Scientific Objectives of Observing Time
The main goal of this proposal is to plan coordinated observations between HINODE instruments and the solar telescopes in the Canary Islands. The combination of the capabilities of the ground-based telescopes and SOT, SOT-SP and EIS will allow to get high precision spectropolarimetric measurements and imaging observations at the highest spatial resolution available in different spectral regions. In the following, we describe in more detail the specific objectives of the proposal.
Small photospheric magnetic elements: faculae and bright points, their radiativestructure, magnetic configuration and relationship to solar irradiance variations
It is currently known that solar irradiance variations in timescales of the order of 1 day to a solar rotation are due to the magnetic field emerging mainly in the form of sunspots and faculae. However, it is not yet clear to which extent the small magnetic elements emerging in the solar atmosphere contribute to the variations. The study of their radiative properties, morphology and coverage of solar disc obtained from high resolution data is therefore of great importance. In previous years, several observational campaigns have allowed us to progress in this line of research (Domingo et al., 2005, Cabello and Domingo, 2006, Ortiz et al., 2006, Balmaceda et al., 2008, Balmaceda et al., 2010). In particular, we are interested in studying small magnetic elements such as network bright points, small faculae and pores. From a set of observations at different wavelengths, i.e. different heights in the solar atmosphere, we would like to obtain information about their radiative structure. The new sensitive magnetometers are now able to detect magnetic signal in regions that were not possible to resolve with previous instruments. Small magnetic elements, like isolated bright points of forming structures as filigree, are interesting since their formation and lifetimes fluctuate when continuum intensity is compared with the magnetic field, as intensification and decaying occur. Measures of bright points and statistics (as in Balmaceda et al., 2008) can clarify the matter, including spectropolarimetric analysis which can reveal convective collapses. Novel polarimetric instrumentation (as IMaX onboard the balloon Sunrise, Martınez Pillet et al. 2010, Solanki et al. 2010) allowed to study size, density and dynamics of small magnetic elements, in longitudinal and transverse magnetograms, velocities, etc. However, Sunrise
mission had a limited duration on time. For longer studies, also ground-based data could be used. Among others, studies on dynamics and rotation of small magnetic elements have been performed with both SST (Balmaceda et al., 2010) and Sunrise (Bonet et al., 2010). Continuation of these works would be highly compelling.With IMaX vector-magnetograph data in the Fe I line (525.02 nm), it was possible to investigate the relationship of small magnetic elements and bright points detected in G-band. This did allow, in turn, to study their contribution to solar irradiance variations specially in the UV region making use of SUFI data: CN, Ca II, OH and the mixed filters, at 388.35, 396.9, 300, 312, 225 nm respectively (Reithm¨uller (2010), Hirzberger (2010)). Observations at different μ-values will be necessary in order to study the center-to-limb variation of these properties. We are also interested in studying chromospheric structures such as Ca-jets and their relationship with the photosphere and upper layers (transition zone, corona) in combination with EIS HINODE and XRT observations. We would like to scan the solar disc with μ-intervals of 0.2 from center to limb, 30 minutes at
each position. Related with these CLV observations, the group is involved in the definition and preparation of the PHI instrument on-board the Solar Orbiter satellite, one of its main characteristics being out-of-the-ecliptic measurements. Observations performed close to the limb in ground based observatories could help prepare the possible scenarios the instrument will encounter, and where to focus when working.
Evolution of magnetic topology in decaying active regions (In colaboration with Louise Harra, Sarah Matthews, Lucie Green and Deborah Baker at UCL/MSSL)
The Sun frequently ejects magnetic field and plasma into the interplanetary environment in events known as coronal mass ejections (CMEs). These events are one method by which the Sun removes magnetic field from the atmosphere, and they are thought to derive their energy from that contained in the magnetic field. This campaign can clarify the fundamental processes that take place in active regions which ultimately lead to the conditions necessary for an eruption. Strong flux concentrations rise to the photosphere where they form regions known as active regions. After a few days, the active region field begins to disperse and a strong convergence of the opposite magnetic polarities toward the magnetic neutral line is often observed. Flux is then seen to disappear along the neutral line, possibly due to magnetic reconnection and submergence through the photosphere. This disappearance is known as flux cancellation and during this time CMEs are produced. The combination of ground–based telescopes and HINODE can provide the high cadence and high resolution observations of the magnetic field which are required to test the models of flux cancellation and to determine how flux cancellation effects the magnetic topology of the active region. The mission will allow us to determine whether magnetic reconnection is taking place and, if so, whether it is taking place in the photosphere, chromosphere or corona. Knowing the answers to these questions will help us understand how the topology of the magnetic field is evolving, ultimately answering a key question in solar physics of how flux ropes are formed. Flux ropes are crucial to all CME models but so it is not yet understood when or how they form. These observations will provide the information required to understand the processes taking place in decaying active regions and how this creates the conditions necessary for CMEs. We aim at study the evolution of active region magnetic field during the decay phase. Investigate the origin of flows toward the magnetic neutral line which have associated flux cancellation. Determine where in the solar atmosphere reconnection is taking place and how this effects the magnetic topology. Active region that has fully emerged will be a suitable target and the requirements include high cadence vector magnetic data as well as observations of photosphere, chromosphere and corona. Combining UV and EUV plasma motion data, i.e. velocity data, with high resolution magnetic field vector data will be required in order to identify specific locations of reconnection
Observing Time 2011 Proposal Form
in the lower solar atmosphere and how they relate to EUV AR outflows viewed in EIS. Joint observations with HINODE’s EIS and XRT for corona are also required. Data in photospheric (G-band) and chromospheric (Ca II, HK) lines together with the information acquired with SOT-SP for magnetic field vector data, will give us complementary information to achieve our objectives.
Horizontal flows around active regions: moat-penumbra relation
Study of horizontal flows has unveiled the relation between the presence of penumbra and large outflows (moat flows) around solar active regions (Vargas Dom´ınguez et al 2007, Vargas Domınguez et al 2008). The granular pattern surrounding active regions is perturbed by the presence of magnetic elements (MMFs, Moving Magnetic Features) moving radially outwardswhile immersed in the moat flow. Recent findings by Sainz Dalda & Martınez Pillet (2005), and Ravindra (2006) establish that the penumbral filaments extend beyond the photometric sunspot boundary and cross the region dominated by the moat flow. Cabrera Solana et al (2006) found Evershed clouds as precursors of MMFs around sunspots. Analysis of long time series will help us to determine and clarify the link between flows inside and outside penumbrae and establish the actual connection with the well-known Evershed Flow which is still unclear. Data in G-band and G-continuum will be suitable to track proper motions of structures. Moreover, very recent investigations (Vargas Domınguez et al, 2009) reinforce the idea that individual solar pores display purely inward motions in their nearest vicinity. Solar pores time series will be useful in scenarios where penumbrae are just about to be formed. Dopplergrams and magnetograms will bring us complementary information to clarify this matter. |
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