Marco Stangalini

MHD wave transmission in the Sun's atmosphere

MHD wave propagation inside the Suns atmosphere is closely related to the magnetic field topology. For example, magneti c fields are able to lower the cutoff frequency for acoustic waves thus allowing waves which would otherwise be trapped below the photosphere to propagate into the upper atmosphere. Another example is that MHD waves can be transmitted or converted into other forms of waves at altitudes where the sound speed equals the Alfven speed. We take advantage of the large field-of-view provided b y the IBIS experiment to study the wave propagation at two heights in the solar atmosphere, as sampled by the photospheric Fe 617.3 nm spectral line and the chromospheric Ca 854.2 nm spectral line, and its relationship to the local magneti c field. Among other things, we find substantial leakage of waves with 5-minute periods in the chromosphere at the edges of a pore and in the diffused magnetic field surrounding it. By using spectro-polarimetric inversions of Hinode SOT/SP data, we also find a relationship between the photospheric power spectrum and the magnetic field inclination angle; in p articular, well-defined transmission peaks around 25 ◦ for 5 minutes waves and around 15 ◦ for 3 minutes waves. We propose a very simple model based upon wave transmission theory to explain this behavior. Finally, an analysis of both the power spectra and chromospheric amplification spectra suggests the presence of longitudinal acoustic waves along the magnetic field lines.

Diffusion of magnetic elements in a supergranular cell

Small scale magnetic fields (magnetic elements) are ubiquitous in the solar photosphere. Their interaction can provide energy to the upper atmospheric layers, and contribute to heat the solar corona. In this work, the dynamic properties of magnetic elements in the quiet Sun are investigated. The high number of magnetic elements detected in a supergranular cell allowed us to compute their displacement spectrum ((Δr){sup 2})∝τ{sup γ} (with γ > 0, and τ the time since the first detection), separating the contribution of the network (NW) and the internetwork (IN) regions. In particular, we found γ = 1.27 ± 0.05 and γ = 1.08 ± 0.11 in NW (at smaller and larger scales, respectively), and γ = 1.44 ± 0.08 in IN. These results are discussed in light of the literature on the topic, as well as the implications for the build-up of the magnetic network.

The NIR arm of SHARK: System for coronagraphy with High-order Adaptive optics from R to K bands

SHARK is a proposal aimed at investigating the technical feasibility and the scientific capabilities of high-contrast cameras to be implemented at the Large Binocular Telescope (LBT). SHARK foresees two separated channels: near-infrared (NIR) channel and visible, both providing imaging and coronagraphic modes. We describe here the SHARK instrument concept, with particular emphasis on the NIR channel at the level of a conceptual study, performed in the framework of the call for proposals for new LBT instruments. The search for giant extra-Solar planets is the main science case, as we will outline in the paper.

Non-linear propagation of kink waves to the solar chromosphere

Small-scale magnetic field concentrations (magnetic elements) in the quiet Sun are believed to contribute to the energy budget of the upper layers of the Suns atmosphere, as they are observed to support a large number of MHD modes. In recent years, kink waves in magnetic elements were observed at different heights in the solar atmosphere, from the photosphere to the corona. However, the propagation of these waves has not been fully evaluated. Our aim is to investigate the propagation of kink waves in small magnetic elements in the solar atmosphere. We analysed spectropolarimetric data of high-quality and long duration of a photospheric quiet Sun region observed near the disk center with the spectropolarimeter CRISP at the Swedish Solar Telescope (SST), and complemented by simultaneous and co-spatial broad-band chromospheric observations of the same region. Our findings reveal a clear upward propagation of kink waves with frequency above

Photospheric supergranular flows and magnetic flux emergence

~2.6

The spectrum of kink-like oscillations of solar photospheric magnetic elements

mHz. Moreover, the signature of a non-linear propagation process is also observed. By comparing photospheric to chromospheric power spectra, no signature of an energy dissipation is found at least at the atmospheric heights at which the data analysed originate. This implies that most of the energy carried by the kink waves (within the frequency range under study

Three-minute wave enhancement in the solar photosphere

< 17

High-frequency torsional Alfvén waves as an energy source for coronal heating

mHz) flows to upper layers in the Suns atmosphere.

Zernike basis optimization for solar adaptive optics by using information theory.

A recent study carried out on high sensitivity SUNRISE/IMAX data has reported about the existence of areas of limited flux emergence in the quiet Sun. By exploiting an independent and longer (4 hours) data set acquired by HINODE/SOT, we further investigate these regions by analysing their spatial distribution and relation with the supergranular flow. Our findings, while confirming the presence of these calm areas, also show that the rate of emergence of small magnetic elements is largely suppressed at the locations where the divergence of the supergranular plasma flows is positive. This means that the dead calm areas previously reported in literature are not randomly distributed over the solar photosphere but they are linked to the supergranular cells themselves. These results are discussed in the framework of the recent literature.

Polarized Kink Waves in Magnetic Elements: Evidence for Chromospheric Helical Waves

Recently, the availability of new high spatial and temporal resolution observations of the solar photosphere has allowed for the study of the oscillations in small magnetic elements. Small magnetic elements have been found to host a rich variety of oscillations detectable as intensity, longitudinal, or transverse velocity fluctuations that have been interpreted as magneto-hydrodynamic (MHD) waves. Small magnetic elements, at or below the current spatial resolution achieved by modern solar telescopes, are thought to play a relevant role in the energy budget of the upper layers of the Sun’s atmosphere, as they are found to cover a significant fraction of the solar photosphere. Unfortunately, the limited temporal length and/or cadence of the data sets or the presence of seeing-induced effects have prevented accurate estimates of the power spectra of kink-like oscillations in small magnetic elements so far. Motivated by this, we studied kink-like oscillations in small magnetic elements, by exploiting very long duration and high cadence data acquired with the Solar Optical Telescope on board the Hinode satellite. In this paper, we present the results of a statistical study of the power spectral density of kink-like oscillations. We found that small magnetic elements exhibit a large number of spectral features in the range 1−12 mHz. Most of these spectral features are not shared among magnetic elements rather they represent a unique signature of each magnetic element itself.