian box are studied using the MURaM rMHD simulation code. The MHD runs are compared against a reference hydrodynamic (HD) run.

The deviations in stratification for the deeper convective layers is negligible, except for the F-star, where reduction in turbulent pressure due to magnetic fields is substantial. Convective velocities are reduced by a similar percentage for all the cases due to inhibitory effect of strong magnetic fields near the bottom boundary. All four cases show small-scale brightenings in intergranular lanes, corresponding to magnetic field concentrations, but overall effects on the r.m.s contrast and spatial powerspectra are varied. Title: First Results of the Chromospheric MURaM code Authors: Przybylski, D. F.; Cameron, R.; Solanki, S.; Rempel, M. Bibcode: 2021AAS...23810605P Altcode: The solar chromosphere, spanning the region between the photosphere and the transition to the corona, remains one of the least understood parts of the Sun. This is partly because observing the chromosphere and interpreting these observations is full of pitfalls. Also, the simulation of the chromosphere is complex, as the particle densities and collisional rates are too low to maintain local thermodynamic equilibrium (LTE). Additionally, the recombination rates of hydrogen are larger than the dynamical timescales and the populations must be solved in non-equilibrium (NE). Realistic simulations of the chromosphere must treat the magneto-hydrodynamics, time-dependant atomic and molecular chemistry, and radiation transfer simultaneously.

The MURaM radiation-MHD code has previously been used for investigation of the connection between the solar photosphere and corona, ranging from small-scale dynamo generated 'quiet' sun fields to sunspots and complex active regions. Until now these simulations have been performed in LTE, greatly limiting their realism in the solar chromosphere. We have extended MURaM to include NLTE effects following the prescriptions used in the Bifrost code. The low viscocity and resistivity of the MURaM code leads to turbulent convection in the photosphere with kilo-Gauss mixed-polarity magnetic fields. This results in a dynamic chromosphere with strong shocks and a finely structured magnetic field. We discuss the implications of this new model towards observations of chromospheric spectral lines. Title: Modelling the evolution of the Sun's open and total magnetic flux Authors: Krivova, N. A.; Solanki, S. K.; Hofer, B.; Wu, C. -J.; Usoskin, I. G.; Cameron, R. Bibcode: 2021A&A...650A..70K Altcode: 2021arXiv210315603K Solar activity in all its varied manifestations is driven by the magnetic field. Two global quantities are particularly important for many purposes, the Sun's total and open magnetic flux, which can be computed from sunspot number records using models. Such sunspot-driven models, however, do not take into account the presence of magnetic flux during grand minima, such as the Maunder minimum. Here we present a major update of a widely used simple model, which now takes into account the observation that the distribution of all magnetic features on the Sun follows a single power law. The exponent of the power law changes over the solar cycle. This allows for the emergence of small-scale magnetic flux even when no sunspots have been present for multiple decades and leads to non-zero total and open magnetic flux also in the deepest grand minima, such as the Maunder minimum, thus overcoming a major shortcoming of the earlier models. The results of the updated model compare well with the available observations and reconstructions of the solar total and open magnetic flux. This opens up the possibility of improved reconstructions of the sunspot number from time series of the cosmogenic isotope production rate. Title: Nonequilibrium Equation of State in Stellar Atmospheres Authors: Anusha, L. S.; van Noort, M.; Cameron, R. H. Bibcode: 2021ApJ...911...71A Altcode: 2021arXiv210413650A In the stellar chromospheres, radiative energy transport is dominated by only the strongest spectral lines. For these lines, the approximation of local thermodynamic equilibrium (LTE) is known to be very inaccurate, and a state of equilibrium cannot be assumed in general. To calculate the radiative energy transport under these conditions, the population evolution equation must be evaluated explicitly, including all time-dependent terms. We develop a numerical method to solve the evolution equation for the atomic-level populations in a time-implicit way, keeping all time-dependent terms to first order. We show that the linear approximation of the time dependence of the populations can handle very large time steps without losing accuracy. We reproduce the benchmark solutions from earlier, well-established works in terms of non-LTE kinetic equilibrium solutions and typical ionization/recombination timescales in the solar chromosphere. Title: Small-scale dynamo in an F-star: effects on near-surface stratification, convection and intensity Authors: Bhatia, Tanayveer; Cameron, Robert; Solanki, Sami; Peter, Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander Bibcode: 2021csss.confE..75B Altcode: The emission from the photosphere of stars shows a systematic center-to-limb variation. In cool main-sequence stars, the near-surface convection has an impact on this variation, with implications for lightcurves of stars during planetary transits. In the Sun, there is strong evidence for a small-scale dynamo (SSD) maintaining the small-scale magnetic flux. We aim to investigate what additional effects such a field would play for other cool main-sequence stars. In our work we first concentrate on F-stars. This is because they have sonic velocities near the surface, implying a rough equipartition between internal and kinetic energies. In addition, an SSD might create a significant magnetic energy density to impact the results. We investigate the interplay between internal, kinetic and magnetic energies in 3D cartesian box MHD models of a F3V-star in the near-surface convection, using the MURaM radiative-MHD simulation code. Along with a reference hydrodynamic run, two MHD models with self-consistently generated magnetic fields with two different lower boundary conditions are considered. We find that the SSD process creates a magnetic field with energy within an order of magnitude of the internal and the kinetic energy. Compared to the hydrodynamic run, we find slight (~1-3%) but significant deviations in density, gas pressure and temperature stratification. At the surface, this corresponds to a temperature difference of ~130 K. As expected, there is a significant reduction in kinetic energy flux once the SSD is operational. The changes in intensity are more subtle, both in total intensity and granulation pattern. From this we conclude that the presence of an SSD will have a significant impact on the atmospheric structure and intensity characteristics seen at the surface. This makes it clear that it would be important to consider the spatially and temporally averaged effects of the SSD also for global stellar models. Title: Sunspot Simulations: Penumbra Formation and the Fluting Instability Authors: Panja, Mayukh; Cameron, Robert H.; Solanki, Sami K. Bibcode: 2021ApJ...907..102P Altcode: 2020arXiv201111447P The fluting instability has been suggested as the driver of the subsurface structure of sunspot flux tubes. We conducted a series of numerical experiments where we used flux tubes with different initial curvatures to study the effect of the fluting instability on the subsurface structure of spots. We used the MURaM code, which has previously been used to simulate complete sunspots, to first compute four sunspots in the slab geometry and then two complete circular spots of opposite polarities. We find that the curvature of a flux tube indeed determines the degree of fluting the flux tube will undergo—the more curved a flux tube is, the more fluted it becomes. In addition, sunspots with strong curvature have strong horizontal fields at the surface and therefore readily form penumbral filaments. The fluted sunspots eventually break up from below, with lightbridges appearing at the surface several hours after fluting commences. Title: Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagation Authors: Abdalla, H.; Abe, H.; Acero, F.; Acharyya, A.; Adam, R.; Agudo, I.; Aguirre-Santaella, A.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista, R.; Amati, L.; Amato, E.; Ambrosi, G.; Angüner, E. O.; Araudo, A.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Asano, K.; Ascasíbar, Y.; Ashley, M.; Backes, M.; Balazs, C.; Balbo, M.; Balmaverde, B.; Baquero Larriva, A.; Barbosa Martins, V.; Barkov, M.; Baroncelli, L.; Barres de Almeida, U.; Barrio, J. A.; Batista, P. -I.; Becerra González, J.; Becherini, Y.; Beck, G.; Becker Tjus, J.; Belmont, R.; Benbow, W.; Bernardini, E.; Berti, A.; Berton, M.; Bertucci, B.; Beshley, V.; Bi, B.; Biasuzzi, B.; Biland, A.; Bissaldi, E.; Biteau, J.; Blanch, O.; Bocchino, F.; Boisson, C.; Bolmont, J.; Bonanno, G.; Bonneau Arbeletche, L.; Bonnoli, G.; Bordas, P.; Bottacini, E.; Böttcher, M.; Bozhilov, V.; Bregeon, J.; Brill, A.; Brown, A. M.; Bruno, P.; Bruno, A.; Bulgarelli, A.; Burton, M.; Buscemi, M.; Caccianiga, A.; Cameron, R.; Capasso, M.; Caprai, M.; Caproni, A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Carosi, R.; Carosi, A.; Casanova, S.; Cascone, E.; Cauz, D.; Cerny, K.; Cerruti, M.; Chadwick, P.; Chaty, S.; Chen, A.; Chernyakova, M.; Chiaro, G.; Chiavassa, A.; Chytka, L.; Conforti, V.; Conte, F.; Contreras, J. L.; Coronado-Blazquez, J.; Cortina, J.; Costa, A.; Costantini, H.; Covino, S.; Cristofari, P.; Cuevas, O.; D'Ammando, F.; Daniel, M. K.; Davies, J.; Dazzi, F.; De Angelis, A.; de Bony de Lavergne, M.; De Caprio, V.; de Cássia dos Anjos, R.; de Gouveia Dal Pino, E. M.; De Lotto, B.; De Martino, D.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma, F.; de Souza, V.; Delgado, C.; Della Ceca, R.; della Volpe, D.; Depaoli, D.; Di Girolamo, T.; Di Pierro, F.; Díaz, C.; Díaz-Bahamondes, C.; Diebold, S.; Djannati-Ataï, A.; Dmytriiev, A.; Domínguez, A.; Donini, A.; Dorner, D.; Doro, M.; Dournaux, J.; Dwarkadas, V. V.; Ebr, J.; Eckner, C.; Einecke, S.; Ekoume, T. R. N.; Elsässer, D.; Emery, G.; Evoli, C.; Fairbairn, M.; Falceta-Goncalves, D.; Fegan, S.; Feng, Q.; Ferrand, G.; Fiandrini, E.; Fiasson, A.; Fioretti, V.; Foffano, L.; Fonseca, M. V.; Font, L.; Fontaine, G.; Franco, F. J.; Freixas Coromina, L.; Fukami, S.; Fukazawa, Y.; Fukui, Y.; Gaggero, D.; Galanti, G.; Gammaldi, V.; Garcia, E.; Garczarczyk, M.; Gascon, D.; Gaug, M.; Gent, A.; Ghalumyan, A.; Ghirlanda, G.; Gianotti, F.; Giarrusso, M.; Giavitto, G.; Giglietto, N.; Giordano, F.; Glicenstein, J.; Goldoni, P.; González, J. M.; Gourgouliatos, K.; Grabarczyk, T.; Grandi, P.; Granot, J.; Grasso, D.; Green, J.; Grube, J.; Gueta, O.; Gunji, S.; Halim, A.; Harvey, M.; Hassan Collado, T.; Hayashi, K.; Heller, M.; Hernández Cadena, S.; Hervet, O.; Hinton, J.; Hiroshima, N.; Hnatyk, B.; Hnatyk, R.; Hoffmann, D.; Hofmann, W.; Holder, J.; Horan, D.; Hörandel, J.; Horvath, P.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Hughes, G.; Hütten, M.; Iarlori, M.; Inada, T.; Inoue, S.; Insolia, A.; Ionica, M.; Iori, M.; Jacquemont, M.; Jamrozy, M.; Janecek, P.; Jiménez Martínez, I.; Jin, W.; Jung-Richardt, I.; Jurysek, J.; Kaaret, P.; Karas, V.; Karkar, S.; Kawanaka, N.; Kerszberg, D.; Khélifi, B.; Kissmann, R.; Knödlseder, J.; Kobayashi, Y.; Kohri, K.; Komin, N.; Kong, A.; Kosack, K.; Kubo, H.; La Palombara, N.; Lamanna, G.; Lang, R. G.; Lapington, J.; Laporte, P.; Lefaucheur, J.; Lemoine-Goumard, M.; Lenain, J.; Leone, F.; Leto, G.; Leuschner, F.; Lindfors, E.; Lloyd, S.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez, A.; López, M.; López-Coto, R.; Loporchio, S.; Lucarelli, F.; Luque-Escamilla, P. L.; Lyard, E.; Maggio, C.; Majczyna, A.; Makariev, M.; Mallamaci, M.; Mandat, D.; Maneva, G.; Manganaro, M.; Manicò, G.; Marcowith, A.; Marculewicz, M.; Markoff, S.; Marquez, P.; Martí, J.; Martinez, O.; Martínez, M.; Martínez, G.; Martínez-Huerta, H.; Maurin, G.; Mazin, D.; Mbarubucyeye, J. D.; Medina Miranda, D.; Meyer, M.; Micanovic, S.; Miener, T.; Minev, M.; Miranda, J. M.; Mitchell, A.; Mizuno, T.; Mode, B.; Moderski, R.; Mohrmann, L.; Molina, E.; Montaruli, T.; Moralejo, A.; Morales Merino, J.; Morcuende-Parrilla, D.; Morselli, A.; Mukherjee, R.; Mundell, C.; Murach, T.; Muraishi, H.; Nagai, A.; Nakamori, T.; Nemmen, R.; Niemiec, J.; Nieto, D.; Nievas, M.; Nikolajuk, M.; Nishijima, K.; Noda, K.; Nosek, D.; Nozaki, S.; O'Brien, P.; Ohira, Y.; Ohishi, M.; Oka, T.; Ong, R. A.; Orienti, M.; Orito, R.; Orlandini, M.; Orlando, E.; Osborne, J. P.; Ostrowski, M.; Oya, I.; Pagliaro, A.; Palatka, M.; Paneque, D.; Pantaleo, F. R.; Paredes, J. M.; Parmiggiani, N.; Patricelli, B.; Pavletić, L.; Pe'er, A.; Pech, M.; Pecimotika, M.; Peresano, M.; Persic, M.; Petruk, O.; Pfrang, K.; Piatteli, P.; Pietropaolo, E.; Pillera, R.; Pilszyk, B.; Pimentel, D.; Pintore, F.; Pita, S.; Pohl, M.; Poireau, V.; Polo, M.; Prado, R. R.; Prast, J.; Principe, G.; Produit, N.; Prokoph, H.; Prouza, M.; Przybilski, H.; Pueschel, E.; Pühlhofer, G.; Pumo, M. L.; Punch, M.; Queiroz, F.; Quirrenbach, A.; Rando, R.; Razzaque, S.; Rebert, E.; Recchia, S.; Reichherzer, P.; Reimer, O.; Reimer, A.; Renier, Y.; Reposeur, T.; Rhode, W.; Ribeiro, D.; Ribó, M.; Richtler, T.; Rico, J.; Rieger, F.; Rizi, V.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodriguez Ramirez, J. C.; Rodríguez Vázquez, J. J.; Romano, P.; Romeo, G.; Roncadelli, M.; Rosado, J.; Rosales de Leon, A.; Rowell, G.; Rudak, B.; Rujopakarn, W.; Russo, F.; Sadeh, I.; Saha, L.; Saito, T.; Salesa Greus, F.; Sanchez, D.; Sánchez-Conde, M.; Sangiorgi, P.; Sano, H.; Santander, M.; Santos, E. M.; Sanuy, A.; Sarkar, S.; Saturni, F. G.; Sawangwit, U.; Scherer, A.; Schleicher, B.; Schovanek, P.; Schussler, F.; Schwanke, U.; Sciacca, E.; Scuderi, S.; Seglar Arroyo, M.; Sergijenko, O.; Servillat, M.; Seweryn, K.; Shalchi, A.; Sharma, P.; Shellard, R. C.; Siejkowski, H.; Sinha, A.; Sliusar, V.; Slowikowska, A.; Sokolenko, A.; Sol, H.; Specovius, A.; Spencer, S.; Spiga, D.; Stamerra, A.; Stanič, S.; Starling, R.; Stolarczyk, T.; Straumann, U.; Strišković, J.; Suda, Y.; Świerk, P.; Tagliaferri, G.; Takahashi, H.; Takahashi, M.; Tavecchio, F.; Taylor, L.; Tejedor, L. A.; Temnikov, P.; Terrier, R.; Terzic, T.; Testa, V.; Tian, W.; Tibaldo, L.; Tonev, D.; Torres, D. F.; Torresi, E.; Tosti, L.; Tothill, N.; Tovmassian, G.; Travnicek, P.; Truzzi, S.; Tuossenel, F.; Umana, G.; Vacula, M.; Vagelli, V.; Valentino, M.; Vallage, B.; Vallania, P.; van Eldik, C.; Varner, G. S.; Vassiliev, V.; Vázquez Acosta, M.; Vecchi, M.; Veh, J.; Vercellone, S.; Vergani, S.; Verguilov, V.; Vettolani, G. P.; Viana, A.; Vigorito, C. F.; Vitale, V.; Vorobiov, S.; Vovk, I.; Vuillaume, T.; Wagner, S. J.; Walter, R.; Watson, J.; White, M.; White, R.; Wiemann, R.; Wierzcholska, A.; Will, M.; Williams, D. A.; Wischnewski, R.; Wolter, A.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yoshikoshi, T.; Zacharias, M.; Zaharijas, G.; Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.; Zechlin, H.; Zhdanov, V. I.; Živec, M. Bibcode: 2021JCAP...02..048A Altcode: 2020arXiv201001349C The Cherenkov Telescope Array (CTA), the new-generation ground-based observatory for γ astronomy, provides unique capabilities to address significant open questions in astrophysics, cosmology, and fundamental physics. We study some of the salient areas of γ cosmology that can be explored as part of the Key Science Projects of CTA, through simulated observations of active galactic nuclei (AGN) and of their relativistic jets. Observations of AGN with CTA will enable a measurement of γ absorption on the extragalactic background light with a statistical uncertainty below 15% up to a redshift z=2 and to constrain or detect γ halos up to intergalactic-magnetic-field strengths of at least 0.3 pG . Extragalactic observations with CTA also show promising potential to probe physics beyond the Standard Model. The best limits on Lorentz invariance violation from γ astronomy will be improved by a factor of at least two to three. CTA will also probe the parameter space in which axion-like particles could constitute a significant fraction, if not all, of dark matter. We conclude on the synergies between CTA and other upcoming facilities that will foster the growth of γ cosmology. Title: The solar dynamo and flux emergence Authors: Cameron, Robert Bibcode: 2021cosp...43E1728C Altcode: Magnetic flux generated by dynamo action in the solar convection zone is carried by flows from the solar convection zone, through the photosphere, into the chromosphere and corona. During the emergence process a rising magnetic flux loop is given both a random and systematic tilt with respect to the east-west direction. This rise through the photosphere is called flux emergence, and it plays an essential role in the Babcock-Leighton model of the solar dynamo. In this talke we will consider the flows which are responsible for flux emergence. We will then show how the emerged field reverses the polar fields and creates new flux to emerge during the next cycle. Quantitative estimates will be made for the different terms involved in the subsurface magnetic flux budget. Title: Vortex flow properties in simulations of solar plage region: Evidence for their role in chromospheric heating Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K. Bibcode: 2021A&A...645A...3Y Altcode: 2020arXiv201014971Y Context. Vortex flows exist across a broad range of spatial and temporal scales in the solar atmosphere. Small-scale vortices are thought to play an important role in energy transport in the solar atmosphere. However, their physical properties remain poorly understood due to the limited spatial resolution of the observations.
Aims: We explore and analyze the physical properties of small-scale vortices inside magnetic flux tubes using numerical simulations, and investigate whether they contribute to heating the chromosphere in a plage region.
Methods: Using the three-dimensional radiative magnetohydrodynamic simulation code MURaM, we perform numerical simulations of a unipolar solar plage region. To detect and isolate vortices we use the swirling strength criterion and select the locations where the fluid is rotating with an angular velocity greater than a certain threshold. We concentrate on small-scale vortices as they are the strongest and carry most of the energy. We explore the spatial profiles of physical quantities such as density and horizontal velocity inside these vortices. Moreover, to learn their general characteristics, a statistical investigation is performed.
Results: Magnetic flux tubes have a complex filamentary substructure harboring an abundance of small-scale vortices. At the interfaces between vortices strong current sheets are formed that may dissipate and heat the solar chromosphere. Statistically, vortices have higher densities and higher temperatures than the average values at the same geometrical height in the chromosphere.
Conclusions: We conclude that small-scale vortices are ubiquitous in solar plage regions; they are denser and hotter structures that contribute to chromospheric heating, possibly by dissipation of the current sheets formed at their interfaces. Title: Non-equilibrium equation-of-state in stellar atmospheres Authors: Lokanathapura Seetharamabhasari, Anusha; Cameron, Robert; Van Noort, Michiel Bibcode: 2021cosp...43E.985L Altcode: In the stellar atmospheres, radiative energy transport is dominated by only the strongest spectral lines. For these lines, the approximation of local thermo-dynamic equilibrium (LTE) is known to be very inaccurate, and a state of equilibrium cannot be assumed in general. Therefore to understand the structure and dynamics of stellar atmospheres through evolving magneto-hydro-dynamic equations, one needs a non-equilibrium equation of state. To calculate the radiative energy transport under these conditions, the population evolution equation must be evaluated including all time dependent terms. To this end, we have developed a new numerical method to solve the non-LTE non-equilibrium radiative transfer problem. We solve evolution equation for the atomic level populations in a time-implicit way, keeping all time dependent terms to first order. We have tested our method by reproducing earlier works, namely, a) determining chromosperic time-scales of ionization/recombination, b) showing that our non-equilibrium solver evolves to the statistical equilibrium solution obtained from an independent non-LTE spectral synthesis code. In this presentation, I will describe the method, and discuss equilibrium solutions. Title: Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centre Authors: Acharyya, A.; Adam, R.; Adams, C.; Agudo, I.; Aguirre-Santaella, A.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista, R.; Amati, L.; Ambrosi, G.; Angüner, E. O.; Antonelli, L. A.; Aramo, C.; Araudo, A.; Armstrong, T.; Arqueros, F.; Asano, K.; Ascasíbar, Y.; Ashley, M.; Balazs, C.; Ballester, O.; Baquero Larriva, A.; Barbosa Martins, V.; Barkov, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Becerra, J.; Beck, G.; Becker Tjus, J.; Benbow, W.; Benito, M.; Berge, D.; Bernardini, E.; Bernlöhr, K.; Berti, A.; Bertucci, B.; Beshley, V.; Biasuzzi, B.; Biland, A.; Bissaldi, E.; Biteau, J.; Blanch, O.; Blazek, J.; Bocchino, F.; Boisson, C.; Bonneau Arbeletche, L.; Bordas, P.; Bosnjak, Z.; Bottacini, E.; Bozhilov, V.; Bregeon, J.; Brill, A.; Bringmann, T.; Brown, A. M.; Brun, P.; Brun, F.; Bruno, P.; Bulgarelli, A.; Burton, M.; Burtovoi, A.; Buscemi, M.; Cameron, R.; Capasso, M.; Caproni, A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Carosi, R.; Carosi, A.; Casanova, S.; Cascone, E.; Cassol, F.; Catalani, F.; Cauz, D.; Cerruti, M.; Chadwick, P.; Chaty, S.; Chen, A.; Chernyakova, M.; Chiaro, G.; Chiavassa, A.; Chikawa, M.; Chudoba, J.; Çolak, M.; Conforti, V.; Coniglione, R.; Conte, F.; Contreras, J. L.; Coronado-Blazquez, J.; Costa, A.; Costantini, H.; Cotter, G.; Cristofari, P.; D'Aimath, A.; D'Ammando, F.; Damone, L. A.; Daniel, M. K.; Dazzi, F.; De Angelis, A.; De Caprio, V.; de Cássia dos Anjos, R.; de Gouveia Dal Pino, E. M.; De Lotto, B.; De Martino, D.; de Oña Wilhelmi, E.; De Palma, F.; de Souza, V.; Delgado, C.; Delgado Giler, A. G.; della Volpe, D.; Depaoli, D.; Di Girolamo, T.; Di Pierro, F.; Di Venere, L.; Diebold, S.; Dmytriiev, A.; Domínguez, A.; Donini, A.; Doro, M.; Ebr, J.; Eckner, C.; Edwards, T. D. P.; Ekoume, T. R. N.; Elsässer, D.; Evoli, C.; Falceta-Goncalves, D.; Fedorova, E.; Fegan, S.; Feng, Q.; Ferrand, G.; Ferrara, G.; Fiandrini, E.; Fiasson, A.; Filipovic, M.; Fioretti, V.; Fiori, M.; Foffano, L.; Fontaine, G.; Fornieri, O.; Franco, F. J.; Fukami, S.; Fukui, Y.; Gaggero, D.; Galaz, G.; Gammaldi, V.; Garcia, E.; Garczarczyk, M.; Gascon, D.; Gent, A.; Ghalumyan, A.; Gianotti, F.; Giarrusso, M.; Giavitto, G.; Giglietto, N.; Giordano, F.; Giuliani, A.; Glicenstein, J.; Gnatyk, R.; Goldoni, P.; González, M. M.; Gourgouliatos, K.; Granot, J.; Grasso, D.; Green, J.; Grillo, A.; Gueta, O.; Gunji, S.; Halim, A.; Hassan, T.; Heller, M.; Hernández Cadena, S.; Hiroshima, N.; Hnatyk, B.; Hofmann, W.; Holder, J.; Horan, D.; Hörandel, J.; Horvath, P.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Hughes, G.; Humensky, T. B.; Hütten, M.; Iarlori, M.; Inada, T.; Inoue, S.; Iocco, F.; Iori, M.; Jamrozy, M.; Janecek, P.; Jin, W.; Jouvin, L.; Jurysek, J.; Karukes, E.; Katarzyński, K.; Kazanas, D.; Kerszberg, D.; Kherlakian, M. C.; Kissmann, R.; Knödlseder, J.; Kobayashi, Y.; Kohri, K.; Komin, N.; Kubo, H.; Kushida, J.; Lamanna, G.; Lapington, J.; Laporte, P.; Leigui de Oliveira, M. A.; Lenain, J.; Leone, F.; Leto, G.; Lindfors, E.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez, A.; López, M.; López-Coto, R.; Loporchio, S.; Luque-Escamilla, P. L.; Mach, E.; Maggio, C.; Maier, G.; Mallamaci, M.; Malta Nunes de Almeida, R.; Mandat, D.; Manganaro, M.; Mangano, S.; Manicò, G.; Marculewicz, M.; Mariotti, M.; Markoff, S.; Marquez, P.; Martí, J.; Martinez, O.; Martínez, M.; Martínez, G.; Martínez-Huerta, H.; Maurin, G.; Mazin, D.; Mbarubucyeye, J. D.; Medina Miranda, D.; Meyer, M.; Miceli, M.; Miener, T.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Mizuno, T.; Mode, B.; Moderski, R.; Mohrmann, L.; Molina, E.; Montaruli, T.; Moralejo, A.; Morcuende-Parrilla, D.; Morselli, A.; Mukherjee, R.; Mundell, C.; Nagai, A.; Nakamori, T.; Nemmen, R.; Niemiec, J.; Nieto, D.; Nikołajuk, M.; Ninci, D.; Noda, K.; Nosek, D.; Nozaki, S.; Ohira, Y.; Ohishi, M.; Ohtani, Y.; Oka, T.; Okumura, A.; Ong, R. A.; Orienti, M.; Orito, R.; Orlandini, M.; Orlando, S.; Orlando, E.; Ostrowski, M.; Oya, I.; Pagano, I.; Pagliaro, A.; Palatiello, M.; Pantaleo, F. R.; Paredes, J. M.; Pareschi, G.; Parmiggiani, N.; Patricelli, B.; Pavletić, L.; Pe'er, A.; Pecimotika, M.; Pérez-Romero, J.; Persic, M.; Petruk, O.; Pfrang, K.; Piano, G.; Piatteli, P.; Pietropaolo, E.; Pillera, R.; Pilszyk, B.; Pintore, F.; Pohl, M.; Poireau, V.; Prado, R. R.; Prandini, E.; Prast, J.; Principe, G.; Prokoph, H.; Prouza, M.; Przybilski, H.; Pühlhofer, G.; Pumo, M. L.; Queiroz, F.; Quirrenbach, A.; Rainò, S.; Rando, R.; Razzaque, S.; Recchia, S.; Reimer, O.; Reisenegger, A.; Renier, Y.; Rhode, W.; Ribeiro, D.; Ribó, M.; Richtler, T.; Rico, J.; Rieger, F.; Rinchiuso, L.; Rizi, V.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodriguez Ramirez, J. C.; Rojas, G.; Romano, P.; Romeo, G.; Rosado, J.; Rowell, G.; Rudak, B.; Russo, F.; Sadeh, I.; Sæther Hatlen, E.; Safi-Harb, S.; Salesa Greus, F.; Salina, G.; Sanchez, D.; Sánchez-Conde, M.; Sangiorgi, P.; Sano, H.; Santander, M.; Santos, E. M.; Santos-Lima, R.; Sanuy, A.; Sarkar, S.; Saturni, F. G.; Sawangwit, U.; Schussler, F.; Schwanke, U.; Sciacca, E.; Scuderi, S.; Seglar-Arroyo, M.; Sergijenko, O.; Servillat, M.; Seweryn, K.; Shalchi, A.; Sharma, P.; Shellard, R. C.; Siejkowski, H.; Silk, J.; Siqueira, C.; Sliusar, V.; Słowikowska, A.; Sokolenko, A.; Sol, H.; Spencer, S.; Stamerra, A.; Stanič, S.; Starling, R.; Stolarczyk, T.; Straumann, U.; Strišković, J.; Suda, Y.; Suomijarvi, T.; Świerk, P.; Tavecchio, F.; Taylor, L.; Tejedor, L. A.; Teshima, M.; Testa, V.; Tibaldo, L.; Todero Peixoto, C. J.; Tokanai, F.; Tonev, D.; Tosti, G.; Tosti, L.; Tothill, N.; Truzzi, S.; Travnicek, P.; Vagelli, V.; Vallage, B.; Vallania, P.; van Eldik, C.; Vandenbroucke, J.; Varner, G. S.; Vassiliev, V.; Vázquez Acosta, M.; Vecchi, M.; Ventura, S.; Vercellone, S.; Vergani, S.; Verna, G.; Viana, A.; Vigorito, C. F.; Vink, J.; Vitale, V.; Vorobiov, S.; Vovk, I.; Vuillaume, T.; Wagner, S. J.; Walter, R.; Watson, J.; Weniger, C.; White, R.; White, M.; Wiemann, R.; Wierzcholska, A.; Will, M.; Williams, D. A.; Wischnewski, R.; Yanagita, S.; Yang, L.; Yoshikoshi, T.; Zacharias, M.; Zaharijas, G.; Zakaria, A. A.; Zampieri, L.; Zanin, R.; Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.; Zechlin, H.; Zhdanov, V. I.; Živec, M. Bibcode: 2021JCAP...01..057A Altcode: 2020arXiv200716129C We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA's unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale diffuse emission in high-energy gamma rays, constituting a background for dark matter searches for which we adopt state-of-the-art models based on current data. Throughout our analysis, we use up-to-date event reconstruction Monte Carlo tools developed by the CTA consortium, and pay special attention to quantifying the level of instrumental systematic uncertainties, as well as background template systematic errors, required to probe thermally produced dark matter at these energies. Title: A Journey of Exploration to the Polar Regions of a Star: Probing the Solar Poles and the Heliosphere from High Helio-Latitude Authors: Finsterle, W.; Harra, L.; Andretta, V.; Appourchaux, T.; Baudin, F.; Bellot Rubio, L.; Birch, A.; Boumier, P.; Cameron, R. H.; Carlsson, M.; Corbard, T.; Davies, J. A.; Fazakerley, A. N.; Fineschi, S.; Gizon, L. C.; Harrison, R. A.; Hassler, D.; Leibacher, J. W.; Liewer, P. C.; Macdonald, M.; Maksimovic, M.; Murphy, N.; Naletto, G.; Nigro, G.; Owen, C. J.; Martinez-Pillet, V.; Rochus, P. L.; Romoli, M.; Sekii, T.; Spadaro, D.; Veronig, A. Bibcode: 2020AGUFMSH0110005F Altcode: A mission to view the solar poles from high helio-latitudes (above 60°) will build on the experience of Solar Orbiter as well as a long heritage of successful solar missions and instrumentation (e.g. SOHO, STEREO, Hinode, SDO), but will focus for the first time on the solar poles, enabling scientific investigations that cannot be done by any other mission. One of the major mysteries of the Sun is the solar cycle. The activity cycle of the Sun drives the structure and behaviour of the heliosphere and is, of course, the driver of space weather. In addition, solar activity and variability provides fluctuating input into the Earth climate models, and these same physical processes are applicable to stellar systems hosting exoplanets. One of the main obstructions to understanding the solar cycle, and hence all solar activity, is our current lack of understanding of the polar regions. We describe a mission concept that aims to address this fundamental issue. In parallel, we recognise that viewing the Sun from above the polar regions enables further scientific advantages, beyond those related to the solar cycle, such as unique and powerful studies of coronal mass ejection processes, from a global perspective, and studies of coronal structure and activity in polar regions. Not only will these provide important scientific advances for fundamental stellar physics research, they will feed into our understanding of impacts on the Earth and other planets' space environment. Title: Power spectrum of turbulent convection in the solar photosphere Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.; Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M. Bibcode: 2020A&A...644A..44Y Altcode: 2020arXiv201009037Y The solar photosphere provides us with a laboratory for understanding turbulence in a layer where the fundamental processes of transport vary rapidly and a strongly superadiabatic region lies very closely to a subadiabatic layer. Our tools for probing the turbulence are high-resolution spectropolarimetric observations such as have recently been obtained with the two balloon-borne SUNRISE missions, and numerical simulations. Our aim is to study photospheric turbulence with the help of Fourier power spectra that we compute from observations and simulations. We also attempt to explain some properties of the photospheric overshooting flow with the help of its governing equations and simulations. We find that quiet-Sun observations and smeared simulations are consistent with each other and exhibit a power-law behavior in the subgranular range of their Doppler velocity power spectra with a power-law index of ≈ - 2. The unsmeared simulations exhibit a power law that extends over the full range between the integral and Taylor scales with a power-law index of ≈ - 2.25. The smearing, reminiscent of observational conditions, considerably reduces the extent of the power-law-like portion of the power spectra. This suggests that the limited spatial resolution in some observations might eventually result in larger uncertainties in the estimation of the power-law indices. The simulated vertical velocity power spectra as a function of height show a rapid change in the power-law index (at the subgranular range) from roughly the optical depth unity layer, that is, the solar surface, to 300 km above it. We propose that the cause of the steepening of the power-law index is the transition from a super- to a subadiabatic region, in which the dominant source of motions is overshooting convection. A scale-dependent transport of the vertical momentum occurs. At smaller scales, the vertical momentum is more efficiently transported sideways than at larger scales. This results in less vertical velocity power transported upward at small scales than at larger scales and produces a progressively steeper vertical velocity power law below 180 km. Above this height, the gravity work progressively gains importance at all relevant scales, making the atmosphere progressively more hydrostatic and resulting in a gradually less steep power law. Radiative heating and cooling of the plasma is shown to play a dominant role in the plasma energetics in this region, which is important in terms of nonadiabatic damping of the convective motions. Title: Simulations Show that Vortex Flows Could Heat the Chromosphere in Solar Plage Authors: Yadav, N.; Cameron, R.; Solanki, S. Bibcode: 2020SPD....5120107Y Altcode: Recent advances in both, observational techniques and numerical simulations have enabled us to detect small-scale vortices in the solar atmosphere. Vortices are ubiquitous throughout the solar surface and at all layers of the solar atmosphere existing over a wide range of spatial and temporal scales. Small-scale vortices are suggested to play an important role in the energy transport of the solar atmosphere, however, their physical properties remain poorly understood due to limited resolution. We explored the relationship between vortex flows at different spatial scales, analyze their physical properties, and investigate their contribution to Poynting flux transport. Using three-dimensional (3D) radiative magnetohydrodynamic (MHD)simulation code 'MURaM', we perform numerical simulations of a unipolar solar plage region. For detecting and isolating vortices, we use the 'Swirling Strength' criterion. We explore the spatial profiles of physical quantities viz. density, horizontal velocity, etc. inside these vortices. Moreover, to apprehend their general characteristics, a statistical investigation is performed. We found that magnetic flux tubes have a complex filamentary substructure abundant of small-scale vortices. On their interfaces strong current sheets are formed that may dissipate and heat the solar chromosphere. Statistically, vortices have higher densities and higher temperatures than the average values at the same geometrical height. We also degrade our simulation data to get an effective spatial resolution of 50 km, 100 km, 250 km, and 500 km, respectively. Analyzing simulation data at different effective resolutions, we found vortex flows existing over various spatial scales. In high-resolution simulation data, we detect a large number of small-scale vortices. Whereas, in the degraded data with relatively poor resolutions, smaller vortices are averaged-out and larger vortices are detected. The Poynting flux over vortex locations is more than adequate to compensate for the radiative losses in the chromosphere indicating their possible role in the chromospheric heating. Title: A Coronal Loop in a Box: Energy Generation, Heating and Dynamics Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S.; Chitta, P.; Przybylski, D. Bibcode: 2020SPD....5121008B Altcode: In our study we aim at an understanding how the energy to heat the upper atmosphere is generated by the photospheric magneto-convection, transported into the upper atmosphere, and how its dissipation governs the formation of the internal structure of a coronal magnetic loop. In a 3D MHD model we study a coronal loop that is rooted with both footpoints in a shallow convection zone layer. Therefore the driving at the coronal base arises self-consistently from magneto-convection in plage-type areas. To fit into a cartesian box, we straighten the coronal loop. This allows a high spatial resolution within the loop that cannot be achieved in a model of a whole active region. To conduct the numerical experiments we employ the MURaM code that includes heat conduction, radiative transfer and optically thin radiative losses. We find that the Poynting flux into the loop is generated by small-scale photospheric motions within strong magnetic flux concentrations. Turbulent behaviour develops in the upper layers of the atmosphere as a response to the footpoint motions. Vortex flows are found at various heights within the loop. These are organised in swirls that form coherent structures with a magnetic connection from the intergranular lanes in the photosphere through the chromosphere up to several megameters into the corona. In the coronal part of the loop plasma motions perpendicular to the magnetic axis of the swirl are associated with an increased heating rate and thus enhanced temperatures. At any given time, only part of the loop is filled with swirls which leads to a substructure of the loop in terms of temperature and density. Consequently the emission as it would be observed by AIA or XRT reveals transient bright strands that form in response to the heating events related to the swirls. With this model we can build a coherent picture of how the energy flux to heat the upper atmosphere is generated near the solar surface and how this process drives and governs the heating and dynamics of a coronal loop Title: Effects of inclusion of small-scale dynamo in near-surface structure of F-stars Authors: Bhatia, T. S.; Cameron, R.; Solanki, S.; Peter, H.; Przbylski, D.; Witzke, V. Bibcode: 2020SPD....5120704B Altcode: The presence of (unresolved) small-scale mixed polarity regions in the quiet Sun photosphere plays an important role in determining the basal magnetic flux. Observationally, the magnitude of the vertical component of this field is estimated to be ~50-100 G on the Sun. This field is important for determining the energy balance in the chromosphere and may also subtly affect the radiative properties of the photosphere. These fields are believed to be the result of a small-scale dynamo (SSD) operating near the surface. While significant progress has been made in investigating the role of the SSD in the Sun, it is unclear what effects SSDs have on other stars. In particular, for F-stars, the photosheric kinetic and internal energies seem to be of the same order of magnitude. Since there is a rough equipartition in energies for a saturated SSD, deviations from a pure hydrodynamic (HD) stratification are expected. We aim to characterize these deviations. Box simulations of the upper convection zone and the photosphere are carried out using the radiative MHD code MURaM. To obtain SSD simulations, we use initial HD simulations and seed a magnetic field of negligible strength and zero net flux, which we then run till the magnetic field reaches saturation. We consider two different lower boundary conditions (BCs) for the magnetic field to characterize BC-effects: a) only vertical magnetic field is allowed, b) both vertical and horizontal magnetic field is allowed. Both boundary conditions exhibit SSD action. We observe slight increase (fraction of a percent) in the horizontally-averaged temperature profile for both the cases. Other thermodynamic quantities exhibit deviations (~ a percent) depending on the boundary condition considered. In addition, the spatial power spectra of the bolometric intensity shows deviations from the corresponding HD (without magnetic field) run, implying larger power at smaller spatial scales for SSD case. The presence of a SSD results in a significant amount of "quiet"-star magnetic flux with associated changes in the stratification of the atmosphere and spatial distribution of the bolometric intensity. Title: Average motion of emerging solar active region polarities. II. Joy's law Authors: Schunker, H.; Baumgartner, C.; Birch, A. C.; Cameron, R. H.; Braun, D. C.; Gizon, L. Bibcode: 2020A&A...640A.116S Altcode: 2020arXiv200605565S Context. The tilt of solar active regions described by Joy's law is essential for converting a toroidal field to a poloidal field in Babcock-Leighton dynamo models. In thin flux tube models the Coriolis force causes what we observe as Joy's law, acting on east-west flows as they rise towards the surface.
Aims: Our goal is to measure the evolution of the average tilt angle of hundreds of active regions as they emerge, so that we can constrain the origins of Joy's law.
Methods: We measured the tilt angle of the primary bipoles in 153 emerging active regions (EARs) in the Solar Dynamics Observatory Helioseismic Emerging Active Region survey. We used line-of-sight magnetic field measurements averaged over 6 h to define the polarities and measure the tilt angle up to four days after emergence.
Results: We find that at the time of emergence the polarities are on average aligned east-west, and that neither the separation nor the tilt depends on latitude. We do find, however, that EARs at higher latitudes have a faster north-south separation speed than those closer to the equator at the emergence time. After emergence, the tilt angle increases and Joy's law is evident about two days later. The scatter in the tilt angle is independent of flux until about one day after emergence, when we find that higher-flux regions have a smaller scatter in tilt angle than lower-flux regions.
Conclusions: Our finding that active regions emerge with an east-west alignment is consistent with earlier observations, but is still surprising since thin flux tube models predict that tilt angles of rising flux tubes are generated below the surface. Previously reported tilt angle relaxation of deeply anchored flux tubes can be largely explained by the change in east-west separation. We conclude that Joy's law is caused by an inherent north-south separation speed present when the flux first reaches the surface, and that the scatter in the tilt angle is consistent with buffeting of the polarities by supergranulation. Title: Radiative MHD Simulations of Starspots Authors: Panja, M.; Cameron, R.; Solanki, S. Bibcode: 2020SPD....5121117P Altcode: We have performed the first-ever, realistic 3D simulations of the photospheric structure of complete starspots, including their penumbrae, for a range of cool main-sequence stars, namely the spectral types M0V, K0V, and G2V. We used the MHD code MURaM which includes radiative energy transfer and the effects of partial ionization. We explore several fundamental properties like umbral intensity contrast, temperature, and magnetic field strength as functions of spectral type. Our simulations show that there is an increase in spot contrast with the increase in stellar surface temperature, which is consistent with observations. The umbral field strength is determined by the depth at which the optical surface forms and the surface pressures of the host stars. We will present our results and discuss the physics behind them. Title: Reply to the comment of T. Metcalfe and J. van Saders on the Science report "The Sun is less active than other solar-like stars" Authors: Reinhold, T.; Shapiro, A. I.; Solanki, S. K.; Montet, B. T.; Krivova, N. A.; Cameron, R. H.; Amazo-Gómez, E. M. Bibcode: 2020arXiv200704817R Altcode: This is our reply to the comment of T. Metcalfe and J. van Saders on the Science report "The Sun is less active than other solar-like stars" by T. Reinhold, A. I. Shapiro, S. K. Solanki, B. T. Montet, N. A. Krivova, R. H. Cameron, E. M. Amazo-Gomez. We hope that both the comment and our reply lead to fruitful discussions which of the two presented scenarios is more likely. Title: Meridional flow in the Sun’s convection zone is a single cell in each hemisphere Authors: Gizon, Laurent; Cameron, Robert H.; Pourabdian, Majid; Liang, Zhi-Chao; Fournier, Damien; Birch, Aaron C.; Hanson, Chris S. Bibcode: 2020Sci...368.1469G Altcode: The Sun’s magnetic field is generated by subsurface motions of the convecting plasma. The latitude at which the magnetic field emerges through the solar surface (as sunspots) drifts toward the equator over the course of the 11-year solar cycle. We use helioseismology to infer the meridional flow (in the latitudinal and radial directions) over two solar cycles covering 1996-2019. Two data sources are used, which agree during their overlap period of 2001-2011. The time-averaged meridional flow is shown to be a single cell in each hemisphere, carrying plasma toward the equator at the base of the convection zone with a speed of ~4 meters per second at 45° latitude. Our results support the flux-transport dynamo model, which explains the drift of sunspot-emergence latitudes through the meridional flow. Title: Simulations Show that Vortex Flows Could Heat the Chromosphere in Solar Plage Authors: Yadav, Nitin; Cameron, R. H.; Solanki, S. K. Bibcode: 2020ApJ...894L..17Y Altcode: 2020arXiv200413996Y The relationship between vortex flows at different spatial scales and their contribution to the energy balance in the chromosphere is not yet fully understood. We perform three-dimensional (3D) radiation-magnetohydrodynamic simulations of a unipolar solar plage region at a spatial resolution of 10 km using the MURaM code. We use the swirling-strength criterion that mainly detects the smallest vortices present in the simulation data. We additionally degrade our simulation data to smooth out the smaller vortices, so that also the vortices at larger spatial scales can be detected. Vortex flows at various spatial scales are found in our simulation data for different effective spatial resolutions. We conclude that the observed large vortices are likely clusters of much smaller ones that are not yet resolved by observations. We show that the vertical Poynting flux decreases rapidly with reduced effective spatial resolutions and is predominantly carried by the horizontal plasma motions rather than vertical flows. Since the small-scale horizontal motions or the smaller vortices carry most of the energy, the energy transported by vortices deduced from low-resolution data is grossly underestimated. In full-resolution simulation data, the Poynting flux contribution due to vortices is more than adequate to compensate for the radiative losses in plage, indicating their importance for chromospheric heating. Title: Rossby modes in slowly rotating stars: depth dependence in distorted polytropes with uniform rotation Authors: Damiani, C.; Cameron, R. H.; Birch, A. C.; Gizon, L. Bibcode: 2020A&A...637A..65D Altcode: 2020arXiv200305276D Context. Large-scale Rossby waves have recently been discovered based on measurements of horizontal surface and near-surface solar flows.
Aims: We are interested in understanding why it is only equatorial modes that are observed and in modelling the radial structure of the observed modes. To this aim, we have characterised the radial eigenfunctions of r modes for slowly rotating polytropes in uniform rotation.
Methods: We followed Provost et al. (1981, A&A, 94, 126) and considered a linear perturbation theory to describe quasi-toroidal stellar adiabatic oscillations in the inviscid case. We used perturbation theory to write the solutions to the fourth order in the rotational frequency of the star. We numerically solved the eigenvalue problem, concentrating on the type of behaviour exhibited where the stratification is nearly adiabatic.
Results: We find that for free-surface boundary conditions on a spheroid of non-vanishing surface density, r modes can only exist for ℓ = m spherical harmonics in the inviscid case and we compute their depth dependence and frequencies to leading order. For quasi-adiabatic stratification, the sectoral modes with no radial nodes are the only modes which are almost toroidal and the depth dependence of the corresponding horizontal motion scales as rm. For all r modes, except the zero radial order sectoral ones, non-adiabatic stratification plays a crucial role in the radial force balance.
Conclusions: The lack of quasi-toroidal solutions when stratification is close to neutral, except for the sectoral modes without nodes in radius, follows from the need for both horizontal and radial force balance. In the absence of super- or sub-adiabatic stratification and viscosity, both the horizontal and radial parts of the force balance independently determine the pressure perturbation. The only quasi-toroidal cases in which these constraints on the pressure perturbation are consistent are the special cases where ℓ = m and the horizontal displacement scales with rm. Title: Towards a more reliable reconstruction of the historical solar variability: a more realistic description of solar ephemeral magnetic regions Authors: Hofer, Bernhard; Krivova, Natalie A.; Wu, Chi-Ju; Usoskin, Ilya A.; Cameron, Robert Bibcode: 2020EGUGA..2217086H Altcode: Solar irradiance is a crucial input to climate models, but its measurements are only available since 1978. The variability of solar irradiance on climate-relevant time-scales is caused by the competition between bright and dark features formed by the magnetic fields emerging on the solar surface. Thus, models have been developed that reconstruct past irradiance variability from proxies of the solar magnetic activity. The longest direct proxy is the sunspot number. The common problem of such reconstructions is, however, that while sunspots adequately describe the evolution of the active regions (ARs) (large bipolar regions hosting sunspots), the evolution of their smaller counterparts, the ephemeral regions (ERs), is not directly featured by sunspots. At the same time, these small regions are much more numerous and are believed to be the main source of the long-term irradiance changes, which are of special interest to climate models. We develop an improved description of the ephemeral region emergence taking different solar observational constraints into account. The model builds on the SATIRE-T model, in which the emergence of ARs is described by the sunspot number and the emergence of the ERs is linearly linked to that of ARs. The latter, however, implies that whenever the sunspot number drops to zero, no magnetic field emerges in the model. In the new model, the emergence of the ERs is no longer linked to sunspots linearly. Instead, ARs and ERs are considered to be parts of a single power-law size distribution of the emerging magnetic regions. This ensures that even in the absence of ARs (e.g., during the grand minima of solar activity), the emergence rate of ERs remains non-zero. In particular, the solar open magnetic flux reconstructed using this approach does not drop to zero during the Maunder minimum, in agreement with independent reconstructions from the cosmogenic isotope data. Such an improved description of the ERs will allow a better constraint on the maximum solar irradiance drop during grand minima events. This, in turn, will allow a better constraint on the potential solar forcing in the future. Title: The Sun is less active than other solar-like stars Authors: Reinhold, Timo; Shapiro, Alexander I.; Solanki, Sami K.; Montet, Benjamin T.; Krivova, Natalie A.; Cameron, Robert H.; Amazo-Gómez, Eliana M. Bibcode: 2020Sci...368..518R Altcode: 2020arXiv200501401R The magnetic activity of the Sun and other stars causes their brightness to vary. We investigated how typical the Sun’s variability is compared with other solar-like stars, i.e., those with near-solar effective temperatures and rotation periods. By combining 4 years of photometric observations from the Kepler space telescope with astrometric data from the Gaia spacecraft, we were able to measure photometric variabilities of 369 solar-like stars. Most of those with well-determined rotation periods showed higher variability than the Sun and are therefore considerably more active. These stars appear nearly identical to the Sun except for their higher variability. Therefore, we speculate that the Sun could potentially also go through epochs of such high variability. Title: Power spectra of solar brightness variations at various inclinations Authors: Nèmec, N. -E.; Shapiro, A. I.; Krivova, N. A.; Solanki, S. K.; Tagirov, R. V.; Cameron, R. H.; Dreizler, S. Bibcode: 2020A&A...636A..43N Altcode: 2020arXiv200210895N Context. Magnetic features on the surfaces of cool stars lead to variations in their brightness. Such variations on the surface of the Sun have been studied extensively. Recent planet-hunting space telescopes have made it possible to measure brightness variations in hundred thousands of other stars. The new data may undermine the validity of setting the sun as a typical example of a variable star. Putting solar variability into the stellar context suffers, however, from a bias resulting from solar observations being carried out from its near-equatorial plane, whereas stars are generally observed at all possible inclinations.
Aims: We model solar brightness variations at timescales from days to years as they would be observed at different inclinations. In particular, we consider the effect of the inclination on the power spectrum of solar brightness variations. The variations are calculated in several passbands that are routinely used for stellar measurements.
Methods: We employ the surface flux transport model to simulate the time-dependent spatial distribution of magnetic features on both the near and far sides of the Sun. This distribution is then used to calculate solar brightness variations following the Spectral And Total Irradiance REconstruction approach.
Results: We have quantified the effect of the inclination on solar brightness variability at timescales down to a single day. Thus, our results allow for solar brightness records to be made directly comparable to those obtained by planet-hunting space telescopes. Furthermore, we decompose solar brightness variations into components originating from the solar rotation and from the evolution of magnetic features. Title: 3D Radiative MHD Simulations of Starspots Authors: Panja, Mayukh; Cameron, Robert; Solanki, Sami K. Bibcode: 2020ApJ...893..113P Altcode: 2020arXiv200309656P There are no direct spatially resolved observations of spots on stars other than the Sun, and starspot properties are inferred indirectly through lightcurves and spectropolarimetric data. We present the first self-consistent 3D radiative MHD computations of starspots on G2V, K0V, and M0V stars, which will help us to better understand observations of activity, variability, and magnetic fields in late-type main-sequence stars. We used the MURaM code, which has been extensively used to compute "realistic" sunspots, for our simulations. We aim to study how fundamental starspot properties such as intensity contrast, temperature, and magnetic field strength vary with spectral type. We first simulated in 2D multiple spots of each spectral type to find out appropriate initial conditions for our 3D runs. We find that with increasing stellar effective temperature, there is an increase in the temperature difference between the umbra of the spot and its surrounding photosphere, from 350 K on the M0V star to 1400 K on the G2V star. This trend in our simulated starspots is consistent with observations. The magnetic field strengths of all the starspot umbrae are in the 3-4.5 kG range. The G2V and K0V umbrae have comparable magnetic field strengths around 3.5 kG, while the M0V umbra has a relatively higher field strength around 4 kG. We discuss the physical reasons behind both these trends. All of the three starspots develop penumbral filament-like structures with Evershed flows. The average Evershed flow speed drops from 1.32 km s-1 in the G2V penumbra to 0.6 km s-1 in the M0V penumbra. Title: Loss of toroidal magnetic flux by emergence of bipolar magnetic regions Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2020A&A...636A...7C Altcode: 2020arXiv200205436C The polarity of the toroidal magnetic field in the solar convection zone periodically reverses in the course of the 11/22-year solar cycle. Among the various processes that contribute to the removal of "old-polarity" toroidal magnetic flux is the emergence of flux loops forming bipolar regions at the solar surface. We quantify the loss of subsurface net toroidal flux by this process. To this end, we determine the contribution of an individual emerging bipolar loop and show that it is unaffected by surface flux transport after emergence. Together with the linearity of the diffusion process this means that the total flux loss can be obtained by adding the contributions of all emerging bipolar magnetic regions. The resulting total loss rate of net toroidal flux amounts to 1.3 × 1015 Mx s-1 during activity maxima and 6.1 × 1014 Mx s-1 during activity minima, to which ephemeral regions contribute about 90 and 97%, respectively. This rate is consistent with the observationally inferred loss rate of toroidal flux into interplanetary space and corresponds to a decay time of the subsurface toroidal flux of about 12 years, also consistent with a simple estimate based on turbulent diffusivity. Consequently, toroidal flux loss by flux emergence is a relevant contribution to the budget of net toroidal flux in the solar convection zone. The consistency between the toroidal flux loss rate due to flux emergence and what is expected from turbulent diffusion, and the similarity between the corresponding decay time and the length of the solar cycle are important constraints for understanding the solar cycle and the Sun's internal dynamics. Title: The relationship between flux emergence and subsurface toroidal magnetic flux Authors: Cameron, R. H.; Jiang, J. Bibcode: 2019A&A...631A..27C Altcode: 2019arXiv190906828C
Aims: The 1D mean-field equation describing the evolution of the subsurface toroidal field can be used with the observed surface radial field to model the subsurface toroidal flux density. Our aim is to test this model and determine the relationship between the observationally inferred surface toroidal field (as a proxy for flux emergence), and the modelled subsurface toroidal flux density.
Methods: We used a combination of sunspot area observations and the surface toroidal field inferred from Wilcox Solar Observatory (WSO) line-of-sight magnetic field observations. We then compared them with the results of a 1D mean-field evolution equation for the subsurface toroidal field, driven by the observed radial field from the National Solar Observatory/Kitt Peak and SOLIS observations.
Results: We derive calibration curves relating the subsurface toroidal flux density to the observed surface toroidal field strengths and sunspot areas. The calibration curves are for two regimes, one corresponding to ephemeral region emergence outside of the butterfly wings, the other to active region emergence in the butterfly wings. We discuss this in terms of the size and vertical velocity associated with the two types of flux emergence. Title: Monte Carlo studies for the optimisation of the Cherenkov Telescope Array layout Authors: Acharyya, A.; Agudo, I.; Angüner, E. O.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista, R.; Amans, J. -P.; Amati, L.; Amato, E.; Ambrosi, G.; Antonelli, L. A.; Aramo, C.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Asano, K.; Ashkar, H.; Balazs, C.; Balbo, M.; Balmaverde, B.; Barai, P.; Barbano, A.; Barkov, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Becerra González, J.; Becker Tjus, J.; Bellizzi, L.; Benbow, W.; Bernardini, E.; Bernardos, M. I.; Bernlöhr, K.; Berti, A.; Berton, M.; Bertucci, B.; Beshley, V.; Biasuzzi, B.; Bigongiari, C.; Bird, R.; Bissaldi, E.; Biteau, J.; Blanch, O.; Blazek, J.; Boisson, C.; Bonanno, G.; Bonardi, A.; Bonavolontá, C.; Bonnoli, G.; Bordas, P.; Böttcher, M.; Bregeon, J.; Brill, A.; Brown, A. M.; Brügge, K.; Brun, P.; Bruno, P.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Cameron, R.; Canestrari, R.; Capalbi, M.; Caproni, A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Caroff, S.; Carosi, R.; Casanova, S.; Cascone, E.; Cassol, F.; Catalani, F.; Catalano, O.; Cauz, D.; Cerruti, M.; Chaty, S.; Chen, A.; Chernyakova, M.; Chiaro, G.; Cieślar, M.; Colak, S. M.; Conforti, V.; Congiu, E.; Contreras, J. L.; Cortina, J.; Costa, A.; Costantini, H.; Cotter, G.; Cristofari, P.; Cumani, P.; Cusumano, G.; D'Aí, A.; D'Ammando, F.; Dangeon, L.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caprio, V.; de Cássia dos Anjos, R.; De Frondat, F.; de Gouveia Dal Pino, E. M.; De Lotto, B.; De Martino, D.; de Naurois, M.; de Oña Wilhelmi, E.; de Palma, F.; de Souza, V.; Del Santo, M.; Delgado, C.; della Volpe, D.; Di Girolamo, T.; Di Pierro, F.; Di Venere, L.; Díaz, C.; Diebold, S.; Djannati-Ataï, A.; Dmytriiev, A.; Dominis Prester, D.; Donini, A.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Ebr, J.; Ekoume, T. R. N.; Elsässer, D.; Emery, G.; Falceta-Goncalves, D.; Fedorova, E.; Fegan, S.; Feng, Q.; Ferrand, G.; Fiandrini, E.; Fiasson, A.; Filipovic, M.; Fioretti, V.; Fiori, M.; Flis, S.; Fonseca, M. V.; Fontaine, G.; Freixas Coromina, L.; Fukami, S.; Fukui, Y.; Funk, S.; Füßling, M.; Gaggero, D.; Galanti, G.; Garcia López, R. J.; Garczarczyk, M.; Gascon, D.; Gasparetto, T.; Gaug, M.; Ghalumyan, A.; Gianotti, F.; Giavitto, G.; Giglietto, N.; Giordano, F.; Giroletti, M.; Gironnet, J.; Glicenstein, J. -F.; Gnatyk, R.; Goldoni, P.; González, J. M.; González, M. M.; Gourgouliatos, K. N.; Grabarczyk, T.; Granot, J.; Green, D.; Greenshaw, T.; Grondin, M. -H.; Gueta, O.; Hadasch, D.; Hassan, T.; Hayashida, M.; Heller, M.; Hervet, O.; Hinton, J.; Hiroshima, N.; Hnatyk, B.; Hofmann, W.; Horvath, P.; Hrabovsky, M.; Hrupec, D.; Humensky, T. B.; Hütten, M.; Inada, T.; Iocco, F.; Ionica, M.; Iori, M.; Iwamura, Y.; Jamrozy, M.; Janecek, P.; Jankowsky, D.; Jean, P.; Jouvin, L.; Jurysek, J.; Kaaret, P.; Kadowaki, L. H. S.; Karkar, S.; Kerszberg, D.; Khélifi, B.; Kieda, D.; Kimeswenger, S.; Kluźniak, W.; Knapp, J.; Knödlseder, J.; Kobayashi, Y.; Koch, B.; Kocot, J.; Komin, N.; Kong, A.; Kowal, G.; Krause, M.; Kubo, H.; Kushida, J.; Kushwaha, P.; La Parola, V.; La Rosa, G.; Lallena Arquillo, M.; Lang, R. G.; Lapington, J.; Le Blanc, O.; Lefaucheur, J.; Leigui de Oliveira, M. A.; Lemoine-Goumard, M.; Lenain, J. -P.; Leto, G.; Lico, R.; Lindfors, E.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez, A.; López, M.; Lopez-Oramas, A.; López-Coto, R.; Loporchio, S.; Luque-Escamilla, P. L.; Lyard, E.; Maccarone, M. C.; Mach, E.; Maggio, C.; Majumdar, P.; Malaguti, G.; Mallamaci, M.; Mandat, D.; Maneva, G.; Manganaro, M.; Mangano, S.; Marculewicz, M.; Mariotti, M.; Martí, J.; Martínez, M.; Martínez, G.; Martínez-Huerta, H.; Masuda, S.; Maxted, N.; Mazin, D.; Meunier, J. -L.; Meyer, M.; Micanovic, S.; Millul, R.; Minaya, I. A.; Mitchell, A.; Mizuno, T.; Moderski, R.; Mohrmann, L.; Montaruli, T.; Moralejo, A.; Morcuende, D.; Morlino, G.; Morselli, A.; Moulin, E.; Mukherjee, R.; Munar, P.; Mundell, C.; Murach, T.; Nagai, A.; Nagayoshi, T.; Naito, T.; Nakamori, T.; Nemmen, R.; Niemiec, J.; Nieto, D.; Nievas Rosillo, M.; Nikołajuk, M.; Ninci, D.; Nishijima, K.; Noda, K.; Nosek, D.; Nöthe, M.; Nozaki, S.; Ohishi, M.; Ohtani, Y.; Okumura, A.; Ong, R. A.; Orienti, M.; Orito, R.; Ostrowski, M.; Otte, N.; Ou, Z.; Oya, I.; Pagliaro, A.; Palatiello, M.; Palatka, M.; Paoletti, R.; Paredes, J. M.; Pareschi, G.; Parmiggiani, N.; Parsons, R. D.; Patricelli, B.; Pe'er, A.; Pech, M.; Peñil Del Campo, P.; Pérez-Romero, J.; Perri, M.; Persic, M.; Petrucci, P. -O.; Petruk, O.; Pfrang, K.; Piel, Q.; Pietropaolo, E.; Pohl, M.; Polo, M.; Poutanen, J.; Prandini, E.; Produit, N.; Prokoph, H.; Prouza, M.; Przybilski, H.; Pühlhofer, G.; Punch, M.; Queiroz, F.; Quirrenbach, A.; Rainò, S.; Rando, R.; Razzaque, S.; Reimer, O.; Renault-Tinacci, N.; Renier, Y.; Ribeiro, D.; Ribó, M.; Rico, J.; Rieger, F.; Rizi, V.; Rodriguez Fernandez, G.; Rodriguez-Ramirez, J. C.; Rodrí-guez Vázquez, J. J.; Romano, P.; Romeo, G.; Roncadelli, M.; Rosado, J.; Rowell, G.; Rudak, B.; Rugliancich, A.; Rulten, C.; Sadeh, I.; Saha, L.; Saito, T.; Sakurai, S.; Salesa Greus, F.; Sangiorgi, P.; Sano, H.; Santander, M.; Santangelo, A.; Santos-Lima, R.; Sanuy, A.; Satalecka, K.; Saturni, F. G.; Sawangwit, U.; Schlenstedt, S.; Schovanek, P.; Schussler, F.; Schwanke, U.; Sciacca, E.; Scuderi, S.; Sedlaczek, K.; Seglar-Arroyo, M.; Sergijenko, O.; Seweryn, K.; Shalchi, A.; Shellard, R. C.; Siejkowski, H.; Sillanpää, A.; Sinha, A.; Sironi, G.; Sliusar, V.; Slowikowska, A.; Sol, H.; Specovius, A.; Spencer, S.; Spengler, G.; Stamerra, A.; Stanič, S.; Stawarz, Ł.; Stefanik, S.; Stolarczyk, T.; Straumann, U.; Suomijarvi, T.; Świerk, P.; Szepieniec, T.; Tagliaferri, G.; Tajima, H.; Tam, T.; Tavecchio, F.; Taylor, L.; Tejedor, L. A.; Temnikov, P.; Terzic, T.; Testa, V.; Tibaldo, L.; Todero Peixoto, C. J.; Tokanai, F.; Tomankova, L.; Tonev, D.; Torres, D. F.; Tosti, G.; Tosti, L.; Tothill, N.; Toussenel, F.; Tovmassian, G.; Travnicek, P.; Trichard, C.; Umana, G.; Vagelli, V.; Valentino, M.; Vallage, B.; Vallania, P.; Valore, L.; Vandenbroucke, J.; Varner, G. S.; Vasileiadis, G.; Vassiliev, V.; Vázquez Acosta, M.; Vecchi, M.; Vercellone, S.; Vergani, S.; Vettolani, G. P.; Viana, A.; Vigorito, C. F.; Vink, J.; Vitale, V.; Voelk, H.; Vollhardt, A.; Vorobiov, S.; Wagner, S. J.; Walter, R.; Werner, F.; White, R.; Wierzcholska, A.; Will, M.; Williams, D. A.; Wischnewski, R.; Yang, L.; Yoshida, T.; Yoshikoshi, T.; Zacharias, M.; Zampieri, L.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.; Zechlin, H.; Zenin, A.; Zhdanov, V. I.; Zimmer, S.; Zorn, J. Bibcode: 2019APh...111...35A Altcode: 2019arXiv190401426A The Cherenkov Telescope Array (CTA) is the major next-generation observatory for ground-based very-high-energy gamma-ray astronomy. It will improve the sensitivity of current ground-based instruments by a factor of five to twenty, depending on the energy, greatly improving both their angular and energy resolutions over four decades in energy (from 20 GeV to 300 TeV). This achievement will be possible by using tens of imaging Cherenkov telescopes of three successive sizes. They will be arranged into two arrays, one per hemisphere, located on the La Palma island (Spain) and in Paranal (Chile). We present here the optimised and final telescope arrays for both CTA sites, as well as their foreseen performance, resulting from the analysis of three different large-scale Monte Carlo productions. Title: Solar activity: periodicities beyond 11 years are consistent with random forcing Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2019A&A...625A..28C Altcode: Power spectra of solar activity based on historical records of sunspot numbers and on cosmogenic isotopes show peaks with enhanced power apart from the dominant 11-year solar cycle, such as the 90-year Gleissberg cycle or the 210-year de Vries cycle. In a previous paper we have shown that the overall shape of the power spectrum is well represented by the results of the generic normal form model for a noisy and weakly nonlinear limit cycle, with parameters all determined by observations. Using this model as a null case, we show here that all local peaks with enhanced power, apart from the 11-year band, are consistent with realization noise. Even a 3σ peak is expected to occur with a probability of about 0.25 at least once among the 216 period bins resolved by the cosmogenic isotope data. This casts doubt upon interpretations of such peaks in terms of intrinsic periodicities of the solar dynamo process. Title: Average motion of emerging solar active region polarities. I. Two phases of emergence Authors: Schunker, H.; Birch, A. C.; Cameron, R. H.; Braun, D. C.; Gizon, L.; Burston, R. B. Bibcode: 2019A&A...625A..53S Altcode: 2019arXiv190311839S
Aims: Our goal is to constrain models of active region formation by tracking the average motion of active region polarity pairs as they emerge onto the surface.
Methods: We measured the motion of the two main opposite polarities in 153 emerging active regions using line-of-sight magnetic field observations from the Solar Dynamics Observatory Helioseismic Emerging Active Region (SDO/HEAR) survey. We first measured the position of each of the polarities eight hours after emergence, when they could be clearly identified, using a feature recognition method. We then tracked their location forwards and backwards in time.
Results: We find that, on average, the polarities emerge with an east-west orientation and the separation speed between the polarities increases. At about 0.1 days after emergence, the average separation speed reaches a peak value of 229 ± 11 ms-1, and then starts to decrease. About 2.5 days after emergence the polarities stop separating. We also find that the separation and the separation speed in the east-west direction are systematically larger for active regions that have higher flux. The scatter in the location of the polarities increases from about 5 Mm at the time of emergence to about 15 Mm at two days after emergence.
Conclusions: Our results reveal two phases of the emergence process defined by the rate of change of the separation speed as the polarities move apart. Phase 1 begins when the opposite polarity pairs first appear at the surface, with an east-west alignment and an increasing separation speed. We define Phase 2 to begin when the separation speed starts to decrease, and ends when the polarities have stopped separating. This is consistent with a previous study: the peak of a flux tube breaks through the surface during Phase 1. During Phase 2 the magnetic field lines are straightened by magnetic tension, so that the polarities continue to move apart, until they eventually lie directly above their anchored subsurface footpoints. The scatter in the location of the polarities is consistent with the length and timescales of supergranulation, supporting the idea that convection buffets the polarities as they separate. Title: Solar activity: intrinsic periodicities beyond 11 years Authors: Cameron, Robert; Schuessler, Manfred Bibcode: 2019arXiv190305398C Altcode: Power spectra of solar activity based on historical records of sunspot numbers and on cosmogenic isotopes show peaks with enhanced power apart from the dominant 11-year solar cycle, such as the 90-year Gleissberg cycle or the 210-year de Vries cycle. In a previous paper we have shown that the overall shape of the power spectrum is well represented by the results of the generic normal form model for a noisy and weakly nonlinear limit cycle, with parameters all determined by observations. Using this model as a null case, we show here that all local peaks with enhanced power, apart from the 11-year band, are consistent with realisation noise. Even a $3\sigma$ peak is expected to occur with a probability of about 0.25 at least once among the 216 period bins resolved by the cosmogenic isotope data. This casts doubt upon interpretations of such peaks in terms of intrinsic periodicities of the solar dynamo process. Title: Starspot rotation rates versus activity cycle phase: Butterfly diagrams of Kepler stars are unlike that of the Sun Authors: Nielsen, M. B.; Gizon, L.; Cameron, R. H.; Miesch, M. Bibcode: 2019A&A...622A..85N Altcode: 2018arXiv181206414N Context. During the solar magnetic activity cycle the emergence latitudes of sunspots change, leading to the well-known butterfly diagram. This phenomenon is poorly understood for other stars since starspot latitudes are generally unknown. The related changes in starspot rotation rates caused by latitudinal differential rotation can, however, be measured.
Aims: Using the set of 3093 Kepler stars with measured activity cycles, we aim to study the temporal change in starspot rotation rates over magnetic activity cycles, and how this relates to the activity level, the mean rotation rate of the star, and its effective temperature.
Methods: We measured the photometric variability as a proxy for the magnetic activity and the spot rotation rate in each quarter over the duration of the Kepler mission. We phase-folded these measurements with the cycle period. To reduce random errors, we performed averages over stars with comparable mean rotation rates and effective temperature at fixed activity-cycle phases.
Results: We detect a clear correlation between the variation of activity level and the variation of the starspot rotation rate. The sign and amplitude of this correlation depends on the mean stellar rotation and - to a lesser extent - on the effective temperature. For slowly rotating stars (rotation periods between 15 - 28 days), the starspot rotation rates are clearly anti-correlated with the level of activity during the activity cycles. A transition is observed around rotation periods of 10 - 15 days, where stars with an effective temperature above 4200 K instead show positive correlation.
Conclusions: Our measurements can be interpreted in terms of a stellar "butterfly diagram", but these appear different from that of the Sun since the starspot rotation rates are either in phase or anti-phase with the activity level. Alternatively, the activity cycle periods observed by Kepler are short (around 2.5 years) and may therefore be secondary cycles, perhaps analogous to the solar quasi-biennial oscillations.

Rotation and activity tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A85 Title: The solar dynamo: Inferences from observations Authors: Cameron, Robert Bibcode: 2018csc..confE...4C Altcode: We will show that the observed large-scale structure of the poloidal and toroidal magnetic fields, together with the differential rotation and surface meridional flow argue strongly in favour of a Babcock-Leighton dynamo. The cycle-to-cycle variability is consistent with the idea that flux emergence takes place in a turbulent environment, and we will discuss some of the implications of this in the context of the model. Title: Statistical constraints on active region emergence from the surface motion of the polarities Authors: Schunker, Hannah; Birch, Aaron; Cameron, Robert; Braun, Doug; Gizon, Laurent Bibcode: 2018csc..confE..45S Altcode: We measured the motion of the two main opposite polarities in 154 emerging active regions using line-of-sight magnetograms from SDO/HMI. Our results reveal two phases of the emergence process defined by the rate of change of the separation speed as the polarities move apart. Phase one begins when the opposite polarity pairs first appear at the surface, with an east-west alignment and an increasing separation speed of 1.6 +/- 0.4 km/s. Phase two begins when the separation speed starts to decrease, about 0.1 days after emergence, and ends about 2.5 days after emergence when the polarities have stopped separating. This is consistent with the picture of Chen, Rempel, & Fan (2017): during phase one, the peak of a flux tube breaks through the surface and then, during phase two, the magnetic field lines are straightened by magnetic tension to eventually lie directly above their subsurface footpoints. The scatter in the location of the polarities is consistent with the length and time scales of supergranulation, supporting the idea that convection buffets the polarities as they separate. On average, the polarities emerge with an east-west orientation with the tilt angle developing over time independent of flux, in contrast to predictions from thin flux tube theory. Title: VizieR Online Data Catalog: Starspot rotation rates vs. activity cycle phase (Nielsen+, 2019) Authors: Nielsen, M. B.; Gizon, L.; Cameron, R. H.; Miesch, M. Bibcode: 2018yCat..36220085N Altcode: Activity cycle parameters for 3093 stars observed by Kepler, with measured cycle periods from Reinhold et al. (2017A&A...603A..52R, Cat. J/A+A/603/A52). The integral, A, of the power density spectrum around the mean rotation rate (nurot, from McQuillan et al. (2014ApJS..211...24M, Cat. J/ApJS/211/24)) is used as proxy for magnetic activity. This and the rotation rate, nu, are traced from quarters Q1 to Q17 of Kepler observations.

(1 data file). Title: Origin of the hemispheric asymmetry of solar activity Authors: Schüssler, M.; Cameron, R. H. Bibcode: 2018A&A...618A..89S Altcode: 2018arXiv180710061S The frequency spectrum of the hemispheric asymmetry of solar activity shows enhanced power for the period ranges around 8.5 years and between 30 and 50 years. This can be understood as the sum and beat periods of the superposition of two dynamo modes: a dipolar mode with a (magnetic) period of about 22 years and a quadrupolar mode with a period between 13 and 15 years. An updated Babcock-Leighton-type dynamo model with weak driving as indicated by stellar observations shows an excited dipole mode and a damped quadrupole mode in the correct range of periods. Random excitation of the quadrupole by stochastic fluctuations of the source term for the poloidal field leads to a time evolution of activity and asymmetry that is consistent with the observational results. Title: Chromospheric activity catalogue of 4454 cool stars. Questioning the active branch of stellar activity cycles Authors: Boro Saikia, S.; Marvin, C. J.; Jeffers, S. V.; Reiners, A.; Cameron, R.; Marsden, S. C.; Petit, P.; Warnecke, J.; Yadav, A. P. Bibcode: 2018A&A...616A.108B Altcode: 2018A&A...616A.108S; 2018arXiv180311123B Context. Chromospheric activity monitoring of a wide range of cool stars can provide valuable information on stellar magnetic activity and its dependence on fundamental stellar parameters such as effective temperature and rotation.
Aims: We compile a chromospheric activity catalogue of 4454 cool stars from a combination of archival HARPS spectra and multiple other surveys, including the Mount Wilson data that have recently been released by the NSO. We explore the variation in chromospheric activity of cool stars along the main sequence for stars with different effective temperatures. Additionally, we also perform an activity-cycle period search and investigate its relation with rotation.
Methods: The chromospheric activity index, S-index, was measured for 304 main-sequence stars from archived high-resolution HARPS spectra. Additionally, the measured and archived S-indices were converted into the chromospheric flux ratio log RHK'. The activity-cycle periods were determined using the generalised Lomb-Scargle periodogram to study the active and inactive branches on the rotation - activity-cycle period plane.
Results: The global sample shows that the bimodality of chromospheric activity, known as the Vaughan-Preston gap, is not prominent, with a significant percentage of the stars at an intermediate-activity level around R'HK = -4.75. Independently, the cycle period search shows that stars can lie in the region intermediate between the active and inactive branch, which means that the active branch is not as clearly distinct as previously thought.
Conclusions: The weakening of the Vaughan-Preston gap indicates that cool stars spin down from a higher activity level and settle at a lower activity level without a sudden break at intermediate activity. Some cycle periods are close to the solar value between the active and inactive branch, which suggests that the solar dynamo is most likely a common case of the stellar dynamo.

Full Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/616/A108 Title: VizieR Online Data Catalog: Cool stars chromospheric activity catalog (Boro Saikia+, 2018) Authors: Boro Saikia, S.; Marvin, C. J.; Jeffers, S. V.; Reiners, A.; Cameron, R.; Marsden, S. C.; Petit, P.; Warnecke, J.; Yadav, A. P. Bibcode: 2018yCat..36160108B Altcode: We tabulate chromospheric activity of cool stars determined from CaII H and K lines. The catalogue is created by combining archival HARPS spectra (Lovis et al. 2011, Cat. J/A+A/528/112, Bonfils et al. 2013A&A...549A.109B) and multiple other surveys (Baliunas et al. 1995ApJ...438..269B, Duncan et al. 1991ApJS...76..383D, Cat. III/159, Arriagada et al. 2012, Cat. J/ApJS/200/15, Henry et al. 1996, Cat. J/AJ/111/439, Gray et al. 2006, Cat. J/AJ/132/161, Hall et al. 2009, Cat. J/AJ/138/312, Wright et al. 2004, Cat. J/ApJS/152/261, Issacson & Fischer 2010, Cat. J/ApJ/725/875). The stellar properties are taken from HIPPARCOS (Cat. I/239).

(1 data file). Title: Observing and modeling the poloidal and toroidal fields of the solar dynamo Authors: Cameron, R. H.; Duvall, T. L.; Schüssler, M.; Schunker, H. Bibcode: 2018A&A...609A..56C Altcode: 2017arXiv171007126C Context. The solar dynamo consists of a process that converts poloidal magnetic field to toroidal magnetic field followed by a process that creates new poloidal field from the toroidal field.
Aims: Our aim is to observe the poloidal and toroidal fields relevant to the global solar dynamo and to see if their evolution is captured by a Babcock-Leighton dynamo.
Methods: We used synoptic maps of the surface radial field from the KPNSO/VT and SOLIS observatories, to construct the poloidal field as a function of time and latitude; we also used full disk images from Wilcox Solar Observatory and SOHO/MDI to infer the longitudinally averaged surface azimuthal field. We show that the latter is consistent with an estimate of the longitudinally averaged surface azimuthal field due to flux emergence and therefore is closely related to the subsurface toroidal field.
Results: We present maps of the poloidal and toroidal magnetic fields of the global solar dynamo. The longitude-averaged azimuthal field observed at the surface results from flux emergence. At high latitudes this component follows the radial component of the polar fields with a short time lag of between 1-3 years. The lag increases at lower latitudes. The observed evolution of the poloidal and toroidal magnetic fields is described by the (updated) Babcock-Leighton dynamo model. Title: The Global Solar Dynamo Authors: Cameron, R. H.; Dikpati, M.; Brandenburg, A. Bibcode: 2018smf..book..367C Altcode: No abstract at ADS Title: The Fermi Large Area Telescope: 9 years of on-orbit performance Authors: Cameron, R.; Fermi Large Area Telescope Collaboration Bibcode: 2017ifs..confE.128C Altcode: 2017PoS...312E.128C No abstract at ADS Title: The Global Solar Dynamo Authors: Cameron, R. H.; Dikpati, M.; Brandenburg, A. Bibcode: 2017SSRv..210..367C Altcode: 2016arXiv160201754C; 2016SSRv..tmp....5C A brief summary of the various observations and constraints that underlie solar dynamo research are presented. The arguments that indicate that the solar dynamo is an alpha-omega dynamo of the Babcock-Leighton type are then shortly reviewed. The main open questions that remain are concerned with the subsurface dynamics, including why sunspots emerge at preferred latitudes as seen in the familiar butterfly wings, why the cycle is about 11 years long, and why the sunspot groups emerge tilted with respect to the equator (Joy's law). Next, we turn to magnetic helicity, whose conservation property has been identified with the decline of large-scale magnetic fields found in direct numerical simulations at large magnetic Reynolds numbers. However, magnetic helicity fluxes through the solar surface can alleviate this problem and connect theory with observations, as will be discussed. Title: Cherenkov Telescope Array Contributions to the 35th International Cosmic Ray Conference (ICRC2017) Authors: Acero, F.; Acharya, B. S.; Acín Portella, V.; Adams, C.; Agudo, I.; Aharonian, F.; Samarai, I. Al; Alberdi, A.; Alcubierre, M.; Alfaro, R.; Alfaro, J.; Alispach, C.; Aloisio, R.; Alves Batista, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.; Antonelli, L. A.; Antonuccio, V.; Antoranz, P.; Aramo, C.; Araya, M.; Arcaro, C.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Arrieta, M.; Asano, K.; Asano, A.; Ashley, M.; Aubert, P.; Singh, C. B.; Babic, A.; Backes, M.; Bajtlik, S.; Balazs, C.; Balbo, M.; Ballester, O.; Ballet, J.; Ballo, L.; Balzer, A.; Bamba, A.; Bandiera, R.; Barai, P.; Barbier, C.; Barcelo, M.; Barkov, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Bauer, C.; Becciani, U.; Becherini, Y.; Becker Tjus, J.; Bednarek, W.; Belfiore, A.; Benbow, W.; Benito, M.; Berge, D.; Bernardini, E.; Bernardini, M. G.; Bernardos, M.; Bernhard, S.; Bernlöhr, K.; Bertinelli Salucci, C.; Bertucci, B.; Besel, M. -A.; Beshley, V.; Bettane, J.; Bhatt, N.; Bhattacharyya, W.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Bilinsky, A.; Bird, R.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch, O.; Blasi, P.; Blazek, J.; Boccato, C.; Bockermann, C.; Boehm, C.; Bohacova, M.; Boisson, C.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Böttcher, M.; Boutonnet, C.; Bouyjou, F.; Bowman, L.; Bozhilov, V.; Braiding, C.; Brau-Nogué, S.; Bregeon, J.; Briggs, M.; Brill, A.; Brisken, W.; Bristow, D.; Britto, R.; Brocato, E.; Brown, A. M.; Brown, S.; Brügge, K.; Brun, P.; Brun, P.; Brun, F.; Brunetti, L.; Brunetti, G.; Bruno, P.; Bryan, M.; Buckley, J.; Bugaev, V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Caccianiga, A.; Cameron, R.; Canelli, F.; Canestrari, R.; Capalbi, M.; Capasso, M.; Capitanio, F.; Caproni, A.; Capuzzo-Dolcetta, R.; Caraveo, P.; Cárdenas, V.; Cardenzana, J.; Cardillo, M.; Carlile, C.; Caroff, S.; Carosi, R.; Carosi, A.; Carquín, E.; Carr, J.; Casandjian, J. -M.; Casanova, S.; Cascone, E.; Castro-Tirado, A. J.; Castroviejo Mora, J.; Catalani, F.; Catalano, O.; Cauz, D.; Celestino Silva, C.; Celli, S.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Chakraborty, N.; Champion, C.; Chatterjee, A.; Chaty, S.; Chaves, R.; Chen, A.; Chen, X.; Cheng, K.; Chernyakova, M.; Chikawa, M.; Chitnis, V. R.; Christov, A.; Chudoba, J.; Cieślar, M.; Clark, P.; Coco, V.; Colafrancesco, S.; Colin, P.; Colombo, E.; Colome, J.; Colonges, S.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Cornat, R.; Cortina, J.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Covone, G.; Cristofari, P.; Criswell, S. J.; Crocker, R.; Croston, J.; Crovari, C.; Cuadra, J.; Cuevas, O.; Cui, X.; Cumani, P.; Cusumano, G.; D'Aì, A.; D'Ammando, F.; D'Avanzo, P.; D'Urso, D.; Da Vela, P.; Dale, Ø.; Dang, V. T.; Dangeon, L.; Daniel, M.; Davids, I.; Dawson, B.; Dazzi, F.; De Angelis, A.; De Caprio, V.; de Cássia dos Anjos, R.; De Cesare, G.; De Franco, A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De Lisio, C.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; De Lucia, M.; de Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma, F.; De Persio, F.; de Souza, V.; Decock, J.; Deil, C.; Deiml, P.; Del Santo, M.; Delagnes, E.; Deleglise, G.; Delfino Reznicek, M.; Delgado, C.; Delgado Mengual, J.; Della Ceca, R.; della Volpe, D.; Detournay, M.; Devin, J.; Di Girolamo, T.; Di Giulio, C.; Di Pierro, F.; Di Venere, L.; Diaz, L.; Díaz, C.; Dib, C.; Dickinson, H.; Diebold, S.; Digel, S.; Djannati-Ataï, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Donnarumma, I.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Downes, T.; Drake, G.; Drappeau, S.; Drass, H.; Dravins, D.; Drury, L.; Dubus, G.; Dundas Morå, K.; Durkalec, A.; Dwarkadas, V.; Ebr, J.; Eckner, C.; Edy, E.; Egberts, K.; Einecke, S.; Eisch, J.; Eisenkolb, F.; Ekoume, T. R. N.; Eleftheriadis, C.; Elsässer, D.; Emmanoulopoulos, D.; Ernenwein, J. -P.; Escarate, P.; Eschbach, S.; Espinoza, C.; Evans, P.; Evoli, C.; Fairbairn, M.; Falceta-Goncalves, D.; Falcone, A.; Fallah Ramazani, V.; Farakos, K.; Farrell, E.; Fasola, G.; Favre, Y.; Fede, E.; Fedora, R.; Fedorova, E.; Fegan, S.; Fernandez-Alonso, M.; Fernández-Barral, A.; Ferrand, G.; Ferreira, O.; Fesquet, M.; Fiandrini, E.; Fiasson, A.; Filipovic, M.; Fink, D.; Finley, J. P.; Finley, C.; Finoguenov, A.; Fioretti, V.; Fiorini, M.; Flores, H.; Foffano, L.; Föhr, C.; Fonseca, M. V.; Font, L.; Fontaine, G.; Fornasa, M.; Fortin, P.; Fortson, L.; Fouque, N.; Fraga, B.; Franco, F. J.; Freixas Coromina, L.; Fruck, C.; Fugazza, D.; Fujita, Y.; Fukami, S.; Fukazawa, Y.; Fukui, Y.; Funk, S.; Furniss, A.; Füßling, M.; Gabici, S.; Gadola, A.; Gallant, Y.; Galloway, D.; Gallozzi, S.; Garcia, B.; Garcia, A.; García Gil, R.; Garcia López, R.; Garczarczyk, M.; Gardiol, D.; Gargano, F.; Gargano, C.; Garozzo, S.; Garrido-Ruiz, M.; Gascon, D.; Gasparetto, T.; Gaté, F.; Gaug, M.; Gebhardt, B.; Gebyehu, M.; Geffroy, N.; Genolini, B.; Ghalumyan, A.; Ghedina, A.; Ghirlanda, G.; Giammaria, P.; Gianotti, F.; Giebels, B.; Giglietto, N.; Gika, V.; Gimenes, R.; Giommi, P.; Giordano, F.; Giovannini, G.; Giro, E.; Giroletti, M.; Gironnet, J.; Giuliani, A.; Glicenstein, J. -F.; Gnatyk, R.; Godinovic, N.; Goldoni, P.; Gómez, J. L.; Gómez-Vargas, G.; González, M. M.; González, J. M.; Gothe, K. S.; Gotz, D.; Goullon, J.; Grabarczyk, T.; Graciani, R.; Graham, J.; Grandi, P.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A. J.; Greenshaw, T.; Grenier, I.; Griffiths, S.; Grillo, A.; Grondin, M. -H.; Grube, J.; Guarino, V.; Guest, B.; Gueta, O.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagge, L.; Hahn, J.; Hahn, A.; Hakobyan, H.; Hara, S.; Hardcastle, M. J.; Hassan, T.; Haubold, T.; Haupt, A.; Hayashi, K.; Hayashida, M.; He, H.; Heller, M.; Helo, J. C.; Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrera Llorente, J.; Herrero, A.; Hervet, O.; Hidaka, N.; Hinton, J.; Hiroshima, N.; Hirotani, K.; Hnatyk, B.; Hoang, J. K.; Hoffmann, D.; Hofmann, W.; Holder, J.; Horan, D.; Hörandel, J.; Hörbe, M.; Horns, D.; Horvath, P.; Houles, J.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Huet, J. -M.; Hughes, G.; Hui, D.; Hull, G.; Humensky, T. B.; Hussein, M.; Hütten, M.; Iarlori, M.; Ikeno, Y.; Illa, J. M.; Impiombato, D.; Inada, T.; Ingallinera, A.; Inome, Y.; Inoue, S.; Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Ionica, M.; Iori, M.; Iriarte, A.; Ishio, K.; Israel, G. L.; Iwamura, Y.; Jablonski, C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy, M.; Janecek, P.; Jankowsky, F.; Jankowsky, D.; Jansweijer, P.; Jarnot, C.; Jean, P.; Johnson, C. A.; Josselin, M.; Jung-Richardt, I.; Jurysek, J.; Kaaret, P.; Kachru, P.; Kagaya, M.; Kakuwa, J.; Kalekin, O.; Kankanyan, R.; Karastergiou, A.; Karczewski, M.; Karkar, S.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz, U.; Kawanaka, N.; Kaye, L.; Kazanas, D.; Kelley-Hoskins, N.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kimeswenger, S.; Kimura, S.; Kisaka, S.; Kishida, S.; Kissmann, R.; Kluźniak, W.; Knapen, J.; Knapp, J.; Knödlseder, J.; Koch, B.; Kocot, J.; Kohri, K.; Komin, N.; Kong, A.; Konno, Y.; Kosack, K.; Kowal, G.; Koyama, S.; Kraus, M.; Krause, M.; Krauß, F.; Krennrich, F.; Kruger, P.; Kubo, H.; Kudryavtsev, V.; Kukec Mezek, G.; Kumar, S.; Kuroda, H.; Kushida, J.; Kushwaha, P.; La Palombara, N.; La Parola, V.; La Rosa, G.; Lahmann, R.; Lalik, K.; Lamanna, G.; Landoni, M.; Landriu, D.; Landt, H.; Lang, R. G.; Lapington, J.; Laporte, P.; Le Blanc, O.; Le Flour, T.; Le Sidaner, P.; Leach, S.; Leckngam, A.; Lee, S. -H.; Lee, W. H.; Lees, J. -P.; Lefaucheur, J.; Leigui de Oliveira, M. A.; Lemoine-Goumard, M.; Lenain, J. -P.; Leto, G.; Lico, R.; Limon, M.; Lindemann, R.; Lindfors, E.; Linhoff, L.; Lipniacka, A.; Lloyd, S.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez, M.; Lopez-Coto, R.; Louge, T.; Louis, F.; Louys, M.; Lucarelli, F.; Lucchesi, D.; Luque-Escamilla, P. L.; Lyard, E.; Maccarone, M. C.; Maccarone, T.; Mach, E.; Madejski, G. M.; Maier, G.; Majczyna, A.; Majumdar, P.; Makariev, M.; Malaguti, G.; Malouf, A.; Maltezos, S.; Malyshev, D.; Malyshev, D.; Mandat, D.; Maneva, G.; Manganaro, M.; Mangano, S.; Manigot, P.; Mannheim, K.; Maragos, N.; Marano, D.; Marcowith, A.; Marín, J.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Martí, J.; Martin, J. -M.; Martin, P.; Martin, L.; Martínez, M.; Martínez, G.; Martínez, O.; Marx, R.; Masetti, N.; Massimino, P.; Mastichiadis, A.; Mastropietro, M.; Masuda, S.; Matsumoto, H.; Matthews, N.; Mattiazzo, S.; Maurin, G.; Maxted, N.; Mayer, M.; Mazin, D.; Mazziotta, M. N.; Mc Comb, L.; McHardy, I.; Medina, C.; Melandri, A.; Melioli, C.; Melkumyan, D.; Mereghetti, S.; Meunier, J. -L.; Meures, T.; Meyer, M.; Micanovic, S.; Michael, T.; Michałowski, J.; Mievre, I.; Miller, J.; Minaya, I. A.; Mineo, T.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mitchell, A.; Mizuno, T.; Moderski, R.; Mohammed, M.; Mohrmann, L.; Molijn, C.; Molinari, E.; Moncada, R.; Montaruli, T.; Monteiro, I.; Mooney, D.; Moore, P.; Moralejo, A.; Morcuende-Parrilla, D.; Moretti, E.; Mori, K.; Morlino, G.; Morris, P.; Morselli, A.; Moscato, F.; Motohashi, D.; Moulin, E.; Mueller, S.; Mukherjee, R.; Munar, P.; Mundell, C.; Mundet, J.; Murach, T.; Muraishi, H.; Murase, K.; Murphy, A.; Nagai, A.; Nagar, N.; Nagataki, S.; Nagayoshi, T.; Nagesh, B. K.; Naito, T.; Nakajima, D.; Nakamori, T.; Nakamura, Y.; Nakayama, K.; Naumann, D.; Nayman, P.; Neise, D.; Nellen, L.; Nemmen, R.; Neronov, A.; Neyroud, N.; Nguyen, T.; Nguyen, T. T.; Nguyen Trung, T.; Nicastro, L.; Nicolau-Kukliński, J.; Niemiec, J.; Nieto, D.; Nievas-Rosillo, M.; Nikołajuk, M.; Nishijima, K.; Nishikawa, K. -I.; Nishiyama, G.; Noda, K.; Nogues, L.; Nolan, S.; Nosek, D.; Nöthe, M.; Novosyadlyj, B.; Nozaki, S.; Nunio, F.; O'Brien, P.; Oakes, L.; Ocampo, C.; Ochoa, J. P.; Oger, R.; Ohira, Y.; Ohishi, M.; Ohm, S.; Okazaki, N.; Okumura, A.; Olive, J. -F.; Ong, R. A.; Orienti, M.; Orito, R.; Orlati, A.; Osborne, J. P.; Ostrowski, M.; Otte, N.; Ou, Z.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padovani, M.; Paiano, S.; Paizis, A.; Palacio, J.; Palatiello, M.; Palatka, M.; Pallotta, J.; Panazol, J. -L.; Paneque, D.; Panter, M.; Paoletti, R.; Paolillo, M.; Papitto, A.; Paravac, A.; Paredes, J. M.; Pareschi, G.; Parsons, R. D.; Paśko, P.; Pavy, S.; Pe'er, A.; Pech, M.; Pedaletti, G.; Peñil Del Campo, P.; Perez, A.; Pérez-Torres, M. A.; Perri, L.; Perri, M.; Persic, M.; Petrashyk, A.; Petrera, S.; Petrucci, P. -O.; Petruk, O.; Peyaud, B.; Pfeifer, M.; Piano, G.; Piel, Q.; Pieloth, D.; Pintore, F.; García, C. Pio; Pisarski, A.; Pita, S.; Pizarro, L.; Platos, Ł.; Pohl, M.; Poireau, V.; Pollo, A.; Porthault, J.; Poutanen, J.; Pozo, D.; Prandini, E.; Prasit, P.; Prast, J.; Pressard, K.; Principe, G.; Prokhorov, D.; Prokoph, H.; Prouza, M.; Pruteanu, G.; Pueschel, E.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pürckhauer, S.; Queiroz, F.; Quinn, J.; Quirrenbach, A.; Rafighi, I.; Rainò, S.; Rajda, P. J.; Rando, R.; Rannot, R. C.; Razzaque, S.; Reichardt, I.; Reimer, O.; Reimer, A.; Reisenegger, A.; Renaud, M.; Reposeur, T.; Reville, B.; Rezaeian, A. H.; Rhode, W.; Ribeiro, D.; Ribó, M.; Richer, M. G.; Richtler, T.; Rico, J.; Rieger, F.; Riquelme, M.; Ristori, P. R.; Rivoire, S.; Rizi, V.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodríguez Vázquez, J. J.; Rojas, G.; Romano, P.; Romeo, G.; Roncadelli, M.; Rosado, J.; Rosen, S.; Rosier Lees, S.; Rousselle, J.; Rovero, A. C.; Rowell, G.; Rudak, B.; Rugliancich, A.; Ruíz del Mazo, J. E.; Rujopakarn, W.; Rulten, C.; Russo, F.; Saavedra, O.; Sabatini, S.; Sacco, B.; Sadeh, I.; Sæther Hatlen, E.; Safi-Harb, S.; Sahakian, V.; Sailer, S.; Saito, T.; Sakaki, N.; Sakurai, S.; Salek, D.; Salesa Greus, F.; Salina, G.; Sanchez, D.; Sánchez-Conde, M.; Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.; Santander, M.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Satalecka, K.; Sato, Y.; Saturni, F. G.; Savalle, R.; Sawada, M.; Schanne, S.; Schioppa, E. J.; Schlenstedt, S.; Schmidt, T.; Schmoll, J.; Schneider, M.; Schoorlemmer, H.; Schovanek, P.; Schulz, A.; Schussler, F.; Schwanke, U.; Schwarz, J.; Schweizer, T.; Schwemmer, S.; Sciacca, E.; Scuderi, S.; Seglar-Arroyo, M.; Segreto, A.; Seitenzahl, I.; Semikoz, D.; Sergijenko, O.; Serre, N.; Servillat, M.; Seweryn, K.; Shah, K.; Shalchi, A.; Sharma, M.; Shellard, R. C.; Shilon, I.; Sidoli, L.; Sidz, M.; Siejkowski, H.; Silk, J.; Sillanpää, A.; Simone, D.; Singh, B. B.; Sironi, G.; Sitarek, J.; Sizun, P.; Sliusar, V.; Slowikowska, A.; Smith, A.; Sobczyńska, D.; Sokolenko, A.; Sol, H.; Sottile, G.; Springer, W.; Stahl, O.; Stamerra, A.; Stanič, S.; Starling, R.; Staszak, D.; Stawarz, Ł.; Steenkamp, R.; Stefanik, S.; Stegmann, C.; Steiner, S.; Stella, C.; Stephan, M.; Sternberger, R.; Sterzel, M.; Stevenson, B.; Stodulska, M.; Stodulski, M.; Stolarczyk, T.; Stratta, G.; Straumann, U.; Stuik, R.; Suchenek, M.; Suomijarvi, T.; Supanitsky, A. D.; Suric, T.; Sushch, I.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.; Tagliaferri, G.; Tajima, H.; Takahashi, K.; Takahashi, H.; Takahashi, M.; Takalo, L.; Takami, S.; Takata, J.; Takeda, J.; Tam, T.; Tanaka, M.; Tanaka, T.; Tanaka, Y.; Tanaka, S.; Tanci, C.; Tavani, M.; Tavecchio, F.; Tavernet, J. -P.; Tayabaly, K.; Tejedor, L. A.; Temme, F.; Temnikov, P.; Terada, Y.; Terrazas, J. C.; Terrier, R.; Terront, D.; Terzic, T.; Tescaro, D.; Teshima, M.; Testa, V.; Thoudam, S.; Tian, W.; Tibaldo, L.; Tiengo, A.; Tiziani, D.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tomastik, J.; Tonachini, A.; Tonev, D.; Tornikoski, M.; Torres, D. F.; Torresi, E.; Tosti, G.; Totani, T.; Tothill, N.; Toussenel, F.; Tovmassian, G.; Trakarnsirinont, N.; Travnicek, P.; Trichard, C.; Trifoglio, M.; Troyano Pujadas, I.; Tsirou, M.; Tsujimoto, S.; Tsuru, T.; Uchiyama, Y.; Umana, G.; Uslenghi, M.; Vagelli, V.; Vagnetti, F.; Valentino, M.; Vallania, P.; Valore, L.; Van den Berg, A. M.; van Driel, W.; van Eldik, C.; van Soelen, B.; Vandenbroucke, J.; Vanderwalt, J.; Varner, G. S.; Vasileiadis, G.; Vassiliev, V.; Vázquez, J. R.; Vázquez Acosta, M.; Vecchi, M.; Vega, A.; Veitch, P.; Venault, P.; Venter, C.; Vercellone, S.; Veres, P.; Vergani, S.; Verzi, V.; Vettolani, G. P.; Veyssiere, C.; Viana, A.; Vicha, J.; Vigorito, C.; Villanueva, J.; Vincent, P.; Vink, J.; Visconti, F.; Vittorini, V.; Voelk, H.; Voisin, V.; Vollhardt, A.; Vorobiov, S.; Vovk, I.; Vrastil, M.; Vuillaume, T.; Wagner, S. J.; Wagner, R.; Wagner, P.; Wakely, S. P.; Walstra, T.; Walter, R.; Ward, M.; Ward, J. E.; Warren, D.; Watson, J. J.; Webb, N.; Wegner, P.; Weiner, O.; Weinstein, A.; Weniger, C.; Werner, F.; Wetteskind, H.; White, M.; White, R.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wilcox, P.; Wilhelm, A.; Wilkinson, M.; Will, M.; Williams, D. A.; Winter, M.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, T.; Yadav, K. K.; Yaguna, C.; Yamamoto, T.; Yamamoto, H.; Yamane, N.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yelos, D.; Yoshida, T.; Yoshida, M.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zaborov, D.; Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel, F.; Zanin, R.; Zanmar Sanchez, R.; Zaric, D.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A. A.; Zech, A.; Zechlin, H.; Zhdanov, V. I.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Zink, A.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zorn, J. Bibcode: 2017arXiv170903483A Altcode: 2017arXiv170903483C List of contributions from the Cherenkov Telescope Array Consortium presented at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea. Title: Observing and modelling the poloidal and toroidal magnetic fields of the global dynamo Authors: Cameron, Robert; Duvall, Thomas; Schüssler, Manfred; Schunker, Hannah Bibcode: 2017SPD....4830601C Altcode: The large scale solar dynamo is a cycle where poloidal flux is generated from toroidal flux, and toroidal flux is generated from poloidal flux. The toroidal and poloidal fields can be inferred from observations, and the Babcock-Leighton model shows how differential rotation and flux emergence explain the observed evolution of the fields. Title: The nature of solar brightness variations Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Yeo, K. L.; Schmutz, W. K. Bibcode: 2017NatAs...1..612S Altcode: 2017arXiv171104156S Determining the sources of solar brightness variations1,2, often referred to as solar noise3, is important because solar noise limits the detection of solar oscillations3, is one of the drivers of the Earth's climate system4,5 and is a prototype of stellar variability6,7—an important limiting factor for the detection of extrasolar planets. Here, we model the magnetic contribution to solar brightness variability using high-cadence8,9 observations from the Solar Dynamics Observatory (SDO) and the Spectral And Total Irradiance REconstruction (SATIRE)10,11 model. The brightness variations caused by the constantly evolving cellular granulation pattern on the solar surface were computed with the Max Planck Institute for Solar System Research (MPS)/University of Chicago Radiative Magnetohydrodynamics (MURaM)12 code. We found that the surface magnetic field and granulation can together precisely explain solar noise (that is, solar variability excluding oscillations) on timescales from minutes to decades, accounting for all timescales that have so far been resolved or covered by irradiance measurements. We demonstrate that no other sources of variability are required to explain the data. Recent measurements of Sun-like stars by the COnvection ROtation and planetary Transits (CoRoT)13 and Kepler14 missions uncovered brightness variations similar to that of the Sun, but with a much wider variety of patterns15. Our finding that solar brightness variations can be replicated in detail with just two well-known sources will greatly simplify future modelling of existing CoRoT and Kepler as well as anticipated Transiting Exoplanet Survey Satellite16 and PLAnetary Transits and Oscillations of stars (PLATO)17 data. Title: Evidence for photometric activity cycles in 3203 Kepler stars Authors: Reinhold, Timo; Cameron, Robert H.; Gizon, Laurent Bibcode: 2017A&A...603A..52R Altcode: 2017arXiv170503312R Context. In recent years it has been claimed that the length of stellar activity cycles is determined by the stellar rotation rate. It has been observed that the cycle period increases with rotation period along two distinct sequences, known as the active and inactive sequences. In this picture the Sun occupies a solitary position between the two sequences. Whether the Sun might undergo a transitional evolutionary stage is currently under debate.
Aims: Our goal is to measure cyclic variations of the stellar light curve amplitude and the rotation period using four years of Kepler data. Periodic changes in the light curve amplitude or the stellar rotation period are associated with an underlying activity cycle.
Methods: Using a recent sample of active stars we compute the rotation period and the variability amplitude for each individual Kepler quarter and search for periodic variations of both time series. To test for periodicity in each stellar time series we consider Lomb-Scargle periodograms and use a selection based on a false alarm probability (FAP).
Results: We detect amplitude periodicities in 3203 stars between 0.5 < Pcyc < 6 yr covering rotation periods between 1 < Prot < 40 days. Given our sample size of 23 601 stars and our selection criteria that the FAP is less than 5%, this number is almost three times higher than that expected from pure noise. We do not detect periodicities in the rotation period beyond those expected from noise. Our measurements reveal that the cycle period shows a weak dependence on rotation rate, slightly increasing for longer rotation periods. We further show that the shape of the variability deviates from a pure sine curve, consistent with observations of the solar cycle. The cycle shape does not show a statistically significant dependence on effective temperature.
Conclusions: We detect activity cycles in more than 13% of our final sample with a FAP of 5% (calculated by randomly shuffling the measured 90-day variability measurements for each star). Our measurements do not support the existence of distinct sequences in the Prot-Pcyc plane, although there is some evidence for the inactive sequence for rotation periods between 5-25 days. Unfortunately, the total observing time is too short to draw sound conclusions on activity cycles with similar lengths to that of the solar cycle.

A table containing all cycle periods and time series is only available in electronic form at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/603/A52 Title: Understanding Solar Cycle Variability Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2017ApJ...843..111C Altcode: 2017arXiv170510746C The level of solar magnetic activity, as exemplified by the number of sunspots and by energetic events in the corona, varies on a wide range of timescales. Most prominent is the 11-year solar cycle, which is significantly modulated on longer timescales. Drawing from dynamo theory, together with the empirical results of past solar activity and similar phenomena for solar-like stars, we show that the variability of the solar cycle can be essentially understood in terms of a weakly nonlinear limit cycle affected by random noise. In contrast to ad hoc “toy models” for the solar cycle, this leads to a generic normal-form model, whose parameters are all constrained by observations. The model reproduces the characteristics of the variable solar activity on timescales between decades and millennia, including the occurrence and statistics of extended periods of very low activity (grand minima). Comparison with results obtained with a Babcock-Leighton-type dynamo model confirm the validity of the normal-mode approach. Title: Effects of pH and Redox Gradients on Prebiotic Organic Synthesis and the Generation of Free Energy in Simulated Hydrothermal Systems Authors: Barge, L. M.; Flores, E.; Abedian, Y.; Maltais, T.; Cameron, R.; Hermis, N.; Chin, K.; Russell, M. J.; Baum, M. M. Bibcode: 2017LPICo1967.4179B Altcode: Hydrothermal minerals in alkaline vents can promote phosphorus and organic concentration, redox reactions driven by catalytic metal sulfides, and the ambient pH and redox gradients can affect the synthesis of organics. Title: Evolution of the Sun's non-axisymmetric toroidal field Authors: Martin-Belda, D.; Cameron, R. H. Bibcode: 2017A&A...603A..53M Altcode: 2017arXiv170310075M
Aims: We aim to infer the sub-surface distribution of the Sun's non-axisymmetric azimuthal magnetic flux from observable quantities, such as the surface magnetic field and the large scale plasma flows.
Methods: We have built a kinematic flux transport model of the solar dynamo based on the Babcock-Leighton framework. We constructed the source term for the poloidal field using SOLIS magnetograms spanning three solar cycles. Based on this source we calculated the azimuthal flux below the surface. The flux transport model has two free parameters which we constrained using sunspot observations from cycle 22. We compared the model results with observations from cycle 23.
Results: The structure of the azimuthal field is mainly axisymmetric. The departures from axisymmetry represent, on average, 3% of the total azimuthal flux. Owing to its relative weakness, the non-axisymmetric structure of the azimuthal field does not have a significant impact on the location in which the emergences appear or on the amount of flux contained in them. We find that the probability of emergence is a function of the ratio between the flux content of an active region and the underlying azimuthal flux. Title: VizieR Online Data Catalog: Activity cycles in 3203 Kepler stars (Reinhold+, 2017) Authors: Reinhold, T.; Cameron, R. H.; Gizon, L. Bibcode: 2017yCat..36030052R Altcode: Rvar time series, sine fit parameters, mean rotation periods, and false alarm probabilities of all 3203 Kepler stars are presented. For simplicity, the KIC number and the fit parameters of a certain star are repeated in each line. The fit function to the Rvar(t) time series equals y_fit=Acyc*sin(2*pi/(Pcyc*365)*(t-t0))+Offset.

(2 data files). Title: Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7-3946 Authors: Acero, F.; Aloisio, R.; Amans, J.; Amato, E.; Antonelli, L. A.; Aramo, C.; Armstrong, T.; Arqueros, F.; Asano, K.; Ashley, M.; Backes, M.; Balazs, C.; Balzer, A.; Bamba, A.; Barkov, M.; Barrio, J. A.; Benbow, W.; Bernlöhr, K.; Beshley, V.; Bigongiari, C.; Biland, A.; Bilinsky, A.; Bissaldi, E.; Biteau, J.; Blanch, O.; Blasi, P.; Blazek, J.; Boisson, C.; Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonnoli, G.; Braiding, C.; Brau-Nogué, S.; Bregeon, J.; Brown, A. M.; Bugaev, V.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Böttcher, M.; Cameron, R.; Capalbi, M.; Caproni, A.; Caraveo, P.; Carosi, R.; Cascone, E.; Cerruti, M.; Chaty, S.; Chen, A.; Chen, X.; Chernyakova, M.; Chikawa, M.; Chudoba, J.; Cohen-Tanugi, J.; Colafrancesco, S.; Conforti, V.; Contreras, J. L.; Costa, A.; Cotter, G.; Covino, S.; Covone, G.; Cumani, P.; Cusumano, G.; D'Ammando, F.; D'Urso, D.; Daniel, M.; Dazzi, F.; De Angelis, A.; De Cesare, G.; De Franco, A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; De Lisio, C.; de los Reyes Lopez, R.; De Lotto, B.; de Naurois, M.; De Palma, F.; Del Santo, M.; Delgado, C.; della Volpe, D.; Di Girolamo, T.; Di Giulio, C.; Di Pierro, F.; Di Venere, L.; Doro, M.; Dournaux, J.; Dumas, D.; Dwarkadas, V.; Díaz, C.; Ebr, J.; Egberts, K.; Einecke, S.; Elsässer, D.; Eschbach, S.; Falceta-Goncalves, D.; Fasola, G.; Fedorova, E.; Fernández-Barral, A.; Ferrand, G.; Fesquet, M.; Fiandrini, E.; Fiasson, A.; Filipović, M. D.; Fioretti, V.; Font, L.; Fontaine, G.; Franco, F. J.; Freixas Coromina, L.; Fujita, Y.; Fukui, Y.; Funk, S.; Förster, A.; Gadola, A.; Garcia López, R.; Garczarczyk, M.; Giglietto, N.; Giordano, F.; Giuliani, A.; Glicenstein, J.; Gnatyk, R.; Goldoni, P.; Grabarczyk, T.; Graciani, R.; Graham, J.; Grandi, P.; Granot, J.; Green, A. J.; Griffiths, S.; Gunji, S.; Hakobyan, H.; Hara, S.; Hassan, T.; Hayashida, M.; Heller, M.; Helo, J. C.; Hinton, J.; Hnatyk, B.; Huet, J.; Huetten, M.; Humensky, T. B.; Hussein, M.; Hörandel, J.; Ikeno, Y.; Inada, T.; Inome, Y.; Inoue, S.; Inoue, T.; Inoue, Y.; Ioka, K.; Iori, M.; Jacquemier, J.; Janecek, P.; Jankowsky, D.; Jung, I.; Kaaret, P.; Katagiri, H.; Kimeswenger, S.; Kimura, S.; Knödlseder, J.; Koch, B.; Kocot, J.; Kohri, K.; Komin, N.; Konno, Y.; Kosack, K.; Koyama, S.; Kraus, M.; Kubo, H.; Kukec Mezek, G.; Kushida, J.; La Palombara, N.; Lalik, K.; Lamanna, G.; Landt, H.; Lapington, J.; Laporte, P.; Lee, S.; Lees, J.; Lefaucheur, J.; Lenain, J. -P.; Leto, G.; Lindfors, E.; Lohse, T.; Lombardi, S.; Longo, F.; Lopez, M.; Lucarelli, F.; Luque-Escamilla, P. L.; López-Coto, R.; Maccarone, M. C.; Maier, G.; Malaguti, G.; Mandat, D.; Maneva, G.; Mangano, S.; Marcowith, A.; Martí, J.; Martínez, M.; Martínez, G.; Masuda, S.; Maurin, G.; Maxted, N.; Melioli, C.; Mineo, T.; Mirabal, N.; Mizuno, T.; Moderski, R.; Mohammed, M.; Montaruli, T.; Moralejo, A.; Mori, K.; Morlino, G.; Morselli, A.; Moulin, E.; Mukherjee, R.; Mundell, C.; Muraishi, H.; Murase, K.; Nagataki, S.; Nagayoshi, T.; Naito, T.; Nakajima, D.; Nakamori, T.; Nemmen, R.; Niemiec, J.; Nieto, D.; Nievas-Rosillo, M.; Nikołajuk, M.; Nishijima, K.; Noda, K.; Nogues, L.; Nosek, D.; Novosyadlyj, B.; Nozaki, S.; Ohira, Y.; Ohishi, M.; Ohm, S.; Okumura, A.; Ong, R. A.; Orito, R.; Orlati, A.; Ostrowski, M.; Oya, I.; Padovani, M.; Palacio, J.; Palatka, M.; Paredes, J. M.; Pavy, S.; Pe'er, A.; Persic, M.; Petrucci, P.; Petruk, O.; Pisarski, A.; Pohl, M.; Porcelli, A.; Prandini, E.; Prast, J.; Principe, G.; Prouza, M.; Pueschel, E.; Pühlhofer, G.; Quirrenbach, A.; Rameez, M.; Reimer, O.; Renaud, M.; Ribó, M.; Rico, J.; Rizi, V.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodríguez Vázquez, J. J.; Romano, P.; Romeo, G.; Rosado, J.; Rousselle, J.; Rowell, G.; Rudak, B.; Sadeh, I.; Safi-Harb, S.; Saito, T.; Sakaki, N.; Sanchez, D.; Sangiorgi, P.; Sano, H.; Santander, M.; Sarkar, S.; Sawada, M.; Schioppa, E. J.; Schoorlemmer, H.; Schovanek, P.; Schussler, F.; Sergijenko, O.; Servillat, M.; Shalchi, A.; Shellard, R. C.; Siejkowski, H.; Sillanpää, A.; Simone, D.; Sliusar, V.; Sol, H.; Stanič, S.; Starling, R.; Stawarz, Ł.; Stefanik, S.; Stephan, M.; Stolarczyk, T.; Szanecki, M.; Szepieniec, T.; Tagliaferri, G.; Tajima, H.; Takahashi, M.; Takeda, J.; Tanaka, M.; Tanaka, S.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Terada, Y.; Tescaro, D.; Teshima, M.; Testa, V.; Thoudam, S.; Tokanai, F.; Torres, D. F.; Torresi, E.; Tosti, G.; Townsley, C.; Travnicek, P.; Trichard, C.; Trifoglio, M.; Tsujimoto, S.; Vagelli, V.; Vallania, P.; Valore, L.; van Driel, W.; van Eldik, C.; Vandenbroucke, J.; Vassiliev, V.; Vecchi, M.; Vercellone, S.; Vergani, S.; Vigorito, C.; Vorobiov, S.; Vrastil, M.; Vázquez Acosta, M. L.; Wagner, S. J.; Wagner, R.; Wakely, S. P.; Walter, R.; Ward, J. E.; Watson, J. J.; Weinstein, A.; White, M.; White, R.; Wierzcholska, A.; Wilcox, P.; Williams, D. A.; Wischnewski, R.; Wojcik, P.; Yamamoto, T.; Yamamoto, H.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yoshida, T.; Yoshida, M.; Yoshiike, S.; Yoshikoshi, T.; Zacharias, M.; Zampieri, L.; Zanin, R.; Zavrtanik, M.; Zavrtanik, D.; Zdziarski, A.; Zech, A.; Zechlin, H.; Zhdanov, V.; Ziegler, A.; Zorn, J. Bibcode: 2017ApJ...840...74A Altcode: 2017arXiv170404136C We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7-3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti)correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H I emission. We present a series of simulated images of RX J1713.7-3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H I observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (I.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator. Title: High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI Authors: Jafarzadeh, S.; Solanki, S. K.; Stangalini, M.; Steiner, O.; Cameron, R. H.; Danilovic, S. Bibcode: 2017ApJS..229...10J Altcode: 2016arXiv161109302J We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations of both horizontal displacement and intensity in magnetic bright points found in the 300 nm and the Ca II H 396.8 nm passbands of the filter imager on board the Sunrise balloon-borne solar observatory. Phase differences between the oscillations at the two atmospheric layers corresponding to the two passbands reveal upward propagating waves at high frequencies (up to 30 mHz). Weak signatures of standing as well as downward propagating waves are also obtained. Both compressible and incompressible (kink) waves are found in the small-scale magnetic features. The two types of waves have different, though overlapping, period distributions. Two independent estimates give a height difference of approximately 450 ± 100 km between the two atmospheric layers sampled by the employed spectral bands. This value, together with the determined short travel times of the transverse and longitudinal waves provide us with phase speeds of 29 ± 2 km s-1 and 31 ± 2 km s-1, respectively. We speculate that these phase speeds may not reflect the true propagation speeds of the waves. Thus, effects such as the refraction of fast longitudinal waves may contribute to an overestimate of the phase speed. Title: Kinematics of Magnetic Bright Features in the Solar Photosphere Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez, D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M. Bibcode: 2017ApJS..229....8J Altcode: 2016arXiv161007634J Convective flows are known as the prime means of transporting magnetic fields on the solar surface. Thus, small magnetic structures are good tracers of turbulent flows. We study the migration and dispersal of magnetic bright features (MBFs) in intergranular areas observed at high spatial resolution with Sunrise/IMaX. We describe the flux dispersal of individual MBFs as a diffusion process whose parameters are computed for various areas in the quiet-Sun and the vicinity of active regions from seeing-free data. We find that magnetic concentrations are best described as random walkers close to network areas (diffusion index, γ =1.0), travelers with constant speeds over a supergranule (γ =1.9{--}2.0), and decelerating movers in the vicinity of flux emergence and/or within active regions (γ =1.4{--}1.5). The three types of regions host MBFs with mean diffusion coefficients of 130 km2 s-1, 80-90 km2 s-1, and 25-70 km2 s-1, respectively. The MBFs in these three types of regions are found to display a distinct kinematic behavior at a confidence level in excess of 95%. Title: An update of Leighton's solar dynamo model Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2017A&A...599A..52C Altcode: 2016arXiv161109111C In 1969, Leighton developed a quasi-1D mathematical model of the solar dynamo, building upon the phenomenological scenario of Babcock published in 1961. Here we present a modification and extension of Leighton's model. Using the axisymmetric component (longitudinal average) of the magnetic field, we consider the radial field component at the solar surface and the radially integrated toroidal magnetic flux in the convection zone, both as functions of latitude. No assumptions are made with regard to the radial location of the toroidal flux. The model includes the effects of (I) turbulent diffusion at the surface and in the convection zone; (II) poleward meridional flow at the surface and an equatorward return flow affecting the toroidal flux; (III) latitudinal differential rotation and the near-surface layer of radial rotational shear; (iv) downward convective pumping of magnetic flux in the shear layer; and (v) flux emergence in the form of tilted bipolar magnetic regions treated as a source term for the radial surface field. While the parameters relevant for the transport of the surface field are taken from observations, the model condenses the unknown properties of magnetic field and flow in the convection zone into a few free parameters (turbulent diffusivity, effective return flow, amplitude of the source term, and a parameter describing the effective radial shear). Comparison with the results of 2D flux transport dynamo codes shows that the model captures the essential features of these simulations. We make use of the computational efficiency of the model to carry out an extended parameter study. We cover an extended domain of the 4D parameter space and identify the parameter ranges that provide solar-like solutions. Dipole parity is always preferred and solutions with periods around 22 yr and a correct phase difference between flux emergence in low latitudes and the strength of the polar fields are found for a return flow speed around 2 m s-1, turbulent diffusivity below about 80 km2s-1, and dynamo excitation not too far above the threshold (linear growth rate less than 0.1 yr-1). Title: Inflows towards active regions and the modulation of the solar cycle: A parameter study Authors: Martin-Belda, D.; Cameron, R. H. Bibcode: 2017A&A...597A..21M Altcode: 2016A&A...597A..21M; 2016arXiv160901199M
Aims: We aim to investigate how converging flows towards active regions affect the surface transport of magnetic flux, as well as their impact on the generation of the Sun's poloidal field. The inflows constitute a potential non-linear mechanism for the saturation of the global dynamo and may contribute to the modulation of the solar cycle in the Babcock-Leighton framework.
Methods: We build a surface flux transport code incorporating a parametrized model of the inflows and run simulations spanning several cycles. We carry out a parameter study to assess how the strength and extension of the inflows affect the build-up of the global dipole field. We also perform simulations with different levels of activity to investigate the potential role of the inflows in the saturation of the global dynamo.
Results: We find that the interaction of neighbouring active regions can lead to the occasional formation of single-polarity magnetic flux clumps that are inconsistent with observations. We propose the darkening caused by pores in areas of high magnetic field strength as a possible mechanism preventing this flux-clumping. We find that inflows decrease the amplitude of the axial dipole moment by 30%, relative to a no-inflows scenario. Stronger (weaker) inflows lead to larger (smaller) reductions of the axial dipole moment. The relative amplitude of the generated axial dipole is about 9% larger after very weak cycles than after very strong cycles. This supports the idea that the inflows are a non-linear mechanism that is capable of saturating the global dynamo and contributing to the modulation of the solar cycle within the Babcock-Leighton framework. Title: Babcock-Leighton Solar Dynamo: The Role of Downward Pumping and the Equatorward Propagation of Activity Authors: Karak, Bidya Binay; Cameron, Robert Bibcode: 2016ApJ...832...94K Altcode: 2016arXiv160506224K The key elements of the Babcock-Leighton dynamos are the generation of poloidal field through decay and the dispersal of tilted bipolar active regions and the generation of toroidal field through the observed differential rotation. These models are traditionally known as flux transport dynamo models as the equatorward propagations of the butterfly wings in these models are produced due to an equatorward flow at the bottom of the convection zone. Here we investigate the role of downward magnetic pumping near the surface using a kinematic Babcock-Leighton model. We find that the pumping causes the poloidal field to become predominately radial in the near-surface shear layer, which allows the negative radial shear to effectively act on the radial field to produce a toroidal field. We observe a clear equatorward migration of the toroidal field at low latitudes as a consequence of the dynamo wave even when there is no meridional flow in the deep convection zone. Both the dynamo wave and the flux transport type solutions are thus able to reproduce some of the observed features of the solar cycle including the 11-year periodicity. The main difference between the two types of solutions is the strength of the Babcock-Leighton source required to produce the dynamo action. A second consequence of the magnetic pumping is that it suppresses the diffusion of fields through the surface, which helps to allow an 11-year cycle at (moderately) larger values of magnetic diffusivity than have previously been used. Title: Comparing Time-Distance Results within a Coronal Hole to the Quiet Sun Authors: Hess Webber, Shea A.; Pesnell, W. Dean; Duvall, Thomas, Jr.; Birch, Aaron; Cameron, Robert Bibcode: 2016usc..confE...1H Altcode: Time-distance helioseismology studies perturbations in solar wave modes. We use these techniques with SDO/HMI time-distance velocity-tracked dopplergram data to investigate differences between f -mode wave propagation within a coronal hole feature and without. We use symmetry arguments to enhance the signal-to-noise ratio of the cross-correlation results. We then look for phase and amplitude discrepancies between the coronal hole and quiet sun by comparing statistically significant differences between the regions. Title: A solar-like magnetic cycle on the mature K-dwarf 61 Cygni A (HD 201091) Authors: Boro Saikia, S.; Jeffers, S. V.; Morin, J.; Petit, P.; Folsom, C. P.; Marsden, S. C.; Donati, J. -F.; Cameron, R.; Hall, J. C.; Perdelwitz, V.; Reiners, A.; Vidotto, A. A. Bibcode: 2016A&A...594A..29B Altcode: 2016arXiv160601032B Context. The long-term monitoring of magnetic cycles in cool stars is a key diagnostic in understanding how dynamo generation and amplification of magnetic fields occur in stars similar in structure to the Sun.
Aims: We investigated the temporal evolution of a possible magnetic cycle of 61 Cyg A. The magnetic cycle is determined from 61 Cyg A's large-scale field over its activity cycle using spectropolarimetric observations and compared to the solar large-scale magnetic field.
Methods: We used the tomographic technique of Zeeman Doppler imaging (ZDI) to reconstruct the large-scale magnetic geometry of 61 Cyg A over multiple observational epochs spread over a time span of nine years. We investigated the time evolution of the different components of the large-scale field and compared it with the evolution of the star's chromospheric activity by measuring the flux in three different chromospheric indicators: Ca II H&K, Hα and Ca II infrared triplet lines. We also compared our results with the star's coronal activity using XMM-Newton observations.
Results: The large-scale magnetic geometry of 61 Cyg A exhibits polarity reversals in both poloidal and toroidal field components, in phase with its chromospheric activity cycle. We also detect weak solar-like differential rotation with a shear level similar to that of the Sun. During our observational time span of nine years, 61 Cyg A exhibits solar- like variations in its large-scale field geometry as it evolves from minimum activity to maximum activity and vice versa. During its activity minimum in epoch 2007.59, ZDI reconstructs a simple dipolar geometry which becomes more complex when it approaches activity maximum in epoch 2010.55. The radial field flips polarity and reverts back to a simple geometry in epoch 2013.61. The field is strongly dipolar and the evolution of the dipole component of the field is reminiscent of solar behaviour. The polarity reversal of the large-scale field indicates a magnetic cycle that is in phase with the chromospheric and coronal cycle. Title: Observed and simulated power spectra of kinetic and magnetic energy retrieved with 2D inversions Authors: Danilovic, S.; Rempel, M.; van Noort, M.; Cameron, R. Bibcode: 2016A&A...594A.103D Altcode: 2016arXiv160706242D Context. Information on the origin of internetwork magnetic field is hidden at the smallest spatial scales.
Aims: We try to retrieve the power spectra with certainty to the highest spatial frequencies allowed by current instrumentation.
Methods: To accomplish this, we use a 2D inversion code that is able to recover information up to the instrumental diffraction limit.
Results: The retrieved power spectra have shallow slopes that extend further down to much smaller scales than has been found before. They do not seem to show any power law. The observed slopes at subgranular scales agree with those obtained from recent local dynamo simulations. Small differences are found for the vertical component of kinetic energy that suggest that observations suffer from an instrumental effect that is not taken into account.
Conclusions: Local dynamo simulations quantitatively reproduce the observed magnetic energy power spectra on the scales of granulation down to the resolution limit of Hinode/SP, within the error bars inflicted by the method used and the instrumental effects replicated. Title: Contributions of the Cherenkov Telescope Array (CTA) to the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016) Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril, Ó.; Acero, F.; Acharya, B. S.; Adams, C.; Agnetta, G.; Aharonian, F.; Akhperjanian, A.; Albert, A.; Alcubierre, M.; Alfaro, J.; Alfaro, R.; Allafort, A. J.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.; Antonelli, L. A.; Antonucci, M.; Antonuccio, V.; Antoranz, P.; Aramo, C.; Aravantinos, A.; Araya, M.; Arcaro, C.; Arezki, B.; Argan, A.; Armstrong, T.; Arqueros, F.; Arrabito, L.; Arrieta, M.; Asano, K.; Ashley, M.; Aubert, P.; Singh, C. B.; Babic, A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs, C.; Balbo, M.; Balis, D.; Balkowski, C.; Ballester, O.; Ballet, J.; Balzer, A.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barcelo, M.; Barkov, M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.; Bastieri, D.; Bauer, C.; Becciani, U.; Becherini, Y.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico Ventura, D.; Berdugo, J.; Berge, D.; Bernardini, E.; Bernardini, M. G.; Bernhard, S.; Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Beshley, V.; Bhatt, N.; Bhattacharjee, P.; Bhattacharyya, W.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Bilinsky, A.; Bilnik, W.; Biondo, B.; Bird, R.; Bird, T.; Bissaldi, E.; Bitossi, M.; Blanch, O.; Blasi, P.; Blazek, J.; Bockermann, C.; Boehm, C.; Bogacz, L.; Bogdan, M.; Bohacova, M.; Boisson, C.; Boix, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonifacio, P.; Bonnarel, F.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Böttcher, M.; Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Bowman, L.; Braiding, C.; Brantseg, T.; Brau-Nogué, S.; Bregeon, J.; Briggs, M.; Brigida, M.; Bringmann, T.; Brisken, W.; Bristow, D.; Britto, R.; Brocato, E.; Bron, S.; Brook, P.; Brooks, W.; Brown, A. M.; Brügge, K.; Brun, F.; Brun, P.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Buanes, T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev, V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Cadoux, F.; Calvo Tovar, J.; Cameron, R.; Canelli, F.; Canestrari, R.; Capalbi, M.; Capasso, M.; Capobianco, G.; Caproni, A.; Caraveo, P.; Cardenzana, J.; Cardillo, M.; Carius, S.; Carlile, C.; Carosi, A.; Carosi, R.; Carquín, E.; Carr, J.; Carroll, M.; Carter, J.; Carton, P. -H.; Casandjian, J. -M.; Casanova, S.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina, A.; Castroviejo Mora, J.; Catalani, F.; Catalano, O.; Catalanotti, S.; Cauz, D.; Cavazzani, S.; Cerchiara, P.; Chabanne, E.; Chadwick, P.; Chaleil, T.; Champion, C.; Chatterjee, A.; Chaty, S.; Chaves, R.; Chen, A.; Chen, X.; Chen, X.; Cheng, K.; Chernyakova, M.; Chiappetti, L.; Chikawa, M.; Chinn, D.; Chitnis, V. 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V.; Vuillaume, T.; Wagner, R.; Wagner, R.; Wagner, S. J.; Wakely, S. P.; Walstra, T.; Walter, R.; Walther, T.; Ward, J. E.; Ward, M.; Warda, K.; Warren, D.; Wassberg, S.; Watson, J. J.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weiner, O.; Weinstein, A.; Wells, R.; Werner, F.; Wetteskind, H.; White, M.; White, R.; Więcek, M.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wilcox, P.; Wild, N.; Wilhelm, A.; Wilkinson, M.; Will, M.; Will, M.; Williams, D. A.; Williams, J. T.; Willingale, R.; Wilson, N.; Winde, M.; Winiarski, K.; Winkler, H.; Winter, M.; Wischnewski, R.; Witt, E.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, E.; Wu, T.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamane, N.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yelos, D.; Yoshida, A.; Yoshida, M.; Yoshida, T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel, F.; Zanmar Sanchez, R.; Zaric, D.; Zavrtanik, D.; Zavrtanik, M.; Zdziarski, A.; Zech, A.; Zechlin, H.; Zhao, A.; Zhdanov, V.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Zink, A.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zorn, J.; Żychowski, P. Bibcode: 2016arXiv161005151C Altcode: List of contributions from the Cherenkov Telescope Array (CTA) Consortium presented at the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma 2016), July 11-15, 2016, in Heidelberg, Germany. Title: MESA meets MURaM. Surface effects in main-sequence solar-like oscillators computed using three-dimensional radiation hydrodynamics simulations Authors: Ball, W. H.; Beeck, B.; Cameron, R. H.; Gizon, L. Bibcode: 2016A&A...592A.159B Altcode: 2016arXiv160602713B Context. Space-based observations of solar-like oscillators have identified large numbers of stars in which many individual mode frequencies can be precisely measured. However, current stellar models predict oscillation frequencies that are systematically affected by simplified modelling of the near-surface layers.
Aims: We use three-dimensional radiation hydrodynamics simulations to better model the near-surface equilibrium structure of dwarfs with spectral types F3, G2, K0 and K5, and examine the differences between oscillation mode frequencies computed in stellar models with and without the improved near-surface equilibrium structure.
Methods: We precisely match stellar models to the simulations' gravities and effective temperatures at the surface, and to the temporally- and horizontally-averaged densities and pressures at their deepest points. We then replace the near-surface structure with that of the averaged simulation and compute the change in the oscillation mode frequencies. We also fit the differences using several parametric models currently available in the literature.
Results: The surface effect in the stars of solar-type and later is qualitatively similar and changes steadily with decreasing effective temperature. In particular, the point of greatest frequency difference decreases slightly as a fraction of the acoustic cut-off frequency and the overall scale of the surface effect decreases. The surface effect in the hot, F3-type star follows the same trend in scale (I.e. it is larger in magnitude) but shows a different overall variation with mode frequency. We find that a two-term fit using the cube and inverse of the frequency divided by the mode inertia is best able to reproduce the surface terms across all four spectral types, although the scaled solar term and a modified Lorentzian function also match the three cooler simulations reasonably well.
Conclusions: Three-dimensional radiation hydrodynamics simulations of near-surface convection can be averaged and combined with stellar structure models to better predict oscillation mode frequencies in solar-like oscillators. Our simplified results suggest that the surface effect is generally larger in hotter stars (and correspondingly smaller in cooler stars) and of similar shape in stars of solar type and cooler. However, we cannot presently predict whether this will remain so when other components of the surface effect are included. Title: The global solar dynamo Authors: Cameron, Robert Bibcode: 2016cosp...41E.286C Altcode: I will review our understanding of the solar dynamo, concentrating on how observations constrain the theoretical possibilities. Possibilities for future progress, including understanding the Sun in the solar-stellar context will be outlined. Title: Solar activity in the coming decades Authors: Cameron, Robert Bibcode: 2016cosp...41E.287C Altcode: I will discuss the current state of our understanding of the solar dynamo with an emphasis on the extent to which we can predict solar activity on timescales from years to decades. Possible paths which might lead to progress will be outlined and assessed. Title: A low upper limit on the subsurface rise speed of solar active regions Authors: Birch, A. C.; Schunker, H.; Braun, D. C.; Cameron, R.; Gizon, L.; Lo ptien, B.; Rempel, M. Bibcode: 2016SciA....2E0557B Altcode: 2016arXiv160705250B Magnetic field emerges at the surface of the Sun as sunspots and active regions. This process generates a poloidal magnetic field from a rising toroidal flux tube, it is a crucial but poorly understood aspect of the solar dynamo. The emergence of magnetic field is also important because it is a key driver of solar activity. We show that measurements of horizontal flows at the solar surface around emerging active regions, in combination with numerical simulations of solar magnetoconvection, can constrain the subsurface rise speed of emerging magnetic flux. The observed flows imply that the rise speed of the magnetic field is no larger than 150 m/s at a depth of 20 Mm, that is, well below the prediction of the (standard) thin flux tube model but in the range expected for convective velocities at this depth. We conclude that convective flows control the dynamics of rising flux tubes in the upper layers of the Sun and cannot be neglected in models of flux emergence. Title: Surface flux transport simulations. Inflows towards active regions and the modulation of the solar cycle. Authors: Martin-Belda, David; Cameron, Robert Bibcode: 2016cosp...41E1255M Altcode: Aims. We investigate the way near-surface converging flows towards active regions affect the build-up of magnetic field at the Sun's polar caps. In the Babcock-Leighton dynamo framework, this modulation of the polar fields could explain the variability of the solar cycle. Methods. We develop a surface flux transport code incorporating a parametrized model of the inflows and run simulations spanning several cycles. We carry out a parameter study to test how the strength and extension of the inflows affect the amplitude of the polar fields. Results. Inflows are seen to play an important role in the build-up of the polar fields, and can act as the non-linearity feedback mechanism required to limit the strength of the solar cycles in the Babcock-Leighton dynamo framework. Title: The origin of Total Solar Irradiance variability on timescales less than a day Authors: Shapiro, Alexander; Krivova, Natalie; Schmutz, Werner; Solanki, Sami K.; Leng Yeo, Kok; Cameron, Robert; Beeck, Benjamin Bibcode: 2016cosp...41E1774S Altcode: Total Solar Irradiance (TSI) varies on timescales from minutes to decades. It is generally accepted that variability on timescales of a day and longer is dominated by solar surface magnetic fields. For shorter time scales, several additional sources of variability have been proposed, including convection and oscillation. However, available simplified and highly parameterised models could not accurately explain the observed variability in high-cadence TSI records. We employed the high-cadence solar imagery from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory and the SATIRE (Spectral And Total Irradiance Reconstruction) model of solar irradiance variability to recreate the magnetic component of TSI variability. The recent 3D simulations of solar near-surface convection with MURAM code have been used to calculate the TSI variability caused by convection. This allowed us to determine the threshold timescale between TSI variability caused by the magnetic field and convection. Our model successfully replicates the TSI measurements by the PICARD/PREMOS radiometer which span the period of July 2010 to February 2014 at 2-minute cadence. Hence, we demonstrate that solar magnetism and convection can account for TSI variability at all timescale it has ever been measured (sans the 5-minute component from p-modes). Title: Solar Cycle 25: Another Moderate Cycle? Authors: Cameron, R. H.; Jiang, J.; Schüssler, M. Bibcode: 2016ApJ...823L..22C Altcode: 2016arXiv160405405C Surface flux transport simulations for the descending phase of Cycle 24 using random sources (emerging bipolar magnetic regions) with empirically determined scatter of their properties provide a prediction of the axial dipole moment during the upcoming activity minimum together with a realistic uncertainty range. The expectation value for the dipole moment around 2020 (2.5 ± 1.1 G) is comparable to that observed at the end of Cycle 23 (about 2 G). The empirical correlation between the dipole moment during solar minimum and the strength of the subsequent cycle thus suggests that Cycle 25 will be of moderate amplitude, not much higher than that of the current cycle. However, the intrinsic uncertainty of such predictions resulting from the random scatter of the source properties is considerable and fundamentally limits the reliability with which such predictions can be made before activity minimum is reached. Title: The turbulent diffusion of toroidal magnetic flux as inferred from properties of the sunspot butterfly diagram Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2016A&A...591A..46C Altcode: 2016arXiv160407340C Context. In order to match observed properties of the solar cycle, flux-transport dynamo models require the toroidal magnetic flux to be stored in a region of low magnetic diffusivity, typically located at or below the bottom of the convection zone.
Aims: We infer the turbulent magnetic diffusivity affecting the toroidal field on the basis of empirical data.
Methods: We considered the time evolution of mean latitude and width of the activity belts of solar cycles 12-23 and their dependence on cycle strength. We interpreted the decline phase of the cycles as a diffusion process.
Results: The activity level of a given cycle begins to decline when the centers of its equatorward propagating activity belts come within their (full) width (at half maximum) from the equator. This happens earlier for stronger cycles because their activity belts are wider. From that moment on, the activity and the belt width decrease in the same manner for all cycles, independent of their maximum activity level. In terms of diffusive cancellation of opposite-polarity toroidal flux across the equator, we infer the turbulent diffusivity experienced by the toroidal field, wherever it is located, to be in the range 150-450 km2 s-1. Strong diffusive latitudinal spreading of the toroidal flux underneath the activity belts can be inhibited by an inflow toward the toroidal field bands in the convection zone with a magnitude of several meters per second.
Conclusions: The inferred value of the turbulent magnetic diffusivity affecting the toroidal field agrees, to order of magnitude, with estimates based on mixing-length models for the solar convection zone. This is at variance with the requirement of flux-transport dynamo models. The inflows required to keep the toroidal field bands together before they approach the equator are similar to the inflows toward the activity belts observed with local helioseismology. Title: Statistical Differences in Time-Distance Helioseismology Results Authors: Hess Webber, Shea A.; Pesnell, William D.; Duvall, Thomas; Cameron, Robert; Birch, A. C. Bibcode: 2016SPD....4720301H Altcode: Time-distance helioseismology studies phase correlations in solar wave modes. We use these techniques to investigate the phase differences in f-mode wave propagation within a coronal hole feature and without. We isolate the coronal hole boundary location using edge detection techniques on SDO AIA data. We then use this location information to inform the analysis of the corresponding HMI time-distance velocity tracked data product, provided by Stanford's JSOC archive. We look at time-distance results inside the coronal hole, outside the coronal hole, the coronal hole data as a whole, and an independent quiet sun region. We use Student's t-Test to evaluate the significance of the differences between the various regions. Title: Babcock-Leighton solar dynamo: the role of downward pumping and the equatorward propagation of activity Authors: Karak, Bidya Binay; Cameron, Robert Bibcode: 2016SPD....47.0717K Altcode: We investigate the role of downward magnetic pumping near the surface using a kinematic Babcock-Leighton model. We find that the pumping causes the poloidal field to become predominately radial in the near-surface shear layer. This allows the negative radial shear in the near-surface layer to effectively act on the radial field to produce a toroidal field. Consequently, we observe a clear equatorward migration of the toroidal field at low latitudes even when there is no meridional flow in the deep CZ. We show a case where the period of a dynamo wave solution is approximately 11 years. Flux transport models are also shown with periods close to 11 years. Both the dynamo wave and flux transport dynamo are thus able to reproduce some of the observed features of solar cycle. The main difference between the two types of dynamo is the value of $\alpha$ required to produce dynamo action. In both types of dynamo, the surface meridional flow helps to advect and build the polar field in high latitudes, while in flux transport dynamo the equatorward flow near the bottom of CZ advects toroidal field to cause the equatorward migration in butterfly wings and this advection makes the dynamo easier by transporting strong toroidal field to low latitudes where $\alpha$ effect works. Another conclusion of our study is that the magnetic pumping suppresses the diffusion of fields through the photospheric surface which helps to achieve the 11-year dynamo cycle at a moderately larger value of magnetic diffusivity than has previously been used. Title: Semi-empirical Long-term Reconstruction of the Heliospheric Parameters: Validation by Cosmogenic Radionuclide Records Authors: Asvestari, E.; Usoskin, I. G.; Cameron, R. H.; Krivova, N. A. Bibcode: 2016ASPC..504..269A Altcode: We have developed a semi-empirical model that describes the heliospheric modulation of galactic cosmic rays considering different heliospheric parameters. This model is an improvement of a previous model. The parameters of the model are fitted using the observations and reconstructions of the heliospheric parameters for the period 1976 - 2013, which includes the latest very weak solar minimum. The modulation potential is computed since 1610 using different reconstructions of the open solar magnetic flux and it is then used to compute the production and distribution of cosmogenic isotope 14C, which was subsequently compared with terrestrial archives in tree rings. It is shown that the group sunspot number series by Svalgaard & Schatten (2015) is inconsistent with the data, while other series agree well. Title: Surface flux transport simulations: Effect of inflows toward active regions and random velocities on the evolution of the Sun's large-scale magnetic field Authors: Martin-Belda, D.; Cameron, R. H. Bibcode: 2016A&A...586A..73M Altcode: 2015arXiv151202541M
Aims: We aim to determine the effect of converging flows on the evolution of a bipolar magnetic region (BMR), and to investigate the role of these inflows in the generation of poloidal flux. We also discuss whether the flux dispersal due to turbulent flows can be described as a diffusion process.
Methods: We developed a simple surface flux transport model based on point-like magnetic concentrations. We tracked the tilt angle, the magnetic flux and the axial dipole moment of a BMR in simulations with and without inflows and compared the results. To test the diffusion approximation, simulations of random walk dispersal of magnetic features were compared against the predictions of the diffusion treatment.
Results: We confirm the validity of the diffusion approximation to describe flux dispersal on large scales. We find that the inflows enhance flux cancellation, but at the same time affect the latitudinal separation of the polarities of the bipolar region. In most cases the latitudinal separation is limited by the inflows, resulting in a reduction of the axial dipole moment of the BMR. However, when the initial tilt angle of the BMR is small, the inflows produce an increase in latitudinal separation that leads to an increase in the axial dipole moment in spite of the enhanced flux destruction. This can give rise to a tilt of the BMR even when the BMR was originally aligned parallel to the equator. Title: Limitations of force-free magnetic field extrapolations: Revisiting basic assumptions Authors: Peter, H.; Warnecke, J.; Chitta, L. P.; Cameron, R. H. Bibcode: 2015A&A...584A..68P Altcode: 2015arXiv151004642P Context. Force-free extrapolations are widely used to study the magnetic field in the solar corona based on surface measurements.
Aims: The extrapolations assume that the ratio of internal energy of the plasma to magnetic energy, the plasma β, is negligible. Despite the widespread use of this assumption observations, models, and theoretical considerations show that β is of the order of a few percent to more than 10%, and thus not small. We investigate what consequences this has for the reliability of extrapolation results.
Methods: We use basic concepts starting with force and energy balance to infer relations between plasma β and free magnetic energy to study the direction of currents in the corona with respect to the magnetic field, and to estimate the errors in the free magnetic energy by neglecting effects of the plasma (β ≪ 1). A comparison with a 3D magneto-hydrodynamics (MHD) model supports our basic considerations.
Results: If plasma β is of the order of the relative free energy (the ratio of the free magnetic energy to the total magnetic energy) then the pressure gradient can balance the Lorentz force. This is the case in solar corona, and therefore the currents are not properly described. In particular, the error in terms of magnetic energy by neglecting the plasma is of the order of the free magnetic energy, so that the latter cannot be reliably determined by an extrapolation.
Conclusions: While a force-free extrapolation might capture the magnetic structure and connectivity of the coronal magnetic field, the derived currents and free magnetic energy are not reliable. Thus quantitative results of extrapolations on the location and amount of heating in the corona (through current dissipation) and on the energy storage of the magnetic field (e.g. for eruptive events) are limited. Title: Toward the construction of a medium size prototype Schwarzschild-Couder telescope for CTA Authors: Rousselle, J.; Byrum, K.; Cameron, R.; Connaughton, V.; Errando, M.; Griffiths, S.; Guarino, V.; Humensky, T. B.; Jenke, P.; Kaaret, P.; Kieda, D.; Limon, M.; Mognet, I.; Mukherjee, R.; Nieto, D.; Okumura, A.; Peck, A.; Petrashyk, A.; Ribeiro, D.; Stevenson, B.; Vassiliev, V.; Yu, P. Bibcode: 2015SPIE.9603E..05R Altcode: The construction of a prototype Schwarzschild-Couder telescope (pSCT) started in early June 2015 at the Fred Lawrence Whipple Observatory in Southern Arizona, as a candidate medium-sized telescope for the Cherenkov Telescope Array (CTA). Compared to current Davies-Cotton telescopes, this novel instrument with an aplanatic two-mirror optical system will offer a wider field-of-view and improved angular resolution. In addition, the reduced plate scale of the camera allows the use of highly-integrated photon detectors such as silicon photo multipliers. As part of CTA, this design has the potential to greatly improve the performance of the next generation ground-based observatory for very high-energy (E>60 GeV) gamma-ray astronomy. In this contribution we present the design and performance of both optical and alignment systems of the pSCT. Title: Three-dimensional simulations of near-surface convection in main-sequence stars. III. The structure of small-scale magnetic flux concentrations Authors: Beeck, B.; Schüssler, M.; Cameron, R. H.; Reiners, A. Bibcode: 2015A&A...581A..42B Altcode: 2015arXiv150504739B Context. The convective envelopes of cool main-sequence stars harbour magnetic fields with a complex global and local structure. These fields affect the near-surface convection and the outer stellar atmospheres in many ways and are responsible for the observable magnetic activity of stars.
Aims: Our aim is to understand the local structure in unipolar regions with moderate average magnetic flux density. These correspond to plage regions covering a substantial fraction of the surface of the Sun (and likely also the surface of other Sun-like stars) during periods of high magnetic activity.
Methods: We analyse the results of 18 local-box magnetohydrodynamics simulations covering the upper layers of the convection zones and the photospheres of cool main-sequence stars of spectral types F to early M. The average vertical field in these simulations ranges from 20 to 500 G.
Results: We find a substantial variation of the properties of the surface magnetoconvection between main-sequence stars of different spectral types. As a consequence of a reduced efficiency of the convective collapse of flux tubes, M dwarfs lack bright magnetic structures in unipolar regions of moderate field strength. The spatial correlation between velocity and the magnetic field as well as the lifetime of magnetic structures and their sizes relative to the granules vary significantly along the model sequence of stellar types.

Movies associated to Fig. A.1 are available in electronic form at http://www.aanda.org Title: Three-dimensional simulations of near-surface convection in main-sequence stars. IV. Effect of small-scale magnetic flux concentrations on centre-to-limb variation and spectral lines Authors: Beeck, B.; Schüssler, M.; Cameron, R. H.; Reiners, A. Bibcode: 2015A&A...581A..43B Altcode: 2015arXiv150504744B Context. Magnetic fields affect the local structure of the photosphere of stars. They can considerably influence the radiative properties near the optical surface, flow velocities, and the temperature and pressure profiles. This has an impact on observables such as limb darkening and spectral line profiles.
Aims: We aim at understanding qualitatively the influence of small magnetic flux concentrations in unipolar plage regions on the centre-to-limb variation of the intensity and its contrast and on the shape of spectral line profiles in cool main-sequence stars.
Methods: We analyse the bolometric and continuum intensity and its angular dependence of 24 radiative magnetohydrodynamic simulations of the near-surface layers of main-sequence stars with six different sets of stellar parameters (spectral types F to early M) and four different average magnetic field strengths (including the non-magnetic case). We also calculated disc-integrated profiles of three spectral lines.
Results: The small magnetic flux concentrations formed in the magnetic runs of simulations have a considerable impact on the intensity and its centre-to-limb variation. In some cases, the difference in limb darkening between magnetic and non-magnetic runs is larger than the difference between the spectral types. Spectral lines are not only broadened owing to the Zeeman effect, but are also strongly affected by the modified thermodynamical structure and flow patterns. This indirect magnetic impact on the line profiles is often bigger than that of the Zeeman effect.
Conclusions: The effects of the magnetic field on the radiation leaving the star can be considerable and is not restricted to spectral line broadening and polarisation by the Zeeman effect. The inhomogeneous structure of the magnetic field on small length scales and its impact on (and spatial correlation with) the local thermodynamical structure and the flow field near the surface influence the measurement of the global field properties and stellar parameters. These effects need to be taken into account in the interpretation of observations.

Appendix A is available in electronic form at http://www.aanda.org Title: A Medium Sized Schwarzschild-Couder Cherenkov Telescope Mechanical Design Proposed for the Cherenkov Telescope Array Authors: Byrum, K.; Humensky, T. B.; Benbow, W.; Cameron, R.; Criswell, S.; Errando, M.; Guarino, V.; Kaaret, P.; Kieda, D.; Mukherjee, R.; Naumann, D.; Nieto, D.; Northrop, R.; Okumura, A.; Roache, E.; Rousselle, J.; Schlenstedt, S.; Sternberger, R.; Vassiliev, V.; Wakely, S.; Zhao, H. Bibcode: 2015arXiv150903074B Altcode: The Cherenkov Telescope Array (CTA) is an international next-generation ground-based gamma-ray observatory. CTA will be implemented as southern and northern hemisphere arrays of tens of small, medium and large-sized imaging Cherenkov telescopes with the goal of improving the sensitivity over the current-generation experiments by an order of magnitude. CTA will provide energy coverage from ~20 GeV to more than 300 TeV. The Schwarzschild-Couder (SC) medium size (9.5m) telescopes will feature a novel aplanatic two-mirror optical design capable of accommodating a wide field-of-view with significantly improved angular resolution as compared to the traditional Davies-Cotton optical design. A full-scale prototype SC medium size telescope structure has been designed and will be constructed at the Fred Lawrence Whipple Observatory in southern Arizona during the fall of 2015. concentrate on the novel features of the design. Title: CTA Contributions to the 34th International Cosmic Ray Conference (ICRC2015) Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril, Ó.; Acero, F.; Acharya, B. S.; Actis, M.; Agnetta, G.; Aguilar, J. A.; Aharonian, F.; Akhperjanian, A.; Albert, A.; Alcubierre, M.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte, I.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.; Antonelli, L. A.; Antonucci, M.; Antonuccio, V.; Antoranz, P.; Aramo, C.; Aravantinos, A.; Argan, A.; Armstrong, T.; Arnaldi, H.; Arnold, L.; Arrabito, L.; Arrieta, M.; Arrieta, M.; Asano, K.; Asorey, H. G.; Aune, T.; Singh, C. B.; Babic, A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs, C.; Balbo, M.; Balis, D.; Balkowski, C.; Ballester, O.; Ballet, J.; Balzer, A.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.; Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becherini, Y.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico Ventura, D.; Berdugo, J.; Berge, D.; Bernardini, E.; Bernhard, S.; Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Bhatt, N.; Bhattacharjee, P.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Billotta, S.; Bilnik, W.; Biondo, B.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch Bigas, O.; Blasi, P.; Boehm, C.; Bogacz, L.; Bogdan, M.; Bohacova, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonifacio, P.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Bottani, A.; Böttcher, M.; Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Braiding, C.; Brandt, L.; Brau-Nogué, S.; Bregeon, J.; Bretz, T.; Briggs, M.; Brigida, M.; Bringmann, T.; Brisken, W.; Brocato, E.; Brook, P.; Brown, A. M.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Bryan, M.; Buanes, T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev, V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Cameron, R.; Camprecios, J.; Canelli, F.; Canestrari, R.; Cantu, S.; Capalbi, M.; Capasso, M.; Capobianco, G.; Caraveo, P.; Cardenzana, J.; Carius, S.; Carlile, C.; Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carroll, M.; Carter, J.; Carton, P. -H.; Caruso, R.; Casandjian, J. -M.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina, A.; Catalano, O.; Catalanotti, S.; Cavazzani, S.; Cazaux, S.; Cefalà, M.; Cerchiara, P.; Cereda, M.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaty, S.; Chaves, R.; Cheimets, P.; Chen, A.; Chen, X.; Chernyakova, M.; Chiappetti, L.; Chikawa, M.; Chinn, D.; Chitnis, V. R.; Cho, N.; Christov, A.; Chudoba, J.; Cieślar, M.; Cillis, A.; Ciocci, M. A.; Clay, R.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colombo, E.; Colome, J.; Colonges, S.; Compin, M.; Conforti, V.; Connaughton, V.; Connell, S.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corbel, S.; Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Covone, G.; Crimi, G.; Criswell, S. J.; Crocker, R.; Croston, J.; Cusumano, G.; Da Vela, P.; Dale, Ø.; D'Ammando, F.; Dang, D.; Daniel, M.; Davids, I.; Dawson, B.; Dazzi, F.; de Aguiar Costa, B.; De Angelis, A.; de Araujo Cardoso, R. F.; De Caprio, V.; De Cesare, G.; De Franco, A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma, F.; de Souza, V.; Decock, G.; Deil, C.; Del Santo, M.; Delagnes, E.; Deleglise, G.; Delgado, C.; della Volpe, D.; Deloye, P.; Depaola, G.; Detournay, M.; Dettlaff, A.; Di Girolamo, T.; Di Giulio, C.; Di Paola, A.; Di Pierro, F.; Di Sciascio, G.; Díaz, C.; Dick, J.; Dickinson, H.; Diebold, S.; Diez, V.; Digel, S.; Dipold, J.; Disset, G.; Distefano, A.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominik, N.; Dominis Prester, D.; Donat, A.; Donnarumma, I.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Doyle, K.; Drake, G.; Dravins, D.; Drury, L.; Dubus, G.; Dumas, D.; Dumm, J.; Durand, D.; D'Urso, D.; Dwarkadas, V.; Dyks, J.; Dyrda, M.; Ebr, J.; Echaniz, J. C.; Edy, E.; Egberts, K.; Egberts, K.; Eger, P.; Einecke, S.; Eisch, J.; Eisenkolb, F.; Eleftheriadis, C.; Elsässer, D.; Emmanoulopoulos, D.; Engelbrecht, C.; Engelhaupt, D.; Ernenwein, J. -P.; Errando, M.; Eschbach, S.; Etchegoyen, A.; Evans, P.; Fairbairn, M.; Falcone, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Farrell, E.; Farrell, S.; Fasola, G.; Fegan, S.; Feinstein, F.; Ferenc, D.; Fernandez, A.; Fernandez-Alonso, M.; Ferreira, O.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Filipčič, A.; Filipovic, M.; Fink, D.; Finley, C.; Finley, J. P.; Finoguenov, A.; Fioretti, V.; Fiorini, M.; Firpo Curcoll, R.; Fleischhack, H.; Flores, H.; Florin, D.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fontes, B.; Forest, F.; Fornasa, M.; Förster, A.; Fortin, P.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franco, F. J.; Frankowski, A.; Frega, N.; Freire Mota Albuquerque, I.; Freixas Coromina, L.; Fresnillo, L.; Fruck, C.; Fuessling, M.; Fugazza, D.; Fujita, Y.; Fukami, S.; Fukazawa, Y.; Fukuda, T.; Fukui, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gadola, A.; Galante, N.; Gall, D. D.; Gallant, Y.; Galloway, D.; Gallozzi, S.; Gao, S.; Garcia, B.; García Gil, R.; Garcia López, R.; Garczarczyk, M.; Gardiol, D.; Gargano, C.; Gargano, F.; Garozzo, S.; Garrecht, F.; Garrido, D.; Garrido, L.; Gascon, D.; Gaskins, J.; Gaudemard, J.; Gaug, M.; Gaweda, J.; Geffroy, N.; Gérard, L.; Ghalumyan, A.; Ghedina, A.; Ghigo, M.; Ghislain, P.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giglietto, N.; Gika, V.; Gimenes, R.; Giomi, M.; Giommi, P.; Giordano, F.; Giovannini, G.; Giro, E.; Giroletti, M.; Giuliani, A.; Glicenstein, J. -F.; Godinovic, N.; Goldoni, P.; Gomez Berisso, M.; Gomez Vargas, G. A.; Gonzalez, M. M.; González, A.; González, F.; González Muñoz, A.; Gothe, K. 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J.; Wakely, S. P.; Walter, R.; Walther, T.; Ward, J. E.; Ward, M.; Warda, K.; Warwick, R.; Wassberg, S.; Watson, J.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Wells, R.; Werner, F.; Werner, M.; Wetteskind, H.; White, M.; White, R.; Więcek, M.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wild, N.; Wilhelm, A.; Wilkinson, M.; Will, M.; Williams, D. A.; Williams, J. T.; Willingale, R.; Winde, M.; Winiarski, K.; Winkler, H.; Wischnewski, R.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, E.; Wu, T.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yebras, J. M.; Yelos, D.; Yeung, W.; Yoshida, A.; Yoshida, T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zabalza, V.; Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel, F.; Zanin, R.; Zanmar Sanchez, R.; Zavrtanik, D.; Zavrtanik, M.; Zdziarski, A.; Zech, A.; Zechlin, H.; Zhao, A.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zurbach, C.; Żychowski, P. Bibcode: 2015arXiv150805894C Altcode: List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands. Title: The Cause of the Weak Solar Cycle 24 Authors: Jiang, J.; Cameron, R. H.; Schüssler, M. Bibcode: 2015ApJ...808L..28J Altcode: 2015arXiv150701764J The ongoing 11 year cycle of solar activity is considerably less vigorous than the three cycles before. It was preceded by a very deep activity minimum with a low polar magnetic flux, the source of the toroidal field responsible for solar magnetic activity in the subsequent cycle. Simulation of the evolution of the solar surface field shows that the weak polar fields and thus the weakness of the present cycle 24 are mainly caused by a number of bigger bipolar regions emerging at low latitudes with a “wrong” (i.e., opposite to the majority for this cycle) orientation of their magnetic polarities in the north-south direction, which impaired the growth of the polar field. These regions had a particularly strong effect since they emerged within +/- 10^\circ latitude from the solar equator. Title: Construction of a Schwarzschild-Couder telescope as a candidate for the Cherenkov Telescope Array: Implementation of the opti Authors: Rousselle, J.; Byrum, K.; Cameron, R.; Connaughton, V.; Errando, M.; Guarino, V.; Humensky, B.; Jenke, P.; Kieda, D.; Mukherjee, R.; Nieto Castano, D.; Okumura, A.; Petrashyk, A.; Vassiliev, V. Bibcode: 2015ICRC...34..938R Altcode: 2015PoS...236..938R; 2015arXiv150901143R We present the design and the status of procurement of the optical system of the prototype Schwarzschild-Couder telescope (pSCT), for which construction is scheduled to begin in fall at the Fred Lawrence Whipple Observatory in southern Arizona, USA. The Schwarzschild-Couder telescope is a candidate for the medium-sized telescopes of the Cherenkov Telescope Array, which utilizes imaging atmospheric Cherenkov techniques to observe gamma rays in the energy range of 60Gev-60TeV. The pSCT novel aplanatic optical system is made of two segmented aspheric mirrors. The primary mirror has 48 mirror panels with an aperture of 9.6 m, while the secondary, made of 24 panels, has an diameter of 5.4 m. The resulting point spread function (PSF) is required to be better than 4 arcmin within a field of view of 6.4 degrees (80% of the field of view), which corresponds to a physical size of 6.4 mm on the focal plane. This goal represents a challenge for the inexpensive fabrication of aspheric mirror panels and for the precise alignment of the optical system as well as for the rigidity of the optical support structure. In this submission we introduce the design of the Schwarzschild-Couder optical system and describe the solutions adopted for the manufacturing of the mirror panels and their integration with the optical support structure. Title: A Medium Sized Schwarzschild-Couder Cherenkov Telescope Design Proposed for the Cherenkov Telescope Array Authors: Benbow, W.; Byrum, K.; Cameron, R.; Criswell, S.; Errando, M.; Guarino, V.; Humensky, B.; Kaaret, P.; Kieda, D.; Mukherjee, R.; Naumann, D.; Nieto, D.; Northrop, R.; Okumura, A.; Roache, E.; Rousselle, J.; Schlenstedt, S.; Sternberger, R.; Vassiliev, V.; Wakely, S.; Zhao, H. A. Bibcode: 2015ICRC...34.1029B Altcode: 2015PoS...236.1029B No abstract at ADS Title: Characterising exoplanets and their environment with UV transmission spectroscopy Authors: Fossati, L.; Bourrier, V.; Ehrenreich, D.; Haswell, C. A.; Kislyakova, K. G.; Lammer, H.; Lecavelier des Etangs, A.; Alibert, Y.; Ayres, T. R.; Ballester, G. E.; Barnes, J.; Bisikalo, D. V.; Collier, A.; Cameron; Czesla, S.; Desert, J. -M.; France, K.; Guedel, M.; Guenther, E.; Helling, Ch.; Heng, K.; Homstrom, M.; Kaltenegger, L.; Koskinen, T.; Lanza, A. F.; Linsky, J. L.; Mordasini, C.; Pagano, I.; Pollacco, D.; Rauer, H.; Reiners, A.; Salz, M.; Schneider, P. C.; Shematovich, V. I.; Staab, D.; Vidotto, A. A.; Wheatley, P. J.; Wood, B. E.; Yelle, R. V. Bibcode: 2015arXiv150301278F Altcode: Exoplanet science is now in its full expansion, particularly after the CoRoT and Kepler space missions that led us to the discovery of thousands of extra-solar planets. The last decade has taught us that UV observations play a major role in advancing our understanding of planets and of their host stars, but the necessary UV observations can be carried out only by HST, and this is going to be the case for many years to come. It is therefore crucial to build a treasury data archive of UV exoplanet observations formed by a dozen "golden systems" for which observations will be available from the UV to the infrared. Only in this way we will be able to fully exploit JWST observations for exoplanet science, one of the key JWST science case. Title: The Solar cycle: looking forward Authors: Cameron, Robert H. Bibcode: 2015HiA....16..111C Altcode: We discuss predictions for cycle 24 and the way forward if progress is to be made for cycle 25 and beyond. Title: The crucial role of surface magnetic fields for the solar dynamo Authors: Cameron, Robert; Schüssler, Manfred Bibcode: 2015Sci...347.1333C Altcode: 2015arXiv150308469C Sunspots and the plethora of other phenomena occurring in the course of the 11-year cycle of solar activity are a consequence of the emergence of magnetic flux at the solar surface. The observed orientations of bipolar sunspot groups imply that they originate from toroidal (azimuthally orientated) magnetic flux in the convective envelope of the Sun. We show that the net toroidal magnetic flux generated by differential rotation within a hemisphere of the convection zone is determined by the emerged magnetic flux at the solar surface and thus can be calculated from the observed magnetic field distribution. The main source of the toroidal flux is the roughly dipolar surface magnetic field at the polar caps, which peaks around the minima of the activity cycle. Title: Simulated magnetic flows in the solar photosphere Authors: Danilovic, S.; Cameron, R. H.; Solanki, S. K. Bibcode: 2015A&A...574A..28D Altcode: 2014arXiv1408.6159D Context. Recent Sunrise/IMaX observations have revealed supersonic magnetic flows.
Aims: Our aim is to determine the origin of these flows by using realistic magnetohydrodynamics simulations.
Methods: We simulated cancellation and emergence of magnetic flux through the solar photosphere. Our first numerical experiment started with a magnetic field of both polarities. To simulate emergence into a region with pre-existing field, we introduced a large-scale horizontally uniform sheet of a horizontal field. We followed the subsequent evolution and created synthetic polarimetric observations, including known instrumental effects of the Sunrise/IMaX and Hinode/SP instruments. We compared the simulated and observed spectropolarimetric signals.
Results: Strongly blue- and redshifted Stokes V signals are produced in locations where strong line-of-sight velocities coincide with the strong line-of-sight component of the magnetic field. The size and strength of simulated events is smaller than observed, and they are mostly associated with downflows, contrary to observations. In a few cases where they appear above a granule, single blue-lobed Stokes V are produced by strong gradients in magnetic field and velocity. No change of magnetic field sign is detected along the line of sight in these instances. More high-speed magnetised flows occurred when an emergence was simulated than when no horizontal field was added.
Conclusions: The simulations indicate that the observed events result from magnetic flux emergences in which reconnection may take place, but does not seem to be necessary.

The movies are available in electronic form at http://www.aanda.org Title: Magnetic Flux Transport at the Solar Surface Authors: Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.; Gizon, L.; Upton, L. Bibcode: 2015sac..book..491J Altcode: No abstract at ADS Title: Magnetic Flux Transport at the Solar Surface Authors: Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.; Gizon, L.; Upton, L. Bibcode: 2014SSRv..186..491J Altcode: 2014SSRv..tmp...43J; 2014arXiv1408.3186J After emerging to the solar surface, the Sun's magnetic field displays a complex and intricate evolution. The evolution of the surface field is important for several reasons. One is that the surface field, and its dynamics, sets the boundary condition for the coronal and heliospheric magnetic fields. Another is that the surface evolution gives us insight into the dynamo process. In particular, it plays an essential role in the Babcock-Leighton model of the solar dynamo. Describing this evolution is the aim of the surface flux transport model. The model starts from the emergence of magnetic bipoles. Thereafter, the model is based on the induction equation and the fact that after emergence the magnetic field is observed to evolve as if it were purely radial. The induction equation then describes how the surface flows—differential rotation, meridional circulation, granular, supergranular flows, and active region inflows—determine the evolution of the field (now taken to be purely radial). In this paper, we review the modeling of the various processes that determine the evolution of the surface field. We restrict our attention to their role in the surface flux transport model. We also discuss the success of the model and some of the results that have been obtained using this model. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha, Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung, Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank Bibcode: 2014atnf.prop.6430C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Interpreting the Helioseismic and Magnetic Imager (HMI) Multi-Height Velocity Measurements Authors: Nagashima, Kaori; Löptien, Björn; Gizon, Laurent; Birch, Aaron C.; Cameron, Robert; Couvidat, Sebastien; Danilovic, Sanja; Fleck, Bernhard; Stein, Robert Bibcode: 2014SoPh..289.3457N Altcode: 2014arXiv1404.3569N; 2014SoPh..tmp...84N The Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) filtergrams, taken at six wavelengths around the Fe I 6173.3 Å line, contain information about the line-of-sight velocity over a range of heights in the solar atmosphere. Multi-height velocity inferences from these observations can be exploited to study wave motions and energy transport in the atmosphere. Using realistic convection-simulation datasets provided by the STAGGER and MURaM codes, we generate synthetic filtergrams and explore several methods for estimating Dopplergrams. We investigate at which height each synthetic Dopplergram correlates most strongly with the vertical velocity in the model atmospheres. On the basis of the investigation, we propose two Dopplergrams other than the standard HMI-algorithm Dopplergram produced from HMI filtergrams: a line-center Dopplergram and an average-wing Dopplergram. These two Dopplergrams correlate most strongly with vertical velocities at the heights of 30 - 40 km above (line center) and 30 - 40 km below (average wing) the effective height of the HMI-algorithm Dopplergram. Therefore, we can obtain velocity information from two layers separated by about a half of a scale height in the atmosphere, at best. The phase shifts between these multi-height Dopplergrams from observational data as well as those from the simulated data are also consistent with the height-difference estimates in the frequency range above the photospheric acoustic-cutoff frequency. Title: The Role of Subsurface Flows in Solar Surface Convection: Modeling the Spectrum of Supergranular and Larger Scale Flows Authors: Lord, J. W.; Cameron, R. H.; Rast, M. P.; Rempel, M.; Roudier, T. Bibcode: 2014ApJ...793...24L Altcode: 2014arXiv1407.2209L We model the solar horizontal velocity power spectrum at scales larger than granulation using a two-component approximation to the mass continuity equation. The model takes four times the density scale height as the integral (driving) scale of the vertical motions at each depth. Scales larger than this decay with height from the deeper layers. Those smaller are assumed to follow a Kolmogorov turbulent cascade, with the total power in the vertical convective motions matching that required to transport the solar luminosity in a mixing length formulation. These model components are validated using large-scale radiative hydrodynamic simulations. We reach two primary conclusions. (1) The model predicts significantly more power at low wavenumbers than is observed in the solar photospheric horizontal velocity spectrum. (2) Ionization plays a minor role in shaping the observed solar velocity spectrum by reducing convective amplitudes in the regions of partial helium ionization. The excess low wavenumber power is also seen in the fully nonlinear three-dimensional radiative hydrodynamic simulations employing a realistic equation of state. This adds to other recent evidence suggesting that the amplitudes of large-scale convective motions in the Sun are significantly lower than expected. Employing the same feature tracking algorithm used with observational data on the simulation output, we show that the observed low wavenumber power can be reproduced in hydrodynamic models if the amplitudes of large-scale modes in the deep layers are artificially reduced. Since the large-scale modes have reduced amplitudes, modes on the scale of supergranulation and smaller remain important to convective heat flux even in the deep layers, suggesting that small-scale convective correlations are maintained through the bulk of the solar convection zone. Title: Effects of the Scatter in Sunspot Group Tilt Angles on the Large-scale Magnetic Field at the Solar Surface Authors: Jiang, J.; Cameron, R. H.; Schüssler, M. Bibcode: 2014ApJ...791....5J Altcode: 2014arXiv1406.5564J The tilt angles of sunspot groups represent the poloidal field source in Babcock-Leighton-type models of the solar dynamo and are crucial for the build-up and reversals of the polar fields in surface flux transport (SFT) simulations. The evolution of the polar field is a consequence of Hale's polarity rules, together with the tilt angle distribution which has a systematic component (Joy's law) and a random component (tilt-angle scatter). We determine the scatter using the observed tilt angle data and study the effects of this scatter on the evolution of the solar surface field using SFT simulations with flux input based upon the recorded sunspot groups. The tilt angle scatter is described in our simulations by a random component according to the observed distributions for different ranges of sunspot group size (total umbral area). By performing simulations with a number of different realizations of the scatter we study the effect of the tilt angle scatter on the global magnetic field, especially on the evolution of the axial dipole moment. The average axial dipole moment at the end of cycle 17 (a medium-amplitude cycle) from our simulations was 2.73 G. The tilt angle scatter leads to an uncertainty of 0.78 G (standard deviation). We also considered cycle 14 (a weak cycle) and cycle 19 (a strong cycle) and show that the standard deviation of the axial dipole moment is similar for all three cycles. The uncertainty mainly results from the big sunspot groups which emerge near the equator. In the framework of Babcock-Leighton dynamo models, the tilt angle scatter therefore constitutes a significant random factor in the cycle-to-cycle amplitude variability, which strongly limits the predictability of solar activity. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha, Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung, Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank Bibcode: 2014atnf.prop.6049C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Migration of Ca II H bright points in the internetwork Authors: Jafarzadeh, S.; Cameron, R. H.; Solanki, S. K.; Pietarila, A.; Feller, A.; Lagg, A.; Gandorfer, A. Bibcode: 2014A&A...563A.101J Altcode: 2014arXiv1401.7522J Context. The migration of magnetic bright point-like features (MBP) in the lower solar atmosphere reflects the dispersal of magnetic flux as well as the horizontal flows of the atmospheric layer they are embedded in.
Aims: We analyse trajectories of the proper motion of intrinsically magnetic, isolated internetwork Ca ii H MBPs (mean lifetime 461 ± 9 s) to obtain their diffusivity behaviour.
Methods: We use seeing-free high spatial and temporal resolution image sequences of quiet-Sun, disc-centre observations obtained in the Ca ii H 3968 Å passband of the Sunrise Filter Imager (SuFI) onboard the Sunrise balloon-borne solar observatory. Small MBPs in the internetwork are automatically tracked. The trajectory of each MBP is then calculated and described by a diffusion index (γ) and a diffusion coefficient (D). We also explore the distribution of the diffusion indices with the help of a Monte Carlo simulation.
Results: We find γ = 1.69 ± 0.08 and D = 257 ± 32 km2 s-1 averaged over all MBPs. Trajectories of most MBPs are classified as super-diffusive, i.e. γ > 1, with the determined γ being the largest obtained so far to our knowledge. A direct correlation between D and timescale (τ) determined from trajectories of all MBPs is also obtained. We discuss a simple scenario to explain the diffusivity of the observed, relatively short-lived MBPs while they migrate within a small area in a supergranule (i.e. an internetwork area). We show that the scatter in the γ values obtained for individual MBPs is due to their limited lifetimes.
Conclusions: The super-diffusive MBPs can be described as random walkers (due to granular evolution and intergranular turbulence) superposed on a large systematic (background) velocity, caused by granular, mesogranular, and supergranular flows. Title: Physical causes of solar cycle amplitude variability Authors: Cameron, R. H.; Jiang, J.; Schüssler, M.; Gizon, L. Bibcode: 2014JGRA..119..680C Altcode: The level of solar activity varies from cycle to cycle. This variability is probably caused by a combination of nonlinear and random effects. Based on surface flux transport simulations, we show that the observed inflows into active regions and toward the activity belts provide an important nonlinearity in the framework of Babcock-Leighton model for the solar dynamo. Inclusion of these inflows also leads to a reproduction of the observed proportionality between the open heliospheric flux during activity minima and the maximum sunspot number of the following cycle. A substantial component of the random variability of the cycle strength is associated with the cross-equatorial flux plumes that occur when large, highly tilted sunspot groups emerge close to the equator. We show that the flux transported by these events is important for the amplitude of the polar fields and open flux during activity minima. The combined action of inflows and cross-equatorial flux plumes provides an explanation for the weakness of the polar fields at the end of solar cycle 23 (and hence for the relative weakness of solar cycle 24). Title: Can Surface Flux Transport Account for the Weak Polar Field in Cycle 23? Authors: Jiang, Jie; Cameron, Robert H.; Schmitt, Dieter; Schüssler, Manfred Bibcode: 2014crh..book..289J Altcode: No abstract at ADS Title: Snowmass Cosmic Frontiers 6 (CF6) Working Group Summary --The Bright Side of the Cosmic Frontier: Cosmic Probes of Fundamental Physics Authors: Beatty, J. J.; Nelson, A. E.; Olinto, A.; Sinnis, G.; Abeysekara, A. U.; Anchordoqui, L. A.; Aramaki, T.; Belz, J.; Buckley, J. H.; Byrum, K.; Cameron, R.; Chen, M-C.; Clark, K.; Connolly, A.; Cowen, D.; DeYoung, T.; Dumm, P. von Doetinchem J.; Errando, M.; Farrar, G.; Ferrer, F.; Fortson, L.; Funk, S.; Grant, D.; Griffiths, S.; Groß, A.; Hailey, C.; Hogan, C.; Holder, J.; Humensky, B.; Kaaret, P.; Klein, S. R.; Krawczynski, H.; Krennrich, F.; Krings, K.; Krizmanic, J.; Kusenko, A.; Linnemann, J. T.; MacGibbon, J. H.; Matthews, J.; McCann, A.; Mitchell, J.; Mukherjee, R.; Nitz, D.; Ong, R. A.; Orr, M.; Otte, N.; Paul, T.; Resconi, E.; Sanchez-Conde, M. A.; Sokolsky, P.; Stecker, F.; Stump, D.; Taboada, I.; Thomson, G. B.; Tollefson, K.; von Doetinchem, P.; Ukwatta, T.; Vandenbroucke, J.; Vasileiou, V.; Vassileiv, V. V.; Weiler, T. J.; Williams, D. A.; Weinstein, A.; Wood, M.; Zitzer, B. Bibcode: 2013arXiv1310.5662B Altcode: Report of the CF6 Working Group at Snowmass 2013. Topics addressed include ultra-high energy cosmic rays, neutrinos, gamma rays, baryogenesis, and experiments probing the fundamental nature of spacetime. Title: Three-dimensional simulations of near-surface convection in main-sequence stars. II. Properties of granulation and spectral lines Authors: Beeck, B.; Cameron, R. H.; Reiners, A.; Schüssler, M. Bibcode: 2013A&A...558A..49B Altcode: 2013arXiv1308.4873B Context. The atmospheres of cool main-sequence stars are structured by convective flows from the convective envelope that penetrate the optically thin layers and lead to structuring of the stellar atmospheres analogous to solar granulation. The flows have considerable influence on the 3D structure of temperature and pressure and affect the profiles of spectral lines formed in the photosphere.
Aims: For the set of six 3D radiative (M)HD simulations of cool main-sequence stars described in the first paper of this series, we analyse the near-surface layers. We aim at describing the properties of granulation of different stars and at quantifying the effects on spectral lines of the thermodynamic structure and flows of 3D convective atmospheres.
Methods: We detected and tracked granules in brightness images from the simulations to analyse their statistical properties, as well as their evolution and lifetime. We calculated spatially resolved spectral line profiles using the line synthesis code SPINOR. To enable a comparison to stellar observations, we implemented a numerical disc-integration, which includes (differential) rotation.
Results: Although the stellar parameters change considerably along the model sequence, the properties of the granules are very similar. The impact of the 3D structure of the atmospheres on line profiles is measurable in disc-integrated spectra. Line asymmetries caused by convection are modulated by stellar rotation.
Conclusions: The 3D structure of cool stellar atmospheres as shaped by convective flows has to be taken into account when using photospheric lines to determine stellar parameters. Title: Polar plumes' orientation and the Sun's global magnetic field Authors: de Patoul, Judith; Inhester, Bernd; Cameron, Robert Bibcode: 2013A&A...558L...4D Altcode: 2013arXiv1309.5916D
Aims: We characterize the orientation of polar plumes as a tracer of the large-scale coronal magnetic field configuration. We monitor in particular the north and south magnetic pole locations and the magnetic opening during 2007-2008 and provide some understanding of the variations in these quantities.
Methods: The polar plume orientation is determined by applying the Hough-wavelet transform to a series of EUV images and extracting the key Hough space parameters of the resulting maps. The same procedure is applied to the polar cap field inclination derived from extrapolating magnetograms generated by a surface flux transport model.
Results: We observe that the position where the magnetic field is radial (the Sun's magnetic poles) reflects the global organization of magnetic field on the solar surface, and we suggest that this opens the possibility of both detecting flux emergence anywhere on the solar surface (including the far side) and better constraining the reorganization of the corona after flux emergence. Title: Three-dimensional simulations of near-surface convection in main-sequence stars. I. Overall structure Authors: Beeck, B.; Cameron, R. H.; Reiners, A.; Schüssler, M. Bibcode: 2013A&A...558A..48B Altcode: 2013arXiv1308.4874B Context. The near-surface layers of cool main-sequence stars are structured by convective flows, which are overshooting into the atmosphere. The flows and the associated spatio-temporal variations of density and temperature affect spectral line profiles and thus have an impact on estimates of stellar properties such as effective temperature, gravitational acceleration, and abundances.
Aims: We aim at identifying distinctive properties of the thermodynamic structure of the atmospheres of different stars and understand their causes.
Methods: We ran comprehensive 3D radiation hydrodynamics simulations of the near-surface layers of six simulated stars of spectral type F3V to M2V with the MURaM code. We carry out a systematic parameter study of the mean stratifications, flow structures, and the energy flux in these stars.
Results: We find monotonic trends along the lower main sequence in granule size, flow velocity, and intensity contrast. The convection in the M-star models differs substantially from that of the hotter stars, mainly owing to the more gradual transition from convective to radiative energy transport.
Conclusions: While the basic mechanisms driving surface convection in cool stars are the same, the properties of the convection vary along the main sequence. Apart from monotonic trends in rms velocity, intensity contrast, granule size, etc., there is a transition between "naked" and "hidden" granulation around spectral type K5V caused by the (highly non-linear) temperature dependence of the opacity. These variations have to be taken into account when stellar parameters are derived from spectra.

Appendix A is available in electronic form at http://www.aanda.org Title: Helioseismology of sunspots: how sensitive are travel times to the Wilson depression and to the subsurface magnetic field? Authors: Schunker, H.; Gizon, L.; Cameron, R. H.; Birch, A. C. Bibcode: 2013A&A...558A.130S Altcode: 2013arXiv1303.6307S To assess the ability of helioseismology to probe the subsurface structure and magnetic field of sunspots, we need to determine how helioseismic travel times depend on perturbations to sunspot models. Here we numerically simulate the propagation of f, p1, and p2 wave packets through magnetic sunspot models. Among the models we considered, a ±50 km change in the height of the Wilson depression and a change in the subsurface magnetic field geometry can both be detected above the observational noise level. We also find that the travel-time shifts due to changes in a sunspot model must be modeled by computing the effects of changing the reference sunspot model, and not by computing the effects of changing the subsurface structure in the quiet-Sun model. For p1 modes, the latter is wrong by a factor of four. In conclusion, numerical modeling of MHD wave propagation is an essential tool for interpreting the effects of sunspots on seismic waveforms. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha, Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung, Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank Bibcode: 2013atnf.prop.5777C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Limits to solar cycle predictability: Cross-equatorial flux plumes Authors: Cameron, R. H.; Dasi-Espuig, M.; Jiang, J.; Işık, E.; Schmitt, D.; Schüssler, M. Bibcode: 2013A&A...557A.141C Altcode: 2013arXiv1308.2827C Context. Within the Babcock-Leighton framework for the solar dynamo, the strength of a cycle is expected to depend on the strength of the dipole moment or net hemispheric flux during the preceding minimum, which depends on how much flux was present in each hemisphere at the start of the previous cycle and how much net magnetic flux was transported across the equator during the cycle. Some of this transport is associated with the random walk of magnetic flux tubes subject to granular and supergranular buffeting, some of it is due to the advection caused by systematic cross-equatorial flows such as those associated with the inflows into active regions, and some crosses the equator during the emergence process.
Aims: We aim to determine how much of the cross-equatorial transport is due to small-scale disorganized motions (treated as diffusion) compared with other processes such as emergence flux across the equator.
Methods: We measure the cross-equatorial flux transport using Kitt Peak synoptic magnetograms, estimating both the total and diffusive fluxes.
Results: Occasionally a large sunspot group, with a large tilt angle emerges crossing the equator, with flux from the two polarities in opposite hemispheres. The largest of these events carry a substantial amount of flux across the equator (compared to the magnetic flux near the poles). We call such events cross-equatorial flux plumes. There are very few such large events during a cycle, which introduces an uncertainty into the determination of the amount of magnetic flux transported across the equator in any particular cycle. As the amount of flux which crosses the equator determines the amount of net flux in each hemisphere, it follows that the cross-equatorial plumes introduce an uncertainty in the prediction of the net flux in each hemisphere. This leads to an uncertainty in predictions of the strength of the following cycle. Title: No evidence for planetary influence on solar activity Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2013A&A...557A..83C Altcode: 2013arXiv1307.5988C Context. Recently, Abreu et al. (2012, A&A. 548, A88) proposed a long-term modulation of solar activity through tidal effects exerted by the planets. This claim is based upon a comparison of (pseudo-)periodicities derived from records of cosmogenic isotopes with those arising from planetary torques on an ellipsoidally deformed Sun.
Aims: We examined the statistical significance of the reported similarity of the periods.
Methods: The tests carried out by Abreu et al. were repeated with artificial records of solar activity in the form of white or red noise. The tests were corrected for errors in the noise definition as well as in the apodisation and filtering of the random series.
Results: The corrected tests provide probabilities for chance coincidence that are higher than those claimed by Abreu et al. by about 3 and 8 orders of magnitude for white and red noise, respectively. For an unbiased choice of the width of the frequency bins used for the test (a constant multiple of the frequency resolution) the probabilities increase by another two orders of magnitude to 7.5% for red noise and 22% for white noise.
Conclusions: The apparent agreement between the periodicities in records of cosmogenic isotopes as proxies for solar activity and planetary torques is statistically insignificant. There is no evidence for a planetary influence on solar activity. Title: Sunspot group tilt angles and the strength of the solar cycle (Corrigendum) Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron, R.; Peñuela, T. Bibcode: 2013A&A...556C...3D Altcode: No abstract at ADS Title: CTA contributions to the 33rd International Cosmic Ray Conference (ICRC2013) Authors: CTA Consortium, The; :; Abril, O.; Acharya, B. S.; Actis, M.; Agnetta, G.; Aguilar, J. A.; Aharonian, F.; Ajello, M.; Akhperjanian, A.; Alcubierre, M.; Aleksic, J.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte, I.; Aloisio, R.; Amato, E.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Angüner, E. O.; Antonelli, L. A.; Antonuccio, V.; Antonucci, M.; Antoranz, P.; Aravantinos, A.; Argan, A.; Arlen, T.; Aramo, C.; Armstrong, T.; Arnaldi, H.; Arrabito, L.; Asano, K.; Ashton, T.; Asorey, H. G.; Aune, T.; Awane, Y.; Baba, H.; Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.; Balbo, M.; Balis, D.; Balkowski, C.; Ballet, J.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.; Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becerra, J.; Becerra, J.; Becherini, Y.; Bechtol, K. C.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Belluso, M.; Benbow, W.; Berdugo, J.; Berge, D.; Berger, K.; Bernard, F.; Bernardino, T.; Bernlöhr, K.; Bertucci, B.; Bhat, N.; Bhattacharyya, S.; Biasuzzi, B.; Bigongiari, C.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.; Bobkov, A.; Boccone, V.; Böttcher, M.; Bogacz, L.; Bogart, J.; Bogdan, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas, P.; Borgland, A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.; Bouchet, L.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.; Bretz, T.; Briggs, M.; Brigida, M.; Bringmann, T.; Britto, R.; Brook, P.; Brun, P.; Brunetti, L.; Bruno, P.; Bucciantini, N.; Buanes, T.; Buckley, J.; Bühler, R.; Bugaev, V.; Bulgarelli, A.; Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron, R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo, P.; Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carter, J.; Carton, P. -H.; Caruso, R.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina, A.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerchiara, P.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaves, R.; Cheimets, P.; Chen, A.; Chiang, J.; Chiappetti, L.; Chikawa, M.; Chitnis, V. R.; Chollet, F.; Christof, A.; Chudoba, J.; Cieślar, M.; Cillis, A.; Cilmo, M.; Codino, A.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino, S.; Crimi, G.; Criswell, S. J.; Croston, J.; Cusumano, G.; Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.; Davids, I.; Dazzi, F.; de Angelis, A.; De Caprio, V.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.; de Lotto, B.; De Luca, A.; de Naurois, M.; de Oliveira, Y.; de Oña Wilhelmi, E.; de Palma, F.; de Souza, V.; Decerprit, G.; Decock, G.; Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; della Volpe, D.; Demange, P.; Depaola, G.; Dettlaff, A.; Di Girolamo, T.; Di Giulio, C.; Di Paola, A.; Di Pierro, F.; di Sciascio, G.; Díaz, C.; Dick, J.; Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dwarkadas, V.; Dyks, J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke, S.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Evans, P. A.; Falcone, A.; Faltenbacher, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Farrell, E.; Fasola, G.; Favill, B. W.; Fede, E.; Federici, S.; Fegan, S.; Feinstein, F.; Ferenc, D.; Ferrando, P.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Fillin-Martino, E.; Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll, R.; Flandrini, E.; Fleischhack, H.; Flores, H.; Florin, D.; Focke, W.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fornasa, M.; Förster, A.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franco, F. J.; Frankowski, A.; Fransson, C.; Fraser, G. 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M.; Mirzoyan, R.; Mistò, A.; Mizuno, T.; Moal, B.; Moderski, R.; Mognet, I.; Molinari, E.; Molinaro, M.; Montaruli, T.; Monte, C.; Monteiro, I.; Moore, P.; Moralejo Olaizola, A.; Mordalska, M.; Morello, C.; Mori, K.; Morlino, G.; Morselli, A.; Mottez, F.; Moudden, Y.; Moulin, E.; Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi, H.; Murase, K.; StJ. Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo, M.; Nayman, P.; Nedbal, D.; Neise, D.; Nellen, L.; Neronov, A.; Neustroev, V.; Neyroud, N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.; Niemiec, J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nishikawa, K. -I.; Noda, K.; Nolan, S.; Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.; Oakes, L.; O'Brien, P. T.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okuda, T.; Okumura, A.; Olive, J. -F.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J. P.; Ostrowski, M.; Otero, L. 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C.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.; Stella, C.; Stergioulas, N.; Sternberger, R.; Sterzel, M.; Stinzing, F.; Stodulski, M.; Stolarczyk, Th.; Straumann, U.; Strazzeri, E.; Stringhetti, L.; Suarez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. -H.; Sun, S.; Supanitsky, A. D.; Suric, T.; Sutcliffe, P.; Sykes, J. M.; Szanecki, M.; Szepieniec, T.; Szostek, A.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, G.; Tammi, J.; Tanaka, M.; Tanaka, S.; Tasan, J.; Tavani, M.; Tavernet, J. -P.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada, Y.; Terrier, R.; Teshima, M.; Testa, V.; Tezier, D.; Thayer, J.; Thuermann, D.; Tibaldo, L.; Tibaldo, L.; Tibolla, O.; Tiengo, A.; Timpanaro, M. C.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tonachini, A.; Torii, K.; Tornikoski, M.; Torres, D. F.; Torres, M.; Toscano, S.; Toso, G.; Tosti, G.; Totani, T.; Toussenel, F.; Tovmassian, G.; Travnicek, P.; Treves, A.; Trifoglio, M.; Troyano, I.; Tsinganos, K.; Ueno, H.; Umana, G.; Umehara, K.; Upadhya, S. S.; Usher, T.; Uslenghi, M.; Vagnetti, F.; Valdes-Galicia, J. F.; Vallania, P.; Vallejo, G.; van Driel, W.; van Eldik, C.; Vandenbrouke, J.; Vanderwalt, J.; Vankov, H.; Vasileiadis, G.; Vassiliev, V.; Veberic, D.; Vegas, I.; Vercellone, S.; Vergani, S.; Verzi, V.; Vettolani, G. P.; Veyssière, C.; Vialle, J. P.; Viana, A.; Videla, M.; Vigorito, C.; Vincent, P.; Vincent, S.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Voisin, V.; Vollhardt, A.; von Gunten, H. -P.; Vorobiov, S.; Vuerli, C.; Waegebaert, V.; Wagner, R.; Wagner, R. G.; Wagner, S.; Wakely, S. P.; Walter, R.; Walther, T.; Warda, K.; Warwick, R. S.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Werner, M.; Wetteskind, H.; White, R. J.; Wierzcholska, A.; Wiesand, S.; Wilhelm, A.; Wilkinson, M. I.; Williams, D. A.; Willingale, R.; Winde, M.; Winiarski, K.; Wischnewski, R.; Wiśniewski, Ł.; Wojcik, P.; Wood, M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yebras, J. M.; Yelos, D.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zacharias, M.; Zajczyk, A.; Zampieri, L.; Zanin, R.; Zdziarski, A.; Zech, A.; Zhao, A.; Zhou, X.; Zietara, K.; Ziolkowski, J.; Ziółkowski, P.; Zitelli, V.; Zurbach, C.; Zychowski, P. Bibcode: 2013arXiv1307.2232C Altcode: Compilation of CTA contributions to the proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), which took place in 2-9 July, 2013, in Rio de Janeiro, Brazil Title: Can Surface Flux Transport Account for the Weak Polar Field in Cycle 23? Authors: Jiang, Jie; Cameron, Robert H.; Schmitt, Dieter; Schüssler, Manfred Bibcode: 2013SSRv..176..289J Altcode: 2011SSRv..tmp..212J; 2011SSRv..tmp...69J; 2011arXiv1104.4183J; 2011SSRv..tmp..136J; 2011SSRv..tmp..368J To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations. Title: First evidence of interaction between longitudinal and transverse waves in solar magnetic elements Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.; Martínez Pillet, V. Bibcode: 2013A&A...554A.115S Altcode: 2013arXiv1304.7088S Small-scale magnetic fields are thought to play an important role in the heating of the outer solar atmosphere. By taking advantage of the unprecedented high-spatial and temporal cadence of the Imaging Magnetograph eXperiment (IMaX), the filter vector polarimeter on board the Sunrise balloon-borne observatory, we study the transversal and longitudinal velocity oscillations in small magnetic elements. The results of this analysis are then compared to magnetohydrodynamic (MHD) simulations, showing excellent agreement. We found buffeting-induced transverse oscillations with velocity amplitudes of the order of 1-2 km s-1 to be common along with longitudinal oscillations with amplitudes ~0.4 km s-1. Moreover, we also found an interaction between transverse oscillations and longitudinal velocity oscillations, showing a ± 90° phase lag at the frequency at which they exhibit the maximum coherence in the power spectrum. Our results are consistent with the theoretical picture in which MHD longitudinal waves are excited inside small magnetic elements as a response of the flux tube to the forcing action of the granular flows. Title: Modeling solar cycles 15 to 21 using a flux transport dynamo Authors: Jiang, J.; Cameron, R. H.; Schmitt, D.; Işık, E. Bibcode: 2013A&A...553A.128J Altcode: 2013arXiv1304.5730J Context. The Sun's polar fields and open flux around the time of activity minima have been considered to be strongly correlated with the strength of the subsequent maximum of solar activity.
Aims: We aim to investigate the behavior of a Babcock-Leighton dynamo with a source poloidal term that is based on the observed sunspot areas and tilts. In particular, we investigate whether the toroidal fields at the base of convection zone from the model are correlated with the observed solar cycle activity maxima.
Methods: We used a flux transport dynamo model that includes convective pumping and a poloidal source term based on the historical record of sunspot group areas, locations, and tilt angles to simulate solar cycles 15 to 21.
Results: We find that the polar fields near minima and the toroidal flux at the base of the convection zone are both highly correlated with the subsequent maxima of solar activity levels (r = 0.85 and r = 0.93, respectively).
Conclusions: The Babcock-Leighton dynamo is consistent with the observationally inferred correlations. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Ojha, Roopesh; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Cheung, Teddy; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone; Schinzel, Frank Bibcode: 2013atnf.prop.5452C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Introducing the CTA concept Authors: Acharya, B. S.; Actis, M.; Aghajani, T.; Agnetta, G.; Aguilar, J.; Aharonian, F.; Ajello, M.; Akhperjanian, A.; Alcubierre, M.; Aleksić, J.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte, I.; Amato, E.; Anderson, J.; Angüner, E. O.; Antonelli, L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Armstrong, T.; Arnaldi, H.; Arrabito, L.; Asano, K.; Ashton, T.; Asorey, H. G.; Awane, Y.; Baba, H.; Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.; Balbo, M.; Balis, D.; Balkowski, C.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.; Bastieri, D.; Bauer, C.; Baushev, A.; Becerra, J.; Becherini, Y.; Bechtol, K. C.; Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Belluso, M.; Benbow, W.; Berdugo, J.; Berger, K.; Bernard, F.; Bernardino, T.; Bernlöhr, K.; Bhat, N.; Bhattacharyya, S.; Bigongiari, C.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.; Bobkov, A.; Boccone, V.; Boettcher, M.; Bogacz, L.; Bogart, J.; Bogdan, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas, P.; Borgland, A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.; Bouchet, L.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.; Bretz, T.; Briggs, M.; Bringmann, T.; Brook, P.; Brun, P.; Brunetti, L.; Buanes, T.; Buckley, J.; Buehler, R.; Bugaev, V.; Bulgarelli, A.; Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron, R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo, P.; Carmona, E.; Carosi, A.; Carr, J.; Carton, P. -H.; Casanova, S.; Casiraghi, M.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chen, A.; Chiang, J.; Chiappetti, L.; Chikawa, M.; Chitnis, V. R.; Chollet, F.; Chudoba, J.; Cieślar, M.; Cillis, A.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.; Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino, S.; Crimi, G.; Criswell, S. J.; Croston, J.; Cusumano, G.; Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.; Davids, I.; Dazzi, F.; De Angelis, A.; De Caprio, V.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de Mello Neto, J. R. T.; de Naurois, M.; de Oliveira, Y.; de Oña Wilhelmi, E.; de Souza, V.; Decerprit, G.; Decock, G.; Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; Della Volpe, D.; Demange, P.; Depaola, G.; Dettlaff, A.; Di Paola, A.; Di Pierro, F.; Díaz, C.; Dick, J.; Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dyks, J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke, S.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Evans, P.; Falcone, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Fasola, G.; Favill, B.; Fede, E.; Federici, S.; Fegan, S.; Feinstein, F.; Ferenc, D.; Ferrando, P.; Fesquet, M.; Fiasson, A.; Fillin-Martino, E.; Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll, R.; Flores, H.; Florin, D.; Focke, W.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fornasa, M.; Förster, A.; Fortson, L.; Fouque, N.; Franckowiak, A.; Fransson, C.; Fraser, G.; Frei, R.; Albuquerque, I. F. M.; Fresnillo, L.; Fruck, C.; Fujita, Y.; Fukazawa, Y.; Fukui, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gabriele, R.; Gadola, A.; Galante, N.; Gall, D.; Gallant, Y.; Gámez-García, J.; García, B.; Garcia López, R.; Gardiol, D.; Garrido, D.; Garrido, L.; Gascon, D.; Gaug, M.; Gaweda, J.; Gebremedhin, L.; Geffroy, N.; Gerard, L.; Ghedina, A.; Ghigo, M.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Gika, V.; Giommi, P.; Girard, N.; Giro, E.; Giuliani, A.; Glanzman, T.; Glicenstein, J. -F.; Godinovic, N.; Golev, V.; Gomez Berisso, M.; Gómez-Ortega, J.; Gonzalez, M. M.; González, A.; González, F.; González Muñoz, A.; Gothe, K. 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A.; Kushida, J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.; La Rosa, G.; Lacombe, K.; Lamanna, G.; Lande, J.; Languignon, D.; Lapington, J.; Laporte, P.; Lavalley, C.; Le Flour, T.; Le Padellec, A.; Lee, S. -H.; Lee, W. H.; Leigui de Oliveira, M. A.; Lelas, D.; Lenain, J. -P.; Leopold, D. J.; Lerch, T.; Lessio, L.; Lieunard, B.; Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart, H.; Lohse, T.; Lombardi, S.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas, A.; Lorca, A.; Lorenz, E.; Lubinski, P.; Lucarelli, F.; Lüdecke, H.; Ludwin, J.; Luque-Escamilla, P. L.; Lustermann, W.; Luz, O.; Lyard, E.; Maccarone, M. C.; Maccarone, T. J.; Madejski, G. 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M.; Mirzoyan, R.; Mizuno, T.; Moal, B.; Moderski, R.; Mognet, I.; Molinari, E.; Molinaro, M.; Montaruli, T.; Monteiro, I.; Moore, P.; Moralejo Olaizola, A.; Mordalska, M.; Morello, C.; Mori, K.; Mottez, F.; Moudden, Y.; Moulin, E.; Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi, H.; Murase, K.; Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo, M.; Nayman, P.; Nedbal, D.; Neise, D.; Nellen, L.; Neustroev, V.; Neyroud, N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.; Niemiec, J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nolan, S.; Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.; O'Brien, P.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okuda, T.; Okumura, A.; Olive, J. -F.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J.; Ostrowski, M.; Otero, L. A.; Otte, N.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padilla, L.; Paiano, S.; Paillot, D.; Paizis, A.; Palanque, S.; Palatka, M.; Pallota, J.; Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Paoletti, R.; Papayannis, A.; Papyan, G.; Paredes, J. M.; Pareschi, G.; Parks, G.; Parraud, J. -M.; Parsons, D.; Paz Arribas, M.; Pech, M.; Pedaletti, G.; Pelassa, V.; Pelat, D.; Perez, M. d. C.; Persic, M.; Petrucci, P. -O.; Peyaud, B.; Pichel, A.; Pita, S.; Pizzolato, F.; Platos, Ł.; Platzer, R.; Pogosyan, L.; Pohl, M.; Pojmanski, G.; Ponz, J. D.; Potter, W.; Poutanen, J.; Prandini, E.; Prast, J.; Preece, R.; Profeti, F.; Prokoph, H.; Prouza, M.; Proyetti, M.; Puerto-Gimenez, I.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł, R.; Quel, E. J.; Quinn, J.; Quirrenbach, A.; Racero, E.; Rajda, P. J.; Ramon, P.; Rando, R.; Rannot, R. C.; Rataj, M.; Raue, M.; Reardon, P.; Reimann, O.; Reimer, A.; Reimer, O.; Reitberger, K.; Renaud, M.; Renner, S.; Reville, B.; Rhode, W.; Ribó, M.; Ribordy, M.; Richer, M. G.; Rico, J.; Ridky, J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P. R.; Riviére, A.; Rivoire, S.; Rob, L.; Roeser, U.; Rohlfs, R.; Rojas, G.; Romano, P.; Romaszkan, W.; Romero, G. E.; Rosen, S.; Rosier Lees, S.; Ross, D.; Rouaix, G.; Rousselle, J.; Rousselle, S.; Rovero, A. C.; Roy, F.; Royer, S.; Rudak, B.; Rulten, C.; Rupiński, M.; Russo, F.; Ryde, F.; Sacco, B.; Saemann, E. O.; Saggion, A.; Sahakian, V.; Saito, K.; Saito, T.; Saito, Y.; Sakaki, N.; Sakonaka, R.; Salini, A.; Sanchez, F.; Sanchez-Conde, M.; Sandoval, A.; Sandaker, H.; Sant'Ambrogio, E.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Sartore, N.; Sasaki, H.; Satalecka, K.; Sawada, M.; Scalzotto, V.; Scapin, V.; Scarcioffolo, M.; Schafer, J.; Schanz, T.; Schlenstedt, S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.; Schovanek, P.; Schroedter, M.; Schultz, C.; Schultze, J.; Schulz, A.; Schure, K.; Schwab, T.; Schwanke, U.; Schwarz, J.; Schwarzburg, S.; Schweizer, T.; Schwemmer, S.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.; Seweryn, K.; Sharma, M.; Shayduk, M.; Shellard, R. C.; Shi, J.; Shibata, T.; Shibuya, A.; Shum, E.; Sidoli, L.; Sidz, M.; Sieiro, J.; Sikora, M.; Silk, J.; Sillanpää, A.; Singh, B. B.; Sitarek, J.; Skole, C.; Smareglia, R.; Smith, A.; Smith, D.; Smith, J.; Smith, N.; Sobczyńska, D.; Sol, H.; Sottile, G.; Sowiński, M.; Spanier, F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling, R.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.; Stergioulas, N.; Sternberger, R.; Sterzel, M.; Stinzing, F.; Stodulski, M.; Straumann, U.; Strazzeri, E.; Stringhetti, L.; Suarez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. -H.; Sun, S.; Supanitsky, A. D.; Suric, T.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.; Szostek, A.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, G.; Tammi, J.; Tanaka, M.; Tanaka, S.; Tasan, J.; Tavani, M.; Tavernet, J. -P.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada, Y.; Terrier, R.; Teshima, M.; Testa, V.; Tezier, D.; Thuermann, D.; Tibaldo, L.; Tibolla, O.; Tiengo, A.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Torii, K.; Tornikoski, M.; Torres, D. F.; Torres, M.; Tosti, G.; Totani, T.; Toussenel, F.; Tovmassian, G.; Travnicek, P.; Trifoglio, M.; Troyano, I.; Tsinganos, K.; Ueno, H.; Umehara, K.; Upadhya, S. S.; Usher, T.; Uslenghi, M.; Valdes-Galicia, J. F.; Vallania, P.; Vallejo, G.; van Driel, W.; van Eldik, C.; Vandenbrouke, J.; Vanderwalt, J.; Vankov, H.; Vasileiadis, G.; Vassiliev, V.; Veberic, D.; Vegas, I.; Vercellone, S.; Vergani, S.; Veyssiére, C.; Vialle, J. P.; Viana, A.; Videla, M.; Vincent, P.; Vincent, S.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt, A.; von Gunten, H. -P.; Vorobiov, S.; Vuerli, C.; Waegebaert, V.; Wagner, R.; Wagner, R. G.; Wagner, S.; Wakely, S. P.; Walter, R.; Walther, T.; Warda, K.; Warwick, R.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Werner, M.; Wetteskind, H.; White, R.; Wierzcholska, A.; Wiesand, S.; Wilkinson, M.; Williams, D. A.; Willingale, R.; Winiarski, K.; Wischnewski, R.; Wiśniewski, Ł.; Wood, M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yebras, J. M.; Yelos, D.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza, V.; Zacharias, M.; Zajczyk, A.; Zanin, R.; Zdziarski, A.; Zech, A.; Zhao, A.; Zhou, X.; Ziętara, K.; Ziolkowski, J.; Ziółkowski, P.; Zitelli, V.; Zurbach, C.; Żychowski, P.; CTA Consortium Bibcode: 2013APh....43....3A Altcode: 2013APh....43....3C The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. Title: Coupled model for the formation of an active region corona Authors: Chen, Feng; Bingert, Sven; Peter, Hardi; Cameron, Robert; Schüssler; , Manfred; Cheung, Mark C. M. Bibcode: 2013enss.confE..21C Altcode: We will present the first model that couples the formation of an active region corona to a model of the emergence. This allows us to study when, where, and why active region loops form, and how they evolve. For this we use an existing 3D radiation MHD model of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a coronal model. Our 3D MHD coronal model accounts for the braiding of the magnetic field lines that induces currents in the corona that is getting filled with the emerging magnetic field. Starting with a basically field-free atmosphere we follow the flux emergence until numerous individually identifiable hot coronal loops have been formed. The temperatures in the coronal loops of well above 1 MK are reached at densities corresponding to actually observed active region loops. The loops develop over a very short time period of the order of several minutes through the evaporation of material from the chromosphere. Because we have full access to the heating rate as a function of time and space in our computational domain we can determine the conditions under which these loops form. Title: On the relation between continuum brightness and magnetic field in solar active regions Authors: Danilovic, S.; Röhrbein, D.; Cameron, R. H.; Schüssler, M. Bibcode: 2013A&A...550A.118D Altcode: Context. Variations of solar irradiance are mainly determined by the changing coverage of the visible solar disk with magnetic flux concentrations. The relationship between brightness and field strength is an important ingredient for models and reconstructions of irradiance variations.
Aims: We assess the effect of limited observational resolution on the relationship between brightness and magnetic field by comparing comprehensive MHD simulations with observational results.
Methods: Simulations of magnetoconvection representing the near-surface layers of a plage region were used to determine maps of the continuum brightness and Stokes profiles for the Fe i line at 630.22 nm. After convolving with instrumental profiles, synthetic observations of the magnetic field were generated by applying a Stokes inversion code. We compare the resulting relation between brightness and apparent vertical magnetic field to the corresponding outcome derived from real observations of a plage region with the Hinode satellite.
Results: Consideration of the image smearing effects due to the limited resolution of the observations transform the largely monotonic relation between brightness and field strength at the original resolution of the simulations into a profile with a maximum at intermediate field strength, which is in good agreement with the observations.
Conclusions: Considering the effect of limited observational resolution renders the relation between brightness and magnetic field from comprehensive MHD simulations consistent with observational results. This is a necessary prerequisite for the utilization of simulations for models and reconstruction of solar irradiance variations. Title: MHD waves in small magnetic elements: comparing IMaX observations to simulations. Authors: Stangalini, M.; Solanki, S. K.; Cameron, R. Bibcode: 2013MmSAI..84..444S Altcode: Small-scale magnetic fields are thought to play an important role in the heating of the outer solar atmosphere. By exploiting the high-spatial and temporal resolution of IMaX, the bidimensional spectropolarimeter on board the Sunrise balloon-borne observatory, we study the excitation of MHD waves in small magnetic elements, providing clues on the interaction of the magnetic structures with the photospheric forcing and the ambient acoustic field. The large fraction of magnetic features observed by IMaX made it possible to study the interaction between the photospheric granulation and the flux tubes from a statistical point-of-view. In particular we find a 90 degree phase lag with an high confidence level between the horizontal displacements of the flux tubes and the velocity perturbations measured inside them. We also find that the observational results are in excellent agreement with MHD simulations. This result suggests that the horizontal displacement of small-scale magnetic features by the surrounding granulation excites longitudinal waves within the magnetic elements. Title: MHD simulation of the inner-heliospheric magnetic field Authors: Wiengarten, T.; Kleimann, J.; Fichtner, H.; Cameron, R.; Jiang, J.; Kissmann, R.; Scherer, K. Bibcode: 2013JGRA..118...29W Altcode: 2013arXiv1303.4260W Maps of the radial magnetic field at a heliocentric distance of 10 solar radii are used as boundary conditions in the MHD code CRONOS to simulate a three-dimensional inner-heliospheric solar wind emanating from the rotating Sun out to 1 AU. The input data for the magnetic field are the result of solar surface flux transport modeling using observational data of sunspot groups coupled with a current-sheet source surface model. Among several advancements, this allows for higher angular resolution than that of comparable observational data from synoptic magnetograms. The required initial conditions for the other MHD quantities are obtained following an empirical approach using an inverse relation between flux tube expansion and radial solar wind speed. The computations are performed for representative solar minimum and maximum conditions, and the corresponding state of the solar wind up to the Earth's orbit is obtained. After a successful comparison of the latter with observational data, they can be used to drive outer-heliospheric models. Title: Are the strengths of solar cycles determined by converging flows towards the activity belts? Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2012A&A...548A..57C Altcode: 2012arXiv1210.7644C It is proposed that the observed near-surface inflows towards the active regions and sunspot zones provide a nonlinear feedback mechanism that limits the amplitude of a Babcock-Leighton-type solar dynamo and determines the variation of the cycle strength. This hypothesis is tested with surface flux transport simulations including converging latitudinal flows that depend on the surface distribution of magnetic flux. The inflows modulate the build-up of polar fields (represented by the axial dipole) by reducing the tilt angles of bipolar magnetic regions and by affecting the cross-equator transport of leading-polarity magnetic flux. With flux input derived from the observed record of sunspot groups, the simulations cover the period between 1874 and 1980 (corresponding to solar cycles 11 to 20). The inclusion of the inflows leads to a strong correlation of the simulated axial dipole strength during activity minimum with the observed amplitude of the subsequent cycle. This in agreement with empirical correlations and in line with what is expected from a Babcock-Leighton-type dynamo. The results provide evidence that the latitudinal inflows are a key ingredient in determining the amplitude of solar cycles. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone Bibcode: 2012atnf.prop.5094C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Surface flux evolution constraints for flux transport dynamos Authors: Cameron, R. H.; Schmitt, D.; Jiang, J.; Işık, E. Bibcode: 2012A&A...542A.127C Altcode: 2012arXiv1205.1136C The surface flux transport (SFT) model of solar magnetic fields involves empirically well-constrained velocity and magnetic fields. The basic evolution of the Sun's large-scale surface magnetic field is well described by this model. The azimuthally averaged evolution of the SFT model can be compared to the surface evolution of the flux transport dynamo (FTD), and the evolution of the SFT model can be used to constrain several near-surface properties of the FTD model. We compared the results of the FTD model with different upper boundary conditions and diffusivity profiles against the results of the SFT model. Among the ingredients of the FTD model, downward pumping of magnetic flux, related to a positive diffusivity gradient, has a significant effect in slowing down the diffusive radial transport of magnetic flux through the solar surface. Provided the pumping was strong enough to give rise to a downflow of a magnetic Reynolds number of 5 in the near-surface boundary layer, the FTD using a vertical boundary condition matches the SFT model based on the average velocities above the boundary layer. The FTD model with a potential field was unable to match the SFT results. Title: Waves as the Source of Apparent Twisting Motions in Sunspot Penumbrae Authors: Bharti, L.; Cameron, R. H.; Rempel, M.; Hirzberger, J.; Solanki, S. K. Bibcode: 2012ApJ...752..128B Altcode: 2012arXiv1204.2221B The motion of dark striations across bright filaments in a sunspot penumbra has become an important new diagnostic of convective gas flows in penumbral filaments. The nature of these striations has, however, remained unclear. Here, we present an analysis of small-scale motions in penumbral filaments in both simulations and observations. The simulations, when viewed from above, show fine structure with dark lanes running outward from the dark core of the penumbral filaments. The dark lanes either occur preferentially on one side or alternate between both sides of the filament. We identify this fine structure with transverse (kink) oscillations of the filament, corresponding to a sideways swaying of the filament. These oscillations have periods in the range of 5-7 minutes and propagate outward and downward along the filament. Similar features are found in observed G-band intensity time series of penumbral filaments in a sunspot located near disk center obtained by the Broadband Filter Imager on board the Hinode. We also find that some filaments show dark striations moving to both sides of the filaments. Based on the agreement between simulations and observations we conclude that the motions of these striations are caused by transverse oscillations of the underlying bright filaments. Title: Vortices, shocks, and heating in the solar photosphere: effect of a magnetic field Authors: Moll, R.; Cameron, R. H.; Schüssler, M. Bibcode: 2012A&A...541A..68M Altcode: 2012arXiv1201.5981M
Aims: We study the differences between non-magnetic and magnetic regions in the flow and thermal structure of the upper solar photosphere.
Methods: Radiative MHD simulations representing a quiet region and a plage region, respectively, which extend into the layers around the temperature minimum, are analyzed.
Results: The flow structure in the upper photospheric layers of the two simulations is considerably different: the non-magnetic simulation is dominated by a pattern of moving shock fronts while the magnetic simulation shows vertically extended vortices associated with magnetic flux concentrations. Both kinds of structures induce substantial local heating. The resulting average temperature profiles are characterized by a steep rise above the temperature minimum due to shock heating in the non-magnetic case and by a flat photospheric temperature gradient mainly caused by Ohmic dissipation in the magnetic run.
Conclusions: Shocks in the quiet Sun and vortices in the strongly magnetized regions represent the dominant flow structures in the layers around the temperature minimum. They are closely connected with dissipation processes providing localized heating. Title: Magnetohydrodynamics of the Weakly Ionized Solar Photosphere Authors: Cheung, Mark C. M.; Cameron, Robert H. Bibcode: 2012ApJ...750....6C Altcode: 2012arXiv1202.1937C We investigate the importance of ambipolar diffusion and Hall currents for high-resolution comprehensive ("realistic") photospheric simulations. To do so, we extended the radiative magnetohydrodynamics code MURaM to use the generalized Ohm's law under the assumption of local thermodynamic equilibrium. We present test cases comparing analytical solutions with numerical simulations for validation of the code. Furthermore, we carried out a number of numerical experiments to investigate the impact of these neutral-ion effects in the photosphere. We find that, at the spatial resolutions currently used (5-20 km per grid point), the Hall currents and ambipolar diffusion begin to become significant—with flows of 100 m s-1 in sunspot light bridges, and changes of a few percent in the thermodynamic structure of quiet-Sun magnetic features. The magnitude of the effects is expected to increase rapidly as smaller-scale variations are resolved by the simulations. Title: Break up of returning plasma after the 7 June 2011 filament eruption by Rayleigh-Taylor instabilities Authors: Innes, D. E.; Cameron, R. H.; Fletcher, L.; Inhester, B.; Solanki, S. K. Bibcode: 2012A&A...540L..10I Altcode: 2012arXiv1202.4981I Context. A prominence eruption on 7 June 2011 produced spectacular curtains of plasma falling through the lower corona. At the solar surface they created an incredible display of extreme ultraviolet brightenings.
Aims: To identify and analyze some of the local instabilities which produce structure in the falling plasma.
Methods: The structures were investigated using SDO/AIA 171 Å and 193 Å images in which the falling plasma appeared dark against the bright coronal emission.
Results: Several instances of the Rayleigh-Taylor instability were investigated. In two cases the Alfvén velocity associated with the dense plasma could be estimated from the separation of the Rayleigh-Taylor fingers. A second type of feature, which has the appearance of self-similar branching horns was discussed.

Appendix A and two movies are available in electronic form at http://www.aanda.org Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone Bibcode: 2012atnf.prop.4533C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Diffusivity of Isolated Internetwork Ca II H Bright Points Observed by SuFI/SUNRISE Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Feller, A.; Pietarila, A.; Lagg, A.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knoelker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A. Bibcode: 2012decs.confE..99J Altcode: We analyze trajectories of the proper motion of intrinsically magnetic, isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to obtain their diffusivity behaviors. We use high spatial and temporal resolution image sequences of quiet-Sun, disc-centre observations obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager (SuFI) on board the SUNRISE balloon-borne solar observatory. In order to avoid misidentification, the BPs are semi-manually selected and then automatically tracked. The trajectory of each BP is then calculated and its diffusion index is described by a power law exponent, using which we classify the BPs' trajectories into sub-, normal and super- diffusive. In addition, the corresponding diffusion coefficients (D) based on the observed displacements are consequently computed. We find a strong super-diffusivity at a height sampled by the SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to the temperature minimum). We find that 74% of the identified tiny BPs are super-diffusive, 18% move randomly (i.e. their motion corresponds to normal diffusion) and only 8% belong to the sub-diffusion regime. In addition, we find that 53% of the super-diffusion regime (i.e. 39% of all BPs) have the diffusivity index of 2 which are termed as "Ballistic BPs". Finally, we explore the distribution of diffusion index with the help of a simple simulation. The results suggest that the BPs are random walkers superposed by a systematic (background) velocity in which the magnitude of each component (and hence their ratio) depends on the time and spatial scales. We further discuss a simple sketch to explain the diffusivity of observed BPs while they migrate within a supergranule (i.e. internetwork areas) or close to the network regions. Title: To the top of the photosphere Authors: Cameron, Robert Bibcode: 2012decs.confE..17C Altcode: We will discuss the interaction of convection and magnetic fields in the solar photosphere. In particular we will concentrate on the broad range of time and spatial scales over which structures are generated and evolve. The importance of waves, vortices and braiding of the magnetic footpoints will be mentioned, as well as future problems which need to be tackled. Title: Simulations of the solar near-surface layers with the CO5BOLD, MURaM, and Stagger codes Authors: Beeck, B.; Collet, R.; Steffen, M.; Asplund, M.; Cameron, R. H.; Freytag, B.; Hayek, W.; Ludwig, H. -G.; Schüssler, M. Bibcode: 2012A&A...539A.121B Altcode: 2012arXiv1201.1103B Context. Radiative hydrodynamic simulations of solar and stellar surface convection have become an important tool for exploring the structure and gas dynamics in the envelopes and atmospheres of late-type stars and for improving our understanding of the formation of stellar spectra.
Aims: We quantitatively compare results from three-dimensional, radiative hydrodynamic simulations of convection near the solar surface generated with three numerical codes (CO5BOLD, MURaM, and Stagger) and different simulation setups in order to investigate the level of similarity and to cross-validate the simulations.
Methods: For all three simulations, we considered the average stratifications of various quantities (temperature, pressure, flow velocity, etc.) on surfaces of constant geometrical or optical depth, as well as their temporal and spatial fluctuations. We also compared observables, such as the spatially resolved patterns of the emerging intensity and of the vertical velocity at the solar optical surface as well as the center-to-limb variation of the continuum intensity at various wavelengths.
Results: The depth profiles of the thermodynamical quantities and of the convective velocities as well as their spatial fluctuations agree quite well. Slight deviations can be understood in terms of differences in box size, spatial resolution and in the treatment of non-gray radiative transfer between the simulations.
Conclusions: The results give confidence in the reliability of the results from comprehensive radiative hydrodynamic simulations. Title: Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy Authors: Actis, M.; Agnetta, G.; Aharonian, F.; Akhperjanian, A.; Aleksić, J.; Aliu, E.; Allan, D.; Allekotte, I.; Antico, F.; Antonelli, L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Arnaldi, H.; Artmann, S.; Asano, K.; Asorey, H.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.; Balis, D.; Bamba, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.; Bastieri, D.; Bauer, C.; Becerra, J.; Becherini, Y.; Bechtol, K.; Becker, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Beilicke, M.; Belluso, M.; Benallou, M.; Benbow, W.; Berdugo, J.; Berger, K.; Bernardino, T.; Bernlöhr, K.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Blake, S.; Blanch, O.; Bobkov, A. A.; Bogacz, L.; Bogdan, M.; Boisson, C.; Boix, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Borkowski, J.; Botner, O.; Bottani, A.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.; Bretz, T.; Briggs, M. S.; Brun, P.; Brunetti, L.; Buckley, J. H.; Bugaev, V.; Bühler, R.; Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron, R.; Canestrari, R.; Cantu, S.; Carmona, E.; Carosi, A.; Carr, J.; Carton, P. H.; Casiraghi, M.; Castarede, H.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti, B.; Cerruti, M.; Chadwick, P. M.; Chiang, J.; Chikawa, M.; Cieślar, M.; Ciesielska, M.; Cillis, A.; Clerc, C.; Colin, P.; Colomé, J.; Compin, M.; Conconi, P.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corlier, M.; Corona, P.; Corpace, O.; Corti, D.; Cortina, J.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino, S.; Croston, J.; Cusumano, G.; Daniel, M. K.; Dazzi, F.; de Angelis, A.; de Cea Del Pozo, E.; de Gouveia Dal Pino, E. M.; de Jager, O.; de La Calle Pérez, I.; de La Vega, G.; de Lotto, B.; de Naurois, M.; de Oña Wilhelmi, E.; de Souza, V.; Decerprit, B.; Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; Dettlaff, T.; di Paolo, A.; di Pierro, F.; Díaz, C.; Dick, J.; Dickinson, H.; Digel, S. W.; Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Domainko, W.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Durand, D.; Dyks, J.; Dyrda, M.; Edy, E.; Egberts, K.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Falcone, A. D.; Farakos, K.; Farnier, C.; Federici, S.; Feinstein, F.; Ferenc, D.; Fillin-Martino, E.; Fink, D.; Finley, C.; Finley, J. P.; Firpo, R.; Florin, D.; Föhr, C.; Fokitis, E.; Font, Ll.; Fontaine, G.; Fontana, A.; Förster, A.; Fortson, L.; Fouque, N.; Fransson, C.; Fraser, G. W.; Fresnillo, L.; Fruck, C.; Fujita, Y.; Fukazawa, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gadola, A.; Galante, N.; Gallant, Y.; García, B.; García López, R. J.; Garrido, D.; Garrido, L.; Gascón, D.; Gasq, C.; Gaug, M.; Gaweda, J.; Geffroy, N.; Ghag, C.; Ghedina, A.; Ghigo, M.; Gianakaki, E.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giro, E.; Giubilato, P.; Glanzman, T.; Glicenstein, J. -F.; Gochna, M.; Golev, V.; Gómez Berisso, M.; González, A.; González, F.; Grañena, F.; Graciani, R.; Granot, J.; Gredig, R.; Green, A.; Greenshaw, T.; Grimm, O.; Grube, J.; Grudzińska, M.; Grygorczuk, J.; Guarino, V.; Guglielmi, L.; Guilloux, F.; Gunji, S.; Gyuk, G.; Hadasch, D.; Haefner, D.; Hagiwara, R.; Hahn, J.; Hallgren, A.; Hara, S.; Hardcastle, M. J.; Hassan, T.; Haubold, T.; Hauser, M.; Hayashida, M.; Heller, R.; Henri, G.; Hermann, G.; Herrero, A.; Hinton, J. A.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Horns, D.; Hrupec, D.; Huan, H.; Huber, B.; Huet, J. -M.; Hughes, G.; Hultquist, K.; Humensky, T. B.; Huppert, J. -F.; Ibarra, A.; Illa, J. M.; Ingjald, J.; Inoue, Y.; Inoue, S.; Ioka, K.; Jablonski, C.; Jacholkowska, A.; Janiak, M.; Jean, P.; Jensen, H.; Jogler, T.; Jung, I.; Kaaret, P.; Kabuki, S.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.; Kapala, M.; Karastergiou, A.; Karczewski, M.; Karkar, S.; Karlsson, N.; Kasperek, J.; Katagiri, H.; Katarzyński, K.; Kawanaka, N.; Kȩdziora, B.; Kendziorra, E.; Khélifi, B.; Kieda, D.; Kifune, T.; Kihm, T.; Klepser, S.; Kluźniak, W.; Knapp, J.; Knappy, A. R.; Kneiske, T.; Knödlseder, J.; Köck, F.; Kodani, K.; Kohri, K.; Kokkotas, K.; Komin, N.; Konopelko, A.; Kosack, K.; Kossakowski, R.; Kostka, P.; Kotuła, J.; Kowal, G.; Kozioł, J.; Krähenbühl, T.; Krause, J.; Krawczynski, H.; Krennrich, F.; Kretzschmann, A.; Kubo, H.; Kudryavtsev, V. A.; Kushida, J.; La Barbera, N.; La Parola, V.; La Rosa, G.; López, A.; Lamanna, G.; Laporte, P.; Lavalley, C.; Le Flour, T.; Le Padellec, A.; Lenain, J. -P.; Lessio, L.; Lieunard, B.; Lindfors, E.; Liolios, A.; Lohse, T.; Lombardi, S.; Lopatin, A.; Lorenz, E.; Lubiński, P.; Luz, O.; Lyard, E.; Maccarone, M. C.; Maccarone, T.; Maier, G.; Majumdar, P.; Maltezos, S.; Małkiewicz, P.; Mañá, C.; Manalaysay, A.; Maneva, G.; Mangano, A.; Manigot, P.; Marín, J.; Mariotti, M.; Markoff, S.; Martínez, G.; Martínez, M.; Mastichiadis, A.; Matsumoto, H.; Mattiazzo, S.; Mazin, D.; McComb, T. J. L.; McCubbin, N.; McHardy, I.; Medina, C.; Melkumyan, D.; Mendes, A.; Mertsch, P.; Meucci, M.; Michałowski, J.; Micolon, P.; Mineo, T.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mizuno, T.; Moal, B.; Moderski, R.; Molinari, E.; Monteiro, I.; Moralejo, A.; Morello, C.; Mori, K.; Motta, G.; Mottez, F.; Moulin, E.; Mukherjee, R.; Munar, P.; Muraishi, H.; Murase, K.; Murphy, A. Stj.; Nagataki, S.; Naito, T.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Nayman, P.; Nedbal, D.; Niedźwiecki, A.; Niemiec, J.; Nikolaidis, A.; Nishijima, K.; Nolan, S. J.; Nowak, N.; O'Brien, P. T.; Ochoa, I.; Ohira, Y.; Ohishi, M.; Ohka, H.; Okumura, A.; Olivetto, C.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J. P.; Ostrowski, M.; Otero, L.; Otte, A. N.; Ovcharov, E.; Oya, I.; Oziȩbło, A.; Paiano, S.; Pallota, J.; Panazol, J. L.; Paneque, D.; Panter, M.; Paoletti, R.; Papyan, G.; Paredes, J. M.; Pareschi, G.; Parsons, R. D.; Paz Arribas, M.; Pedaletti, G.; Pepato, A.; Persic, M.; Petrucci, P. O.; Peyaud, B.; Piechocki, W.; Pita, S.; Pivato, G.; Płatos, Ł.; Platzer, R.; Pogosyan, L.; Pohl, M.; Pojmański, G.; Ponz, J. D.; Potter, W.; Prandini, E.; Preece, R.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quel, E.; Quirrenbach, A.; Rajda, P.; Rando, R.; Rataj, M.; Raue, M.; Reimann, C.; Reimann, O.; Reimer, A.; Reimer, O.; Renaud, M.; Renner, S.; Reymond, J. -M.; Rhode, W.; Ribó, M.; Ribordy, M.; Rico, J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P.; Rivoire, S.; Rob, L.; Rodriguez, S.; Roeser, U.; Romano, P.; Romero, G. E.; Rosier-Lees, S.; Rovero, A. C.; Roy, F.; Royer, S.; Rudak, B.; Rulten, C. B.; Ruppel, J.; Russo, F.; Ryde, F.; Sacco, B.; Saggion, A.; Sahakian, V.; Saito, K.; Saito, T.; Sakaki, N.; Salazar, E.; Salini, A.; Sánchez, F.; Sánchez Conde, M. Á.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Scalzotto, V.; Scapin, V.; Scarcioffolo, M.; Schanz, T.; Schlenstedt, S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.; Schroedter, M.; Schultz, C.; Schultze, J.; Schulz, A.; Schwanke, U.; Schwarzburg, S.; Schweizer, T.; Seiradakis, J.; Selmane, S.; Seweryn, K.; Shayduk, M.; Shellard, R. C.; Shibata, T.; Sikora, M.; Silk, J.; Sillanpää, A.; Sitarek, J.; Skole, C.; Smith, N.; Sobczyńska, D.; Sofo Haro, M.; Sol, H.; Spanier, F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling, R. L. C.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.; Stergioulas, N.; Sternberger, R.; Stinzing, F.; Stodulski, M.; Straumann, U.; Suárez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. H.; Sun, S.; Supanitsky, A. D.; Sutcliffe, P.; Szanecki, M.; Szepieniec, T.; Szostek, A.; Szymkowiak, A.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, R. G.; Tam, P. H.; Tanaka, M.; Tanimori, T.; Tavani, M.; Tavernet, J. -P.; Tchernin, C.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada, Y.; Terrier, R.; Teshima, M.; Testa, V.; Tibaldo, L.; Tibolla, O.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Torres, D. F.; Tosti, G.; Totani, T.; Toussenel, F.; Vallania, P.; Vallejo, G.; van der Walt, J.; van Eldik, C.; Vandenbroucke, J.; Vankov, H.; Vasileiadis, G.; Vassiliev, V. V.; Vegas, I.; Venter, L.; Vercellone, S.; Veyssiere, C.; Vialle, J. P.; Videla, M.; Vincent, P.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt, A.; Volpe, F.; von Gunten, H. P.; Vorobiov, S.; Wagner, S.; Wagner, R. M.; Wagner, B.; Wakely, S. P.; Walter, P.; Walter, R.; Warwick, R.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Wetteskind, H.; White, R.; Wierzcholska, A.; Wilkinson, M. I.; Williams, D. A.; Winde, M.; Wischnewski, R.; Wiśniewski, Ł.; Wolczko, A.; Wood, M.; Xiong, Q.; Yamamoto, T.; Yamaoka, K.; Yamazaki, R.; Yanagita, S.; Yoffo, B.; Yonetani, M.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza, V.; Zagdański, A.; Zajczyk, A.; Zdziarski, A.; Zech, A.; Ziȩtara, K.; Ziółkowski, P.; Zitelli, V.; Zychowski, P. Bibcode: 2011ExA....32..193A Altcode: 2011ExA...tmp..121A; 2010arXiv1008.3703C Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA. Title: Fermi Detection of a Luminous γ-Ray Pulsar in a Globular Cluster Authors: Freire, P. C. C.; Abdo, A. A.; Ajello, M.; Allafort, A.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G.; Cameron, R.; Camilo, F.; Caraveo, P. A.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cognard, I.; Cohen-Tanugi, J.; Cominsky, L. R.; de Palma, F.; Dermer, C. D.; do Couto e Silva, E.; Dormody, M.; Drell, P. S.; Dubois, R.; Dumora, D.; Espinoza, C. M.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M. -H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hadasch, D.; Harding, A. K.; Jóhannesson, G.; Johnson, A. S.; Johnson, T. J.; Johnston, S.; Katagiri, H.; Kataoka, J.; Keith, M.; Kerr, M.; Knödlseder, J.; Kramer, M.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S. -H.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Lyne, A. G.; Manchester, R. N.; Marelli, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ozaki, M.; Paneque, D.; Parent, D.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Porter, T. A.; Rainò, S.; Ransom, S. M.; Ray, P. S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Romani, R. W.; Roth, M.; Sadrozinski, H. F. -W.; Saz Parkinson, P. M. Sgrò, C.; Shannon, R.; Siskind, E. J. Smith, D. A.; Smith, P. D.; Spinelli, P.; Stappers, B. W.; Suson, D. J.; Takahashi, H.; Tanaka, T.; Tauris, T. M.; Thayer, J. B.; Theureau, G.; Thompson, D. J.; Thorsett, S. E.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Troja, E.; Vandenbroucke, J.; Van Etten, A.; Vasileiou, V.; Venter, C.; Vianello, G.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Wood, K. S.; Yang, Z.; Ziegler, M.; Zimmer, S. Bibcode: 2011Sci...334.1107F Altcode: 2011Sci...334.1107.; 2011arXiv1111.3754T We report on the Fermi Large Area Telescope’s detection of γ-ray (>100 mega-electron volts) pulsations from pulsar J1823-3021A in the globular cluster NGC 6624 with high significance (∼7 σ). Its γ-ray luminosity, Lγ = (8.4 ± 1.6) × 1034 ergs per second, is the highest observed for any millisecond pulsar (MSP) to date, and it accounts for most of the cluster emission. The nondetection of the cluster in the off-pulse phase implies that it contains <32 γ-ray MSPs, not ∼100 as previously estimated. The γ-ray luminosity indicates that the unusually large rate of change of its period is caused by its intrinsic spin-down. This implies that J1823-3021A has the largest magnetic field and is the youngest MSP ever detected and that such anomalous objects might be forming at rates comparable to those of the more normal MSPs. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone Bibcode: 2011atnf.prop.4337C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Vortices in simulations of solar surface convection Authors: Moll, R.; Cameron, R. H.; Schüssler, M. Bibcode: 2011A&A...533A.126M Altcode: 2011arXiv1108.0800M We report on the occurrence of small-scale vortices in simulations of the convective solar surface. Using an eigenanalysis of the velocity gradient tensor, we find the subset of high-vorticity regions in which the plasma is swirling. The swirling regions form an unsteady, tangled network of filaments in the turbulent downflow lanes. Near-surface vertical vortices are underdense and cause a local depression of the optical surface. They are potentially observable as bright points in the dark intergranular lanes. Vortex features typically exist for a few minutes, during which they are moved and twisted by the motion of the ambient plasma. The bigger vortices found in the simulations are possibly, but not necessarily, related to observations of granular-scale spiraling pathlines in "cork animations" or feature tracking.

Three movies are available in electronic form at http://www.aanda.org Title: Decay of a simulated mixed-polarity magnetic field in the solar surface layers Authors: Cameron, R.; Vögler, A.; Schüssler, M. Bibcode: 2011A&A...533A..86C Altcode: 2011arXiv1108.1155C Magnetic flux is continuously being removed and replenished on the solar surface. To understand the removal process we carried out 3D radiative MHD simulations of the evolution of patches of photospheric magnetic field with equal amounts of positive and negative flux. We find that the flux is removed at a rate corresponding to an effective turbulent diffusivity, ηeff, of 100-340 km2 s-1, depending on the boundary conditions. For average unsigned flux densities above about 70 Gauss, the percentage of surface magnetic energy coming from different field strengths is almost invariant. The overall process is then one where magnetic elements are advected by the horizontal granular motions and occasionally come into contact with opposite-polarity elements. These reconnect above the photosphere on a comparatively short time scale after which the U loops produced rapidly escape through the upper surface while the downward retraction of inverse-U loops is significantly slower, because of the higher inertia and lower plasma beta in the deeper layers. Title: Is there a non-monotonic relation between photospheric brightness and magnetic field strength in solar plage regions? Authors: Röhrbein, D.; Cameron, R.; Schüssler, M. Bibcode: 2011A&A...532A.140R Altcode: Context. The relationship between the brightness and field strength of small-scale solar magnetic features is an important factor for solar irradiance variations and a constraint for simulations of solar magneto-convection.
Aims: We wish to clarify the origin of the apparent discrepancy between observational results and radiative MHD simulations.
Methods: Maps of (bolometric) brightness and magnetic field strength from the simulation of a plage region were convolved and rebinned to mimic observations obtained with telescopes with finite aperture.
Results: Image smearing changes the monotonic relation between brightness and field strength obtained at the original resolution of the simulation into a profile with a maximum at intermediate field strength, which is in qualitative agreement with the observations. This result is mainly due to the smearing of strong magnetic fields at the bright edges of magnetic structures into the weakly magnetized adjacent areas.
Conclusions: Observational and simulation results are qualitatively consistent with each other if the finite spatial resolution of the observations is taken into account. Title: Constructing and Characterising Solar Structure Models for Computational Helioseismology Authors: Schunker, H.; Cameron, R. H.; Gizon, L.; Moradi, H. Bibcode: 2011SoPh..271....1S Altcode: 2011SoPh..tmp..124S; 2011arXiv1105.0219S; 2011SoPh..tmp..179S; 2011SoPh..tmp..248S In local helioseismology, numerical simulations of wave propagation are useful to model the interaction of solar waves with perturbations to a background solar model. However, the solution to the linearised equations of motion include convective modes that can swamp the helioseismic waves that we are interested in. In this article, we construct background solar models that are stable against convection, by modifying the vertical pressure gradient of Model S (Christensen-Dalsgaard et al., 1996, Science272, 1286) relinquishing hydrostatic equilibrium. However, the stabilisation affects the eigenmodes that we wish to remain as close to Model S as possible. In a bid to recover the Model S eigenmodes, we choose to make additional corrections to the sound speed of Model S before stabilisation. No stabilised model can be perfectly solar-like, so we present three stabilised models with slightly different eigenmodes. The models are appropriate to study the f and p1 to p4 modes with spherical harmonic degrees in the range from 400 to 900. Background model CSM has a modified pressure gradient for stabilisation and has eigenfrequencies within 2% of Model S. Model CSM_A has an additional 10% increase in sound speed in the top 1 Mm resulting in eigenfrequencies within 2% of Model S and eigenfunctions that are, in comparison with CSM, closest to those of Model S. Model CSM_B has a 3% decrease in sound speed in the top 5 Mm resulting in eigenfrequencies within 1% of Model S and eigenfunctions that are only marginally adversely affected. These models are useful to study the interaction of solar waves with embedded three-dimensional heterogeneities, such as convective flows and model sunspots. We have also calculated the response of the stabilised models to excitation by random near-surface sources, using simulations of the propagation of linear waves. We find that the simulated power spectra of wave motion are in good agreement with an observed SOHO/MDI power spectrum. Overall, our convectively stabilised background models provide a good basis for quantitative numerical local helioseismology. The models are available for download from http://www.mps.mpg.de/projects/seismo/NA4/. Title: EUV jets, type III radio bursts and sunspot waves investigated using SDO/AIA observations Authors: Innes, D. E.; Cameron, R. H.; Solanki, S. K. Bibcode: 2011A&A...531L..13I Altcode: 2011arXiv1106.3417I Context. Quasi-periodic plasma jets are often ejected from the Sun into interplanetary space. The commonly observed signatures are day-long sequences of type III radio bursts.
Aims: The aim is to identify the source of quasi-periodic jets observed on 3 Aug. 2010 in the Sun's corona and in interplanetary space.
Methods: Images from the Solar Dynamics Observatory (SDO) at 211 Å are used to identify the solar source of the type III radio bursts seen in WIND/WAVES dynamic spectra. We analyse a 2.5 h period during which six strong bursts are seen. The radio signals are cross-correlated with emission from extreme ultraviolet (EUV) jets coming from the western side of a sunspot in AR 11092. The jets are further cross-correlated with brightening at a small site on the edge of the sunspot umbra, and the brightening with 3-min sunspot intensity oscillations.
Results: The radio bursts correlate very well with the EUV jets. The EUV jet emission also correlates well with brightening at what looks like their footpoint at the edge of the umbra. The jet emission lags the radio signals and the footpoint brightening by about 30 s because the EUV jets take time to develop. For 10-15 min after strong EUV jets are ejected, the footpoint brightens at roughly 3 min intervals. In both the EUV images and the extracted light curves, it looks as though the brightening is related to the 3-min sunspot oscillations, although the correlation coefficient is rather low. The only open field near the jets is rooted in the sunspot.
Conclusions: Active region EUV/X-ray jets and interplanetary electron streams originate on the edge of the sunspot umbra. They form along a current sheet between the sunspot open field and closed field connecting to underlying satellite flux. Sunspot running penumbral waves cause roughly 3-min jet footpoint brightening. The relationship between the waves and jets is less clear.

Movie is available in electronic form at http://www.aanda.org Title: Universality of the Small-scale Dynamo Mechanism Authors: Moll, R.; Pietarila Graham, J.; Pratt, J.; Cameron, R. H.; Müller, W. -C.; Schüssler, M. Bibcode: 2011ApJ...736...36M Altcode: 2011arXiv1105.0546M We quantify possible differences between turbulent dynamo action in the Sun and the dynamo action studied in idealized simulations. For this purpose, we compare Fourier-space shell-to-shell energy transfer rates of three incrementally more complex dynamo simulations: an incompressible, periodic simulation driven by random flow, a simulation of Boussinesq convection, and a simulation of fully compressible convection that includes physics relevant to the near-surface layers of the Sun. For each of the simulations studied, we find that the dynamo mechanism is universal in the kinematic regime because energy is transferred from the turbulent flow to the magnetic field from wavenumbers in the inertial range of the energy spectrum. The addition of physical effects relevant to the solar near-surface layers, including stratification, compressibility, partial ionization, and radiative energy transport, does not appear to affect the nature of the dynamo mechanism. The role of inertial-range shear stresses in magnetic field amplification is independent from outer-scale circumstances, including forcing and stratification. Although the shell-to-shell energy transfer functions have similar properties to those seen in mean-flow driven dynamos in each simulation studied, the saturated states of these simulations are not universal because the flow at the driving wavenumbers is a significant source of energy for the magnetic field. Title: Universality of the Small-Scale Dynamo Mechanism Authors: Pietarila Graham, Jonathan; Moll, R.; Pratt, J.; Cameron, R.; Mueller, W.; Schuessler, M. Bibcode: 2011SPD....42.1621P Altcode: 2011BAAS..43S.1621P We quantify possible differences between turbulent dynamo action in the Sun and the dynamo action studied in idealized simulation. For this purpose we compare Fourier-space shell-to-shell energy transfer rates of three incrementally more complex dynamo simulations: an incompressible, periodic simulation driven by random flow, a simulation of Boussinesq convection, and a simulation of fully compressible convection that includes physics relevant to the near-surface layers of the Sun. For each of the simulations studied, we find that energy is transferred from the turbulent flow to the magnetic field from length-scales in the inertial range of the energy spectrum. The addition of physical effects relevant to the solar near-surface layers, including stratification, compressibility, partial ionization, and radiative energy transport, does not appear to affect the nature of the dynamo mechanism. The role of inertial-range shear stresses in magnetic field amplification is independent from outer-scale circumstances, including forcing and stratification. Although shell-to-shell energy transfer functions have similar properties in each simulation studied, the saturated states of these simulations are not universal; the flow at the driving scales is a significant source of energy for the magnetic field. The mechanism of energy-transfer in kinematic small-scale dynamo simulations exhibits universal properties.

This work has been supported by the Max-Planck Society in the framework of the Interinstitutional Research Initiative Turbulent transport and ion heating, reconnection and electron acceleration in solar and fusion plasmas</u> of the MPI for Solar System Research, Katlenburg-Lindau, and the Institute for Plasma Physics, Garching (project MIF-IF-A-AERO8047). Title: SLiM: A Code for the Simulation of Wave Propagation through an Inhomogeneous, Magnetised Solar Atmosphere Authors: Cameron, R.; Gizon, L.; Daiffallah, K. Bibcode: 2011ascl.soft05004C Altcode: The semi-spectral linear MHD (SLiM) code follows the interaction of linear waves through an inhomogeneous three-dimensional solar atmosphere. The background model allows almost arbitrary perturbations of density, temperature, sound speed as well as magnetic and velocity fields. The code is useful in understanding the helioseismic signatures of various solar features, including sunspots. Title: The solar magnetic field since 1700. II. Physical reconstruction of total, polar and open flux Authors: Jiang, J.; Cameron, R. H.; Schmitt, D.; Schüssler, M. Bibcode: 2011A&A...528A..83J Altcode: 2011arXiv1102.1270J We have used semi-synthetic records of emerging sunspot groups based on sunspot number data as input for a surface flux transport model to reconstruct the evolution of the large-scale solar magnetic field and the open heliospheric flux from the year 1700 onward. The statistical properties of the semi-synthetic sunspot group records reflect those of the observed Royal Greenwich Observatory photoheliographic results. These include correlations between the sunspot numbers and sunspot group latitudes, longitudes, areas and tilt angles. The reconstruction results for the total surface flux, the polar field, and the heliospheric open flux (determined by a current sheet source surface extrapolation) agree well with the available observational or empirically derived data and reconstructions. We confirm a significant positive correlation between the polar field during activity minimum periods and the strength of the subsequent sunspot cycle, which has implications for flux transport dynamo models for the solar cycle. Just prior to the Dalton minimum, at the end of the 18th century, a long cycle was followed by a weak cycle. We find that introducing a possibly "lost" cycle between 1793 and 1800 leads to a shift of the minimum of the open flux by 15 years which is inconsistent with the cosmogenic isotope record. Title: The solar magnetic field since 1700. I. Characteristics of sunspot group emergence and reconstruction of the butterfly diagram Authors: Jiang, J.; Cameron, R. H.; Schmitt, D.; Schüssler, M. Bibcode: 2011A&A...528A..82J Altcode: 2011arXiv1102.1266J We use the historic record of sunspot groups compiled by the Royal Greenwich Observatory together with the sunspot number to derive the dependence of the statistical properties of sunspot emergence on the cycle phase and strength. In particular we discuss the latitude, longitude, area and tilt angle of sunspot groups as functions of the cycle strength and of time during the solar cycle. Using these empirical characteristics the time-latitude diagram of sunspot group emergence (butterfly diagram) is reconstructed from 1700 onward on the basis of the Wolf and group sunspot numbers. This reconstruction will be useful in studies of the long-term evolution of the Sun's magnetic field. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone Bibcode: 2011atnf.prop.3824C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Transport of Magnetic Flux from the Canopy to the Internetwork Authors: Pietarila, A.; Cameron, R. H.; Danilovic, S.; Solanki, S. K. Bibcode: 2011ApJ...729..136P Altcode: 2011arXiv1102.1397P Recent observations have revealed that 8% of linear polarization patches in the internetwork (INW) quiet Sun are fully embedded in downflows. These are not easily explained with the typical scenarios for the source of INW fields which rely on flux emergence from below. Using radiative MHD simulations, we explore a scenario where magnetic flux is transported from the magnetic canopy overlying the INW into the photosphere by means of downward plumes associated with convective overshoot. We find that if a canopy-like magnetic field is present in the simulation, the transport of flux from the canopy is an important process for seeding the photospheric layers of the INW with magnetic field. We propose that this mechanism is relevant for the Sun as well, and it could naturally explain the observed INW linear polarization patches entirely embedded in downflows. Title: 3D Numerical Simulations of f-Mode Propagation Through Magnetic Flux Tubes Authors: Daiffallah, K.; Abdelatif, T.; Bendib, A.; Cameron, R.; Gizon, L. Bibcode: 2011SoPh..268..309D Altcode: 2010SoPh..tmp..204D; 2010SoPh..tmp..228D; 2010arXiv1008.2531D Three-dimensional numerical simulations have been used to study the scattering of a surface-gravity wave packet by vertical magnetic-flux tubes, with radii from 200 km to 3 Mm, embedded in stratified polytropic atmosphere. The scattered wave has been found to consist primarily of m=0 (axisymmetric) and m=1 modes. The ratio of the amplitude of these two modes was found to be strongly dependent on the radius of the flux tube. The kink mode is the dominant mode excited in tubes with a small radius, while the sausage mode is dominant for large tubes. Simulations of this type provide a simple, efficient, and robust way to start to understand the seismic signature of flux tubes, which have recently begun to be observed. Title: Constructing Semi-Empirical Sunspot Models for Helioseismology Authors: Cameron, R. H.; Gizon, L.; Schunker, H.; Pietarila, A. Bibcode: 2011SoPh..268..293C Altcode: 2010arXiv1003.0528C; 2010SoPh..tmp..167C One goal of helioseismology is to determine the subsurface structure of sunspots. In order to do so, it is important to understand first the near-surface effects of sunspots on solar waves, which are dominant. Here we construct simplified, cylindrically-symmetric sunspot models that are designed to capture the magnetic and thermodynamics effects coming from about 500 km below the quiet-Sun τ5000=1 level to the lower chromosphere. We use a combination of existing semi-empirical models of sunspot thermodynamic structure (density, temperature, pressure): the umbral model of Maltby et al. (1986, Astrophys. J. 306, 284) and the penumbral model of Ding and Fang (1989, Astron. Astrophys. 225, 204). The OPAL equation-of-state tables are used to derive the sound-speed profile. We smoothly merge the near-surface properties to the quiet-Sun values about 1 Mm below the surface. The umbral and penumbral radii are free parameters. The magnetic field is added to the thermodynamic structure, without requiring magnetostatic equilibrium. The vertical component of the magnetic field is assumed to have a Gaussian horizontal profile, with a maximum surface field strength fixed by surface observations. The full magnetic-field vector is solenoidal and determined by the on-axis vertical field, which, at the surface, is chosen such that the field inclination is 45° at the umbral - penumbral boundary. We construct a particular sunspot model based on SOHO/MDI observations of the sunspot in active region NOAA 9787. The helioseismic signature of the model sunspot is studied using numerical simulations of the propagation of f, p1, and p2 wave packets. These simulations are compared against cross-covariances of the observed wave field. We find that the sunspot model gives a helioseismic signature that is similar to the observations. Title: Quenching of the alpha effect in the Sun -- what observations are telling us Authors: Cameron, R. H. Bibcode: 2011ASInC...2..143C Altcode: 2011arXiv1108.1308C The Babcock-Leighton type of dynamo has received recent support in terms of the discovery in the observational records of systematic cycle-to-cycle variations in the tilt angle of sunspot groups. It has been proposed that these variations might be the consequence of the observed inflow into the active region belt. Furthermore simulations have shown that such inflows restrict the creation of net poloidal flux, in effect acting to quench the alpha effect associated with the Coriolis force acting on rising flux tubes. In this paper we expand on these ideas. Title: Small-scale dynamo in solar surface simulations Authors: Graham, J. P.; Moll, R.; Cameron, R.; Schüssler, M. Bibcode: 2010AGUFMNG51C..01G Altcode: A magneto-convection simulation incorporating essential physical processes governing solar surface convection exhibits turbulent small-scale dynamo action. By presenting a derivation of the energy balance equation and transfer functions for compressible magnetohydrodynamics (MHD), we quantify the source of magnetic energy on a scale-by-scale basis. We rule out the two alternative mechanisms for the generation of small-scale magnetic field in the simulations: tangling of magnetic field lines associated with the turbulent cascade and Alfvenization of small-scale velocity fluctuations ("turbulent induction"). Instead, we find the dominant source of small-scale magnetic energy is stretching by inertial-range fluid motions of small-scale magnetic field lines against the magnetic tension force to produce (against Ohmic dissipation) more small-scale magnetic field. The scales involved become smaller with increasing Reynolds number, which identifies the dynamo as a small-scale turbulent dynamo. Comparisons are made between the details of the dynamo mechanism in compressible magneto-convection, Boussinesq convection, and randomly-forced incompressible turbulence. Net energy transfers (kinematic phase): work against magnetic tension (stretching) is 95% of magnetic energy generated; work against magnetic pressure (compression) is 5%. The latter is involved in the breaking down larger-scale field (25%) into smaller-scale field (30%) as part of the cascade. The dominant producer of magnetic energy is the stretching of magnetic field lines against the magnetic tension force (turbulent dynamo action).

Fluid motions at a scale of ~140km create magnetic energy predominately at a scale of ~65km. As the three wave-vectors must form a triad, the scale of the magnetic field being stretched must is 80+/-40km. All 3 scales are in the inertial range: this is turbulent small-scale dynamo. Title: Modeling the Subsurface Structure of Sunspots Authors: Moradi, H.; Baldner, C.; Birch, A. C.; Braun, D. C.; Cameron, R. H.; Duvall, T. L.; Gizon, L.; Haber, D.; Hanasoge, S. M.; Hindman, B. W.; Jackiewicz, J.; Khomenko, E.; Komm, R.; Rajaguru, P.; Rempel, M.; Roth, M.; Schlichenmaier, R.; Schunker, H.; Spruit, H. C.; Strassmeier, K. G.; Thompson, M. J.; Zharkov, S. Bibcode: 2010SoPh..267....1M Altcode: 2009arXiv0912.4982M; 2010SoPh..tmp..171M While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat. Title: Erratum: Erratum to: Helioseismology of Sunspots: A Case Study of NOAA Region 9787 Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch, A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.; Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.; Zharkov, S. Bibcode: 2010SSRv..156..257G Altcode: 2010SSRv..tmp...99G No abstract at ADS Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert; Abraham, Falcone Bibcode: 2010atnf.prop.3546C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Mesogranular structure in a hydrodynamical simulation Authors: Matloch, Ł.; Cameron, R.; Shelyag, S.; Schmitt, D.; Schüssler, M. Bibcode: 2010A&A...519A..52M Altcode: 2010arXiv1007.0387M
Aims: We analyse mesogranular flow patterns in a three-dimensional hydrodynamical simulation of solar surface convection in order to determine its characteristics.
Methods: We calculate divergence maps from horizontal velocities obtained with the local correlation tracking (LCT) method. Mesogranules are identified as patches of positive velocity divergence. We track the mesogranules to obtain their size and lifetime distributions. We vary the analysis parameters to verify if the pattern has characteristic scales.
Results: The characteristics of the resulting flow patterns depend on the averaging time and length used in the analysis.
Conclusions: We conclude that the mesogranular patterns do not exhibit intrinsic length and time scales. Title: Changes of the Solar Meridional Velocity Profile During Cycle 23 Explained by Flows Toward the Activity Belts Authors: Cameron, R. H.; Schüssler, M. Bibcode: 2010ApJ...720.1030C Altcode: 2010arXiv1007.2548C The solar meridional flow is an important ingredient in Babcock-Leighton type models of the solar dynamo. Global variations of this flow have been suggested to explain the variations in the amplitudes and lengths of the activity cycles. Recently, cycle-related variations in the amplitude of the P 1 2 term in the Legendre decomposition of the observed meridional flow have been reported. The result is often interpreted in terms of an overall variation in the flow amplitude during the activity cycle. Using a semi-empirical model based upon the observed distribution of magnetic flux on the solar surface, we show that the reported variations of the P 1 2 term can be explained by the observed localized inflows into the active region belts. No variation of the overall meridional flow amplitude is required. Title: Surface Flux Transport Modeling for Solar Cycles 15-21: Effects of Cycle-Dependent Tilt Angles of Sunspot Groups Authors: Cameron, R. H.; Jiang, J.; Schmitt, D.; Schüssler, M. Bibcode: 2010ApJ...719..264C Altcode: 2010arXiv1006.3061C We model the surface magnetic field and open flux of the Sun from 1913 to 1986 using a surface flux transport model, which includes the observed cycle-to-cycle variation of sunspot group tilts. The model reproduces the empirically derived time evolution of the solar open magnetic flux and the reversal times of the polar fields. We find that both the polar field and the axial dipole moment resulting from this model around cycle minimum correlate with the strength of the following cycle. Title: Saturation and time dependence of geodynamo models Authors: Schrinner, M.; Schmitt, D.; Cameron, R.; Hoyng, P. Bibcode: 2010GeoJI.182..675S Altcode: 2009arXiv0909.2181S In this study we address the question under which conditions a saturated velocity field stemming from geodynamo simulations leads to an exponential growth of the magnetic field in a corresponding kinematic calculation. We perform global self-consistent geodynamo simulations and calculate the evolution of a kinematically advanced tracer field. The self-consistent velocity field enters the induction equation in each time step, but the tracer field does not contribute to the Lorentz force. This experiment has been performed by Cattaneo and Tobias and is closely related to the test field method by Schrinner et al. We find two dynamo regimes in which the tracer field either grows exponentially or approaches a state aligned with the actual self-consistent magnetic field after an initial transition period. Both regimes can be distinguished by the Rossby number and coincide with the dipolar and multipolar dynamo regimes identified by Christensen and Aubert. Dipolar dynamos with low Rossby number are kinematically stable whereas the tracer field grows exponentially in the multipolar dynamo regime. This difference in the saturation process for dynamos in both regimes comes along with differences in their time variability. Within our sample of 20 models, solely kinematically unstable dynamos show dipole reversals and large excursions. The complicated time behaviour of these dynamos presumably relates to the alternating growth of several competing dynamo modes. On the other hand, dynamos in the low Rossby number regime exhibit a rather simple time dependence and their saturation merely results in a fluctuation of the fundamental dynamo mode about its critical state. Title: Sunspot group tilt angles and the strength of the solar cycle Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron, R.; Peñuela, T. Bibcode: 2010A&A...518A...7D Altcode: 2010arXiv1005.1774D Context. It is well known that the tilt angles of active regions increase with their latitude (Joy's law). It has never been checked before, however, whether the average tilt angles change from one cycle to the next. Flux transport models show the importance of tilt angles for the reversal and build up of magnetic flux at the poles, which is in turn correlated to the strength of the next cycle.
Aims: Here we analyse time series of tilt angle measurements and look for a possible relationship of the tilt angles with other solar cycle parameters, in order to glean information on the solar dynamo and to estimate their potential for predicting solar activity.
Methods: We employed tilt angle data from Mount Wilson and Kodaikanal observatories covering solar cycles 15 to 21. We analyse the latitudinal distribution of the tilt angles (Joy's law), their variation from cycle to cycle, and their relationship to other solar cycle parameters, such as the strength (or total area covered by sunspots in a cycle), amplitude, and length.
Results: The two main results of our analysis follow. 1. We find an anti-correlation between the mean normalised tilt angle of a given cycle and the strength (or amplitude) of that cycle, with a correlation coefficient of rc = -0.95 (99.9% confidence level) and rc = -0.93 (99.76% confidence level) for Mount Wilson and Kodaikanal data, respectively. 2. The product of the cycle's averaged tilt angle and the strength of the same cycle displays a significant correlation with the strength of the next cycle (rc = 0.65 at 89% confidence level and rc = 0.70 at 92% confidence level for Mount Wilson and Kodaikanal data, respectively). An even better correlation is obtained between the source term of the poloidal flux in Babcock-Leighton-type dynamos (which contains the tilt angle) and the amplitude of the next cycle. Further we confirm the linear relationship (Joy's law) between the tilt angle and latitude with slopes of 0.26 and 0.28 for Mount Wilson and Kodaikanal data, respectively. In addition, we obtain good positive correlations between the normalised-area-weighted tilt angle and the length of the following cycle, whereas the strength or the amplitude of the next cycle does not appear to be correlated to the tilt angles of the current cycle alone.
Conclusions: The results of this study indicate that, in combination with the cycle strength, the active region tilt angles play an important role in building up the polar fields at cycle minimum. Title: Expansion of magnetic flux concentrations: a comparison of Hinode SOT data and models Authors: Pietarila, A.; Cameron, R.; Solanki, S. K. Bibcode: 2010A&A...518A..50P Altcode: 2010arXiv1005.3405P Context. The expansion of network magnetic fields with height is a fundamental property of flux tube models. A rapid expansion is required to form a magnetic canopy.
Aims: We characterize the observed expansion properties of magnetic network elements and compare them with the thin flux tube and sheet approximations, as well as with magnetoconvection simulations.
Methods: We used data from the Hinode SOT NFI NaD1 channel and spectropolarimeter to study the appearance of magnetic flux concentrations seen in circular polarization as a function of position on the solar disk. We compared the observations with synthetic observables from models based on the thin flux tube approximation and magnetoconvection simulations with two different upper boundary conditions for the magnetic field (potential and vertical).
Results: The observed circular polarization signal of magnetic flux concentrations changes from unipolar at disk center to bipolar near the limb, which implies an expanding magnetic field. The observed expansion agrees with expansion properties derived from the thin flux sheet and tube approximations. Magnetoconvection simulations with a potential field as the upper boundary condition for the magnetic field also produce bipolar features near the limb while a simulation with a vertical field boundary condition does not.
Conclusions: The near-limb apparent bipolar magnetic features seen in high-resolution Hinode observations can be interpreted using a simple flux sheet or tube model. This lends further support to the idea that magnetic features with vastly varying sizes have similar relative expansion rates. The numerical simulations presented here are less useful in interpreting the expansion since the diagnostics we are interested in are strongly influenced by the choice of the upper boundary condition for the magnetic field in the purely photospheric simulations. Title: The Effect of Activity-related Meridional Flow Modulation on the Strength of the Solar Polar Magnetic Field Authors: Jiang, J.; Işik, E.; Cameron, R. H.; Schmitt, D.; Schüssler, M. Bibcode: 2010ApJ...717..597J Altcode: 2010arXiv1005.5317J We studied the effect of the perturbation of the meridional flow in the activity belts detected by local helioseismology on the development and strength of the surface magnetic field at the polar caps. We carried out simulations of synthetic solar cycles with a flux transport model, which follows the cyclic evolution of the surface field determined by flux emergence and advective transport by near-surface flows. In each hemisphere, an axisymmetric band of latitudinal flows converging toward the central latitude of the activity belt was superposed onto the background poleward meridional flow. The overall effect of the flow perturbation is to reduce the latitudinal separation of the magnetic polarities of a bipolar magnetic region and thus diminish its contribution to the polar field. As a result, the polar field maximum reached around cycle activity minimum is weakened by the presence of the meridional flow perturbation. For a flow perturbation consistent with helioseismic observations, the polar field is reduced by about 18% compared to the case without inflows. If the amplitude of the flow perturbation depends on the cycle strength, its effect on the polar field provides a nonlinearity that could contribute to limiting the amplitude of a Babcock-Leighton type dynamo. Title: Developing Physics-Based Procedures for Local Helioseismic Probing of Sunspots and Magnetic Regions Authors: Birch, Aaron; Braun, D. C.; Crouch, A.; Rempel, M.; Fan, Y.; Centeno, R.; Toomre, J.; Haber, D.; Hindman, B.; Featherstone, N.; Duvall, T., Jr.; Jackiewicz, J.; Thompson, M.; Stein, R.; Gizon, L.; Cameron, R.; Saidi, Y.; Hanasoge, S.; Burston, R.; Schunker, H.; Moradi, H. Bibcode: 2010AAS...21630805B Altcode: We have initiated a project to test and improve the local helioseismic techniques of time-distance and ring-diagram analysis. Our goals are to develop and implement physics-based methods that will (1) enable the reliable determinations of subsurface flow, magnetic field, and thermal structure in regions of strong magnetic fields and (2) be quantitatively tested with realistic solar magnetoconvection simulations in the presence of sunspot-like magnetic fields. We are proceeding through a combination of improvements in local helioseismic measurements, forward modeling of the helioseismic wavefield, kernel computations, inversions, and validation through numerical simulations. As improvements over existing techniques are made they will be applied to the SDO/HMI observations. This work is funded through the the NASA Heliophysics Science Division through the Solar Dynamics Observatory (SDO) Science Center program. Title: The solar cycle and the current solar minimum Authors: Cameron, R.; Jiang, J.; Schmitt, D.; Schuessler, M. Bibcode: 2010EGUGA..1215494C Altcode: In this talk we discuss the evolution of the Sun's large-scale magnetic field, on timescales relevant to the solar cycle. This evolution can be modeled using the surface flux transport equations, and we will outline the ingredients which go into the model. Special attention will be paid to the term describing the emergence of new flux onto the solar surface. The results of the model will be compared against observations covering most of the twentieth century, and in particular we will discuss what determines the surface field during solar minima. Title: Turbulent Small-Scale Dynamo Action in Solar Surface Simulations Authors: Pietarila Graham, Jonathan; Cameron, Robert; Schüssler, Manfred Bibcode: 2010ApJ...714.1606P Altcode: 2010ApJ...714.1606G; 2010arXiv1002.2750P We demonstrate that a magneto-convection simulation incorporating essential physical processes governing solar surface convection exhibits turbulent small-scale dynamo action. By presenting a derivation of the energy balance equation and transfer functions for compressible magnetohydrodynamics, we quantify the source of magnetic energy on a scale-by-scale basis. We rule out the two alternative mechanisms for the generation of the small-scale magnetic field in the simulations: the tangling of magnetic field lines associated with the turbulent cascade and Alfvénization of small-scale velocity fluctuations ("turbulent induction"). Instead, we find that the dominant source of small-scale magnetic energy is stretching by inertial-range fluid motions of small-scale magnetic field lines against the magnetic tension force to produce (against Ohmic dissipation) more small-scale magnetic field. The scales involved become smaller with increasing Reynolds number, which identifies the dynamo as a small-scale turbulent dynamo. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Burrows, David; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert Bibcode: 2010atnf.prop.3161C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Convectively stabilised background solar models for local helioseismology Authors: Schunker, H.; Cameron, R.; Gizon, L. Bibcode: 2010arXiv1002.1969S Altcode: In local helioseismology numerical simulations of wave propagation are useful to model the interaction of solar waves with perturbations to a background solar model. However, the solution to the equations of motions include convective modes that can swamp the waves we are interested in. For this reason, we choose to first stabilise the background solar model against convection by altering the vertical pressure gradient. Here we compare the eigenmodes of our convectively stabilised model with a standard solar model (Model S) and find a good agreement. Title: Modeling the Sun's Open Magnetic Flux and the Heliospheric Current Sheet Authors: Jiang, J.; Cameron, R.; Schmitt, D.; Schüssler, M. Bibcode: 2010ApJ...709..301J Altcode: 2009arXiv0912.0108J By coupling a solar surface flux transport model with an extrapolation of the heliospheric field, we simulate the evolution of the Sun's open magnetic flux and the heliospheric current sheet (HCS) based on observational data of sunspot groups since 1976. The results are consistent with measurements of the interplanetary magnetic field near Earth and with the tilt angle of the HCS as derived from extrapolation of the observed solar surface field. This opens the possibility for an improved reconstruction of the Sun's open flux and the HCS into the past on the basis of empirical sunspot data. Title: Numerical Simulations of Quiet Sun Oscillations Authors: Schunker, H.; Cameron, R.; Gizon, L. Bibcode: 2009ASPC..416...49S Altcode: We develop a quiet Sun background model to be used for the numerical simulation of solar oscillations and explore the properties of this model using the three-dimensional Semi-spectral Linear MHD (SLiM) code. We first suggest criteria for defining a convectively stable, but solar-like, background model. A first step in the development of such a solar-like model is presented and we demonstrate that it meets the first of the criteria by comparing the power spectrum of the simulation with SoHO/MDI observations. Title: Expansion of Magnetic Flux Concentrations with Height: A Comparison of Hinode SOT Data and MHD Simulations Authors: Pietarila, A.; Cameron, R.; Solanki, S. Bibcode: 2009ASPC..415...91P Altcode: The Hinode SOT (Tsuneta et al. 2008) NFI Na I D1 and SP Fe I data sampled at different positions on the solar disk provide a unique diagnostic for studying the expansion of magnetic flux concentrations with height. We make a comparative study of SOT observations and 2-dimensional (2D) radiative MHD-simulations to see how well the simulations capture the expansion properties. The expansion of flux concentrations is clearly seen in the SOT Na I D1 data, where most of the magnetic features appear unipolar at disk center while close to the limb bipolar appearance strongly dominates. This trend, albeit not as strong, is seen in the SP data as well. Some aspects of the observations are qualitatively reproduced by simulations with a potential (as opposed to vertical) upper boundary condition for the magnetic field. Title: Radiative MHD simulations of sunspot structure Authors: Rempel, M.; Schuessler, M.; Cameron, R.; Knoelker, M. Bibcode: 2009AGUFMSH53B..07R Altcode: For a long time radiative MHD simulations of entire sunspots from first principles were out of reach due to insufficient computing resources. Over the past 4 years simulations have evolved from 6x6x2 Mm size domains focusing on the details of umbral dots to simulations covering a pair of opposite polarity sunspots in a 100x50x6 Mm domain. Numerical simulations point toward a common magneto convective origin of umbral dots and filaments in the inner and outer penumbra. Most recent simulations also capture the processes involved in the formation of an extended outer penumbra with strong horizontal outflows averaging around 5 km/s in the photosphere. In this talk I will briefly review the progress made in this field over the past 4 years and discuss in detail the magneto convective origin of penumbral fine structure as well as the Evershed flow. Title: Solar surface magnetoconvection simulations: A brief review of solar dermatology Authors: Cameron, Robert Bibcode: 2009ScChG..52.1665C Altcode: Rapid improvement in the speed of computers has enabled realistic simulations of magnetoconvective processes in the surface layers of the Sun. The simulations now cover a wide range of features found in observations. In many cases a direct comparison with the observations is justified, and in all cases our understanding and interpretation of the observations is being improved. Current and future opportunities and difficulties will be discussed. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Burrows, David; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert Bibcode: 2009atnf.prop.2654C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Radiative MHD simulations of sunspot structure Authors: Rempel, M.; Schüssler, M.; Cameron, R.; Knölker, M. Bibcode: 2009iac..talk..192R Altcode: 2009iac..talk..106R No abstract at ADS Title: Modelling of solar mesogranulation Authors: Matloch, L.; Cameron, R.; Schmitt, D.; Schüssler, M. Bibcode: 2009A&A...504.1041M Altcode: We study whether mesogranulation flow patterns at the solar surface can arise solely from the statistical properties of granules and intergranular lanes. We have developed one- and two-dimensional models with local interaction rules between the artificial “granules” mimicking the actual physical processes on the solar surface. Defining mesogranulation according to the age of intergranular (downflow) lanes corresponding to the often applied “cork method”, as well as the areas of divergence of the horizontal velocity (two-dimensional model), we find that mesogranular patterns are present in our models. Our study of the dependence of the properties of the mesogranular patterns on the model parameter and interaction rules reveals that the patterns do not possess intrinsic length and time scales.

Appendix is only available in electronic from at http://www.aanda.org Title: Penumbral Structure and Outflows in Simulated Sunspots Authors: Rempel, M.; Schüssler, M.; Cameron, R. H.; Knölker, M. Bibcode: 2009Sci...325..171R Altcode: 2009arXiv0907.2259R Sunspots are concentrations of magnetic field on the visible solar surface that strongly affect the convective energy transport in their interior and surroundings. The filamentary outer regions (penumbrae) of sunspots show systematic radial outward flows along channels of nearly horizontal magnetic field. These flows were discovered 100 years ago and are present in all fully developed sunspots. By using a comprehensive numerical simulation of a sunspot pair, we show that penumbral structures with such outflows form when the average magnetic field inclination to the vertical exceeds about 45 degrees. The systematic outflows are a component of the convective flows that provide the upward energy transport and result from anisotropy introduced by the presence of the inclined magnetic field. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Corbel, Stephane; Edwards, Philip; Sadler, Elaine; Burrows, David; Thompson, David J.; Gehrels, Neil; Tingay, Steven; Wieringa, Mark; Grenier, Isabelle; Chaty, Sylvain; Dubus, Guillaume; Cameron, Robert Bibcode: 2009atnf.prop.2459C Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Radiative MHD Simulations of Sunspot Structure Authors: Rempel, Matthias D.; Schuessler, M.; Cameron, R.; Knoelker, M. Bibcode: 2009SPD....40.0604R Altcode: We summarize the recent progress made in magneto convection simulations of sunspot structure. Over the past 4 years simulations have evolved from local 6x6x2 Mm size domains focusing on the details of umbral dots to simulations covering a pair of opposite polarity spots in a 100x50x6 Mm domain. The simulations point out the common magneto convective origin of umbral dots and filaments in the inner penumbra and most recently also reveal the processes involved in the formation of an extended outer penumbra with strong horizontal outflows averaging around 5 km/s in the photosphere. Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787 Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch, A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.; Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.; Zharkov, S. Bibcode: 2009SSRv..144..249G Altcode: 2008SSRv..tmp..188G; 2010arXiv1002.2369G Various methods of helioseismology are used to study the subsurface properties of the sunspot in NOAA Active Region 9787. This sunspot was chosen because it is axisymmetric, shows little evolution during 20-28 January 2002, and was observed continuously by the MDI/SOHO instrument. AR 9787 is visible on helioseismic maps of the farside of the Sun from 15 January, i.e. days before it crossed the East limb. Oscillations have reduced amplitudes in the sunspot at all frequencies, whereas a region of enhanced acoustic power above 5.5 mHz (above the quiet-Sun acoustic cutoff) is seen outside the sunspot and the plage region. This enhanced acoustic power has been suggested to be caused by the conversion of acoustic waves into magneto-acoustic waves that are refracted back into the interior and re-emerge as acoustic waves in the quiet Sun. Observations show that the sunspot absorbs a significant fraction of the incoming p and f modes around 3 mHz. A numerical simulation of MHD wave propagation through a simple model of AR 9787 confirmed that wave absorption is likely to be due to the partial conversion of incoming waves into magneto-acoustic waves that propagate down the sunspot. Wave travel times and mode frequencies are affected by the sunspot. In most cases, wave packets that propagate through the sunspot have reduced travel times. At short travel distances, however, the sign of the travel-time shifts appears to depend sensitively on how the data are processed and, in particular, on filtering in frequency-wavenumber space. We carry out two linear inversions for wave speed: one using travel-times and phase-speed filters and the other one using mode frequencies from ring analysis. These two inversions give subsurface wave-speed profiles with opposite signs and different amplitudes. The travel-time measurements also imply different subsurface flow patterns in the surface layer depending on the filtering procedure that is used. Current sensitivity kernels are unable to reconcile these measurements, perhaps because they rely on imperfect models of the power spectrum of solar oscillations. We present a linear inversion for flows of ridge-filtered travel times. This inversion shows a horizontal outflow in the upper 4 Mm that is consistent with the moat flow deduced from the surface motion of moving magnetic features. From this study of AR 9787, we conclude that we are currently unable to provide a unified description of the subsurface structure and dynamics of the sunspot. Title: ATCA monitoring of gamma-ray loud AGN in support of the Fermi mission Authors: Tingay, Steven; Macquart, Jean-Pierre; Lovell, Jim; Edwards, Philip; Sadler, Elaine; Ojha, Roopesh; Romani, Roger W.; Kadler, Matthias; Murphy, David; Gehrels, Neil; Michelson, Peter; Cameron, Robert Bibcode: 2009atnf.prop.1995T Altcode: Following a successful pilot investigation to determine the feasibility of monitoring bright gamma-ray AGN at 7 mm throughout the year (C1730), we propose a continuation of the project into a one year phase of observations that will support the Fermi mission following its June 2008 launch. The goal of this project is to monitor Fermi-identified AGN at 4.8, 8.6, 17, 19, 38, and 40 GHz at monthly intervals, tracking variability in the AGN (in particular flaring activity) that can be related to gamma-ray variability observed by Fermi and pc-scale structural variability observed by our concurrent Southern Hemipshere VLBI monitoring program in support of Fermi. The ATCA, VLBI, and Fermi data will contribute to a multi-wavelength AGN database that will help us understand the origins of high energy emission in AGN. Title: ATCA follow-up of unidentified flaring Fermi gamma-ray sources Authors: Edwards, Philip; Sadler, Elaine; Romani, Roger W.; Tingay, Steven; Wieringa, Mark; Michelson, Peter; Cameron, Robert Bibcode: 2009atnf.prop.2222E Altcode: This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for which no counterpart is known, which we expect to occur predominantly for sources with |b|<1.5degrees. As Fermi source localizations are often better than 10arcmin, we will initially make simultaneous 5GHz/9GHz observation, for which the primary beam is matched to the Fermi error region. If a radio counterpart can be identified, we will make follow-up observations at higher frequencies to help characterise the Spectral Energy Distribution of the source, and to monitor the evolution of the outburst at radio frequencies. History indicates this rapid localization and follow-up of flaring sources may well be critical in identifying a new class (or classes) of high energy object. Title: Countercell Meridional Flow and Latitudinal Distribution of the Solar Polar Magnetic Field Authors: Jiang, J.; Cameron, R.; Schmitt, D.; Schüssler, M. Bibcode: 2009ApJ...693L..96J Altcode: Recent observations indicate that the latitudinal profile of the magnetic flux shows a pronounced decrease close to the solar north pole during the minimum phase of solar cycle 23. Using a surface flux transport model, we have performed numerical experiments to study the conditions that could lead to such a latitudinal distribution. We find that a strong decrease of the magnetic field near the poles results if a weak countercell of the meridional flow at high latitudes with an equatorward speed of a few m s-1 is present. Title: Surface-Focused Seismic Holography of Sunspots: II. Expectations from Numerical Simulations Using Sound-Speed Perturbations Authors: Birch, A. C.; Braun, D. C.; Hanasoge, S. M.; Cameron, R. Bibcode: 2009SoPh..254...17B Altcode: 2008SoPh..tmp..186B Helioseismic observations of sunspots show that wave travel times, at fixed horizontal phase speed, depend on the temporal frequency of the waves employed in the data analysis. This frequency variation has been suggested to be consistent with near-surface (vertical length scales of order one Mm or smaller) changes in wave propagation properties relative to the quiet Sun. We investigate this suggestion by employing numerical simulations of acoustic-wave propagation through models with horizontally and vertically inhomogeneous structure. Standard methods of surface-focused helioseismic holography are applied to the resulting simulated wave fields. We find that the travel-time shifts measured using holography from the simulations with deep sound-speed perturbations (relative to a plane-parallel quiet-Sun model) do not show a systematic frequency dependence at phase speeds above about 20 km s−1. However, shallow sound-speed perturbations, similar to those proposed to model the acoustic scattering properties of sunspots observed with Hankel analysis, produce systematic frequency dependence at these phase speeds. In both cases, positive travel-time shifts can be caused by positive sound-speed perturbations. The details of the travel-time shifts are, however, model dependent. Title: Helioseismology of Sunspots: A Case Study of NOAA Region 9787 Authors: Gizon, L.; Schunker, H.; Baldner, C. S.; Basu, S.; Birch, A. C.; Bogart, R. S.; Braun, D. C.; Cameron, R.; Duvall, T. L.; Hanasoge, S. M.; Jackiewicz, J.; Roth, M.; Stahn, T.; Thompson, M. J.; Zharkov, S. Bibcode: 2009odsm.book..249G Altcode: Various methods of helioseismology are used to study the subsurface properties of the sunspot in NOAA Active Region 9787. This sunspot was chosen because it is axisymmetric, shows little evolution during 20-28 January 2002, and was observed continuously by the MDI/SOHO instrument. AR 9787 is visible on helioseismic maps of the farside of the Sun from 15 January, i.e. days before it crossed the East limb. Title: A Robust Correlation between Growth Rate and Amplitude of Solar Cycles: Consequences for Prediction Methods Authors: Cameron, R.; Schüssler, M. Bibcode: 2008ApJ...685.1291C Altcode: We consider the statistical relationship between the growth rate of activity in the early phase of a solar cycle with its subsequent amplitude on the basis of four data sets of global activity indices (Wolf sunspot number, group sunspot number, sunspot area, and 10.7 cm radio flux). In all cases, a significant correlation is found: stronger cycles tend to rise faster. Owing to the overlapping of sunspot cycles, this correlation leads to an amplitude-dependent shift of the solar minimum epoch. We show that this effect explains the correlations underlying various so-called precursor methods for the prediction of solar cycle amplitudes and also affects the prediction tool of Dikpati et al. based on a dynamo model. Inferences as to the nature of the solar dynamo mechanism resulting from predictive schemes which (directly or indirectly) use the timing of solar minima should therefore be treated with caution. Title: Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation Authors: Cameron, R.; Gizon, L.; Duvall, T. L., Jr. Bibcode: 2008SoPh..251..291C Altcode: 2008arXiv0802.1603C; 2008SoPh..tmp...51C The propagation of solar waves through the sunspot of AR 9787 is observed by using temporal cross-correlations of SOHO/MDI Dopplergrams. We then use three-dimensional MHD numerical simulations to compute the propagation of wave packets through self-similar magnetohydrostatic sunspot models. The simulations are set up in such a way as to allow a comparison with observed cross-covariances (except in the immediate vicinity of the sunspot). We find that the simulation and the f-mode observations are in good agreement when the model sunspot has a peak field strength of 3 kG at the photosphere and less so for lower field strengths. Constraining the sunspot model with helioseismology is only possible because the direct effect of the magnetic field on the waves has been fully taken into account. Our work shows that the full-waveform modeling of sunspots is feasible. Title: The seismic effects of a sunspot Authors: Schunker, H.; Cameron, R.; Gizon, L. Bibcode: 2008ESPM...12..3.5S Altcode: We simulate the helioseismic wave field by using the three-dimensional Semi-spectral Linear MHD (SLiM) code and exciting small-amplitude waves by sources distributed in the near-surface layers of a model solar atmosphere.Our model atmosphere is realistic in the sense that it has a standard sound-speed profile. Our source function is a realization drawn from a random process specified by a statistical description of solar convection. We obtain a quiet-Sun power spectrum of wave motions, which is consistent with Doppler observations. In order to study wave propagation through sunspots, we derive a simplified monolithic model sunspot embedded in the quiet-Sun model atmosphere. The corresponding wave field computed with SLiM is then compared with MDI observations of f- and p-mode scattering by magnetic region AR9787. The comparison is encouraging as the numerical simulation is able to reproduce wave absorption and scattering phase shifts. As part of our analysis, we show the advantage of computing a reference quiet-Sun wave field using the same realization of the sources for the purpose of comparisons and noise reduction. Title: Radiative magnetohydrodynamic simulations of solar pores Authors: Cameron, R.; Schüssler, M.; Vögler, A.; Zakharov, V. Bibcode: 2007A&A...474..261C Altcode: Context: Solar pores represent a class of magnetic structures intermediate between small-scale magnetic flux concentrations in intergranular lanes and fully developed sunspots with penumbrae.
Aims: We study the structure, energetics, and internal dynamics of pore-like magnetic structures by means of exploratory numerical simulations.
Methods: The MURaM code has been used to carry out several 3D radiative MHD simulations for pores of various sizes and with different boundary conditions.
Results: The general properties of the simulated pores (morphology, continuum intensity, magnetic field geometry, surrounding flow pattern, mean height profiles of temperature, pressure, and density) are consistent with observational results. No indications for the formation of penumbral structure are found. The simulated pores decay by gradually shedding magnetic flux into the surrounding pattern of intergranular downflows (“turbulent erosion”). When viewed under an angle (corresponding to observations outside solar disc center), granules behind the pore appear brightened.
Conclusions: Radiative MHD simulations capture many observed properties of solar pores. Title: Photospheric magnetoconvection Authors: Cameron, Robert; Vögler, Alexander; Schüssler, Manfred Bibcode: 2007IAUS..239..475C Altcode: No abstract at ADS Title: Solar Cycle Prediction Using Precursors and Flux Transport Models Authors: Cameron, R.; Schüssler, M. Bibcode: 2007ApJ...659..801C Altcode: 2006astro.ph.12693C We study the origin of the predictive skill of some methods to forecast the strength of solar activity cycles. A simple flux transport model for the azimuthally averaged radial magnetic field at the solar surface is used, which contains a source term describing the emergence of new flux based on observational sunspot data. We consider the magnetic flux diffusing over the equator as a predictor, since this quantity is directly related to the global dipole field from which a Babcock-Leighton dynamo generates the toroidal field for the next activity cycle. If the source is represented schematically by a narrow activity belt drifting with constant speed over a fixed range of latitudes between activity minima, our predictor shows considerable predictive skill, with correlation coefficients up to 0.95 for past cycles. However, the predictive skill is completely lost when the actually observed emergence latitudes are used. This result originates from the fact that the precursor amplitude is determined by the sunspot activity a few years before solar minimum. Since stronger cycles tend to rise faster to their maximum activity (known as the Waldmeier effect), the temporal overlapping of cycles leads to a shift of the minimum epochs that depends on the strength of the following cycle. This information is picked up by precursor methods and also by our flux transport model with a schematic source. Therefore, their predictive skill does not require a memory, i.e., a physical connection between the surface manifestations of subsequent activity cycles. Title: SLiM: a code for the simulation of wave propagation through an inhomogeneous, magnetised solar atmosphere Authors: Cameron, R.; Gizon, L.; Daiffallah, K. Bibcode: 2007AN....328..313C Altcode: 2010arXiv1002.2344C In this paper we describe the semi-spectral linear MHD (SLiM) code which we have written to follow the interaction of linear waves through an inhomogeneous three-dimensional solar atmosphere. The background model allows almost arbitrary perturbations of density, temperature, sound speed as well as magnetic and velocity fields. We give details of several of the tests we have used to check the code. The code will be useful in understanding the helioseismic signatures of various solar features, including sunspots. Title: Solar mesogranulation as a cellular automaton effect Authors: Matloch, L.; Cameron, R.; Schmitt, D.; Schüssler, M. Bibcode: 2007msfa.conf..339M Altcode: We present a simple cellular automaton model of solar granulation that captures the granular cell characteristics in terms of lifetime and size distributions. We show that mesogranulation, as defined in observational data, is an intrinsic feature of such a cell system. Title: Helioseismology at MPS Authors: Gizon, L.; Cameron, R.; Jackiewicz, J.; Roth, M.; Schunker, H.; Stahn, T. Bibcode: 2007msfa.conf...89G Altcode: Research in solar and stellar seismology at the Max Planck Institute for Solar System Research (MPS) is supported by the Junior Research Group "Helio- and Asteroseismology" of the Max Planck Society since September 2005. A presentation of the current topics of research is given, with particular emphasis on local helioseismology. Title: Three-dimensional numerical simulation of wave propagation through a model sunspot Authors: Cameron, R.; Gizon, L. Bibcode: 2006ESASP.624E..63C Altcode: 2006soho...18E..63C No abstract at ADS Title: ChaMP Serendipitous Galaxy Cluster Survey Authors: Barkhouse, W. A.; Green, P. J.; Vikhlinin, A.; Kim, D. -W.; Perley, D.; Cameron, R.; Silverman, J.; Mossman, A.; Burenin, R.; Jannuzi, B. T.; Kim, M.; Smith, M. G.; Smith, R. C.; Tananbaum, H.; Wilkes, B. J. Bibcode: 2006ApJ...645..955B Altcode: 2006astro.ph..3521B We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 deg2, we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about ~10-14 ergs cm-2 s-1, with a median cluster core radius of 21''. For 56 of the 130 X-ray fields, we use the ChaMP's deep NOAO 4 m MOSAIC g', r', and i' imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore- and background contamination and provides photometric redshifts to z~0.7. From the overlapping 6.1 deg2 X-ray/optical imaging, we find 115 optical clusters (of which 11% are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5-2 keV) is LX=(2.65+/-0.19)×1043 ergs s-1. The clusters in our sample that are only detected in our optical data are poorer on average (~4 σ) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions. Title: High field strength modified ABC and rotor dynamos Authors: Cameron, Robert; Galloway, David Bibcode: 2006MNRAS.367.1163C Altcode: 2006MNRAS.tmp..233C The Archontis dynamo was the first stationary dynamo discovered which saturates with almost equal magnetic and kinetic energies in the limit of large Reynolds numbers. In this paper we present two further examples, one based on a series of numerical calculations and the other on the analytic rotor dynamos of Herzenberg. The forcing and flow in these new examples lack some of the symmetries of the Archontis dynamo are therefore more generic. The saturation mechanism is thus not a unique property of the Archontis dynamo.

For the numerical solutions, we also have investigated the structure and stability of the flow and field near the stagnation points and those streamlines which enter and leave them. These structures play an important part in the operation of the dynamo mechanism, and the way they interact with one another is mirrored in the analytic example based on the Herzenberg rotors. Title: Extending the X-ray Luminosity Function of AGN to High Redshift Authors: Silverman, J.; Green, P.; Barkhouse, W.; Cameron, R.; Kim, M.; Kim, D. -W.; Wilkes, B.; Hasinger, G.; Full Champ Project, The Bibcode: 2006ESASP.604..795S Altcode: 2005astro.ph.11552S; 2006xru..conf..795S X-ray surveys of the extragalactic universe are now able to detect significant numbers of AGN out to high redshift (z~5). We highlight some results from the Chandra Multiwavelength Project (ChaMP) to measure the X-ray luminosity function out to these early epochs. At z > 3, we show that the comoving space density of luminous (log Lx > 44.5) AGN has a behavior similar to the optical QSO luminosity function. With a newly compiled sample of AGN from ChaMP supplemented with those from additional surveys including the Chandra Deep fields, we present a preliminary measure of the luminosity function in the hard (2-8 keV) band. With 37 AGN at z > 3, we continue to see a decline in the space density at high redshift over a wider range in luminosity. We discuss the need to identify a larger sample of obscured AGN at high redshift to determine if an early epoch of hidden supermassive black hole growth occurred. Title: Saturation properties of the Archontis dynamo Authors: Cameron, Robert; Galloway, David Bibcode: 2006MNRAS.365..735C Altcode: 2005MNRAS.tmp.1100C This paper discusses the generation and subsequent non-linear limiting of magnetic fields by motions in a periodic flow driven by a force whose components are proportional to (sinz, sinx, siny). This problem was originally studied by Archontis; the purpose of the present work is to remove certain complications present in the original model in order to understand better the underlying physical mechanism which limits the total magnetic energy growth. At high Reynolds numbers the resulting dynamos end up with almost equal total magnetic and kinetic energies, and thus yield fields strong enough to be astrophysically relevant. Until now, the existence of such dynamos has been doubted, so this demonstration of an example appears very important. At least up to Reynolds numbers of 800, these solutions are laminar and attracting.

We then present an argument showing that any stationary, incompressible dynamo can be used to create a family of solutions with an arbitrary ratio of magnetic to kinetic energies in the limit of large Reynolds numbers. The stability of such solutions is also discussed. Title: Simulations of Solar Pores Authors: Cameron, R.; Vögler, A.; Schüssler, M.; Zakharov, V. Bibcode: 2005ESASP.600E..11C Altcode: 2005ESPM...11...11C; 2005dysu.confE..11C No abstract at ADS Title: The structure of small-scale magnetic flux tubes Authors: Cameron, Robert; Galloway, David Bibcode: 2005MNRAS.358.1025C Altcode: 2005MNRAS.tmp..199C Three main mechanisms have been described to determine the maximum field strength and structure of a solar or stellar magnetic flux tube. This paper attempts to relate them to one another through a series of magnetoconvective calculations. The first process is the balancing of the Lorentz force by radial gradients in the buoyancy force. It was first found in the Boussinesq regime, where it was studied in the late 1970s by Galloway, Proctor & Weiss. A similar balance can occur in the fully compressible case, where we refer to it as quasi-Boussinesq (QB). The second process involves a balance between an outward-directed radial pressure gradient and radial gradients in the buoyancy force outside the tube. This is the mechanism proposed in the early 1990s by Kerswell & Childress (the KC mechanism). The third mechanism, convective collapse (CC), is a process whereby a flux tube can evolve to a high field strength because of an instability due to the superadiabaticity of the material within the tube. Until now, it has been studied using the so-called `thin flux tube' approximation in which convective motions are ignored even though there is a background superadiabatic density stratification. Here we place these three mechanisms in a unified framework and explore the transitions between the solutions as various parameters are varied. In particular, we show that the QB solutions are preferred for a wide range of parameters, whereas CC solutions occur only in very specific circumstances. In particular, on the Sun, the latter are probably limited to flux tubes with radii less than approximately 10 km, the turbulent magnetic diffusivity length-scale. Title: The Decay of a Simulated Pore Authors: Cameron, R.; Vögler, A.; Shelyag, S.; Schüssler, M. Bibcode: 2004ASPC..325...57C Altcode: Using MURaM -- Max-Planck Institut für Aeronomie University of Chicago Radiative Magnetohydrodynamics -- an MHD code which includes radiative transfer and partial ionization, we have studied the decay phase of a solar pore. The simulations are sufficiently realistic in their treatment of the photosphere to allow a direct comparison with observations, both current and those of upcoming missions such as SolarB. As well as discussing the structure and decay of pores, we show the formation of shallow, field aligned, convective rolls which are an important feature of our solutions. Title: Finding the Obscured AGN with ChAMP Authors: Aldcroft, T.; Green, P.; Silverman, J.; Cameron, R.; Kim, D.; Wilkes, B.; ChaMP Collaboration Bibcode: 2004HEAD....8.3506A Altcode: 2004BAAS...36..973A X-ray surveys with \textit{Chandra} and \textit{XMM} provide the most complete census of accretion powered luminosity in the universe. Coupled with recent advances suggesting an intimate connection between galaxy and supermassive black hole evolution, X-ray AGN surveys have emerged as a powerful tool for investigating topics from galaxies to large scale cosmology. One empirical input which plays a key role in modeling is the distribution of obscuration in AGN. Obscuration changes the AGN spectral contribution to the hard Cosmic X-ray Background (CXRB), the apparent luminosity of AGN, and can even make them entirely "disappear", so understanding this phenomenon is important. Using X-ray and optical imaging and spectroscopic data from the \textit{Chandra} Multiwavelength Project (ChaMP), we have assembled a sample of ∼ 900 AGN, covering 3.8 square degrees to a uniform flux limit of 2.7× 10-15 ergs cm-2 sec-1. Using direct spectral fitting with \textit{CIAO/Sherpa} we estimate the intrinsic absorbing column NH in each source. Because of the large sample size, we are able to determine the NH distribution within each of six flux bins, confirming the trend of increasing obscuration at lower fluxes and providing the strongest constraints to date on the obscured fraction. We discuss the implications for modeling of the CXRB and AGN luminosity function. Title: Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei. II. Prediction from Our Sweeping Magnetic Twist Model for the Wiggled Parts of Active Galactic Nucleus Jets and Tails Authors: Kigure, Hiromitsu; Uchida, Yutaka; Nakamura, Masanori; Hirose, Shigenobu; Cameron, Robert Bibcode: 2004ApJ...608..119K Altcode: 2004astro.ph..2545K Distributions of Faraday rotation measure (FRM) and the projected magnetic field derived by a three-dimensional simulation of MHD jets are investigated based on our ``sweeping magnetic twist model.'' FRM and Stokes parameters were calculated to be compared with radio observations of large-scale wiggled AGN jets on kiloparsec scales. We propose that the FRM distribution can be used to discuss the three-dimensional structure of the magnetic field around jets and the validity of existing theoretical models, together with the projected magnetic field derived from Stokes parameters. In a previous paper we investigated the basic straight part of AGN jets by using the result of a two-dimensional axisymmetric simulation. The derived FRM distribution has a general tendency to have a gradient across the jet axis, which is due to the toroidal component of the magnetic field generated by the rotation of the accretion disk. In this paper we consider the wiggled structure of the AGN jets by using the result of a three-dimensional simulation. Our numerical results show that the distributions of FRM and the projected magnetic field have a clear correlation with the large-scale structure of the jet itself, namely, three-dimensional helix. Distributions, seeing the jet from a certain direction, show a good matching with those in a part of the 3C 449 jet. This suggests that the jet has a helical structure and that the magnetic field (especially the toroidal component) plays an important role in the dynamics of the wiggle formation because it is due to a current-driven helical kink instability in our model. Title: X-ray Emitting AGN Unveiled by the Chandra Multiwavelength Project Authors: Silverman, J.; Green, P.; Aldcroft, T.; Kim, D.; Barkhouse, W.; Cameron, R.; Wilkes, B. Bibcode: 2004ASPC..311..321S Altcode: 2004apsd.conf..321S; 2003astro.ph.10907S We present an X-ray and optical analysis of a flux limited (f2.0-8.0 keV > 10-14 erg s-1 cm-2) sample of 126 AGN detected in 16 Chandra fields. This work represents a small though significant subset of the Chandra Multiwavelength Project (ChaMP). We have chosen this limiting flux to have a reasonable degree of completeness (50%) in our optical spectroscopic identifications. The optical counterparts of these AGN are characterized as either broad emission line AGN (BLAGN; 59%), narrow emission line galaxies (NELG; 20%) or absorption line galaxies (ALG; 12%) without any evidence of an AGN signature. Based on their X-ray luminosity and spectral properties, we show that NELG and ALG are primarily the hosts of obscured AGN with an intrinsic absorbing column in the range of 1021.5< NH<1023.3 cm-2. While most of the BLAGN are unobscured, there are a few with substantial absorption. X-ray surveys such as the ChaMP nicely complement optical surveys such as the SDSS to completely determine the demographics of the AGN population. Title: Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei. I. Predictions from our Sweeping Magnetic Twist Model Authors: Uchida, Yutaka; Kigure, Hiromitsu; Hirose, Shigenobu; Nakamura, Masanori; Cameron, Robert Bibcode: 2004ApJ...600...88U Altcode: 2003astro.ph..9605U Using the numerical data of MHD simulation for active galactic nucleus (AGN) jets based on our ``sweeping magnetic twist model,'' we calculated the Faraday rotation measure (FRM) and the Stokes parameters to compare with observations. We propose that the FRM distribution can be used to discuss the three-dimensional structure of magnetic field around jets, together with the projected magnetic field derived from the Stokes parameters. In the present paper, we assumed the basic straight part of the AGN jet and used the data of axisymmetric simulation. The FRM distribution that we derived has a general tendency to have gradient across the jet axis, which is due to the toroidal component of the helical magnetic field generated by the rotation of the accretion disk. This kind of gradient in the FRM distribution is actually observed in some AGN jets, which suggests a helical magnetic field around the jets and thus supports our MHD model. Following this success, we are now extending our numerical observation to the wiggled part of the jets, using the data of three-dimensional simulation based on our model, in an upcoming paper. Title: Stormy Weather Authors: Cameron, Robert Bibcode: 2004ChNew..11...22C Altcode: No abstract at ADS Title: An Investigation of Loop-Type CMEs with a 3D MHD Simulation Authors: Kuwabara, J.; Uchida, Y.; Cameron, R. Bibcode: 2003ASPC..289..389K Altcode: 2003aprm.conf..389K CMEs have erupted filaments (core) and flux loops that lie over the filament (leading edge) and a cavity between the core and leading edge. In one model ``Flux loops are pushed up by erupted filaments and expand upwards" which roughly explains much about CMEs. But there are some CMEs with characteristics that are inexplicable with this model, which have a twisted structure along the loop and the structure of a convex lens at the loop top (Illing and Hundhausen 2000). We consider Torsional Alfven Wave (TAW) propagation as the cause of these characteristics for some CMEs, and have studied this with a 3D MHD simulation. As a result, we found that TAW propagation most likely explains these characteristics for some CMEs and that a TAW can carry out plasma from the chromosphere to coronal space along the loop. We propose a new scenario about the occurrence of CMEs based on results of our simulation and observations. Title: Optical spectroscopic followup of serendipitous Chandra sources: the Chandra Multiwavelength Project (ChaMP) Authors: Silverman, J.; Green, P.; Wilkes, B.; Foltz, C.; Smith, P.; Smith, C.; Kim, Dong-Woo; Morris, D.; Mossman, A.; Cameron, R.; Adelberger, K.; ChaMP Collaboration Bibcode: 2003AN....324...97S Altcode: A primary goal of the Chandra Multiwavelength Project (ChaMP) is to investigate the evolution of Active Galactic Nuclei (AGN) and quasars by measuring the luminosity function out to z>=4 including obscured AGN that have been missed by previous surveys. To do so, we are acquiring spectra of optical counterparts to serendipitious X-ray sources detected by Chandra for classification and redshift determination. We have amassed about 200 spectra using the FLWO 1.5m, WIYN 3.5m, CTIO/4m, Magellan and the MMT 6.5m. We have classified the majority of optical counterparts as 65 AGN, 14 galaxies. The remaining counterparts are either stars (8 clusters (1 fields. With a limiting magnitude of r'=22 for spectroscopic followup, we are able to detect quasars out to z ~ 5 and galaxies out to z ~ 0.7. This preliminary sample forms the foundation for our measurement of the X-ray luminosity function of AGNs out to z ~ 4. Title: Quantitative measure of quiet photospheric magnetic fields Authors: Zirin, H.; Cameron, R. Bibcode: 2002AAS...200.3903Z Altcode: 2002BAAS...34..701Z We have analyzed a set of 110 Stokes V spectra of the quiet Sun taken with the spectrovideomagnetograph at BBSO June 23, 2000. The 480x512 pixel spectrograms are bundled into 3 pixel (1 arc sec) spectra, giving 160 distinct spectra on each frame, or 16400 spectra overall. An element of magnetic network was included in each spectrogram, so that actual splitting measurements could be used to check absolute calibration of the field measures. In each case we measured the V signal in both 5250 and 5247 and compared the values. If the ratio was 3:2 as given by the g-factors, the data must represent true measured magnetic fields, since random noise does not understand g-factors. We find the mean field on each spectrum to range from 3 to 49 gauss in the different frames, and the median absolute field, from 13 to 30 G. In all cases the difference between V(5250) and 1.5xV( 5247) is zero within 1.2 standard errors. To check the popular ``emperor's new clothes" model in which the fields measured are due to invisible spots with kilogauss fields, we calculate the mean value of 1.5xV(5247)/0.78- V(5250), expected to be zero for that model. Rather than zero, that result is typically 3 standard errors from zero, and invariably negative. That result means that the V(5250) is not saturated, as would be expected in the kilogauss model. Thus the emperor, in fact, has no clothes. The fields measured in network elements run from 250 to 700 gauss, and are typically confirmed within 20% by the measured splitting. The existence of fields of mixed polarity and strength >10 gauss everywhere in the photosphere gives an explanation for the support of the chromosphere, which has a scale height of 1000 Km instead of the expected hydrostatic scale height <200 Km, as well as the filtering out of unionized high-FIP elements, which cannot be supported by the magnetic fields, from the solar wind. Title: The true structure of weak solar magnetic fields Authors: Zirin, H.; Cameron, R. Bibcode: 2002ocnd.confE..30Z Altcode: No abstract at ADS Title: Loop-Type CME Produced by Magnetic Reconnection of Two Large Loops at the Associated Arcade Flare Authors: Uchida, Y.; Kuwabara, J.; Cameron, R.; Suzuki, I.; Tanaka, T.; Kouduma, K. Bibcode: 2002mwoc.conf..199U Altcode: We claim from observational analyses that there are, at least, two distinctly different types among CME's: One with a bubble shape expanding roughly isotropically with constant velocity caused by explosive flares (Bubble-type), and the other with a large loop shape whose anchor point in the middle is released by the occurrence of an arcade flare between the footpoints of CME's, rising with acceleration and deformation (Loop-type). The characteristic difference between these types is that the footpoints stay fixed on the solar surface in the Loop-type, whereas the structure does not have such fixed footpoints for the Bubble-type since the skirts of the bubble (Moreton wave and EIT wave separately propagating) sweep on the solar surface. We investigate MHD models for these two types of CME's, fulfilling the observed characteristics described above, with our 3D MHD simulations, and show dynamic behaviors of those with movies. We believe that these are examples of new generation approach with time-dependent 3D MHD modelling, allowing actual comparison of dynamic models with dynamic results from advanced observations. Title: The Chandra Multi-wavelength Project (ChaMP): Preliminary results of X-ray Analysis Authors: Kim, D. -W.; Cameron, R.; Drake, J.; Freeman, P.; Fruscione, A.; Gaetz, T. J.; Green, P. J.; Grimes, J.; Ghosh, H.; Kashyap, V.; Schlegel, E.; Vikhlinin, A.; Wilkes, B.; Tananbaum, H. Bibcode: 2001tysc.confE.222K Altcode: We present preliminary results of X-ray data analysis as part of the Chandra Multi-wavelength Project. We describe basic data corrections, screening and source analysis procedures. About 1/4 of 160 fields selected in AO1 and AO2 have been processed through the ChaMP X-pipeline. About 2000 sources are detected (this number may not be prorated). Average X-ray source properties in terms of LogN-LogS, X-ray color, optical color and X-ray to optical luminosity ratio are discussed. Title: Optical Classification of Chandra Serendipitous Sources by the ChaMP Authors: Green, Paul J.; Cameron, Robert Bibcode: 2001tysc.confE..53G Altcode: We describe our ongoing optical imaging and spectroscopy of a deep, wide-area sample of serendipitous X-ray sources detected in Chandra archival images. The Chandra Multiwavelength Project (ChaMP) thus enables studies of the nature, evolution, and clustering of X-ray selected AGN and galaxies. Chandra's subarcsecond astrometry enables unambiguous identification of optical counterparts, and the broadband X-ray sensitivity (0.3-8keV) means that our sample is less affected by absorption than previous optical, UV, or soft X-ray surveys. Unlike radio surveys , the ChaMP will allow the first complete census of the intrinsic population of AGN (not just the radio bright fraction). We present initial results that will eventually encompass a sample of thousands of serendipitous sources detected in 150 Chandra archival images, to constrain the X-ray luminosity function and its evolution. Title: The Field Strength of the Quiet Sun Magnetic Elements Authors: Zirin, H.; Cameron, R. Bibcode: 2001AAS...198.7105Z Altcode: 2001BAAS...33..893Z By attaching the videomagnetograph to the Coude spectrograph at BBSO, we can measure weak fields down to 10-20 gauss, and splittings down to 200 gauss. Using Stenflo's technique of comparing 5250 and 5247, we find no saturation; the lines (corrected for g-factor) give equal results within a few per cent and are truly weak. The V measurements are calibrated by comparison to Zeeman splitting measures above 200 gauss. The filling factor is unity and there are no hidden strong fields. We find noevidence for kilogauss fileds in the quiet Sun. While noise limits the agreement of the two lines below 20 gauss, there is a detectable V signal almost everywhere on the Sun, both unipolar and mixed, of the order of 5 gauss. We call the new instrument the spectrovideo-magnetograph (SPVMG). This work supported by the NSF. Title: Blast Waves in the Magnetized Solar Atmosphere Authors: Cameron, R.; Uchida, Y. Bibcode: 2001AGUSM..SH42A09C Altcode: Solar flares convert large amounts of magnetic energy into thermal and bulk plasma motions. Such large changes in the magnetic field and plasma properties excite the available wave modes. Not all modes are equally excited of course and, in principle, this can be used to probe the flare mechanism. In practice however we are still at the stage of identifying the different modes we see. The initial breakthrough in this regard occurred in the early 1970s when Uchida (Uchida 1968) identified the previously observed Moreton waves (Moreton and Ramsey 1960) as the skirt of a fast mode shock propagating in the Corona. This picture has remained essentially unchanged since. In the 1990s the regular observation of the sun in EUV wavelengths revealed the existence of a new blast related wave: the EIT wave. The most distinctive difference between the behavior of the two types of waves is their different velocities, with the Moreton wave being about twice as fast as the EIT wave. Where the two waves are similar however is in the fact that they can both propagate almost isotropically. For the Moreton wave this is expected as the Moreton wave is a fast mode disturbance. For the EIT wave the isotropic behavior suggests that the information is also being carried by the fast mode. We suggest that the difference between the two types of modes is not in the way the information is being carried, but rather in the information content of the two different types of waves. The Moreton wave conveys the information of the sharp, rapid energy release associated with the impulsive phase of the flare. The EIT wave conveys information as to the ejection of excess mass and energy from the system via the slow mode. Unlike the simple spiked structure which characterizes the impulsive phase, the time-scale associated with the energy release is determined by the bulk mass motion along the magnetic field lines - typically the slow mode velocity.. It will be shown that this variation in the `source term' of the EIT disturbance gives rise to an apparent velocity consistent with the EIT observations. Title: Spectovideomagnetograph results and the Stokes V assymmetry Authors: Cameron, R.; Zirin, H. Bibcode: 2001AAS...198.7104C Altcode: 2001BAAS...33R.893C The Spectrovideomagnetograph at Big Bear Solar Observatory was used to obtain several thousand individual spectra of small elements on the solar surface. These measurements display the well known Stokes V assymmetry, however because the BBSO SPVMG has a significant different spatial and temporal resolution than previous measurements, the assymmetry has different properties. In this poster we present our measurements of the assymmetry and use them to place constraints on the mechanism producing the assymmetry. We then discuss how the assymmetry contaminates other quantities derived from the SPVMG measurements, and how this contamination can be minimized and controlled in our data set. Title: Rotational Signature of Disk Spicules in H-alpha Authors: Lee, C.; Cameron, R.; Wang, H. Bibcode: 2001AGUSM..SP41B09L Altcode: The Littrow spectrograph at Big Bear Solar Observatory (BBSO) can produce a 4-dimensional data array, the intensity as a function of position, wavelength and time. A week long observation at BBSO was carried out on August 25-30, 1997. The spectral scan data is unique in the sense that Doppler maps can be constructed free from mis-alignment problems. We selected the best data set obtained on August 26 for the present study. A number of disk spicules were identified and analysed by considering their Doppler map and time evolution at different wavelengths. It is estimated that 1/3 of the chosen disk spicules are found to display rotational signature. The result is the first clearest demonstration of spicule rotation. The cloud model of Beckers' was used to determine a lower bound for the angular velocity. Title: The Spectrovideomagnetograph Reveals the True Strength of Photospheric Magnetic Fields Authors: Zirin, H.; Cameron, R. Bibcode: 2001AGUSM..SH32C04Z Altcode: We present new observations of weak solar magnetic fields from an instrument which we term the spectrovideomagnetograph (SPVMG). The sensing system of the videomagnetograph is attached to the Coude spectrograph at Big Bear and yields a high sensitivity. Using the criteria introduced by Stenflo, we measure the Stokes V and I components for the lines FeI 5250 and 5247 in hundreds of spectra. We find that from 20 to 350 gauss derived field strengths are strictly proportional to the g-factor and show no saturation. Hence the widely accepted strong invisible magnetic elements postulated by Stenflo do not exist. The filling factor is near unity. We measure the Zeeman splitting directly down to 200 gauss and find good correspondence with our V measure. We find that the area (outside of sunspots) of the solar surface occupied by magnetic field of different strengths follows a power law in the inverse square of the field strength. This applies to fields down to 200G. This has obvious relevance for turbulent surface dynamo models. We find that at least 90% of the solar surface is covered by weak fields above 5 gauss, sometimes unipolar and sometimes mixed. Title: Investigation of Coronal Mass Ejections I. Loop-type with Arcade Flare between the Fixed Legs, and Bubble-type Due to Flare Blast Waves Authors: Uchida, Y.; Tanaka, T.; Hata, M.; Cameron, R. Bibcode: 2001PASA...18..345U Altcode: In this paper, we give arguments that there are two types of coronal mass ejection (CME). The first type of CME discussed here is the `loop-type', whose occurrence is related to an arcade flare somewhere between the footpoints. It was found that there were pre-event magnetic connections between the flare location and the locations of the footpoints of a CME of this type, and that these connections disappeared after the event. This suggests that the footpoints of loop-type CMEs are special prescribed points, and this was verified by the observation that the footpoints do not move in this type of CME. The other type of CME is the `bubble-type', which is associated with the flare blast from explosive flares. We confirmed the association of this type of CME with the so-called EIT (Extreme Ultra-violet Imaging Telescope) waves, but the velocity of expansion of the bubble is twice or more greater than that of the EIT waves depending on events. Although EIT waves were widely considered to be Moreton waves viewed by SoHO/EIT in the solar activity minimum period, recent simultaneous observations of both have revealed that the EIT wave is something different from the Moreton wave, and propagates separately with a velocity less than half that of a Moreton wave. We therefore propose a new overall picture: the bubble-type CMEs are the flare-produced MHD blast waves themselves, whose skirt is identified as a Moreton wave. EIT waves may be interpreted as follows: the slow-mode gas motions from the source cause secondary long wavelength fast-mode waves which are trapped in the 'waveguide' in the low corona. The secondary long-wavelength wave in the fast-mode, which is trapped in the low corona, has a slower propagation velocity due to the nature of the waves trapped in a 'waveguide'. This trapped wave induces slow-mode motions of the gas through a mode-coupling process in the high chromosphere, where the propagation velocities of the fast-and slow-mode waves match. Three-dimensional MHD simulations for these two types of CME are in progress, and are previewed in this paper. Title: The Chandra Multi-wavelength Project (ChaMP): a Serendipitous Survey with Chandra Archival Data. Authors: Wilkes, B. J.; Green, P.; Brissenden, R.; Cameron, R.; Dobrzycki, A.; Drake, J.; Evans, N.; Fruscione, A.; Gaetz, T.; Garcia, M.; Ghosh, H.; Grimes, J.; Grindlay, J.; Hooper, E.; Karovska, M.; Kashyap, V.; Kim, D. -W.; Kowal, K.; Marshall, H.; Mossman, A.; Morris, D.; Nichols, J.; Szentgyorgyi, A.; Tananbaum, H.; van Speybroeck, L.; Vikhlinin, A.; Virani, S.; Zhao, P. Bibcode: 2001ASPC..232...47W Altcode: 2000astro.ph.11377W; 2001newf.conf...47W The launch of the Chandra X-ray Observatory in July 1999 opened a new era in X-ray astronomy. Its unprecedented, <0.5" spatial resolution and low background are providing views of the X-ray sky 10-100 times fainter than previously possible. We have initiated a serendipitous survey (ChaMP) using Chandra archival data to flux limits covering the range between those reached by current satellites and those of the small area Chandra deep surveys. We estimate the survey will cover ~5 sq.deg./year to X-ray fluxes (2-10 keV) in the range 1E(-13)-6E(-16) erg/cm^2/s discovering ~2000 new X-ray sources, ~80% of which are expected to be AGN. The ChaMP has two parts, the extragalactic survey (ChaMP) and the galactic plane survey (ChaMPlane). ChaMP promises profoundly new science return on a number of key questions at the current frontier of many areas of astronomy including (1) locating and studying high redshift clusters and so constraining cosmological parameters (2) defining the true population of AGN, including those that are absorbed, and so constraining the accretion history of the universe, (3) filling in the gap in the luminosity/redshift plane between Chandra deep and previous surveys in studying the CXRB, (4) studying coronal emission from late-type stars and (5) search for CVs and quiescent Low-Mass X-ray Binaries (qLXMBs) to measure their luminosity functions. In this paper we summarize the status, predictions and initial results from the X-ray analysis and optical imaging. Title: The Spectrovideomagnetograph Reveals the True Strength of Quiet Sun Magnetic Fields Authors: Zirin, H.; Cameron, R. Bibcode: 2000AAS...197.5107Z Altcode: 2000BAAS...32.1489Z We present new observations of weak solar magnetic fields with a technique, which we term the spectro-videomagnetograph (SPVMG) which permits direct measurement of splittings as small as 200 gauss. Using the technique of Stenflo we compared the Stokes V-component for the 5250 and 5247 lines. Contrary to Stenflo's results, we find no evidence for strong fields with small filling factor; i. e., the field strengths measured as 200 gaussare really 200 gauss and not some stronger field partly filling the sample. For the weakest measured fields this cannot be absolutely established, but the evidence supports the existence of field elements at least as weak as 200 gauss. Observations of active regions also yield new results. In many cases of fields near inversion lines, we find doubled sets of Zeeman components, as well as `flags,' broad components, usually confined to one side of the line, extending to displacements corresponding to thousands of gauss, with no corresponding component on the opposite side of the line. We show examples of these spectra, along with slit jaw images, but have only a limited understanding of the field structures they represent. We also have examples of the V-splitting increasing as we approach the inversion line. We are struggling to understand these and will at least show them, with or without explanation. Finally, the regions involving these anomalous Zeeman patterns seem to flare more frequently, although statistics are limited. This work has been supported by the NSF under ATM-9726147. Title: The Chandra Multi-wavelength Project (ChaMP): X-ray Data Analysis Authors: Kim, D. -W.; Cameron, R.; Drake, J.; Fruscione, A.; Gaetz, T. J.; Garcia, M.; Green, P. J.; Grimes, J.; Kashyap, V.; Prestwich, A.; Schlegel, E.; Vikhlinin, A.; Virani, S. N.; Wilkes, B.; Tananbaum, H.; Freedman, D.; ChaMP Collaboration Bibcode: 2000HEAD....5.2604K Altcode: 2000BAAS...32.1223K We present step-by-step X-ray data analysis procedures as part of the Chandra Multi-wavelength Project. They consist of additional data corrections and data screening post CXC Standard Data Processing Rev 1 and the determination of sources and their X-ray properties. Using 3 deep ACIS imaging fields (MS 1137.5+6625, CL0848.6+4453 and A0620-00) with exposure times ranging from 50 ks to 190 ks, we discuss in particular gain correction, aspect correction, removing bad pixels and node boundaries, removing ACIS flaring pixels, streak correction for the S4 chip and excluding high background intervals. Optimal parameters for source detection and X-ray source properties such as X-ray colors are also discussed. Title: The ChaMP: Keck Spectroscopy of Serendipitous Chandra Sources Authors: Green, P. J.; Chaffee, F. H.; Cameron, R.; Virani, S. N.; Dey, A.; Jannuzi, B.; Kindt, A.; van Speybroeck, L.; Tananbaum, H.; Wilkes, B.; ChaMP Collaboration Bibcode: 2000HEAD....5.2618G Altcode: 2000BAAS...32.1226G We describe the X-ray and optical characteristics of faint serendipitous X-ray sources detected during a deep (120ksec) Chandra exposure with ACIS. While the target is MS 1137.5+6625, the second most distant cluster of galaxies in the Einstein Extended Medium Sensitivity Survey (EMSS) at redshift 0.78, as part of the Chandra Multiwavelength Project (ChaMP), we obtained Keck spectroscopy of a dozen optical counterparts in an adjacent field (7 arcmin off-axis) that reveals an intriguing variety of objects, dominated by AGN and galaxies between redshifts of 0.5 to 2. Title: The Chandra Multi-wavelength Project (ChaMP): a serendipitous X-ray Survey using Chandra Archival Data Authors: Wilkes, B.; Green, P.; Cameron, R.; Evans, N.; Ghosh, H.; Kim, D. W.; Tananbaum, H.; ChaMP Collaboration Bibcode: 2000HEAD....5.2105W Altcode: 2000BAAS...32.1212W The Chandra X-ray Observatory, launched in July 1999, has begun a new era in X-ray astronomy. Its unprecedented, ~ 0.5" spatial resolution and low background provide views of the X-ray sky 10-100 times fainter than previously possible. We have begun a serendipitous X-ray survey using Chandra archival data to flux limits in between those reached by earlier satellites and those of the small area, Chandra deep surveys. The survey will cover ~ 5 sq.deg. per year to X-ray fluxes (2-10 keV) in the range 10-13}-6{-16 erg cm2 s-1 and include ~3000 sources per year, ~ 70% of which are expected to be active galactic nuclei (AGN). Optical imaging of the ChaMP fields is underway at NOAO and SAO telescopes using SDSS g',r',z' colors with which we will be able to classify the X-ray sources into object types and, in some cases, estimate their redshifts. We are also planning to obtain optical spectroscopy of a well-defined subset of fields to allow confirmation of classification and redshift determination. All X-ray and optical results and supporting optical data will be placed in the ChaMP archive within a year of the completion of our data analysis. Over the five years of Chandra operations, ChaMP will provide both a major resource for Chandra observers and a key research tool for the study of the cosmic X-ray background and the individual source populations which comprise it. ChaMP promises profoundly new science return on a number of key questions at the current frontier of many areas of astronomy including the Cosmic X-ray Background, locating and studying high redshift clusters and so constraining cosmological parameters, defining the true population of quasars and studying coronal emission from late-type stars that are almost fully convective. An overview of the ChaMP will be presented including an introduction to our methods and early results many of which will be presented in more detail in accompanying papers at this meeting. Title: Tangential Field Changes in the Great Flare of 1990 May 24 Authors: Cameron, Robert; Sammis, Ian Bibcode: 1999ApJ...525L..61C Altcode: We examine the great (solar) flare of 1990 May 24 that occurred in active region NOAA 6063. The Big Bear Solar Observatory videomagnetograph Stokes V and I images show a change in the longitudinal field before and after the flare. Since the flare occurred near the limb, the change reflects a rearrangement of the tangential components of the magnetic field. These observations lack the 180° ambiguity that characterizes vector magnetograms. Title: Chromospheric Sources of Coronal Rays Authors: Zirin, H.; Cameron, R. Bibcode: 1999AAS...194.7808Z Altcode: 1999BAAS...31..962Z TRACE images in the 171A FeIX line show coronal rays or small streamers from network elements. We obtained chromospheric images in center and wing of Hα at BBSO to investigate the relation of these to spicule activity at the base, as well as to brightenings and other changes in the underlying chromosphere. There is a close match of the brightest Hα centerline elements to coronal rays; other network elements are seen. Spicule activity does not appear to play a big role. The coronal changes are fairly slow. We shall also present new data on spicule lifetimes. Title: Axisymmetric Magnetoconvection in a Twisted Field: the effect of Compressibility Authors: Cameron, R. Bibcode: 1999AAS...194.5615C Altcode: 1999BAAS...31..914C The magnetic flux threading the solar surface is believed to be concentrated by convective motions into kilogauss strength flux tubes. What is less well known is the extent to which convective motions also concentrates the vertical current threading the solar surface. This question can be addressed using the non-ideal MHD approximation. As is the case with most such nonlinear problems a numerical treatment is called for. This issue is perhaps best treated in an axisymmetric geometry, where the computational cost of the calculations remains modest (2 (1)/(2) dimensional) compared with a full 3 dimensional simulation, and where flux tubes rather than flux sheets (which form in 2 (1)/(2) dimensional planar simulations) are produced. The problem then equates to that of twisted, axisymmetric magnetoconvection, which has been treated in the Boussinesq problem by Jones and Galloway (1993). The results obtained in the Boussinesq problem indicate that the problem is sensitive to the way in which the azimuthal components are generated by the boundary conditions. This paper extends that work by including the effect of compressibility. Compressible axisymmetric magnetoconvection has two non-dimensional parameters in addition to those describing the Boussinesq problem. To isolate the effect of compressibility, we treat the same cases as Jones and Galloway, and vary the two additional parameters. Title: Variability of Solar UV Irradiance Related to Bright Magnetic Features Observed in Call K-Line: Relationship between Lyman alpha and K-line Report for UARS funding agency Authors: Zirin, Harold; Cameron, Robert Bibcode: 1999STIN...9910690Z Altcode: In this report we comment on the relationship between the Lyman alpha and Calcium K-line emission from the Sun. We firstly examine resolved Lyman alpha images (from TRACE) and resolved K-line images. We find that the Lyman alpha emission is consistent with a linear dependence on the K-line emission. As this is in conflict with the analysis of Johannesson et al.(1995, 1998) we proceed by comparing the disk integrated Lyman alpha flux as a function of ratio between the disk integrated Mg II core and wing fluxes (Johannesson et al (1998) having previously found a linear dependence between this index and the BBSO K-line index). We find that a reasonably good fit can be obtained, however note the discrepancies which lead Johannesson et al to consider the square root relationship. We suggest an alternative interpretation of the discrepancy. Title: A new estimate of the solar meridional flow Authors: Cameron, R.; Hopkins, A. Bibcode: 1998SoPh..183..263C Altcode: We present a new method for measuring the solar magnetic meridional flow, and provide a comparison with other recent work. We have performed a least-squares fit to azimuthally averaged Mount Wilson Observatory synoptic data encompassing Carrington rotations 1722 to 1929 to produce an estimate of the solar meridional flow. A parametric fit to our results expresses the solar meridional flow as v(φ) = 28.5 sin2.5 φ cos φ. Title: New Studies of Polar Spicules Authors: Zirin, H.; Cameron, R. Bibcode: 1998AAS...192.1506Z Altcode: 1998BAAS...30..840Z We have studied several hundred images of solar spicules obtained on June 18 and 19 and July 15 of 1997. The observations were made at BBSO with the 65cm telescope feeding a Zeiss 1/4 Angstroms filter and a 1536x1024 Kodak CCD. Overexposed observations were made above the limb as well as normal exposures on the limb. The filter was tuned to Hα -0.65A and a 30sec interval was used. We were limited to a single wavelength because new software was being installed in a new control computer. The images obtained were processed by high-pass digital filtering of the original FITS images and reregistered by an FFT technique. The image scale is 0.17 arcsec per pixel. The disk was observed on June 18, 1997 to detect the sources of macrospicules and the limb was observed by overexposure on June 19 to determine the height trajectory of the faintest Hα We found that: Many more spicules go up than come down. There are numerous double and multiple spicules. The macrospicules come from normal network elements and start with an "Eiffel tower" shape. There is evidence of magnetic changes underlying these features. Both long macrospicules and complex eruptions are important at the pole. There is some evidence for rotation in spicules. Title: A Combined X-Ray and Gamma Ray Study of the Seyfert Galaxies NGC 7469 and NGC 3227 Authors: Cameron, Robert Bibcode: 1996rxte.prop10293C Altcode: We propose XTE observations of the Seyfert 1 galaxies NGC 7469 and NGC 3227, to be combined with gamma ray spectra of these AGN obtained with the Compton OSSE instrument. The combined XTE and OSSE data, providing continuous energy coverage from 2 keV to >1 MeV, will be used to test and refine the increasingly complex Seyfert spectral models in this energy range. The known variability of these Seyferts may also give information on the separate emission components in the broadband X-ray spectra, since we expect correlated variability between the intrinsic source X-ray flux and reflected emission. Finally, improved models for Seyfert AGN will provide better constraints on the contribution of Seyferts to the diffuse X-ray background. Title: The Hard X-Ray Telescope Mission Authors: Gorenstein, P.; Joensen, K.; Romaine, S.; Worrall, D.; Cameron, R.; Weisskopf, M.; Ramsey, B.; Bilbro, J.; Kroeger, R.; Gehrels, N.; Parsons, A.; Smither, R.; Christensen, F.; Citterio, O.; von Ballmoos, P. Bibcode: 1995AAS...187.7203G Altcode: 1995BAAS...27Q1388G The Hard X-Ray Telescope (HXT) mission concept contains focusing telescopes that collectively, observe simultaneously from the ultraviolet to 100 keV and in several narrow bands extending to 1 MeV. In pointed observations HXT is expected to have an order of magnitude more sensitivity and much finer angular resolution in the 10 to 100 keV band than all current and currently planned future missions, and considerably more sensitivity for detecting narrow lines in the 100 keV to 1 MeV regime. The detectors are small, cooled arrays of relatively low mass with very good energy resolution and some polarization sensitivity. HXT contains two types of hard X-ray telescopes. One type, called the modular modular telescope (MMT) utilizes a novel type of multilayer coating and small graze angles to extend the regime of focusing to 100keV. There is a two stage imaging detector at each focus, a CCD for X-rays < 10 keV followed down stream by either a germanium strip array or cadmium zinc telluride array for 10-100 keV X-rays. The other type of telescope, called the Laue Crystal Telescope (LCT) is a single adjustable array of several hundred Ge crystals that focus by Laue scattering. Individual picomotors adjust the angle of each crystal to diffract photons of a fixed energy to the same point along the optic axis where they converge upon a movable array of cooled germanium detectors. The LCT will have high sensitivity for detecting narrow X-ray lines of known energy such as those expected from Type 1 supernova. The UV monitor is a three telescope system that provides coverage in the ultraviolet band for study of time correlated changes across the broad electromagnetic spectrum of an AGN such as are expected in ``reverberation'' models. A WWW page will be created as a public bulletin board. This work is supported by NASA grant NAG8-1194 Title: New Observations of the Optical Spectrum of SiO + and the Prediction of Its Rotational Spectrum Authors: Zhang, L.; Cameron, R.; Holt, R. A.; Scholl, T. J.; Rosner, S. D. Bibcode: 1993ApJ...418..307Z Altcode: The (0, 0) and (1, 0) bands of the B2Σ+-Χ2Σ+ system of 28Si16O+ have been observed with very high resolution using the technique of laser-induced fluorescence from a mass-selected fast ion beam. The data yield values of the υ" = 0 rotational and fine-structure constants with an improvement in precision by about an order of magnitude over earlier work. This makes it possible to predict the frequencies of pure rotational transitions within this vibrational level at a level of precision that allows unambiguous comparison with molecular lines observed in interstellar clouds. In particular, the transition (J = 5/2, N = 2) → (J = 3/2, N = 1), which has been considered as the source of the observed U86.2 line at 86,243.45(40) MHz, is predicted to occur at 86,037(6) MHz. Title: Search for solar axions Authors: Lazarus, D. M.; Smith, G. C.; Cameron, R.; Melissinos, A. C.; Ruoso, G.; Semertzidis, Y. K.; Nezrick, F. A. Bibcode: 1992PhRvL..69.2333L Altcode: We have searched for a flux of axions produced in the Sun by exploiting their conversion to x rays in a static magnetic field. The signature of a solar axion flux would be an increase in the rate of x rays detected in a magnetic telescope when the Sun passes within its acceptance. From the absence of such a signal we set a 3σ limit on the axion coupling to two photons gaγγ≡1/M<3.6×10-9 GeV-1, provided the axion mass ma<0.03 eV and <7.7×10-9 GeV-1 for 0.03 <ma<0.11 eV. Title: GRO J0422+32 Authors: Harmon, B. A.; Wilson, R. B.; Fishman, G. J.; Meegan, C. A.; Paciesas, W. S.; Briggs, M. S.; Finger, M. H.; Cameron, R.; Kroeger, R.; Grove, E. Bibcode: 1992IAUC.5584....2H Altcode: 1992IAUC.5584....1H B. A. Harmon, R. B. Wilson, G. J. Fishman, and C. A. Meegan, Marshall Space Flight Center, NASA; W. S. Paciesas and M. S. Briggs, University of Alabama, Huntsville; M. H. Finger, Computer Sciences Corporation; R. Cameron, Universities Space Research Association; and R. Kroeger, and E. Grove, Naval Research Laboratory, report for BATSE and OSSE: "The hard x-ray/gamma-ray transient discovered by the BATSE experiment on the Compton Observatory (IAUC 5580) continued to emit at high intensity, about 3 Crab (40-230 keV), over the past three days. The Observatory was re-pointed on Aug. 11.07 UT, so that the source is observable by all four Compton instruments. An improved location based on combined BATSE and OSSE data is R.A. = 4h22m.1, Decl. = +32 49' (equinox J2000.0; uncertainty radius of 0.2 deg). A significant flux is seen to at least 500 keV, with a hard spectrum. The source continues to show strong variability on all timescales." Title: GRO/OSSE Observations of Nuclear Line Emission from the Intense Flares of June 1991 Authors: Murphy, R. J.; Share, G. H.; Johnson, W. N.; Kinzer, R. L.; Kroeger, R.; Kurfess, J. D.; Strickman, M. S.; Grove, J. E.; Cameron, R.; Jung, G.; Grabelsky, D.; Matz, S. M.; Purcell, W.; Ulmer, M. P.; Frye, G.; Jenkins, T.; Jensen, C. Bibcode: 1992AAS...180.3407M Altcode: 1992BAAS...24Q.784M The Oriented Scintillation Spectroscopy Experiment (OSSE) on the Compton Gamma Ray Observatory is comprised of 4 independently-oriented large-area ( ~ 500 cm(2) /detector at 511 keV) NaI detectors covering the energy range from 0.050 to 10 MeV. Solar observations are typically performed with two of the detectors staring at the Sun and two alternating between viewing the Sun and viewing background regions on two-minute timescales. In June of 1991, OSSE observed 4 of the X10+ flares from Active Region 6659. Intense gamma-ray line emission at 0.511 MeV (positron annihilation) and 2.223 MeV (neutron capture), and from several deexcitation lines of carbon and oxygen were recorded. Using a combination of data from sunward-pointing and off-pointing detectors to avoid saturation effects during the intense portions of the flares, background-subtracted spectra have been obtained. These spectra were fit to derive photon fluxes for the above-mentioned gamma-ray lines. Preliminary lower limits to the integrated fluxes in the 2.223 MeV line (not accounting for saturation effects and based on data collected only during the OSSE observation times) are about 300, 200, 30 and 100 photons/cm(2) for the June 4, 6, 9 and 11 flares, respectively. This is to be compared to a fluence of about 300 photons/cm(2) for the 1982 June 3 flare observed by the SMM Gamma-Ray Spectrometer. Integrated fluxes for the other lines will be presented and compared to line flux measurements of flares obtained with the SMM/GRS. This work is supported under NASA contract S10987C. Title: GRO/OSSE Observations of the Intense June 1991 Flares from AR 6659 Authors: Share, G. H.; Murphy, R. J.; Johnson, W. N.; Kinzer, R. L.; Kroeger, R.; Kurfess, J. D.; Strickman, M. S.; Cameron, R.; Jung, G.; Grabelsky, D.; Matz, S. M.; Purcell, W.; Ulmer, M. P.; Frye, G.; Jenkins, T.; Jensen, C. Bibcode: 1991BAAS...23.1388S Altcode: No abstract at ADS Title: A search for the coherent production of axions in the milli eV range Authors: Cameron, R.; Melissinos, A. C.; Semertzidis, Y.; Cantatore, G.; Rizzo, C.; Ruoso, P.; Zavattini, E.; Halama, H.; Lazarus, D. Bibcode: 1991pafi.rept...18C Altcode: Axions provide a natural explanation for the absence of CP violation in the strong interaction. As weakly interacting light particles they are also candidates for the much sought after dark matter allegedly responsible for our lack of understanding of galactic dynamics. Beam dump, particle decay and astrophysical measurements carried out over the past decade have failed to provide positive evidence for their existence over a wide range of masses and coupling strengths. This experiment attempts to produce and detect scalar and pseudoscalar particles coherently produced through the interaction of laser photons with the virtual photons of the magnetic fields of superconducting dipole magnets as manifested by small changes in the polarization state of the laser light. A limit on the coupling of the axion to 2 photons of g(sub a gamma gamma) less than 6.67 x 10(exp -7) GeV(exp -1) was achieved. Title: An Experiment to Produce Light Pseudoscalars and QED Vacuum Polarization Authors: Semertzidis, Y.; Cameron, R.; Cantatore, G.; Melissions, A. C.; Rogers, J. T.; Halama, H. J.; Moskowitz, B. E.; Prodell, A. G.; Nezrick, F. A.; Zavattini, E. Bibcode: 1990coax.conf..137S Altcode: No abstract at ADS