Special Session 11
From solar physics to astrophysics:
the Sun as Rosetta stone for understanding astrophysical processes
--------------------------------------------------------INVITED
--------------------------------------------------------1) --The solar-stellar connection: new insights from the Kepler mission
Bonanno A.
INAF Osservatorio Astrofisico di Catania, Italy
One of the most promising models of the solar activity cycle is based on the idea that the meridional
circulation determines the period of the solar cycle if the eddy diffusivity is low enough. On the other hand,
magnetic fields appear to be ubiquitous in almost all types of stars although the underlying generation
mechanism can be very different along the HR diagram. In this context the high-quality photometric data
provided by the Kepler mission provide important information on the possible dynamo actions in fast-rotating
solar-type stars. In particular, new results of spectroscopic and photometric analysis of two young solar-twin
stars in the field of view of the Kepler space telescope will be presented, and the implications for the present
solar dynamo theories will be discussed.
2) --From Helio- to Asteroseismology and the progress in stellar physics
Di Mauro M.P.
INAF- IAPS, Roma, Italy
During the last decades, numerous observational and theoretical efforts in the study of solar oscillations,
have brought to a detailed knowledge of the interior of the Sun. While this discipline has not yet exhausted
its resources and scientists are still working on further refinements of the solar models and to solve the
numerous still open questions, Asteroseismology, which aims to infer the structural properties of stars which
display multi-mode pulsations, has just entered in its golden age. In fact, the space missions CoRoT and
Kepler dedicated to the observation of stellar oscillations, have already revealed primary results on the
structural properties of the stars and produced a revolution in the way we study the stellar interiors.
Here I will introduce the modern era of Helio- and Asteroseismology with emphasis on results obtained for
the Sun and its solar-like counterparts.
3) --3D Seismic Tomography of the Sun
Gizon L.
Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany
Local helioseismology arose from the need to probe the solar convection zone in three dimensions, in order
to study convection and other transport processes as well as the emergence of magnetic structures. Solar
seismic waves leave their signature in Doppler velocity images of the Sun, which have been recorded from
space by the SOHO and SDO satellites every minute over the last fifteen years. Local helioseismology relies
on the spatial and temporal correlations of the random wave field; this in contrast with global helioseismology
which is based on measurements of the frequencies of the global modes of oscillation of the Sun. As shown
by mathematicians and geophysicists the two-point correlation function contains fundamental information; it
plays a role similar to a Green's function in seismic modeling. I will present recent advances in local
helioseismology: stringent upper limits on subsurface convective velocities, the (controversial) detection of
magnetic activity before emergence, numerical simulations of MHD wave propagation through sunspots,
tests using realistic simulations of magneto-convection, and inversions using adjoin methods.
4) ---The Solar Chromosphere: new techniques and insights
Hansteen V.H.
University of Oslo, Norway
A number of increasingly sophisticated numerical simulations spanning the convection zone to corona have
shed considerable light on the workings of the solar chromosphere. This includes the importance of the
magnetic field and the interplay between waves and the structure of the chromospheric plasma.
Complementing the numerical models, high cadence temporal and high resolution spatial observations, both
space based and on the ground, are changing and challenging previously held views. In this talk we will
discuss the interplay between simulations and observations: how the simulations can aid interpretation of
the observations and how observations help improve the physics present in the models.
5) --Internal gravity waves and dynamics of the solar atmosphere
Jefferies S.
University of Hawaii, USA
Internal gravity waves are waves that are driven by the gravitational and buoyancy forces. Such waves are
believed to be efficiently generated in the Sun's atmosphere by convective overshoot at the convection zonephotosphere boundary and are expected to be omnipresent in the outer solar atmosphere up to the height
where they break. Their potential to transport energy and momentum over large distances in the atmosphere
and to drive flows in the photosphere and chromosphere, potentially makes them a key player in the
dynamics of the solar atmosphere. Unfortunately, the long periods and shallow propagation angles of these
waves have made them hard to detect and characterize and they have received scant attention. Despite
these difficulties, recent observations confirm their presence in the solar atmosphere and verify that
atmospheric gravity waves (AGWs) play a significant role transporting energy into the chromosphere. In
addition to the expected AGWs with upward energy and downward phase direction at frequencies below the
Lamb frequency, there is also growing observational evidence for waves in the Sun’s atmosphere with
downward energy and upward phase propagation, i.e. with the signature of downward propagating internal
gravity waves. These anomalous waves are found at spatial and temporal frequencies unexpected by theory
and are especially interesting as their horizontal wave-vectors extend well below 1 Mm-1 thus offering the
potential to couple to large-scale phenomena such as supergranulation.
6) --An MHD model for the formation of episodic jet from black holes: an analogy with the coronal mass ejection
in the Sun
Yuan Feng
Shangai Astronomical Observatory, China
Episodic ejection of plasma blobs have been observed in many black hole systems. While steady,
continuous jets are believed to be associated with large-scale open magnetic fields, what causes the
episodic ejection of blobs remains unclear. Here by analogy with the coronal mass ejection on the Sun, we
propose a magnetohydrodynamical model for episodic ejections from black holes associated with the closed
magnetic fields in an accretion flow. Shear and turbulence of the accretion flow deform the field and result in
the formation of a flux rope in the disk corona. Energy and helicity are accumulated and stored until a
threshold is reached. The system then loses its equilibrium and the flux rope is thrust outward by the
magnetic compression force in a catastrophic way. Our calculations show that for parameters appropriate for
the black hole in our Galactic center, the plasmoid can attain relativistic speeds in about 35 minutes.
7) --3D Magnetic Reconnection on the Sun
Parnell C.E
University of St. Andrews, UK
Magnetic reconnection is an important process that is prevalent in a wide range of astrophysical bodies. It is
the mechanism by which a magnetic field may restructure, on both global and local scales, and is thus one of
the main processes that release free magnetic energy. Hence, it is thought to play a role in a wide range of
dynamic phenomena including solar flares and CMEs. The characteristics of three-dimensional reconnection
will be reviewed revealing its diversity in contrast to two dimensional reconnection. Reconnection in the
vicinity of null points, as well as in their absence, will be discussed. By considering particular numerical 3D
magnetohydrodynamic models of reconnection associated with solar phenomena, we show how magnetic
reconnection can lead to complex magnetic topologies resulting in wide spread and rapid energy release.
--------------------------------------------------------ORALE
--------------------------------------------------------1) --The multiscale nature of magnetic pattern on the solar surface
Berrilli F., Scardigli S., Del Moro D.
Universita' degli Studi Tor Vergata, Roma, Italy
Multiscale magnetic underdense regions (voids) appear in high resolution magnetograms of quiet solar
surface. These regions may be considered a signature of the underlying convective structure. The study of
the associated pattern paves the way for the study of turbulent convective scales from granular to global.
In order to address the question of magnetic pattern driven by turbulent convection we used a novel
automatic void detection method to calculate void distributions. The absence of preferred scales of
organization in the calculated distributions supports the multiscale nature of flows on the solar surface and
the absence of preferred convective scales.
2) ---Collapsing diffusive magnetic field configurations in solar atmosphere and interstellar medium
Kruglov, A.
Institute of Applied Physics RAS, Nizhny Novgorod, Russia
Usually diffusion spreads the diffusing substance. It turns out that in conditions characteristic to cosmic
plasmas (solar atmosphere, interstellar medium) there exist magnetic field configurations (`knots')
that collapse under the action of magnetic diffusion. The following three conditions are sufficient for this: 1.
plasma resistivity is linear and local; 2. resistivity tensor component across the magnetic field is higher than
along the magnetic field; 3. medium movements are not perturbed by changes in the magnetic field. (The
latter one is probably not necessary.) Electric current density increases in course of collapse. Collapse
completes in finite time with a short peak in current density and Joule heating. During peak-free evolution the
magnetic field `avoids' nulls due to resistivity anisotropy. This enables us to define a `topological
charge' that is invariant under peak-free evolution and changes by +1 or -1 at the final stage of knot collapse.
This dissipation mechanism is expected to act at the inner scale of MHD turbulence, where magnetic
diffusion takes over MHD nonlinearity. Such structures exist for 2D field in 1D space (plane-parallel or
axisymmetric geometry), 3D field in 2D (photosphere) and 3D space (interstellar medium). The 1D case was
studied numerically, for 1D, 2D and 3D cases qualitative results and analytical estimates are provided.
The number of 2D knots sufficient to heat a solar active region is estimated as ~2 per Mm^2 (for B=10^3 Gs).
3) --Sunspot evolution observed with SST
Falco, M.(1) , Zuccarello F. (1), Cristaldi A. (1), Guglielmino S.L. (2), Criscuoli S. (3)
(1) Universita' degli Studi di Catania, Italy
(2) INAF Osservatorio Astrofisico di Catania, Italy
(3) National Solar Observatory, Sacramento Peak, NM, USA
We report on the evolution of an active region observed with SST at extreme high spatial resolution (0.15”).
We use spectropolarimetric data in the Fe I pair at 630.2 nm to study the behavior of the magnetic field in the
penumbral region around a well developed sunspot. Interestingly, wide-band images show twisting motions
of the penumbral filaments. Moreover, we investigate if MMFs are present during the evolution of the
sunspot. Brightenings in Ca II H line are also noticed, indicating the occurrence of transient phenomena in
the chromosphere.
4) ---Interactions in active regions observed with SST and Hinode
Cristaldi A. (1), Guglielmino G.L. (2), Zuccarello F. (1), Falco M. (1), Criscuoli S. (3)
(1) Universita' degli Studi di Catania, Italy
(2) INAF Osservatorio Astrofisico di Catania, Italy
(3) National Solar Observatory, Sacramento Peak, NM, USA
Ca II H brightenings are good proxies of transient phenomena occurring in the solar chromosphere.
We analyze temporal series of Ca II H filtergrams taken with SST at extreme high resolution (0.15”) at
different line positions, simultaneously with spectropolarimetric data in the Fe I pair at 630.2 nm and
Hinode/SOT data, to study the interactions between flux systems. Ca II H core brightenings appear to
connect sunspots during their evolution. They may grow and become compact flare events.
5) ---A novel method to determine temperature gradients in Stellar Atmospheres
Criscuoli S., Uitenbroek H.
National Solar Observatory, Sacramento Peak, NM, USA
The Temperature stratification of the atmosphere of a star is one of the most important physical properties
that determine the shape of its spectrum. One-dimensional atmosphere models provide information about
this stratification, but their description might not be unique or sufficiently descriptive of the physical conditions
of a star. For instance, employment of 1D models has been shown to be inadequate to describe Solar
Irradiance variations recently measured by the SIM radiometers onboard the SORCE spacecraft, as these
suggest temporal variations of temperature gradients, that 1D atmosphere models cannot properly account
for. With full benefit of absolute radiometry at high spatial resolution the accurate determination of radiation
temperatures would be feasible via an inversion of the Planck function. Unfortunately, absolute
measurements are hard to achieve, in particular from the ground, where the unknown and varying absorption
in the telluric atmosphere and the unknown efficiency of instruments constitute significant barriers. We
propose a method based on measurements of radiation temperature at two pairs of continuum spectral
wavelengths. Each pair is chosen so that their H- opacity is similar, thus ensuring that they form at very close
heights, and therefore providing independent measurements of the temperature at the same formation
height. Gradients are then estimated by temperature differences between the two pairs. By theoretical
considerations and results from numerical simulations we show this method to be viable.
6) --Spatial distribution of the magnetic helicity flux measured with SDO/HMI in active regions hosting flares and
CMEs
Romano P. (1), Zuccarello F. (2)
(1) INAF Osservatorio Astrofisico di Catania, Italy
(2) Universita' degli Studi di Catania, Italy
The accumulation of magnetic helicity via emergence of new magnetic flux and/or shearing photospheric
motions is considered an important tool for understanding the processes that lead to eruptive phenomena. In
a previous work the amount of magnetic helicity injected into the corona through the photosphere in a
sample of active regions (ARs) during their passage across the solar disk was measured by inferring the
apparent motion of photospheric footpoints of magnetic field lines from a time series of MDI full-disk lineof-sight magnetograms. The temporal variation of the maps of magnetic helicity flux was analysed by
measuring the fragmentation of the patches that are characterized by the flux of magnetic helicity. The more
fragmented the maps of the magnetic helicity flux were, the higher was the flare and coronal mass ejection
(CME) frequency. In order to further investigate the temporal correlation between the number of these
patches and the flare and the CME occurrence, another sample of ARs observed with a higher spatial
resolution by SDO/HMI has been analyzed. The results indicate that not only the accumulation of magnetic
helicity in the corona, but also its positive and negative fragmentation and distribution should be taken into
account to provide a more confident indication of AR complexity and flare/CME productivity.
7) ---The variability of the Sun and Sun-like stars
Shapiro A.I., Schmutz W. , Cessateur G., Tagirov R., Rozanov E.
Physikalisch-Meteorologishes Observatorium Davos, World Radiation Center, Davos Dorf, Switzerland
The solar irradiance is known to change on time scales of minutes to decades, and it is suspected that its
substantial fluctuations are partially responsible for natural climate variations. We are developing a Code for
Solar Irradiance (COSI) that allows the physical modeling of the entire solar spectrum composed of quiet
Sun and active regions.
COSI is actively used for the interpretations of the data from the recent European missions PROBA2 and
PICARD. We present the modeling of the solar rotational cycle and lunar eclipses observed by the
radiometers onboard these missions. We show that these observations provide a sensitive tool to test the
models for the solar atmosphere and variability.
We compare the variabilities of the Sun and Sun-like stars using recent measurements and reconstructions
of the spectral solar irradiance. We show that when more stellar data become available the comparison of
the Sun and Sun-like stars will ultimately allow to independently test the existing reconstructions of the solar
irradiance.
--------------------------------------------------------POSTER
--------------------------------------------------------1) --Effects of unresolved magnetic field on Fe I 617.3 and 630.2 nm line shapes
Criscuoli S. (1,2), Ermolli I. (2), Giorgi F. (2) and Uitenbroek H. (1)
(1) National Solar Observatory, Sacramento Peak, New Mexico, USA
(2) INAF Osservatorio Astronomico di Roma, Italy
We studied the dependence on the magnetic flux of parameters describing the two Fe I lines at 630.2 and
617.3 nm. In particular, we analyze the line core intensity (IC), full width half maximum (FWHM), and
equivalent width (EQW) of Stokes I and circular polarized signals measured at the two studied lines on
NOAA 11169. This region was observed with IBIS at the Dunn Solar Telescope on March 17th, 2011. Our
study was aimed at obtaining a line diagnostic sensitive to effects of small scale magnetic features
unresolved on the observations. Our results show that IC is sensitive to both temperature and magnetic flux
variations, while FWHM is sensitive mostly to magnetic field variations. On the other hand, EQW resulted
almost insensitive to magnetic field variation and mostly sensitive to temperature changes. Variations of few
percents of the measured line parameters are found on data spatially degraded to represent quiet Sun, diskcentre conditions on medium resolution observations. Among the two investigated lines, the 617.3 nm
proved to be sensitive to temperature variations induced by unresolved magnetic fields, while the 630.2 nm
turned out to be a good diagnostic of magnetic flux. The amount of line parameters variations can be
observed with spectrographs and full-disk imagers as SOLIS/VSM and SDO/HMI; these can be therefore
employed to investigate physical properties of quiet Sun regions.
2) --Power asymmetry in bipolar active regions
Giannattasio, F., Stangalini, M., Del Moro, D., Berrilli, F.
Universita' degli Studi Tor Vergata, Roma, Italy
Velocity oscillations, as Doppler-observed in the lower solar atmosphere, strongly interact with magnetic
fields. Power is reduced by a factor from 2 to 3 within magnetic regions, depending on frequency, depth, and
the flux tube model adopted. In this work, three-hours, and 45 seconds cadence, SDO dopplergrams and
magnetograms of 12 different bipolar active regions are used to investigate the relation between velocity
fluctuations and magnetic fields. Our findings demonstrate that there is a systematic asymmetry within active
regions, where power is enhanced in the trailing spots.
3) --L12-2 inversions of a large scale emerging flux mantle
Guglielmino S.L. (1), Martínez Pillet V. (2), Ruiz Cobo B.(2), del Toro Iniesta J.C. (3), Bellot Rubio L.R. (3),
Solanki S.K. (4) et al.
(1) INAF Osservatorio Astrofisico di Catania
(2) IAC Instituto de Astrofísica de Canarias, La Laguna, Spain
(3) IAA Instituto de Astrofísica de Andalucía, Granada, Spain
(4) Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany
We present the analysis of a flux emergence event observed with the IMaX magnetograph flown aboard the
Sunrise balloon. IMaX took a 15’ sequence with cadence of 31 s along the Fe I line at 525.0 nm, acquiring
only Stokes I and V at 12 line positions (L12-2 mode). This sequence shows the emergence of a flux mantle
at mesogranular scale, cospatial with a large exploding granule. An undesired cross-talk between Stokes U
and V was found in such L12-2 data. We show that the use of a modified version of the SIR inversion code is
able to remove such effect in inferring the physical quantities of interest.
4) --Decameter Observations of Zebra-Stripe Patterns
Koval A.A., Stanislavsky A.A., Konovalenko A.A., Dorovskyy V.V., Abranin E.P.
Institute of Radio Astronomy, Kharkiv, Ukraine
The zebra stripes were observed for the solar event of August 16, 2002 at low frequencies between 17.3329.82 MHz by the UTR-2 decameter antenna array. The radio event was with a long-duration M5/2n flare
and was included the Type II and IV radio bursts, a full-halo CME. The multiple zebra-pattern structures were
observed over ten minutes. They consist of numerous fragments of stripes with various frequency drifts. The
frequency drift of their main braid varied from ~-0.07 MHz/s to ~-0.18 MHz/s, and the frequency-drift rate of
braid stripes is approximately ~-(0.03-0.04) MHz/s. Some zebra-stripe patterns had even a positive drift rate.
Our records show that the frequency width of the braids can both increase and decrease with the frequency
decrease. The instantaneous frequency bandwidth and the duration for individual stripes of the zebra
patterns varied. So far, after more than thirty years of investigations the discussion of zebra-pattern
formation has not been dropped. The appearance of these rare structures for decameter wavelengths range
and their "bombardment" of dynamic spectrum allow us to verify an exist hypotheses and reveal new
morphological features. The feasible theories of origin of zebra-stripes are considered.
5) --Interacting coronae of two T Tauri stars
Massi M. (1), Ros E.(2), et al.
(1) Max-Planck-Institut für Radioastronomie, Bonn, Germany
(2) Departament d'Astronomia i Astrofísica, Univ. de València, Valencia, Spain
We present new high resolution radio (VLBA) images of the binary V773 Tau A, comprising two, young,
solar-mass stars. The flaring activity appear to recur on the orbital period when the two stars are near
periastron. The flares are interpreted to be the result of interactions between coronal streamers.
6) --An orphan penumbra observed with Hinode and DOT
Zuccarello F. (1), Guglielmino S.L. (2)
(1) Universita' degli Studi di Catania, Italy
(2) INAF Osservatorio Astrofisico di Catania, Italy
Orphan penumbrae are filamentary structures, very similar to the penumbral filaments, but that are not
adjacent to any sunspot umbra. We observed an orphan penumbra in NOAA 11089 during a coordinate
observational campaign, involving the Hinode/SOT and DOT telescopes. The spectropolarimetric
measurements indicate the presence of both significant upflows and downflows in the orphan penumbra
region, that decrease in time. A neutral line is present in the region, with a strong horizontal component of
the vector magnetic field. We investigate the association of such structure with other features in the low
chromosphere.